Author name code: depontieu
ADS astronomy entries on 2022-09-14
author:"De Pontieu, Bart"
------------------------------------------------------------------------
Title: A novel inversion method to determine the coronal magnetic
field including the impact of bound-free absorption
Authors: Martinez-Sykora, Juan; Hansteen, Viggo H.; De Pontieu, Bart;
Landi, Enrico
Bibcode: 2022arXiv220813984M
Altcode:
The magnetic field governs the corona; hence it is a crucial parameter
to measure. Unfortunately, existing techniques for estimating its
strength are limited by strong assumptions and limitations. These
techniques include photospheric or chromospheric field extrapolation
using potential or non-linear-force-free methods, estimates based on
coronal seismology, or by direct observations via, e.g., the Cryo-NIRSP
instrument on DKIST which will measure the coronal magnetic field,
but only off the limb. Alternately, in this work we investigate a
recently developed approach based on the magnetic-field-induced (MIT)
transition of the \fex~257.261~Å. In order to examine this approach,
we have synthesized several \fex\ lines from two 3D magnetohydrodynamic
simulations, one modeling an emerging flux region and the second an
established mature active region. In addition, we take bound-free
absorption from neutral hydrogen and helium and singly ionised
helium into account. The absorption from cool plasma that occurs at
coronal heights has a significant impact on determining the magnetic
field. We investigate in detail the challenges of using these \fex\
lines to measure the field, considering their density and temperature
dependence. We present a novel approach to deriving the magnetic field
from the MIT using inversions of the differential emission measure as a
function of the temperature, density, and magnetic field. This approach
successfully estimates the magnetic field strength (up to \%18 relative
error) in regions that do not suffer from significant absorption and
that have relatively strong coronal magnetic fields ($>250$~G). This
method allows the masking of regions where absorption is significant.
Title: Genesis and Coronal-jet-generating Eruption of a Solar
Minifilament Captured by IRIS Slit-raster Spectra
Authors: Panesar, Navdeep K.; Tiwari, Sanjiv K.; Moore, Ronald L.;
Sterling, Alphonse C.; De Pontieu, Bart
Bibcode: 2022arXiv220900059P
Altcode:
We present the first IRIS Mg II slit-raster spectra that fully capture
the genesis and coronal-jet-generating eruption of a central-disk solar
minifilament. The minifilament arose in a negative-magnetic-polarity
coronal hole. The Mg II spectroheliograms verify that the minifilament
plasma temperature is chromospheric. The Mg II spectra show that
the erupting minifilament's plasma has blueshifted upflow in the
jet spire's onset and simultaneous redshifted downflow at the
location of the compact jet bright point (JBP). From the Mg II
spectra together with AIA EUV images and HMI magnetograms, we find:
(i) the minifilament forms above a flux cancelation neutral line
at an edge of a negative-polarity network flux clump; (ii) during
the minifilament's fast-eruption onset and jet-spire onset, the
JBP begins brightening over the flux-cancelation neutral line. From
IRIS2 inversion of the Mg II spectra, the JBP's Mg II bright plasma
has electron density, temperature, and downward (red-shift) Doppler
speed of 1012 cm^-3, 6000 K, and 10 kms, respectively, and the growing
spire shows clockwise spin. We speculate: (i) during the slow rise
of the erupting minifilament-carrying twisted flux rope, the top of
the erupting flux-rope loop, by writhing, makes its field direction
opposite that of encountered ambient far-reaching field; (ii) the
erupting kink then can reconnect with the far-reaching field to make
the spire and reconnect internally to make the JBP. We conclude that
this coronal jet is normal in that magnetic flux cancelation builds a
minifilament-carrying twisted flux rope and triggers the JBP-generating
and jet-spire-generating eruption of the flux rope.
Title: Emergence of internetwork magnetic fields into the chromosphere
and transition region
Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, L. R.; Sainz
Dalda, A.; Esteban Pozuelo, Sara
Bibcode: 2022cosp...44.2511G
Altcode:
Internetwork (IN) magnetic fields are highly dynamic, short-lived
magnetic structures that populate the interior of supergranular
cells. Since they are spread all over the Sun, they may hold a
significant fraction of the total magnetic energy stored in the
photosphere. Therefore, it is crucial to understand their role in the
quiet Sun magnetism and impact on the energetics and dynamics of the
solar atmosphere. To provide new insights into this topic, we studied
three flux emergence events and followed them as they emerge into the
photosphere and reach the chromosphere and transition region. We used
coordinated, high-resolution, multiwavelength observations obtained with
the Swedish 1-m Solar Telescope (SST) and the Interface Region Imaging
Spectrograph (IRIS). SST Fe I 6173 and Mg I b$_2$ 5173 magnetograms
show the footpoints of the IN bipoles emerging at the solar surface
and rising toward the upper solar atmosphere. For the first time, our
spectropolarimetric measurements in the Ca II 8542 \AA\/ line provide
direct observational evidence that IN fields are capable of reaching
the chromosphere. IRIS observations reveal another important piece of
information - small-scale IN loops can even reach transition region
heights, and locally heat the upper solar atmosphere.
Title: Fine-scale, Dot-like, Brightenings in an Emerging Flux Region:
SolO/EUI Observations, and Bifrost MHD Simulations
Authors: Tiwari, Sanjiv Kumar; Berghmans, David; De Pontieu, Bart;
Hansteen, Viggo; Panesar, Navdeep Kaur
Bibcode: 2022cosp...44.2529T
Altcode:
Numerous tiny bright dots are observed in SolO's EUI/\hri\ data
of an emerging flux region (a coronal bright point) in 174 \AA,
emitted by the coronal plasma at $\sim$1 MK. These dots are roundish,
with a diameter of 675$\pm$300 km, a lifetime of 50$\pm$35 seconds,
and an intensity enhancement of 30% $\pm$10% from their immediate
surroundings. About half of the dots remain isolated during their
evolution and move randomly and slowly ($<$10 \kms). The other half
show extensions, appearing as a small loop or surge/jet, with intensity
propagations below 30\,\kms. Some dots form at the end of a fine-scale
explosion. Many of the bigger and brighter EUI/HRI dots are discernible
in SDO/AIA 171 \AA\ channel, have significant EM in the temperature
range of 1--2 MK, and are often located at polarity inversion lines
observed in HMI LOS magnetograms. Bifrost MHD simulations of an emerging
flux region do show dots in synthetic Fe IX/X images, although dots
in simulations are not as pervasive as in observations. The dots
in simulations show distinct Doppler signatures -- blueshifts and
redshifts coexist, or a redshift of the order of 10 \kms\ is followed
by a blueshift of similar or higher magnitude. The synthetic images of
O V/VI and Si IV lines, which form in the transition region, also show
the dots that are observed in Fe IX/X images, often expanded in size,
or extended as a loop, and always with stronger Doppler velocities (up
to 100 \kms) than that in Fe IX/X lines. Our results, together with the
field geometry of dots in the simulations, suggest that most dots in
emerging flux regions form in the lower solar atmosphere (at $\approx$1
Mm) by magnetic reconnection between emerging and pre-existing/emerged
magnetic field. The dots are smaller in Fe IX/X images (than in O V/VI
& Si IV lines) most likely because only the hottest counterpart of
the magnetic reconnection events is visible in the hotter emission. Some
dots might be manifestations of magneto-acoustic shocks (from the
lower atmosphere) through the line formation region of Fe IX/X. A
small number of dots could also be a response of supersonic downflows
impacting transition-region/chromospheric density.
Title: Detailed Description of the Collision Frequency in the Solar
Atmosphere
Authors: Wargnier, Q. M.; Martínez-Sykora, J.; Hansteen, V. H.;
De Pontieu, B.
Bibcode: 2022ApJ...933..205W
Altcode:
This work aims to provide an accurate description and calculations of
collision frequencies in conditions relevant to the solar atmosphere. To
do so, we focus on the detailed description of the collision
frequency in the solar atmosphere based on a classical formalism with
Chapman-Cowling collision integrals, as described by Zhdanov. These
collision integrals allow linking the macroscopic transport fluxes
of multifluid models to the kinetic scales involved in the Boltzmann
equations. In this context, the collision frequencies are computed
accurately while being consistent at the kinetic level. We calculate
the collision frequencies based on this formalism and compare them with
approaches commonly used in the literature for conditions typical of the
solar atmosphere. To calculate the collision frequencies, we focus on
the collision integral data provided by Bruno et al., which is based on
a multicomponent hydrogen-helium mixture used for conditions typical for
the atmosphere of Jupiter. We perform a comparison with the classical
formalism of Vranjes & Krstic and Leake & Linton. We highlight
the differences obtained in the distribution of the cross sections as
functions of the temperature. Then, we quantify the disparities obtained
in numerical simulations of a 2.5D solar atmosphere by calculating
collision frequencies and ambipolar diffusion. This strategy allows
us to validate and assess the accuracy of these collision frequencies
for conditions typical of the solar atmosphere.
Title: Parallel Plasma Loops and the Energization of the Solar Corona
Authors: Peter, Hardi; Chitta, Lakshmi Pradeep; Chen, Feng; Pontin,
David I.; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.;
Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain,
Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.;
Testa, Paola; Tiwari, Sanjiv K.; Walsh, Robert W.; Warren, Harry P.
Bibcode: 2022ApJ...933..153P
Altcode: 2022arXiv220515919P
The outer atmosphere of the Sun is composed of plasma heated to
temperatures well in excess of the visible surface. We investigate
short cool and warm (<1 MK) loops seen in the core of an active
region to address the role of field-line braiding in energizing these
structures. We report observations from the High-resolution Coronal
imager (Hi-C) that have been acquired in a coordinated campaign with
the Interface Region Imaging Spectrograph (IRIS). In the core of the
active region, the 172 Å band of Hi-C and the 1400 Å channel of IRIS
show plasma loops at different temperatures that run in parallel. There
is a small but detectable spatial offset of less than 1″ between
the loops seen in the two bands. Most importantly, we do not see
observational signatures that these loops might be twisted around each
other. Considering the scenario of magnetic braiding, our observations
of parallel loops imply that the stresses put into the magnetic field
have to relax while the braiding is applied: the magnetic field never
reaches a highly braided state on these length scales comparable to
the separation of the loops. This supports recent numerical 3D models
of loop braiding in which the effective dissipation is sufficiently
large that it keeps the magnetic field from getting highly twisted
within a loop.
Title: On the relationship between spicules and coronal bright points
Authors: Bose, Souvik; De Pontieu, Bart; Rouppe van der Voort, Luc;
Nóbrega Siverio, Daniel
Bibcode: 2022cosp...44.2522B
Altcode:
Coronal bright points (CBPs) are a set of small-scale, lower coronal
loop systems connecting opposite magnetic polarities and are primarily
characterized by enhanced emission in the extreme ultraviolet (EUV)
wavelengths and X-rays. Being ubiquitous they are thought to play a
definite role in heating the solar corona. This study aims to explore
the chromospheric components associated with a CBP by focusing on
spicules and small-scaled flux emergence. We used high-resolution
observations in H$\beta$ and Fe I 617.3 nm spectral lines obtained
from the Swedish 1-m Solar Telescope (SST) in coordination with the
images acquired from the Atmospheric Imaging Assembly (AIA) instrument
on-board the Solar Dynamics Observatory (SDO). On-disk spicules were
automatically detected by employing advanced image processing techniques
on the Dopplergrams derived from H$\beta$, and Mile-Eddington inversions
of the Fe I 617.3 nm line provided the photospheric vector magnetic
field. The AIA co-observations were co-aligned to SST with the latter
serving as a reference. We find abundant occurrences of chromospheric
spicules close to the "footpoints" of the CBP. The orientation of the
spicules is predominantly aligned along with CBP loops which further
indicates that they form a fundamental part of the same magnetic
structure. Several examples of the spatio-temporal evolution indicate
that much of the chromospheric plasma is heated to coronal temperatures
implying that spicules potentially supply mass and energy to the CBP
loops. Furthermore, we study chromospheric and corresponding coronal
responses to two magnetic flux emergence events and their impact on the
dynamics of the CBP. This study presents unique and unambiguous evidence
that connects chromospheric spicular dynamics and flux emergence with
a CBP for the very first time using high-resolution observations.
Title: SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots
in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation
Authors: Tiwari, Sanjiv K.; Hansteen, Viggo H.; De Pontieu, Bart;
Panesar, Navdeep K.; Berghmans, David
Bibcode: 2022ApJ...929..103T
Altcode: 2022arXiv220306161T
We report on the presence of numerous tiny bright dots in and around
an emerging flux region (an X-ray/coronal bright point) observed with
SolO's EUI/HRIEUV in 174 Å. These dots are roundish and have
a diameter of 675 ± 300 km, a lifetime of 50 ± 35 s, and an intensity
enhancement of 30% ± 10% above their immediate surroundings. About
half of the dots remain isolated during their evolution and move
randomly and slowly (<10 km s-1). The other half show
extensions, appearing as a small loop or surge/jet, with intensity
propagations below 30 km s-1. Many of the bigger and brighter
HRIEUV dots are discernible in the SDO/AIA 171 Å channel,
have significant emissivity in the temperature range of 1-2 MK, and
are often located at polarity inversion lines observed in SDO/HMI LOS
magnetograms. Although not as pervasive as in observations, a Bifrost
MHD simulation of an emerging flux region does show dots in synthetic
Fe IX/X images. These dots in the simulation show distinct Doppler
signatures-blueshifts and redshifts coexist, or a redshift of the
order of 10 km s-1 is followed by a blueshift of similar
or higher magnitude. The synthetic images of O V/VI and Si IV lines,
which represent transition region radiation, also show the dots that
are observed in Fe IX/X images, often expanded in size, or extended
as a loop, and always with stronger Doppler velocities (up to 100
km s-1) than that in Fe IX/X lines. Our observation and
simulation results, together with the field geometry of dots in the
simulation, suggest that most dots in emerging flux regions form in the
lower solar atmosphere (at ≍ 1 Mm) by magnetic reconnection between
emerging and preexisting/emerged magnetic field. Some dots might be
manifestations of magnetoacoustic shocks through the line formation
region of Fe IX/X emission.
Title: Chromospheric emission from nanoflare heating in RADYN
simulations
Authors: Bakke, H.; Carlsson, M.; Rouppe van der Voort, L.; Gudiksen,
B. V.; Polito, V.; Testa, P.; De Pontieu, B.
Bibcode: 2022A&A...659A.186B
Altcode: 2022arXiv220111961B
Context. Heating signatures from small-scale magnetic reconnection
events in the solar atmosphere have proven to be difficult to
detect through observations. Numerical models that reproduce flaring
conditions are essential in understanding how nanoflares may act as a
heating mechanism of the corona.
Aims: We study the effects of
non-thermal electrons in synthetic spectra from 1D hydrodynamic RADYN
simulations of nanoflare heated loops to investigate the diagnostic
potential of chromospheric emission from small-scale events.
Methods: The Mg II h and k, Ca II H and K, Ca II 854.2 nm, and Hα and
Hβ chromospheric lines were synthesised from various RADYN models of
coronal loops subject to electron beams of nanoflare energies. The
contribution function to the line intensity was computed to better
understand how the atmospheric response to the non-thermal electrons
affects the formation of spectral lines and the detailed shape of
their spectral profiles.
Results: The spectral line signatures
arising from the electron beams highly depend on the density of the
loop and the lower cutoff energy of the electrons. Low-energy (5 keV)
electrons deposit their energy in the corona and transition region,
producing strong plasma flows that cause both redshifts and blueshifts
of the chromospheric spectra. Higher-energy (10 and 15 keV) electrons
deposit their energy in the lower transition region and chromosphere,
resulting in increased emission from local heating. Our results indicate
that effects from small-scale events can be observed with ground-based
telescopes, expanding the list of possible diagnostics for the presence
and properties of nanoflares.
Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE). II. Flares and Eruptions
Authors: Cheung, Mark C. M.; Martínez-Sykora, Juan; Testa, Paola;
De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
Vanessa; Kerr, Graham S.; Reeves, Katharine K.; Fletcher, Lyndsay; Jin,
Meng; Nóbrega-Siverio, Daniel; Danilovic, Sanja; Antolin, Patrick;
Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward;
Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc L.; Boerner, Paul;
Jaeggli, Sarah; Nitta, Nariaki V.; Daw, Adrian; Carlsson, Mats; Golub,
Leon; The
Bibcode: 2022ApJ...926...53C
Altcode: 2021arXiv210615591C
Current state-of-the-art spectrographs cannot resolve the fundamental
spatial (subarcseconds) and temporal (less than a few tens of
seconds) scales of the coronal dynamics of solar flares and eruptive
phenomena. The highest-resolution coronal data to date are based on
imaging, which is blind to many of the processes that drive coronal
energetics and dynamics. As shown by the Interface Region Imaging
Spectrograph for the low solar atmosphere, we need high-resolution
spectroscopic measurements with simultaneous imaging to understand the
dominant processes. In this paper: (1) we introduce the Multi-slit Solar
Explorer (MUSE), a spaceborne observatory to fill this observational
gap by providing high-cadence (<20 s), subarcsecond-resolution
spectroscopic rasters over an active region size of the solar transition
region and corona; (2) using advanced numerical models, we demonstrate
the unique diagnostic capabilities of MUSE for exploring solar coronal
dynamics and for constraining and discriminating models of solar flares
and eruptions; (3) we discuss the key contributions MUSE would make
in addressing the science objectives of the Next Generation Solar
Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme
Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope
(and other ground-based observatories) can operate as a distributed
implementation of the NGSPM. This is a companion paper to De Pontieu
et al., which focuses on investigating coronal heating with MUSE.
Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE). I. Coronal Heating
Authors: De Pontieu, Bart; Testa, Paola; Martínez-Sykora, Juan;
Antolin, Patrick; Karampelas, Konstantinos; Hansteen, Viggo; Rempel,
Matthias; Cheung, Mark C. M.; Reale, Fabio; Danilovic, Sanja; Pagano,
Paolo; Polito, Vanessa; De Moortel, Ineke; Nóbrega-Siverio, Daniel;
Van Doorsselaere, Tom; Petralia, Antonino; Asgari-Targhi, Mahboubeh;
Boerner, Paul; Carlsson, Mats; Chintzoglou, Georgios; Daw, Adrian;
DeLuca, Edward; Golub, Leon; Matsumoto, Takuma; Ugarte-Urra, Ignacio;
McIntosh, Scott W.; the MUSE Team
Bibcode: 2022ApJ...926...52D
Altcode: 2021arXiv210615584D
The Multi-slit Solar Explorer (MUSE) is a proposed mission composed of
a multislit extreme ultraviolet (EUV) spectrograph (in three spectral
bands around 171 Å, 284 Å, and 108 Å) and an EUV context imager (in
two passbands around 195 Å and 304 Å). MUSE will provide unprecedented
spectral and imaging diagnostics of the solar corona at high spatial
(≤0.″5) and temporal resolution (down to ~0.5 s for sit-and-stare
observations), thanks to its innovative multislit design. By obtaining
spectra in four bright EUV lines (Fe IX 171 Å, Fe XV 284 Å, Fe XIX-Fe
XXI 108 Å) covering a wide range of transition regions and coronal
temperatures along 37 slits simultaneously, MUSE will, for the first
time, "freeze" (at a cadence as short as 10 s) with a spectroscopic
raster the evolution of the dynamic coronal plasma over a wide range of
scales: from the spatial scales on which energy is released (≤0.″5)
to the large-scale (~170″ × 170″) atmospheric response. We use
numerical modeling to showcase how MUSE will constrain the properties of
the solar atmosphere on spatiotemporal scales (≤0.″5, ≤20 s) and
the large field of view on which state-of-the-art models of the physical
processes that drive coronal heating, flares, and coronal mass ejections
(CMEs) make distinguishing and testable predictions. We describe the
synergy between MUSE, the single-slit, high-resolution Solar-C EUVST
spectrograph, and ground-based observatories (DKIST and others), and
the critical role MUSE plays because of the multiscale nature of the
physical processes involved. In this first paper, we focus on coronal
heating mechanisms. An accompanying paper focuses on flares and CMEs.
Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE): II. Flares and Eruptions
Authors: Cheung, Chun Ming Mark; Martinez-Sykora, Juan; Testa, Paola;
De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
Vanessa; Kerr, Graham; Reeves, Katharine; Fletcher, Lyndsay; Jin,
Meng; Nobrega, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred,
Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope,
Dana; Takasao, Shinsuke; DeRosa, Marc; Boerner, Paul; Jaeggli, Sarah;
Nitta, Nariaki; Daw, Adrian; Carlsson, Mats; Golub, Leon
Bibcode: 2021AGUFMSH51A..08C
Altcode:
Current state-of-the-art spectrographs cannot resolve the fundamental
spatial (sub-arcseconds) and temporal scales (less than a few tens
of seconds) of the coronal dynamics of solar flares and eruptive
phenomena. The highest resolution coronal data to date are based on
imaging, which is blind to many of the processes that drive coronal
energetics and dynamics. As shown by IRIS for the low solar atmosphere,
we need high-resolution spectroscopic measurements with simultaneous
imaging to understand the dominant processes. In this paper: (1)
we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne
observatory to fill this observational gap by providing high-cadence
(<20 s), sub-arcsecond resolution spectroscopic rasters over an
active region size of the solar transition region and corona; (2)
using advanced numerical models, we demonstrate the unique diagnostic
capabilities of MUSE for exploring solar coronal dynamics, and for
constraining and discriminating models of solar flares and eruptions;
(3) we discuss the key contributions MUSE would make in addressing the
science objectives of the Next Generation Solar Physics Mission (NGSPM),
and how MUSE, the high-throughput EUV Solar Telescope (EUVST) and the
Daniel K Inouye Solar Telescope (and other ground-based observatories)
can operate as a distributed implementation of the NGSPM. This is a
companion paper to De Pontieu et al. (2021, also submitted to SH-17),
which focuses on investigating coronal heating with MUSE.
Title: Demonstration of Chromospheric Magnetic Mapping with CLASP2.1
Authors: McKenzie, David; Ishikawa, Ryohko; Trujillo Bueno, Javier;
Auchere, F.; Kobayashi, Ken; Winebarger, Amy; Kano, Ryouhei; Song,
Donguk; Okamoto, Joten; Rachmeler, Laurel; De Pontieu, Bart; Vigil,
Genevieve; Belluzzi, Luca; Alsina Ballester, Ernest; del Pino Aleman,
Tanausu; Bethge, Christian; Sakao, Taro; Stepan, Jiri
Bibcode: 2021AGUFMSH52A..06M
Altcode:
Probing the magnetic nature of the Suns atmosphere requires measurement
of the Stokes I, Q, U and V profiles of relevant spectral lines (of
which Q, U and V encode the magnetic field information). Many of the
magnetically sensitive lines formed in the chromosphere and transition
region are in the ultraviolet spectrum, necessitating observations
above the absorbing terrestrial atmosphere. The Chromospheric
Layer Spectro-Polarimeter (CLASP2) sounding rocket was flown
successfully in April 2019, as a follow-on to the successful flight in
September 2015 of the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP). Both projects were funded by NASAs Heliophysics Technology
and Instrument Development for Science (H-TIDeS) program to develop
and test a technique for observing the Sun in ultraviolet light,
and for quantifying the polarization of that light. By demonstrating
successful measurement and interpretation of the polarization in
hydrogen Lyman-alpha and the Mg II h and k spectral lines, the CLASP
and CLASP2 missions are vital first steps towards routine quantitative
characterization of the local thermal and magnetic conditions in the
solar chromosphere. In October of 2021, we re-flew the CLASP2 payload
with a modified observing program to further demonstrate the maturity
of the UV spectropolarimetry techniques, and readiness for development
into a satellite observatory. During the reflight, called CLASP2.1,
the spectrograph slit was scanned across an active region plage to
acquire a two-dimensional map of Stokes V/I, to demonstrate the ability
of UV spectropolarimetry to yield chromospheric magnetic fields over
a large area. This presentation will display preliminary results from
the flight of CLASP2.1.
Title: Probing the physics of coronal heating with the Multi-slit
Solar Explorer (MUSE)
Authors: De Pontieu, Bart; Testa, Paola; Martinez-Sykora, Juan;
Cheung, Chun Ming Mark
Bibcode: 2021AGUFMSH55B1836D
Altcode:
The Multi-slit Solar Explorer (MUSE) is a proposed NASA MIDEX mission,
currently in Phase A, composed of a multi-slit EUV spectrograph (in
three narrow spectral bands centered around 171Å, 284Å, and 108Å)
and an EUV context imager (in two narrow passbands around 195Å and
304Å). MUSE will provide unprecedented spectral and imaging diagnostics
of the solar corona at high spatial (~0.5 arcseconds), and temporal
resolution (down to ~0.5 seconds) thanks to its innovative multi-slit
design. By obtaining spectra in 4 bright EUV lines (Fe IX 171Å,
Fe XV 284Å, Fe XIX-XXI 108Å) covering a wide range of transition
region and coronal temperatures along 37 slits simultaneously, MUSE
will for the first time be able to ``freeze" (at a cadence as short as
10 seconds) with a spectroscopic raster the evolution of the dynamic
coronal plasma over a wide range of scales: from the spatial scales
on which energy is released (<0.5 arcsec) to the large-scale often
active-region size (~ 170 arcsec x 170 arcsec) atmospheric response. We
use advanced numerical modeling to showcase how MUSE will constrain
the properties of the solar atmosphere on the spatio-temporal scales
(<0.5 arcsec, <20 seconds) and large field-of-view on which
various state-of-the-art models of the physical processes that drive
coronal heating, solar flares and coronal mass ejections (CMEs)
make distinguishing and testable predictions. We describe how the
synergy between MUSE, the single-slit, high-resolution Solar-C EUVST
spectrograph, and ground-based observatories (DKIST and others) can
address how the solar atmosphere is energized, and the critical role
MUSE plays because of the multi-scale nature of the physical processes
involved. We focus on how comparisons between MUSE observations and
theoretical models will significantly further our understanding of
coronal heating mechanisms. This is a companion paper to Cheung et
al. (2021), also submitted to SH-17.
Title: Unsupervised Machine Learning for the Identification of
Preflare Spectroscopic Signatures
Authors: Woods, Magnus M.; Sainz Dalda, Alberto; De Pontieu, Bart
Bibcode: 2021ApJ...922..137W
Altcode:
The study of the preflare environment is of great importance to
understanding what drives solar flares. k-means clustering, an
unsupervised machine-learning technique, has the ability to cluster
large data set in a way that would be impractical or impossible for a
human to do. In this paper we present a study using k-means clustering
to identify possible preflare signatures in spectroscopic observations
of the Mg II h and k spectral lines made by NASA's Interface Region
Imaging Spectrometer. Our analysis finds that spectral profiles showing
single-peak Mg II h and k and single-peaked emission in the Mg II UV
triplet lines are associated with preflare activity up to 40 minutes
prior to flaring. Subsequent inversions of these spectral profiles
reveal increased temperature and electron density in the chromosphere,
which suggest that significant heating events in the chromosphere may
be associated with precursor signals to flares.
Title: Evidence of the multi-thermal nature of spicular
downflows. Impact on solar atmospheric heating
Authors: Bose, Souvik; Rouppe van der Voort, Luc; Joshi, Jayant;
Henriques, Vasco M. J.; Nóbrega-Siverio, Daniel; Martínez-Sykora,
Juan; De Pontieu, Bart
Bibcode: 2021A&A...654A..51B
Altcode: 2021arXiv210802153B
Context. Spectroscopic observations of the emission lines formed in the
solar transition region commonly show persistent downflows on the order
of 10−15 km s−1. The cause of such downflows, however, is
still not fully clear and has remained a matter of debate.
Aims:
We aim to understand the cause of such downflows by studying the coronal
and transition region responses to the recently reported chromospheric
downflowing rapid redshifted excursions (RREs) and their impact on the
heating of the solar atmosphere.
Methods: We have used two sets
of coordinated data from the Swedish 1 m Solar Telescope, the Interface
Region Imaging Spectrograph, and the Solar Dynamics Observatory for
analyzing the response of the downflowing RREs in the transition
region and corona. To provide theoretical support, we use an already
existing 2.5D magnetohydrodynamic simulation of spicules performed
with the Bifrost code.
Results: We find ample occurrences of
downflowing RREs and show several examples of their spatio-temporal
evolution, sampling multiple wavelength channels ranging from the cooler
chromospheric to the hotter coronal channels. These downflowing features
are thought to be likely associated with the returning components of
the previously heated spicular plasma. Furthermore, the transition
region Doppler shifts associated with them are close to the average
redshifts observed in this region, which further implies that these
flows could (partly) be responsible for the persistent downflows
observed in the transition region. We also propose two mechanisms -
(i) a typical upflow followed by a downflow and (ii) downflows along a
loop -from the perspective of a numerical simulation that could explain
the ubiquitous occurrence of such downflows. A detailed comparison
between the synthetic and observed spectral characteristics reveals a
distinctive match and further suggests an impact on the heating of the
solar atmosphere.
Conclusions: We present evidence that suggests
that at least some of the downflowing RREs are the chromospheric
counterparts of the transition region and lower coronal downflows. Movies associated to Figs. 1-3, 8, and 10 are available at https://www.aanda.org
Title: In the Trenches of the Solar-stellar Connection. IV. Solar
Full-disk Scans of C II, Si IV, and Mg II by the Interface Region
Imaging Spectrograph
Authors: Ayres, Thomas; De Pontieu, Bart; Testa, Paola
Bibcode: 2021ApJ...916...36A
Altcode:
About once a month, the Interface Region Imaging Spectrograph conducts
day-long raster scans of the full Sun in three ultraviolet spectral
channels. These full-disk mosaics are valuable in the solar context,
but provide a unique connection to the distant, unresolved stars. Here,
10 deep-exposure scans (4-8 s per slit step), collected during the
peak and decline of sunspot Cycle 24, were analyzed. Spatial spectra
(2″ pixels) of resonance lines of C II (T ~ 104 K), Si IV
(8 × 104 K), and Mg II (8 × 103 K) were fitted
with a pseudo-Gaussian model to track the emission strengths, widths,
and shifts in the various surface features that comprise the quiet
Sun and active regions. The full-disk mosaic spectra compare well to
tracings of solar-twin α Centauri A (HD 128620; G2 V). The contrast
between disk-average spectra from cycles MIN and MAX is relatively
modest (~50% in Si IV), but, remarkably, the brightest solar pixels
in active regions, at 2″ resolution, exceed the global-average
intensities of the most active Sun-like stars, suggesting a deeper
solar-stellar connection. Si IV shows a conspicuous bright ring at the
limb, whereas optically thicker C II and Mg II are suppressed (more
so for the latter). The Si IV emission favors the bright knots of the
large-scale supergranulation network, while the cooler Mg II emission
is more ubiquitous and C II intermediate. The non-Gaussian profile
of full-disk C IV, similar in formation temperature to Si IV, was
previously interpreted as a combination of narrow and broad dynamical
components, but the prevalence of the characteristic line shape in the
finest resolution spatial pixels of Si IV here provides support for
alternative formation scenarios, for example, invoking κ-distributions.
Title: Mapping of Solar Magnetic Fields from the Photosphere to the
Top of the Chromosphere with CLASP2
Authors: McKenzie, D.; Ishikawa, R.; Trujillo Bueno, J.; Auchere, F.;
del Pino Aleman, T.; Okamoto, T.; Kano, R.; Song, D.; Yoshida, M.;
Rachmeler, L.; Kobayashi, K.; Narukage, N.; Kubo, M.; Ishikawa, S.;
Hara, H.; Suematsu, Y.; Sakao, T.; Bethge, C.; De Pontieu, B.; Vigil,
G.; Winebarger, A.; Alsina Ballester, E.; Belluzzi, L.; Stepan, J.;
Asensio Ramos, A.; Carlsson, M.; Leenaarts, J.
Bibcode: 2021AAS...23810603M
Altcode:
Coronal heating, chromospheric heating, and the heating &
acceleration of the solar wind, are well-known problems in solar
physics. Additionally, knowledge of the magnetic energy that
powers solar flares and coronal mass ejections, important drivers
of space weather, is handicapped by imperfect determination of the
magnetic field in the sun's atmosphere. Extrapolation of photospheric
magnetic measurements into the corona is fraught with difficulties and
uncertainties, partly due to the vastly different plasma beta between
the photosphere and the corona. Better results in understanding
the coronal magnetic field should be derived from measurements of
the magnetic field in the chromosphere. To that end, we are pursuing
quantitative determination of the magnetic field in the chromosphere,
where plasma beta transitions from greater than unity to less than
unity, via ultraviolet spectropolarimetry. The CLASP2 mission, flown
on a sounding rocket in April 2019, succeeded in measuring all four
Stokes polarization parameters in UV spectral lines formed by singly
ionized Magnesium and neutral Manganese. Because these ions produce
spectral lines under different conditions, CLASP2 thus was able to
quantify the magnetic field properties at multiple heights in the
chromosphere simultaneously, as shown in the recent paper by Ishikawa
et al. In this presentation we will report the findings of CLASP2,
demonstrating the variation of magnetic fields along a track on
the solar surface and as a function of height in the chromosphere;
and we will illustrate what is next for the CLASP missions and the
demonstration of UV spectropolarimetry in the solar chromosphere.
Title: A New View of the Solar Interface Region from the Interface
Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, Bart; Polito, Vanessa; Hansteen, Viggo; Testa,
Paola; Reeves, Katharine K.; Antolin, Patrick; Nóbrega-Siverio,
Daniel Elias; Kowalski, Adam F.; Martinez-Sykora, Juan; Carlsson,
Mats; McIntosh, Scott W.; Liu, Wei; Daw, Adrian; Kankelborg, Charles C.
Bibcode: 2021SoPh..296...84D
Altcode: 2021arXiv210316109D
The Interface Region Imaging Spectrograph (IRIS) has been obtaining
near- and far-ultraviolet images and spectra of the solar atmosphere
since July 2013. IRIS is the highest resolution observatory to provide
seamless coverage of spectra and images from the photosphere into the
low corona. The unique combination of near- and far-ultraviolet spectra
and images at sub-arcsecond resolution and high cadence allows the
tracing of mass and energy through the critical interface between the
surface and the corona or solar wind. IRIS has enabled research into the
fundamental physical processes thought to play a role in the low solar
atmosphere such as ion-neutral interactions, magnetic reconnection, the
generation, propagation, and dissipation of waves, the acceleration of
non-thermal particles, and various small-scale instabilities. IRIS has
provided insights into a wide range of phenomena including the discovery
of non-thermal particles in coronal nano-flares, the formation and
impact of spicules and other jets, resonant absorption and dissipation
of Alfvénic waves, energy release and jet-like dynamics associated
with braiding of magnetic-field lines, the role of turbulence and the
tearing-mode instability in reconnection, the contribution of waves,
turbulence, and non-thermal particles in the energy deposition during
flares and smaller-scale events such as UV bursts, and the role of flux
ropes and various other mechanisms in triggering and driving CMEs. IRIS
observations have also been used to elucidate the physical mechanisms
driving the solar irradiance that impacts Earth's upper atmosphere,
and the connections between solar and stellar physics. Advances in
numerical modeling, inversion codes, and machine-learning techniques
have played a key role. With the advent of exciting new instrumentation
both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST)
and the Atacama Large Millimeter/submillimeter Array (ALMA), and
space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim
to review new insights based on IRIS observations or related modeling,
and highlight some of the outstanding challenges.
Title: Emergence of Internetwork Magnetic Fields through the Solar
Atmosphere
Authors: Gošić, M.; De Pontieu, B.; Bellot Rubio, L. R.; Sainz Dalda,
A.; Pozuelo, S. Esteban
Bibcode: 2021ApJ...911...41G
Altcode: 2021arXiv210302213G
Internetwork (IN) magnetic fields are highly dynamic, short-lived
magnetic structures that populate the interior of supergranular
cells. Since they emerge all over the Sun, these small-scale fields
bring a substantial amount of flux, and therefore energy, to the solar
surface. Because of this, IN fields are crucial for understanding
the quiet Sun (QS) magnetism. However, they are weak and produce very
small polarization signals, which is the reason why their properties
and impact on the energetics and dynamics of the solar atmosphere are
poorly known. Here we use coordinated, high-resolution, multiwavelength
observations obtained with the Swedish 1 m Solar Telescope and the
Interface Region Imaging Spectrograph (IRIS) to follow the evolution
of IN magnetic loops as they emerge into the photosphere and reach
the chromosphere and transition region. We studied in this paper three
flux emergence events having total unsigned magnetic fluxes of 1.9 ×
1018, 2.5 × 1018, and 5.3 × 1018
Mx. The footpoints of the emerging IN bipoles are clearly seen
to appear in the photosphere and to rise up through the solar
atmosphere, as observed in Fe I 6173 Å and Mg I b2 5173
Å magnetograms, respectively. For the first time, our polarimetric
measurements taken in the chromospheric Ca II 8542 Å line provide
direct observational evidence that IN fields are capable of reaching the
chromosphere. Moreover, using IRIS data, we study the effects of these
weak fields on the heating of the chromosphere and transition region.
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
Bibcode: 2021SoPh..296...70R
Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
Title: Mapping solar magnetic fields from the photosphere to the
base of the corona
Authors: Ishikawa, Ryohko; Bueno, Javier Trujillo; del Pino Alemán,
Tanausú; Okamoto, Takenori J.; McKenzie, David E.; Auchère,
Frédéric; Kano, Ryouhei; Song, Donguk; Yoshida, Masaki; Rachmeler,
Laurel A.; Kobayashi, Ken; Hara, Hirohisa; Kubo, Masahito; Narukage,
Noriyuki; Sakao, Taro; Shimizu, Toshifumi; Suematsu, Yoshinori; Bethge,
Christian; De Pontieu, Bart; Dalda, Alberto Sainz; Vigil, Genevieve D.;
Winebarger, Amy; Ballester, Ernest Alsina; Belluzzi, Luca; Štěpán,
Jiří; Ramos, Andrés Asensio; Carlsson, Mats; Leenaarts, Jorrit
Bibcode: 2021SciA....7.8406I
Altcode: 2021arXiv210301583I
Routine ultraviolet imaging of the Sun's upper atmosphere shows the
spectacular manifestation of solar activity; yet we remain blind to
its main driver, the magnetic field. Here we report unprecedented
spectropolarimetric observations of an active region plage and
its surrounding enhanced network, showing circular polarization in
ultraviolet (Mg II $h$ & $k$ and Mn I) and visible (Fe I) lines. We
infer the longitudinal magnetic field from the photosphere to the
very upper chromosphere. At the top of the plage chromosphere the
field strengths reach more than 300 gauss, strongly correlated with
the Mg II $k$ line core intensity and the electron pressure. This
unique mapping shows how the magnetic field couples the different
atmospheric layers and reveals the magnetic origin of the heating in
the plage chromosphere.
Title: Coronal observations with the Multi-Slit Solar Explorer (MUSE)
Authors: De Pontieu, Bart; Lemen, James; Cheung, Mark; Boerner, Paul
Bibcode: 2021cosp...43E1803D
Altcode:
Observations of the corona are key to constrain magnetic field
models of the solar atmosphere. In this abstract we describe novel
observations that will be enabled by the Multi-Slit Solar Explorer
(MUSE), a proposed MIDEX mission for studying the dynamics of the
corona and transition region. MUSE will use both conventional and novel
spectral imaging techniques, coupled to state-of-the-art numerical
modeling. MUSE will obtain EUV spectra and images with the highest
resolution in space (1/3 arcsec) and time (1-4 s) ever achieved for
the transition region and corona, along 37 slits and a large context
FOV simultaneously. The science goals of MUSE are to understand the
physical mechanisms responsible for energy release in the corona
and for driving flares and coronal mass ejections. MUSE contains two
instruments: an EUV spectrograph and an EUV context imager. The MUSE
spectrograph employs a novel multi-slit design that enables a 100x
improvement in spectral scanning rates, which will reveal crucial
information about the dynamics of the physical processes that are not
observable with current instruments. MUSE will provide key constraints
on the morphology and dynamics of the magnetic field. We will discuss
the MUSE design and how it has been optimized to minimize effects
from overlapping spectra dispersed from different slits. We will also
illustrate how MUSE observations will lead to a better understanding
of how the dynamic magnetic field drives flares and eruptions.
Title: Fine-scale explosive energy release at sites of magnetic
flux cancellation in the core of a solar active region: Hi-C 2.1,
IRIS and SDO observations
Authors: Tiwari, Sanjiv Kumar; Moore, Ronald; De Pontieu, Bart;
Winebarger, Amy; Panesar, Navdeep Kaur
Bibcode: 2021cosp...43E1779T
Altcode:
The second sounding-rocket flight of the High-Resolution Coronal Imager
(Hi-C 2.1) provided unprecedentedly-high spatial and temporal resolution
(~250 km, 4.4 s) coronal EUV images of Fe IX/X emission at 172 A, of
a solar active region (AR NOAA 12712) near solar disk center. Three
morphologically-different types (I: dot-like, II: loop-like, &
III: surge/jet-like) of fine-scale sudden brightening events (tiny
microflares) are seen within and at the ends of an arch filament system
in the core of the AR. Although type Is resemble IRIS bombs (in size,
and brightness with respect to surroundings), our dot-like events are
apparently much hotter, and shorter in span (70 s). Because Dot-like
brightenings are not as clearly discernible in AIA 171 A as in Hi-C 172
A, they were not reported before. We complement the 5-minute-duration
Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images,
and IRIS UV spectra and slit-jaw images to examine, at the sites of
these events, brightenings and flows in the transition region and corona
and evolution of magnetic flux in the photosphere. Most, if not all,
of the events are seated at sites of opposite-polarity magnetic flux
convergence (sometimes driven by adjacent flux emergence), implying
flux cancellation at the microflare's polarity inversion line. In the
IRIS spectra and images, we find confirming evidence of field-aligned
outflow from brightenings at the ends of loops of the arch filament
system. In types I and II the explosion is confined, while in type
III the explosion is ejective and drives jet-like outflow. The light
curves from Hi-C, AIA and IRIS peak nearly simultaneously for many
of these events and none of the events display a systematic cooling
sequence as seen in typical coronal flares, suggesting that these tiny
brightening events have chromospheric/transition-region origin.
Title: ALMA and IRIS Observations of the Solar
Chromosphere. II. Structure and Dynamics of Chromospheric Plages
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski,
Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.;
Sainz Dalda, Alberto
Bibcode: 2021ApJ...906...83C
Altcode: 2020arXiv201205970C
We propose and employ a novel empirical method for determining
chromospheric plage regions, which seems to better isolate a plage from
its surrounding regions than other methods commonly used. We caution
that isolating a plage from its immediate surroundings must be done
with care in order to successfully mitigate statistical biases that,
for instance, can impact quantitative comparisons between different
chromospheric observables. Using this methodology, our analysis suggests
that λ = 1.25 mm free-free emission in plage regions observed with
the Atacama Large Millimeter/submillimeter Array (ALMA)/Band6 may
not form in the low chromosphere as previously thought, but rather
in the upper chromospheric parts of dynamic plage features (such as
spicules and other bright structures), i.e., near geometric heights
of transition-region temperatures. We investigate the high degree of
similarity between chromospheric plage features observed in ALMA/Band6
(at 1.25 mm wavelengths) and the Interface Region Imaging Spectrograph
(IRIS)/Si IV at 1393 Å. We also show that IRIS/Mg II h and k are
not as well correlated with ALMA/Band6 as was previously thought,
and we discuss discrepancies with previous works. Lastly, we report
indications of chromospheric heating due to propagating shocks supported
by the ALMA/Band6 observations.
Title: ALMA and IRIS Observations of the Solar Chromosphere. I. An
On-disk Type II Spicule
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Hansteen, Viggo; de la Cruz Rodríguez, Jaime; Szydlarski,
Mikolaj; Jafarzadeh, Shahin; Wedemeyer, Sven; Bastian, Timothy S.;
Sainz Dalda, Alberto
Bibcode: 2021ApJ...906...82C
Altcode: 2020arXiv200512717C
We present observations of the solar chromosphere obtained
simultaneously with the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Interface Region Imaging Spectrograph. The observatories
targeted a chromospheric plage region of which the spatial distribution
(split between strongly and weakly magnetized regions) allowed the
study of linear-like structures in isolation, free of contamination
from background emission. Using these observations in conjunction with
a radiative magnetohydrodynamic 2.5D model covering the upper convection
zone all the way to the corona that considers nonequilibrium ionization
effects, we report the detection of an on-disk chromospheric spicule
with ALMA and confirm its multithermal nature.
Title: High Resolution Observations of the Low Atmospheric Response
to Small Heating Events in Active Regions
Authors: Testa, P.; Rouppe van der Voort, L.; De Pontieu, B.; Bakke, H.
Bibcode: 2020AGUFMSH004..03T
Altcode:
We investigate the low atmospheric response to small heating events
(nano/micro-flares) by analyzing coordinated active region observations
with IRIS and SST, and also using the simultaneous SDO/AIA observations
to study the coronal emission. The events we observe as intense
brightenings in the chromosphere and transition region are clearly
associated with heating of the overlying loops to high temperatures
(5-10MK), as is clear from the strong Fe XVIII emission observed in
the 94A SDO/AIA passband. Some of the chromospheric brightenings have
been observed with the SST with the CRISP instrument in Ca II 8542 and
H-alpha, as well as with the new CHROMIS instrument in Ca II K, which
provides unprecedented resolution. We will present the rich spectral
diagnostics offered by IRIS and SST for these events, including insights
we obtained by applying a k-means clustering analysis to the SST and
IRIS spectra during the heating events. Our observations will help
provide more stringent constraints on the properties of non-thermal
particles in nanoflares and microflares.
Title: Fine-scale explosive energy release at sites of magnetic
flux cancellation in the core of a solar active region: Hi-C 2.1,
IRIS and SDO observations
Authors: Tiwari, S. K.; Panesar, N. K.; Moore, R. L.; De Pontieu,
B.; Winebarger, A. R.
Bibcode: 2020AGUFMSH0010007T
Altcode:
The second sounding-rocket flight of the High-Resolution Coronal Imager
(Hi-C 2.1) provided unprecedentedly-high spatial and temporal resolution
(~250 km, 4.4 s) coronal EUV images of Fe IX/X emission at 172 Å, of
a solar active region (AR NOAA 12712) near solar disk center. Three
morphologically-different types (I: dot-like, II: loop-like, &
III: surge/jet-like) of fine-scale sudden brightening events (tiny
microflares) are seen within and at the ends of an arch filament system
in the core of the AR. Although type Is resemble IRIS bombs (in size,
and brightness with respect to surroundings), our dot-like events are
apparently much hotter, and shorter in span (70 s). Because Dot-like
brightenings are not as clearly discernible in AIA 171 Å as in Hi-C 172
Å, they were not reported before. We complement the 5-minute-duration
Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images,
and IRIS UV spectra and slit-jaw images to examine, at the sites of
these events, brightenings and flows in the transition region and corona
and evolution of magnetic flux in the photosphere. Most, if not all,
of the events are seated at sites of opposite-polarity magnetic flux
convergence (sometimes driven by adjacent flux emergence), implying
flux cancellation at the microflare's polarity inversion line. In the
IRIS spectra and images, we find confirming evidence of field-aligned
outflow from brightenings at the ends of loops of the arch filament
system. In types I and II the explosion is confined, while in type
III the explosion is ejective and drives jet-like outflow. The light
curves from Hi-C, AIA and IRIS peak nearly simultaneously for many
of these events and none of the events display a systematic cooling
sequence as seen in typical coronal flares, suggesting that these tiny
brightening events have chromospheric/transition-region origin.
Title: ALMA and IRIS Observations Highlighting the Dynamics and
Structure of Chromospheric Plage
Authors: Chintzoglou, G.; De Pontieu, B.; Martinez-Sykora, J.;
Hansteen, V. H.; de la Cruz Rodriguez, J.; Szydlarski, M.; Jafarzadeh,
S.; Wedemeyer, S.; Bastian, T.; Sainz Dalda, A.
Bibcode: 2020AGUFMSH0010009C
Altcode:
We present observations of the solar chromosphere obtained
simultaneously with the Atacama Large Millimeter/submillimeter Array
(ALMA) and the Interface Region Imaging Spectrograph (IRIS). The
observatories targeted a chromospheric plage region of which the spatial
distribution (split between strongly and weakly magnetized regions)
allowed the study of linear-like structures in isolation, free of
contamination from background emission. Using these observations
in conjunction with a radiative magnetohydrodynamic 2.5D model
covering the upper convection zone all the way to the corona
that considers non-equilibrium ionization effects, we report the
detection of an on-disk chromospheric spicule with ALMA and confirm
its multithermal nature. In addition, we discuss the strikingly high
degree of similarity between chromospheric plage features observed
in ALMA/Band6 and IRIS/\ion{Si}{4} (also reproduced in our model)
suggesting that ALMA/Band6 does not observe in the low chromosphere as
previously thought but rather observes the upper chromospheric parts
of structures such as spicules and other bright structures above plage
at geometric heights near transition region temperatures. We also show
that IRIS/\ion{Mg}{2} is not as well correlated with ALMA/Band6 as was
previously thought. For these comparisons, we propose and employ a novel
empirical method for the determination of plage regions, which seems
to better isolate plage from its surrounding regions as compared to
other methods commonly used. We caution that isolating plage from its
immediate surroundings must be done with care to mitigate statistical
bias in quantitative comparisons between different chromospheric
observables. Lastly, we report indications for chromospheric heating
due to traveling shocks supported by the ALMA/Band6 observations.
Title: Observations of Solar Spicules at Millimeter and Ultraviolet
Wavelengths
Authors: Bastian, T.; De Pontieu, B.; Shimojo, M.; Iwai, K.;
Alissandrakis, C.; Nindos, A.; Vial, J. C.; White, S. M.
Bibcode: 2020AGUFMSH004..08B
Altcode:
Solar spicules are a ubiquitous chromospheric phenomenon in which
multitudes of dynamic jets with temperatures of order 104
K extend thousands of kilometers into the solar atmosphere. Recent
progress has been made refining the observational characteristics
of spicules using the Hinode Solar Optical Telescope (SOT) and the
Interface Region Imaging Spectrograph (IRIS) observations at optical
and ultraviolet wavelengths, respectively. Two types of spicule
have been identified. Type I spicules, prevalent in solar active
regions, have upward speeds of order 25 km/s and lifetimes of 3-7
min. They may be the limb counterpart to shock-wave-driven fibrils
commonly seen against the solar disk in active regions. In contrast,
type II spicules, more common in quiet regions and coronal holes,
display upward speeds of 50-150 km/s, lifetimes of 30-110 s, and
appear to be partially heated to temperatures of 105 K and
higher. These observations have provoked intense interest in spicules
and have led to proposals that type II spicules play a central role
as a source of hot plasma in the corona. Nevertheless, their role in
mass and energy transport between the lower and upper layers of the
solar atmosphere remains an outstanding problem. Here, we report
imaging observations of solar spicules at millimeter wavelengths using
the Atacama Large Millimeter-submillimeter Array (ALMA) with arcsecond
angular resolution. Continuum millimeter wavelength radiation forms
under conditions of local thermodynamic equilibrium, thereby providing a
complementary tool to UV lines, which form under non-LTE conditions. The
observations were made on 2018 December 24-25 at λ=1.25 mm and λ=3
mm. The ALMA observations pose special challenges, particularly at
1.25 mm, where the limited field of view of the instrument motivated
us to use a novel mosaic imaging technique: multiple pointings were
assembled to form a single map with an angular resolution of 1" x 0.7"
on a cadence of roughly 2 min. In contrast, we were able to image at 3
mm continuously, with a map cadence of 2 s and an angular resolution of
2.3" x 1.3". We compare and contrast the morphology and dynamics
of mm-λ observations of spicules with those obtained by IRIS at UV
wavelengths and place constraints on spicule temperatures and masses
using the joint millimeter-wavelength observations.
Title: On the velocity drift between ions in the solar atmosphere
Authors: Martínez-Sykora, J.; Szydlarski, M.; Hansteen, V. H.;
De Pontieu, B.
Bibcode: 2020AGUFMSH0010017M
Altcode:
Very recent results that compare ALMA and IRIS observations with 2D
radiative MHD including non-equilibrium ionization and ambipolar
diffusion models of the type II spicules reveal that these models
may underestimate the energy dissipated in the chromosphere. The
solar atmosphere is composed of many species that are populated at
different ionization and excitation levels. The upper chromosphere,
transition region, and corona are nearly collisionless. Consequently,
slippage between, for instance, ions and neutral particles, or
interactions between separate species, may play an important role
in the local momentum and energy balance. The interaction between
species is missing in the 2D radiative MHD model. We have developed a
3D multi-fluid and multi-species numerical code (Ebysus) to investigate
such effects. Ebysus is capable of treating species (e.g., hydrogen,
helium, etc) and fluids (neutrals, excited and ionized elements)
separately. Treating different species as different fluids leads
to drifts between different ions and an electric field that couple
these motions. Different ionized species and momentum exchange can
dissipate this velocity drift, i.e., convert wave kinetic energy into
thermal energy. High-frequency Alfven waves, driven for instance by
reconnection, thought to occur in the solar atmosphere, can drive such
multi-ion velocity drifts.
Title: Investigating the Chromospheric Footpoints of the Solar Wind
Authors: Bryans, Paul; McIntosh, Scott W.; Brooks, David H.; De
Pontieu, Bart
Bibcode: 2020ApJ...905L..33B
Altcode:
Coronal holes present the source of the fast solar wind. However,
the fast solar wind is not unimodal—there are discrete, but subtle,
compositional, velocity, and density structures that differentiate
different coronal holes as well as wind streams that originate within
one coronal hole. In this Letter we exploit full-disk observational
"mosaics" performed by the Interface Region Imaging Spectrograph
(IRIS) spacecraft to demonstrate that significant spectral variation
exists within the chromospheric plasma of coronal holes. The spectral
differences outline the boundaries of some—but not all—coronal
holes. In particular, we show that the "peak separation" of the Mg
II h line at 2803 Å illustrates changes in what appear to be open
magnetic features within a coronal hole. These observations point
to a chromospheric source for the inhomogeneities found in the fast
solar wind. These chromospheric signatures can provide additional
constraints on magnetic field extrapolations close to the source,
potentially on spatial scales smaller than from traditional coronal hole
detection methods based on intensity thresholding in the corona. This
is of increased importance with the advent of Parker Solar Probe and
Solar Orbiter and the ability to accurately establish the connectivity
between their in situ measurements and remote sensing observations of
the solar atmosphere.
Title: The correlation between chromospheric and coronal heating in
active region plage
Authors: De Pontieu, B.; Hansteen, V. H.; Winebarger, A. R.
Bibcode: 2020AGUFMSH0010010D
Altcode:
The upper transition region at the footpoints of the hottest loops in
active regions is known as moss, highly structured and dynamic 1 MK
plasma that is formed at the same heights as dynamic chromospheric jets
emanating from the underlying plage regions. Moss provides an excellent
laboratory to disentangle the complex interface between chromosphere and
corona and to study how chromospheric and coronal heating mechanisms
are spatio-temporally correlated (if at all). This is because moss is
very sensitive to changes in the local heating rate and, since it is
formed in a thin, corrugated layer, avoids the confusion introduce
by line-of-sight superposition taht affects optically thin coronal
diagnostics. Previous results based on lower-resolution instruments
(e.g., TRACE, SDO/AIA) suggested a puzzling mismatch between low
chromospheric and upper TR emission. We will present results based on
analysis of a unique coordinated dataset from IRIS and the sounding
rocket HiC. The HiC 2.1 flight took place in 2018 and obtained several
minutes of sub-arcsecond resolution images of the upper TR in Fe IX
171A, while IRIS obtained high-resolution rasters in the Mg II h &
k lines at high cadence. Our analysis will focus on spatio-temporal
correlations between the properties of the optically thick Mg II h
& k lines, and the intensities of the HiC 2.1 images. We will
also exploit the recently developed IRIS2 database to invert the
Mg II h & k profiles and study correlations between the derived
chromospheric temperature, density, and micro-turbulence (as a function
of height in the chromosphere) and the overlying upper TR and coronal
emission. Our analysis provides insight and constraints on the nature
and (dis)similarities of the heating mechanisms in both the chromosphere
and corona.
Title: The Solar-C (EUVST) mission: the latest status
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko; Suematsu,
Yoshinori; Hara, Hirohisa; Tsuzuki, Toshihiro; Katsukawa, Yukio; Kubo,
Masahito; Ishikawa, Ryoko; Watanabe, Tetsuya; Toriumi, Shin; Ichimoto,
Kiyoshi; Nagata, Shin'ichi; Hasegawa, Takahiro; Yokoyama, Takaaki;
Watanabe, Kyoko; Tsuno, Katsuhiko; Korendyke, Clarence M.; Warren,
Harry; De Pontieu, Bart; Boerner, Paul; Solanki, Sami K.; Teriaca,
Luca; Schuehle, Udo; Matthews, Sarah; Long, David; Thomas, William;
Hancock, Barry; Reid, Hamish; Fludra, Andrzej; Auchère, Frederic;
Andretta, Vincenzo; Naletto, Giampiero; Poletto, Luca; Harra, Louise
Bibcode: 2020SPIE11444E..0NS
Altcode:
Solar-C (EUVST) is the next Japanese solar physics mission to
be developed with significant contributions from US and European
countries. The mission carries an EUV imaging spectrometer with
slit-jaw imaging system called EUVST (EUV High-Throughput Spectroscopic
Telescope) as the mission payload, to take a fundamental step towards
answering how the plasma universe is created and evolves and how the
Sun influences the Earth and other planets in our solar system. In
April 2020, ISAS (Institute of Space and Astronautical Science) of JAXA
(Japan Aerospace Exploration Agency) has made the final down-selection
for this mission as the 4th in the series of competitively chosen
M-class mission to be launched with an Epsilon launch vehicle in mid
2020s. NASA (National Aeronautics and Space Administration) has selected
this mission concept for Phase A concept study in September 2019 and
is in the process leading to final selection. For European countries,
the team has (or is in the process of confirming) confirmed endorsement
for hardware contributions to the EUVST from the national agencies. A
recent update to the mission instrumentation is to add a UV spectral
irradiance monitor capability for EUVST calibration and scientific
purpose. This presentation provides the latest status of the mission
with an overall description of the mission concept emphasizing on key
roles of the mission in heliophysics research from mid 2020s.
Title: Chromospheric response to emergence of internetwork magnetic
fields
Authors: Gosic, M.; De Pontieu, B.; Bellot Rubio, L.; Sainz Dalda, A.
Bibcode: 2020AGUFMSH0010006G
Altcode:
Internetwork (IN) magnetic fields are weak, short-lived, but highly
dynamic magnetic structures that emerge all over the Sun. They
bring an enormous amount of magnetic flux and energy to the solar
surface. Therefore, IN fields are of paramount importance for
maintenance of the QS magnetism. Since these fields are ubiquitous,
they may have a substantial impact on the energetics and dynamics of the
solar atmosphere. In this work, we use coordinated, high-resolution,
multiwavelength observations obtained with the Interface Region
Imaging Spectrograph (IRIS) and the Swedish 1 m Solar Telescope (SST)
to follow the evolution of IN magnetic loops as they emerge into the
photosphere. The footpoints of the emerging IN bipoles are clearly
visible as they appear in the photosphere and rise up through the
solar atmosphere, as seen in SST magnetograms taken in the Fe I
6173 Å and Mg I b2 5173 Å lines, respectively. Our polarimetric
measurements, taken in the Ca II 8542 Å line, provide the first
direct observational evidence that IN fields are capable of reaching
the chromosphere. Moreover, using IRIS data, we describe in detail
how individual IN bipoles affect the dynamics and energetics of the
chromosphere and transition region.
Title: Chromospheric and TR diagnostics in a large scale numerical
simulation of flux emergence: Synthetic vs Real observables
Authors: Hansteen, V. H.; De Pontieu, B.; Testa, P.; Gosic, M.;
Martinez-Sykora, J.
Bibcode: 2020AGUFMSH0010021H
Altcode:
Field stored just below or rising to the photosphere will break through
the surface and enter the upper atmosphere once the gradient of the
subphotospheric field strength becomes sufficiently large. Opposite
polarity flux bundles will reconnect in the photosphere and above,
to form steadily longer loops that expand into the outer solar
atmosphere, forming the corona. Some of the emerging flux is likely
due to a local dynamo, but also the direct emergence of large scale
magnetic structures from below is important, even in the quiet Sun. A
significant proportion of this field likely reaches the chromosphere
and may leave imprint on chromospheric dynamics and energetics. Using
large scale numerical models (72x72x60) Mm and the high resolution
spectra and slit jaw images from IRIS, as well as photospheric data
from Hinode/SOT, and SDO/HMI we study the interactions between the
magnetic flux caught in the granular flow field and the chromosphere
and chromospheric field above. We will compare synthetic observables
of the photospheric Fe I 617.3 nm line, the chromospheric Mg II h&k
lines, and the transition region Si IV lines, with their observational
counterparts. We will also generate synthetic ALMA band 3 images. The
comparison of synthetic observational data will let us draw conclusions
as to the validity of the numerical modeling and the importance of flux
emergence for the dynamics and energetics of the outer solar atmosphere.
Title: IRIS Observations of the Low-atmosphere Counterparts of Active
Region Outflows
Authors: Polito, Vanessa; De Pontieu, Bart; Testa, Paola; Brooks,
David H.; Hansteen, Viggo
Bibcode: 2020ApJ...903...68P
Altcode: 2020arXiv201015945P
Active region (AR) outflows have been studied in detail since
the launch of Hinode/EIS and are believed to provide a possible
source of mass and energy to the slow solar wind. In this work, we
investigate the lower atmospheric counterpart of AR outflows using
observations from the Interface Region Imaging Spectrograph (IRIS). We
find that the IRIS Si IV, C II> and Mg II transition region (TR)
and chromospheric lines exhibit different spectral features in the
outflows as compared to neighboring regions at the footpoints ("moss")
of hot AR loops. The average redshift of Si IV in the outflow region
(≍5.5 km s-1) is smaller than typical moss (≍12-13
km s-1) and quiet Sun (≍7.5 km s-1) values,
while the C II line is blueshifted (≍-1.1-1.5 km s-1),
in contrast to the moss where it is observed to be redshifted by
about ≍2.5 km s-1. Further, we observe that the low
atmosphere underneath the coronal outflows is highly structured, with
the presence of blueshifts in Si IV and positive Mg II k2 asymmetries
(which can be interpreted as signatures of chromospheric upflows)
which are mostly not observed in the moss. These observations show a
clear correlation between the coronal outflows and the chromosphere
and TR underneath, which has not been shown before. Our work strongly
suggests that these regions are not separate environments and should
be treated together, and that current leading theories of AR outflows,
such as the interchange reconnection model, need to take into account
the dynamics of the low atmosphere.
Title: Observations and Modeling of the Onset of Fast Reconnection
in the Solar Transition Region
Authors: Guo, L. -J.; De Pontieu, Bart; Huang, Y. -M.; Peter, H.;
Bhattacharjee, A.
Bibcode: 2020ApJ...901..148G
Altcode: 2020arXiv200911475G
Magnetic reconnection is a fundamental plasma process that plays a
critical role not only in energy release in the solar atmosphere, but
also in fusion, astrophysics, and other space plasma environments. One
of the challenges in explaining solar observations in which reconnection
is thought to play a critical role is to account for the transition of
the dynamics from a slow quasi-continuous phase to a fast and impulsive
energetic burst of much shorter duration. Despite the theoretical
progress in identifying mechanisms that might lead to rapid onset,
a lack of observations of this transition has left models poorly
constrained. High-resolution spectroscopic observations from NASA's
Interface Region Imaging Spectrograph now reveal tell-tale signatures
of the abrupt transition of reconnection from a slow phase to a fast,
impulsive phase during UV bursts or explosive events in the Sun's
atmosphere. Our observations are consistent with numerical simulations
of the plasmoid instability, and provide evidence for the onset of
fast reconnection mediated by plasmoids and new opportunities for
remote-sensing diagnostics of reconnection mechanisms on the Sun.
Title: On the Velocity Drift between Ions in the Solar Atmosphere
Authors: Martínez-Sykora, Juan; Szydlarski, Mikolaj; Hansteen,
Viggo H.; De Pontieu, Bart
Bibcode: 2020ApJ...900..101M
Altcode: 2020arXiv200800069M
The solar atmosphere is composed of many species, which are populated
at different ionization and excitation levels. The upper chromosphere,
transition region, and corona are nearly collisionless. Consequently,
slippage between, for instance, ions and neutral particles, or
interactions between separate species, may play important roles. We
have developed a 3D MFMS numerical code (Ebysus) to investigate such
effects. Ebysus is capable of treating species (e.g., hydrogen,
helium, etc.) and fluids (neutrals, excited and ionized elements)
separately, including nonequilibrium ionization, momentum exchange,
radiation, thermal conduction, and other complex processes in the solar
atmosphere. Treating different species as different fluids leads to
drifts between different ions and an electric field that couples these
motions. The coupling for two ionized fluids can lead to an anti-phase
rotational motion between them. Different ionized species and momentum
exchange can dissipate this velocity drift, i.e., convert wave kinetic
energy into thermal energy. High-frequency Alfvén waves driven by,
e.g., reconnection thought to occur in the solar atmosphere, can drive
such multi-ion velocity drifts.
Title: High-resolution observations of the solar photosphere,
chromosphere, and transition region. A database of coordinated IRIS
and SST observations
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson,
M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.;
Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques,
V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.;
Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.;
Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.;
Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski,
M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P.
Bibcode: 2020A&A...641A.146R
Altcode: 2020arXiv200514175R
NASA's Interface Region Imaging Spectrograph (IRIS) provides
high-resolution observations of the solar atmosphere through ultraviolet
spectroscopy and imaging. Since the launch of IRIS in June 2013, we
have conducted systematic observation campaigns in coordination with
the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides
complementary high-resolution observations of the photosphere and
chromosphere. The SST observations include spectropolarimetric imaging
in photospheric Fe I lines and spectrally resolved imaging in the
chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present
a database of co-aligned IRIS and SST datasets that is open for
analysis to the scientific community. The database covers a variety
of targets including active regions, sunspots, plages, the quiet Sun,
and coronal holes.
Title: Coronal Mini-jets in an Activated Solar Tornado-like Prominence
Authors: Chen, Huadong; Zhang, Jun; De Pontieu, Bart; Ma, Suli; Kliem,
Bernhard; Priest, Eric
Bibcode: 2020ApJ...899...19C
Altcode: 2020arXiv200608252C
High-resolution observations from the Interface Region Imaging
Spectrometer reveal the existence of a particular type of small
solar jet, which arose singly or in clusters from a tornado-like
prominence suspended in the corona. In this study, we perform a detailed
statistical analysis of 43 selected mini-jets in the tornado event. Our
results show that the mini-jets typically have (1) a projected length
of 1.0-6.0 Mm, (2) a width of 0.2-1.0 Mm, (3) a lifetime of 10-50 s,
(4) a velocity of 100-350 km s-1, and (5) an acceleration
of 3-20 km s-2. Based on spectral diagnostics and EM-Loci
analysis, these jets seem to be multithermal small-scale plasma
ejections with an estimated average electron density of ∼2.4 ×
1010 cm-3 and an approximate mean temperature of
∼2.6 × 105 K. Their mean kinetic energy density, thermal
energy density, and dissipated magnetic field strength are roughly
estimated to be ∼9 erg cm-3, 3 erg cm-3, and
16 G, respectively. The accelerations of the mini-jets, the UV and EUV
brightenings at the footpoints of some mini-jets, and the activation
of the host prominence suggest that the tornado mini-jets are probably
created by fine-scale external or internal magnetic reconnections (a)
between the prominence field and the enveloping or background field or
(b) between twisted or braided flux tubes within the prominence. The
observations provide insight into the geometry of such reconnection
events in the corona and have implications for the structure of the
prominence magnetic field and the instability that is responsible for
the eruption of prominences and coronal mass ejections.
Title: Observation and Modeling of High-temperature Solar Active
Region Emission during the High-resolution Coronal Imager Flight of
2018 May 29
Authors: Warren, Harry P.; Reep, Jeffrey W.; Crump, Nicholas A.;
Ugarte-Urra, Ignacio; Brooks, David H.; Winebarger, Amy R.; Savage,
Sabrina; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub,
Leon; Kobayashi, Ken; McKenzie, David; Morton, Richard; Rachmeler,
Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert
Bibcode: 2020ApJ...896...51W
Altcode:
Excellent coordinated observations of NOAA active region 12712 were
obtained during the flight of the High-resolution Coronal Imager (Hi-C)
sounding rocket on 2018 May 29. This region displayed a typical active
region core structure with relatively short, high-temperature loops
crossing the polarity inversion line and bright "moss" located at the
footpoints of these loops. The differential emission measure (DEM) in
the active region core is very sharply peaked at about 4 MK. Further,
there is little evidence for impulsive heating events in the moss, even
at the high spatial resolution and cadence of Hi-C. This suggests that
active region core heating is occurring at a high frequency and keeping
the loops close to equilibrium. To create a time-dependent simulation of
the active region core, we combine nonlinear force-free extrapolations
of the measured magnetic field with a heating rate that is dependent
on the field strength and loop length and has a Poisson waiting time
distribution. We use the approximate solutions to the hydrodynamic
loop equations to simulate the full ensemble of active region core
loops for a range of heating parameters. In all cases, we find that
high-frequency heating provides the best match to the observed DEM. For
selected field lines, we solve the full hydrodynamic loop equations,
including radiative transfer in the chromosphere, to simulate transition
region and chromospheric emission. We find that for heating scenarios
consistent with the DEM, classical signatures of energy release,
such as transition region brightenings and chromospheric evaporation,
are weak, suggesting that they would be difficult to detect.
Title: The Drivers of Active Region Outflows into the Slow Solar Wind
Authors: Brooks, David H.; Winebarger, Amy R.; Savage, Sabrina; Warren,
Harry P.; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub,
Leon; Kobayashi, Ken; McIntosh, Scott W.; McKenzie, David; Morton,
Richard; Rachmeler, Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert
Bibcode: 2020ApJ...894..144B
Altcode: 2020arXiv200407461B
Plasma outflows from the edges of active regions have been suggested as
a possible source of the slow solar wind. Spectroscopic measurements
show that these outflows have an enhanced elemental composition,
which is a distinct signature of the slow wind. Current spectroscopic
observations, however, do not have sufficient spatial resolution to
distinguish what structures are being measured or determine the driver
of the outflows. The High-resolution Coronal Imager (Hi-C) flew on a
sounding rocket in 2018 May and observed areas of active region outflow
at the highest spatial resolution ever achieved (250 km). Here we use
the Hi-C data to disentangle the outflow composition signatures observed
with the Hinode satellite during the flight. We show that there are
two components to the outflow emission: a substantial contribution
from expanded plasma that appears to have been expelled from closed
loops in the active region core and a second contribution from dynamic
activity in active region plage, with a composition signature that
reflects solar photospheric abundances. The two competing drivers of the
outflows may explain the variable composition of the slow solar wind.
Title: Is the High-Resolution Coronal Imager Resolving Coronal
Strands? Results from AR 12712
Authors: Williams, Thomas; Walsh, Robert W.; Winebarger, Amy R.;
Brooks, David H.; Cirtain, Jonathan W.; De Pontieu, Bart; Golub,
Leon; Kobayashi, Ken; McKenzie, David E.; Morton, Richard J.; Peter,
Hardi; Rachmeler, Laurel A.; Savage, Sabrina L.; Testa, Paola; Tiwari,
Sanjiv K.; Warren, Harry P.; Watkinson, Benjamin J.
Bibcode: 2020ApJ...892..134W
Altcode: 2020arXiv200111254W
Following the success of the first mission, the High-Resolution
Coronal Imager (Hi-C) was launched for a third time (Hi-C 2.1)
on 2018 May 29 from the White Sands Missile Range, NM, USA. On this
occasion, 329 s of 17.2 nm data of target active region AR 12712 were
captured with a cadence of ≈4 s, and a plate scale of 0.129 arcsec
pixel-1. Using data captured by Hi-C 2.1 and co-aligned
observations from SDO/AIA 17.1 nm, we investigate the widths of 49
coronal strands. We search for evidence of substructure within the
strands that is not detected by AIA, and further consider whether these
strands are fully resolved by Hi-C 2.1. With the aid of multi-scale
Gaussian normalization, strands from a region of low emission that can
only be visualized against the contrast of the darker, underlying moss
are studied. A comparison is made between these low-emission strands
and those from regions of higher emission within the target active
region. It is found that Hi-C 2.1 can resolve individual strands as
small as ≈202 km, though the more typical strand widths seen are
≈513 km. For coronal strands within the region of low emission, the
most likely width is significantly narrower than the high-emission
strands at ≈388 km. This places the low-emission coronal strands
beneath the resolving capabilities of SDO/AIA, highlighting the need
for a permanent solar observatory with the resolving power of Hi-C.
Title: The Formation Height of Millimeter-wavelength Emission in
the Solar Chromosphere
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; de la Cruz
Rodriguez, Jaime; Chintzoglou, Georgios
Bibcode: 2020ApJ...891L...8M
Altcode: 2020arXiv200110645M
In the past few years, the ALMA radio telescope has become available
for solar observations. ALMA diagnostics of the solar atmosphere are of
high interest because of the theoretically expected linear relationship
between the brightness temperature at millimeter wavelengths and
the local gas temperature in the solar atmosphere. Key for the
interpretation of solar ALMA observations is understanding where in
the solar atmosphere the ALMA emission originates. Recent theoretical
studies have suggested that ALMA bands at 1.2 (band 6) and 3 mm
(band 3) form in the middle and upper chromosphere at significantly
different heights. We study the formation of ALMA diagnostics using
a 2.5D radiative MHD model that includes the effects of ion-neutral
interactions (ambipolar diffusion) and nonequilibrium ionization
of hydrogen and helium. Our results suggest that in active regions
and network regions, observations at both wavelengths most often
originate from similar heights in the upper chromosphere, contrary to
previous results. Nonequilibrium ionization increases the opacity in the
chromosphere so that ALMA mostly observes spicules and fibrils along the
canopy fields. We combine these modeling results with observations from
IRIS, SDO, and ALMA to suggest a new interpretation for the recently
reported "dark chromospheric holes," regions of very low temperatures
in the chromosphere.
Title: IRIS Observations of Short-term Variability in Moss Associated
with Transient Hot Coronal Loops
Authors: Testa, Paola; Polito, Vanessa; De Pontieu, Bart
Bibcode: 2020ApJ...889..124T
Altcode: 2019arXiv191008201T
We observed rapid variability (≲60 s) at the footpoints of transient,
hot (∼8-10 MK) coronal loops in active region cores, with the
Interface Region Imaging Spectrograph (IRIS). The high spatial (∼0"33)
and temporal (≲5-10 s) resolution of IRIS is often crucial for the
detection of this variability. We show how, in combination with 1D RADYN
loop modeling, these IRIS spectral observations of the transition region
(TR) and chromosphere provide powerful diagnostics of the properties of
coronal heating and energy transport (thermal conduction or nonthermal
electrons, NTEs). Our simulations of nanoflare-heated loops indicate
that emission in the Mg II triplet can be used as a sensitive diagnostic
for nonthermal particles. In our events, we observe a large variety
of IRIS spectral properties (intensity, Doppler shifts, broadening,
chromospheric/TR line ratios, Mg II triplet emission) even for
different footpoints of the same coronal events. In several events,
we find spectroscopic evidence for NTEs (e.g., TR blueshifts and Mg
II triplet emission), suggesting that particle acceleration can occur
even for very small magnetic reconnection events, which are generally
below the detection threshold of hard X-ray instruments that provide
direct detection of emission of nonthermal particles.
Title: Ion-neutral Interactions and Nonequilibrium Ionization in
the Solar Chromosphere
Authors: Martínez-Sykora, Juan; Leenaarts, Jorrit; De Pontieu,
Bart; Nóbrega-Siverio, Daniel; Hansteen, Viggo H.; Carlsson, Mats;
Szydlarski, Mikolaj
Bibcode: 2020ApJ...889...95M
Altcode: 2019arXiv191206682M
The thermal structure of the chromosphere is regulated through a
complex interaction of various heating processes, radiative cooling,
and the ionization degree of the plasma. Here, we study the impact on
the thermal properties of the chromosphere when including the combined
action of nonequilibrium ionization (NEI) of hydrogen and helium and
ion-neutral interaction effects. We have performed a 2.5D radiative
magnetohydrodynamic simulation using the Bifrost code. This model
includes ion-neutral interaction effects by solving the generalized
Ohm' s law (GOL) as well as NEI for hydrogen and helium. The GOL
equation includes ambipolar diffusion and the Hall term. We compare
this simulation with another simulation that computes the ionization in
local thermodynamic equilibrium (LTE) including ion-neutral interaction
effects. Our numerical models reveal substantial thermal differences
in magneto-acoustic shocks, the wake behind the shocks, spicules,
low-lying magnetic loops, and the transition region. In particular,
we find that heating through ambipolar diffusion in shock wakes is
substantially less efficient, while in the shock fronts themselves it
is more efficient, under NEI conditions than when assuming LTE.
Title: Understanding the Structure of Rapid Intensity Fluctuations
in the Chromosphere with IRIS
Authors: Schmit, D.; De Pontieu, B.; Winebarger, A.; Rachmeler, L.;
Daw, A.
Bibcode: 2020ApJ...889..112S
Altcode:
Several recent data sets have taken advantage of the unique capabilities
of orbital and suborbital spacecraft to image the chromosphere
and transition region at a very high cadence. We find that both
the chromosphere and transition region exhibit spatially coherent
transient features at frequencies above 80 mHz. We have analyzed
narrowband imaging data from H I Lyα 1215 Å (provided by CLASP),
Mg II k 2796 Å, and Si IV 1400 Å (provided by the Interface Region
Imaging Spectrograph). We categorize the spatial structure of these
rapid fluctuations in different magnetic environments. Intensity
fluctuations above the noise level are observed in plages in all
passbands. We have found jet-like features in 1215 and 1400 Å data
that extend from the edges of plages as well as network magnetic
concentrations. We have not found any recurrent features that are
identified in both 1400 and 1215 Å data. Short loop-like features
were only found in 1400 Å data. Temperature minimum grains generate
non-propagating features in 1400 Å data. We compare our observations
with previous research on dynamic chromospheric phenomena at lower
frequencies. Candidate mechanisms, related to both jets and waves,
predict chromospheric and transition region intensity fluctuations at
high temporal frequencies, which can now be observationally probed.
Title: The multi-thermal chromosphere. Inversions of ALMA and
IRIS data
Authors: da Silva Santos, J. M.; de la Cruz Rodríguez, J.; Leenaarts,
J.; Chintzoglou, G.; De Pontieu, B.; Wedemeyer, S.; Szydlarski, M.
Bibcode: 2020A&A...634A..56D
Altcode: 2019arXiv191209886D
Context. Numerical simulations of the solar chromosphere predict a
diverse thermal structure with both hot and cool regions. Observations
of plage regions in particular typically feature broader and brighter
chromospheric lines, which suggests that they are formed in hotter
and denser conditions than in the quiet Sun, but also implies a
nonthermal component whose source is unclear.
Aims: We revisit
the problem of the stratification of temperature and microturbulence
in plage and the quiet Sun, now adding millimeter (mm) continuum
observations provided by the Atacama Large Millimiter Array (ALMA) to
inversions of near-ultraviolet Interface Region Imaging Spectrograph
(IRIS) spectra as a powerful new diagnostic to disentangle the
two parameters. We fit cool chromospheric holes and track the fast
evolution of compact mm brightenings in the plage region.
Methods: We use the STiC nonlocal thermodynamic equilibrium (NLTE)
inversion code to simultaneously fit real ultraviolet and mm spectra
in order to infer the thermodynamic parameters of the plasma.
Results: We confirm the anticipated constraining potential of ALMA
in NLTE inversions of the solar chromosphere. We find significant
differences between the inversion results of IRIS data alone compared to
the results of a combination with the mm data: the IRIS+ALMA inversions
have increased contrast and temperature range, and tend to favor lower
values of microturbulence (∼3-6 km s-1 in plage compared
to ∼4-7 km s-1 from IRIS alone) in the chromosphere. The
average brightness temperature of the plage region at 1.25 mm is 8500
K, but the ALMA maps also show much cooler (∼3000 K) and hotter
(∼11 000 K) evolving features partially seen in other diagnostics. To
explain the former, the inversions require the existence of localized
low-temperature regions in the chromosphere where molecules such as CO
could form. The hot features could sustain such high temperatures due to
non-equilibrium hydrogen ionization effects in a shocked chromosphere
- a scenario that is supported by low-frequency shock wave patterns
found in the Mg II lines probed by IRIS.
Title: Observations and modeling of the onset of fast reconnection
in the solar transition region
Authors: Bhattacharjee, Amitava; Guo, Lijia; de Pontieu, Bart; Huang,
Yi-Min; Peter, Hardi
Bibcode: 2020APS..DPPP10005B
Altcode:
Magnetic reconnection is a fundamental plasma process that plays a
critical role not only in energy release in the solar atmosphere, but
also in fusion, astrophysical, and other space plasma environments. One
of the challenges in explaining solar observations in which reconnection
is thought to play a critical role is to account for the transition
of the dynamics from a slow quasi-continuous phase to a fast and
impulsive energetic burst of much shorter duration. Despite the
theoretical progress in identifying mechanisms that might lead
to rapid onset, a lack of observations of this transition has left
models poorly constrained. High-resolution spectroscopic observations
from NASA's Interface Region Imaging Spectrograph (IRIS) now reveal
tell-tale signatures of the abrupt transition of reconnection from
a slow phase to a fast, impulsive phase during explosive events in
the Sun's atmosphere. Our observations are consistent with numerical
simulations of the plasmoid instability, and provide evidence for the
onset of fast reconnection mediated by plasmoids and new opportunities
for remote-sensing diagnostics of reconnection mechanisms on the Sun.
Title: The Multi-slit Approach to Coronal Spectroscopy with the
Multi-slit Solar Explorer (MUSE)
Authors: De Pontieu, Bart; Martínez-Sykora, Juan; Testa, Paola;
Winebarger, Amy R.; Daw, Adrian; Hansteen, Viggo; Cheung, Mark C. M.;
Antolin, Patrick
Bibcode: 2020ApJ...888....3D
Altcode: 2019arXiv190908818D
The Multi-slit Solar Explorer (MUSE) is a proposed mission aimed
at understanding the physical mechanisms driving the heating of the
solar corona and the eruptions that are at the foundation of space
weather. MUSE contains two instruments, a multi-slit extreme ultraviolet
(EUV) spectrograph and a context imager. It will simultaneously
obtain EUV spectra (along 37 slits) and context images with the
highest resolution in space (0.″33-0.″4) and time (1-4 s) ever
achieved for the transition region (TR) and corona. The MUSE science
investigation will exploit major advances in numerical modeling, and
observe at the spatial and temporal scales on which competing models
make testable and distinguishable predictions, thereby leading to a
breakthrough in our understanding of coronal heating and the drivers
of space weather. By obtaining spectra in four bright EUV lines (Fe
IX 171 Å, Fe XV 284 Å, Fe XIX 108Å, Fe XXI 108 Å) covering a wide
range of TR and coronal temperatures along 37 slits simultaneously,
MUSE will be able to “freeze” the evolution of the dynamic
coronal plasma. We describe MUSE’s multi-slit approach and show
that the optimization of the design minimizes the impact of spectral
lines from neighboring slits, generally allowing line parameters to
be accurately determined. We also describe a Spectral Disambiguation
Code to resolve multi-slit ambiguity in locations where secondary lines
are bright. We use simulations of the corona and eruptions to perform
validation tests and show that the multi-slit disambiguation approach
allows accurate determination of MUSE observables in locations where
significant multi-slit contamination occurs.
Title: Solar Hα features with hot onsets. IV. Network fibrils
Authors: Rutten, Robert J.; Rouppe van der Voort, Luc H. M.; De
Pontieu, Bart
Bibcode: 2019A&A...632A..96R
Altcode: 2019arXiv190809315R
Even in quiet areas underneath coronal holes the solar chromosphere
contains ubiquitous heating events. They tend to be small scale and
short lived, hence difficult to identify. Here we do not address
their much-debated contribution to outer-atmosphere heating,
but their aftermaths. We performed a statistical analysis of
high-resolution observations in the Balmer Hα line to suggest
that many slender dark Hα fibrils spreading out from network
represent cooling gas that outlines tracks of preceding rapid
type II spicule events or smaller similar but as yet unresolved
heating agents in which the main gas constituent, hydrogen, ionizes
at least partially. Subsequent recombination then causes dark Hα
fibrils enhanced by nonequilibrium overopacity. We suggest that the
extraordinary fibrilar appearance of the Hα chromosphere around network
results from intermittent, frequent small-scale prior heating. Movies associated to Fig. 3 and blinkers are available at https://www.aanda.org
Title: MUSE: the Multi-Slit Solar Explorer
Authors: De Pontieu, B.; Lemen, J. R.; Cheung, C. M. M.
Bibcode: 2019AGUFMSH33A..07D
Altcode:
The Multi-Slit Solar Explorer (MUSE) is a proposed MIDEX mission
for studying the dynamics of the corona and transition region using
both conventional and novel spectral imaging techniques, coupled to
state-of-the-art numerical modeling. MUSE will obtain EUV spectra
and images with the highest resolution in space (1/3 arcsec) and
time (1-4 s) ever achieved for the transition region and corona,
along 37 slits and a large context FOV simultaneously. The science
goals of MUSE are to understand the physical mechanisms responsible
for energy release in the corona and for driving flares and coronal
mass ejections. MUSE contains two instruments: an EUV spectrograph and
an EUV context imager. Both leverage extensive heritage from previous
high-resolution instruments such as IRIS and the HiC rocket payload. The
MUSE spectrograph employs a novel multi-slit design that enables a
100x improvement in spectral scanning rates, which will reveal crucial
information about the dynamics of the physical processes that are not
observable with current instruments. MUSE will address its science
goals by observing at the spatial and temporal scales on which advanced
numerical models make distinguishing and testable predictions. We will
discuss the MUSE design and how it has been optimized to minimize
effects from overlapping spectra dispersed from different slits. We
will also describe the robust compressed sensing techniques (or spectral
disambiguation code) developed to allow accurate spectral analysis from
the multi-slit observations of MUSE, as illustrated with 3D radiative
MHD models. The MUSE consortium includes LMSAL, SAO, UCB, MSU, GSFC,
MSFC, HAO, ITA Oslo, and other institutions.
Title: Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar
Magnetic Network Lanes
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.;
Winebarger, Amy R.; Tiwari, Sanjiv K.; Savage, Sabrina L.; Golub, Leon
E.; Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain,
Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.;
Peter, Hardi; Testa, Paola; Walsh, Robert W.; Warren, Harry P.
Bibcode: 2019ApJ...887L...8P
Altcode: 2019arXiv191102331P
We present high-resolution, high-cadence observations of six,
fine-scale, on-disk jet-like events observed by the High-resolution
Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We
combine the Hi-C 2.1 images with images from the Solar Dynamics
Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and the Interface
Region Imaging Spectrograph (IRIS), and investigate each event’s
magnetic setting with co-aligned line-of-sight magnetograms from the
SDO/Helioseismic and Magnetic Imager (HMI). We find that (i) all six
events are jetlet-like (having apparent properties of jetlets), (ii)
all six are rooted at edges of magnetic network lanes, (iii) four of
the jetlet-like events stem from sites of flux cancelation between
majority-polarity network flux and merging minority-polarity flux, and
(iv) four of the jetlet-like events show brightenings at their bases
reminiscent of the base brightenings in coronal jets. The average
spire length of the six jetlet-like events (9000 ± 3000 km) is three
times shorter than that for IRIS jetlets (27,000 ± 8000 km). While
not ruling out other generation mechanisms, the observations suggest
that at least four of these events may be miniature versions of both
larger-scale coronal jets that are driven by minifilament eruptions
and still-larger-scale solar eruptions that are driven by filament
eruptions. Therefore, we propose that our Hi-C events are driven by
the eruption of a tiny sheared-field flux rope, and that the flux rope
field is built and triggered to erupt by flux cancelation.
Title: Fine-scale explosive energy release at sites of magnetic flux
cancellation in the core of the solar active region observed by Hi-C
2.1, IRIS and SDO
Authors: Tiwari, S. K.; Panesar, N. K.; Moore, R. L.; De Pontieu,
B.; Winebarger, A. R.
Bibcode: 2019AGUFMSH31C3323T
Altcode:
The second sounding-rocket flight of the High-Resolution Coronal Imager
(Hi-C 2.1) provided unprecedentedly-high spatial and temporal resolution
Title: Diagnostics of nanoflare heating in active region core loops
from chromospheric and transition region observations and modeling
Authors: Testa, P.; Polito, V.; De Pontieu, B.; Reale, F.; Graham, D.
Bibcode: 2019AGUFMSH13B..07T
Altcode:
Rapid variability at the footpoints of active region coronal loops
has been observed (Testa et al. 2013, 2014), and provides powerful
diagnostics of the properties of coronal heating and energy transport
(e.g., Testa et al. 2014, Polito et al. 2018, Reale et al. 2019, Testa
et al. 2019). We will present results of our detailed analysis of
a dozen of IRIS/AIA observations of footpoints brightenings associated
with coronal heating, and will present the distribution of the observed
properties (e.g., duration of brightenings, intensity ratios, Doppler
shifts, non-thermal broadening,..). We will discuss the properties
of coronal heating as inferred from the coupling of these high
spatial, spectral, and temporal resolution chromospheric/transition
region/coronal observations, with modeling. We will also
present results of a new algorithm we have developed for an automatic
detection of these footpoint brightenings in AIA observations (Graham
et al. 2019), which will allow us, in our next step, to significantly
expand the number of events detected, and build more robust statistics
of the properties of nanoflares in active region loops.
Title: Fine-scale Explosive Energy Release at Sites of Prospective
Magnetic Flux Cancellation in the Core of the Solar Active Region
Observed by Hi-C 2.1, IRIS, and SDO
Authors: Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.;
De Pontieu, Bart; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.;
Rachmeler, Laurel A.; Kobayashi, Ken; Testa, Paola; Warren, Harry P.;
Brooks, David H.; Cirtain, Jonathan W.; McKenzie, David E.; Morton,
Richard J.; Peter, Hardi; Walsh, Robert W.
Bibcode: 2019ApJ...887...56T
Altcode: 2019arXiv191101424T
The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial
and temporal resolution (∼250 km, 4.4 s) coronal EUV images of Fe IX/X
emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21-19:01:56
UT. Three morphologically different types (I: dot-like; II: loop-like;
III: surge/jet-like) of fine-scale sudden-brightening events (tiny
microflares) are seen within and at the ends of an arch filament system
in the core of the AR. Although type Is (not reported before) resemble
IRIS bombs (in size, and brightness with respect to surroundings),
our dot-like events are apparently much hotter and shorter in span
(70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI
magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw
images to examine, at the sites of these events, brightenings and
flows in the transition region and corona and evolution of magnetic
flux in the photosphere. Most, if not all, of the events are seated
at sites of opposite-polarity magnetic flux convergence (sometimes
driven by adjacent flux emergence), implying likely flux cancellation
at the microflare’s polarity inversion line. In the IRIS spectra
and images, we find confirming evidence of field-aligned outflow from
brightenings at the ends of loops of the arch filament system. In types
I and II the explosion is confined, while in type III the explosion
is ejective and drives jet-like outflow. The light curves from Hi-C,
AIA, and IRIS peak nearly simultaneously for many of these events,
and none of the events display a systematic cooling sequence as seen in
typical coronal flares, suggesting that these tiny brightening events
have chromospheric/transition region origin.
Title: Can superposition of evaporative flows explain broad IRIS Fe
XXI line profiles during flares?
Authors: Polito, V.; Testa, P.; De Pontieu, B.
Bibcode: 2019AGUFMSH44A..07P
Altcode:
The observation of the high-temperature (>10MK) IRIS Fe XXI 1354A
line with the Interface Region Imaging Spectrograph (IRIS) has provided
significant insights into the chromospheric evaporation process in
flares. In particular, the line is often observed to be completely
blueshifted, in contrast to previous observations at lower spatial
and spectral resolution, and in agreement with predictions from
theoretical models. Interestingly, the line is also observed to be
mostly symmetric and significantly broader than expected from thermal
motions (assuming the peak formation temperature of the ion is in
equilibrium). One popular interpretation for the non-thermal broadening
is the superposition of flows from different loop strands. In this work,
we test this scenario by forward-modelling the Fe XXI line profile
assuming different possible observational scenarios using hydrodynamic
simulations of multi-thread flare loops with the 1D RADYN code. Our
results indicate that the superposition of flows alone cannot easily
reproduce both the symmetry and the significant broadening of the line
and that some other physical process, such as turbulence, or a much
larger ion temperature than previously expected, likely needs to be
invoked in order to explain the observed profiles.
Title: The High-Resolution Coronal Imager, Flight 2.1
Authors: Rachmeler, Laurel A.; Winebarger, Amy R.; Savage, Sabrina L.;
Golub, Leon; Kobayashi, Ken; Vigil, Genevieve D.; Brooks, David H.;
Cirtain, Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton,
Richard J.; Peter, Hardi; Testa, Paola; Tiwari, Sanjiv K.; Walsh,
Robert W.; Warren, Harry P.; Alexander, Caroline; Ansell, Darren;
Beabout, Brent L.; Beabout, Dyana L.; Bethge, Christian W.; Champey,
Patrick R.; Cheimets, Peter N.; Cooper, Mark A.; Creel, Helen K.;
Gates, Richard; Gomez, Carlos; Guillory, Anthony; Haight, Harlan;
Hogue, William D.; Holloway, Todd; Hyde, David W.; Kenyon, Richard;
Marshall, Joseph N.; McCracken, Jeff E.; McCracken, Kenneth; Mitchell,
Karen O.; Ordway, Mark; Owen, Tim; Ranganathan, Jagan; Robertson,
Bryan A.; Payne, M. Janie; Podgorski, William; Pryor, Jonathan; Samra,
Jenna; Sloan, Mark D.; Soohoo, Howard A.; Steele, D. Brandon; Thompson,
Furman V.; Thornton, Gary S.; Watkinson, Benjamin; Windt, David
Bibcode: 2019SoPh..294..174R
Altcode: 2019arXiv190905942R
The third flight of the High-Resolution Coronal Imager (Hi-C 2.1)
occurred on May 29, 2018; the Sounding Rocket was launched from White
Sands Missile Range in New Mexico. The instrument has been modified
from its original configuration (Hi-C 1) to observe the solar corona
in a passband that peaks near 172 Å, and uses a new, custom-built
low-noise camera. The instrument targeted Active Region 12712, and
captured 78 images at a cadence of 4.4 s (18:56:22 - 19:01:57 UT; 5
min and 35 s observing time). The image spatial resolution varies due
to quasi-periodic motion blur from the rocket; sharp images contain
resolved features of at least 0.47 arcsec. There are coordinated
observations from multiple ground- and space-based telescopes providing
an unprecedented opportunity to observe the mass and energy coupling
between the chromosphere and the corona. Details of the instrument
and the data set are presented in this paper.
Title: Unfolding Overlappogram Data: Preparing for the COOL-AID
instrument on Hi-C FLARE
Authors: Winebarger, A. R.; De Pontieu, B.; Cheung, C. M. M.;
Martinez-Sykora, J.; Hansteen, V. H.; Testa, P.; Golub, L.; Savage,
S. L.; Samra, J.; Reeves, K.
Bibcode: 2019AGUFMSH33A..06W
Altcode:
During a solar flare, energy released in the corona streams to the solar
chromosphere, where plasma is heated and then evaporated upward. The
magnitude of these velocities and their evolution as a function of time
can provide quantitative information on the magnitude of energy released
and the method by which it is transported in a solar flare. Measuring
these velocities, however, is quite challenging. Typically, they are
measured with single slit spectrometers, where light passing through
a long but narrow slit is dispersed and emission lines formed across
a range of temperatures are observed. The main issue with using
single slit spectrometers to make this measurement is that they are
rarely pointed at the right place at the right time. Additionally,
their fields of view are limited by narrow slit widths, and although
rastering can effectively expand the field of view, it does so at the
cost of time. This combination means that single slit spectrometers
cannot adequately capture the evolution of the flare velocities. On
the contrary, slitless spectrometers can make "overlappograms'',
which provide both imaging and spectral information over a large field
of view. However, spatial information from different spectral lines
can overlap in the dispersion direction, making the data difficult
to interpret. Furthermore, the spectral resolution of slitless
spectrometers are limited and typically worse than single-slit
spectrometers, since no line fitting (and hence sub-pixel sampling) is
possible. For the next generation of the High-resolution Coronal
Imager (Hi-C) Rocket Experiment, which we are proposing to launch during
a solar flare, we are including the COronal OverLapagram - Ancillary
Imaging Diagnostics (COOL-AID) instrument. COOL-AID is a slitless
spectrometer based on the COronal Spectrographic Imager in the EUV
(COSIE) design, but with a narrow passband coating around 12.9 nm (the
same passband as the primary Hi-C telescope), a spatial resolution of
~1"x2", and a velocity resolution of ~5 km/s. The goal of the COOL-AID
instrument is to determine the velocity associated with the Fe XXI
12.9 nm spectral line during a solar flare. In this talk, we will
demonstrate the unfolding method developed by Cheung et al (2019) to
determine the velocity information from a simulated COOL-AID data set.
Title: Investigating Pre-flare Signatures with K-means Clustering
Authors: Woods, M.; De Pontieu, B.; Sainz Dalda, A.
Bibcode: 2019AGUFMSH31E3348W
Altcode:
We present the results of a large statistical study of pre-flare
activity using spectroscopic data from the IRIS spacecraft, analysed
using K-means clustering. Solar flares are large energy releases
whose effects are observed throughout the solar atmosphere. They
are also heavily correlated with eruptions and CMEs, which extend
their influence into the greater heliosphere. Many models exist
that attempt to explain the triggering of flares and eruptions,
but not all have clear observational signatures related to them. The
identification of reliable pre-flare signatures is therefore highly
important to not only furthering our understanding the processes
that lead to flaring and eruptions, but also to efforts to predict
the occurrence of such events. We compiled a data set of over
100 flare events with pre-flare coverage, comprising a range of GOES
classes and eruptivities. The individual spectra from these data were
then standardised for direct comparison, and the unsupervised machine
learning technique K-means clustering was run upon them. This allowed
us to investigate the types of spectra that were observed prior to
flaring, and how these spectra are distributed both spatially and
temporally. Additionally we investigated how these spectral clusters
are related to the eruptivity of the flares that they precede.
Title: A comprehensive three-dimensional radiative magnetohydrodynamic
simulation of a solar flare
Authors: Cheung, M. C. M.; Rempel, M.; Chintzoglou, G.; Chen, F.;
Testa, P.; Martínez-Sykora, J.; Sainz Dalda, A.; DeRosa, M. L.;
Malanushenko, A.; Hansteen, V.; De Pontieu, B.; Carlsson, M.; Gudiksen,
B.; McIntosh, S. W.
Bibcode: 2019NatAs...3..160C
Altcode: 2018NatAs...3..160C
Solar and stellar flares are the most intense emitters of X-rays and
extreme ultraviolet radiation in planetary systems1,2. On
the Sun, strong flares are usually found in newly emerging sunspot
regions3. The emergence of these magnetic sunspot groups
leads to the accumulation of magnetic energy in the corona. When
the magnetic field undergoes abrupt relaxation, the energy released
powers coronal mass ejections as well as heating plasma to temperatures
beyond tens of millions of kelvins. While recent work has shed light
on how magnetic energy and twist accumulate in the corona4
and on how three-dimensional magnetic reconnection allows for rapid
energy release5,6, a self-consistent model capturing how
such magnetic changes translate into observable diagnostics has remained
elusive. Here, we present a comprehensive radiative magnetohydrodynamics
simulation of a solar flare capturing the process from emergence to
eruption. The simulation has sufficient realism for the synthesis of
remote sensing measurements to compare with observations at visible,
ultraviolet and X-ray wavelengths. This unifying model allows us to
explain a number of well-known features of solar flares7,
including the time profile of the X-ray flux during flares, origin
and temporal evolution of chromospheric evaporation and condensation,
and sweeping of flare ribbons in the lower atmosphere. Furthermore,
the model reproduces the apparent non-thermal shape of coronal X-ray
spectra, which is the result of the superposition of multi-component
super-hot plasmas8 up to and beyond 100 million K.
Title: The Solar-C_EUVST mission
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko;
Ichimoto, Kiyoshi; Suematsu, Yoshinori; Hara, Hirohisa; Katsukawa,
Yukio; Kubo, Masahito; Toriumi, Shin; Watanabe, Tetsuya; Yokoyama,
Takaaki; Korendyke, Clarence M.; Warren, Harry P.; Tarbell, Ted; De
Pontieu, Bart; Teriaca, Luca; Schühle, Udo H.; Solanki, Sami; Harra,
Louise K.; Matthews, Sarah; Fludra, A.; Auchère, F.; Andretta, V.;
Naletto, G.; Zhukov, A.
Bibcode: 2019SPIE11118E..07S
Altcode:
Solar-C EUVST (EUV High-Throughput Spectroscopic Telescope) is a
solar physics mission concept that was selected as a candidate for
JAXA competitive M-class missions in July 2018. The onboard science
instrument, EUVST, is an EUV spectrometer with slit-jaw imaging
system that will simultaneously observe the solar atmosphere from the
photosphere/chromosphere up to the corona with seamless temperature
coverage, high spatial resolution, and high throughput for the first
time. The mission is designed to provide a conclusive answer to the
most fundamental questions in solar physics: how fundamental processes
lead to the formation of the solar atmosphere and the solar wind, and
how the solar atmosphere becomes unstable, releasing the energy that
drives solar flares and eruptions. The entire instrument structure
and the primary mirror assembly with scanning and tip-tilt fine
pointing capability for the EUVST are being developed in Japan, with
spectrograph and slit-jaw imaging hardware and science contributions
from US and European countries. The mission will be launched and
installed in a sun-synchronous polar orbit by a JAXA Epsilon vehicle in
2025. ISAS/JAXA coordinates the conceptual study activities during the
current mission definition phase in collaboration with NAOJ and other
universities. The team is currently working towards the JAXA final
down-selection expected at the end of 2019, with strong support from
US and European colleagues. The paper provides an overall description
of the mission concept, key technologies, and the latest status.
Title: Multi-component Decomposition of Astronomical Spectra by
Compressed Sensing
Authors: Cheung, Mark C. M.; De Pontieu, Bart; Martínez-Sykora,
Juan; Testa, Paola; Winebarger, Amy R.; Daw, Adrian; Hansteen, Viggo;
Antolin, Patrick; Tarbell, Theodore D.; Wuelser, Jean-Pierre; Young,
Peter; MUSE Team
Bibcode: 2019ApJ...882...13C
Altcode: 2019arXiv190203890C
The signal measured by an astronomical spectrometer may be due to
radiation from a multi-component mixture of plasmas with a range of
physical properties (e.g., temperature, Doppler velocity). Confusion
between multiple components may be exacerbated if the spectrometer
sensor is illuminated by overlapping spectra dispersed from different
slits, with each slit being exposed to radiation from a different
portion of an extended astrophysical object. We use a compressed sensing
method to robustly retrieve the different components. This method can
be adopted for a variety of spectrometer configurations, including
single-slit, multi-slit (e.g., the proposed MUlti-slit Solar Explorer
mission), and slot spectrometers (which produce overlappograms).
Title: New View of the Solar Chromosphere
Authors: Carlsson, Mats; De Pontieu, Bart; Hansteen, Viggo H.
Bibcode: 2019ARA&A..57..189C
Altcode:
The solar chromosphere forms a crucial, yet complex and until recently
poorly understood, interface between the solar photosphere and the
heliosphere. Advances in high-resolution instrumentation, adaptive
optics, image reconstruction techniques, and space-based observatories
allow unprecedented high-resolution views of the finely structured and
highly dynamic chromosphere. Dramatic progress in numerical computations
allows 3D radiative magnetohydrodynamic forward models to take the place
of the previous generation of 1D semiempirical atmosphere models. These
new models provide deep insight into complex nonlocal thermodynamic
equilibrium chromospheric diagnostics and enable physics-based
interpretations of observations. This combination of modeling and
observations has led to new insights into the role of shock waves,
transverse magnetic waves, magnetic reconnection and flux emergence
in the chromospheric energy balance, the formation of spicules,
the impact of ion-neutral interactions, and the connectivity between
chromosphere and transition region. During the next few years, the
advent of new instrumentation (integral-field-unit spectropolarimetry)
and observatories (ALMA, DKIST), coupled with novel inversion codes and
expansion of existing numerical models to deal with ever more complex
physical processes (including multifluid approaches), is expected to
lead to major new insights into the dominant heating processes in the
chromosphere and beyond.
Title: Automated Detection of Rapid Variability of Moss Using SDO/AIA
and Its Connection to the Solar Corona
Authors: Graham, David R.; De Pontieu, Bart; Testa, Paola
Bibcode: 2019ApJ...880L..12G
Altcode:
Active region moss—the upper transition region of hot loops—was
observed exhibiting rapid intensity variability on timescales of order
15 s by Testa et al. in a short time series (∼150 s) data set from
Hi-C (High-resolution Coronal Imager). The intensity fluctuations in
the subarcsecond 193A images (∼1.5 MK plasma) were uncharacteristic
of steadily heated moss and were considered an indication of heating
events connected to the corona. Intriguingly, these brightenings
displayed a connection to the ends of transient hot loops seen in
the corona. Following the same active region, AR11520, for 6 days,
we demonstrate an algorithm designed to detect the same temporal
variability in lower resolution Atmospheric Imaging Assembly (AIA)
data, significantly expanding the number of events detected. Multiple
analogous regions to the Hi-C data are successfully detected, showing
moss that appears to “sparkle” prior to clear brightening of
connected high-temperature loops; this is confirmed by the hot AIA
channels and the isolated Fe XVIII emission. The result is illuminating,
as the same behavior has recently been shown by Polito et al. while
simulating nanoflares with a beam of electrons depositing their energy
in the lower atmosphere. Furthermore, the variability is localized
mostly to the hot core of the region, hence we reinforce the diagnostic
potential of moss variability as the driver of energy release in the
corona. The ubiquitous nature of this phenomenon, and the ability to
detect it in data with extended time series, and large fields of view,
opens a new window into investigating the coronal heating mechanism.
Title: Can the Superposition of Evaporative Flows Explain Broad Fe
XXI Profiles during Solar Flares?
Authors: Polito, Vanessa; Testa, Paola; De Pontieu, Bart
Bibcode: 2019ApJ...879L..17P
Altcode:
The observation of the high-temperature (≳10 MK) Fe XXI 1354.1
Å line with the Interface Region Imaging Spectrograph has provided
significant insights into the chromospheric evaporation process in
flares. In particular, the line is often observed to be completely
blueshifted, in contrast to previous observations at lower spatial
and spectral resolution, and in agreement with predictions from
theoretical models. Interestingly, the line is also observed to be
mostly symmetric and significantly broader than expected from thermal
motions (assuming the peak formation temperature of the ion is in
equilibrium). One popular interpretation for the nonthermal broadening
is the superposition of flows from different loop strands. In this
work, we test this scenario by forward-modeling the Fe XXI line profile
assuming different possible observational scenarios using hydrodynamic
simulations of multi-thread flare loops with the 1D RADYN code. Our
results indicate that the superposition of flows alone cannot easily
reproduce both the symmetry and the significant broadening of the line
and that some other physical process, such as turbulence, or a much
larger ion temperature than previously expected, likely needs to be
invoked in order to explain the observed profiles.
Title: Fine-scale explosive energy release at sites of magnetic
flux cancellation in the core of the solar active region observed
by HiC2.1, IRIS and SDO
Authors: Tiwari, Sanjiv K.; Panesar, Navdeep; Moore, Ronald L.;
De Pontieu, Bart; Testa, Paola; Winebarger, Amy R.
Bibcode: 2019AAS...23411702T
Altcode:
The second sounding-rocket flight of the High-Resolution Coronal Imager
(HiC2.1) provided unprecedentedly-high spatial and temporal resolution
(150 km, 4.5 s) coronal EUV images of Fe IX/X emission at 172 Å, of
a solar active region (AR NOAA 12712) near solar disk center. Three
morphologically-different types (I: dot-like, II: loop-like, &
III: surge/jet-like) of fine-scale sudden brightening events (tiny
microflares) are seen within and at the ends of an arch filament
system in the core of the AR. We complement the 5-minute-duration
HiC2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images, and
IRIS UV spectra and slit-jaw images to examine, at the sites of these
events, brightenings and flows in the transition region and corona
and evolution of magnetic flux in the photosphere. Most, if not all,
of the events are seated at sites of opposite-polarity magnetic flux
convergence (sometimes driven by adjacent flux emergence), implying
flux cancellation at the polarity inversion line. In the IRIS spectra
and images, we find confirming evidence of field-aligned outflow from
brightenings at the ends of loops of the arch filament system. These
outflows from both ends of the arch filament system are seen as
bi-directional flows in the arch filament system, suggesting that the
well-known counter-streaming flows in large classical filaments could be
driven in the same way as in this arch filament system: by fine-scale
jet-like explosions from fine-scale sites of mixed-polarity field in
the feet of the sheared field that threads the filament. Plausibly,
the flux cancellation at these sites prepares and triggers a fine scale
core-magnetic-field structure (a small sheared/twisted core field or
flux rope along and above the cancellation line) to explode. In types
I & II the explosion is confined, while in type III the explosion
is ejective and drives jet-like outflow in the manner of larger jets
in coronal holes, quiet regions, and active regions.
Title: Radiative MHD Simulation of a Solar Flare
Authors: Cheung, Mark; Rempel, Matthias D.; Chintzoglou, Georgios;
Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
DeRosa, Marc L.; Malanushenko, Anna; Hansteen, Viggo; Carlsson, Mats;
De Pontieu, Bart; Gudiksen, Boris; McIntosh, Scott W.
Bibcode: 2019AAS...23431005C
Altcode:
We present a radiative MHD simulation of a solar flare. The
computational domain captures the near-surface layers of the convection
zone and overlying atmosphere. Inspired by the observed evolution of
NOAA Active Region (AR) 12017, a parasitic bipolar region is imposed
to emerge in the vicinity of a pre-existing sunspot. The emergence of
twisted magnetic flux generates shear flows that create a pre-existing
flux rope underneath the canopy field of the sunspot. Following erosion
of the overlying bootstrapping field, the flux rope erupts. Rapid
release of magnetic energy results in multi-wavelength synthetic
observables (including X-ray spectra, narrowband EUV images, Doppler
shifts of EUV lines) that are consistent with flare observations. This
works suggests the super-position of multi-thermal, superhot (up
to 100 MK) plasma may be partially responsible for the apparent
non-thermal shape of coronal X-ray sources in flares. Implications
for remote sensing observations of other astrophysical objects is also
discussed. This work is an important stepping stone toward high-fidelity
data-driven MHD models.
Title: Evolution of bipolar internetwork magnetic fields
Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, Luis Ramon
Bibcode: 2019AAS...23431102G
Altcode:
Internetwork (IN) magnetic fields can be found inside supergranular
cells all over the solar surface. Thanks to their abundance and
appearance rate, IN fields are considered to be an essential contributor
to the magnetic flux and energy budget of the solar photosphere, and
may also play a major role in the energy budget of the chromosphere
and transition region. Therefore, it is crucial to understand how
IN magnetic fields appear, evolve, interact with the preexisting
magnetic structures, and what impact they have on the upper solar
atmosphere. Here, we analyze spatio-temporal evolution of IN magnetic
bipolar structures, i.e, loops and clusters, employing multi-instrument
(IRIS and SST), multi-wavelength observations of IN regions with the
highest sensitivity and resolution possible. For the first time, our
observations allow us to describe in detail how IN bipoles emerge in
the photosphere and even reach the chromosphere. We estimate the field
strengths of these IN magnetic structures both in the photosphere and
the chromosphere, using full Stokes measurements in Fe I 6173 Å, Mg I
b2 5173 Å, and Ca II 8542 Å. Employing the IRIS FUV and
NUV spectra, we show that IN fields contribute to the chromospheric
and transition region heating through interaction with the preexisting
ambient fields.
Title: On the Origin of the Magnetic Energy in the Quiet Solar
Chromosphere
Authors: Martínez-Sykora, Juan; Hansteen, Viggo H.; Gudiksen, Boris;
Carlsson, Mats; De Pontieu, Bart; Gošić, Milan
Bibcode: 2019ApJ...878...40M
Altcode: 2019arXiv190404464M
The presence of magnetic field is crucial in the transport of energy
through the solar atmosphere. Recent ground-based and space-borne
observations of the quiet Sun have revealed that magnetic field
accumulates at photospheric heights, via a local dynamo or from
small-scale flux emergence events. However, most of this small-scale
magnetic field may not expand into the chromosphere due to the entropy
drop with height at the photosphere. Here we present a study that uses
a high-resolution 3D radiative MHD simulation of the solar atmosphere
with non-gray and non-LTE radiative transfer and thermal conduction
along the magnetic field to reveal that (1) the net magnetic flux
from the simulated quiet photosphere is not sufficient to maintain a
chromospheric magnetic field (on average), (2) processes in the lower
chromosphere, in the region dominated by magnetoacoustic shocks,
are able to convert kinetic energy into magnetic energy, (3) the
magnetic energy in the chromosphere increases linearly in time until
the rms of the magnetic field strength saturates at roughly 4-30 G
(horizontal average) due to conversion from kinetic energy, (4) and
that the magnetic features formed in the chromosphere are localized
to this region.
Title: Multi-component Decomposition of Astronomical Spectra by
Compressed Sensing
Authors: Cheung, Mark; De Pontieu, Bart; Martinez-Sykora, Juan; Testa,
Paola; Winebarger, Amy R.; Daw, Adrian N.; Hansteen, Viggo; Antolin,
Patrick; Tarbell, Theodore D.; Wuelser, Jean-Pierre; Young, Peter R.
Bibcode: 2019AAS...23411603C
Altcode:
The signal measured by an astronomical spectrometer may be due to
radiation from a multi-component mixture of plasmas with a range of
physical properties (e.g. temperature, Doppler velocity). Confusion
between multiple components may be exacerbated if the spectrometer
sensor is illuminated by overlapping spectra dispersed from different
slits, with each slit being exposed to radiation from a different
portion of an extended astrophysical object. We use a compressed sensing
method to robustly retrieve the different components. This method can
be adopted for a variety of spectrometer configurations, including
single-slit, multi-slit (e.g., the proposed MUlti-slit Solar Explorer
mission; MUSE) and slot spectrometers (which produce overlappograms).
Title: Spectral Evidence for Heating at Large Column Mass in Umbral
Solar Flare Kernels. I. IRIS Near-UV Spectra of the X1 Solar Flare
of 2014 October 25
Authors: Kowalski, Adam F.; Butler, Elizabeth; Daw, Adrian N.;
Fletcher, Lyndsay; Allred, Joel C.; De Pontieu, Bart; Kerr, Graham S.;
Cauzzi, Gianna
Bibcode: 2019ApJ...878..135K
Altcode: 2019arXiv190502111K
The GOES X1 flare SOL2014-10-25T17:08:00 was a three-ribbon solar
flare observed with the Interface Region Imaging Spectrograph (IRIS)
in the near-UV (NUV) and far-UV. One of the flare ribbons crossed
a sunspot umbra, producing a dramatic, ∼1000% increase in the NUV
continuum radiation. We comprehensively analyze the UV spectral data
of the umbral flare brightenings, which provide new challenges for
radiative-hydrodynamic modeling of the chromospheric velocity field and
the white-light continuum radiation. The emission line profiles in the
umbral flare brightenings exhibit redshifts and profile asymmetries,
but these are significantly smaller than in another, well-studied
X-class solar flare. We present a ratio of the NUV continuum intensity
to the Fe II λ2814.45 intensity. This continuum-to-line ratio is a
new spectral diagnostic of significant heating at high column mass
(log m/[g cm-2] > -2) during solar flares because the
continuum and emission line radiation originate from relatively similar
temperatures but moderately different optical depths. The full spectral
readout of these IRIS data also allow for a comprehensive survey of the
flaring NUV landscape: in addition to many lines of Fe II and Cr II, we
identify a new solar flare emission line, He I λ2829.91 (as previously
identified in laboratory and early-type stellar spectra). The Fermi/GBM
hard X-ray data provide inputs to radiative-hydrodynamic models (which
will be presented in Paper II) in order to better understand the large
continuum-to-line ratios, the origin of the white-light continuum
radiation, and the role of electron beam heating in the low atmosphere.
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: McKenzie, D. E.; Ishikawa, R.; Trujillo Bueno, J.; Auchére,
F.; Rachmeler, L. A.; Kubo, M.; Kobayashi, K.; Winebarger, A. R.;
Bethge, C. W.; Narukage, N.; Kano, R.; Ishikawa, S.; de Pontieu,
B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Štěpán, J.; del Pino
Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A.
Bibcode: 2019ASPC..526..361M
Altcode:
The hydrogen Lyman-α line at 121.6 nm and the Mg k line at 279.5
nm are especially relevant for deciphering the magnetic structure
of the chromosphere since their line-center signals are formed in
the chromosphere and transition region, with unique sensitivities to
magnetic fields. We propose the Chromospheric LAyer Spectro-Polarimeter
(CLASP2), to build upon the success of the first CLASP flight, which
measured the linear polarization in H I Lyman-α. The existing CLASP
instrument will be refitted to measure all four Stokes parameters in
the 280 nm range, including variations due to the anisotropic radiation
pumping, the Hanle effect, and the Zeeman effect.
Title: Recovering Thermodynamics from Spectral Profiles observed by
IRIS: A Machine and Deep Learning Approach
Authors: Sainz Dalda, Alberto; de la Cruz Rodríguez, Jaime; De
Pontieu, Bart; Gošić, Milan
Bibcode: 2019ApJ...875L..18S
Altcode: 2019arXiv190408390S
Inversion codes allow the reconstruction of a model atmosphere from
observations. With the inclusion of optically thick lines that form in
the solar chromosphere, such modeling is computationally very expensive
because a non-LTE evaluation of the radiation field is required. In this
study, we combine the results provided by these traditional methods
with machine and deep learning techniques to obtain similar-quality
results in an easy-to-use, much faster way. We have applied these
new methods to Mg II h and k lines observed by the Interface Region
Imaging Spectrograph (IRIS). As a result, we are able to reconstruct the
thermodynamic state (temperature, line-of-sight velocity, nonthermal
velocities, electron density, etc.) in the chromosphere and upper
photosphere of an area equivalent to an active region in a few CPU
minutes, speeding up the process by a factor of 105 -
106. The open-source code accompanying this Letter will
allow the community to use IRIS observations to open a new window to
a host of solar phenomena.
Title: The solar chromosphere at millimetre and ultraviolet
wavelengths. I. Radiation temperatures and a detailed comparison
Authors: Jafarzadeh, S.; Wedemeyer, S.; Szydlarski, M.; De Pontieu,
B.; Rezaei, R.; Carlsson, M.
Bibcode: 2019A&A...622A.150J
Altcode: 2019arXiv190105763J
Solar observations with the Atacama Large Millimeter/submillimeter
Array (ALMA) provide us with direct measurements of the brightness
temperature in the solar chromosphere. We study the temperature
distributions obtained with ALMA Band 6 (in four sub-bands at 1.21,
1.22, 1.29, and 1.3 mm) for various areas at, and in the vicinity of,
a sunspot, comprising quasi-quiet and active regions with different
amounts of underlying magnetic fields. We compare these temperatures
with those obtained at near- and far-ultraviolet (UV) wavelengths
(and with the line-core intensities of the optically-thin far-UV
spectra), co-observed with the Interface Region Imaging Spectrograph
(IRIS) explorer. These include the emission peaks and cores of the Mg
II k 279.6 nm and Mg II h 280.4 nm lines as well as the line cores
of C II 133.4 nm, O I 135.6 nm, and Si IV 139.4 nm, sampling the
mid-to-high chromosphere and the low transition region. Splitting the
ALMA sub-bands resulted in an slight increase of spatial resolution in
individual temperature maps, thus, resolving smaller-scale structures
compared to those produced with the standard averaging routines. We
find that the radiation temperatures have different, though somewhat
overlapping, distributions in different wavelengths and in the various
magnetic regions. Comparison of the ALMA temperatures with those of
the UV diagnostics should, however, be interpreted with great caution,
the former is formed under the local thermodynamic equilibrium (LTE)
conditions, the latter under non-LTE. The mean radiation temperature
of the ALMA Band 6 is similar to that extracted from the IRIS C II
line in all areas with exception of the sunspot and pores where the C
II poses higher radiation temperatures. In all magnetic regions, the
Mg II lines associate with the lowest mean radiation temperatures in
our sample. These will provide constraints for future numerical models.
Title: Evidence of Twisting and Mixed-polarity Solar Photospheric
Magnetic Field in Large Penumbral Jets: IRIS and Hinode Observations
Authors: Tiwari, Sanjiv K.; Moore, Ronald L.; De Pontieu, Bart;
Tarbell, Theodore D.; Panesar, Navdeep K.; Winebarger, Amy R.;
Sterling, Alphonse C.
Bibcode: 2018ApJ...869..147T
Altcode: 2018arXiv181109554T
A recent study using Hinode (Solar Optical Telescope/Filtergraph
[SOT/FG]) data of a sunspot revealed some unusually large penumbral
jets that often repeatedly occurred at the same locations in the
penumbra, namely, at the tail of a penumbral filament or where the
tails of multiple penumbral filaments converged. These locations had
obvious photospheric mixed-polarity magnetic flux in Na I 5896 Stokes-V
images obtained with SOT/FG. Several other recent investigations have
found that extreme-ultraviolet (EUV)/X-ray coronal jets in quiet-Sun
regions (QRs), in coronal holes (CHs), and near active regions (ARs)
have obvious mixed-polarity fluxes at their base, and that magnetic
flux cancellation prepares and triggers a minifilament flux-rope
eruption that drives the jet. Typical QR, CH, and AR coronal jets are
up to 100 times bigger than large penumbral jets, and in EUV/X-ray
images they show a clear twisting motion in their spires. Here,
using Interface Region Imaging Spectrograph (IRIS) Mg II k λ2796 SJ
images and spectra in the penumbrae of two sunspots, we characterize
large penumbral jets. We find redshift and blueshift next to each
other across several large penumbral jets, and we interpret these as
untwisting of the magnetic field in the jet spire. Using Hinode/SOT
(FG and SP) data, we also find mixed-polarity magnetic flux at the
base of these jets. Because large penumbral jets have a mixed-polarity
field at their base and have a twisting motion in their spires, they
might be driven the same way as QR, CH, and AR coronal jets.
Title: IRIS and SDO Observations of Solar Jetlets Resulting from
Network-edge Flux Cancelation
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.;
Tiwari, Sanjiv K.; De Pontieu, Bart; Norton, Aimee A.
Bibcode: 2018ApJ...868L..27P
Altcode: 2018arXiv181104314P
Recent observations show that the buildup and triggering of minifilament
eruptions that drive coronal jets result from magnetic flux cancelation
at the neutral line between merging majority- and minority-polarity
magnetic flux patches. We investigate the magnetic setting of 10
on-disk small-scale UV/EUV jets (jetlets, smaller than coronal X-ray
jets but larger than chromospheric spicules) in a coronal hole by using
IRIS UV images and SDO/AIA EUV images and line-of-sight magnetograms
from SDO/HMI. We observe recurring jetlets at the edges of magnetic
network flux lanes in the coronal hole. From magnetograms coaligned
with the IRIS and AIA images, we find, clearly visible in nine cases,
that the jetlets stem from sites of flux cancelation proceeding at
an average rate of ∼1.5 × 1018 Mx hr-1, and
show brightenings at their bases reminiscent of the base brightenings
in larger-scale coronal jets. We find that jetlets happen at many
locations along the edges of network lanes (not limited to the base
of plumes) with average lifetimes of 3 minutes and speeds of 70 km
s-1. The average jetlet-base width (4000 km) is three
to four times smaller than for coronal jets (∼18,000 km). Based on
these observations of 10 obvious jetlets, and our previous observations
of larger-scale coronal jets in quiet regions and coronal holes, we
infer that flux cancelation is an essential process in the buildup and
triggering of jetlets. Our observations suggest that network jetlet
eruptions might be small-scale analogs of both larger-scale coronal
jets and the still-larger-scale eruptions producing CMEs.
Title: First high-resolution look at the quiet Sun with ALMA at 3mm
Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos,
S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu,
T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V.
Bibcode: 2018A&A...619L...6N
Altcode: 2018arXiv181005223N
We present an overview of high-resolution quiet Sun observations,
from disk center to the limb, obtained with the Atacama Large
millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun
regions were observed at a resolution of up to 2.5″ by 4.5″. We
produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full-disk
solar images. The images show well the chromospheric network, which,
based on the unique segregation method we used, is brighter than the
average over the fields of view of the observed regions by ∼305
K while the intranetwork is less bright by ∼280 K, with a slight
decrease of the network/intranetwork contrast toward the limb. At 3
mm the network is very similar to the 1600 Å images, with somewhat
larger size. We detect, for the first time, spicular structures,
rising up to 15″ above the limb with a width down to the image
resolution and brightness temperature of ∼1800 K above the local
background. No trace of spicules, either in emission or absorption,
is found on the disk. Our results highlight the potential of ALMA for
the study of the quiet chromosphere.
Title: Instrument Calibration of the Interface Region Imaging
Spectrograph (IRIS) Mission
Authors: Wülser, J. -P.; Jaeggli, S.; De Pontieu, B.; Tarbell,
T.; Boerner, P.; Freeland, S.; Liu, W.; Timmons, R.; Brannon, S.;
Kankelborg, C.; Madsen, C.; McKillop, S.; Prchlik, J.; Saar, S.;
Schanche, N.; Testa, P.; Bryans, P.; Wiesmann, M.
Bibcode: 2018SoPh..293..149W
Altcode:
The Interface Region Imaging Spectrograph (IRIS) is a NASA small
explorer mission that provides high-resolution spectra and images of
the Sun in the 133 - 141 nm and 278 - 283 nm wavelength bands. The
IRIS data are archived in calibrated form and made available to the
public within seven days of observing. The calibrations applied to
the data include dark correction, scattered light and background
correction, flat fielding, geometric distortion correction, and
wavelength calibration. In addition, the IRIS team has calibrated the
IRIS absolute throughput as a function of wavelength and has been
tracking throughput changes over the course of the mission. As a
resource for the IRIS data user, this article describes the details
of these calibrations as they have evolved over the first few years
of the mission. References to online documentation provide access to
additional information and future updates.
Title: CLASP Constraints on the Magnetization and Geometrical
Complexity of the Chromosphere-Corona Transition Region
Authors: Trujillo Bueno, J.; Štěpán, J.; Belluzzi, L.; Asensio
Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Ishikawa,
R.; Kano, R.; Winebarger, A.; Auchère, F.; Narukage, N.; Kobayashi,
K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
Bibcode: 2018ApJ...866L..15T
Altcode: 2018arXiv180908865T
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a
suborbital rocket experiment that on 2015 September 3 measured
the linear polarization produced by scattering processes in the
hydrogen Lyα line of the solar disk radiation. The line-center
photons of this spectral line radiation mostly stem from the
chromosphere-corona transition region (TR). These unprecedented
spectropolarimetric observations revealed an interesting surprise,
namely that there is practically no center-to-limb variation (CLV) in
the Q/I line-center signals. Using an analytical model, we first show
that the geometric complexity of the corrugated surface that delineates
the TR has a crucial impact on the CLV of the Q/I and U/I line-center
signals. Second, we introduce a statistical description of the solar
atmosphere based on a 3D model derived from a state-of-the-art radiation
magnetohydrodynamic simulation. Each realization of the statistical
ensemble is a 3D model characterized by a given degree of magnetization
and corrugation of the TR, and for each such realization we solve the
full 3D radiative transfer problem taking into account the impact
of the CLASP instrument degradation on the calculated polarization
signals. Finally, we apply the statistical inference method presented
in a previous paper to show that the TR of the 3D model that produces
the best agreement with the CLASP observations has a relatively weak
magnetic field and a relatively high degree of corrugation. We emphasize
that a suitable way to validate or refute numerical models of the upper
solar chromosphere is by confronting calculations and observations
of the scattering polarization in ultraviolet lines sensitive to the
Hanle effect.
Title: A Statistical Inference Method for Interpreting the CLASP
Observations
Authors: Štěpán, J.; Trujillo Bueno, J.; Belluzzi, L.; Asensio
Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Kano, R.;
Winebarger, A.; Auchère, F.; Ishikawa, R.; Narukage, N.; Kobayashi,
K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
Bibcode: 2018ApJ...865...48S
Altcode: 2018arXiv180802725S
On 2015 September 3, the Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP) successfully measured the linear polarization produced by
scattering processes in the hydrogen Lyα line of the solar disk
radiation, revealing conspicuous spatial variations in the Q/I and U/I
signals. Via the Hanle effect, the line-center Q/I and U/I amplitudes
encode information on the magnetic field of the chromosphere-corona
transition region, but they are also sensitive to the three-dimensional
structure of this corrugated interface region. With the help of a simple
line-formation model, here we propose a statistical inference method
for interpreting the Lyα line-center polarization observed by CLASP.
Title: An on Orbit Determination of Point Spread Functions for the
Interface Region Imaging Spectrograph
Authors: Courrier, Hans; Kankelborg, Charles; De Pontieu, Bart;
Wülser, Jean-Pierre
Bibcode: 2018SoPh..293..125C
Altcode:
Using the 2016 Mercury transit of the Sun, we characterize on orbit
spatial point spread functions (PSFs) for the Near- (NUV) and Far- (FUV)
Ultra-Violet spectrograph channels of NASA's Interface Region Imaging
Spectrograph (IRIS). A semi-blind Richardson-Lucy deconvolution method
is used to estimate PSFs for each channel. Corresponding estimates
of Modulation Transfer Functions (MTFs) indicate resolution of 2.47
cycles/arcsec in the NUV channel near 2796 Å and 2.55 cycles/arcsec
near 2814 Å. In the short (≈1336 Å ) and long (≈1394 Å )
wavelength FUV channels, our MTFs show pixel-limited resolution (3.0
cycles/arcsec). The PSF estimates perform well under deconvolution,
removing or significantly reducing instrument artifacts in the Mercury
transit spectra. The usefulness of the PSFs is demonstrated in a case
study of an isolated explosive event. PSF estimates and deconvolution
routines are provided through a SolarSoft module.
Title: Current State of UV Spectro-Polarimetry and its Future
Direction
Authors: Ishikawa, Ryohko; Sakao, Taro; Katsukawa, Yukio; Hara,
Hirohisa; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito;
Auchere, Frederic; De Pontieu, Bart; Winebarger, Amy; Kobayashi,
. Ken; Kano, Ryouhei; Narukage, Noriyuki; Trujillo Bueno, Javier;
Song, Dong-uk; Manso Sainz, Rafael; Asensio Ramos, Andres; Leenaarts,
Jorritt; Carlsson, Mats; Bando, Takamasa; Ishikawa, Shin-nosuke;
Tsuneta, Saku; Belluzzi, Luca; Suematsu, Yoshinori; Giono, Gabriel;
Yoshida, Masaki; Goto, Motoshi; Del Pino Aleman, Tanausu; Stepan,
Jiri; Okamoto, Joten; Tsuzuki, Toshihiro; Uraguchi, Fumihiro; Champey,
Patrick; Alsina Ballester, Ernest; Casini, Roberto; McKenzie, David;
Rachmeler, Laurel; Bethge, Christian
Bibcode: 2018cosp...42E1564I
Altcode:
To obtain quantitative information on the magnetic field in low beta
regions (i.e., upper chromosphere and above) has been increasingly
important to understand the energetic phenomena of the outer
solar atmosphere such as flare, coronal heating, and the solar wind
acceleration. In the UV range, there are abundant spectral lines that
originate in the upper chromosphere and transition region. However,
the Zeeman effect in these spectral lines does not give rise to easily
measurable polarization signals because of the weak magnetic field
strength and the larger Doppler broadening compared with the Zeeman
effect. Instead, the Hanle effect in UV lines is expected to be a
suitable diagnostic tool of the magnetic field in the upper atmospheric
layers. To investigate the validity of UV spectro-polarimetry and
the Hanle effect, the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP), which is a NASA sounding- rocket experiment, was launched at
White Sands in US on September 3, 2015. During its 5 minutes ballistic
flight, it successfully performed spectro-polarimetric observations
of the hydrogen Lyman-alpha line (121.57 nm) with an unprecedentedly
high polarization sensitivity of 0.1% in this wavelength range. CLASP
observed the linear polarization produced by scattering process in VUV
lines for the first time and detected the polarization signals which
indicate the operation of the Hanle effect. Following the success
of CLASP, we are confident that UV spectro-polarimetry is the way
to proceed, and we are planning the second flight of CLASP (CLASP2:
Chromospheric LAyer SpectroPolarimeter 2). For this second flight we
will carry out spectro-polarimetry in the Mg II h and k lines around
280 nm, with minimum modifications of the CLASP1 instrument. The linear
polarization in the Mg II k line is induced by scattering processes and
the Hanle effect, being sensitive to magnetic field strengths of 5 to 50
G. In addition, the circular polarizations in the Mg II h and k lines
induced by the Zeeman effect can be measurable in at least plage and
active regions. The combination of the Hanle and Zeeman effects could
help us to more reliably infer the magnetic fields of the upper solar
chromosphere. CLASP2 was selected for flight and is being developed for
launch in the spring of 2019.Based on these sounding rocket experiments
(CLASP1 and 2), we aim at establishing the strategy and refining the
instrument concept for future space missions to explore the enigmatic
atmospheric layers via UV spectro-polarimetry.
Title: Emergence of internetwork magnetic fields through the solar
atmosphere
Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, L. R.
Bibcode: 2018cosp...42E1261G
Altcode:
Internetwork (IN) magnetic fields are highly dynamic, short-lived
magnetic structures that populate the interior of supergranular
cells. Since they emerge all over the Sun, these small-scale fields
bring a substantial amount of flux, and therefore energy, to the solar
surface. Because of this, IN fields are crucial for understanding the
quiet Sun magnetism. However, they are weak and produce very small
polarization signals, which is the reason why their properties and
impact on the energetics and dynamics of the solar atmosphere are
largely unknown. Here we use coordinated IRIS and SST observations
of IN regions at high spatial and temporal resolution. They give us
the opportunity to follow the evolution of IN magnetic loops as they
emerge into the photosphere. For the first time, our polarimetric
measurements provide a direct observational evidence of IN fields
reaching the chromosphere. Moreover, we show that IN magnetic loops
contribute to the chromospheric and transition region heating through
interaction with preexisting ambient fields.
Title: Impact of Type II Spicules in the Corona: Simulations and
Synthetic Observables
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; De Moortel, Ineke;
Hansteen, Viggo H.; Carlsson, Mats
Bibcode: 2018ApJ...860..116M
Altcode: 2018arXiv180506475M
The role of type II spicules in the corona has been a much debated topic
in recent years. This paper aims to shed light on the impact of type
II spicules in the corona using novel 2.5D radiative MHD simulations,
including ion-neutral interaction effects with the Bifrost code. We
find that the formation of simulated type II spicules, driven by
the release of magnetic tension, impacts the corona in various
manners. Associated with the formation of spicules, the corona
exhibits (1) magneto-acoustic shocks and flows, which supply mass
to coronal loops, and (2) transversal magnetic waves and electric
currents that propagate at Alfvén speeds. The transversal waves and
electric currents, generated by the spicule’s driver and lasting
for many minutes, are dissipated and heat the associated loop. These
complex interactions in the corona can be connected with blueshifted
secondary components in coronal spectral lines (red-blue asymmetries)
observed with Hinode/EIS and SOHO/SUMER, as well as the EUV counterpart
of type II spicules and propagating coronal disturbances observed with
the 171 Å and 193 Å SDO/AIA channels.
Title: Erratum: “A First Comparison of Millimeter Continuum and
Mg II Ultraviolet Line Emission from the Solar Chromosphere”
(2017, ApJL,
845, L19)
Authors: Bastian, T. S.; Chintzoglou, G.; De Pontieu, B.; Shimojo,
M.; Schmit, D.; Leenaarts, J.; Loukitcheva, M.
Bibcode: 2018ApJ...860L..16B
Altcode:
No abstract at ADS
Title: An Innovative Approach to a High Resolution Coronal Imager
(T-07): MUSE, the Multi-Slit Solar Explorer
Authors: Tarbell, Theodore D.; De Pontieu, Bart
Bibcode: 2018tess.conf41004T
Altcode:
The Next Generation Solar Physics Mission Science Objectives Team
recommended three instruments flying in space simultaneously: a
spectrometer with wide temperature coverage (T-09), a high resolution
coronal imager (T-07), and a photospheric and chromospheric magnetograph
and spectrograph (T-01,4,5). The coronal imager was inspired by the
Hi-C rocket payload, whose successful flight in 2012 gave us a new
view of the corona at resolution approximately 4 times higher (linear
dimension) than AIA. For example, it showed tantalizing evidence of
coronal heating by braiding of field lines. LMSAL and SAO have designed
a payload that goes beyond the basic requirements for T-07 by combining
an imager like Hi-C with a novel multi-slit EUV spectrograph that
obtains complete line profiles in three coronal temperature ranges over
an extended field-of-view (FOV). This payload is MUSE, the Multi-Slit
Solar Explorer, a Small Explorer mission recently selected by NASA
for a Phase A study, which could lead to a launch in 2022. MUSE will
provide unprecendented observations of the dynamics of the corona and
transition region to illuminate the physical processes that heat the
multi-million degree solar corona, accelerate the solar wind and drive
solar activity (CMEs and flares). Using multi-slit coronal spectroscopy
MUSE will exploit a 100x improvement in spectral raster cadence to
reveal temperatures, velocities and non-thermal processes over a wide
temperature range to diagnose physical processes that remain invisible
to current or planned instruments. MUSE will obtain simultaneous EUV
spectra and images with the highest resolution in space (1/3 arcsec)
and time (1-4 s) ever achieved for the transition region and corona,
along 35 slits over a FOV similar to that of IRIS, and a larger context
imager FOV. The MUSE science investigation will exploit recent advances
in numerical modeling and build on the success of IRIS by combining
numerical modeling with a uniquely capable observatory. The MUSE
consortium is led by LMSAL and includes SAO, MSU, ITA Oslo, Stanford,
ARC, GSFC, MSFC and other institutions.
Title: Emergence of internetwork magnetic fields through the solar
atmosphere
Authors: Gosic, Milan; De Pontieu, Bart; Bellot Rubio, Luis
Bibcode: 2018tess.conf21701G
Altcode:
Internetwork (IN) magnetic fields are highly dynamic, short-lived
magnetic structures that populate the interior of supergranular
cells. Since they emerge all over the Sun, these small-scale fields
bring a substantial amount of flux, and therefore energy, to the solar
surface. Because of this, IN fields are crucial for understanding the
quiet Sun magnetism. However, they are weak and produce very small
polarization signals, which is the reason why their properties and
impact on the energetics and dynamics of the solar atmosphere are
largely unknown. Here we use coordinated IRIS and SST observations
of IN regions at high spatial and temporal resolution. They give us
the opportunity to follow the evolution of IN magnetic loops as they
emerge into the photosphere. For the first time, our polarimetric
measurements provide a direct observational evidence of IN fields
reaching the chromosphere. Moreover, we show that IN magnetic loops
contribute to the chromospheric and transition region heating through
interaction with preexisting ambient fields.
Title: Observations of Large Penumbral Jets from IRIS and Hinode
Authors: Tiwari, Sanjiv K.; Moore, Ronald Lee; De Pontieu, Bart;
Tarbell, Theodore D.; Panesar, Navdeep Kaur; Winebarger, Amy R.;
Sterling, Alphonse C.
Bibcode: 2018tess.conf40807T
Altcode:
Recent observations from Hinode (SOT/FG) revealed the presence of
large penumbral jets (widths ≥ 500 km, larger than normal penumbral
microjets, which have widths < 400 km) repeatedly occurring at
the same locations in a sunspot penumbra, at the tail of a penumbral
filament or where the tails of several penumbral filaments apparently
converge (Tiwari et al. 2016, ApJ). These locations were observed
to have mixed-polarity flux in Stokes-V images from SOT/FG. Large
penumbral jets displayed direct signatures in AIA 1600, 304, 171,
and 193 channels; thus they were heated to at least transition region
temperatures. Because large jets could not be detected in AIA 94 Å,
whether they had any coronal-temperature plasma remains unclear. In
the present work, for another sunspot, we use IRIS Mg II k 2796
slit jaw images and spectra and magnetograms from Hinode SOT/FG and
SOT/SP to examine: whether penumbral jets spin, similar to spicules
and coronal jets in the quiet Sun and coronal holes; whether they stem
from mixed-polarity flux; and whether they produce discernible coronal
emission, especially in AIA 94 Å images.
Title: First analysis of solar structures in 1.21 mm full-disc ALMA
image of the Sun
Authors: Brajša, R.; Sudar, D.; Benz, A. O.; Skokić, I.; Bárta,
M.; De Pontieu, B.; Kim, S.; Kobelski, A.; Kuhar, M.; Shimojo, M.;
Wedemeyer, S.; White, S.; Yagoubov, P.; Yan, Y.
Bibcode: 2018A&A...613A..17B
Altcode: 2017arXiv171106130B
Context. Various solar features can be seen in emission or absorption
on maps of the Sun in the millimetre and submillimetre wavelength
range. The recently installed Atacama Large Millimetre/submillimetre
Array (ALMA) is capable of observing the Sun in that wavelength range
with an unprecedented spatial, temporal and spectral resolution. To
interpret solar observations with ALMA, the first important step is to
compare solar ALMA maps with simultaneous images of the Sun recorded in
other spectral ranges.
Aims: The first aim of the present work
is to identify different structures in the solar atmosphere seen in the
optical, infrared, and EUV parts of the spectrum (quiet Sun, active
regions, prominences on the disc, magnetic inversion lines, coronal
holes and coronal bright points) in a full-disc solar ALMA image. The
second aim is to measure the intensities (brightness temperatures) of
those structures and to compare them with the corresponding quiet Sun
level.
Methods: A full-disc solar image at 1.21 mm obtained on
December 18, 2015, during a CSV-EOC campaign with ALMA is calibrated and
compared with full-disc solar images from the same day in Hα line, in
He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4
nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness
temperatures of various structures are determined by averaging over
corresponding regions of interest in the calibrated ALMA image.
Results: Positions of the quiet Sun, active regions, prominences on
the disc, magnetic inversion lines, coronal holes and coronal bright
points are identified in the ALMA image. At the wavelength of 1.21
mm, active regions appear as bright areas (but sunspots are dark),
while prominences on the disc and coronal holes are not discernible
from the quiet Sun background, despite having slightly less intensity
than surrounding quiet Sun regions. Magnetic inversion lines appear as
large, elongated dark structures and coronal bright points correspond
to ALMA bright points.
Conclusions: These observational results
are in general agreement with sparse earlier measurements at similar
wavelengths. The identification of coronal bright points represents
the most important new result. By comparing ALMA and other maps,
it was found that the ALMA image was oriented properly and that the
procedure of overlaying the ALMA image with other images is accurate
at the 5 arcsec level. The potential of ALMA for physics of the solar
chromosphere is emphasised.
Title: Chromospheric Heating due to Cancellation of Quiet Sun
Internetwork Fields
Authors: Gošić, M.; de la Cruz Rodríguez, J.; De Pontieu, B.; Bellot
Rubio, L. R.; Carlsson, M.; Esteban Pozuelo, S.; Ortiz, A.; Polito, V.
Bibcode: 2018ApJ...857...48G
Altcode: 2018arXiv180207392G
The heating of the solar chromosphere remains one of the most
important questions in solar physics. Our current understanding is that
small-scale internetwork (IN) magnetic fields play an important role
as a heating agent. Indeed, cancellations of IN magnetic elements in
the photosphere can produce transient brightenings in the chromosphere
and transition region. These bright structures might be the signature
of energy release and plasma heating, probably driven by the magnetic
reconnection of IN field lines. Although single events are not expected
to release large amounts of energy, their global contribution to the
chromosphere may be significant due to their ubiquitous presence
in quiet Sun regions. In this paper, we study cancellations of IN
elements and analyze their impact on the energetics and dynamics of
the quiet Sun atmosphere. We use high-resolution, multiwavelength,
coordinated observations obtained with the Interface Region Imaging
Spectrograph and the Swedish 1 m Solar Telescope (SST) to identify
cancellations of IN magnetic flux patches and follow their evolution. We
find that, on average, these events live for ∼3 minutes in the
photosphere and ∼12 minutes in the chromosphere and/or transition
region. Employing multi-line inversions of the Mg II h and k lines,
we show that cancellations produce clear signatures of heating in the
upper atmospheric layers. However, at the resolution and sensitivity
accessible to the SST, their number density still seems to be one
order of magnitude too low to explain the global chromospheric heating.
Title: Chromospheric counterparts of solar transition region
unresolved fine structure loops
Authors: Pereira, Tiago M. D.; Rouppe van der Voort, Luc; Hansteen,
Viggo H.; De Pontieu, Bart
Bibcode: 2018A&A...611L...6P
Altcode: 2018arXiv180304415P
Low-lying loops have been discovered at the solar limb in transition
region temperatures by the Interface Region Imaging Spectrograph
(IRIS). They do not appear to reach coronal temperatures, and it
has been suggested that they are the long-predicted unresolved fine
structures (UFS). These loops are dynamic and believed to be visible
during both heating and cooling phases. Making use of coordinated
observations between IRIS and the Swedish 1-m Solar Telescope, we study
how these loops impact the solar chromosphere. We show for the first
time that there is indeed a chromospheric signal of these loops, seen
mostly in the form of strong Doppler shifts and a conspicuous lack of
chromospheric heating. In addition, we find that several instances have
a inverse Y-shaped jet just above the loop, suggesting that magnetic
reconnection is driving these events. Our observations add several
puzzling details to the current knowledge of these newly discovered
structures; this new information must be considered in theoretical
models. Two movies associated to Fig. 1 are available at https://www.aanda.org
Title: Bridging the Gap: Capturing the Lyα Counterpart of a Type-II
Spicule and Its Heating Evolution with VAULT2.0 and IRIS Observations
Authors: Chintzoglou, Georgios; De Pontieu, Bart; Martínez-Sykora,
Juan; Pereira, Tiago M. D.; Vourlidas, Angelos; Tun Beltran, Samuel
Bibcode: 2018ApJ...857...73C
Altcode: 2018arXiv180303405C
We present results from an observing campaign in support of the
VAULT2.0 sounding rocket launch on 2014 September 30. VAULT2.0 is a Lyα
(1216 Å) spectroheliograph capable of providing spectroheliograms at
high cadence. Lyα observations are highly complementary to the IRIS
observations of the upper chromosphere and the low transition region
(TR) but have previously been unavailable. The VAULT2.0 data provide new
constraints on upper-chromospheric conditions for numerical models. The
observing campaign was closely coordinated with the IRIS mission. Taking
advantage of this simultaneous multi-wavelength coverage of target
AR 12172 and by using state-of-the-art radiative-MHD simulations of
spicules, we investigate in detail a type-II spicule associated with
a fast (300 km s-1) network jet recorded in the campaign
observations. Our analysis suggests that spicular material exists
suspended high in the atmosphere but at lower temperatures (seen in
Lyα) until it is heated and becomes visible in TR temperatures as a
network jet. The heating begins lower in the spicule and propagates
upwards as a rapidly propagating thermal front. The front is then
observed as fast, plane-of-the-sky motion typical of a network jet,
but contained inside the pre-existing spicule. This work supports
the idea that the high speeds reported in network jets should not be
taken as real mass upflows but only as apparent speeds of a rapidly
propagating heating front along the pre-existing spicule.
Title: Investigating the Response of Loop Plasma to Nanoflare Heating
Using RADYN Simulations
Authors: Polito, V.; Testa, P.; Allred, J.; De Pontieu, B.; Carlsson,
M.; Pereira, T. M. D.; Gošić, Milan; Reale, Fabio
Bibcode: 2018ApJ...856..178P
Altcode: 2018arXiv180405970P
We present the results of 1D hydrodynamic simulations of coronal
loops that are subject to nanoflares, caused by either in situ
thermal heating or nonthermal electron (NTE) beams. The synthesized
intensity and Doppler shifts can be directly compared with Interface
Region Imaging Spectrograph (IRIS) and Atmospheric Imaging Assembly
(AIA) observations of rapid variability in the transition region (TR)
of coronal loops, associated with transient coronal heating. We find
that NTEs with high enough low-energy cutoff ({E}{{C}})
deposit energy in the lower TR and chromosphere, causing blueshifts
(up to ∼20 km s-1) in the IRIS Si IV lines, which
thermal conduction cannot reproduce. The {E}{{C}} threshold
value for the blueshifts depends on the total energy of the events
(≈5 keV for 1024 erg, up to 15 keV for 1025
erg). The observed footpoint emission intensity and flows, combined
with the simulations, can provide constraints on both the energy of the
heating event and {E}{{C}}. The response of the loop plasma
to nanoflares depends crucially on the electron density: significant
Si IV intensity enhancements and flows are observed only for initially
low-density loops (<109 cm-3). This provides
a possible explanation of the relative scarcity of observations of
significant moss variability. While the TR response to single heating
episodes can be clearly observed, the predicted coronal emission (AIA
94 Å) for single strands is below current detectability and can only
be observed when several strands are heated closely in time. Finally,
we show that the analysis of the IRIS Mg II chromospheric lines can
help further constrain the properties of the heating mechanisms.
Title: Transverse Wave Induced Kelvin-Helmholtz Rolls in Spicules
Authors: Antolin, P.; Schmit, D.; Pereira, T. M. D.; De Pontieu, B.;
De Moortel, I.
Bibcode: 2018ApJ...856...44A
Altcode: 2018arXiv180300821A
In addition to their jet-like dynamic behavior, spicules usually exhibit
strong transverse speeds, multi-stranded structure, and heating from
chromospheric to transition region temperatures. In this work we first
analyze Hinode and IRIS observations of spicules and find different
behaviors in terms of their Doppler velocity evolution and collective
motion of their sub-structure. Some have a Doppler shift sign change
that is rather fixed along the spicule axis, and lack coherence in
the oscillatory motion of strand-like structure, matching rotation
models, or long-wavelength torsional Alfvén waves. Others exhibit a
Doppler shift sign change at maximum displacement and coherent motion
of their strands, suggesting a collective magnetohydrodynamic (MHD)
wave. By comparing with an idealized 3D MHD simulation combined with
radiative transfer modeling, we analyze the role of transverse MHD
waves and associated instabilities in spicule-like features. We find
that transverse wave induced Kelvin-Helmholtz (TWIKH) rolls lead to
coherence of strand-like structure in imaging and spectral maps, as seen
in some observations. The rapid transverse dynamics and the density
and temperature gradients at the spicule boundary lead to ring-shaped
Mg II k and Ca II H source functions in the transverse cross-section,
potentially allowing IRIS to capture the Kelvin-Helmholtz instability
dynamics. Twists and currents propagate along the spicule at Alfvénic
speeds, and the temperature variations within TWIKH rolls, produce the
sudden appearance/disappearance of strands seen in Doppler velocity
and in Ca II H intensity. However, only a mild intensity increase in
higher-temperature lines is obtained, suggesting there is an additional
heating mechanism at work in spicules.
Title: A comparison of solar ALMA observations and model based
predictions of the brightness temperature
Authors: Brajša, R.; Kuhar, M.; Benz, A. O.; Skokić, I.; Sudar,
D.; Wedemeyer, S.; Báarta, M.; De Pontieu, B.; Kim, S.; Kobelski,
A.; Shimojo, M.; White, S.; Yagoubov, P.; Yan, Y.; Ludwig, H. G.;
Temmer, M.; Saar, S. H.; Selhorst, C. L.; Beuc, R.
Bibcode: 2018CEAB...42....1B
Altcode:
The new facility Atacama Large Millimeter/submillimeter Array (ALMA) is
capable of observing the Sun in the wavelength range from 0.3 mm to 10
mm with an unprecedented spatial, temporal and spectral resolution. The
first aim of the present work is to identify different structures
in the solar atmosphere (quiet Sun, active regions, filaments on the
disc, and coronal holes) in a full disc solar ALMA image at 1.21 mm
obtained on December 18, 2015 during a CSV-EOC campaign. It is compared
with full disc solar images from the same day in the Hα line (Cerro
Tololo Observatory, NISP), and at three EUV wavelengths (30.4 nm,
21.1 nm, 17.1 nm; a composite SDO image). Positions of the quiet Sun
areas, active regions, filaments on the disc, and coronal holes are
identified in the ALMA image. To interpret solar observations with ALMA
it is important to compare the measured and calculated intensities
of various solar structures. So, the second aim of this work is to
calculate the intensity (brightness temperature) for those structures
(quiet Sun, active regions, filaments on the disc, and coronal holes)
for a broad wavelength range (from 0.3 mm to 10 mm), closely related
to that of the ALMA, and to compare the results with available
ALMA observations. Thermal bremsstrahlung is the dominant radiation
mechanism for explanation of the observed phenomena. A procedure for
calculating the brightness temperature for a given wavelength and
model atmosphere, which integrates the radiative transfer equation
for thermal bremsstrahlung, is used. At the wavelength of 1.21 mm
active regions appear as bright areas, while filaments on the disc and
coronal holes are not discernible from the quiet Sun background. The
models generally agree with the observed results: Active regions are
bright primarily due to higher densities, filaments can appear bright,
dark or not at all and coronal holes cannot be easily identified.
Title: The temporal evolution of explosive events and its implication
on reconnection dynamics
Authors: Guo, L.; Liu, W.; De Pontieu, B.; Huang, Y. M.; Peter, H.;
Bhattacharjee, A.
Bibcode: 2017AGUFMSH43A2803G
Altcode:
Transition-region explosive events and other bursts seen in extreme UV
light are characterized by broad spectral line profiles, and the more
violent ones show a strong enhancement of emission. They are thought
to be driven by magnetic reconnection, because of their characteristic
spectral profiles often indicating strong Alfvénic flows, and because
of the fact that they typically occur where magnetic flux concentrations
of opposite polarity intersect. In this presentation, we will focus
on the temporal evolution of transition-region explosive events. In
particular, we will investigate fast onsets of these events and the
rapid oscillations of intensity during these event. The fast onset
refers to the beginning of an explosive event, where the intensities
and the widths of its line profiles increase dramatically (often within
less than 10 seconds) and the rapid oscillations of intensity refer
to blinks of emission that usually last less than 10 seconds during
the event. In order to interpret and understand underlying mechanisms
of these observations, we conduct numerical simulation of an explosive
event and calculate its spectra. We observe a similar temporal evolution
in the synthetic Si IV spectra when the explosive event is driven by
time-dependent reconnection—plasmoid instability. The qualitative
agreement between observations and simulations suggests that the
temporal evolution of Si IV spectra of explosive events are closely
related to reconnection dynamics.
Title: MUSE, the Multi-Slit Solar Explorer
Authors: Lemen, J. R.; Tarbell, T. D.; De Pontieu, B.; Wuelser, J. P.
Bibcode: 2017AGUFMSH51B2494L
Altcode:
The Multi-Slit Solar Explorer (MUSE) has been selected for a Phase A
study for the NASA Heliophysics Small Explorer program. The science
objective of MUSE is to make high spatial and temporal resolution
imaging and spectral observations of the solar corona and transition
region in order to probe the mechanisms responsible for energy release
in the corona and understand the dynamics of the solar atmosphere. The
physical processes are responsible for heating the corona, accelerating
the solar wind, and the rapid release of energy in CMEs and flares. The
observations will be tightly coupled to state-of-the-art numerical
modeling to provide significantly improved estimates for understanding
and anticipating space weather. MUSE contains two instruments:
an EUV spectrograph and an EUV context imager. Both have similar
spatial resolutions and leverage extensive heritage from previous
high-resolution instruments such as IRIS and the HiC rocket payload. The
MUSE spectrograph employs a novel multi-slit design that enables a
100x improvement in spectral scanning rates, which will reveal crucial
information about the dynamics (e.g., temperature, velocities) of the
physical processes that are not observable with current instruments. The
MUSE investigation builds on the success of IRIS by combining numerical
modeling with a uniquely capable observatory: MUSE will obtain EUV
spectra and images with the highest resolution in space (1/3 arcsec) and
time (1-4 s) ever achieved for the transition region and corona, along
35 slits and a large context FOV simultaneously. The MUSE consortium
includes LMSAL, SAO, Stanford, ARC, HAO, GSFC, MSFC, MSU, and ITA Oslo.
Title: Chromospheric Heating Driven by Cancellations of Internetwork
Magnetic Flux
Authors: Gosic, M.; de la Cruz Rodriguez, J.; De Pontieu, B.; Bellot
Rubio, L.; Esteban Pozuelo, S.; Ortiz-Carbonell, A. N.
Bibcode: 2017AGUFMSH41C..02G
Altcode:
The heating of the solar chromosphere remains to be one of the
most important questions in solar physics. It is believed that this
phenomenon may significantly be supported by small-scale internetwork
(IN) magnetic fields. Indeed, cancellations of IN magnetic flux can
generate transient brightenings in the chromosphere and transition
region. These bright structures might be the signature of energy release
and plasma heating, probably driven by magnetic reconnection of IN field
lines. Using high resolution, multiwavelength, coordinated observations
recorded with the Interface Region Imaging Spectrograph (IRIS) and
the Swedish 1-m Solar Telescope (SST), we analyzed cancellations of IN
flux and their impact on the energetics and dynamics of the quiet Sun
atmosphere. From their temporal and spatial evolution, we determine that
these events can heat locally the upper atmospheric layers. However,
employing multi-line inversions of the Mg II h & k lines, we show
that cancellations, although occurring ubiquitously over IN regions,
are not capable of sustaining the total radiative losses of the quiet
Sun chromosphere.
Title: Observation and modelling of the Fe XXI line profile observed
by IRIS during the impulsive phase of flares
Authors: Polito, V.; Testa, P.; De Pontieu, B.; Allred, J. C.
Bibcode: 2017AGUFMSH41A2741P
Altcode:
The observation of the high temperature (above 10 MK) Fe XXI 1354.1 A
line with the Interface Region Imaging Spectrograph (IRIS) has provided
significant insights into the chromospheric evaporation process in
flares. In particular, the line is often observed to be completely
blueshifted, in contrast to previous observations at lower spatial
and spectral resolution, and in agreement with predictions from
theoretical models. Interestingly, the line is also observed to be
mostly symmetric and with a large excess above the thermal width. One
popular interpretation for the excess broadening is given by assuming
a superposition of flows from different loop strands. In this work,
we perform a statistical analysis of Fe XXI line profiles observed
by IRIS during the impulsive phase of flares and compare our results
with hydrodynamic simulations of multi-thread flare loops performed
with the 1D RADYN code. Our results indicate that the multi-thread
models cannot easily reproduce the symmetry of the line and that some
other physical process might need to be invoked in order to explain
the observed profiles.
Title: Observations and Modeling of Transition Region and Coronal
Heating Associated with Spicules
Authors: De Pontieu, B.; Martinez-Sykora, J.; De Moortel, I.;
Chintzoglou, G.; McIntosh, S. W.
Bibcode: 2017AGUFMSH43A2793D
Altcode:
Spicules have been proposed as significant contributorsto the coronal
energy and mass balance. While previous observationshave provided
a glimpse of short-lived transient brightenings in thecorona that
are associated with spicules, these observations have beencontested
and are the subject of a vigorous debate both on the modelingand
the observational side so that it remains unclear whether plasmais
heated to coronal temperatures in association with spicules. We use
high-resolution observations of the chromosphere and transition region
with the Interface Region Imaging Spectrograph (IRIS) and ofthe corona
with the Atmospheric Imaging Assembly (AIA) onboard theSolar Dynamics
Observatory (SDO) to show evidence of the formation of coronal
structures as a result of spicular mass ejections andheating of
plasma to transition region and coronaltemperatures. Our observations
suggest that a significant fraction of the highly dynamic loop fan
environment associated with plage regions may be the result of the
formation of such new coronal strands, a process that previously had
been interpreted as the propagation of transient propagating coronal
disturbances (PCD)s. Our observationsare supported by 2.5D radiative
MHD simulations that show heating tocoronal temperatures in association
with spicules. Our results suggest that heating and strong flows play
an important role in maintaining the substructure of loop fans, in
addition to the waves that permeate this low coronal environment. Our
models also matches observations ofTR counterparts of spicules and
provides an elegant explanation forthe high apparent speeds of these
"network jets".
Title: Bridging the Gap: Capturing the Lyα Counterpart of a Type-II
Spicule and its Heating Evolution with VAULT2.0 and IRIS Campaign
Observations
Authors: Chintzoglou, G.; De Pontieu, B.; Martinez-Sykora, J.; Mendes
Domingos Pereira, T.; Vourlidas, A.; Tun Beltran, S.
Bibcode: 2017AGUFMSH43A2794C
Altcode:
We present the analysis of data from the observing campaign in support
to the VAULT2.0 sounding rocket launch on September 30, 2014. VAULT2.0
is a Lyα (1216 Å) spectroheliograph capable of providing fast
cadence spectroheliograms of high-spectral purity. High resolution
Lyα observations are highly complementary with the IRIS observations
of the upper chromosphere and the low transition region but have
previously been unavailable. The VAULT2.0 data provide critical, new
upper-chromospheric constraints for numerical models. The observing
campaign was closely coordinated with the IRIS mission. Taking
advantage of this simultaneous multi-wavelength coverage of target
AR 12172 and by using state-of-the-art radiative-MHD simulations of
spicules, we are able to perform a detailed investigation of a type-II
spicule associated with a fast apparent network jet recorded in the
campaign observations during the VAULT2.0 flight. Our unique analysis
suggests that spicular material exists suspended in lower temperatures
until it rapidly gets heated and becomes visible in transition-region
temperatures as an apparent network jet.
Title: Constraints on active region coronal heating properties
from observations and modeling of chromospheric, transition region,
and coronal emission
Authors: Testa, P.; Polito, V.; De Pontieu, B.; Carlsson, M.; Reale,
F.; Allred, J. C.; Hansteen, V. H.
Bibcode: 2017AGUFMSH43A2804T
Altcode:
We investigate coronal heating properties in active region cores in
non-flaring conditions, using high spatial, spectral, and temporal
resolution chromospheric/transition region/coronal observations coupled
with detailed modeling. We will focus, in particular, on observations
with the Interface Region Imaging Spectrograph (IRIS), joint with
observations with Hinode (XRT and EIS) and SDO/AIA. We will discuss
how these observations and models (1D HD and 3D MHD, with the RADYN
and Bifrost codes) provide useful diagnostics of the coronal heating
processes and mechanisms of energy transport.
Title: Dynamics in the Chromosphere Imaged at Four Second Cadence
Authors: Schmit, D.; De Pontieu, B.
Bibcode: 2017AGUFMSH43A2795S
Altcode:
In this work we present analysis of rapid intensity fluctuations
that are observed in the chromosphere and transition region using the
slit-jaw datasets of IRIS and CLASP. While chromospheric oscillations
have been a topic of interest for 30 years, the instrumentation to image
those dynamics at high-cadence has only recently been developed. We use
filtergraph data from 1215A, 2800A, and 1400A to examine the occurrence
rate and morphology of rapid intensity fluctuations in different
magnetic environments. There are indications of rapidly propagating
disturbances with phase speeds greater than 100 km/s in all passbands
although the morphology of the features differs significantly between
passbands. The relationship between intensity fluctuations, spicules,
and waves is discussed.
Title: Intermittent Reconnection and Plasmoids in UV Bursts in the
Low Solar Atmosphere
Authors: Rouppe van der Voort, L.; De Pontieu, B.; Scharmer, G. B.;
de la Cruz Rodríguez, J.; Martínez-Sykora, J.; Nóbrega-Siverio,
D.; Guo, L. J.; Jafarzadeh, S.; Pereira, T. M. D.; Hansteen, V. H.;
Carlsson, M.; Vissers, G.
Bibcode: 2017ApJ...851L...6R
Altcode: 2017arXiv171104581R
Magnetic reconnection is thought to drive a wide variety of dynamic
phenomena in the solar atmosphere. Yet, the detailed physical mechanisms
driving reconnection are difficult to discern in the remote sensing
observations that are used to study the solar atmosphere. In this
Letter, we exploit the high-resolution instruments Interface Region
Imaging Spectrograph and the new CHROMIS Fabry-Pérot instrument at
the Swedish 1-m Solar Telescope (SST) to identify the intermittency
of magnetic reconnection and its association with the formation of
plasmoids in so-called UV bursts in the low solar atmosphere. The Si IV
1403 Å UV burst spectra from the transition region show evidence of
highly broadened line profiles with often non-Gaussian and triangular
shapes, in addition to signatures of bidirectional flows. Such profiles
had previously been linked, in idealized numerical simulations, to
magnetic reconnection driven by the plasmoid instability. Simultaneous
CHROMIS images in the chromospheric Ca II K 3934 Å line now provide
compelling evidence for the presence of plasmoids by revealing highly
dynamic and rapidly moving brightenings that are smaller than 0.″2 and
that evolve on timescales of the order of seconds. Our interpretation
of the observations is supported by detailed comparisons with synthetic
observables from advanced numerical simulations of magnetic reconnection
and associated plasmoids in the chromosphere. Our results highlight
how subarcsecond imaging spectroscopy sensitive to a wide range of
temperatures combined with advanced numerical simulations that are
realistic enough to compare with observations can directly reveal the
small-scale physical processes that drive the wide range of phenomena
in the solar atmosphere.
Title: What Causes the High Apparent Speeds in Chromospheric and
Transition Region Spicules on the Sun?
Authors: De Pontieu, Bart; Martínez-Sykora, Juan; Chintzoglou,
Georgios
Bibcode: 2017ApJ...849L...7D
Altcode: 2017arXiv171006803D
Spicules are the most ubuiquitous type of jets in the solar
atmosphere. The advent of high-resolution imaging and spectroscopy
from the Interface Region Imaging Spectrograph (IRIS) and ground-based
observatories has revealed the presence of very high apparent motions of
order 100-300 km s-1 in spicules, as measured in the plane of
the sky. However, line of sight measurements of such high speeds have
been difficult to obtain, with values deduced from Doppler shifts in
spectral lines typically of order 30-70 km s-1. In this work,
we resolve this long-standing discrepancy using recent 2.5D radiative
MHD simulations. This simulation has revealed a novel driving mechanism
for spicules in which ambipolar diffusion resulting from ion-neutral
interactions plays a key role. In our simulation, we often see that
the upward propagation of magnetic waves and electrical currents
from the low chromosphere into already existing spicules can lead to
rapid heating when the currents are rapidly dissipated by ambipolar
diffusion. The combination of rapid heating and the propagation of these
currents at Alfvénic speeds in excess of 100 km s-1 leads
to the very rapid apparent motions, and often wholesale appearance,
of spicules at chromospheric and transition region temperatures. In
our simulation, the observed fast apparent motions in such jets are
actually a signature of a heating front, and much higher than the
mass flows, which are of order 30-70 km s-1. Our results
can explain the behavior of transition region “network jets” and
the very high apparent speeds reported for some chromospheric spicules.
Title: Comparison of Solar Fine Structure Observed Simultaneously
in Lyα and Mg II h
Authors: Schmit, D.; Sukhorukov, A. V.; De Pontieu, B.; Leenaarts,
J.; Bethge, C.; Winebarger, A.; Auchère, F.; Bando, T.; Ishikawa,
R.; Kano, R.; Kobayashi, K.; Narukage, N.; Trujillo Bueno, J.
Bibcode: 2017ApJ...847..141S
Altcode: 2017arXiv170900035S
The Chromospheric Lyman Alpha Spectropolarimeter (CLASP) observed the
Sun in H I Lyα during a suborbital rocket flight on 2015 September
3. The Interface Region Imaging Telescope (IRIS) coordinated with the
CLASP observations and recorded nearly simultaneous and co-spatial
observations in the Mg II h and k lines. The Mg II h and Lyα lines
are important transitions, energetically and diagnostically, in the
chromosphere. The canonical solar atmosphere model predicts that these
lines form in close proximity to each other and so we expect that the
line profiles will exhibit similar variability. In this analysis, we
present these coordinated observations and discuss how the two profiles
compare over a region of quiet Sun at viewing angles that approach the
limb. In addition to the observations, we synthesize both line profiles
using a 3D radiation-MHD simulation. In the observations, we find that
the peak width and the peak intensities are well correlated between the
lines. For the simulation, we do not find the same relationship. We
have attempted to mitigate the instrumental differences between IRIS
and CLASP and to reproduce the instrumental factors in the synthetic
profiles. The model indicates that formation heights of the lines
differ in a somewhat regular fashion related to magnetic geometry. This
variation explains to some degree the lack of correlation, observed
and synthesized, between Mg II and Lyα. Our analysis will aid in the
definition of future observatories that aim to link dynamics in the
chromosphere and transition region.
Title: Two-dimensional Radiative Magnetohydrodynamic Simulations of
Partial Ionization in the Chromosphere. II. Dynamics and Energetics
of the Low Solar Atmosphere
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Carlsson, Mats;
Hansteen, Viggo H.; Nóbrega-Siverio, Daniel; Gudiksen, Boris V.
Bibcode: 2017ApJ...847...36M
Altcode: 2017arXiv170806781M
We investigate the effects of interactions between ions and
neutrals on the chromosphere and overlying corona using 2.5D
radiative MHD simulations with the Bifrost code. We have extended
the code capabilities implementing ion-neutral interaction effects
using the generalized Ohm’s law, I.e., we include the Hall term
and the ambipolar diffusion (Pedersen dissipation) in the induction
equation. Our models span from the upper convection zone to the corona,
with the photosphere, chromosphere, and transition region partially
ionized. Our simulations reveal that the interactions between ionized
particles and neutral particles have important consequences for the
magnetothermodynamics of these modeled layers: (1) ambipolar diffusion
increases the temperature in the chromosphere; (2) sporadically the
horizontal magnetic field in the photosphere is diffused into the
chromosphere, due to the large ambipolar diffusion; (3) ambipolar
diffusion concentrates electrical currents, leading to more violent
jets and reconnection processes, resulting in (3a) the formation of
longer and faster spicules, (3b) heating of plasma during the spicule
evolution, and (3c) decoupling of the plasma and magnetic field in
spicules. Our results indicate that ambipolar diffusion is a critical
ingredient for understanding the magnetothermodynamic properties in the
chromosphere and transition region. The numerical simulations have been
made publicly available, similar to previous Bifrost simulations. This
will allow the community to study realistic numerical simulations with
a wider range of magnetic field configurations and physics modules
than previously possible.
Title: IRISpy: Analyzing IRIS Data in Python
Authors: Ryan, Daniel; Christe, Steven; Mumford, Stuart; Baruah,
Ankit; Timothy, Shelbe; Pereira, Tiago; De Pontieu, Bart
Bibcode: 2017SPD....4811508R
Altcode:
IRISpy is a new community-developed open-source software library
for analysing IRIS level 2 data. It is written in Python, a free,
cross-platform, general-purpose, high-level programming language. A
wide array of scientific computing software packages have already been
developed in Python, from numerical computation (NumPy, SciPy, etc.),
to visualization and plotting (matplotlib), to solar-physics-specific
data analysis (SunPy). IRISpy is currently under development as a
SunPy-affiliated package which means it depends on the SunPy library,
follows similar standards and conventions, and is developed with the
support of of the SunPy development team. IRISpy’s has two primary
data objects, one for analyzing slit-jaw imager data and another
for analyzing spectrograph data. Both objects contain basic slicing,
indexing, plotting, and animating functionality to allow users to easily
inspect, reduce and analyze the data. As part of this functionality the
objects can output SunPy Maps, TimeSeries, Spectra, etc. of relevant
data slices for easier inspection and analysis. Work is also ongoing
to provide additional data analysis functionality including derivation
of systematic measurement errors (e.g. readout noise), exposure time
correction, residual wavelength calibration, radiometric calibration,
and fine scale pointing corrections. IRISpy’s code base is publicly
available through github.com and can be contributed to by anyone. In
this poster we demonstrate IRISpy’s functionality and future goals
of the project. We also encourage interested users to become involved
in further developing IRISpy.
Title: Impact of Type II Spicules into the Corona
Authors: Martinez-Sykora, Juan; De Pontieu, Bart; Carlsson, Mats;
Hansteen, Viggo H.; Pereira, Tiago M. D.
Bibcode: 2017SPD....4810403M
Altcode:
In the lower solar atmosphere, the chromosphere is permeated by jets,
in which plasma is propelled at speeds of 50-150 km/s into the Sun’s
atmosphere or corona. Although these spicules may play a role in heating
the million-degree corona and are associated with Alfvén waves that
help drive the solar wind, their generation remains mysterious. We
implemented in the radiative MHD Bifrost code the effects of partial
ionization using the generalized Ohm’s law. This code also solves
the full MHD equations with non-grey and non-LTE radiative transfer
and thermal conduction along magnetic field lines. The ion-neutral
collision frequency is computed using recent studies that improved the
estimation of the cross sections under chromospheric conditions (Vranjes
& Krstic 2013). Self-consistently driven jets (spicules type II)
in magnetohydrodynamic simulations occur ubiquitously when magnetic
tension is confined and transported upwards through interactions
between ions and neutrals, and impulsively released to drive flows,
heat plasma, generate Alfvén waves, and may play an important role in
maintaining the substructure of loop fans. This mechanism explains how
spicular plasma can be heated to millions of degrees and how Alfvén
waves are generated in the chromosphere.
Title: A First Comparison of Millimeter Continuum and Mg II
Ultraviolet Line Emission from the Solar Chromosphere
Authors: Bastian, T. S.; Chintzoglou, G.; De Pontieu, B.; Shimojo,
M.; Schmit, D.; Leenaarts, J.; Loukitcheva, M.
Bibcode: 2017ApJ...845L..19B
Altcode: 2017arXiv170604532B
We present joint observations of the Sun by the Atacama Large
Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging
Spectrograph (IRIS). Both millimeter/submillimeter-λ continuum emission
and ultraviolet (UV) line emission originate from the solar chromosphere
and both have the potential to serve as powerful and complementary
diagnostics of physical conditions in this enigmatic region of the solar
atmosphere. The observations were made of a solar active region on 2015
December 18 as part of the ALMA science verification effort. A map of
the Sun’s continuum emission was obtained by ALMA at a wavelength of
1.25 mm (239 GHz). A contemporaneous map was obtained by IRIS in the
Mg II h doublet line at 2803.5 Å. While a clear correlation between
the 1.25 mm brightness temperature TB and the Mg II h
line radiation temperature Trad is observed, the slope
is <1, perhaps as a result of the fact that these diagnostics
are sensitive to different parts of the chromosphere and that the
Mg II h line source function includes a scattering component. There
is a significant difference (35%) between the mean TB
(1.25 mm) and mean Trad (Mg II). Partitioning the maps
into “sunspot,” “quiet areas,” and “plage regions” we
find the relation between the IRIS Mg II h line Trad and
the ALMA TB region-dependent. We suggest this may be the
result of regional dependences of the formation heights of the IRIS
and ALMA diagnostics and/or the increased degree of coupling between
the UV source function and the local gas temperature in the hotter,
denser gas in plage regions.
Title: Point-Spread Functions for the Near Ultraviolet Channel of
the Interface Region Imaging Spectrograph (IRIS)
Authors: Courrier, Hans; Kankelborg, Charles C.; De Pontieu, Bart;
Wülser, Jean-Pierre
Bibcode: 2017SPD....4811701C
Altcode:
We present point-spread functions (PSFs) for the near ultraviolet (NUV)
spectrograph channel of the Interface Region Imaging Spectrograph
(IRIS). The hard edge terminus of the 2016 Mercury transit of the
Sun is used to measure the PSFs near instrument center field of view
using an iterative semi-blind deconvolution method. The resulting PSFs
exhibit an asymmetrical core with broader wings when compared to the
theoretical diffraction limited PSFs. Deconvolution of our PSFs from
the original Level 2 images produces images with improved stray light
characteristics and increased contrast.
Title: Chromospheric heating due to internetwork magnetic flux
cancellations
Authors: Gosic, Milan; de la Cruz Rodriguez, Jaime; De Pontieu, Bart;
Bellot Rubio, Luis; Ortiz, Ada; Esteban Pozuelo, Sara
Bibcode: 2017SPD....4810404G
Altcode:
The heating of the solar chromosphere is one of the most intriguing
unanswered problems in solar physics. It is believed that this
phenomenon may significantly be supported by small-scale internetwork
(IN) magnetic fields. Indeed, cancellations of IN magnetic flux
patches might be an efficient way to transport flux and energy from
the photosphere to the chromosphere. Because of this, it is essential
to determine where they occur, the rates at which they proceed, and
understand their influence on the chromosphere. Here we study the
spatial and temporal evolution of IN cancelling patches using high
resolution, multiwavelength, coordinated observations obtained with
the Interface Region Imaging Spectrograph (IRIS) and the Swedish
1-m Solar Telescope (SST). Employing multi-line inversions of the
Mg II h&k lines we show that cancelling events, while occurring
ubiquitously over IN regions, produce clear signatures of heating in
the upper atmospheric layers. Using the RADYN code we determine the
energy released due to cancellations of IN elements and discuss about
their impact on the dynamics and energetics of the solar chromosphere.
Title: MUSE: the Multi-Slit Solar Explorer
Authors: Tarbell, Theodore D.; De Pontieu, Bart
Bibcode: 2017SPD....4811008T
Altcode:
The Multi-Slit Solar Explorer is a proposed Small Explorer mission
for studying the dynamics of the corona and transition region
using both conventional and novel spectral imaging techniques. The
physical processes that heat the multi-million degree solar corona,
accelerate the solar wind and drive solar activity (CMEs and flares)
remain poorly known. A breakthrough in these areas can only come
from radically innovative instrumentation and state-of-the-art
numerical modeling and will lead to better understanding of space
weather origins. MUSE’s multi-slit coronal spectroscopy will use a
100x improvement in spectral raster cadence to fill a crucial gap in
our knowledge of Sun-Earth connections; it will reveal temperatures,
velocities and non-thermal processes over a wide temperature range to
diagnose physical processes that remain invisible to current or planned
instruments. MUSE will contain two instruments: an EUV spectrograph (SG)
and EUV context imager (CI). Both have similar spatial resolution and
leverage extensive heritage from previous high-resolution instruments
such as IRIS and the HiC rocket payload. The MUSE investigation will
build on the success of IRIS by combining numerical modeling with a
uniquely capable observatory: MUSE will obtain EUV spectra and images
with the highest resolution in space (1/3 arcsec) and time (1-4 s)
ever achieved for the transition region and corona, along 35 slits
and a large context FOV simultaneously. The MUSE consortium includes
LMSAL, SAO, Stanford, ARC, HAO, GSFC, MSFC, MSU, ITA Oslo and other
institutions.
Title: Realistic radiative MHD simulation of a solar flare
Authors: Rempel, Matthias D.; Cheung, Mark; Chintzoglou, Georgios;
Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
DeRosa, Marc L.; Viktorovna Malanushenko, Anna; Hansteen, Viggo H.;
De Pontieu, Bart; Carlsson, Mats; Gudiksen, Boris; McIntosh, Scott W.
Bibcode: 2017SPD....4840001R
Altcode:
We present a recently developed version of the MURaM radiative
MHD code that includes coronal physics in terms of optically thin
radiative loss and field aligned heat conduction. The code employs
the "Boris correction" (semi-relativistic MHD with a reduced speed
of light) and a hyperbolic treatment of heat conduction, which allow
for efficient simulations of the photosphere/corona system by avoiding
the severe time-step constraints arising from Alfven wave propagation
and heat conduction. We demonstrate that this approach can be used
even in dynamic phases such as a flare. We consider a setup in which
a flare is triggered by flux emergence into a pre-existing bipolar
active region. After the coronal energy release, efficient transport
of energy along field lines leads to the formation of flare ribbons
within seconds. In the flare ribbons we find downflows for temperatures
lower than ~5 MK and upflows at higher temperatures. The resulting
soft X-ray emission shows a fast rise and slow decay, reaching a peak
corresponding to a mid C-class flare. The post reconnection energy
release in the corona leads to average particle energies reaching 50
keV (500 MK under the assumption of a thermal plasma). We show that
hard X-ray emission from the corona computed under the assumption of
thermal bremsstrahlung can produce a power-law spectrum due to the
multi-thermal nature of the plasma. The electron energy flux into the
flare ribbons (classic heat conduction with free streaming limit) is
highly inhomogeneous and reaches peak values of about 3x1011
erg/cm2/s in a small fraction of the ribbons, indicating
regions that could potentially produce hard X-ray footpoint sources. We
demonstrate that these findings are robust by comparing simulations
computed with different values of the saturation heat flux as well as
the "reduced speed of light".
Title: Observations and Numerical Models of Solar Coronal Heating
Associated with Spicules
Authors: De Pontieu, B.; De Moortel, I.; Martinez-Sykora, J.; McIntosh,
S. W.
Bibcode: 2017ApJ...845L..18D
Altcode: 2017arXiv171006790D
Spicules have been proposed as significant contributors to the mass
and energy balance of the corona. While previous observations have
provided a glimpse of short-lived transient brightenings in the
corona that are associated with spicules, these observations have
been contested and are the subject of a vigorous debate both on the
modeling and the observational side. Therefore, it remains unclear
whether plasma is heated to coronal temperatures in association with
spicules. We use high-resolution observations of the chromosphere and
transition region (TR) with the Interface Region Imaging Spectrograph
and of the corona with the Atmospheric Imaging Assembly on board
the Solar Dynamics Observatory to show evidence of the formation
of coronal structures associated with spicular mass ejections and
heating of plasma to TR and coronal temperatures. Our observations
suggest that a significant fraction of the highly dynamic loop fan
environment associated with plage regions may be the result of the
formation of such new coronal strands, a process that previously had
been interpreted as the propagation of transient propagating coronal
disturbances. Our observations are supported by 2.5D radiative MHD
simulations that show heating to coronal temperatures in association
with spicules. Our results suggest that heating and strong flows
play an important role in maintaining the substructure of loop fans,
in addition to the waves that permeate this low coronal environment.
Title: Evidence from IRIS that Sunspot Large Penumbral Jets Spin
Authors: Tiwari, Sanjiv K.; Moore, Ronald L.; De Pontieu, Bart;
Tarbell, Theodore D.; Panesar, Navdeep K.; Winebarger, Amy; Sterling,
Alphonse C.
Bibcode: 2017SPD....4810506T
Altcode:
Recent observations from {\it Hinode} (SOT/FG) revealed the presence of
large penumbral jets (widths $\ge$500 km, larger than normal penumbral
microjets, which have widths $<$ 400 km) repeatedly occurring at the
same locations in a sunspot penumbra, at the tail of a filament or where
the tails of several penumbral filaments apparently converge (Tiwari et
al. 2016, ApJ). These locations were observed to have mixed-polarity
flux in Stokes-V images from SOT/FG. Large penumbral jets displayed
direct signatures in AIA 1600, 304, 171, and 193 channels; thus they
were heated to at least transition region temperatures. Because
large jets could not be detected in AIA 94 \AA, whether they had
any coronal-temperature plasma remains unclear. In the present work,
for another sunspot, we use IRIS Mg II k 2796 Å slit jaw images and
spectra and magnetograms from Hinode SOT/FG and SOT/SP to examine:
whether penumbral jets spin, similar to spicules and coronal jets in the
quiet Sun and coronal holes; whether they stem from mixed-polarity flux;
and whether they produce discernible coronal emission, especially in
AIA 94 Å images. The few large penumbral jets for which we have IRIS
spectra show evidence of spin. If these have mixed-polarity at their
base, then they might be driven the same way as coronal jets and CMEs.
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: Rachmeler, Laurel; E McKenzie, David; Ishikawa, Ryohko;
Trujillo Bueno, Javier; Auchère, Frédéric; Kobayashi, Ken;
Winebarger, Amy; Bethge, Christian; Kano, Ryouhei; Kubo, Masahito;
Song, Donguk; Narukage, Noriyuki; Ishikawa, Shin-nosuke; De Pontieu,
Bart; Carlsson, Mats; Yoshida, Masaki; Belluzzi, Luca; Stepan, Jiri;
del Pino Alemná, Tanausú; Ballester, Ernest Alsina; Asensio Ramos,
Andres
Bibcode: 2017SPD....4811010R
Altcode:
We present the instrument, science case, and timeline of the CLASP2
sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
Spectro-Polarimeter) sounding rocket flight in 2015 resulted in
the first-ever linear polarization measurements of solar hydrogen
Lyman-alpha line, which is sensitive to the Hanle effect and can be used
to constrain the magnetic field and geometric complexity of the upper
chromosphere. Ly-alpha is one of several upper chromospheric lines that
contain magnetic information. In the spring of 2019, we will re-fly
the modified CLASP telescope to measure the full Stokes profile of Mg
II h & k near 280 nm. This set of lines is sensitive to the upper
chromospheric magnetic field via both the Hanle and the Zeeman effects.
Title: An innovative browser-based data exploration tool with
simultaneous scrolling in time and wavelength domains
Authors: Slater, Gregory L.; Schiff, David; De Pontieu, Bart; Tarbell,
Theodore D.; Freeland, Samuel L.
Bibcode: 2017SPD....4810624S
Altcode:
We present Cruiser, a new web tool for the precision interactive
blending of image series across time and wavelength domains. Scrolling
in two dimensions enables discovery and investigation of similarities
and differences in structure and evolution across multiple
wavelengths. Cruiser works in the latest versions of standards compliant
browsers on both desktop and IOS platforms. Co-aligned data cubes
have been generated for AIA, IRIS, and Hinode SOT FG, and image data
from additional instruments, both space-based and ground-based, can be
data sources. The tool has several movie playing and image adjustment
controls which will be described in the poster and demonstrated on a
MacOS notebook and iPad.
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: Rachmeler, Laurel A.; McKenzie, D. E.; Ishikawa, R.;
Trujillo-Bueno, J.; Auchere, F.; Kobayashi, K.; Winebarger, A.;
Bethge, C.; Kano, R.; Kubo, M.; Song, D.; Narukage, N.; Ishikawa, S.;
De Pontieu, B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Stepan, J.;
del Pino Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A.
Bibcode: 2017shin.confE..79R
Altcode:
We present the instrument, science case, and timeline of the CLASP2
sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
Spectro-Polarimeter) sounding rocket flight in 2015 resulted in
the first-ever linear polarization measurements of solar hydrogen
Lyman-alpha line, which is sensitive to the Hanle effect and can be used
to constrain the magnetic field and geometric complexity of the upper
chromosphere. Ly-alpha is one of several upper chromospheric lines that
contain magnetic information. In the spring of 2019, we will re-fly
the modified CLASP telescope to measure the full Stokes profile of Mg
II h & k near 280 nm. This set of lines is sensitive to the upper
chromospheric magnetic field via both the Hanle and the Zeeman effects.
Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric
Imaging
Authors: Shimojo, M.; Bastian, T. S.; Hales, A. S.; White, S. M.;
Iwai, K.; Hills, R. E.; Hirota, A.; Phillips, N. M.; Sawada, T.;
Yagoubov, P.; Siringo, G.; Asayama, S.; Sugimoto, M.; Brajša, R.;
Skokić, I.; Bárta, M.; Kim, S.; de Gregorio-Monsalvo, I.; Corder,
S. A.; Hudson, H. S.; Wedemeyer, S.; Gary, D. E.; De Pontieu, B.;
Loukitcheva, M.; Fleishman, G. D.; Chen, B.; Kobelski, A.; Yan, Y.
Bibcode: 2017SoPh..292...87S
Altcode: 2017arXiv170403236S
Observations of the Sun at millimeter and submillimeter wavelengths
offer a unique probe into the structure, dynamics, and heating of the
chromosphere; the structure of sunspots; the formation and eruption
of prominences and filaments; and energetic phenomena such as jets
and flares. High-resolution observations of the Sun at millimeter and
submillimeter wavelengths are challenging due to the intense, extended,
low-contrast, and dynamic nature of emission from the quiet Sun,
and the extremely intense and variable nature of emissions associated
with energetic phenomena. The Atacama Large Millimeter/submillimeter
Array (ALMA) was designed with solar observations in mind. The
requirements for solar observations are significantly different from
observations of sidereal sources and special measures are necessary
to successfully carry out this type of observations. We describe the
commissioning efforts that enable the use of two frequency bands,
the 3-mm band (Band 3) and the 1.25-mm band (Band 6), for continuum
interferometric-imaging observations of the Sun with ALMA. Examples of
high-resolution synthesized images obtained using the newly commissioned
modes during the solar-commissioning campaign held in December 2015
are presented. Although only 30 of the eventual 66 ALMA antennas
were used for the campaign, the solar images synthesized from the
ALMA commissioning data reveal new features of the solar atmosphere
that demonstrate the potential power of ALMA solar observations. The
ongoing expansion of ALMA and solar-commissioning efforts will continue
to enable new and unique solar observing capabilities.
Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping
Authors: White, S. M.; Iwai, K.; Phillips, N. M.; Hills, R. E.; Hirota,
A.; Yagoubov, P.; Siringo, G.; Shimojo, M.; Bastian, T. S.; Hales,
A. S.; Sawada, T.; Asayama, S.; Sugimoto, M.; Marson, R. G.; Kawasaki,
W.; Muller, E.; Nakazato, T.; Sugimoto, K.; Brajša, R.; Skokić, I.;
Bárta, M.; Kim, S.; Remijan, A. J.; de Gregorio, I.; Corder, S. A.;
Hudson, H. S.; Loukitcheva, M.; Chen, B.; De Pontieu, B.; Fleishmann,
G. D.; Gary, D. E.; Kobelski, A.; Wedemeyer, S.; Yan, Y.
Bibcode: 2017SoPh..292...88W
Altcode: 2017arXiv170504766W
The Atacama Large Millimeter/submillimeter Array (ALMA) radio
telescope has commenced science observations of the Sun starting
in late 2016. Since the Sun is much larger than the field of view
of individual ALMA dishes, the ALMA interferometer is unable to
measure the background level of solar emission when observing the
solar disk. The absolute temperature scale is a critical measurement
for much of ALMA solar science, including the understanding of energy
transfer through the solar atmosphere, the properties of prominences,
and the study of shock heating in the chromosphere. In order to provide
an absolute temperature scale, ALMA solar observing will take advantage
of the remarkable fast-scanning capabilities of the ALMA 12 m dishes
to make single-dish maps of the full Sun. This article reports on the
results of an extensive commissioning effort to optimize the mapping
procedure, and it describes the nature of the resulting data. Amplitude
calibration is discussed in detail: a path that uses the two loads in
the ALMA calibration system as well as sky measurements is described
and applied to commissioning data. Inspection of a large number of
single-dish datasets shows significant variation in the resulting
temperatures, and based on the temperature distributions, we derive
quiet-Sun values at disk center of 7300 K at λ =3 mm and 5900 K at
λ =1.3 mm. These values have statistical uncertainties of about 100
K, but systematic uncertainties in the temperature scale that may be
significantly larger. Example images are presented from two periods
with very different levels of solar activity. At a resolution of about
25″, the 1.3 mm wavelength images show temperatures on
the disk that vary over about a 2000 K range. Active regions and plages
are among the hotter features, while a large sunspot umbra shows up as
a depression, and filament channels are relatively cool. Prominences
above the solar limb are a common feature of the single-dish images.
Title: On the generation of solar spicules and Alfvénic waves
Authors: Martínez-Sykora, J.; De Pontieu, B.; Hansteen, V. H.;
Rouppe van der Voort, L.; Carlsson, M.; Pereira, T. M. D.
Bibcode: 2017Sci...356.1269M
Altcode: 2017arXiv171007559M
In the lower solar atmosphere, the chromosphere is permeated by jets
known as spicules, in which plasma is propelled at speeds of 50 to
150 kilometers per second into the corona. The origin of the spicules
is poorly understood, although they are expected to play a role in
heating the million-degree corona and are associated with Alfvénic
waves that help drive the solar wind. We compare magnetohydrodynamic
simulations of spicules with observations from the Interface Region
Imaging Spectrograph and the Swedish 1-m Solar Telescope. Spicules
are shown to occur when magnetic tension is amplified and transported
upward through interactions between ions and neutrals or ambipolar
diffusion. The tension is impulsively released to drive flows, heat
plasma (through ambipolar diffusion), and generate Alfvénic waves.
Title: Indication of the Hanle Effect by Comparing the Scattering
Polarization Observed by CLASP in the Lyα and Si III 120.65 nm Lines
Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.;
Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa,
Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.;
Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.;
Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso
Sainz, R.; De Pontieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
Bibcode: 2017ApJ...841...31I
Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding
rocket experiment that has provided the first successful measurement
of the linear polarization produced by scattering processes in
the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In
this paper, we report that the Si III line at 120.65 nm also shows
scattering polarization and we compare the scattering polarization
signals observed in the Lyα and Si III lines in order to search for
observational signatures of the Hanle effect. We focus on four selected
bright structures and investigate how the U/I spatial variations vary
between the Lyα wing, the Lyα core, and the Si III line as a function
of the total unsigned photospheric magnetic flux estimated from Solar
Dynamics Observatory/Helioseismic and Magnetic Imager observations. In
an internetwork region, the Lyα core shows an antisymmetric spatial
variation across the selected bright structure, but it does not show
it in other more magnetized regions. In the Si III line, the spatial
variation of U/I deviates from the above-mentioned antisymmetric
shape as the total unsigned photospheric magnetic flux increases. A
plausible explanation of this difference is the operation of the Hanle
effect. We argue that diagnostic techniques based on the scattering
polarization observed simultaneously in two spectral lines with very
different sensitivities to the Hanle effect, like Lyα and Si III,
are of great potential interest for exploring the magnetism of the
upper solar chromosphere and transition region.
Title: Polarization Calibration of the Chromospheric Lyman-Alpha
SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV
Range. Part II: In-Flight Calibration
Authors: Giono, G.; Ishikawa, R.; Narukage, N.; Kano, R.; Katsukawa,
Y.; Kubo, M.; Ishikawa, S.; Bando, T.; Hara, H.; Suematsu, Y.;
Winebarger, A.; Kobayashi, K.; Auchère, F.; Trujillo Bueno, J.;
Tsuneta, S.; Shimizu, T.; Sakao, T.; Cirtain, J.; Champey, P.; Asensio
Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
Bibcode: 2017SoPh..292...57G
Altcode:
The Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding
rocket instrument designed to measure for the first time the linear
polarization of the hydrogen Lyman-α line (121.6 nm). The instrument
was successfully launched on 3 September 2015 and observations were
conducted at the solar disc center and close to the limb during the
five-minutes flight. In this article, the disc center observations are
used to provide an in-flight calibration of the instrument spurious
polarization. The derived in-flight spurious polarization is consistent
with the spurious polarization levels determined during the pre-flight
calibration and a statistical analysis of the polarization fluctuations
from solar origin is conducted to ensure a 0.014% precision on the
spurious polarization. The combination of the pre-flight and the
in-flight polarization calibrations provides a complete picture of
the instrument response matrix, and a proper error transfer method
is used to confirm the achieved polarization accuracy. As a result,
the unprecedented 0.1% polarization accuracy of the instrument in the
vacuum ultraviolet is ensured by the polarization calibration.
Title: Discovery of Scattering Polarization in the Hydrogen Lyα
Line of the Solar Disk Radiation
Authors: Kano, R.; Trujillo Bueno, J.; Winebarger, A.; Auchère, F.;
Narukage, N.; Ishikawa, R.; Kobayashi, K.; Bando, T.; Katsukawa, Y.;
Kubo, M.; Ishikawa, S.; Giono, G.; Hara, H.; Suematsu, Y.; Shimizu,
T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.; Goto, M.; Belluzzi, L.;
Štěpán, J.; Asensio Ramos, A.; Manso Sainz, R.; Champey, P.;
Cirtain, J.; De Pontieu, B.; Casini, R.; Carlsson, M.
Bibcode: 2017ApJ...839L..10K
Altcode: 2017arXiv170403228K
There is a thin transition region (TR) in the solar atmosphere where
the temperature rises from 10,000 K in the chromosphere to millions
of degrees in the corona. Little is known about the mechanisms that
dominate this enigmatic region other than the magnetic field plays a
key role. The magnetism of the TR can only be detected by polarimetric
measurements of a few ultraviolet (UV) spectral lines, the Lyα line
of neutral hydrogen at 121.6 nm (the strongest line of the solar UV
spectrum) being of particular interest given its sensitivity to the
Hanle effect (the magnetic-field-induced modification of the scattering
line polarization). We report the discovery of linear polarization
produced by scattering processes in the Lyα line, obtained with
the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket
experiment. The Stokes profiles observed by CLASP in quiet regions of
the solar disk show that the Q/I and U/I linear polarization signals are
of the order of 0.1% in the line core and up to a few percent in the
nearby wings, and that both have conspicuous spatial variations with
scales of ∼10 arcsec. These observations help constrain theoretical
models of the chromosphere-corona TR and extrapolations of the
magnetic field from photospheric magnetograms. In fact, the observed
spatial variation from disk to limb of polarization at the line core
and wings already challenge the predictions from three-dimensional
magnetohydrodynamical models of the upper solar chromosphere.
Title: IRIS and SDO/AIA observations of coronal heating associated
with spicules
Authors: De Pontieu, B.; De Moortel, I.; Mcintosh, S. W.
Bibcode: 2016AGUFMSH42B..07D
Altcode:
Chromospheric spicules have been proposed as significant contributors
to the coronal energy and mass balance. While previous observations
have provided a glimpse of short-lived transient brightenings in
the corona that are associated with spicules, these observations
have been contested and the subject of a vigorous debate both on the
modeling and the observational side so that it remains unclear whether
plasma associated with spicules is heated to coronal temperatures. We
use high-resolution observations of the chromosphere and transition
region with the Interface Region Imaging Spectrograph (IRIS) and of
the corona with the Atmospheric Imaging Assembly (AIA) onboard the
Solar Dynamics Observatory (SDO) to show evidence of the formation of
coronal structures as a result of spicular mass ejections and subsequent
heating of plasma first to transition region and later to coronal
temperatures. Our observations suggest that much of the highly dynamic
loop fan environment associated with plage regions may be the result
of the formation of such new coronal strands, a process that previously
had been interpreted as the propagation of transient propagating coronal
disturbances (PCD)s. Our results suggest that heating and strong flows
play an important role in maintaining the substructure of loop fans,
in addition to the waves that permeate this low coronal environment.
Title: Coronal Heating Properties in the Core of Solar Active Regions
Authors: Testa, P.; Reale, F.; De Pontieu, B.
Bibcode: 2016AGUFMSH33A..02T
Altcode:
The Interface Region Imaging Spectrograph (IRIS) provides unprecedented
high spatial, temporal and spectral resolution observations of the
chromosphere and transition region. Joint with coronal observations
with Hinode (XRT and EIS), and SDO/AIA, these data cover from the
upper photosphere to the corona. I will discuss how IRIS observations
of footpoints of hot active region loops in non-flaring conditions,
coupled with detailed HD and MHD modeling including chromosphere,
transition region and corona, provide tight constraints on the coronal
heating mechanisms in the core of active regions.
Title: The importance of high-resolution observations of the solar
corona
Authors: Winebarger, A. R.; Cirtain, J. W.; Golub, L.; Walsh, R. W.;
De Pontieu, B.; Savage, S. L.; Rachmeler, L.; Kobayashi, K.; Testa,
P.; Brooks, D.; Warren, H.; Mcintosh, S. W.; Peter, H.; Morton, R. J.;
Alexander, C. E.; Tiwari, S. K.
Bibcode: 2016AGUFMSH31B2577W
Altcode:
The spatial and temporal resolutions of the available coronal
observatories are inadequate to resolve the signatures of coronal
heating. High-resolution and high-cadence observations available with
the Interface Region Imaging Spectrograph (IRIS) and the High-resolution
Coronal Imager (Hi-C) instrument hint that 0.3 arcsec resolution images
and < 10 s cadence provide the necessary resolution to detect
heating events. Hi-C was launched from White Sands Missile Range on
July 11, 2012 (before the launch with IRIS) and obtained images of
a solar active region in the 19.3 nm passband. In this presentation,
I will discuss the potential of combining a flight in Hi-C with a 17.1
nm passband, in conjunction with IRIS. This combination will provide,
for the first time, a definitive method of tracing the energy flow
between the chromosphere and corona and vice versa.
Title: Probing the Physical Connection between Solar Prominences
and Coronal Rain
Authors: Liu, W.; Antolin, P.; Sun, X.; Vial, J. C.; Guo, L.; Gibson,
S. E.; Berger, T. E.; Okamoto, J.; De Pontieu, B.
Bibcode: 2016AGUFMSH43C2587L
Altcode:
Solar prominences and coronal rain are intimately related phenomena,
both involving cool material at chromospheric temperatures within the
hot corona and both playing important roles as part of the return flow
of the chromosphere-corona mass cycle. At the same time, they exhibit
distinct morphologies and dynamics not yet well understood. Quiescent
prominences consist of numerous long-lasting, filamentary downflow
threads, while coronal rain is more transient and falls comparably
faster along well-defined curved paths. We report here a novel, hybrid
prominence-coronal rain complex in an arcade-fan geometry observed
by SDO/AIA and IRIS, which provides new insights to the underlying
physics of such contrasting behaviors. We found that the supra-arcade
fan region hosts a prominence sheet consisting of meandering threads
with broad line widths. As the prominence material descends to the
arcade, it turns into coronal rain sliding down coronal loops with
line widths 2-3 times narrower. This contrast suggests that distinct
local plasma and magnetic conditions determine the fate of the cool
material, a scenario supported by our magnetic field extrapolations
from SDO/HMI. Specifically, the supra-arcade fan (similar to those
in solar flares) is likely situated in a current sheet, where the
magnetic field is weak and the plasma-beta could be close to unity, thus
favoring turbulent flows like those prominence threads. In contrast,
the underlying arcade has a stronger magnetic field and most likely a
low-beta environment, such that the material is guided along magnetic
field lines to appear as coronal rain. We will discuss the physical
implications of these observations beyond the phenomena of prominences
and coronal rain.
Title: An On Orbit Determination of Point Spread Functions for the
Interface Region Imaging Spectrograph (IRIS)
Authors: Courrier, H.; Kankelborg, C. C.; De Pontieu, B.; Wuelser,
J. P.
Bibcode: 2016AGUFMSH31B2576C
Altcode:
IRIS is a small explorer spacecraft that observes the solar photosphere,
chromosphere, transition region, and corona using a combination of
slit based spectrograph and slit-jaw imagers. The hard edge terminus
of the May 09, 2016 Mercury transit observed by IRIS is used to measure
on-orbit point spread functions (PSFs) for the near ultra-violet (NUV)
and far ultra-violet (FUV) spectrograph channels. The contribution of
the measured PSFs on spectrograph resolution is investigated.
Title: Discovery of Ubiquitous Fast-Propagating Intensity Disturbances
by the Chromospheric Lyman Alpha Spectropolarimeter (CLASP)
Authors: Kubo, M.; Katsukawa, Y.; Suematsu, Y.; Kano, R.; Bando,
T.; Narukage, N.; Ishikawa, R.; Hara, H.; Giono, G.; Tsuneta, S.;
Ishikawa, S.; Shimizu, T.; Sakao, T.; Winebarger, A.; Kobayashi, K.;
Cirtain, J.; Champey, P.; Auchère, F.; Trujillo Bueno, J.; Asensio
Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
Bibcode: 2016ApJ...832..141K
Altcode:
High-cadence observations by the slit-jaw (SJ) optics system of the
sounding rocket experiment known as the Chromospheric Lyman Alpha
Spectropolarimeter (CLASP) reveal ubiquitous intensity disturbances
that recurrently propagate in either the chromosphere or the transition
region or both at a speed much higher than the speed of sound. The
CLASP/SJ instrument provides a time series of two-dimensional images
taken with broadband filters centered on the Lyα line at a 0.6 s
cadence. The multiple fast-propagating intensity disturbances appear in
the quiet Sun and in an active region, and they are clearly detected in
at least 20 areas in a field of view of 527″ × 527″ during the 5
minute observing time. The apparent speeds of the intensity disturbances
range from 150 to 350 km s-1, and they are comparable
to the local Alfvén speed in the transition region. The intensity
disturbances tend to propagate along bright elongated structures away
from areas with strong photospheric magnetic fields. This suggests
that the observed fast-propagating intensity disturbances are related
to the magnetic canopy structures. The maximum distance traveled by
the intensity disturbances is about 10″, and the widths are a few
arcseconds, which are almost determined by a pixel size of 1.″03. The
timescale of each intensity pulse is shorter than 30 s. One possible
explanation for the fast-propagating intensity disturbances observed
by CLASP is magnetohydrodynamic fast-mode waves.
Title: On the Misalignment between Chromospheric Features and the
Magnetic Field on the Sun
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Carlsson, Mats;
Hansteen, Viggo
Bibcode: 2016ApJ...831L...1M
Altcode: 2016arXiv160702551M
Observations of the upper chromosphere show an enormous amount of
intricate fine structure. Much of this comes in the form of linear
features, which are most often assumed to be well aligned with the
direction of the magnetic field in the low plasma β regime that is
thought to dominate the upper chromosphere. We use advanced radiative
magnetohydrodynamic simulations, including the effects of ion-neutral
interactions (using the generalized Ohm’s law) in the partially
ionized chromosphere, to show that the magnetic field is often not well
aligned with chromospheric features. This occurs where the ambipolar
diffusion is large, I.e., ions and neutral populations decouple as
the ion-neutral collision frequency drops, allowing the field to
slip through the neutral population; where currents perpendicular to
the field are strong; and where thermodynamic timescales are longer
than or similar to those of ambipolar diffusion. We find this often
happens in dynamic spicule or fibril-like features at the top of the
chromosphere. This has important consequences for field extrapolation
methods, which increasingly use such upper chromospheric features
to help constrain the chromospheric magnetic field: our results
invalidate the underlying assumption that these features are aligned
with the field. In addition, our results cast doubt on results from
1D hydrodynamic models, which assume that plasma remains on the same
field lines. Finally, our simulations show that ambipolar diffusion
significantly alters the amount of free energy available in the coronal
part of our simulated volume, which is likely to have consequences
for studies of flare initiation.
Title: What Is the Source of Quiet Sun Transition Region Emission?
Authors: Schmit, D. J.; De Pontieu, Bart
Bibcode: 2016ApJ...831..158S
Altcode: 2016arXiv160807620S
Dating back to the first observations of the on-disk corona, there has
been a qualitative link between the photosphere’s magnetic network
and enhanced transition-temperature plasma emission. These observations
led to the development of a general model that describes emission
structures through the partitioning of the atmospheric volume with
different magnetic loop geometries that exhibit different energetic
equilibria. Does the internetwork produce transition-temperature
emission? What fraction of network flux connects to the corona? How
does quiet Sun emission compare with low-activity Sun-like stars? In
this work, we revisit the canonical model of the quiet Sun, with
high-resolution observations from the Interface Region Imaging
Spectrograph (IRIS) and HMI in hand, to address those questions. We
use over 900 deep exposures of Si IV 1393 Å from IRIS along with
nearly simultaneous HMI magnetograms to quantify the correlation
between transition-temperature emission structures and magnetic
field concentrations through a number of novel statistics. Our
observational results are coupled with analysis of the Bifrost MHD
model and a large-scale potential field model. Our results paint a
complex portrait of the quiet Sun. We measure an emission signature
in the distant internetwork that cannot be attributed to network
contribution. We find that the dimmest regions of emission are not
linked to the local vertical magnetic field. Using the MHD simulation,
we categorize the emission contribution from cool mid-altitude loops
and high-altitude coronal loops and discuss the potential emission
contribution of spicules. Our results provide new constraints on the
coupled solar atmosphere so that we can build on our understanding
of how dynamic thermal and magnetic structures generate the observed
phenomena in the transition region.
Title: Flare-associated Fast-mode Coronal Wave Trains Detected by
SDO/AIA: Recent Observational Advances
Authors: Liu, Wei; Ofman, Leon; Downs, Cooper; Cheung, Mark; De
Pontieu, Bart
Bibcode: 2016usc..confE.107L
Altcode:
Quasi-periodic Fast Propagating wave trains (QFPs) are new observational
phenomena discovered by SDO/AIA in extreme ultraviolet (EUV). They
were interpreted as fast-mode magnetosonic waves using MHD modeling,
and also found to be closely related to quasi-periodic pulsations
in solar flare emission ranging from radio to X-ray wavelengths. The
significance of QFPs lies in their diagnostic potential (and possibly
in flare energy transport), because they can provide critical clues to
flare energy release and serve as new tools for coronal seismology. In
this presentation, we report recent advances in observing QFPs. In
particular, using differential emission measure (DEM) inversion,
we found clear evidence of heating and cooling cycles that are
consistent with alternating compression and rarefaction expected for
magnetosonic wave pulses. We also found that different local magnetic
and plasma environments can lead to two distinct types of QFPs located
in different spatial domains with respect to their accompanying coronal
mass ejections (CMEs). More interestingly, from a statistical survey of
over 100 QFP events, we found a preferential association with eruptive
flares rather than confined flares. We will discuss the implications
of these results and the potential roles of QFPs in coronal heating,
energy transport, and solar eruptions.
Title: Joint SDO and IRIS Observations of a Novel, Hybrid
Prominence-Coronal Rain Complex
Authors: Liu, Wei; Antolin, Patrick; Sun, Xudong; Gao, Lijia; Vial,
Jean-Claude; Gibson, Sarah; Okamoto, Takenori; Berger, Thomas;
Uitenbroek, Han; De Pontieu, Bart
Bibcode: 2016usc..confE..99L
Altcode:
Solar prominences and coronal rain are intimately related phenomena,
both involving cool material at chromospheric temperatures within the
hot corona and both playing important roles as part of the return flow
of the chromosphere-corona mass cycle. At the same time, they exhibit
distinct morphologies and dynamics not yet well understood. Quiescent
prominences consist of numerous long-lasting, filamentary downflow
threads, while coronal rain is more transient and falls comparably
faster along well-defined curved paths. We report here a novel, hybrid
prominence-coronal rain complex in an arcade-fan geometry observed
by SDO/AIA and IRIS, which provides new insights to the underlying
physics of such contrasting behaviors. We found that the supra-arcade
fan region hosts a prominence sheet consisting of meandering threads
with broad line widths. As the prominence material descends to the
arcade, it turns into coronal rain sliding down coronal loops with
line widths 2-3 times narrower. This contrast suggests that distinct
local plasma and magnetic conditions determine the fate of the cool
material, a scenario supported by our magnetic field extrapolations
from SDO/HMI. Specifically, the supra-arcade fan (similar to those
in solar flares; e.g., McKenzie 2013) is likely situated in a current
sheet, where the magnetic field is weak and the plasma-beta could be
close to unity, thus favoring turbulent flows like those prominence
threads. In contrast, the underlying arcade has a stronger magnetic
field and most likely a low-beta environment, such that the material
is guided along magnetic field lines to appear as coronal rain. We
will discuss the physical implications of these observations beyond
prominence and coronal rain.
Title: Investigation of the role of magnetic cancellation in
triggering solar eruptions in NOAA AR12017
Authors: Chintzoglou, G.; Cheung, M. C. M.; De Pontieu, B.
Bibcode: 2016usc..confE.121C
Altcode:
During its evolution, NOAA AR12017 was the source of 3 Coronal Mass
Ejections (CMEs) and a multitude of energetic flares. In its early
stages of its evolution it appeared to emerge as a single bipole, which
was followed by the emergence of a smaller (secondary) bipole near
its pre-existing leading polarity, forming a new polarity inversion
line (PIL) between the non-conjugated opposite polarities as well as
an evolving magnetic topology in the solar corona. Using photospheric
magnetic field observations from SDO/HMI, spectra and imaging from IRIS
covering the photosphere and transition region, coronal observations
from SDO/AIA and flare centroids from RHESSI, we investigate the
cause(s) of activity associated with the new PIL. The time range of
the observations spans several hours prior and up to the time of the
X1.0 flare (associated with a CME eruption). Continuous photospheric
cancellation correlates with flaring activity in the X-rays right at
the new PIL, which suggests that cancellation is dominant mechanism
for the activity of this extremely flare-productive AR.
Title: On the Connection between Propagating Solar Coronal
Disturbances and Chromospheric Footpoints
Authors: Bryans, P.; McIntosh, S. W.; De Moortel, I.; De Pontieu, B.
Bibcode: 2016ApJ...829L..18B
Altcode:
The Interface Region Imaging Spectrograph (IRIS) provides an
unparalleled opportunity to explore the (thermal) interface between the
chromosphere, transition region, and the coronal plasma observed by the
Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory
(SDO). The SDO/AIA observations of coronal loop footpoints show
strong recurring upward propagating signals—“propagating coronal
disturbances” (PCDs) with apparent speeds of the order of 100-120 km
s-1. That signal has a clear signature in the slit-jaw images
of IRIS in addition to identifiable spectral signatures and diagnostics
in the Mg iih (2803 Å) line. In analyzing the Mg iih line, we are able
to observe the presence of magnetoacoustic shock waves that are also
present in the vicinity of the coronal loop footpoints. We see there is
enough of a correspondence between the shock propagation in Mg iih, the
evolution of the Si IV line profiles, and the PCD evolution to indicate
that these waves are an important ingredient for PCDs. In addition, the
strong flows in the jet-like features in the IRIS Si IV slit-jaw images
are also associated with PCDs, such that waves and flows both appear
to be contributing to the signals observed at the footpoints of PCDs.
Title: High Spatial Resolution Fe XII Observations of Solar Active
Regions
Authors: Testa, Paola; De Pontieu, Bart; Hansteen, Viggo
Bibcode: 2016ApJ...827...99T
Altcode: 2016arXiv160604603T
We use UV spectral observations of active regions with the Interface
Region Imaging Spectrograph (IRIS) to investigate the properties of
the coronal Fe xii 1349.4 Å emission at unprecedented high spatial
resolution (∼0.33″). We find that by using appropriate observational
strategies (I.e., long exposures, lossless compression), Fe xii emission
can be studied with IRIS at high spatial and spectral resolution, at
least for high-density plasma (e.g., post-flare loops and active region
moss). We find that upper transition region (TR; moss) Fe xii emission
shows very small average Doppler redshifts ({v}{{D}} ∼ 3
km s-1) as well as modest non-thermal velocities (with an
average of ∼24 km s-1 and the peak of the distribution at
∼15 km s-1). The observed distribution of Doppler shifts
appears to be compatible with advanced three-dimensional radiative
MHD simulations in which impulsive heating is concentrated at the TR
footpoints of a hot corona. While the non-thermal broadening of Fe
xii 1349.4 Å peaks at similar values as lower resolution simultaneous
Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) measurements of
Fe xii 195 Å, IRIS observations show a previously undetected tail
of increased non-thermal broadening that might be suggestive of the
presence of subarcsecond heating events. We find that IRIS and EIS
non-thermal line broadening measurements are affected by instrumental
effects that can only be removed through careful analysis. Our results
also reveal an unexplained discrepancy between observed 195.1/1349.4
Å Fe xii intensity ratios and those predicted by the CHIANTI atomic
database.
Title: Chromospheric LAyer SpectroPolarimeter (CLASP2)
Authors: Narukage, Noriyuki; McKenzie, David E.; Ishikawa, Ryoko;
Trujillo-Bueno, Javier; De Pontieu, Bart; Kubo, Masahito; Ishikawa,
Shin-nosuke; Kano, Ryouhei; Suematsu, Yoshinori; Yoshida, Masaki;
Rachmeler, Laurel A.; Kobayashi, Ken; Cirtain, Jonathan W.; Winebarger,
Amy R.; Asensio Ramos, Andres; del Pino Aleman, Tanausu; Štępán,
Jiri; Belluzzi, Luca; Larruquert, Juan Ignacio; Auchère, Frédéric;
Leenaarts, Jorrit; Carlsson, Mattias J. L.
Bibcode: 2016SPIE.9905E..08N
Altcode:
The sounding rocket Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP) was launched on September 3rd, 2015, and successfully detected
(with a polarization accuracy of 0.1 %) the linear polarization signals
(Stokes Q and U) that scattering processes were predicted to produce
in the hydrogen Lyman-alpha line (Lyα 121.567 nm). Via the Hanle
effect, this unique data set may provide novel information about the
magnetic structure and energetics in the upper solar chromosphere. The
CLASP instrument was safely recovered without any damage and we have
recently proposed to dedicate its second flight to observe the four
Stokes profiles in the spectral region of the Mg II h and k lines
around 280 nm; in these lines the polarization signals result from
scattering processes and the Hanle and Zeeman effects. Here we describe
the modifications needed to develop this new instrument called the
"Chromospheric LAyer SpectroPolarimeter" (CLASP2).
Title: Emergence of Granular-sized Magnetic Bubbles Through the
Solar Atmosphere. III. The Path to the Transition Region
Authors: Ortiz, Ada; Hansteen, Viggo H.; Bellot Rubio, Luis Ramón;
de la Cruz Rodríguez, Jaime; De Pontieu, Bart; Carlsson, Mats;
Rouppe van der Voort, Luc
Bibcode: 2016ApJ...825...93O
Altcode: 2016arXiv160400302O
We study, for the first time, the ascent of granular-sized magnetic
bubbles from the solar photosphere through the chromosphere into the
transition region and above. Such events occurred in a flux emerging
region in NOAA 11850 on 2013 September 25. During that time, the
first co-observing campaign between the Swedish 1-m Solar Telescope
(SST) and the Interface Region Imaging Spectrograph (IRIS) spacecraft
was carried out. Simultaneous observations of the chromospheric Hα
656.28 nm and Ca II 854.2 nm lines, plus the photospheric Fe I 630.25
nm line, were made with the CRISP spectropolarimeter at the Spitzer
Space Telescope (SST) reaching a spatial resolution of 0.″14. At
the same time, IRIS was performing a four-step dense raster of the
emerging flux region, taking slit jaw images at 133 (C II, transition
region), 140 (Si IV, transition region), 279.6 (Mg II k, core, upper
chromosphere), and 283.2 nm (Mg II k, wing, photosphere). Spectroscopy
of several lines was performed by the IRIS spectrograph in the far-
and near-ultraviolet, of which we have used the Si IV 140.3 and the
Mg II k 279.6 nm lines. Coronal images from the Atmospheric Imaging
Assembly of the Solar Dynamics Observatory were used to investigate
the possible coronal signatures of the flux emergence events. The
photospheric and chromospheric properties of small-scale emerging
magnetic bubbles have been described in detail in Ortiz et al. Here
we are able to follow such structures up to the transition region. We
describe the properties, including temporal delays, of the observed
flux emergence in all layers. We believe this may be an important
mechanism of transporting energy and magnetic flux from subsurface
layers to the transition region and corona.
Title: Coordinated Solar Observation and Event Searches using the
Heliophysics Events Knowledgebase (HEK)
Authors: Timmons, Ryan; Hurlburt, Neal E.; De Pontieu, Bart
Bibcode: 2016SPD....4730903T
Altcode:
We present capabilities of the HEK for joint searches, returning
overlapping data from multiple instruments (IRIS, Hinode) that also
include particular solar features and events (active regions, (large)
flares, sunspots, etc.). The new search tools aid the process of finding
observations of particular interest from non-synoptic instruments. They
also include new data products: processed cutout cubes of SOT-FG and
AIA data co-aligned with IRIS.
Title: Amplitudes of MHD Waves in Sunspots
Authors: Norton, Aimee Ann; Cally, Paul; Baldner, Charles; Kleint,
Lucia; Tarbell, Theodore D.; De Pontieu, Bart; Scherrer, Philip H.;
Rajaguru, Paul
Bibcode: 2016SPD....47.1009N
Altcode:
The conversion of p-modes into MHD waves by strong magnetic fields
occurs mainly in the sub-photospheric layers. The photospheric
signatures of MHD waves are weak due to low amplitudes at the beta=1
equipartion level where mode-conversion occurs. We report on small
amplitude oscillations observed in the photosphere with Hinode SOT/SP
in which we analyze time series for sunspots ARs 12186 (11.10.2014)
and 12434 (17.10.2015). No significant magnetic field oscillations
are recovered in the umbra or penumbra in the ME inversion. However,
periodicities in the inclination angle are found at the umbral/penumbral
boundary with 5 minute periods. Upward propagating waves are indicated
in the intensity signals correlated between HMI and AIA at different
heights. We compare SP results with the oscillations observed in HMI
data. Simultaneous IRIS data shows transition region brightening above
the umbral core.
Title: Physics & Diagnostics of the Drivers of Solar Eruptions
Authors: Cheung, Mark; Rempel, Matthias D.; Martinez-Sykora, Juan;
Testa, Paola; Hansteen, Viggo H.; Viktorovna Malanushenko, Anna;
Sainz Dalda, Alberto; DeRosa, Marc L.; De Pontieu, Bart; Carlsson,
Mats; Chen, Feng; McIntosh, Scott W.; Gudiksen, Boris
Bibcode: 2016SPD....47.0607C
Altcode:
We provide an update on our NASA Heliophysics Grand Challenges Research
(HGCR) project on the ‘Physics & Diagnostics of the Drivers of
Solar Eruptions’. This presentation will focus on results from a
data-inspired, 3D radiative MHD model of a solar flare. The model
flare results from the interaction of newly emerging flux with a
pre-existing active region. Synthetic observables from the model
reproduce observational features compatible with actual flares. These
include signatures of coronal magnetic reconnection, chromospheric
evaporation, EUV flare arcades, sweeping motion of flare ribbons
and sunquakes.
Title: Spectro-polarimetric observation in UV with CLASP to probe
the chromosphere and transition region
Authors: Kano, Ryouhei; Ishikawa, Ryohko; Winebarger, Amy R.; Auchère,
Frédéric; Trujillo Bueno, Javier; Narukage, Noriyuki; Kobayashi,
Ken; Bando, Takamasa; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-Nosuke; Giono, Gabriel; Hara, Hirohisa; Suematsu, Yoshinori;
Shimizu, Toshifumi; Sakao, Taro; Tsuneta, Saku; Ichimoto, Kiyoshi;
Goto, Motoshi; Cirtain, Jonathan W.; De Pontieu, Bart; Casini, Roberto;
Manso Sainz, Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi,
Luca; Carlsson, Mats
Bibcode: 2016SPD....4710107K
Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a NASA
sounding-rocket experiment that was performed in White Sands in
the US on September 3, 2015. During its 5-minute ballistic flight,
CLASP successfully made the first spectro-polarimetric observation in
the Lyman-alpha line (121.57 nm) originating in the chromosphere and
transition region. Since the Lyman-alpha polarization is sensitive
to magnetic field of 10-100 G by the Hanle effect, we aim to infer
the magnetic field information in such upper solar atmosphere with
this experiment.The obtained CLASP data showed that the Lyman-alpha
scattering polarization is about a few percent in the wings and
the order of 0.1% in the core near the solar limb, as it had been
theoretically predicted, and that both polarization signals have a
conspicuous spatio-temporal variability. CLASP also observed another
upper-chromospheric line, Si III (120.65 nm), whose critical field
strength for the Hanle effect is 290 G, and showed a measurable
scattering polarization of a few % in this line. The polarization
properties of the Si III line could facilitate the interpretation of
the scattering polarization observed in the Lyman-alpha line.In this
presentation, we would like to show how the upper chromosphere and
transition region are seen in the polarization of these UV lines and
discuss the possible source of these complicated polarization signals.
Title: Solar Observations with the Atacama Large
Millimeter/submillimeter Array (ALMA)
Authors: Kobelski, A.; Bastian, T. S.; Bárta, M.; Brajša, R.; Chen,
B.; De Pontieu, B.; Fleishman, G.; Gary, D.; Hales, A.; Hills, R.;
Hudson, H.; Hurford, G.; Loukitcheva, M.; Iwai, K.; Krucker, S.;
Shimojo, M.; Skokić, I.; Wedemeyer, S.; White, S.; Yan, Y.; ALMA
Solar Development Team
Bibcode: 2016ASPC..504..327K
Altcode:
The Atacama Large Millimeter/Submillimeter Array (ALMA) is a
joint North American, European, and East Asian project that opens
the mm-sub mm wavelength part of the electromagnetic spectrum for
general astrophysical exploration, providing high-resolution imaging
in frequency bands currently ranging from 84 GHz to 950 GHz (300
microns to 3 mm). It is located in the Atacama desert in northern
Chile at an elevation of 5000 m. Despite being a general purpose
instrument, provisions have been made to enable solar observations
with ALMA. Radiation emitted at ALMA wavelengths originates mostly
from the chromosphere, which plays an important role in the transport
of matter and energy, and the in heating the outer layers of the solar
atmosphere. Despite decades of research, the solar chromosphere remains
a significant challenge: both to observe, owing to the complicated
formation mechanisms of currently available diagnostics; and to
understand, as a result of the complex nature of the structure and
dynamics of the chromosphere. ALMA has the potential to change the
scene substantially as it serves as a nearly linear thermometer at
high spatial and temporal resolution, enabling us to study the complex
interaction of magnetic fields and shock waves and yet-to-be-discovered
dynamical processes. Moreover, ALMA will play an important role in
the study of energetic emissions associated with solar flares at
sub-THz frequencies.
Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
Bibcode: 2016SSRv..200....1W
Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.
Title: The Rapid Acquisition Imaging Spectrograph Experiment (RAISE)
Sounding Rocket Investigation
Authors: Laurent, Glenn T.; Hassler, Donald M.; Deforest, Craig;
Slater, David D.; Thomas, Roger J.; Ayres, Thomas; Davis, Michael; de
Pontieu, Bart; Diller, Jed; Graham, Roy; Michaelis, Harald; Schuele,
Udo; Warren, Harry
Bibcode: 2016JAI.....540006L
Altcode:
We present a summary of the solar observing Rapid Acquisition
Imaging Spectrograph Experiment (RAISE) sounding rocket program
including an overview of the design and calibration of the instrument,
flight performance, and preliminary chromospheric results from the
successful November 2014 launch of the RAISE instrument. The RAISE
sounding rocket payload is the fastest scanning-slit solar ultraviolet
imaging spectrograph flown to date. RAISE is designed to observe the
dynamics and heating of the solar chromosphere and corona on time
scales as short as 100-200ms, with arcsecond spatial resolution and
a velocity sensitivity of 1-2km/s. Two full spectral passbands over
the same one-dimensional spatial field are recorded simultaneously
with no scanning of the detectors or grating. The two different
spectral bands (first-order 1205-1251Å and 1524-1569Å) are imaged
onto two intensified Active Pixel Sensor (APS) detectors whose focal
planes are individually adjusted for optimized performance. RAISE
reads out the full field of both detectors at 5-10Hz, recording up
to 1800 complete spectra (per detector) in a single 6-min rocket
flight. This opens up a new domain of high time resolution spectral
imaging and spectroscopy. RAISE is designed to observe small-scale
multithermal dynamics in Active Region (AR) and quiet Sun loops,
identify the strength, spectrum and location of high frequency waves
in the solar atmosphere, and determine the nature of energy release
in the chromospheric network.
Title: On the Active Region Bright Grains Observed in the Transition
Region Imaging Channels of IRIS
Authors: Skogsrud, H.; Rouppe van der Voort, L.; De Pontieu, B.
Bibcode: 2016ApJ...817..124S
Altcode: 2015arXiv151205263S
The Interface Region Imaging Spectrograph (IRIS) provides spectroscopy
and narrow band slit-jaw (SJI) imaging of the solar chromosphere
and transition region at unprecedented spatial and temporal
resolutions. Combined with high-resolution context spectral imaging of
the photosphere and chromosphere as provided by the Swedish 1 m Solar
Telescope (SST), we can now effectively trace dynamic phenomena through
large parts of the solar atmosphere in both space and time. IRIS SJI
1400 images from active regions, which primarily sample the transition
region with the Si IV 1394 and 1403 Å lines, reveal ubiquitous bright
“grains” which are short-lived (two to five minute) bright roundish
small patches of sizes 0.″5-1.″7 that generally move limbward with
velocities up to about 30 km s-1. In this paper, we show
that many bright grains are the result of chromospheric shocks impacting
the transition region. These shocks are associated with dynamic fibrils
(DFs), most commonly observed in Hα. We find that the grains show the
strongest emission in the ascending phase of the DF, that the emission
is strongest toward the top of the DF, and that the grains correspond
to a blueshift and broadening of the Si IV lines. We note that the
SJI 1400 grains can also be observed in the SJI 1330 channel which
is dominated by C II lines. Our observations show that a significant
part of the active region transition region dynamics is driven from
the chromosphere below rather than from coronal activity above. We
conclude that the shocks that drive DFs also play an important role
in the heating of the upper chromosphere and lower transition region.
Title: A publicly available simulation of an enhanced network region
of the Sun
Authors: Carlsson, Mats; Hansteen, Viggo H.; Gudiksen, Boris V.;
Leenaarts, Jorrit; De Pontieu, Bart
Bibcode: 2016A&A...585A...4C
Altcode: 2015arXiv151007581C
Context. The solar chromosphere is the interface between the
solar surface and the solar corona. Modelling of this region is
difficult because it represents the transition from optically
thick to thin radiation escape, from gas-pressure domination to
magnetic-pressure domination, from a neutral to an ionised state,
from MHD to plasma physics, and from near-equilibrium (LTE) to
non-equilibrium conditions.
Aims: Our aim is to provide the
community with realistic simulations of the magnetic solar outer
atmosphere. This will enable detailed comparison of existing and
upcoming observations with synthetic observables from the simulations,
thereby elucidating the complex interactions of magnetic fields and
plasma that are crucial for our understanding of the dynamic outer
atmosphere.
Methods: We used the radiation magnetohydrodynamics
code Bifrost to perform simulations of a computational volume
with a magnetic field topology similar to an enhanced network
area on the Sun.
Results: The full simulation cubes are
made available from the Hinode Science Data Centre Europe. The
general properties of the simulation are discussed, and limitations
are discussed. The Hinode Science Data Centre Europe (http://www.sdc.uio.no/search/simulations).
Title: Time Dependent Nonequilibrium Ionization of Transition Region
Lines Observed with IRIS
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo H.;
Gudiksen, Boris
Bibcode: 2016ApJ...817...46M
Altcode: 2015arXiv151200865M
The properties of nonstatistical equilibrium ionization of silicon
and oxygen ions are analyzed in this work. We focus on five solar
targets (quiet Sun; coronal hole; plage; quiescent active region,
AR; and flaring AR) as observed with the Interface Region Imaging
Spectrograph (IRIS). IRIS is best suited for this work owing to the
high cadence (up to 0.5 s), high spatial resolution (up to 0.″32),
and high signal-to-noise ratios for O IV λ1401 and Si IV λ1402. We
find that the observed intensity ratio between lines of three times
ionized silicon and oxygen ions depends on their total intensity
and that this correlation varies depending on the region observed
(quiet Sun, coronal holes, plage, or active regions) and on the
specific observational objects present (spicules, dynamic loops, jets,
microflares, or umbra). In order to interpret the observations, we
compare them with synthetic profiles taken from 2D self-consistent
radiative MHD simulations of the solar atmosphere, where the
statistical equilibrium or nonequilibrium treatment of silicon and
oxygen is applied. These synthetic observations show vaguely similar
correlations to those in the observations, I.e., between the intensity
ratios and their intensities, but only in the nonequilibrium case do
we find that (some of) the observations can be reproduced. We conclude
that these lines are formed out of statistical equilibrium. We use
our time-dependent nonequilibrium ionization simulations to describe
the physical mechanisms behind these observed properties.
Title: Flare-associated Fast-mode Coronal Wave Trains Discovered by
SDO/AIA: Physical Properties and Implications
Authors: Liu, W.; Ofman, L.; Downs, C.; Cheung, C. M. M.; Broder,
B.; De Pontieu, B.
Bibcode: 2015AGUFMSH54B..02L
Altcode:
Quasi-periodic Fast Propagating wave trains (QFPs) are a new
observational phenomenon discovered in extreme ultraviolet (EUV) by
the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
Observatory (SDO). They are fast-mode magnetosonic waves, closely
related to quasi-periodic pulsations in solar flare emission ranging
from radio to X-ray wavelengths. The significance of QFPs lies in their
diagnostic potential, because they can provide critical clues to flare
energy release and serve as new tools for coronal seismology. In
this presentation, we report recent advances in observing and
modeling QFPs. For example, using differential emission measure (DEM)
inversion, we found clear evidence of heating and cooling cycles that
are consistent with alternating compression and rarefaction expected
for magnetosonic wave pulses. Moreover, recent IRIS observations
of QFP source regions revealed sawtooth-like flare ribbon motions,
indicative of pulsed magnetic reconnection, that are correlated with QFP
excitation. More interestingly, from a survey of over 100 QFP events,
we found a preferential association with eruptive flares rather than
confined flares. We will discuss the implications of these results
and the potential roles of QFPs in coronal heating, energy transport,
and solar eruptions.
Title: SSALMON - The Solar Simulations for the Atacama Large
Millimeter Observatory Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson,
H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu,
B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.;
Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.;
Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier,
A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M.
Bibcode: 2015AdSpR..56.2679W
Altcode: 2015arXiv150205601W
The Solar Simulations for the Atacama Large Millimeter Observatory
Network (SSALMON) was initiated in 2014 in connection with two ALMA
development studies. The Atacama Large Millimeter/submillimeter Array
(ALMA) is a powerful new tool, which can also observe the Sun at
high spatial, temporal, and spectral resolution. The international
SSALMONetwork aims at co-ordinating the further development of solar
observing modes for ALMA and at promoting scientific opportunities
for solar physics with particular focus on numerical simulations,
which can provide important constraints for the observing modes and
can aid the interpretation of future observations. The radiation
detected by ALMA originates mostly in the solar chromosphere - a
complex and dynamic layer between the photosphere and corona, which
plays an important role in the transport of energy and matter and the
heating of the outer layers of the solar atmosphere. Potential targets
include active regions, prominences, quiet Sun regions, flares. Here,
we give a brief overview over the network and potential science cases
for future solar observations with ALMA.
Title: Combining IRIS/Hinode Observations and Modeling: a Pathfinder
for Coronal Heating
Authors: Antolin, P.; Okamoto, J.; De Pontieu, B.
Bibcode: 2015AGUFMSH13C2451A
Altcode:
The combination of imaging and spectroscopic instruments with multiple
temperature diagnostics at high spatial, temporal and spectral
resolution can allow to recover the 3D plasma flow and thermodynamic
evolution associated with specific coronal heating mechanisms. Although
very hard considering the complexity of the solar atmosphere, this
approach is becoming possible now through combination of instruments
such as IRIS and Hinode, and with proper guiding from advanced numerical
simulations and forward modeling. In this talk I will review recent
examples of this approach, focusing on a particular, recently published,
case study, that serves as a pathfinder in the search for the dominant
coronal heating mechanism. In this case, resonant absorption, a long
hypothesised wave-related energy conversion mechanism is spotted
in action for the first time, and is characterised by a peculiar 3D
motion of the plasma. With the help of 3D MHD numerical simulations and
forward modeling the observational signatures of resonant absorption
are characterised, matching very well the observational results. The
process through which this mechanism can lead to observed significant
heating in the solar corona is further identified: the resonant
flow becomes turbulent following dynamic instabilities and heats
the plasma. I will show how this resonance + instability process is
expected in different scenarios of the solar atmosphere (the corona,
prominences and spicules) and can potentially explain several observed
features that remain so far unexplained.
Title: Properties of moss emission from joint FeXII IRIS and Hinode
observations of active region plasma
Authors: Testa, P.; De Pontieu, B.; Hansteen, V. H.
Bibcode: 2015AGUFMSH31D..06T
Altcode:
IRIS provides unprecedented high resolution observations of the solar
chromosphere and transition region. Joint with Hinode XRT and EIS,
and SDO/AIA, these observations cover from the upper photosphere to
the corona and provide tight constraints on the mechanisms of energy
transport and heating of the plasma to coronal temperatures. We present
new IRIS and Hinode coronal studies of the corona in non-flaring
conditions, and compare the spectral line properties of FeXII emission
observed with EIS and IRIS in active region moss. We will discuss
the implications for the heating of hot coronal loops in the core of
active regions.
Title: Connections between heating processes in the chromosphere,
transition region and low corona
Authors: De Pontieu, B.
Bibcode: 2015AGUFMSH31B2408D
Altcode:
We exploit the high spatio-temporal and spectral resolution of
observations with the Interface Region Imaging Spectrograph (IRIS)
and the Swedish Solar Telescope to investigate how chromospheric,
transition region and coronal heating are connected, in particular in
plage regions at the footpoints of hot coronal loops. We investigate the
spatio-temporal properties of low chromospheric heating, as diagnosed
with the Mg II h and k lines, and study their connection with moss
emission, often used as a proxy for coronal heating. In addition,
we show how chromospheric dynamic events such as jets impact the
transition region and low corona.
Title: Impact of the Ion-Neutral Interaction Effects in the Solar
Chromosphere
Authors: Martínez-Sykora, J.; De Pontieu, B.; Hansteen, V. H.;
Carlsson, M.
Bibcode: 2015AGUFMSH31B2411M
Altcode:
The complexity of the chromosphere is due to various regime changes
that take place across it. Consequently, the interpretation of
chromospheric observations is a challenging task. It is thus crucial
to combine these observations with advanced radiative-MHD numerical
modeling. Because the photosphere, chromosphere and transition region
are partially ionized, the interaction between ionized and neutral
particles has important consequences on the magneto-thermodynamics
of these regions. We implemented the effects of partial ionization
using generalized Ohm's law in the Bifrost code (Gudiksen et al. 2011)
which solves the full MHD equations with non-grey and non-LTE radiative
transfer and thermal conduction along magnetic field lines. We perform
2.5D simulations which combines large and small scales structures. This
leads to a highly dynamic chromosphere with large variety of physical
processes which have not been reproduced with smaller simulations. The
implementation of partial ionization effects impact our modeled
radiative-MHD atmosphere, such as producing chromospheric heating and
diffusion of photospheric magnetic field into the upper-chromosphere. We
will also focus on which observables of these processes can be revealed
with chromospheric observations.
Title: The Formation of Iris Diagnostics. VIII. Iris Observations
in the C II 133.5 nm Multiplet.
Authors: Rathore, Bhavna; Pereira, Tiago M. D.; Carlsson, Mats;
De Pontieu, Bart
Bibcode: 2015ApJ...814...70R
Altcode: 2015arXiv151004845R
The C ii 133.5 nm multiplet has been observed by NASA’s Interface
Region Imaging Spectrograph (IRIS) in unprecedented spatial
resolution. The aims of this work are to characterize these new
observations of the C ii lines, place them in context with previous
work, and to identify any additional value the C ii lines bring when
compared with other spectral lines. We make use of wide, long exposure
IRIS rasters covering the quiet Sun and an active region. Line
properties such as velocity shift and width are extracted from
individual spectra and analyzed. The lines have a variety of shapes
(mostly single-peak or double-peak), are strongest in active regions
and weaker in the quiet Sun. The ratio between the 133.4 and 133.5 nm
components is always less than 1.8, indicating that their radiation
is optically thick in all locations. Maps of the C ii line widths are
a powerful new diagnostic of chromospheric structures, and their line
shifts are a robust velocity diagnostic. Compared with earlier quiet Sun
observations, we find similar absolute intensities and mean line widths,
but smaller redshifts; this difference can perhaps be attributed to
differences in spectral resolution and spatial coverage. The C ii
intensity maps are somewhat similar to those of transition region
lines, but also share some features with chromospheric maps such as
those from the Mg ii k line, indicating that they are formed between
the upper chromosphere and transition region. C ii intensity, width,
and velocity maps can therefore be used to gather additional information
about the upper chromosphere.
Title: The Formation of IRIS Diagnostics. VI. The Diagnostic Potential
of the C II Lines at 133.5 nm in the Solar Atmosphere
Authors: Rathore, Bhavna; Carlsson, Mats; Leenaarts, Jorrit; De
Pontieu, Bart
Bibcode: 2015ApJ...811...81R
Altcode: 2015arXiv150804423R
We use 3D radiation magnetohydrodynamic models to investigate how the
thermodynamic quantities in the simulation are encoded in observable
quantities, thus exploring the diagnostic potential of the C ii 133.5
nm lines. We find that the line core intensity is correlated with the
temperature at the formation height but the correlation is rather weak,
especially when the lines are strong. The line core Doppler shift is a
good measure of the line-of-sight velocity at the formation height. The
line width is both dependent on the width of the absorption profile
(thermal and non-thermal width) and an opacity broadening factor of
1.2-4 due to the optically thick line formation with a larger broadening
for double peak profiles. The C ii 133.5 nm lines can be formed both
higher and lower than the core of the Mg ii k line depending on the
amount of plasma in the 14-50 kK temperature range. More plasma in
this temperature range gives a higher C ii 133.5 nm formation height
relative to the Mg ii k line core. The synthetic line profiles have been
compared with Interface Region Imaging Spectrograph observations. The
derived parameters from the simulated line profiles cover the parameter
range seen in observations but, on average, the synthetic profiles are
too narrow. We interpret this discrepancy as a combination of a lack
of plasma at chromospheric temperatures in the simulation box and too
small non-thermal velocities. The large differences in the distribution
of properties between the synthetic profiles and the observed ones
show that the C ii 133.5 nm lines are powerful diagnostics of the
upper chromosphere and lower transition region.
Title: Numerical Simulations of Coronal Heating through Footpoint
Braiding
Authors: Hansteen, V.; Guerreiro, N.; De Pontieu, B.; Carlsson, M.
Bibcode: 2015ApJ...811..106H
Altcode: 2015arXiv150807234H
Advanced three-dimensional (3D) radiative MHD simulations now reproduce
many properties of the outer solar atmosphere. When including a domain
from the convection zone into the corona, a hot chromosphere and corona
are self-consistently maintained. Here we study two realistic models,
with different simulated areas, magnetic field strength and topology,
and numerical resolution. These are compared in order to characterize
the heating in the 3D-MHD simulations which self-consistently
maintains the structure of the atmosphere. We analyze the heating
at both large and small scales and find that heating is episodic and
highly structured in space, but occurs along loop-shaped structures,
and moves along with the magnetic field. On large scales we find that
the heating per particle is maximal near the transition region and that
widely distributed opposite-polarity field in the photosphere leads
to a greater heating scale height in the corona. On smaller scales,
heating is concentrated in current sheets, the thicknesses of which are
set by the numerical resolution. Some current sheets fragment in time,
this process occurring more readily in the higher-resolution model
leading to spatially highly intermittent heating. The large-scale
heating structures are found to fade in less than about five minutes,
while the smaller, local, heating shows timescales of the order of two
minutes in one model and one minutes in the other, higher-resolution,
model.
Title: Ellerman Bombs at High Resolution. III. Simultaneous
Observations with IRIS and SST
Authors: Vissers, G. J. M.; Rouppe van der Voort, L. H. M.; Rutten,
R. J.; Carlsson, M.; De Pontieu, B.
Bibcode: 2015ApJ...812...11V
Altcode: 2015arXiv150700435V
Ellerman bombs (EBs) are transient brightenings of the extended wings
of the solar Balmer lines in emerging active regions. We describe
their properties in the ultraviolet lines sampled by the Interface
Region Imaging Spectrograph (IRIS), using simultaneous imaging
spectroscopy in Hα with the Swedish 1-m Solar Telescope (SST) and
ultraviolet images from the Solar Dynamics Observatory for Ellerman
bomb detection and identification. We select multiple co-observed
EBs for detailed analysis. The IRIS spectra strengthen the view that
EBs mark reconnection between bipolar kilogauss fluxtubes with the
reconnection and the resulting bi-directional jet located within the
solar photosphere and shielded by overlying chromospheric fibrils in
the cores of strong lines. The spectra suggest that the reconnecting
photospheric gas underneath is heated sufficiently to momentarily reach
stages of ionization normally assigned to the transition region and the
corona. We also analyze similar outburst phenomena that we classify as
small flaring arch filaments and ascribe to reconnection at a higher
location. They have different morphologies and produce hot arches in
million-Kelvin diagnostics.
Title: Observed Variability of the Solar Mg II h Spectral Line
Authors: Schmit, D.; Bryans, P.; De Pontieu, B.; McIntosh, S.;
Leenaarts, J.; Carlsson, M.
Bibcode: 2015ApJ...811..127S
Altcode: 2015arXiv150804714S
The Mg ii h&k doublet are two of the primary spectral lines observed
by the Sun-pointing Interface Region Imaging Spectrograph (IRIS). These
lines are tracers of the magnetic and thermal environment that spans
from the photosphere to the upper chromosphere. We use a double-Gaussian
model to fit the Mg ii h profile for a full-Sun mosaic data set taken
on 2014 August 24. We use the ensemble of high-quality profile fits to
conduct a statistical study on the variability of the line profile as
it relates the magnetic structure, dynamics, and center-to-limb viewing
angle. The average internetwork profile contains a deeply reversed
core and is weakly asymmetric at h2. In the internetwork, we find a
strong correlation between h3 wavelength and profile asymmetry as well
as h1 width and h2 width. The average reversal depth of the h3 core
is inversely related to the magnetic field. Plage and sunspots exhibit
many profiles that do not contain a reversal. These profiles also occur
infrequently in the internetwork. We see indications of magnetically
aligned structures in plage and network in statistics associated with
the line core, but these structures are not clear or extended in the
internetwork. The center-to-limb variations are compared to predictions
of semi-empirical model atmospheres. We measure a pronounced limb
darkening in the line core that is not predicted by the model. The
aim of this work is to provide a comprehensive measurement baseline
and preliminary analysis on the observed structure and formation of
the Mg ii profiles observed by IRIS.
Title: CLASP: A UV Spectropolarimeter on a Sounding Rocket for
Probing theChromosphere-Corona Transition Regio
Authors: Ishikawa, Ryohko; Kano, Ryouhei; Winebarger, Amy; Auchere,
Frederic; Trujillo Bueno, Javier; Bando, Takamasa; Narukage,
Noriyuki; Kobayashi, Ken; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-nosuke; Giono, Gabriel; Tsuneta, Saku; Hara, Hirohisa; Suematsu,
Yoshinori; Shimizu, Toshifumi; Sakao, Taro; Ichimoto, Kiyoshi;
Cirtain, Jonathan; De Pontieu, Bart; Casini, Roberto; Manso Sainz,
Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi, Luca
Bibcode: 2015IAUGA..2254536I
Altcode:
The wish to understand the energetic phenomena of the outer solar
atmosphere makes it increasingly important to achieve quantitative
information on the magnetic field in the chromosphere-corona
transition region. To this end, we need to measure and model the
linear polarization produced by scattering processes and the Hanle
effect in strong UV resonance lines, such as the hydrogen Lyman-alpha
line. A team consisting of Japan, USA, Spain, France, and Norway has
been developing a sounding rocket experiment called the Chromospheric
Lyman-alpha Spectro-Polarimeter (CLASP). The aim is to detect the
scattering polarization produced by anisotropic radiation pumping in
the hydrogen Lyman-alpha line (121.6 nm), and via the Hanle effect to
try to constrain the magnetic field vector in the upper chromosphere
and transition region. In this talk, we will present an overview
of our CLASP mission, its scientific objectives, ground tests made,
and the latest information on the launch planned for the Summer of 2015.
Title: The Atacama Large Millimeter/Submillimeter Array: a New Asset
for Solar and Heliospheric Physics
Authors: Bastian, Timothy S.; Barta, Miroslav; Brajsa, Roman; Chen,
Bin; De Pontieu, Bart; Fleishman, Gregory; Gary, Dale; Hales, Antonio;
Hills, Richard; Hudson, Hugh; Iwai, Kazamasu; Shimojo, Masumi; White,
Stephen; Wedemeyer, Sven; Yan, Yihua
Bibcode: 2015IAUGA..2257295B
Altcode:
The Atacama Large Millimeter/Submillimeter Array (ALMA) is a joint
North American, European, and East Asian interferometric array that
opens the mm-submm wavelength part of the electromagnetic spectrum
for general astrophysical exploration, providing high-resolution
imaging in frequency bands ranging from 86 to 950 GHz. Despite being
a general purpose instrument, provisions have been made to enable
solar observations with ALMA. Radiation emitted at ALMA wavelengths
originates mostly from the chromosphere, which plays an important
role in the transport of energy and matter and the heating of the
outer layers of the solar atmosphere. In this paper we describe
recent efforts to ensure that ALMA can be usefully exploited by
the scientific community to address outstanding questions in solar
physics. We summarize activities under North American and European
ALMA development studies, including instrument testing, calibration
and imaging strategies, a science simulations. With the support of
solar observations, ALMA joins next-generation groundbased instruments
that can be used alone or in combination with other ground-based and
space-based instruments to address outstanding questions in solar
and heliospheric physics. Opportunities for the wider community to
contribute to these efforts will be highlighted.
Title: Resonant Absorption of Transverse Oscillations and Associated
Heating in a Solar Prominence. II. Numerical Aspects
Authors: Antolin, P.; Okamoto, T. J.; De Pontieu, B.; Uitenbroek,
H.; Van Doorsselaere, T.; Yokoyama, T.
Bibcode: 2015ApJ...809...72A
Altcode: 2015arXiv150609108A
Transverse magnetohydrodynamic (MHD) waves are ubiquitous in
the solar atmosphere and may be responsible for generating the
Sun’s million-degree outer atmosphere. However, direct evidence
of the dissipation process and heating from these waves remains
elusive. Through advanced numerical simulations combined with
appropriate forward modeling of a prominence flux tube, we provide
the observational signatures of transverse MHD waves in prominence
plasmas. We show that these signatures are characterized by a
thread-like substructure, strong transverse dynamical coherence,
an out-of-phase difference between plane-of-the-sky motions and
line-of-sight velocities, and enhanced line broadening and heating
around most of the flux tube. A complex combination between resonant
absorption and Kelvin-Helmholtz instabilities (KHIs) takes place
in which the KHI extracts the energy from the resonant layer and
dissipates it through vortices and current sheets, which rapidly
degenerate into turbulence. An inward enlargement of the boundary
is produced in which the turbulent flows conserve the characteristic
dynamics from the resonance, therefore guaranteeing detectability of
the resonance imprints. We show that the features described in the
accompanying paper through coordinated Hinode and Interface Region
Imaging Spectrograph observations match the numerical results well.
Title: Resonant Absorption of Transverse Oscillations and Associated
Heating in a Solar Prominence. I. Observational Aspects
Authors: Okamoto, Takenori J.; Antolin, Patrick; De Pontieu, Bart;
Uitenbroek, Han; Van Doorsselaere, Tom; Yokoyama, Takaaki
Bibcode: 2015ApJ...809...71O
Altcode: 2015arXiv150608965O
Transverse magnetohydrodynamic waves have been shown to be ubiquitous
in the solar atmosphere and can, in principle, carry sufficient energy
to generate and maintain the Sun’s million-degree outer atmosphere
or corona. However, direct evidence of the dissipation process of these
waves and subsequent heating has not yet been directly observed. Here we
report on high spatial, temporal, and spectral resolution observations
of a solar prominence that show a compelling signature of so-called
resonant absorption, a long hypothesized mechanism to efficiently
convert and dissipate transverse wave energy into heat. Aside
from coherence in the transverse direction, our observations show
telltale phase differences around 180° between transverse motions
in the plane-of-sky and line-of-sight velocities of the oscillating
fine structures or threads, and also suggest significant heating from
chromospheric to higher temperatures. Comparison with advanced numerical
simulations support a scenario in which transverse oscillations trigger
a Kelvin-Helmholtz instability (KHI) at the boundaries of oscillating
threads via resonant absorption. This instability leads to numerous
thin current sheets in which wave energy is dissipated and plasma is
heated. Our results provide direct evidence for wave-related heating
in action, one of the candidate coronal heating mechanisms.
Title: What Do IRIS Observations of Mg II k Tell Us about the Solar
Plage Chromosphere?
Authors: Carlsson, Mats; Leenaarts, Jorrit; De Pontieu, Bart
Bibcode: 2015ApJ...809L..30C
Altcode: 2015arXiv150804888C
We analyze observations from the Interface Region Imaging Spectrograph
of the Mg ii k line, the Mg ii UV subordinate lines, and the O i
135.6 {nm} line to better understand the solar plage chromosphere. We
also make comparisons with observations from the Swedish 1-m Solar
Telescope of the Hα line, the Ca ii 8542 line, and Solar Dynamics
Observatory/Atmospheric Imaging Assembly observations of the coronal
19.3 {nm} line. To understand the observed Mg ii profiles, we compare
these observations to the results of numerical experiments. The
single-peaked or flat-topped Mg ii k profiles found in plage imply a
transition region at a high column mass and a hot and dense chromosphere
of about 6500 K. This scenario is supported by the observed large-scale
correlation between moss brightness and filled-in profiles with very
little or absent self-reversal. The large wing width found in plage
also implies a hot and dense chromosphere with a steep chromospheric
temperature rise. The absence of emission in the Mg ii subordinate
lines constrain the chromospheric temperature and the height of the
temperature rise while the width of the O i 135.6 {nm} line sets a
limit to the non-thermal velocities to around 7 km s-1.
Title: On the Temporal Evolution of Spicules Observed with IRIS,
SDO, and Hinode
Authors: Skogsrud, H.; Rouppe van der Voort, L.; De Pontieu, B.;
Pereira, T. M. D.
Bibcode: 2015ApJ...806..170S
Altcode: 2015arXiv150502525S
Spicules are ubiquitous, fast moving jets observed off-limb in
chromospheric spectral lines. Combining the recently launched Interface
Region Imaging Spectrograph with the Solar Dynamics Observatory and
Hinode, we have a unique opportunity to study spicules simultaneously
in multiple passbands and from a seeing free environment. This makes
it possible to study their thermal evolution over a large range of
temperatures. A recent study showed that spicules appear in several
chromospheric and transition region spectral lines, suggesting that
spicules continue their evolution in hotter passbands after they
fade from Ca ii H. In this follow-up paper, we answer some of the
questions that were raised in the introductory study. In addition,
we study spicules off-limb in C ii 1330 Å for the first time. We find
that Ca ii H spicules are more similar to Mg ii 2976 Å spicules than
initially reported. For a sample of 54 spicules, we find that 44% of
Si iv 1400 Å spicules are brighter toward the top; 56% of the spicules
show an increase in Si iv emission when the Ca ii H component fades. We
find several examples of spicules that fade from passbands other than
Ca ii H, and we observe that if a spicule fades from a passband,
it also generally fades from the passbands with lower formation
temperatures. We discuss what these new, multi-spectral results mean
for the classification of type I and II spicules.
Title: The Formation of IRIS Diagnostics. IV. The Mg II Triplet
Lines as a New Diagnostic for Lower Chromospheric Heating
Authors: Pereira, Tiago M. D.; Carlsson, Mats; De Pontieu, Bart;
Hansteen, Viggo
Bibcode: 2015ApJ...806...14P
Altcode: 2015arXiv150401733P
A triplet of subordinate lines of Mg ii exists in the region around
the h&k lines. In solar spectra these lines are seen mostly
in absorption, but in some cases can become emission lines. The
aim of this work is to study the formation of this triplet, and
investigate any diagnostic value they can bring. Using 3D radiative
magnetohydrodynamic simulations of quiet Sun and flaring flux emergence,
we synthesize spectra and investigate how spectral features respond
to the underlying atmosphere. We find that emission in the lines
is rare and is typically caused by a steep temperature increase in
the lower chromosphere (above 1500 K, with electron densities above
1017 m-3). In both simulations the lines are
sensitive to temperature increases taking place at column masses ≳5
· 10-4 g cm-2. Additional information can
also be inferred from the peak-to-wing ratio and shape of the line
profiles. Using observations from NASA's Interface Region Imaging
Spectrograph we find both absorption and emission line profiles with
similar shapes to the synthetic spectra, which suggests that these lines
represent a useful diagnostic that complements the Mg ii h&k lines.
Title: First High-resolution Spectroscopic Observations of an Erupting
Prominence Within a Coronal Mass Ejection by the Interface Region
Imaging Spectrograph (IRIS)
Authors: Liu, Wei; De Pontieu, Bart; Vial, Jean-Claude; Title, Alan
M.; Carlsson, Mats; Uitenbroek, Han; Okamoto, Takenori J.; Berger,
Thomas E.; Antolin, Patrick
Bibcode: 2015ApJ...803...85L
Altcode: 2015arXiv150204738L
Spectroscopic observations of prominence eruptions associated with
coronal mass ejections (CMEs), although relatively rare, can provide
valuable plasma and three-dimensional geometry diagnostics. We report
the first observations by the Interface Region Imaging Spectrograph
mission of a spectacular fast CME/prominence eruption associated with
an equivalent X1.6 flare on 2014 May 9. The maximum plane-of-sky and
Doppler velocities of the eruption are 1200 and 460 km s-1,
respectively. There are two eruption components separated by ∼200
km s-1 in Doppler velocity: a primary, bright component
and a secondary, faint component, suggesting a hollow, rather than
solid, cone-shaped distribution of material. The eruption involves
a left-handed helical structure undergoing counterclockwise (viewed
top-down) unwinding motion. There is a temporal evolution from upward
eruption to downward fallback with less-than-free-fall speeds and
decreasing nonthermal line widths. We find a wide range of Mg ii k/h
line intensity ratios (less than ∼2 expected for optically-thin
thermal emission): the lowest ever reported median value of 1.17
found in the fallback material, a comparably high value of 1.63 in
nearby coronal rain, and intermediate values of 1.53 and 1.41 in
the two eruption components. The fallback material exhibits a strong
(\gt 5σ ) linear correlation between the k/h ratio and the Doppler
velocity as well as the line intensity. We demonstrate that Doppler
dimming of scattered chromospheric emission by the erupted material
can potentially explain such characteristics.
Title: Toward a Better Understanding of the Solar Atmosphere:
Combining Observations and Numerical Modeling
Authors: De Pontieu, Bart
Bibcode: 2015TESS....110001D
Altcode:
The study of the Sun, our nearest star, is making rapid progress,
through a combination of a host of new space-based and ground-based
observatories coming online and major advances in numerical simulations
that incorporate increasingly complex physical mechanisms. I will
provide an overview of some recent exciting discoveries that highlight
the synergy between numerical modeling and observations with the
Interface Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory
(SDO) and Hinode spacecraft. Some of the topics I will discuss include:
1. recent advances in understanding the dominant heating mechanism(s)
of the solar atmosphere focusing on dissipation of Alfven waves, as
well as the presence of non-thermal particles in small heating events
resulting from magnetic reconnection; 2. heating and reconnection in
the partially ionized chromosphere; 3. the origin of the slow solar
wind; 4. the global nature and long-distance connections governing
the instability of the solar atmosphere and driving eruptions such as
coronal mass ejections.
Title: The role of partial ionization effects in the chromosphere
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo;
Carlsson, Mats
Bibcode: 2015RSPTA.37340268M
Altcode: 2015arXiv150302723M
The energy for the coronal heating must be provided from the
convection zone. However, the amount and the method by which this
energy is transferred into the corona depend on the properties of the
lower atmosphere and the corona itself. We review: (i) how the energy
could be built in the lower solar atmosphere, (ii) how this energy is
transferred through the solar atmosphere, and (iii) how the energy is
finally dissipated in the chromosphere and/or corona. Any mechanism of
energy transport has to deal with the various physical processes in the
lower atmosphere. We will focus on a physical process that seems to
be highly important in the chromosphere and not deeply studied until
recently: the ion-neutral interaction effects in the chromosphere. We
review the relevance and the role of the partial ionization in the
chromosphere and show that this process actually impacts considerably
the outer solar atmosphere. We include analysis of our 2.5D radiative
magnetohydrodynamic simulations with the Bifrost code (Gudiksen et
al. 2011 Astron. Astrophys. 531, A154 (doi:10.1051/0004-6361/201116520))
including the partial ionization effects on the chromosphere
and corona and thermal conduction along magnetic field lines. The
photosphere, chromosphere and transition region are partially ionized
and the interaction between ionized particles and neutral particles
has important consequences on the magneto-thermodynamics of these
layers. The partial ionization effects are treated using generalized
Ohm's law, i.e. we consider the Hall term and the ambipolar diffusion
(Pedersen dissipation) in the induction equation. The interaction
between the different species affects the modelled atmosphere as
follows: (i) the ambipolar diffusion dissipates magnetic energy and
increases the minimum temperature in the chromosphere and (ii) the
upper chromosphere may get heated and expanded over a greater range
of heights. These processes reveal appreciable differences between
the modelled atmospheres of simulations with and without ion-neutral
interaction effects.
Title: Internetwork Chromospheric Bright Grains Observed With IRIS
and SST
Authors: Martínez-Sykora, Juan; Rouppe van der Voort, Luc; Carlsson,
Mats; De Pontieu, Bart; Pereira, Tiago M. D.; Boerner, Paul; Hurlburt,
Neal; Kleint, Lucia; Lemen, James; Tarbell, Ted D.; Title, Alan;
Wuelser, Jean-Pierre; Hansteen, Viggo H.; Golub, Leon; McKillop, Sean;
Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Jaeggli,
Sarah; Kankelborg, Charles
Bibcode: 2015ApJ...803...44M
Altcode: 2015arXiv150203490M
The Interface Region Imaging Spectrograph (IRIS) reveals small-scale
rapid brightenings in the form of bright grains all over coronal holes
and the quiet Sun. These bright grains are seen with the IRIS 1330,
1400, and 2796 Å slit-jaw filters. We combine coordinated observations
with IRIS and from the ground with the Swedish 1 m Solar Telescope
(SST) which allows us to have chromospheric (Ca ii 8542 Å, Ca ii H
3968 Å, Hα, and Mg ii k 2796 Å) and transition region (C ii 1334 Å,
Si iv 1403 Å) spectral imaging, and single-wavelength Stokes maps
in Fe i 6302 Å at high spatial (0\buildrel{\prime\prime}\over{.}
33), temporal, and spectral resolution. We conclude that the IRIS
slit-jaw grains are the counterpart of so-called acoustic grains,
i.e., resulting from chromospheric acoustic waves in a non-magnetic
environment. We compare slit-jaw images (SJIs) with spectra from the
IRIS spectrograph. We conclude that the grain intensity in the 2796
Å slit-jaw filter comes from both the Mg ii k core and wings. The
signal in the C ii and Si iv lines is too weak to explain the presence
of grains in the 1300 and 1400 Å SJIs and we conclude that the grain
signal in these passbands comes mostly from the continuum. Although
weak, the characteristic shock signatures of acoustic grains can often
be detected in IRIS C ii spectra. For some grains, a spectral signature
can be found in IRIS Si iv. This suggests that upward propagating
acoustic waves sometimes reach all the way up to the transition region.
Title: Synthesized Spectra of Optically Thin Emission Lines
Authors: Olluri, K.; Gudiksen, B. V.; Hansteen, V. H.; De Pontieu, B.
Bibcode: 2015ApJ...802....5O
Altcode:
In recent years realistic 3D numerical models of the solar atmosphere
have become available. The models attempt to recreate the solar
atmosphere and mimic observations in the best way, in order to make it
possible to couple complicated observations with physical properties
such as the temperatures, densities, velocities, and magnetic fields. We
here present a study of synthetic spectra created using the Bifrost code
in order to assess how well they fit with previously taken solar data. A
study of the synthetic intensity, nonthermal line widths, Doppler
shifts, and correlations between any two of these three components of
the spectra first assuming statistical equilibrium is made, followed by
a report on some of the effects nonequilibrium ionization will have on
the synthesized spectra. We find that the synthetic intensities compare
well with the observations. The synthetic observations depend on the
assumed resolution and point-spread function (PSF) of the instrument,
and we find a large effect on the results, especially for intensity
and nonthermal line width. The Doppler shifts produce the reported
persistent redshifts for the transition region (TR) lines and blueshifts
for the upper TR and corona lines. The nonthermal line widths reproduce
the well-known turnoff point around (2-3) × 105 K, but
with much lower values than those observed. The nonthermal line widths
tend to increase with decreasing assumed instrumental resolution, also
when nonequilibrium ionization is included. Correlations between the
nonthermal line width of any two TR line studies as reported by Chae et
al. are reproduced, while the correlations of intensity to line width
are reproduced only after applying a PSF to the data. Doppler shift
correlations reported by Doschek for the TR lines and correlations of
Doppler shift to nonthermal line width of the Fe xii 19.5
line reported by Doschek et al. are reproduced.
Title: Homologous Helical Jets: Observations By IRIS, SDO, and Hinode
and Magnetic Modeling With Data-Driven Simulations
Authors: Cheung, Mark C. M.; De Pontieu, B.; Tarbell, T. D.; Fu, Y.;
Tian, H.; Testa, P.; Reeves, K. K.; Martínez-Sykora, J.; Boerner,
P.; Wülser, J. P.; Lemen, J.; Title, A. M.; Hurlburt, N.; Kleint,
L.; Kankelborg, C.; Jaeggli, S.; Golub, L.; McKillop, S.; Saar, S.;
Carlsson, M.; Hansteen, V.
Bibcode: 2015ApJ...801...83C
Altcode: 2015arXiv150101593C
We report on observations of recurrent jets by instruments on board
the Interface Region Imaging Spectrograph, Solar Dynamics Observatory
(SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21,
recurrent coronal jets were observed to emanate from NOAA Active Region
11793. Far-ultraviolet spectra probing plasma at transition region
temperatures show evidence of oppositely directed flows with components
reaching Doppler velocities of ±100 km s-1. Raster Doppler
maps using a Si iv transition region line show all four jets to have
helical motion of the same sense. Simultaneous observations of the
region by SDO and Hinode show that the jets emanate from a source
region comprising a pore embedded in the interior of a supergranule. The
parasitic pore has opposite polarity flux compared to the surrounding
network field. This leads to a spine-fan magnetic topology in the
coronal field that is amenable to jet formation. Time-dependent
data-driven simulations are used to investigate the underlying drivers
for the jets. These numerical experiments show that the emergence of
current-carrying magnetic field in the vicinity of the pore supplies
the magnetic twist needed for recurrent helical jet formation.
Title: Why is Non-Thermal Line Broadening of Spectral Lines in the
Lower Transition Region of the Sun Independent of Spatial Resolution?
Authors: De Pontieu, B.; McIntosh, S.; Martinez-Sykora, J.; Peter,
H.; Pereira, T. M. D.
Bibcode: 2015ApJ...799L..12D
Altcode: 2017arXiv171006807D
Spectral observations of the solar transition region (TR) and
corona show broadening of spectral lines beyond what is expected
from thermal and instrumental broadening. The remaining non-thermal
broadening is significant (5-30 km s-1) and correlated with
intensity. Here we study spectra of the TR Si iv 1403 Å line obtained
at high resolution with the Interface Region Imaging Spectrograph
(IRIS). We find that the large improvement in spatial resolution
(0.″33) of IRIS compared to previous spectrographs (2″) does
not resolve the non-thermal line broadening which, in most regions,
remains at pre-IRIS levels of about 20 km s-1. This
invariance to spatial resolution indicates that the processes behind
the broadening occur along the line-of-sight (LOS) and/or on spatial
scales (perpendicular to the LOS) smaller than 250 km. Both effects
appear to play a role. Comparison with IRIS chromospheric observations
shows that, in regions where the LOS is more parallel to the field,
magneto-acoustic shocks driven from below impact the TR and can lead
to significant non-thermal line broadening. This scenario is supported
by MHD simulations. While these do not show enough non-thermal line
broadening, they do reproduce the long-known puzzling correlation
between non-thermal line broadening and intensity. This correlation
is caused by the shocks, but only if non-equilibrium ionization is
taken into account. In regions where the LOS is more perpendicular
to the field, the prevalence of small-scale twist is likely to play
a significant role in explaining the invariance and correlation with
intensity.
Title: Heating Signatures in the Disk Counterparts of Solar Spicules
in Interface Region Imaging Spectrograph Observations
Authors: Rouppe van der Voort, L.; De Pontieu, B.; Pereira, T. M. D.;
Carlsson, M.; Hansteen, V.
Bibcode: 2015ApJ...799L...3R
Altcode: 2014arXiv1412.4531R
We use coordinated observations with the Interface Region Imaging
Spectrograph (IRIS) and the Swedish 1 m Solar Telescope to identify
the disk counterpart of type II spicules in upper-chromospheric and
transition region (TR) diagnostics. These disk counterparts were
earlier identified through short-lived asymmetries in chromospheric
spectral lines: rapid blue- or red-shifted excursions (RBEs or RREs). We
find clear signatures of RBEs and RREs in Mg II h & k, often with
excursions of the central h3 and k3 absorption features in concert with
asymmetries in co-temporal and co-spatial Hα spectral profiles. We find
spectral signatures for RBEs and RREs in C II 1335 and 1336 Å and Si
IV 1394 and 1403 Å spectral lines and interpret this as a sign that
type II spicules are heated to at least TR temperatures, supporting
other recent work. These C II and Si IV spectral signals are weaker
for a smaller network region than for more extended network regions in
our data. A number of bright features around extended network regions
observed in IRIS slit-jaw imagery SJI 1330 and 1400, recently identified
as network jets, can be clearly connected to Hα RBEs and/or RREs in
our coordinated data. We speculate that at least part of the diffuse
halo around network regions in the IRIS SJI 1330 and 1400 images can
be attributed to type II spicules with insufficient opacity in the C
II and Si IV lines to stand out as single features in these passbands.
Title: The VAULT2.0 Observing Campaign: A Comprehensive Investigation
of the Chromosphere-Corona Interface at Sub-arcsecond scales
Authors: Vourlidas, A.; Korendyke, C.; Tun-Beltran, S. D.; Ugarte-Urra,
I.; Morrill, J. S.; Warren, H. P.; Young, P.; De Pontieu, B.; Gauzzi,
G.; Reardon, K.
Bibcode: 2014AGUFMSH41C4155V
Altcode:
We report the first results from an observing campaign in support of
the VAULT2.0 sounding rocket launch on September 30, 2014. VAULT2.0
is a Lya (1216Å) spectroheliograph capable of 0.3" (~250 km) spatial
resolution. The objective of the VAULT2.0 project is the study of
the chromosphere-corona interface. This interface has acquired renewed
emphasis over the last few years, thanks to high-resolution observations
from Hinode/SOT and EIS instruments and the Lya imaging from the two
VAULT flights. The observations have shown that the upper chromosphere
may play a more important role in heating the corona and in affecting
EUV observations that previously thought: (1) by supplying the mass
via Type-II spicules and, (2) by absorbing coronal emission. Many of
the required clues for further progress are located in sub-arcsecond
structures with temperatures between 10000 and 50000 K, a regime not
accessible by Hinode or SDO. Lyman-alpha observations are, therefore,
ideal, for filling in this gap. The observing campaign in support of
the VAULT2.0 is closely coordinated with the Hinode and IRIS missions
to study the mass/energy flow from the chromosphere to the corona with
joint observations of type-II spicules, and the magnetic connectivity
of coronal loops using the full imaging and spectral capabilities of
IRIS, Hinode and SDO. Several ground-based observatories also provide
important observations (IBIS, BBSO, SOLIS). The VAULT2.0 project is
funded by the NASA LCAS program.
Title: IRIS diagnostics of non-thermal particles in coronal loops
heated by nanoflares
Authors: Testa, P.; De Pontieu, B.; Allred, J. C.; Carlsson, M.;
Reale, F.; Daw, A. N.
Bibcode: 2014AGUFMSH53D..08T
Altcode:
The variability of emission of the "moss", i.e., the upper transition
region (TR) layer of high pressure loops in active regions, provides
stringent constraints on the characteristics of heating events. We
will discuss the new coronal heating diagnostics provided by the
Interface Region Imaging Spectrograph (IRIS) together with SDO/AIA. IRIS
provides imaging and spectral observations of the solar chromosphere
and transition region, at high spatial (0.166 arcsec/pix) and temporal
(down to ~1s) resolution at FUV and NUV wavelengths. We discuss how
simultaneous IRIS and AIA observations, together with loop modeling
(with the RADYN code) including chromosphere, transition region and
corona, allow us to study impulsive heating events (nanoflares) and the
energy transport mechanism between the corona and the lower atmospheric
layers (thermal conduction vs. beams of non-thermal particles). We will
show how the modeling of rapid moss brightenings provides diagnostics
for the presence and properties of non-thermal particles in nanoflares,
which are below the detectability threshold of hard X-ray observations.
Title: Observables of Ion-Neutral Interaction Effects in the Solar
Chromosphere
Authors: Martínez-Sykora, J.; De Pontieu, B.; Hansteen, V. H.;
Pereira, T. M. D.; Leenaarts, J.; Carlsson, M.
Bibcode: 2014AGUFMSH51C4176M
Altcode:
The chromosphere and transition region constitute the interface
between the solar surface and the corona and modulate the flow of
mass and energy into the upper atmosphere. IRIS was launched in 2013
to study the chromosphere and transition region. The complexity of the
chromosphere is due to various regime changes that take place across it,
like: Hydrogen goes from predominantly neutral to predominantly ionized;
the plasma behavior changes from collisional to collision-less; it goes
from gas-pressure dominated to magnetically driven, etc. Consequently,
the interpretation of chromospheric observations in general and those
from IRIS, in particular, is a challenging task. It is thus crucial
to combine IRIS observations with advanced radiative-MHD numerical
modeling. Because the photosphere, chromosphere and transition region
are partially ionized, the interaction between ionized and neutral
particles has important consequences on the magneto-thermodynamics of
these regions. We implemented the effects of partial ionization using
generalized Ohm's law in the Bifrost code (Gudiksen et al. 2011) which
solves the full MHD equations with non-grey and non-LTE radiative
transfer and thermal conduction along magnetic field lines. The
implementation of partial ionization effects impact our modeled
radiative-MHD atmosphere, such as producing chromospheric heating and
diffusion of photospheric magnetic field into the upper-chromosphere. We
will focus on which observables of these processes can be revealed
with IRIS.
Title: Observational Evidence of Resonant Absorption in Oscillating
Prominence
Authors: Okamoto, J.; Antolin, P.; De Pontieu, B.; Uitenbroek, H.;
Van Doorsselaere, T.; Yokoyama, T.
Bibcode: 2014AGUFMSH12A..05O
Altcode:
Coronal heating and the acceleration of the solar wind are unsolved
problems in solar physics. The propagation of Alfven waves along
magnetic field lines is one of the candidate mechanisms for
carrying energy to large distances from the surface and heat the
coronal plasma. However, the dissipation process is still unclear
in observational aspects.The new NASA's solar physics satellite IRIS
(Interface Region Imaging Spectrograph) provides spectral information of
plasma in the chromosphere and transition region with high-spatial and
high-temporal resolution. Hence, we performed observations of a limb
prominence to find evidence and clues of dissipation in collaboration
with Hinode/SOT and SDO/AIA.In our observations, we found a clear
evidence of resonant absorption that takes place on the surface of
the oscillating prominence flux tubes. This mechanism facilitates
the onset of the Kelvin-Helmholtz instability, which deforms the thin
tube's boundaries and generates thin current sheets and turbulence,
leading to dissipation of the wave energy into heat. In this talk, we
will show the observed phenomena and discuss the dissipation mechanism
compared with numerical simulations of an oscillating prominence.
Title: Analysis of Inter-moss Loops in the Solar Transition Region
with IRIS and SDO/AIA: Automatic Event Detection and Characterization
Authors: Fayock, B.; Winebarger, A. R.; De Pontieu, B.
Bibcode: 2014AGUFMSH51C4172F
Altcode:
The transition region of the solar atmosphere is no longer believed
to be exclusively a thin boundary layer connecting the chromosphere
and the corona. Instead, the emission from this region is dominated
by dynamic, low-lying loops with peak temperatures <1 MK. These
loops also appear in AIA data due to the transition region spectral
lines in the AIA passbands, but have not been studied with great
detail. The IRIS instrument has resolved these loops both spatially and
temporally. With an IRIS image cadence of approximately 10 seconds,
we are able to study the evolution of these loops. We have developed
a technique to automatically identify events (i.e., brightenings) on a
pixel-by-pixel basis applying a set of selection criteria. The pixels
are then grouped according to their proximity in space and relative
progression of the event. This method allows us to characterize their
overall lifetime and the rate at which these events occur. Our current
progress includes identification of these groups of events in IRIS data,
determination of their existence in AIA data, and characterization based
on a comparison between the two. If the same events appear in both IRIS
and AIA data, it may suggest that the intrinsic transition region is
not in local thermodynamic equilibrium. We present the results that
follow each integral step in the analysis and provide a preliminary
characterization of a few example events within our data set.
Title: Homologous Helical Jets: Observations by IRIS, SDO and Hinode
and Data-Driven Simulations
Authors: Cheung, C. M. M.; De Pontieu, B.; Tarbell, T. D.; Fu, Y.
Bibcode: 2014AGUFMSH53D..05C
Altcode:
We report on observations of recurrent jets by instruments onboard
the Interface Region Imaging Spectrograph (IRIS), Solar Dynamics
Observatory (SDO) and Hinode spacecrafts. Over a 4-hour period on
July 21st 2013, recurrent coronal jets were observed to emanate from
NOAA Active Region 11793. In more than one instance, double-peaked
FUV spectra probing plasma at transition region temperatures show
evidence of oppositely directed (Doppler) outflows exceeding +/- 100
km/s. Raster Doppler maps using a Si IV transition region line shows
all four jets to have helical motion of the same sense. Time-dependent
data-driven simulations are used to investigate the underlying drivers
for the jets. These numerical experiments show that the emergence of
current-carrying magnetic field in the vicinity of a pore supplies
the magnetic twist needed for recurrent helical jet formation.
Title: Wave Propagation in the Internetwork Chromosphere: Comparing
IRIS Observations of Mg II h and k with Simulations
Authors: Fleck, B.; De Pontieu, B.; Leenaarts, J.; Pereira, T. M. D.;
Straus, T.
Bibcode: 2014AGUFMSH51C4174F
Altcode:
The objective of this study is to explore the dynamics of the
upper internetwork chromosphere using high-resolution spectroscopic
"sit-and-stare" time series obtained with the Interface Region Imaging
Spectrogragh (IRIS) in the Mg II h and k lines. The Mg II h and k lines
reveal a particularly complex spatio-temporal behavior, which strongly
depends on the magnetic field topology. We focus on six parameters in
both the h and k line: the Doppler shift and intensity of the central
reversal (h3 and k3) and the blue and red emission peaks (h2v, h2r,
k2v, k2r). In an effort to better understand what physical parameters
can be extracted from these lines and to put our interpretation of
the observations on more solid grounds, we extend our analysis to
synthetic spectra obtained from numerical simulations and compare the
results to the observations.
Title: First High-resolution Spectroscopic Observations by IRIS
of a Fast, Helical Prominence Eruption Associated with a Coronal
Mass Ejection
Authors: Liu, W.; De Pontieu, B.; Okamoto, T. J.; Vial, J. C.; Title,
A. M.; Antolin, P.; Berger, T. E.; Uitenbroek, H.
Bibcode: 2014AGUFMSH11D..04L
Altcode:
High-resolution spectroscopic observations of prominence eruptions and
associated coronal mass ejections (CMEs) are rare but can provide
valuable plasma and energy diagnostics. New opportunities have
recently become available with the advent of the Interface Region
Imaging Spectrograph (IRIS) mission equipped with high resolution of
0.33-0.4 arcsec in space and 1 km/s in velocity, together with the
Hinode Solar Optical Telescope of 0.2 arcsec spatial resolution. We
report the first result of joint IRIS-Hinode observations of a
spectacular prominence eruption occurring on 2014-May-09. IRIS
detected a maximum redshift of 450 km/s, which, combined with the
plane-of-sky speed of 800 km/s, gives a large velocity vector of 920
km/s at 30 degrees from the sky plane. This direction agrees with the
source location at 30 degrees behind the limb observed by STEREO-A
and indicates a nearly vertical ejection. We found two branches of
redshifts separated by 200 km/s appearing in all strong lines at
chromospheric to transition-region temperatures, including Mg II k/h,
C II, and Si IV, suggesting a hollow, rather than solid, cone in the
velocity space of the ejected material. Opposite blue- and redshifts
on the two sides of the prominence exhibit corkscrew variations both
in space and time, suggestive of unwinding rotations of a left-handed
helical flux rope. Some erupted material returns as nearly streamline
flows, exhibiting distinctly narrow line widths (~10 km/s), about
50% of those of the nearby coronal rain at the apexes of coronal
loops, where the rain material is initially formed out of cooling
condensation. We estimate the mass and kinetic energy of the ejected
and returning material and compare them with those of the associated
CME. We will discuss the implications of these observations for CME
initiation mechanisms.
Title: Why Is Non-thermal Line Broadening of Lower Transition Region
Lines Independent of Spatial Resolution?
Authors: De Pontieu, B.; Mcintosh, S. W.; Martínez-Sykora, J.; Peter,
H.; Pereira, T. M. D.
Bibcode: 2014AGUFMSH51C4175D
Altcode:
Spectral observations of the solar transition region (TR) and
corona typically show broadening of the spectral lines beyond what
is expected from thermal and instrumental broadening. The remaining
non-thermal broadening is significant (10-30 km/s), correlated with
the intensity, and has been attributed to waves, macro and micro
turbulence, nanoflares, etc... Here we study spectra of the low
TR Si IV 1403 Angstrom line obtained at high spatial and spectral
resolution with the Interface Region Imaging Spectrograph (IRIS). We
find that the large improvement in spatial resolution (0.33 arcsec)
of IRIS compared to previous spectrographs (2 arcsec) does not resolve
the non-thermal line broadening which remains at pre-IRIS levels of
20 km/s. This surprising invariance to spatial resolution indicates
that the physical processes behind the non-thermal line broadening
either occur along the line-of-sight (LOS) and/or on spatial scales
(perpendicular to the LOS) smaller than 250 km. Both effects appear
to play a role. Comparison with IRIS chromospheric observations
shows that, in regions where the LOS is more parallel to the field,
magneto-acoustic shocks driven from below impact the low TR leading to
strong non-thermal line broadening from line-of-sight integration across
the shock at the time of impact. This scenario is confirmed by advanced
MHD simulations. In regions where the LOS is perpendicular to the field,
the prevalence of small-scale twist is likely to play a significant
role in explaining the invariance and the correlation with intensity.
Title: On the Multi-threaded Nature of Solar Spicules
Authors: Skogsrud, H.; Rouppe van der Voort, L.; De Pontieu, B.
Bibcode: 2014ApJ...795L..23S
Altcode: 2014arXiv1410.1334S
A dominant constituent in the dynamic chromosphere is spicules. Spicules
at the limb appear as relatively small and dynamic jets that are
observed to stick out everywhere. Many papers emphasize the important
role spicules might play in the energy and mass balance of the
chromosphere and corona. However, many aspects of spicules remain
a mystery. In this Letter, we shed more light on the multi-threaded
nature of spicules and their torsional component. We use high spatial,
spectral, and temporal resolution observations from the Swedish
1 m Solar Telescope in the Hα spectral line. The data target the
limb, and we extract spectra from spicules far out from the limb
to reduce the line-of-sight superposition effect. We discover that
many spicules display very asymmetric spectra with some even showing
multiple peaks. To quantify this asymmetry, we use a double-Gaussian
fitting procedure and find an average velocity difference between the
single-Gaussian components to be between 20 and 30 km s-1
for a sample of 57 spicules. We observe that spicules show significant
substructure where one spicule consists of many "threads." We interpret
the asymmetric spectra as a line-of-sight superposition of threads
in one spicule and therefore have a measure for a perpendicular flow
inside spicules that will be important for future numerical models to
reproduce. In addition, we show examples of λ - x slices perpendicular
across spicules and find spectral tilts in individual threads, providing
further evidence for the complex dynamical nature of spicules.
Title: The High-Resolution Coronal Imager (Hi-C)
Authors: Kobayashi, Ken; Cirtain, Jonathan; Winebarger, Amy R.;
Korreck, Kelly; Golub, Leon; Walsh, Robert W.; De Pontieu, Bart;
DeForest, Craig; Title, Alan; Kuzin, Sergey; Savage, Sabrina; Beabout,
Dyana; Beabout, Brent; Podgorski, William; Caldwell, David; McCracken,
Kenneth; Ordway, Mark; Bergner, Henry; Gates, Richard; McKillop,
Sean; Cheimets, Peter; Platt, Simon; Mitchell, Nick; Windt, David
Bibcode: 2014SoPh..289.4393K
Altcode: 2014SoPh..tmp..104K
The High-Resolution Coronal Imager (Hi-C) was flown on a NASA sounding
rocket on 11 July 2012. The goal of the Hi-C mission was to obtain
high-resolution (≈ 0.3 - 0.4''), high-cadence (≈ 5 seconds)
images of a solar active region to investigate the dynamics of solar
coronal structures at small spatial scales. The instrument consists of
a normal-incidence telescope with the optics coated with multilayers
to reflect a narrow wavelength range around 19.3 nm (including the
Fe XII 19.5-nm spectral line) and a 4096×4096 camera with a plate
scale of 0.1'' pixel−1. The target of the Hi-C rocket
flight was Active Region 11520. Hi-C obtained 37 full-frame images
and 86 partial-frame images during the rocket flight. Analysis of the
Hi-C data indicates the corona is structured on scales smaller than
currently resolved by existing satellite missions.
Title: Probing the solar interface region
Authors: De Pontieu, Bart; Title, Alan; Carlsson, Mats
Bibcode: 2014Sci...346..315D
Altcode:
No abstract at ADS
Title: Hot explosions in the cool atmosphere of the Sun
Authors: Peter, H.; Tian, H.; Curdt, W.; Schmit, D.; Innes, D.;
De Pontieu, B.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
Tarbell, T. D.; Wuelser, J. P.; Martínez-Sykora, Juan; Kleint,
L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.;
Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V.
Bibcode: 2014Sci...346C.315P
Altcode: 2014arXiv1410.5842P
The solar atmosphere was traditionally represented with a simple
one-dimensional model. Over the past few decades, this paradigm shifted
for the chromosphere and corona that constitute the outer atmosphere,
which is now considered a dynamic structured envelope. Recent
observations by the Interface Region Imaging Spectrograph (IRIS) reveal
that it is difficult to determine what is up and down, even in the cool
6000-kelvin photosphere just above the solar surface: This region hosts
pockets of hot plasma transiently heated to almost 100,000 kelvin. The
energy to heat and accelerate the plasma requires a considerable
fraction of the energy from flares, the largest solar disruptions. These
IRIS observations not only confirm that the photosphere is more complex
than conventionally thought, but also provide insight into the energy
conversion in the process of magnetic reconnection.
Title: A Sounding Rocket Experiment for the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP)
Authors: Kubo, M.; Kano, R.; Kobayashi, K.; Bando, T.; Narukage, N.;
Ishikawa, R.; Tsuneta, S.; Katsukawa, Y.; Ishikawa, S.; Suematsu, Y.;
Hara, H.; Shimizu, T.; Sakao, T.; Ichimoto, K.; Goto, M.; Holloway,
T.; Winebarger, A.; Cirtain, J.; De Pontieu, B.; Casini, R.; Auchère,
F.; Trujillo Bueno, J.; Manso Sainz, R.; Belluzzi, L.; Asensio Ramos,
A.; Štěpán, J.; Carlsson, M.
Bibcode: 2014ASPC..489..307K
Altcode:
A sounding-rocket experiment called the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP) is presently under development to measure
the linear polarization profiles in the hydrogen Lyman-alpha (Lyα)
line at 121.567 nm. CLASP is a vacuum-UV (VUV) spectropolarimeter to aim
for first detection of the linear polarizations caused by scattering
processes and the Hanle effect in the Lyα line with high accuracy
(0.1%). This is a fist step for exploration of magnetic fields in
the upper chromosphere and transition region of the Sun. Accurate
measurements of the linear polarization signals caused by scattering
processes and the Hanle effect in strong UV lines like Lyα are
essential to explore with future solar telescopes the strength
and structures of the magnetic field in the upper chromosphere and
transition region of the Sun. The CLASP proposal has been accepted by
NASA in 2012, and the flight is planned in 2015.
Title: The unresolved fine structure resolved: IRIS observations of
the solar transition region
Authors: Hansteen, V.; De Pontieu, B.; Carlsson, M.; Lemen, J.; Title,
A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Pereira,
T. M. D.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
Martínez-Sykora, J.
Bibcode: 2014Sci...346E.315H
Altcode: 2014arXiv1412.3611H
The heating of the outer solar atmospheric layers, i.e., the transition
region and corona, to high temperatures is a long-standing problem
in solar (and stellar) physics. Solutions have been hampered by an
incomplete understanding of the magnetically controlled structure of
these regions. The high spatial and temporal resolution observations
with the Interface Region Imaging Spectrograph (IRIS) at the solar
limb reveal a plethora of short, low-lying loops or loop segments
at transition-region temperatures that vary rapidly, on the time
scales of minutes. We argue that the existence of these loops solves
a long-standing observational mystery. At the same time, based on
comparison with numerical models, this detection sheds light on a
critical piece of the coronal heating puzzle.
Title: Evidence of nonthermal particles in coronal loops heated
impulsively by nanoflares
Authors: Testa, P.; De Pontieu, B.; Allred, J.; Carlsson, M.; Reale,
F.; Daw, A.; Hansteen, V.; Martinez-Sykora, J.; Liu, W.; DeLuca, E. E.;
Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Tian, H.; Lemen, J.;
Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
Kleint, L.; Kankelborg, C.; Jaeggli, S.
Bibcode: 2014Sci...346B.315T
Altcode: 2014arXiv1410.6130T
The physical processes causing energy exchange between the Sun’s
hot corona and its cool lower atmosphere remain poorly understood. The
chromosphere and transition region (TR) form an interface region between
the surface and the corona that is highly sensitive to the coronal
heating mechanism. High-resolution observations with the Interface
Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to
60 seconds) of intensity and velocity on small spatial scales (≲500
kilometers) at the footpoints of hot and dynamic coronal loops. The
observations are consistent with numerical simulations of heating by
beams of nonthermal electrons, which are generated in small impulsive
(≲30 seconds) heating events called “coronal nanoflares.” The
accelerated electrons deposit a sizable fraction of their energy
(≲1025 erg) in the chromosphere and TR. Our analysis
provides tight constraints on the properties of such electron beams
and new diagnostics for their presence in the nonflaring corona.
Title: Prevalence of small-scale jets from the networks of the solar
transition region and chromosphere
Authors: Tian, H.; DeLuca, E. E.; Cranmer, S. R.; De Pontieu, B.;
Peter, H.; Martínez-Sykora, J.; Golub, L.; McKillop, S.; Reeves,
K. K.; Miralles, M. P.; McCauley, P.; Saar, S.; Testa, P.; Weber,
M.; Murphy, N.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli,
S.; Carlsson, M.; Hansteen, V.; McIntosh, S. W.
Bibcode: 2014Sci...346A.315T
Altcode: 2014arXiv1410.6143T
As the interface between the Sun’s photosphere and corona, the
chromosphere and transition region play a key role in the formation and
acceleration of the solar wind. Observations from the Interface Region
Imaging Spectrograph reveal the prevalence of intermittent small-scale
jets with speeds of 80 to 250 kilometers per second from the narrow
bright network lanes of this interface region. These jets have lifetimes
of 20 to 80 seconds and widths of ≤300 kilometers. They originate from
small-scale bright regions, often preceded by footpoint brightenings
and accompanied by transverse waves with amplitudes of ~20 kilometers
per second. Many jets reach temperatures of at least ~105
kelvin and constitute an important element of the transition region
structures. They are likely an intermittent but persistent source of
mass and energy for the solar wind.
Title: On the prevalence of small-scale twist in the solar
chromosphere and transition region
Authors: De Pontieu, B.; Rouppe van der Voort, L.; McIntosh, S. W.;
Pereira, T. M. D.; Carlsson, M.; Hansteen, V.; Skogsrud, H.; Lemen,
J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser,
J. P.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
Martinez-Sykora, J.
Bibcode: 2014Sci...346D.315D
Altcode: 2014arXiv1410.6862D
The solar chromosphere and transition region (TR) form an interface
between the Sun’s surface and its hot outer atmosphere. There,
most of the nonthermal energy that powers the solar atmosphere
is transformed into heat, although the detailed mechanism remains
elusive. High-resolution (0.33-arc second) observations with NASA’s
Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere
and TR that are replete with twist or torsional motions on sub-arc
second scales, occurring in active regions, quiet Sun regions, and
coronal holes alike. We coordinated observations with the Swedish
1-meter Solar Telescope (SST) to quantify these twisting motions and
their association with rapid heating to at least TR temperatures. This
view of the interface region provides insight into what heats the low
solar atmosphere.
Title: An Interface Region Imaging Spectrograph First View on Solar
Spicules
Authors: Pereira, T. M. D.; De Pontieu, B.; Carlsson, M.; Hansteen,
V.; Tarbell, T. D.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt,
N.; Wülser, J. P.; Martínez-Sykora, J.; Kleint, L.; Golub, L.;
McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.; Tian, H.; Jaeggli,
S.; Kankelborg, C.
Bibcode: 2014ApJ...792L..15P
Altcode: 2014arXiv1407.6360P
Solar spicules have eluded modelers and observers for decades. Since
the discovery of the more energetic type II, spicules have become
a heated topic but their contribution to the energy balance of the
low solar atmosphere remains unknown. Here we give a first glimpse of
what quiet-Sun spicules look like when observed with NASA's recently
launched Interface Region Imaging Spectrograph (IRIS). Using IRIS
spectra and filtergrams that sample the chromosphere and transition
region, we compare the properties and evolution of spicules as
observed in a coordinated campaign with Hinode and the Atmospheric
Imaging Assembly. Our IRIS observations allow us to follow the thermal
evolution of type II spicules and finally confirm that the fading
of Ca II H spicules appears to be caused by rapid heating to higher
temperatures. The IRIS spicules do not fade but continue evolving,
reaching higher and falling back down after 500-800 s. Ca II H type
II spicules are thus the initial stages of violent and hotter events
that mostly remain invisible in Ca II H filtergrams. These events
have very different properties from type I spicules, which show lower
velocities and no fading from chromospheric passbands. The IRIS spectra
of spicules show the same signature as their proposed disk counterparts,
reinforcing earlier work. Spectroheliograms from spectral rasters also
confirm that quiet-Sun spicules originate in bushes from the magnetic
network. Our results suggest that type II spicules are indeed the
site of vigorous heating (to at least transition region temperatures)
along extensive parts of the upward moving spicular plasma.
Title: The Impact of a Filament Eruption on Nearby High-lying
Cool Loops
Authors: Harra, L. K.; Matthews, S. A.; Long, D. M.; Doschek, G. A.;
De Pontieu, B.
Bibcode: 2014ApJ...792...93H
Altcode: 2014arXiv1409.0377H
The first spectroscopic observations of cool Mg II loops above the
solar limb observed by NASA's Interface Region Imaging Spectrograph
(IRIS) are presented. During the observation period, IRIS is pointed
off-limb, allowing the observation of high-lying loops, which reach
over 70 Mm in height. Low-lying cool loops were observed by the IRIS
slit-jaw camera for the entire four-hour observing window. There is no
evidence of a central reversal in the line profiles, and the Mg II h/k
ratio is approximately two. The Mg II spectral lines show evidence of
complex dynamics in the loops with Doppler velocities reaching ±40
km s-1. The complex motions seen indicate the presence
of multiple threads in the loops and separate blobs. Toward the end
of the observing period, a filament eruption occurs that forms the
core of a coronal mass ejection. As the filament erupts, it impacts
these high-lying loops, temporarily impeding these complex flows,
most likely due to compression. This causes the plasma motions in the
loops to become blueshifted and then redshifted. The plasma motions
are seen before the loops themselves start to oscillate as they reach
equilibrium following the impact. The ratio of the Mg h/k lines also
increases following the impact of the filament.
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.;
Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou,
C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman,
C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish,
D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.;
Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons,
R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.;
Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.;
Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.;
Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski,
W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.;
Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.;
Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.;
Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson,
M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu,
K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora,
J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.;
Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N.
Bibcode: 2014SoPh..289.2733D
Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D
The Interface Region Imaging Spectrograph (IRIS) small explorer
spacecraft provides simultaneous spectra and images of the photosphere,
chromosphere, transition region, and corona with 0.33 - 0.4 arcsec
spatial resolution, two-second temporal resolution, and 1 km
s−1 velocity resolution over a field-of-view of up to
175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous
orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a
19-cm UV telescope that feeds a slit-based dual-bandpass imaging
spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å,
1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines
formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and
transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw
images in four different passbands (C II 1330, Si IV 1400, Mg II k
2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral
rasters that sample regions up to 130 arcsec × 175 arcsec at a variety
of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to
emission from plasma at temperatures between 5000 K and 10 MK and will
advance our understanding of the flow of mass and energy through an
interface region, formed by the chromosphere and transition region,
between the photosphere and corona. This highly structured and dynamic
region not only acts as the conduit of all mass and energy feeding
into the corona and solar wind, it also requires an order of magnitude
more energy to heat than the corona and solar wind combined. The
IRIS investigation includes a strong numerical modeling component
based on advanced radiative-MHD codes to facilitate interpretation of
observations of this complex region. Approximately eight Gbytes of data
(after compression) are acquired by IRIS each day and made available
for unrestricted use within a few days of the observation.
Title: Detection of Supersonic Downflows and Associated Heating
Events in the Transition Region above Sunspots
Authors: Kleint, L.; Antolin, P.; Tian, H.; Judge, P.; Testa, P.;
De Pontieu, B.; Martínez-Sykora, J.; Reeves, K. K.; Wuelser, J. P.;
McKillop, S.; Saar, S.; Carlsson, M.; Boerner, P.; Hurlburt, N.; Lemen,
J.; Tarbell, T. D.; Title, A.; Golub, L.; Hansteen, V.; Jaeggli, S.;
Kankelborg, C.
Bibcode: 2014ApJ...789L..42K
Altcode: 2014arXiv1406.6816K
Interface Region Imaging Spectrograph data allow us to study the solar
transition region (TR) with an unprecedented spatial resolution of
0.''33. On 2013 August 30, we observed bursts of high Doppler shifts
suggesting strong supersonic downflows of up to 200 km s-1
and weaker, slightly slower upflows in the spectral lines Mg II h
and k, C II 1336, Si IV 1394 Å, and 1403 Å, that are correlated
with brightenings in the slitjaw images (SJIs). The bursty behavior
lasts throughout the 2 hr observation, with average burst durations
of about 20 s. The locations of these short-lived events appear to
be the umbral and penumbral footpoints of EUV loops. Fast apparent
downflows are observed along these loops in the SJIs and in the
Atmospheric Imaging Assembly, suggesting that the loops are thermally
unstable. We interpret the observations as cool material falling
from coronal heights, and especially coronal rain produced along the
thermally unstable loops, which leads to an increase of intensity
at the loop footpoints, probably indicating an increase of density
and temperature in the TR. The rain speeds are on the higher end of
previously reported speeds for this phenomenon, and possibly higher
than the free-fall velocity along the loops. On other observing days,
similar bright dots are sometimes aligned into ribbons, resembling
small flare ribbons. These observations provide a first insight into
small-scale heating events in sunspots in the TR.
Title: IRIS Observations of Twist in the Low Solar Atmosphere
Authors: De Pontieu, Bart; Rouppe van der Voort, Luc; Pereira,
Tiago M. D.; Skogsrud, Haakon; McIntosh, Scott W.; Carlsson, Mats;
Hansteen, Viggo
Bibcode: 2014AAS...22431302D
Altcode:
The Interface Region Imaging Spectrograph (IRIS) small explorer
was launched in June 2013. IRIS’s high-resolution (0.33 arcsec),
high-cadence (2s) images and spectra reveal a solar chromosphere and
transition region that is riddled with twist. This is evidenced by the
presence of ubiquitous torsional motions on very small (subarcsec)
spatial scales. These motions occur in active regions, quiet Sun
and coronal holes on a variety of structures such as spicules at
the limb, rapid-blue/red-shifted events (RBEs and RREs) as well as
low-lying loops. We use IRIS data and observations from the Swedish
Solar Telescope (SST) in La Palma, Spain to describe these motions
quantitatively, study their propagation, and illustrate how such
strong twisting motions are often associated with significant and
rapid heating to at least transition region temperatures.
Title: Diagnostics of coronal heating and mechanisms of energy
transport from IRIS and AIA observations of active region moss
Authors: Testa, Paola; De Pontieu, Bart; Allred, Joel C.; Carlsson,
Mats; Reale, Fabio; Daw, Adrian N.; Hansteen, Viggo
Bibcode: 2014AAS...22431305T
Altcode:
The variability of emission of the "moss", i.e., the upper transition
region (TR) layer of high pressure loops in active regions provides
stringent constraints on the characteristics of heating events. The
Interface Region Imaging Spectrograph (IRIS), launched in June
2013, provides imaging and spectral observations at high spatial
(0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV
and NUV wavelengths, and together with the high spatial and temporal
resolution observations of SDO/AIA, can provide important insights
into the coronal heating mechanisms. We present here an analysis of
the temporal variability properties of moss regions at the footpoints
of hot active region core loops undergoing heating, as observed by IRIS
and AIA, covering emission from the corona to the transition region and
the chromosphere. We model the observations using dynamic loop models
(the Palermo-Harvard code, and RADYN, which also includes the effects of
non-thermal particles) and discuss the implications on energy transport
mechanisms (thermal conduction vs beams of non-thermal particles).
Title: Laboratory Study of Magnetic Reconnection in Partially Ionized
Plasmas Relevant to the Solar Chromosphere
Authors: Fox, William; De Pontieu, Bart; Ji, Hantao; Lawrence,
Eric; Lukin, Vyacheslav; Murphy, Nicholas Arnold; Yamada, Masaaki;
Yoo, Jongsoo
Bibcode: 2014AAS...22432370F
Altcode:
Magnetic reconnection is observed to occur in the solar chromosphere
where plasma is only partially ionized. In order to understand the
effects of partial ionization on the reconnection process, systematic
experiments have been performed in the Magnetic Reconnection Experiment
(MRX) where plasma is controlled from nearly full ionization to partial
ionization of about 1%. It is shown that, when neutrals are added, the
Hall quadrupole field pattern and thus electron flow are unchanged while
the ion outflow speed is reduced due to ion-neutral drag. However,
in contrast to theoretical predictions, the ion diffusion layer
width does not change appreciably. Therefore, the total ion outflow
flux and the normalized reconnection rate are reduced*. Both 2-fluid
and 3-fluid modeling using the HiFi code is used to interpret the
experimental data, and implications to the interpretation of solar
observations will be also discussed. Future plans to study effects of
neutral particles on further details on magnetic reconnection, such
as plasma heating, will be described.* E. Lawrence, H. Ji, M. Yamada,
and J. Yoo, “Laboratory Study of Hall Reconnection in Partially
Ionized Plasmas”, Phys. Rev. Lett. 110, 015001 (2013).
Title: Coordinated IRIS science using the Heliophysics Event
Knowledgebase
Authors: Hurlburt, Neal E.; Freeland, Sam; Timmons, Ryan; De Pontieu,
Bart
Bibcode: 2014AAS...22431301H
Altcode:
We have recently enhanced the capabilities of the Heliophysics Event
Knowledgebase (HEK) to support the complex datasets being produced
by the Interface Region Imaging Spectrograph (IRIS). This includes
tools to incorporate observations from the Solar Dynamics Observatory
and ground-based facilities to generate composite data products. We
will discuss the system and its recent evolution and demonstrate its
ability to support coordinated science investigations.
Title: On the Signatures of Waves and Oscillations in IRIS
Observations
Authors: Fleck, Bernard; Straus, Thomas; De Pontieu, Bart; Leenaarts,
Jorrit; Pereira, Tiago M. D.
Bibcode: 2014AAS...22432305F
Altcode:
The objective of this study is to explore the signatures of acoustic
waves and oscillations in a variety of magnetic field configurations
in the Sun’s atmosphere using high-resolution spectroscopic
“sit-an-stare” time series obtained with the Interface Region
Imaging Spectrogragh (IRIS) in lines formed in the chromosphere and
lower transition region (C II 1335 & 1336, C I 1352, O I 1356,
Si IV 1394 & 1403 and Mg h and k). The occurrence of oscillations
in the transition region is found to strongly depend on the magnetic
field topology. The Mg h and k lines reveal a particularly complex
spatio-temporal behavior. In an effort to better understand what
physical parameters can be extracted from these lines, we extend our
analysis to synthetic spectra obtained from numerical simulations and
compare the results to observations.
Title: IRIS observations of the transition region above sunspots:
oscillations and moving penumbral dots
Authors: Tian, Hui; DeLuca, Ed; Weber, Mark A.; McKillop, Sean;
Reeves, Kathy; Kleint, Lucia; Martinez-Sykora, Juan; De Pontieu,
Bart; Carlsson, Mats
Bibcode: 2014AAS...22431306T
Altcode:
NASA's IRIS mission is providing high-cadence and high-resolution
observations of the solar transition region and chromosphere. We
present results from IRIS observation of the transition region above
sunspots. The major findings can be summarized as following: (1) The C
II and Mg II line profiles are almost Gaussian in the sunspot umbra and
clearly exhibit a deep reversal at the line center in the plage region,
suggesting a greatly reduced opacity in the sunspot atmosphere. (2)
Strongly nonlinear sunspot oscillations can be clearly identified
in not only the slit jaw images of 2796Å, 1400Å and 1330Å, but
also in spectra of the bright Mg II, C II and Si IV lines. The Si
iv oscillation lags those of C ii and Mg ii by 3 and 12 seconds,
respectively. The temporal evolution of the line core is dominated by
the following behavior: a rapid excursion to the blue side, accompanied
by an intensity increase, followed by a linear decrease of the velocity
to the red side. The maximum intensity slightly lags the maximum blue
shift in Si iv , whereas the intensity enhancement slightly precedes the
maximum blue shift in Mg ii . We find a positive correlation between
the maximum velocity and deceleration. These results are consistent
with numerical simulations of upward propagating magneto-acoustic
shock waves. We also demonstrate that the strongly nonlinear line
width oscillation, reported both previously and here, is spurious. (3)
Many small-scale bright dots are present in the penumbral filaments and
light bridges in SJI 1330Å and 1400Å images obtained in high-cadence
observations. They are usually smaller than 1" and often just a couple
of pixels wide. Some bright dots show apparent movement with a speed of
20-60 km/s(either outward or inward). The lifetime of these penumbral
dots is mostly less than 1 min. The most obvious feature of the Si IV
profiles in the bright dots is the enhanced line width. Besides that,
the profile looks normal and no obvious fast flows are detected. The
bright dots in the light bridges even show oscillation patterns. It's
not clear whether these oscillations are triggered by the umbral
oscillations or not.
Title: Exploring the Components of IRIS Spectra: More Shift, Twist,
and Sway Than Shake, Rattle, and Roll
Authors: McIntosh, Scott W.; De Pontieu, Bart; Peter, Hardi
Bibcode: 2014AAS...22431304M
Altcode:
The beautifully rich spectra of the IRIS spacecraft offer an
unparalleled avenue to explore the mass and energy transport processes
which sustain the Sun's outer atmosphere. In this presentation we will
look in detail at the various components of the spectrographic data
and place them in context with Slit-Jaw imaging and EUV imaging from
SDO/AIA. We will show that the line profiles display many intriguing
features including the clear signatures of strong line-of-sight flows
(in all magnetized regions) that are almost always accompanied by
transverse and torsional motions at the finest resolvable scales. We
will demonstrate that many interesting relationships develop when
studying the spectra statistically. These relationships indicate IRIS's
ability to spectrally and temporally resolve the energetic processes
affecting the outer solar atmosphere.
Title: High-resolution Observations of the Shock Wave Behavior for
Sunspot Oscillations with the Interface Region Imaging Spectrograph
Authors: Tian, H.; DeLuca, E.; Reeves, K. K.; McKillop, S.; De Pontieu,
B.; Martínez-Sykora, J.; Carlsson, M.; Hansteen, V.; Kleint, L.;
Cheung, M.; Golub, L.; Saar, S.; Testa, P.; Weber, M.; Lemen, J.;
Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
Kankelborg, C.; Jaeggli, S.; McIntosh, S. W.
Bibcode: 2014ApJ...786..137T
Altcode: 2014arXiv1404.6291T
We present the first results of sunspot oscillations from observations
by the Interface Region Imaging Spectrograph. The strongly nonlinear
oscillation is identified in both the slit-jaw images and the
spectra of several emission lines formed in the transition region and
chromosphere. We first apply a single Gaussian fit to the profiles of
the Mg II 2796.35 Å, C II 1335.71 Å, and Si IV 1393.76 Å lines in the
sunspot. The intensity change is ~30%. The Doppler shift oscillation
reveals a sawtooth pattern with an amplitude of ~10 km s-1
in Si IV. The Si IV oscillation lags those of C II and Mg II by ~3 and
~12 s, respectively. The line width suddenly increases as the Doppler
shift changes from redshift to blueshift. However, we demonstrate
that this increase is caused by the superposition of two emission
components. We then perform detailed analysis of the line profiles at
a few selected locations on the slit. The temporal evolution of the
line core is dominated by the following behavior: a rapid excursion
to the blue side, accompanied by an intensity increase, followed by a
linear decrease of the velocity to the red side. The maximum intensity
slightly lags the maximum blueshift in Si IV, whereas the intensity
enhancement slightly precedes the maximum blueshift in Mg II. We find
a positive correlation between the maximum velocity and deceleration,
a result that is consistent with numerical simulations of upward
propagating magnetoacoustic shock waves.
Title: Sparkling Extreme-ultraviolet Bright Dots Observed with Hi-C
Authors: Régnier, S.; Alexander, C. E.; Walsh, R. W.; Winebarger,
A. R.; Cirtain, J.; Golub, L.; Korreck, K. E.; Mitchell, N.; Platt,
S.; Weber, M.; De Pontieu, B.; Title, A.; Kobayashi, K.; Kuzin, S.;
DeForest, C. E.
Bibcode: 2014ApJ...784..134R
Altcode: 2014arXiv1402.2457R
Observing the Sun at high time and spatial scales is a step toward
understanding the finest and fundamental scales of heating events
in the solar corona. The high-resolution coronal (Hi-C) instrument
has provided the highest spatial and temporal resolution images of
the solar corona in the EUV wavelength range to date. Hi-C observed
an active region on 2012 July 11 that exhibits several interesting
features in the EUV line at 193 Å. One of them is the existence
of short, small brightenings "sparkling" at the edge of the active
region; we call these EUV bright dots (EBDs). Individual EBDs have a
characteristic duration of 25 s with a characteristic length of 680
km. These brightenings are not fully resolved by the SDO/AIA instrument
at the same wavelength; however, they can be identified with respect
to the Hi-C location of the EBDs. In addition, EBDs are seen in other
chromospheric/coronal channels of SDO/AIA, which suggests a temperature
between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time
series, we define four different categories of EBDs: single peak,
double peak, long duration, and bursty. Based on a potential field
extrapolation from an SDO/HMI magnetogram, the EBDs appear at the
footpoints of large-scale, trans-equatorial coronal loops. The Hi-C
observations provide the first evidence of small-scale EUV heating
events at the base of these coronal loops, which have a free magnetic
energy of the order of 1026 erg.
Title: Diagnostics of coronal heating and mechanisms of energy
transport from IRIS and AIA observations of active region moss
Authors: Testa, Paola; Reale, Fabio; De Pontieu, Bart; Hansteen,
Viggo; Carlsson, Mats; Allred, Joel; Daw, Adrian
Bibcode: 2014cosp...40E3323T
Altcode:
The variability of emission of the "moss", i.e., the upper transition
region (TR) layer of high pressure loops in active regions provides
stringent constraints on the characteristics of heating events. The
Interface Region Imaging Spectrograph (IRIS), launched in June
2013, provides imaging and spectral observations at high spatial
(0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV
and NUV wavelengths, and together with the high spatial and temporal
resolution observations of SDO/AIA, can provide important insights
into the coronal heating mechanisms. We present here an analysis of
the temporal variability properties of moss regions at the footpoints
of hot active region core loops undergoing heating, as observed by IRIS
and AIA, covering emission from the corona to the transition region and
the chromosphere. We model the observations using dynamic loop models
(the Palermo-Harvard code, and RADYN, which also includes the effects of
non-thermal particles) and discuss the implications on energy transport
mechanisms (thermal conduction vs beams of non-thermal particles).
Title: Small scale variability in quiet sun and coronal holes
Authors: Martinez-Sykora, Juan; De Pontieu, Bart
Bibcode: 2014cosp...40E2020M
Altcode:
IRIS (Interface Region Imaging Spectrograph) was launched in 2013 and
revealed small-scale rapid brightening variations in large regions
in the quiet sun and coronal holes. Their lifetime is smaller than
a couple of minutes and the distance between them is of a granular
scale. We are going to present a statistical study of their observed
properties such as variability, lifetime, frequency using the images
of the SJI, and velocities, and temperatures using the spectral data
coming IRIS. The spectrograph reveals that most of this emission
comes from the continuum and their properties reveals that most of
these events result from acoustic shocks. We compare our observations
with synthetic observables (using forward modeling with the RH and
multi3D code) from recent numerical 3D radiative-MHD simulations using
the Bifrost code (Gudiksen et al. 2011). Similar rapid brightening
variability of chromospheric synthetic images has been also reproduced
in our simulations with mainly unipolar field. We will describe their
evolution, how they are driven and their thermodynamic properties from
the simulations.
Title: The Evolution of Transition Region Loops Using IRIS and AIA
Authors: Winebarger, Amy; De Pontieu, Bart
Bibcode: 2014cosp...40E3639W
Altcode:
Over the past 50 years, the model for the structure of the solar
transition region has evolved from a simple transition layer between
the cooler chromosphere to the hotter corona to a complex and diverse
regions that is dominated by complete loops that never reach coronal
temperatures. The IRIS slitjaw images show many complete transition
region loops. Several of the ``coronal’’ channels in the SDO AIA
instrument include contributions from weak transition region lines. In
this work, we combine slitjaw images from IRIS with these channels to
determine the evolution of the loops. We develop a simple model for
the temperature and density evolution of the loops that can explain
the simultaneous observations. Finally, we estimate the percentage of
AIA emission that originates in the transition region.
Title: Measuring energy flux of magneto-acoustic wave in the magnetic
elements by using IRIS
Authors: Kato, Yoshiaki; De Pontieu, Bart; Martinez-Sykora, Juan;
Hansteen, Viggo; Pereira, Tiago; Leenaarts, Jorritt; Carlsson, Mats
Bibcode: 2014cosp...40E1423K
Altcode:
NASA's Interface Region Imaging Spectrograph (IRIS) has opened a new
window to explore the chromospheric/coronal waves that potentially
energize the solar atmosphere. By using an imaging spectrograph covering
the Si IV and Mg II h&k lines as well as a slit-jaw imager centered
at Si IV and Mg II k onboard IRIS, we can determine the nature of
propagating magneto-acoustic waves just below and in the transition
region. In this study, we compute the vertically emergent intensity of
the Si IV and Mg II h&k lines from a time series of snapshots of
a magnetic element in a two-dimensional Radiative MHD simulation from
the Bifrost code. We investigate the synthetic line profiles to detect
the slow magneto-acoustic body wave (slow mode) which becomes a slow
shock at the lower chromosphere in the magnetic element. We find that
the Doppler shift of the line core gives the velocity amplitude of the
longitudinal magneto-acoustic body wave. The contribution function of
the line core indicates that the formation of Mg II h&k lines is
associated with the propagating shocks and therefore the time evolution
of the line core intensity represents the propagating shocks projected
on the optical surface. We will report on measurement of the energy
flux of slow modes in the magnetic elements by using IRIS observations.
Title: Coronal rain observed with IRIS
Authors: Antolin, Patrick; Katsukawa, Yukio; De Pontieu, Bart; Kleint,
Lucia; Pereira, Tiago
Bibcode: 2014cosp...40E.105A
Altcode:
New IRIS observations in upper chromospheric and TR lines show abundance
of coronal rain in active regions. The wide range of spectral lines in
which it is observed together with co-observations in cool chromospheric
lines with SOT and SST show clearly that coronal rain has a broad
multi-thermal character. This picture agrees well with the thermal
instability scenario in which the plasma cools down catastrophically
from coronal temperatures. A statistical analysis of the line widths
in the rain provides estimates of the non-thermal line broadening and
temperature. Mainly, we find Gaussian-like distributions of non-thermal
line broadening between 0 and 17 km/s with a peak at 7 km/s and a small
upper tail spanning up to 25 km/s. We also report on short-lived heating
events in umbrae and penumbrae at the end of thermally unstable coronal
loops. Bursts of high redshifts up to 200 km/s in TR lines are found,
accompanied by milder blue shifts. The bright dots sometimes display
coherent structure into a "string of pearls" with striking similarity
to flare ribbons, suggesting a strong heating correlation between the
loops. We discuss these results within the coronal rain scenario.
Title: IRIS observations of twist in the low solar atmosphere
Authors: De Pontieu, Bart; Pereira, Tiago; Rouppe van der Voort, Luc;
Skogsrud, Hakon
Bibcode: 2014cosp...40E.654D
Altcode:
The Interface Region Imaging Spectrograph (IRIS) small explorer
was launched in June 2013. IRIS's high-resolution (0.33 arcsec),
high-cadence (2s) images and spectra reveal a solar chromosphere and
transition region that is riddled with twist. This is evidenced by the
presence of ubiquitous torsional motions on very small (subarcsec)
spatial scales. These motions occur in active regions, quiet Sun
and coronal holes on a variety of structures such as spicules at
the limb, rapid-blue/red-shifted events (RBEs and RREs) as well as
low-lying loops. We use IRIS data and observations from the Swedish
Solar Telescope (SST) in La Palma, Spain to describe these motions
quantitatively and illustrate how such strong twisting motions are often
associated with significant and rapid heating to at least transition
region temperatures.
Title: IRIS observations of transition region unresolved fine
structure
Authors: Hansteen, Viggo; De Pontieu, Bart
Bibcode: 2014cosp...40E1152H
Altcode:
The Interface Region Imaging Spectrograph was launched on 28-June-2013
and has been obtaining high resolution images and spectra in the
far and near ultraviolet since 17-July-2013 covering temperatures
from the photosphere into the corona. We analyze the presence of a
multitude of short, relatively cool transition region loops as visible
at the solar limb in slit jaw images dominated by C II 1335 Angstrom
and Si IV 1402 Angstrom emission. We study the dynamical nature and
temperature evolution of these loops and investigate how they relate to
the so-called "unresolved fine structure" (UFS) that has been proposed
as a dominant source of transition region emission, but that has not
yet been directly observed to date. We will also discuss the physical
nature of this emission.
Title: Comparison between IRIS Data and Numerical Models
Authors: Carlsson, Mats; De Pontieu, Bart; Hansteen, Viggo; Pereira,
Tiago; Leenaarts, Jorritt
Bibcode: 2014cosp...40E.458C
Altcode:
The enigmatic chromosphere is the transition between the solar surface
and the eruptive outer solar atmosphere. The chromosphere harbours
and constrains the mass and energy loading processes that define the
heating of the corona, the acceleration and the composition of the solar
wind, and the energetics and triggering of solar outbursts (filament
eruptions, flares, coronal mass ejections). The chromosphere is arguably
the most difficult and least understood domain of solar physics. All
at once it represents the transition from optically thick to thin
radiation escape, from gas-pressure domination to magnetic-pressure
domination, from neutral to ionised state, from MHD to plasma physics,
and from near-equilibrium ("LTE") to non-equilibrium conditions. IRIS
provides a leap in observational capability of the chromospheric
plasma with an unprecedented combination of high spatial, temporal
and spectral resolution in lines with diagnostic information all the
way from the photosphere to the upper transition region. To fully
extract this information it is necessary to combine the observations
with numerical simulations that include a realistic description of the
complicated physics of the chromosphere. In this talk, we will present
such realistic simulations, spanning the solar atmosphere from the
convection zone to the corona, and synthetic observations calculated
from the simulations. These synthetic observations are compared with
observations from IRIS.
Title: Impact of the Partial Ionization in the solar atmosphere
using 2.5D Radiative MHD Simulations
Authors: Martinez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo;
Carlsson, Mats
Bibcode: 2014cosp...40E2019M
Altcode:
The chromosphere/transition region constitute the interface between
the solar surface and the corona and modulate the flow of mass and
energy into the upper atmosphere. IRIS was launched in 2013 to study the
chromosphere and transition region. The complexity of the chromosphere
is due to various regime changes that take place across it, like:
Hydrogen goes from predominantly neutral to predominantly ionized;
the plasma behavior changes from collisional to collision-less; it goes
from gas-pressure dominated to magnetically driven, etc. Consequently,
the interpretation of chromospheric observations in general and those
from IRIS, in particular, is a challenging task. It is thus crucial
to combine IRIS observations with advanced radiative-MHD numerical
modeling. Because the photosphere, chromosphere and transition region
are partially ionized, the interaction between ionized and neutral
particles has important consequences on the magneto-thermodynamics
of these regions. We implemented the effects of partial ionization
using generalized Ohm's law in the Bifrost code (Gudiksen et al. 2011)
which includes full MHD equations with non-grey and non-LTE radiative
transfer and thermal conduction along magnetic field lines. I will
describe the importance and impact of taking into account partial
ionization effects in the modeled radiative-MHD atmosphere, such as
chromospheric heating, photospheric magnetic field diffused into the
upper-chromosphere which expands into the upper atmosphere filling
the corona with mass, magnetic flux, energy and current, etc.
Title: Effects of flux emergence in the outer solar
atmosphere. Observational advances
Authors: Ortiz Carbonell, Ada; De Pontieu, Bart; Bellot Rubio, L. R.;
Hansteen, Viggo; Rouppe van der Voort, Luc; Carlsson, Mats
Bibcode: 2014cosp...40E2387O
Altcode:
We study granular sized magnetic flux emergence events that occur in
a flux emergence region in NOAA 11850 on September 25, 2013. During
that time, the first co-observing campaign between the Swedish 1 m
Solar Telescope and the IRIS spacecraft was carried out. Simultaneous
observations of the Halpha 656.28 nm and Ca II 854.2 nm chromospheric
lines, and the Fe I 630.25 nm photospheric line, were made with
the CRISP/SST spectropolarimeter reaching a spatial resolution of
0."14. At the same time, IRIS was performing a four-step dense raster
of the said emerging flux region, taking slit-jaw images at 133 (C II
transiti on region), 140 (Si IV, transition region), 279.6 (Mg II k,
core, upper chromosphere), and 283.2 nm (Mg II k, wing, photosphere),
obtaining thus the highest resolution images ever taken of the upper
chromosphere and transition region. The photospheric and chromospheric
properties of the emerging magnetic flux bubbles have been described
in detail in Ortiz et al. (2014). However, in the current work we are
able to follow such lower atmosphere observations of flux emergence
up to the transition region with unprecedented spatial and temporal
resolution. We describe the properties (size, time delays, lifetime,
velocities, temperature) of the observed signatures of flux emergence
in the transition region. We believe this may be an important mechanism
of transporting energy and magnetic flux to the upper layers of the
solar atmosphere, namely the transition region and corona, at least
in cases when active regions are formed by flux emerging through the
photosphere. * Ortiz et al. (2014) ApJ 781, 126
Title: Analysing spectroscopically the propagation of a CME from
its source on the disk to its impact as it propagates outwards
Authors: Harra, Louise K.; Doschek, G. A.; Matthews, Sarah A.; De
Pontieu, Bart; Long, David
Bibcode: 2014cosp...40E1159H
Altcode:
We analyse a complex coronal mass ejection observed by Hinode, SDO and
IRIS. SDO AIA shows that the eruption occurs between several active
regions with flaring occurring in all of them. Hinode EIS observed one
of the flaring active regions that shows a fast outwards propagation
which is related to the CME lifting off. The eruption is then observed
as it propagates away from the Sun, pushing the existing post-flare
loops downwards as it goes. Spectroscopic observations are made during
this time with IRIS measuring the impact that this CME front has as
it pushes the loops downwards. Strong enhancements in the cool Mg II
emission at these locations that show complex dynamics. We discuss
these new observations in context of CME models.
Title: Using IRIS to Study Our Star's Outer Atmosphere's Mass Cycle
Authors: McIntosh, Scott; De Pontieu, Bart
Bibcode: 2014cosp...40E2049M
Altcode:
Through the analysis of IRIS FUV, NUV, and Slit-Jaw Imaging we will
explore the mass cycle of the Sun's outer atmosphere in conjunction
with observations from the Solar Dynamics Observatory and Hinode
Missions. IRIS readily observes upflows, downflows, and a persistent
flux of upward propagating hydrodynamic and magneto-hydrodynamic
waves. We will characterize the statistical and temporal variability
in the components of the various sources in the puzzle.
Title: The Formation of IRIS Diagnostics. III. Near-ultraviolet
Spectra and Images
Authors: Pereira, T. M. D.; Leenaarts, J.; De Pontieu, B.; Carlsson,
M.; Uitenbroek, H.
Bibcode: 2013ApJ...778..143P
Altcode: 2013arXiv1310.1926P
The Mg II h&k lines are the prime chromospheric diagnostics
of NASA's Interface Region Imaging Spectrograph (IRIS). In the
previous papers of this series, we used a realistic three-dimensional
radiative magnetohydrodynamics model to calculate the h&k lines
in detail and investigated how their spectral features relate to the
underlying atmosphere. In this work, we employ the same approach to
investigate how the h&k diagnostics fare when taking into account
the finite resolution of IRIS and different noise levels. In addition,
we investigate the diagnostic potential of several other photospheric
lines and near-continuum regions present in the near-ultraviolet
(NUV) window of IRIS and study the formation of the NUV slit-jaw
images. We find that the instrumental resolution of IRIS has a small
effect on the quality of the h&k diagnostics; the relations
between the spectral features and atmospheric properties are mostly
unchanged. The peak separation is the most affected diagnostic, but
mainly due to limitations of the simulation. The effects of noise
start to be noticeable at a signal-to-noise ratio (S/N) of 20, but we
show that with noise filtering one can obtain reliable diagnostics at
least down to a S/N of 5. The many photospheric lines present in the
NUV window provide velocity information for at least eight distinct
photospheric heights. Using line-free regions in the h&k far wings,
we derive good estimates of photospheric temperature for at least
three heights. Both of these diagnostics, in particular the latter,
can be obtained even at S/Ns as low as 5.
Title: The Formation of IRIS Diagnostics. II. The Formation of the
Mg II h&k Lines in the Solar Atmosphere
Authors: Leenaarts, J.; Pereira, T. M. D.; Carlsson, M.; Uitenbroek,
H.; De Pontieu, B.
Bibcode: 2013ApJ...772...90L
Altcode: 2013arXiv1306.0671L
NASA's Interface Region Imaging Spectrograph (IRIS) small explorer
mission will study how the solar atmosphere is energized. IRIS
contains an imaging spectrograph that covers the Mg II h&k lines
as well as a slit-jaw imager centered at Mg II k. Understanding
the observations requires forward modeling of Mg II h&k line
formation from three-dimensional (3D) radiation-magnetohydrodynamic
(RMHD) models. This paper is the second in a series where we undertake
this modeling. We compute the vertically emergent h&k intensity
from a snapshot of a dynamic 3D RMHD model of the solar atmosphere,
and investigate which diagnostic information about the atmosphere is
contained in the synthetic line profiles. We find that the Doppler
shift of the central line depression correlates strongly with the
vertical velocity at optical depth unity, which is typically located
less than 200 km below the transition region (TR). By combining the
Doppler shifts of the h and k lines we can retrieve the sign of the
velocity gradient just below the TR. The intensity in the central line
depression is anti-correlated with the formation height, especially
in subfields of a few square Mm. This intensity could thus be used to
measure the spatial variation of the height of the TR. The intensity
in the line-core emission peaks correlates with the temperature at
its formation height, especially for strong emission peaks. The peaks
can thus be exploited as a temperature diagnostic. The wavelength
difference between the blue and red peaks provides a diagnostic of the
velocity gradients in the upper chromosphere. The intensity ratio of
the blue and red peaks correlates strongly with the average velocity
in the upper chromosphere. We conclude that the Mg II h&k lines
are excellent probes of the very upper chromosphere just below the
TR, a height regime that is impossible to probe with other spectral
lines. They also provide decent temperature and velocity diagnostics
of the middle chromosphere.
Title: The Formation of IRIS Diagnostics. I. A Quintessential
Model Atom of Mg II and General Formation Properties of the Mg II
h&k Lines
Authors: Leenaarts, J.; Pereira, T. M. D.; Carlsson, M.; Uitenbroek,
H.; De Pontieu, B.
Bibcode: 2013ApJ...772...89L
Altcode: 2013arXiv1306.0668L
NASA's Interface Region Imaging Spectrograph (IRIS) space mission will
study how the solar atmosphere is energized. IRIS contains an imaging
spectrograph that covers the Mg II h&k lines as well as a slit-jaw
imager centered at Mg II k. Understanding the observations will require
forward modeling of Mg II h&k line formation from three-dimensional
(3D) radiation-MHD models. This paper is the first in a series where we
undertake this forward modeling. We discuss the atomic physics pertinent
to h&k line formation, present a quintessential model atom that can
be used in radiative transfer computations, and discuss the effect of
partial redistribution (PRD) and 3D radiative transfer on the emergent
line profiles. We conclude that Mg II h&k can be modeled accurately
with a four-level plus continuum Mg II model atom. Ideally radiative
transfer computations should be done in 3D including PRD effects. In
practice this is currently not possible. A reasonable compromise is to
use one-dimensional PRD computations to model the line profile up to
and including the central emission peaks, and use 3D transfer assuming
complete redistribution to model the central depression.
Title: Detecting Nanoflare Heating Events in Subarcsecond Inter-moss
Loops Using Hi-C
Authors: Winebarger, Amy R.; Walsh, Robert W.; Moore, Ronald;
De Pontieu, Bart; Hansteen, Viggo; Cirtain, Jonathan; Golub, Leon;
Kobayashi, Ken; Korreck, Kelly; DeForest, Craig; Weber, Mark; Title,
Alan; Kuzin, Sergey
Bibcode: 2013ApJ...771...21W
Altcode:
The High-resolution Coronal Imager (Hi-C) flew aboard a NASA sounding
rocket on 2012 July 11 and captured roughly 345 s of high-spatial and
temporal resolution images of the solar corona in a narrowband 193 Å
channel. In this paper, we analyze a set of rapidly evolving loops that
appear in an inter-moss region. We select six loops that both appear in
and fade out of the Hi-C images during the short flight. From the Hi-C
data, we determine the size and lifetimes of the loops and characterize
whether these loops appear simultaneously along their length or
first appear at one footpoint before appearing at the other. Using
co-aligned, co-temporal data from multiple channels of the Atmospheric
Imaging Assembly on the Solar Dynamics Observatory, we determine the
temperature and density of the loops. We find the loops consist of
cool (~105 K), dense (~1010 cm-3)
plasma. Their required thermal energy and their observed evolution
suggest they result from impulsive heating similar in magnitude to
nanoflares. Comparisons with advanced numerical simulations indicate
that such dense, cold and short-lived loops are a natural consequence
of impulsive magnetic energy release by reconnection of braided magnetic
field at low heights in the solar atmosphere.
Title: Chromospheric Lyman Alpha SpectroPolarimeter: CLASP
Authors: Kobayashi, Ken; Kano, R.; Trujillo Bueno, J.; Winebarger,
A. R.; Cirtain, J. W.; Bando, T.; De Pontieu, B.; Ishikawa, R.;
Katsukawa, Y.; Kubo, M.; Narukage, N.; Sakao, T.; Tsuneta, S.;
Auchère, F.; Asensio Ramos, A.; Belluzzi, L.; Carlsson, M.; Casini,
R.; Hara, H.; Ichimoto, K.; Manso Sainz, R.; Shimizu, T.; Stepan,
J.; Suematsu, Y.; Holloway, T.
Bibcode: 2013SPD....44..142K
Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a VUV
spectropolarimeter optimized for measuring the linear polarization of
the Lyman-alpha line (121.6 nm). The Lyman-alpha line is predicted to
show linear polarization caused by atomic scattering in the chromosphere
and modified by the magnetic field through the Hanle effect. The
Hanle effect is sensitive to weaker magnetic fields than Zeeman
effect, and is not canceled by opposing fields, making it sensitive
to tangled or unresolved magnetic field structures. These factors make
the Hanle effect a valuable tool for probing the magnetic field in the
chromosphere above the quiet sun. To meet this goal, CLASP is designed
to measure linear polarization with 0.1% polarization sensitivity
at 0.01 nm spectral resolution and 10" spatial resolution. CLASP is
scheduled to be launched in 2015.
Title: Optimization of Curvilinear Tracing Applied to Solar Physics
and Biophysics
Authors: Aschwanden, Markus; De Pontieu, Bart; Katrukha, Eugene
Bibcode: 2013Entrp..15.3007A
Altcode: 2013arXiv1307.5046A
We developed an automated pattern recognition code that is particularly
well suited to extract one-dimensional curvi-linear features from
two-dimensional digital images. A former version of this {\sl Oriented
Coronal CUrved Loop Tracing (OCCULT)} code was applied to spacecraft
images of magnetic loops in the solar corona, recorded with the NASA
spacecraft {\sl Transition Region And Coronal Explorer (TRACE)} in
extreme ultra-violet wavelengths. Here we apply an advanced version of
this code ({\sl OCCULT-2}) also to similar images from the {\sl Solar
Dynamics Observatory (SDO)}, to chromospheric H-$\alpha$ images obtained
with the {\sl Swedish Solar Telescope (SST)}, and to microscopy images
of microtubule filaments in live cells in biophysics. We provide a full
analytical description of the code, optimize the control parameters,
and compare the automated tracing with visual/manual methods. The
traced structures differ by up to 16 orders of magnitude in size,
which demonstrates the universality of the tracing algorithm.
Title: A Detailed Comparison between the Observed and Synthesized
Properties of a Simulated Type II Spicule
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Leenaarts, Jorrit;
Pereira, Tiago M. D.; Carlsson, Mats; Hansteen, Viggo; Stern, Julie
V.; Tian, Hui; McIntosh, Scott W.; Rouppe van der Voort, Luc
Bibcode: 2013ApJ...771...66M
Altcode: 2013arXiv1305.2397M
We have performed a three-dimensional radiative MHD simulation of the
solar atmosphere. This simulation shows a jet-like feature that shows
similarities to the type II spicules observed for the first time with
Hinode's Solar Optical Telescope. Rapid blueshifted events (RBEs) on the
solar disk are associated with these spicules. Observational results
suggest they may contribute significantly in supplying the corona
with hot plasma. We perform a detailed comparison of the properties
of the simulated jet with those of type II spicules (observed with
Hinode) and RBEs (with ground-based instruments). We analyze a wide
variety of synthetic emission and absorption lines from the simulations
including chromospheric (Ca II 8542 Å, Ca II H, and Hα) to transition
region and coronal temperatures (10,000 K to several million K). We
compare their synthetic intensities, line profiles, Doppler shifts,
line widths, and asymmetries with observations from Hinode/SOT and
EIS, SOHO/SUMER, the Swedish 1 m Solar Telescope, and SDO/AIA. Many
properties of the synthetic observables resemble the observations,
and we describe in detail the physical processes that lead to these
observables. Detailed analysis of the synthetic observables provides
insight into how observations should be analyzed to derive information
about physical variables in such a dynamic event. For example, we
find that line-of-sight superposition in the optically thin atmosphere
requires the combination of Doppler shifts and spectral line asymmetry
to determine the velocity in the jet. In our simulated type II spicule,
the lifetime of the asymmetry of the transition region lines is shorter
than that of the coronal lines. Other properties differ from the
observations, especially in the chromospheric lines. The mass density
of the part of the spicule with a chromospheric temperature is too low
to produce significant opacity in chromospheric lines. The synthetic
Ca II 8542 Å and Hα profiles therefore do not show signal resembling
RBEs. These and other discrepancies are described in detail, and we
discuss which mechanisms and physical processes may need to be included
in the MHD simulations to mimic the thermodynamic processes of the
chromosphere and corona, in particular to reproduce type II spicules.
Title: Status of RAISE, the Rapid Acquisition Imaging Spectrograph
Experiment
Authors: Laurent, Glenn T.; Hassler, D. M.; DeForest, C.; Ayres,
T. R.; Davis, M.; De Pontieu, B.; Schuehle, U.; Warren, H.
Bibcode: 2013SPD....44..145L
Altcode:
The Rapid Acquisition Imaging Spectrograph Experiment (RAISE) sounding
rocket payload is a high speed scanning-slit imaging spectrograph
designed to observe the dynamics and heating of the solar chromosphere
and corona on time scales as short as 100 ms, with 1 arcsec spatial
resolution and a velocity sensitivity of 1-2 km/s. The instrument is
based on a new class of UV/EUV imaging spectrometers that use only
two reflections to provide quasi-stigmatic performance simultaneously
over multiple wavelengths and spatial fields. The design uses an
off-axis parabolic telescope mirror to form a real image of the sun
on the spectrometer entrance aperture. A slit then selects a portion
of the solar image, passing its light onto a near-normal incidence
toroidal grating, which re-images the spectrally dispersed radiation
onto two array detectors. Two full spectral passbands over the same
one-dimensional spatial field are recorded simultaneously with no
scanning of the detectors or grating. The two different spectral
bands (1st-order 1205-1243Å and 1526-1564Å) are imaged onto two
intensified Active Pixel Sensor (APS) detectors whose focal planes are
individually adjusted for optimized performance. The telescope and
grating are coated with B4C to enhance short wavelength (2nd order)
reflectance, enabling the instrument to record the brightest lines
between 602-622Å and 761-780Å at the same time. RAISE reads out the
full field of both detectors at 5-10 Hz, allowing us to record over
1,500 complete spectral observations in a single 5-minute rocket flight,
opening up a new domain of high time resolution spectral imaging and
spectroscopy. We present an overview of the project, a summary of the
maiden flight results, and an update on instrument status.Abstract
(2,250 Maximum Characters): The Rapid Acquisition Imaging Spectrograph
Experiment (RAISE) sounding rocket payload is a high speed scanning-slit
imaging spectrograph designed to observe the dynamics and heating of the
solar chromosphere and corona on time scales as short as 100 ms, with 1
arcsec spatial resolution and a velocity sensitivity of 1-2 km/s. The
instrument is based on a new class of UV/EUV imaging spectrometers
that use only two reflections to provide quasi-stigmatic performance
simultaneously over multiple wavelengths and spatial fields. The design
uses an off-axis parabolic telescope mirror to form a real image of
the sun on the spectrometer entrance aperture. A slit then selects
a portion of the solar image, passing its light onto a near-normal
incidence toroidal grating, which re-images the spectrally dispersed
radiation onto two array detectors. Two full spectral passbands over
the same one-dimensional spatial field are recorded simultaneously with
no scanning of the detectors or grating. The two different spectral
bands (1st-order 1205-1243Å and 1526-1564Å) are imaged onto two
intensified Active Pixel Sensor (APS) detectors whose focal planes are
individually adjusted for optimized performance. The telescope and
grating are coated with B4C to enhance short wavelength (2nd order)
reflectance, enabling the instrument to record the brightest lines
between 602-622Å and 761-780Å at the same time. RAISE reads out the
full field of both detectors at 5-10 Hz, allowing us to record over
1,500 complete spectral observations in a single 5-minute rocket flight,
opening up a new domain of high time resolution spectral imaging and
spectroscopy. We present an overview of the project, a summary of the
maiden flight results, and an update on instrument status.
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, Bart; Title, A. M.; Lemen, J.; Wuelser, J.;
Tarbell, T. D.; Schrijver, C. J.; Golub, L.; Kankelborg, C.; Carlsson,
M.; Hansteen, V. H.; Worden, S.; IRIS Team
Bibcode: 2013SPD....44...03D
Altcode:
The solar chromosphere and transition region (TR) form a highly
structured and dynamic interface region between the photosphere and
the corona. This region not only acts as the conduit of all mass and
energy feeding into the corona and solar wind, it also requires an
order of magnitude more energy to heat than the corona. Nevertheless,
the chromosphere remains poorly understood, because of the complexity
of the required observational and analytical tools: the interface
region is highly complex with transitions from optically thick to
optically thin radiation, from pressure to magnetic field domination,
and large density and temperature contrasts on small spatial scales. The
Interface Region Imaging Spectrograph (IRIS) was selected for a NASA
SMEX mission in 2009 and is scheduled to launch on 26-June-2013 (with
first light scheduled for mid July). IRIS addresses critical questions:
(1) Which types of non-thermal energy dominate in the chromosphere and
beyond? (2) How does the chromosphere regulate mass and energy supply
to the corona and heliosphere? (3) How do magnetic flux and matter
rise through the lower atmosphere, and what role does flux emergence
play in flares and mass ejections? These questions are addressed with
a high-resolution near and far UV imaging spectrometer sensitive to
emission from plasma at temperatures between 5,000 K and 10 MK. IRIS
has a field-of-view of 120 arcsec, a spatial resolution of 0.4 arcsec,
and velocity resolution of 0.5 km/s. The IRIS investigation includes
a strong numerical modeling component based on advanced radiative MHD
codes to facilitate interpretation of observations. We describe the
IRIS instrumentation and numerical modeling, and present the plans for
observations, calibration and data distribution. We will highlight some
of the issues that IRIS observations can help resolve. More information
can be found at http://iris.lmsal.com
Title: Observing Coronal Nanoflares in Active Region Moss
Authors: Testa, Paola; De Pontieu, Bart; Martínez-Sykora, Juan;
DeLuca, Ed; Hansteen, Viggo; Cirtain, Jonathan; Winebarger, Amy;
Golub, Leon; Kobayashi, Ken; Korreck, Kelly; Kuzin, Sergey; Walsh,
Robert; DeForest, Craig; Title, Alan; Weber, Mark
Bibcode: 2013ApJ...770L...1T
Altcode: 2013arXiv1305.1687T
The High-resolution Coronal Imager (Hi-C) has provided Fe XII 193Å
images of the upper transition region moss at an unprecedented spatial
(~0.''3-0.''4) and temporal (5.5 s) resolution. The Hi-C observations
show in some moss regions variability on timescales down to ~15 s,
significantly shorter than the minute-scale variability typically found
in previous observations of moss, therefore challenging the conclusion
of moss being heated in a mostly steady manner. These rapid variability
moss regions are located at the footpoints of bright hot coronal
loops observed by the Solar Dynamics Observatory/Atmospheric Imaging
Assembly in the 94 Å channel, and by the Hinode/X-Ray Telescope. The
configuration of these loops is highly dynamic, and suggestive of
slipping reconnection. We interpret these events as signatures of
heating events associated with reconnection occurring in the overlying
hot coronal loops, i.e., coronal nanoflares. We estimate the order
of magnitude of the energy in these events to be of at least a few
1023 erg, also supporting the nanoflare scenario. These
Hi-C observations suggest that future observations at comparable
high spatial and temporal resolution, with more extensive temperature
coverage, are required to determine the exact characteristics of the
heating mechanism(s).
Title: The Cycling of Material between the Solar Corona and
Chromosphere
Authors: Guerreiro, N.; Hansteen, Viggo; De Pontieu, B.
Bibcode: 2013ApJ...769...47G
Altcode:
Observations of transition region emission lines reveal the presence
of redshifts in lines formed from the top of the chromosphere up
to temperatures of about 2.5 × 105 K and blueshifts for
temperatures above that. However, it is doubtful that the apparent large
downward flows in the lower transition region represents an emptying of
the corona, so some mechanism must be responsible for maintaining the
mass balance between the corona and the lower atmospheric layers. We use
a three-dimensional magnetohydrodynamics code to study the cycling of
mass between the corona, transition region, and chromosphere by adding
a tracer fluid to the simulation in various temperature intervals in the
transition region. We find that most of the material seen in transition
region emission lines formed at temperatures below 3 × 105 K
is material that has been rapidly heated from chromospheric temperatures
and thereafter is pushed down as it cools. This implies that the bulk
of transition region material resides in small loops. In these loops,
the density is high and radiative cooling is efficient.
Title: Interplay of Three Kinds of Motion in the Disk Counterpart
of Type II Spicules: Upflow, Transversal, and Torsional Motions
Authors: Sekse, D. H.; Rouppe van der Voort, L.; De Pontieu, B.;
Scullion, E.
Bibcode: 2013ApJ...769...44S
Altcode: 2013arXiv1304.2304S
Recently, it was shown that the complex dynamical behavior of spicules
has to be interpreted as the result of simultaneous action of three
kinds of motion: (1) field aligned flows, (2) swaying motions, and
(3) torsional motions. We use high-quality observations from the
CRisp Imaging SpectroPolarimeter at the Swedish 1-m Solar Telescope
to investigate signs of these different kinetic modes in spicules on
the disk. Earlier, rapid blue-shifted excursions (RBEs), short-lived
absorption features in the blue wing of chromospheric spectral lines,
were identified as the disk counterpart of type II spicules. Here we
report the existence of similar absorption features in the red wing of
the Ca II 8542 and Hα lines: rapid redshifted excursions (RREs). RREs
are found over the whole solar disk and are located in the same regions
as RBEs: in the vicinity of magnetic field concentrations. RREs have
similar characteristics as RBEs: they have similar lengths, widths,
lifetimes, and average Doppler velocity. The striking similarity
of RREs to RBEs implies that RREs are a manifestation of the same
physical phenomenon and that spicules harbor motions that can result
in a net redshift when observed on-disk. We find that RREs are less
abundant than RBEs: the RRE/RBE detection count ratio is about 0.52
at disk center and 0.74 near the limb. We interpret the higher number
of RBEs and the decreased imbalance toward the limb as an indication
that field-aligned upflows have a significant contribution to the
net Dopplershift of the structure. Most RREs and RBEs are observed in
isolation, but we find many examples of parallel and touching RRE/RBE
pairs which appear to be part of the same spicule. We interpret the
existence of these RRE/RBE pairs and the observation that many RREs
and RBEs have varying Dopplershift along their width as signs that
torsional motion is an important characteristic of spicules. The fact
that most RBEs and RREs are observed in isolation agrees with the idea
that transversal swaying motion is another important kinetic mode. We
find examples of transitions from RRE to RBE and vice versa. These
transitions sometimes appear to propagate along the structure with
speeds between 18 and 108 km s-1 and can be interpreted as
the sign of a transverse (Alfvénic) wave.
Title: Heating of the Magnetic Chromosphere: Observational Constraints
from Ca II λ8542 Spectra
Authors: de la Cruz Rodríguez, J.; De Pontieu, B.; Carlsson, M.;
Rouppe van der Voort, L. H. M.
Bibcode: 2013ApJ...764L..11D
Altcode: 2013arXiv1301.3141D
The heating of the Sun's chromosphere remains poorly understood. While
progress has been made on understanding what drives the quiet-Sun
internetwork chromosphere, chromospheric heating in strong magnetic
field regions continues to present a difficult challenge, mostly
because of a lack of observational constraints. We use high-resolution
spectropolarimetric data from the Swedish 1 m Solar Telescope to
identify the location and spatio-temporal properties of heating in
the magnetic chromosphere. In particular, we report the existence of
raised-core spectral line profiles in the Ca II λ8542 line. These
profiles are characterized by the absence of an absorption line
core, showing a quasi-flat profile between λ ≈ ±0.5 Å, and are
abundant close to magnetic bright points and plage. Comparison with
three-dimensional MHD simulations indicates that such profiles occur
when the line of sight goes through an "elevated temperature canopy"
associated with the expansion with height of the magnetic field of
flux concentrations. This temperature canopy in the simulations is
caused by ohmic dissipation where there are strong magnetic field
gradients. The raised-core profiles are thus indicators of locations
of increased chromospheric heating. We characterize the location and
temporal and spatial properties of such profiles in our observations,
thus providing much stricter constraints on theoretical models of
chromospheric heating mechanisms than before.
Title: On the Temporal Evolution of the Disk Counterpart of Type II
Spicules in the Quiet Sun
Authors: Sekse, D. H.; Rouppe van der Voort, L.; De Pontieu, B.
Bibcode: 2013ApJ...764..164S
Altcode: 2012arXiv1212.4988S
The newly established type II spicule has been speculated to provide
enough hot plasma to play an important role in the mass loading
and heating of the solar corona. With the identification of rapid
blueshifted excursions (RBEs) as the on-disk counterpart of type II
spicules we have analyzed three different high-quality timeseries
with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish
Solar Telescope on La Palma and subjected to an automated detection
routine to detect a large number of RBEs for statistical purposes. Our
observations are of a quiet-Sun region at disk center and we find
lower Doppler velocities, 15-40 km s-1, and Doppler widths,
2-15 km s-1, of RBEs than in earlier coronal hole studies,
30-50 km s-1 and 7-23 km s-1, respectively. In
addition, we examine the spatial dependence of Doppler velocities and
widths along the RBE axis and conclude that there is no clear trend to
this over the field of view or in individual RBEs in the quiet Sun at
disk center. These differences with previous coronal hole studies are
attributed to the more varying magnetic field configuration in quiet-Sun
conditions. Using an extremely high-cadence data set has allowed us
to improve greatly on the determination of lifetimes of RBEs, which we
find to range from 5 to 60 s with an average lifetime of 30 s, as well
as the transverse motions in RBEs, with transverse velocities up to
55 km s-1 and averaging 12 km s-1. Furthermore,
our measurements of the recurrence rates of RBEs provide important
new constraints on coronal heating by spicules. We also see many
examples of a sinusoidal wave pattern in the transverse motion of
RBEs with periods averaging 54 s and amplitudes from 21.5 to 129 km
which agrees well with previous studies of wave motion in spicules at
the limb. We interpret the appearance of RBEs over their full length
within a few seconds as the result of a combination of three kinds
of motions as is earlier reported for spicules. Finally, we look at
the temporal connection between Hα and Ca II 8542 RBEs and find that
Ca II 8542 RBEs in addition to being located closer to the footpoint
also appear before the Hα RBEs. This connection between Ca II 8542
and Hα supports the idea that heating is occurring in spicules and
contributes more weight to the prominence of spicules as a source for
heating and mass loading of the corona.
Title: The Effects of Spatio-temporal Resolution on Deduced Spicule
Properties
Authors: Pereira, Tiago M. D.; De Pontieu, Bart; Carlsson, Mats
Bibcode: 2013ApJ...764...69P
Altcode: 2012arXiv1212.2969P
Spicules have been observed on the Sun for more than a century,
typically in chromospheric lines such as Hα and Ca II H. Recent
work has shown that so-called "type II" spicules may have a role in
providing mass to the corona and the solar wind. In chromospheric
filtergrams these spicules are not seen to fall back down, and they
are shorter lived and more dynamic than the spicules that have been
classically reported in ground-based observations. Observations of
type II spicules with Hinode show fundamentally different properties
from what was previously measured. In earlier work we showed that these
dynamic type II spicules are the most common type, a view that was not
properly identified by early observations. The aim of this work is to
investigate the effects of spatio-temporal resolution in the classical
spicule measurements. Making use of Hinode data degraded to match
the observing conditions of older ground-based studies, we measure
the properties of spicules with a semi-automated algorithm. These
results are then compared to measurements using the original Hinode
data. We find that degrading the data has a significant effect on the
measured properties of spicules. Most importantly, the results from
the degraded data agree well with older studies (e.g., mean spicule
duration more than 5 minutes, and upward apparent velocities of about
25 km s-1). These results illustrate how the combination
of spicule superposition, low spatial resolution and cadence affect
the measured properties of spicules, and that previous measurements
can be misleading.
Title: Energy release in the solar corona from spatially resolved
magnetic braids
Authors: Cirtain, J. W.; Golub, L.; Winebarger, A. R.; de Pontieu,
B.; Kobayashi, K.; Moore, R. L.; Walsh, R. W.; Korreck, K. E.; Weber,
M.; McCauley, P.; Title, A.; Kuzin, S.; Deforest, C. E.
Bibcode: 2013Natur.493..501C
Altcode:
It is now apparent that there are at least two heating mechanisms
in the Sun's outer atmosphere, or corona. Wave heating may be the
prevalent mechanism in quiet solar periods and may contribute to
heating the corona to 1,500,000 K (refs 1, 2, 3). The active corona
needs additional heating to reach 2,000,000-4,000,000 K this heat
has been theoretically proposed to come from the reconnection and
unravelling of magnetic `braids'. Evidence favouring that process has
been inferred, but has not been generally accepted because observations
are sparse and, in general, the braided magnetic strands that are
thought to have an angular width of about 0.2 arc seconds have not been
resolved. Fine-scale braiding has been seen in the chromosphere but not,
until now, in the corona. Here we report observations, at a resolution
of 0.2 arc seconds, of magnetic braids in a coronal active region that
are reconnecting, relaxing and dissipating sufficient energy to heat
the structures to about 4,000,000 K. Although our 5-minute observations
cannot unambiguously identify the field reconnection and subsequent
relaxation as the dominant heating mechanism throughout active regions,
the energy available from the observed field relaxation in our example
is ample for the observed heating.
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Wuelser, J.;
Tarbell, T. D.; Schrijver, C.; Golub, L.; Kankelborg, C. C.; Hansteen,
V. H.; Carlsson, M.
Bibcode: 2012AGUFMSH33D2256D
Altcode:
The solar chromosphere and transition region (TR) form a highly
structured and dynamic interface region between the photosphere and
the corona. This region not only acts as the conduit of all mass and
energy feeding into the corona and solar wind, it also requires an
order of magnitude more energy to heat than the corona. Nevertheless,
the chromosphere remains poorly understood, because of the complexity
of the required observational and analytical tools: the interface
region is highly complex with transitions from optically thick to
optically thin radiation, from pressure to magnetic field domination,
and large density and temperature contrasts on small spatial scales. The
Interface Region Imaging Spectrograph (IRIS) was selected for a NASA
SMEX mission in 2009 and is scheduled to launch in early 2013. IRIS
addresses critical questions: (1) Which types of non-thermal energy
dominate in the chromosphere and beyond? (2) How does the chromosphere
regulate mass and energy supply to the corona and heliosphere? (3)
How do magnetic flux and matter rise through the lower atmosphere, and
what role does flux emergence play in flares and mass ejections? These
questions are addressed with a high-resolution near and far UV imaging
spectrometer sensitive to emission from plasma at temperatures between
5,000 K and 10 MK. IRIS has a field-of-view of 120 arcsec, a spatial
resolution of 0.4 arcsec, and velocity resolution of 0.5 km/s. The
IRIS investigation includes a strong numerical modeling component
based on advanced radiative MHD codes to facilitate interpretation of
observations. We will describe the IRIS instrumentation and numerical
modeling, and present the status of the IRIS observatory development. We
will highlight some of the issues that IRIS observations can help
resolve.
Title: Loop Evolution Observed with AIA and Hi-C
Authors: Mulu-Moore, F.; Winebarger, A. R.; Cirtain, J. W.; Kobayashi,
K.; Korreck, K. E.; Golub, L.; Kuzin, S.; Walsh, R. W.; DeForest,
C.; De Pontieu, B.; Title, A. M.; Weber, M.
Bibcode: 2012AGUFMSH33A2225M
Altcode:
In the past decade, the evolution of EUV loops has been used to infer
the loop substructure. With the recent launch of High Resolution Coronal
Imager (Hi-C), this inference can be validated. In this presentation we
discuss the first results of loop analysis comparing AIA and Hi-C data.
Title: The Fundamental Structure of Coronal Loops
Authors: Winebarger, A. R.; Warren, H. P.; Cirtain, J. W.; Kobayashi,
K.; Korreck, K. E.; Golub, L.; Kuzin, S.; Walsh, R. W.; DeForest,
C.; De Pontieu, B.; Title, A. M.; Weber, M.
Bibcode: 2012AGUFMSH31B..06W
Altcode:
During the past ten years, solar physicists have attempted to infer the
coronal heating mechanism by comparing observations of coronal loops
with hydrodynamic model predictions. These comparisons often used
the addition of sub-resolution strands to explain the observed loop
properties. On July 11, 2012, the High Resolution Coronal Imager (Hi-C)
was launched on a sounding rocket. This instrument obtained images of
the solar corona was 0.2-0.3'' resolution in a narrowband EUV filter
centered around 193 Angstroms. In this talk, we will compare these
high resolution images to simultaneous density measurements obtained
with the Extreme Ultraviolet Imaging Spectrograph (EIS) on Hinode to
determine whether the structures observed with Hi-C are resolved.
Title: Estimating the "Dark" Energy Content of the Solar Corona
Authors: McIntosh, Scott W.; De Pontieu, Bart
Bibcode: 2012ApJ...761..138M
Altcode: 2012arXiv1211.4178M
The discovery of ubiquitous low-frequency (3-5 mHz) Alfvénic waves
in the solar chromosphere (with Hinode/Solar Optical Telescope)
and corona (with CoMP and SDO) has provided some insight into the
non-thermal energy content of the outer solar atmosphere. However,
many questions remain about the true magnitude of the energy flux
carried by these waves. Here we explore the apparent discrepancy in
the resolved coronal Alfvénic wave amplitude (~0.5 km s-1)
measured by the Coronal Multi-channel Polarimeter (CoMP) compared to
those of the Hinode and the Solar Dynamics Observatory (SDO) near the
limb (~20 km s-1). We use a blend of observational data and
a simple forward model of Alfvénic wave propagation to resolve this
discrepancy and determine the Alfvénic wave energy content of the
corona. Our results indicate that enormous line-of-sight superposition
within the coarse spatio-temporal sampling of CoMP hides the strong
wave flux observed by Hinode and SDO and leads to the large non-thermal
line broadening observed. While this scenario has been assumed in
the past, our observations with CoMP of a strong correlation between
the non-thermal line broadening with the low-amplitude, low-frequency
Alfvénic waves observed in the corona provide the first direct evidence
of a wave-related non-thermal line broadening. By reconciling the
diverse measurements of Alfvénic waves, we establish large coronal
non-thermal line widths as direct signatures of the hidden, or "dark,"
energy content in the corona and provide preliminary constraints on
the energy content of the wave motions observed.
Title: Quantifying Spicules
Authors: Pereira, Tiago M. D.; De Pontieu, Bart; Carlsson, Mats
Bibcode: 2012ApJ...759...18P
Altcode: 2012arXiv1208.4404P
Understanding the dynamic solar chromosphere is fundamental in solar
physics. Spicules are an important feature of the chromosphere,
connecting the photosphere to the corona, potentially mediating
the transfer of energy and mass. The aim of this work is to study
the properties of spicules over different regions of the Sun. Our
goal is to investigate if there is more than one type of spicule,
and how spicules behave in the quiet Sun, coronal holes, and active
regions. We make use of high cadence and high spatial resolution Ca
II H observations taken by Hinode/Solar Optical Telescope. Making use
of a semi-automated detection algorithm, we self-consistently track
and measure the properties of 519 spicules over different regions. We
find clear evidence of two types of spicules. Type I spicules show
a rise and fall and have typical lifetimes of 150-400 s and maximum
ascending velocities of 15-40 km s-1, while type II spicules
have shorter lifetimes of 50-150 s, faster velocities of 30-110 km
s-1, and are not seen to fall down, but rather fade at
around their maximum length. Type II spicules are the most common, seen
in the quiet Sun and coronal holes. Type I spicules are seen mostly
in active regions. There are regional differences between quiet-Sun
and coronal hole spicules, likely attributable to the different field
configurations. The properties of type II spicules are consistent with
published results of rapid blueshifted events (RBEs), supporting the
hypothesis that RBEs are their disk counterparts. For type I spicules
we find the relations between their properties to be consistent with
a magnetoacoustic shock wave driver, and with dynamic fibrils as their
disk counterpart. The driver of type II spicules remains unclear from
limb observations.
Title: Persistent Doppler Shift Oscillations Observed with Hinode/EIS
in the Solar Corona: Spectroscopic Signatures of Alfvénic Waves
and Recurring Upflows
Authors: Tian, Hui; McIntosh, Scott W.; Wang, Tongjiang; Ofman, Leon;
De Pontieu, Bart; Innes, Davina E.; Peter, Hardi
Bibcode: 2012ApJ...759..144T
Altcode: 2012arXiv1209.5286T
Using data obtained by the EUV Imaging Spectrometer on board Hinode,
we have performed a survey of obvious and persistent (without
significant damping) Doppler shift oscillations in the corona. We
have found mainly two types of oscillations from February to April
in 2007. One type is found at loop footpoint regions, with a dominant
period around 10 minutes. They are characterized by coherent behavior
of all line parameters (line intensity, Doppler shift, line width,
and profile asymmetry), and apparent blueshift and blueward asymmetry
throughout almost the entire duration. Such oscillations are likely to
be signatures of quasi-periodic upflows (small-scale jets, or coronal
counterpart of type-II spicules), which may play an important role
in the supply of mass and energy to the hot corona. The other type of
oscillation is usually associated with the upper part of loops. They are
most clearly seen in the Doppler shift of coronal lines with formation
temperatures between one and two million degrees. The global wavelets
of these oscillations usually peak sharply around a period in the range
of three to six minutes. No obvious profile asymmetry is found and
the variation of the line width is typically very small. The intensity
variation is often less than 2%. These oscillations are more likely to
be signatures of kink/Alfvén waves rather than flows. In a few cases,
there seems to be a π/2 phase shift between the intensity and Doppler
shift oscillations, which may suggest the presence of slow-mode standing
waves according to wave theories. However, we demonstrate that such a
phase shift could also be produced by loops moving into and out of a
spatial pixel as a result of Alfvénic oscillations. In this scenario,
the intensity oscillations associated with Alfvénic waves are caused by
loop displacement rather than density change. These coronal waves may be
used to investigate properties of the coronal plasma and magnetic field.
Title: Investigating the Reliability of Coronal Emission Measure
Distribution Diagnostics using Three-dimensional Radiative
Magnetohydrodynamic Simulations
Authors: Testa, Paola; De Pontieu, Bart; Martínez-Sykora, Juan;
Hansteen, Viggo; Carlsson, Mats
Bibcode: 2012ApJ...758...54T
Altcode: 2012arXiv1208.4286T
Determining the temperature distribution of coronal plasmas can provide
stringent constraints on coronal heating. Current observations with
the Extreme ultraviolet Imaging Spectrograph (EIS) on board Hinode
and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory provide diagnostics of the emission measure distribution
(EMD) of the coronal plasma. Here we test the reliability of temperature
diagnostics using three-dimensional radiative MHD simulations. We
produce synthetic observables from the models and apply the Monte
Carlo Markov chain EMD diagnostic. By comparing the derived EMDs with
the "true" distributions from the model, we assess the limitations
of the diagnostics as a function of the plasma parameters and the
signal-to-noise ratio of the data. We find that EMDs derived from
EIS synthetic data reproduce some general characteristics of the true
distributions, but usually show differences from the true EMDs that
are much larger than the estimated uncertainties suggest, especially
when structures with significantly different density overlap along
the line of sight. When using AIA synthetic data the derived EMDs
reproduce the true EMDs much less accurately, especially for broad
EMDs. The differences between the two instruments are due to the:
(1) smaller number of constraints provided by AIA data and (2) broad
temperature response function of the AIA channels which provide looser
constraints to the temperature distribution. Our results suggest that
EMDs derived from current observatories may often show significant
discrepancies from the true EMDs, rendering their interpretation
fraught with uncertainty. These inherent limitations to the method
should be carefully considered when using these distributions to
constrain coronal heating.
Title: Chromospheric Lyman-alpha spectro-polarimeter (CLASP)
Authors: Kano, Ryouhei; Bando, Takamasa; Narukage, Noriyuki; Ishikawa,
Ryoko; Tsuneta, Saku; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-nosuke; Hara, Hirohisa; Shimizu, Toshifumi; Suematsu, Yoshinori;
Ichimoto, Kiyoshi; Sakao, Taro; Goto, Motoshi; Kato, Yoshiaki; Imada,
Shinsuke; Kobayashi, Ken; Holloway, Todd; Winebarger, Amy; Cirtain,
Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier;
Štepán, Jiří; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos,
Andres; Auchère, Frédéric; Carlsson, Mats
Bibcode: 2012SPIE.8443E..4FK
Altcode:
One of the biggest challenges in heliophysics is to decipher the
magnetic structure of the solar chromosphere. The importance of
measuring the chromospheric magnetic field is due to both the key role
the chromosphere plays in energizing and structuring the outer solar
atmosphere and the inability of extrapolation of photospheric fields to
adequately describe this key boundary region. Over the last few years,
significant progress has been made in the spectral line formation
of UV lines as well as the MHD modeling of the solar atmosphere. It
is found that the Hanle effect in the Lyman-alpha line (121.567 nm)
is a most promising diagnostic tool for weaker magnetic fields in
the chromosphere and transition region. Based on this groundbreaking
research, we propose the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP) to NASA as a sounding rocket experiment, for making the first
measurement of the linear polarization produced by scattering processes
and the Hanle effect in the Lyman-alpha line (121.567 nm), and making
the first exploration of the magnetic field in the upper chromosphere
and transition region of the Sun. The CLASP instrument consists
of a Cassegrain telescope, a rotating 1/2-wave plate, a dual-beam
spectrograph assembly with a grating working as a beam splitter, and
an identical pair of reflective polarization analyzers each equipped
with a CCD camera. We propose to launch CLASP in December 2014.
Title: The interface region imaging spectrograph for the IRIS Small
Explorer mission
Authors: Wülser, Jean-Pierre; Title, Alan M.; Lemen, James R.; De
Pontieu, Bart; Kankelborg, Charles C.; Tarbell, Theodore D.; Berger,
Thomas E.; Golub, Leon; Kushner, Gary D.; Chou, Catherine Y.; Weingrod,
Isaac; Holmes, Buck; Mudge, Jason; Podgorski, William A.
Bibcode: 2012SPIE.8443E..08W
Altcode:
The Interface Region Imaging Spectrograph (IRIS) is a NASA SMall
EXplorer mission scheduled for launch in January 2013. The primary goal
of IRIS is to understand how the solar atmosphere is energized. The
IRIS investigation combines advanced numerical modeling with a high
resolution UV imaging spectrograph. IRIS will obtain UV spectra
and images with high resolution in space (0.4 arcsec) and time (1s)
focused on the chromosphere and transition region of the Sun, a complex
interface region between the photosphere and corona. The IRIS instrument
uses a Cassegrain telescope to feed a dual spectrograph and slit-jaw
imager that operate in the 133-141 nm and 278-283 nm ranges. This paper
describes the instrument with emphasis on the imaging spectrograph,
and presents an initial performance assessment from ground test results.
Title: Two-dimensional Radiative Magnetohydrodynamic Simulations of
the Importance of Partial Ionization in the Chromosphere
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo
Bibcode: 2012ApJ...753..161M
Altcode: 2012arXiv1204.5991M
The bulk of the solar chromosphere is weakly ionized and interactions
between ionized particles and neutral particles likely have significant
consequences for the thermodynamics of the chromospheric plasma. We
investigate the importance of introducing neutral particles into the
MHD equations using numerical 2.5D radiative MHD simulations obtained
with the Bifrost code. The models span the solar atmosphere from the
upper layers of the convection zone to the low corona, and solve the
full MHD equations with non-gray and non-LTE radiative transfer, and
thermal conduction along the magnetic field. The effects of partial
ionization are implemented using the generalized Ohm's law, i.e.,
we consider the effects of the Hall term and ambipolar diffusion
in the induction equation. The approximations required in going
from three fluids to the generalized Ohm's law are tested in our
simulations. The Ohmic diffusion, Hall term, and ambipolar diffusion
show strong variations in the chromosphere. These strong variations
of the various magnetic diffusivities are absent or significantly
underestimated when, as has been common for these types of studies,
using the semi-empirical VAL-C model as a basis for estimates. In
addition, we find that differences in estimating the magnitude
of ambipolar diffusion arise depending on which method is used to
calculate the ion-neutral collision frequency. These differences
cause uncertainties in the different magnetic diffusivity terms. In
the chromosphere, we find that the ambipolar diffusion is of the same
order of magnitude or even larger than the numerical diffusion used
to stabilize our code. As a consequence, ambipolar diffusion produces
a strong impact on the modeled atmosphere. Perhaps more importantly,
it suggests that at least in the chromospheric domain, self-consistent
simulations of the solar atmosphere driven by magnetoconvection can
accurately describe the impact of the dominant form of resistivity,
i.e., ambipolar diffusion. This suggests that such simulations may
be more realistic in their approach to the lower solar atmosphere
(which directly drives the coronal volume) than previously assumed.
Title: Statistical Properties of the Disk Counterparts of Type
II Spicules from Simultaneous Observations of Rapid Blueshifted
Excursions in Ca II 8542 and Hα
Authors: Sekse, D. H.; Rouppe van der Voort, L.; De Pontieu, B.
Bibcode: 2012ApJ...752..108S
Altcode: 2012arXiv1204.2943S
Spicules were recently found to exist as two different types when a new
class of so-called type II spicules was discovered at the solar limb
with the Solar Optical Telescope on board the Hinode spacecraft. These
type II spicules have been linked with on-disk observations of rapid
blueshifted excursions (RBEs) in the Hα and Ca II 8542 lines. Here
we analyze observations optimized for the detection of RBEs in both
Hα and Ca II 8542 lines simultaneously at a high temporal cadence
taken with the Crisp Imaging Spectropolarimeter at the Swedish Solar
Telescope on La Palma. In this study, we used a high-quality time
sequence for RBEs at different blueshifts and employed an automated
detection routine to detect a large number of RBEs in order to expand
on the statistics of RBEs. We find that the number of detected RBEs
is strongly dependent on the associated Doppler velocity of the images
on which the search is performed. Automatic detection of RBEs at lower
velocities increases the estimated number of RBEs to the same order of
magnitude expected from limb spicules. This shows that RBEs and type
II spicules are indeed exponents of the same phenomenon. Furthermore,
we provide solid evidence that Ca II 8542 RBEs are connected to Hα
RBEs and are located closer to the network regions with the Hα RBEs
being a continuation of the Ca II 8542 RBEs. Our results show that
RBEs have an average lifetime of 83.9 s when observed in both spectral
lines and that the Doppler velocities of RBEs range from 10 to 25 km
s-1 in Ca II 8542 and 30 to 50 km s-1 in Hα. In
addition, we automatically determine the transverse motion of a much
larger sample of RBEs than previous studies, and find that, just like
type II spicules, RBEs undergo significant transverse motions of the
order of 5-10 km s-1. Finally, we find that the intergranular
jets discovered at Big Bear Solar Observatory are a subset of RBEs.
Title: Two components of the coronal emission revealed by both
spectroscopic and imaging observations
Authors: Tian, Hui; McIntosh, Scott W.; De Pontieu, Bart
Bibcode: 2012shin.confE...1T
Altcode:
Boundaries of active regions have been suggested to be possible sources
of the slow solar wind. X-ray and EUV imaging observations often reveal
high-speed ( 100 km/s) quasi-periodic propagating disturbances (PDs)
along the fan-like structures at edges of active regions. Meanwhile EUV
spectroscopic observations of active region boundaries usually reveal
a blue shift of the order of 20 km/s and no periodicity. We think that
the key to solve these discrepancies is the asymmetry of the emission
line profile. The ubiquitous presence of blueward asymmetries of EUV
emission line profiles suggests at least two emission components:
a primary component accounting for the background coronal emission
and a weak secondary component associated with high-speed ( 100 km/s)
upflows. Through jointed imaging and spectroscopic observations, we have
demonstrated that the PDs are responsible for the secondary component
of line profiles and suggested that they may be an efficient means to
provide heated mass into the corona and solar wind. The intermittent
nature of these high-speed outflows (fine-scale jets) suggests that
the mass supply to the corona and solar wind is episodic rather than
continuous. Similar spectroscopic signatures have also been found in
CME-induced dimming regions, suggesting possible solar wind streams from
dimming regions. Unresolved problems include the production mechanism
of these high-speed outflows and the connection between these outflows
to the interplanetary space.
Title: Ubiquitous Torsional Motions in Type II Spicules
Authors: De Pontieu, B.; Carlsson, M.; Rouppe van der Voort, L. H. M.;
Rutten, R. J.; Hansteen, V. H.; Watanabe, H.
Bibcode: 2012ApJ...752L..12D
Altcode: 2012arXiv1205.5006D
Spicules are long, thin, highly dynamic features that jut out
ubiquitously from the solar limb. They dominate the interface between
the chromosphere and corona and may provide significant mass and energy
to the corona. We use high-quality observations with the Swedish 1
m Solar Telescope to establish that so-called type II spicules are
characterized by the simultaneous action of three different types of
motion: (1) field-aligned flows of order 50-100 km s-1,
(2) swaying motions of order 15-20 km s-1, and (3) torsional
motions of order 25-30 km s-1. The first two modes have been
studied in detail before, but not the torsional motions. Our analysis
of many near-limb and off-limb spectra and narrowband images using
multiple spectral lines yields strong evidence that most, if not all,
type II spicules undergo large torsional modulation and that these
motions, like spicule swaying, represent Alfvénic waves propagating
outward at several hundred km s-1. The combined action
of the different motions explains the similar morphology of spicule
bushes in the outer red and blue wings of chromospheric lines, and
needs to be taken into account when interpreting Doppler motions to
derive estimates for field-aligned flows in spicules and determining
the Alfvénic wave energy in the solar atmosphere. Our results also
suggest that large torsional motion is an ingredient in the production
of type II spicules and that spicules play an important role in the
transport of helicity through the solar atmosphere.
Title: Hinode/EIS Line Profile Asymmetries and Their Relationship with
the Distribution of SDO/AIA Propagating Coronal Disturbance Velocities
Authors: Sechler, M.; McIntosh, S. W.; Tian, H.; De Pontieu, B.
Bibcode: 2012ASPC..455..361S
Altcode: 2012arXiv1201.5028S
Using joint observations from Hinode/EIS and the Atmospheric Imaging
Array (AIA) on the Solar Dynamics Observatory (SDO) we explore the
asymmetry of coronal EUV line profiles. We find that asymmetries exist
in all of the spectral lines studied, and not just the hottest lines
as has been recently reported in the literature. Those asymmetries
indicate that the velocities of the second emission component are
relatively consistent across temperature and consistent with the
apparent speed at which material is being inserted from the lower
atmosphere that is visible in the SDO/AIA images as propagating coronal
disturbances. Further, the observed asymmetries are of similar magnitude
(a few percent) and width (determined from the RB analysis) across the
temperature space sampled and in the small region studied. Clearly,
there are two components of emission in the locations where the
asymmetries are identified in the RB analysis, their characteristics
are consistent with those determined from the SDO/AIA data. There is
no evidence from our analysis that this second component is broader
than the main component of the line.
Title: Two Components of the Coronal Emission Revealed by Both
Spectroscopic and Imaging Observations
Authors: Tian, H.; McIntosh, S. W.; De Pontieu, B.
Bibcode: 2012ASPC..456...97T
Altcode:
X-ray and EUV imaging observations often reveal quasi-periodic
propagating disturbances along the fan-like structures at edges of
active regions. These disturbances have historically been interpreted
as being signatures of slow-mode magnetoacoustic waves propagating
into the corona. Recent spectroscopic observations have revealed
the ubiquitous presence of blueward asymmetries of EUV emission line
profiles. Such asymmetries suggest that there are at least two emission
components: a primary component accounting for the background emission
and a secondary component associated with high-speed upflows. Thus, a
single Gaussian fit can not reflect the real physics here. Through joint
imaging and spectroscopic observations, we find a clear association
of the secondary component with the upward propagating disturbances
and conclude that they are more likely to be real plasma outflows
(small-scale recurring jets) rather than slow waves. These outflows
may result from impulsive heating processes in the lower transition
region or chromosphere and could be an efficient means to provide hot
plasma into the corona and possibly also solar wind.
Title: How Low-Quality Observations Affect Spicule Properties
Authors: Pereira, Tiago M. D.; De Pontieu, B.; Carlsson, M.
Bibcode: 2012AAS...22020306P
Altcode:
Spicules have been observed on the sun for more than 80 years, in
several chromospheric lines such as H-alpha and Ca II H. Recent work
has shown that spicules have the potential to drive the solar wind
and heat the chromosphere, making them a hotly contested topic in
solar physics. Despite the wealth of observations available, their
properties are still a matter of debate. Difficulties in measuring
their properties arise because spicules occur on short spatial and
temporal scales, and are very abundant (superimposed) at the limb. Most
of the older observations lacked either the spatial resolution or
cadence necessary to measure spicules. This changed with Hinode/SOT,
which has provided seeing-free observations with high cadence and
spatial resolution. Using SOT observations, we find that in the
quiet sun most spicules are shorter lived and can move much faster
than previously measured. In this work we try to reconcile the recent
results with results from older observations. We degrade SOT data to
match the cadence and resolution of older data sets, and apply the same
semi-automated method to detect and measure the properties of spicules
to both the original and degraded data. We find that degrading the data
has a significant effect on the measured properties of spicules. Most
importantly, the results from the degraded data agree very well
with older studies (e.g. mean spicule duration more than 5 minutes,
and upward velocities of about 25 km/s). These results illustrate how
the combination of spicule superposition, low spatial resolution, and
cadence affect the measured properties of spicules, and that previous
measurements can thus be unreliable.
Title: On the Doppler Velocity of Emission Line Profiles Formed in
the "Coronal Contraflow" that Is the Chromosphere-Corona Mass Cycle
Authors: McIntosh, Scott W.; Tian, Hui; Sechler, Marybeth; De Pontieu,
Bart
Bibcode: 2012ApJ...749...60M
Altcode: 2012arXiv1202.1248M
This analysis begins to explore the complex chromosphere-corona mass
cycle using a blend of imaging and spectroscopic diagnostics. Single
Gaussian fits (SGFs) to hot emission line profiles (formed above 1 MK)
at the base of coronal loop structures indicate material blueshifts
of 5-10 km s-1, while cool emission line profiles (formed
below 1 MK) yield redshifts of a similar magnitude—indicating, to
zeroth order, that a temperature-dependent bifurcating flow exists
on coronal structures. Image sequences of the same region reveal
weakly emitting upward propagating disturbances in both hot and cool
emission with apparent speeds of 50-150 km s-1. Spectroscopic
observations indicate that these propagating disturbances produce a weak
emission component in the blue wing at commensurate speed, but that they
contribute only a few percent to the (ensemble) emission line profile
in a single spatio-temporal resolution element. Subsequent analysis of
imaging data shows material "draining" slowly (~10 km s-1)
out of the corona, but only in the cooler passbands. We interpret
the draining as the return flow of coronal material at the end of
the complex chromosphere-corona mass cycle. Further, we suggest that
the efficient radiative cooling of the draining material produces a
significant contribution to the red wing of cool emission lines that is
ultimately responsible for their systematic redshift as derived from an
SGF when compared to those formed in hotter (conductively dominated)
domains. The presence of counterstreaming flows complicates the line
profiles, their interpretation, and asymmetry diagnoses, but allows
a different physical picture of the lower corona to develop.
Title: Using 3D MHD realistic simulations of the solar corona to
test plasma diagnostics
Authors: Testa, P.; De Pontieu, B.; Martinez-Sykora, J.; Hansteen,
V.; Carlsson, M.
Bibcode: 2012decs.confE..27T
Altcode:
We synthesize coronal images and spectra from advanced 3D MHD
simulations obtained from the state-of-the art Bifrost code, and
explore how well they reproduce coronal observations with SDO/AIA and
Hinode/EIS. We apply standard diagnostic techniques (e.g., density, and
temperature diagnostics) to the synthetic observations and investigate
how accurately the derived physical information matches the plasma
parameters of the model. We discuss the limitations of the diagnostics
and their implications.
Title: Importance of the partial ionization in the chromosphere
using 2D radiative-MHD simulations
Authors: Martinez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo H.
Bibcode: 2012decs.confE..81M
Altcode:
The bulk of the solar chromosphere is weakly ionized and interactions
between ionized particles and neutral particles will have significant
consequences for the thermodynamics of the chromospheric plasma. We
investigate the importance of introducing neutral particles into the
MHD equations using numerical 2.5D radiative MHD simulations obtained
with the Bifrost code. The models span the solar atmosphere from
upper layers of the convection zone to the low corona, and solve the
full MHD equations with non-grey and non-LTE radiative transfer and
thermal conduction along the magnetic field. The effects of partial
ionization are implemented using the generalized Ohm's law, i.e.,
we consider the effects of the Hall and ambipolar diffusion in the
induction equation. The ohmic, Hall, and ambipolar diffusivities show
variations of several orders of magnitude in the chromosphere. These
strong variations of the various magnetic diffusivities are absent
and significantly underestimated when using the semi-empirical VAL-C
model as a basis for estimates. We find that in the chromosphere,
the ambipolar diffusion is of the same order of magnitude or even
larger than the numerical diffusion used to stabilize our code. As
result of this, we can study the effects of it in the simulations. The
ambipolar diffusion produces strong impact on the chromosphere changing
the thermal properties, dynamics and magnetic field evolution.
Title: Propagating waves along spicules
Authors: Okamoto, Joten; De Pontieu, Bart
Bibcode: 2012decs.confE..66O
Altcode:
We investigated the detailed and statistical properties of Alfvenic
waves along spicules in the polar coronal hole using very high cadence
observations of the Solar Optical Telescope onboard Hinode. We
developed a technique for the automated detection of spicules and
high-frequency waves in a time series of images. We detected 89
spicules, and obtained several observational results (i.e., we found a
mix of upward propagating (59%), downward propagating (21%), as well
as standing waves (20%)). We speculate that upward propagating waves
are produced near the solar surface (below the spicule) and downward
propagating waves are caused by reflection of (initially) upward
propagating waves off the transition region at the spicule top. The
mix of upward and downward propagating waves implies that exploiting
these waves to perform seismology of the spicular environment requires
careful analysis and may be problematic.
Title: Potential for diagnostics with IRIS and Mg II lines
Authors: Pereira, Tiago M. D.; Carlsson, Mats; Leenaarts, Jorrit;
Uitenbroek, Han; De Pontieu, Bart; Martinez-Sykora, Juan
Bibcode: 2012decs.confE..13P
Altcode:
The IRIS mission will open up a new window into the solar chromosphere
and transition region. An important diagnostic that IRIS will bring
is the Mg II H and K lines. Radiation from these lines is believed
to be come from a wide range of formation depths, from the higher
photosphere to the onset of the transition region. With a complex
formation mechanism, Mg II H and K suffer from departures from LTE
and partial redistribution (PRD). In this preliminary analysis we will
look into the potential for diagnostics of Mg II H and K. Using a new
parallel version of the RH code we synthesised Mg II H and K spectra
from 3D rMHD simulations of the solar atmosphere. We will discuss
the relevance of several approximations on the final observables,
and will compare the Mg II H and K filtergrams with those of Ca II H,
a robust chromospheric diagnostic line widely used with Hinode/SOT/BFI.
Title: Estimating the (Dark) Energy Content of the Solar Corona
Authors: McIntosh, Scott W.; De Pontieu, Bart
Bibcode: 2012decs.confE.102M
Altcode:
Exploiting the recent discovery of ubiquitous low-frequency (3-5mHz)
Alfvénic waves in the solar chromosphere (with Hinode/SOT), and corona
(with the ground-based CoMP and SDO/AIA) we report on the Alfvénic wave
energy content of the corona using a blend of observational data and
a simple forward model of Alfvénic wave propagation. We explore the
apparent discrepancy in the resolved coronal Alfvénic wave amplitude
( 0.5km/s) measure by CoMP compared to those of the Hinode and SDO
near the limb ( 20km/s).We see that the temporal invariance of the
CoMP coronal non-thermal line widths ably capture the presence of the
hidden, or dark, energy content in the corona. Exploiting the fact
that the magnetic field permeating the corona is ubiquitously carrying
Alfvénic motions of non-negligible amplitude we construct a simple
model of wave propagation using the SOT and AIA measurements as strong
constraints. This model reproduces the key spectroscopic measurements
of the CoMP observations and allows us to place preliminary constraints
on the impact of the coronal magnetic filling factor, the input wave
spectrum, the dissipation on the wave motions observed, in addition
to their energy content.
Title: The Connection of Type II Spicules to the Corona
Authors: Judge, Philip G.; de Pontieu, Bart; McIntosh, Scott W.;
Olluri, Kosovare
Bibcode: 2012ApJ...746..158J
Altcode: 2011arXiv1112.6174D; 2011arXiv1112.6174J
We examine the hypothesis that plasma associated with "Type II"
spicules is heated to coronal temperatures, and that the upward
moving hot plasma constitutes a significant mass supply to the solar
corona. One-dimensional hydrodynamical models including time-dependent
ionization are brought to bear on the problem. These calculations
indicate that heating of field-aligned spicule flows should produce
significant differential Doppler shifts between emission lines formed
in the chromosphere, transition region, and corona. At present,
observational evidence for the computed 60-90 km s-1
differential shifts is weak, but the data are limited by difficulties
in comparing the proper motion of Type II spicules with spectral
and kinematic properties of an associated transition region and
coronal emission lines. Future observations with the upcoming infrared
interferometer spectrometer instrument should clarify if Doppler shifts
are consistent with the dynamics modeled here.
Title: The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)j
Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Bando, T.;
Belluzzi, L.; Casini, R.; Carlsson, M.; Cirtain, J. W.; De Pontieu,
B.; Hara, H.; Ichimoto, K.; Ishikawa, R.; Kano, R.; Katsukawa, Y.;
Kim, T.; Kubo, M.; Manso Sainz, R.; Narukage, N.; Asensio Ramos,
A.; Robinson, B.; Sakao, T.; Shimizu, T.; Stepan, J.; Suematsu, Y.;
Watanabe, H.; West, E.; Winebarger, A. R.
Bibcode: 2011AGUFM.P14C..05K
Altcode:
We present an overview of the Chromospheric Lyman-Alpha
SpectroPolarimeter (CLASP) program. CLASP is a proposed sounding rocket
experiment currently under development as collaboration between Japan,
USA and Spain. The aim is to achieve the first measurement of magnetic
field in the upper chromosphere and transition region of the Sun
through the detection and measurement of Hanle effect polarization
of the Lyman alpha line. The Hanle effect (i.e. the magnetic field
induced modification of the linear polarization due to scattering
processes in spectral lines) is believed to be a powerful tool for
measuring the magnetic field in the upper chromosphere, as it is more
sensitive to weaker magnetic fields than the Zeeman effect, and also
sensitive to magnetic fields tangled at spatial scales too small to be
resolved. The Lyman-alpha (121.567 nm) line has been chosen because
it is a chromospheric/transition-region line, and because the Hanle
effect polarization of the Lyman-alpha line is predicted to be sensitive
to 10-250 Gauss, encompassing the range of interest. Hanle effect is
predicted to be observable as linear polarization or depolarization,
depending on the geometry, with a fractional polarization amplitude
varying between 0.1% and 1% depending on the strength and orientation of
the magnetic field. This quantification of the chromospheric magnetic
field requires a highly sensitive polarization measurement. The
CLASP instrument consists of a large aperture (287 mm) Cassegrain
telescope mated to a polarizing beamsplitter and a matched pair
of grating spectrographs. The polarizing beamsplitter consists
of a continuously rotating waveplate and a linear beamsplitter,
allowing simultaneous measurement of orthogonal polarizations and
in-flight self-calibration. Development of the instrument is underway,
and prototypes of all optical components have been tested using a
synchrotron beamline. The experiment is proposed for flight in 2014.
Title: Quantifying spicules
Authors: Pereira, T. M.; De Pontieu, B.; Carlsson, M.
Bibcode: 2011AGUFMSH34B..01P
Altcode:
Understanding the dynamic solar chromosphere is of paramount importance
in solar physics. Spicules are an important feature of the chromosphere,
connecting the photosphere to the corona, potentially mediating the
transfer of energy and mass. While it is generally accepted that
there is more than one type of spicule, their quick motions, small
spatial scales, and short lifetimes have prevented a systematic study
of their properties over different solar regions. In the present work
we undertake such a study, using Ca H filtergrams from Hinode/SOT and
a semi-automated method to detect and track the spicules. Looking at
different magnetic field configurations (quiet Sun, coronal holes,
active regions), we discuss how the properties of the spicules change,
how the two spicule populations (type I and type II) are connected,
and how spicules are related to other chromospheric phenomena such as
dynamic fibrils.
Title: Forward Modeling of Emission in Solar Dynamics
Observatory/Atmospheric Imaging Assembly Passbands from Dynamic
Three-dimensional Simulations
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Testa, Paola;
Hansteen, Viggo
Bibcode: 2011ApJ...743...23M
Altcode: 2011arXiv1109.0704M
It is typically assumed that emission in the passbands of the
Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory (SDO) is dominated by single or several strong lines
from ions that under equilibrium conditions are formed in a narrow
range of temperatures. However, most SDO/AIA channels also contain
contributions from lines of ions that have formation temperatures
that are significantly different from the "dominant" ion(s). We
investigate the importance of these lines by forward modeling the
emission in the SDO/AIA channels with three-dimensional radiative MHD
simulations of a model that spans the upper layer of the convection
zone to the low corona. The model is highly dynamic. In addition,
we pump a steadily increasing magnetic flux into the corona, in
order to increase the coronal temperature through the dissipation
of magnetic stresses. As a consequence, the model covers different
ranges of coronal temperatures as time progresses. The model covers
coronal temperatures that are representative of plasma conditions in
coronal holes and quiet Sun. The 131, 171, and 304 Å AIA passbands
are found to be the least influenced by the so-called non-dominant
ions, and the emission observed in these channels comes mostly from
plasma at temperatures near the formation temperature of the dominant
ion(s). On the other hand, the other channels are strongly influenced
by the non-dominant ions, and therefore significant emission in these
channels comes from plasma at temperatures that are different from the
"canonical" values. We have also studied the influence of non-dominant
ions on the AIA passbands when different element abundances are assumed
(photospheric and coronal), and when the effects of the electron
density on the contribution function are taken into account.
Title: Wave Propagation and Jet Formation in the Chromosphere
Authors: Heggland, L.; Hansteen, V. H.; De Pontieu, B.; Carlsson, M.
Bibcode: 2011ApJ...743..142H
Altcode: 2011arXiv1112.0037H
We present the results of numerical simulations of wave propagation
and jet formation in solar atmosphere models with different magnetic
field configurations. The presence in the chromosphere of waves with
periods longer than the acoustic cutoff period has been ascribed to
either strong inclined magnetic fields, or changes in the radiative
relaxation time. Our simulations include a sophisticated treatment
of radiative losses, as well as fields with different strengths
and inclinations. Using Fourier and wavelet analysis techniques,
we investigate the periodicity of the waves that travel through the
chromosphere. We find that the velocity signal is dominated by waves
with periods around 5 minutes in regions of strong, inclined field,
including at the edges of strong flux tubes where the field expands,
whereas 3 minute waves dominate in regions of weak or vertically
oriented fields. Our results show that the field inclination is very
important for long-period wave propagation, whereas variations in the
radiative relaxation time have little effect. Furthermore, we find
that atmospheric conditions can vary significantly on timescales of
a few minutes, meaning that a Fourier analysis of wave propagation
can be misleading. Wavelet techniques take variations with time into
account and are more suitable analysis tools. Finally, we investigate
the properties of jets formed by the propagating waves once they reach
the transition region, and find systematic differences between the
jets in inclined-field regions and those in vertical field regions,
in agreement with observations of dynamic fibrils.
Title: Generation and propagation of Alfvenic waves in spicules
Authors: De Pontieu, B.; Okamoto, T. J.; Rouppe van der Voort, L.;
Hansteen, V. H.; Carlsson, M.
Bibcode: 2011AGUFMSH13B1956D
Altcode:
Both spicules and Alfven waves have recently been implicated in
playing a role in the heating of the outer atmosphere. Yet we do
not know how spicules or Alfven waves are generated. Here we focus
on the properties of Alfvenic waves in spicules and their role in
forming spicules. We use high-resolution observations taken with the
Solar Optical Telescope onboard Hinode, and with the CRISP Fabry-Perot
Interferometer at the Swedish Solar Telescope (SST) in La Palma to study
the generation and propagation of Alfvenic waves in spicules and their
disk counterparts. Using automated detection algorithms to identify
propagating waves in limb spicules, we find evidence for both up-
and downward propagating as well as standing waves. Our data suggests
significant reflection of waves in and around spicules and provides
constraints for theoretical models of spicules and wave propagation
through the chromosphere. We also show observational evidence (using
SST data) of the generation of Alfven waves and the role they play in
forming spicules.
Title: Lyman Alpha Spicule Observatory (LASO)
Authors: Chamberlin, P. C.; Allred, J. C.; Airapetian, V.; Gong, Q.;
Mcintosh, S. W.; De Pontieu, B.; Fontenla, J. M.
Bibcode: 2011AGUFMSH33B2064C
Altcode:
The Lyman Alpha Spicule Observatory (LASO) sounding rocket will observe
small-scale eruptive events called "Rapid Blue-shifted Events" (RBEs)
[Rouppe van der Voort et al., 2009], the on-disk equivalent of Type-II
spicules, and extend observations that explore their role in the solar
coronal heating problem [De Pontieu et al., 2011]. LASO utilizes a
new and novel optical design to simultaneously observe two spatial
dimensions at 4.2" spatial resolution (2.1" pixels) over a 2'x2' field
of view with high spectral resolution of 66mÅ (33mÅ pixels) across a
broad 20Å spectral window. This spectral window contains three strong
chromospheric and transition region emissions and is centered on the
strong Hydrogen Lyman-α emission at 1216Å. This instrument makes
it possible to obtain new data crucial to the physical understanding
of these phenomena and their role in the overall energy and momentum
balance from the upper chromosphere to lower corona. LASO was submitted
March 2011 in response to the ROSES SHP-LCAS call.
Title: Testing coronal plasma diagnostics using 3D MHD models of
the solar atmosphere
Authors: Testa, P.; Martinez-Sykora, J.; Hansteen, V. H.; De Pontieu,
B.; Carlsson, M.
Bibcode: 2011AGUFMSH53C..06T
Altcode:
We synthesize coronal images and spectra from advanced 3D radiative
MHD simulations obtained from the state-of-the-art Bifrost code, and
explore how well they reproduce coronal observations with SDO/AIA
and Hinode/EIS and XRT. We apply standard diagnostic techniques
(e.g., density, temperature, abundance diagnostics) to the synthetic
observations and investigate how accurately the derived physical
information matches the plasma parameters of the model. We discuss
the limitations of the diagnostics and their implications.
Title: Two Components of the Coronal Emission Revealed by
Extreme-Ultraviolet Spectroscopic Observations
Authors: Tian, H.; Mcintosh, S. W.; De Pontieu, B.; Martinez-Sykora,
J.; Wang, X.; Sechler, M.
Bibcode: 2011AGUFMSH33A2027T
Altcode:
Recent spectroscopic observations have revealed the ubiquitous presence
of blueward asymmetries of emission lines formed in the solar corona
and transition region. These asymmetries are most prominent in loop
footpoint regions, where a clear correlation of the asymmetry with the
Doppler shift and line width determined from the single-Gaussian fit
is found. Such asymmetries suggest at least two emission components: a
primary component accounting for the background emission and a secondary
component associated with high-speed upflows. The latter has been
proposed to play a vital role in the coronal heating process and there
is no agreement on its properties. Here we slightly modify the initially
developed technique of red-blue (RB) asymmetry analysis and apply it to
both artificial spectra and spectra observed by the Extreme-ultraviolet
Imaging Spectrometer on board Hinode, and demonstrate that the secondary
component usually contributes a few percent of the total emission, has
a velocity ranging from 50 to 150 km/s, and a Gaussian width comparable
to that of the primary one in loop footpoint regions. The results of
the RB asymmetry analysis are then used to guide a double-Gaussian fit
and we find that the obtained properties of the secondary component
are generally consistent with those obtained from the RB asymmetry
analysis. Through a comparison of the location, relative intensity,
and velocity distribution of the blueward secondary component with
the properties of the upward propagating disturbances revealed in
simultaneous images from the Atmospheric Imaging Assembly on board
the Solar Dynamics Observatory, we find a clear association of the
secondary component with the propagating disturbances.
Title: Overview of Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP)
Authors: Narukage, Noriyuki; Tsuneta, Saku; Bando, Takamasa; Kano,
Ryouhei; Kubo, Masahito; Ishikawa, Ryoko; Hara, Hirohisa; Suematsu,
Yoshinori; Katsukawa, Yukio; Watanabe, Hiroko; Ichimoto, Kiyoshi;
Sakao, Taro; Shimizu, Toshifumi; Kobayashi, Ken; Robinson, Brian; Kim,
Tony; Winebarger, Amy; West, Edward; Cirtain, Jonathan; De Pontieu,
Bart; Casini, Roberto; Trujillo Bueno, Javier; Stepan, Jiri; Manso
Sainz, Rafael; Belluzzi, Luca; Asensio Ramos, Andres; Carlsson, Mats
Bibcode: 2011SPIE.8148E..0HN
Altcode: 2011SPIE.8148E..16N
The solar chromosphere is an important boundary, through which all of
the plasma, magnetic fields and energy in the corona and solar wind
are supplied. Since the Zeeman splitting is typically smaller than
the Doppler line broadening in the chromosphere and transition region,
it is not effective to explore weak magnetic fields. However, this is
not the case for the Hanle effect, when we have an instrument with
high polarization sensitivity (~ 0.1%). "Chromospheric Lyman- Alpha
SpectroPolarimeter (CLASP)" is the sounding rocket experiment to detect
linear polarization produced by the Hanle effect in Lyman-alpha line
(121.567 nm) and to make the first direct measurement of magnetic
fields in the upper chromosphere and lower transition region. To
achieve the high sensitivity of ~ 0.1% within a rocket flight (5
minutes) in Lyman-alpha line, which is easily absorbed by materials,
we design the optical system mainly with reflections. The CLASP
consists of a classical Cassegrain telescope, a polarimeter and a
spectrometer. The polarimeter consists of a rotating 1/2-wave plate
and two reflecting polarization analyzers. One of the analyzer also
works as a polarization beam splitter to give us two orthogonal linear
polarizations simultaneously. The CLASP is planned to be launched in
2014 summer.
Title: Two Components of the Solar Coronal Emission Revealed by
Extreme-ultraviolet Spectroscopic Observations
Authors: Tian, Hui; McIntosh, Scott W.; De Pontieu, Bart;
Martínez-Sykora, Juan; Sechler, Marybeth; Wang, Xin
Bibcode: 2011ApJ...738...18T
Altcode: 2011arXiv1106.1141T
Recent spectroscopic observations have revealed the ubiquitous presence
of blueward asymmetries of emission lines formed in the solar corona
and transition region. These asymmetries are most prominent in loop
footpoint regions, where a clear correlation of the asymmetry with the
Doppler shift and line width determined from the single-Gaussian fit
is found. Such asymmetries suggest at least two emission components: a
primary component accounting for the background emission and a secondary
component associated with high-speed upflows. The latter has been
proposed to play a vital role in the coronal heating process and there
is no agreement on its properties. Here we slightly modify the initially
developed technique of red-blue (RB) asymmetry analysis and apply it to
both artificial spectra and spectra observed by the Extreme-ultraviolet
Imaging Spectrometer on board Hinode, and demonstrate that the secondary
component usually contributes a few percent of the total emission,
and has a velocity ranging from 50 to 150 km s-1 and a
Gaussian width comparable to that of the primary one in loop footpoint
regions. The results of the RB asymmetry analysis are then used to
guide a double-Gaussian fit and we find that the obtained properties of
the secondary component are generally consistent with those obtained
from the RB asymmetry analysis. Through a comparison of the location,
relative intensity, and velocity distribution of the blueward secondary
component with the properties of the upward propagating disturbances
revealed in simultaneous images from the Atmospheric Imaging Assembly
on board the Solar Dynamics Observatory, we find a clear association
of the secondary component with the propagating disturbances.
Title: Propagating Waves Along Spicules
Authors: Okamoto, Takenori J.; De Pontieu, Bart
Bibcode: 2011ApJ...736L..24O
Altcode: 2011arXiv1106.4270O
Alfvénic waves are thought to play an important role in coronal heating
and acceleration of solar wind. Here we investigate the statistical
properties of Alfvénic waves along spicules (jets that protrude into
the corona) in a polar coronal hole using high-cadence observations of
the Solar Optical Telescope on board Hinode. We developed a technique
for the automated detection of spicules and high-frequency waves. We
detected 89 spicules and found (1) a mix of upward propagating, downward
propagating, as well as standing waves (occurrence rates of 59%, 21%,
and 20%, respectively); (2) the phase speed gradually increases with
height; (3) upward waves dominant at lower altitudes, standing waves
at higher altitudes; (4) standing waves dominant in the early and late
phases of each spicule, while upward waves were dominant in the middle
phase; (5) in some spicules, we find waves propagating upward (from
the bottom) and downward (from the top) to form a standing wave in the
middle of the spicule; and (6) the medians of the amplitude, period,
and velocity amplitude were 55 km, 45 s, and 7.4 km s-1,
respectively. We speculate that upward propagating waves are produced
near the solar surface (below the spicule) and downward propagating
waves are caused by reflection of (initially) upward propagating
waves off the transition region at the spicule top. The mix of upward
and downward propagating waves implies that exploiting these waves
to perform seismology of the spicular environment requires careful
analysis and may be problematic.
Title: Alfvénic waves with sufficient energy to power the quiet
solar corona and fast solar wind
Authors: McIntosh, Scott W.; de Pontieu, Bart; Carlsson, Mats;
Hansteen, Viggo; Boerner, Paul; Goossens, Marcel
Bibcode: 2011Natur.475..477M
Altcode:
Energy is required to heat the outer solar atmosphere to millions of
degrees (refs 1, 2) and to accelerate the solar wind to hundreds of
kilometres per second (refs 2-6). Alfvén waves (travelling oscillations
of ions and magnetic field) have been invoked as a possible mechanism
to transport magneto-convective energy upwards along the Sun's magnetic
field lines into the corona. Previous observations of Alfvénic waves
in the corona revealed amplitudes far too small (0.5kms-1)
to supply the energy flux (100-200Wm-2) required to
drive the fast solar wind or balance the radiative losses of the
quiet corona. Here we report observations of the transition region
(between the chromosphere and the corona) and of the corona that
reveal how Alfvénic motions permeate the dynamic and finely structured
outer solar atmosphere. The ubiquitous outward-propagating Alfvénic
motions observed have amplitudes of the order of 20kms-1 and
periods of the order of 100-500s throughout the quiescent atmosphere
(compatible with recent investigations), and are energetic enough to
accelerate the fast solar wind and heat the quiet corona.
Title: Direct Imaging of Quasi-periodic Fast Propagating Waves of
~2000 km s-1 in the Low Solar Corona by the Solar Dynamics
Observatory Atmospheric Imaging Assembly
Authors: Liu, Wei; Title, Alan M.; Zhao, Junwei; Ofman, Leon;
Schrijver, Carolus J.; Aschwanden, Markus J.; De Pontieu, Bart;
Tarbell, Theodore D.
Bibcode: 2011ApJ...736L..13L
Altcode: 2011arXiv1106.3150L
Quasi-periodic propagating fast mode magnetosonic waves in the solar
corona were difficult to observe in the past due to relatively low
instrument cadences. We report here evidence of such waves directly
imaged in EUV by the new Atmospheric Imaging Assembly instrument
on board the Solar Dynamics Observatory. In the 2010 August 1 C3.2
flare/coronal mass ejection event, we find arc-shaped wave trains of
1%-5% intensity variations (lifetime ~200 s) that emanate near the
flare kernel and propagate outward up to ~400 Mm along a funnel of
coronal loops. Sinusoidal fits to a typical wave train indicate a phase
velocity of 2200 ± 130 km s-1. Similar waves propagating
in opposite directions are observed in closed loops between two flare
ribbons. In the k-ω diagram of the Fourier wave power, we find a
bright ridge that represents the dispersion relation and can be well
fitted with a straight line passing through the origin. This k-ω
ridge shows a broad frequency distribution with power peaks at 5.5,
14.5, and 25.1 mHz. The strongest signal at 5.5 mHz (period 181 s)
temporally coincides with quasi-periodic pulsations of the flare,
suggesting a common origin. The instantaneous wave energy flux
of (0.1-2.6) × 107 erg cm-2 s-1
estimated at the coronal base is comparable to the steady-state heating
requirement of active region loops.
Title: Lyman Alpha Spicule Observatory (LASO)
Authors: Chamberlin, Phillip C.; Allred, J.; Airapetian, V.; Gong,
Q.; Fontenla, J.; McIntosh, S.; de Pontieu, B.
Bibcode: 2011SPD....42.1506C
Altcode: 2011BAAS..43S.1506C
The Lyman Alpha Spicule Observatory (LASO) sounding rocket will observe
small-scale eruptive events called "Rapid Blue-shifted Events” (RBEs),
the on-disk equivalent of Type-II spicules, and extend observations that
explore their role in the solar coronal heating problem. LASO utilizes
a new and novel optical design to simultaneously observe two spatial
dimensions at 4.2" spatial resolution (2.1” pixels) over a 2'x2'
field of view with high spectral resolution of 66mÅ (33mÅ pixels)
across a broad 20Å spectral window. This spectral window contains three
strong chromospheric and transition region emissions and is centered on
the strong Hydrogen Lyman-α emission at 1216Å. This instrument makes
it possible to obtain new data crucial to the physical understanding
of these phenomena and their role in the overall energy and momentum
balance from the upper chromosphere to lower corona. LASO was submitted
March 2011 in response to the ROSES SHP-LCAS call.
Title: The Interface Region Imaging Spectrograph (IRIS) NASA SMEX
Authors: Lemen, James; Title, A.; De Pontieu, B.; Schrijver, C.;
Tarbell, T.; Wuelser, J.; Golub, L.; Kankelborg, C.
Bibcode: 2011SPD....42.1512L
Altcode: 2011BAAS..43S.1512L
The solar chromosphere and transition region (TR) is highly structured,
dynamic, and intimately connected to the corona. It requires more
than ten times the energy required to heat the corona, and yet it
has received far less interest because of the complexity of the
required observational and analytical tools. In the TR the density
drops by six orders of magnitude and the temperature increases by
three orders of magnitude. Hinode observations reveal the importance
the magnetic field has on this region of the solar atmosphere that
acts as the interface between the photosphere and the corona. The
Interface Region Imaging Spectrograph (IRIS) was selected for a NASA
SMEX mission in 2009 and is scheduled to launch in December 2012. IRIS
addresses critical questions in order to understand the flow of energy
and mass through the chromosphere and TR, namely: (1) Which types of
non-thermal energy dominate in the chromosphere and beyond? (2) How
does the chromosphere regulate mass and energy supply to the corona
and heliosphere? (3) How do magnetic flux and matter rise through the
lower atmosphere, and what roles dos flux emergence play in flares and
mass ejections? These questions are addressed with a high-resolution
imaging spectrometer that observes Near- and Far-VU emissions that
are formed at temperatures between 5,000K and 1.5 x 106
K. IRIS has a field-of-view of 120 arcsec, a spatial resolution
of 0.4 arcsec, and velocity resolution of 0.5 km/s. Members of the
IRIS investigation team are developing advanced radiative MHD codes
to facilitate comparison with and interpretation of observations. We
present the status of the IRIS observatory development, which completed
its Critical Design Review in December 2010.
Title: What do Spectral Line Profile Asymmetries Tell us About the
Solar Atmosphere?
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo;
McIntosh, Scott W.
Bibcode: 2011ApJ...732...84M
Altcode:
Recently, analysis of solar spectra obtained with the EUV Imaging
Spectrograph (EIS) onboard the Hinode satellite has revealed the
ubiquitous presence of asymmetries in transition region (TR) and coronal
spectral line profiles. These asymmetries have been observed especially
at the footpoints of coronal loops and have been associated with strong
upflows that may play a significant role in providing the corona with
hot plasma. Here, we perform a detailed study of the various processes
that can lead to spectral line asymmetries, using both simple forward
models and state-of-the-art three-dimensional radiative MHD simulations
of the solar atmosphere using the Bifrost code. We describe a novel
technique to determine the presence and properties of faint secondary
components in the wings of spectral line profiles. This method is based
on least-squares fitting of observed so-called R(ed)B(lue) asymmetry
profiles with pre-calculated RB asymmetry profiles for a wide variety
of secondary component properties. We illustrate how this method could
be used to perform reliable double Gaussian fits that are not over- or
under-constrained. We also find that spectral line asymmetries appear
in TR and coronal lines that are synthesized from our three-dimensional
MHD simulations. Our models show that the spectral asymmetries are a
sensitive measure of the velocity gradient with height in the TR of
coronal loops. The modeled TR shows a large gradient of velocity that
increases with height: this occurs as a consequence of ubiquitous,
episodic heating at low heights in the model atmosphere. We show
that the contribution function of spectral lines as a function of
temperature is critical for sensitivity to velocity gradients and thus
line asymmetries: lines that are formed over a temperature range that
includes most of the TR are the most sensitive. As a result, lines from
lithium-like ions (e.g., O VI) are found to be the most sensitive to
line asymmetries. We compare the simulated line profiles directly with
line profiles observed in the quiet Sun with SOHO/SUMER and Hinode/EIS
and find that the shape of the profiles is very similar. In addition,
the simulated profiles with the strongest blueward asymmetry occur in
footpoint regions of coronal loops, which is similar to what we observe
with SUMER and EIS. There is however a significant discrepancy between
the simulations and observations: the simulated RB asymmetries are
an order of magnitude smaller than the observations. We discuss the
possible reasons for this discrepancy. In summary, our analysis shows
that observations of spectral line asymmetries can provide a powerful
new diagnostic to help constrain coronal heating models.
Title: Direct Imaging by SDO/AIA of Quasi-periodic Propagating Fast
Mode Magnetosonic Waves of 2000 km/s in the Solar Corona
Authors: Liu, Wei; Title, A. M.; Zhao, J.; Ofman, L.; Schrijver,
C. J.; Aschwanden, M. J.; De Pontieu, B.; Tarbell, T. D.
Bibcode: 2011SPD....42.2114L
Altcode: 2011BAAS..43S.2114L
Quasi-periodic, propagating fast mode magnetosonic waves in the
corona were difficult to observe in the past due to relatively low
instrument cadences. We report here unprecedented evidence of such
waves directly imaged in EUV by the new SDO/AIA instrument. In the 2010
August 1 C3.2 flare/CME event, we find arc-shaped wave trains of 1-5%
intensity variations emanating near the flare kernel and propagating
outward along a funnel of coronal loops. Sinusoidal fits to a typical
wave train indicate a phase velocity of 2350 +/- 210 km/s. Similar
waves propagating in opposite directions are observed in closed loops
between two flare ribbons. In the k-omega diagram of the Fourier wave
power, we find a bright ridge that represents the dispersion relation
and can be well fitted with a straight line passing through the
origin, giving an equal phase and group velocity of 1630 +/- 760 km/s
averaged over the event. This k-omega ridge shows a broad frequency
distribution with prominent power at four non-harmonic frequencies,
5.5, 14.5, 25.1, and 37.9 mHz, among which the 14.5 mHz (period:
69 s) signal is the strongest. The signal at 5.5 mHz (period: 181 s,
same as chromospheric 3-minute oscillations) temporally coincides with
flare pulsations, suggesting a common origin of possibly quasi-periodic
magnetic reconnection. The instantaneous wave energy flux of (0.1-2.6)e7
ergs/cm2/s estimated at the coronal base is comparable to
the steady-state heating requirement of active region loops.
Title: A Sounding Rocket Experiment for Spectropolarimetric
Observations with the Lyα Line at 121.6 nm (CLASP)
Authors: Ishikawa, R.; Bando, T.; Fujimura, D.; Hara, H.; Kano,
R.; Kobiki, T.; Narukage, N.; Tsuneta, S.; Ueda, K.; Wantanabe,
H.; Kobayashi, K.; Trujillo Bueno, J.; Manso Sainz, R.; Stepan, J.;
de Pontieu, B.; Carlsson, M.; Casini, R.
Bibcode: 2011ASPC..437..287I
Altcode:
A team consisting of Japan, USA, Spain, and Norway is developing a
high-throughput Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP),
which is proposed to fly with a NASA sounding rocket in 2014. CLASP will
explore the magnetism of the upper solar chromosphere and transition
region via the Hanle effect of the Lyα line for the first
time. This experiment requires spectropolarimetric observations with
high polarimetric sensitivity (∼0.1%) and wavelength resolution
(0.1 Å). The final spatial resolution (slit width) is being discussed
taking into account the required high signal-to-noise ratio. We have
demonstrated the performance of the Lyα polarimeter by
extensively using the Ultraviolet Synchrotron ORbital Radiation Facility
(UVSOR) at the Institute for Molecular Sciences. In this contribution,
we report these measurements at UVSOR together with the current status
of the CLASP project.
Title: The Spectroscopic Signature of Quasi-periodic Upflows in
Active Region Timeseries
Authors: Tian, Hui; McIntosh, Scott W.; De Pontieu, Bart
Bibcode: 2011ApJ...727L..37T
Altcode: 2010arXiv1012.5112T
Quasi-periodic propagating disturbances are frequently observed in
coronal intensity image sequences. These disturbances have historically
been interpreted as being the signature of slow-mode magnetoacoustic
waves propagating into the corona. The detailed analysis of Hinode EUV
Imaging Spectrometer (EIS) timeseries observations of an active region
(known to contain propagating disturbances) shows strongly correlated,
quasi-periodic, oscillations in intensity, Doppler shift, and line
width. No frequency doubling is visible in the latter. The enhancements
in the moments of the line profile are generally accompanied by a faint,
quasi-periodically occurring, excess emission at ~100 km s-1
in the blue wing of coronal emission lines. The correspondence of
quasi-periodic excess wing emission and the moments of the line profile
indicates that repetitive high-velocity upflows are responsible for
the oscillatory behavior observed. Furthermore, we show that the same
quasi-periodic upflows can be directly identified in a simultaneous
image sequence obtained by the Hinode X-Ray Telescope. These results
are consistent with the recent assertion of De Pontieu & McIntosh
that the wave interpretation of the data is not unique. Indeed, given
that several instances are seen to propagate along the direction of
the EIS slit that clearly shows in-phase, quasi-periodic variations of
intensity, velocity, width (without frequency doubling), and blue wing
enhanced emission, this data set would appear to provide a compelling
example that upflows are more likely to be the main cause of the
quasi-periodicities observed here, as such correspondences are hard
to reconcile in the wave paradigm.
Title: The Spectroscopic Footprint of the Fast Solar Wind
Authors: McIntosh, Scott W.; Leamon, Robert J.; De Pontieu, Bart
Bibcode: 2011ApJ...727....7M
Altcode: 2010arXiv1011.3066M
We analyze a large, complex equatorial coronal hole (ECH) and its
immediate surroundings with a focus on the roots of the fast solar
wind. We start by demonstrating that our ECH is indeed a source of the
fast solar wind at 1 AU by examining in situ plasma measurements in
conjunction with recently developed measures of magnetic conditions
of the photosphere, inner heliosphere, and the mapping of the solar
wind source region. We focus the bulk of our analysis on interpreting
the thermal and spatial dependence of the non-thermal line widths
in the ECH as measured by SOHO/SUMER by placing the measurements in
context with recent studies of ubiquitous Alfvén waves in the solar
atmosphere and line profile asymmetries (indicative of episodic heating
and mass loading of the coronal plasma) that originate in the strong,
unipolar magnetic flux concentrations that comprise the supergranular
network. The results presented in this paper are consistent with a
picture where a significant portion of the energy responsible for
the transport of heated mass into the fast solar wind is provided by
episodically occurring small-scale events (likely driven by magnetic
reconnection) in the upper chromosphere and transition region of the
strong magnetic flux regions that comprise the supergranular network.
Title: The Origins of Hot Plasma in the Solar Corona
Authors: De Pontieu, B.; McIntosh, S. W.; Carlsson, M.; Hansteen,
V. H.; Tarbell, T. D.; Boerner, P.; Martinez-Sykora, J.; Schrijver,
C. J.; Title, A. M.
Bibcode: 2011Sci...331...55D
Altcode:
The Sun's outer atmosphere, or corona, is heated to millions of degrees,
considerably hotter than its surface or photosphere. Explanations for
this enigma typically invoke the deposition in the corona of nonthermal
energy generated by magnetoconvection. However, the coronal heating
mechanism remains unknown. We used observations from the Solar Dynamics
Observatory and the Hinode solar physics mission to reveal a ubiquitous
coronal mass supply in which chromospheric plasma in fountainlike jets
or spicules is accelerated upward into the corona, with much of the
plasma heated to temperatures between ~0.02 and 0.1 million kelvin (MK)
and a small but sufficient fraction to temperatures above 1 MK. These
observations provide constraints on the coronal heating mechanism(s)
and highlight the importance of the interface region between photosphere
and corona.
Title: Automated detection of oscillatory signals in the solar
atmosphere: first results from SDO-AIA data
Authors: Ireland, J.; Young, C.; de Pontieu, B.; McIntosh, S. W.
Bibcode: 2010AGUFMSH11A1615I
Altcode:
Ireland et al. (2010) recently published a Bayesian-probability
based automated oscillation detection algorithm that finds areas
of the solar corona that support spatially contiguous oscillatory
signals. The major advantages of this algorithm are that it requires no
special knowledge of the noise characteristics or possible frequency
content of the signal, yet can calculate a probability that a time
series supports a signal in a given frequency range. This leads to
an algorithm which detects pixel areas where each pixel has a high
probability of supporting an oscillatory signal; however, the pixels
in these areas are not necessarily oscillating coherently. Earlier,
McIntosh et al. (2008) described another algorithm that first Fourier
filters time series data around a known frequency, and then calculates
the local coherence of the filtered signals in order to find areas
of the solar corona that exhibit locally strongly coherent signals
in narrow frequency ranges. The major advantages of this algorithm
are that locally coherent signals are found, and that it is simple
to calculate other parameters such as the phase speed. This leads to
an algorithm that finds groups of pixels that are coherent in narrow
frequency ranges, but that are not necessarily oscillatory in nature. In
this work we combine these two recently published automated oscillatory
signal detection algorithms and compare the new hybrid algorithm to the
progenitor algorithms. The new algorithm is applied to Advanced Imaging
Assembly (AIA) 94, 131, 171, 193, 211 and 335 Å data from the Solar
Dynamics Observatory, and we will give some first results. We also
discuss the use of this algorithm in a detection pipeline to provide
near-real time measurements of groups of coherently oscillating pixels.
Title: Ubiquitous Alfvenic Motions in Quiet Sun, Coronal Hole and
Active Region Corona
Authors: McIntosh, S. W.; de Pontieu, B.; Carlsson, M.; Hansteen,
V. H.; Sdo/Aia Mission Team
Bibcode: 2010AGUFMSH14A..01M
Altcode:
We use observations with AIA onboard SDO and report the discovery of
ubiquitous Alfvenic oscillations in the corona of quiet Sun, active
regions and coronal holes. These Alfvenic oscillations have significant
power, and seem to be connected to the chromospheric Alfvenic
oscillations previously reported with Hinode. We use Monte Carlo
simulations to determine the strength and periods of the waves. Using
unique joint observations of Hinode, the Solar Dynamics Observatory, and
HAO's CoMP instrument we study the excitation of transverse oscillations
as a function of space, time, and temperature. We will discuss the
energetic impact and diagnostic capabilities of this ever-present
process and how it can be used to build a more self-consistent picture
of energy transport into the inner heliosphere. Transverse Oscillations
Observed Above the Solar North Pole in the He II 304Å (bottom) and Fe
IX 171Å (top) channels. Studying the progression of such points with
altitude yields important information about wave propagation into the
magnetically open corona.
Title: The Chromospheric Lyman Alpha SpectroPolarimeter (CLASP)
Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Cirtain,
J. W.; Bando, T.; Kano, R.; Hara, H.; Fujimura, D.; Ueda, K.; Ishikawa,
R.; Watanabe, H.; Ichimoto, K.; Sakao, T.; de Pontieu, B.; Carlsson,
M.; Casini, R.
Bibcode: 2010AGUFMSH11B1632K
Altcode:
Magnetic fields in the solar chromosphere play a key role in the
energy transfer and dynamics of the solar atmosphere. Yet a direct
observation of the chromospheric magnetic field remains one of the
greatest challenges in solar physics. While some advances have been
made for observing the Zeeman effect in strong chromospheric lines,
the effect is small and difficult to detect outside sunspots. The
Hanle effect offers a promising alternative; it is sensitive to weaker
magnetic fields (e.g., 5-500 G for Ly-Alpha), and while its magnitude
saturates at stronger magnetic fields, the linear polarization signals
remain sensitive to the magnetic field orientation. The Hanle effect
is not only limited to off-limb observations. Because the chromosphere
is illuminated by an anisotropic radiation field, the Ly-Alpha line is
predicted to show linear polarization for on-disk, near-limb regions,
and magnetic field is predicted to cause a measurable depolarization. At
disk center, the Ly-Alpha radiation is predicted to be negligible
in the absence of magnetic field, and linearly polarized to an order
of 0.3% in the presence of an inclined magnetic field. The proposed
CLASP sounding rocket instrument is designed to detect 0.3% linear
polarization of the Ly-Alpha line at 1.5 arcsecond spatial resolution
(0.7’’ pixel size) and 10 pm spectral resolution. The instrument
consists of a 30 cm aperture Cassegrain telescope and a dual-beam
spectropolarimeter. The telescope employs a ``cold mirror’’ design
that uses multilayer coatings to reflect only the target wavelength
range into the spectropolarimeter. The polarization analyzer consists of
a rotating waveplate and a polarizing beamsplitter that comprises MgF2
plates placed at Brewster’s Angle. Each output beam of the polarizing
beamsplitter, representing two orthogonal linear polarizations, is
dispersed and focused using a separate spherical varied-line-space
grating, and imaged with a separate 512x512 CCD camera. Prototypes
of key optical components have been fabricated and tested. Instrument
design is being finalized, and the experiment will be proposed for a
2014 flight aboard a NASA sounding rocket.
Title: First results for the Solar Ultraviolet Magnetograph
Investigation (SUMI)
Authors: Moore, R. L.; Cirtain, J. W.; West, E.; Kobayashi, K.;
Robinson, B.; Winebarger, A. R.; Tarbell, T. D.; de Pontieu, B.;
McIntosh, S. W.
Bibcode: 2010AGUFMSH11B1655M
Altcode:
On July 31, 2010 SUMI was launched to 286km above the White
Sands Missile Range to observe active region 11092. SUMI is a
spectro-polarimeter capable of measuring the spectrum for Mg II h &
k at 280 nm and C IV at 155 nm. Simultaneous observations with Hinode
and SDO provide total coverage of the region from the photosphere into
the corona, a very unique and original data set. We will present the
initial results from this first flight of the experiment and demonstrate
the utility of further observations by SUMI.
Title: The role of the chromosphere in filling the corona with hot
plasma (Invited)
Authors: de Pontieu, B.; McIntosh, S. W.; Carlsson, M.; Hansteen,
V. H.; Tarbell, T. D.; Boerner, P.; Martinez-Sykora, J.; Schrijver,
C. J.; Title, A. M.
Bibcode: 2010AGUFMSH21C..03D
Altcode:
We use coordinated observations from the Solar Dynamics Observatory
(SDO), Hinode and the Swedish Solar Telescope (SST) to show how
plasma is heated to coronal temperatures from its source in the
chromosphere. Our observations reveal a ubiquitous mass supply
for the solar corona in which chromospheric plasma is accelerated
upward into the corona with much of the plasma heated to transition
region temperatures, and a small, but significant fraction heated
to temperatures in excess of 1 million K. Our observations show,
for the first time, how chromospheric spicules, fountain-like jets
that have long been considered potential candidates for coronal
heating, are directly associated with heating of plasma to coronal
temperatures. These results provide strong physical constraints on
the mechanism(s) responsible for coronal heating and do not seem
compatible with current models. The association with chromospheric
spicules highlights the importance of the interface region between
the photosphere and corona to gain a full understanding of the coronal
heating problem.
Title: Line profile asymmetries in the transition region: models
and observations
Authors: Martinez-Sykora, J.; de Pontieu, B.; Hansteen, V. H.;
McIntosh, S. W.
Bibcode: 2010AGUFMSH31A1784M
Altcode:
Asymmetries in spectral line profiles provide a wealth of
information on the properties of the emitting plasma along the
line-of-sight. Asymmetries can be produced by the superposition
of profiles with different line-of-sight velocities and/or widths
resulting from the variation of the velocity and/or temperature from
emission sources along the line of sight. Spectral line asymmetries
from synthetic transition region and coronal lines constructed
from realistic 3D models appear similar to those observed with
Hinode/EIS. The simulations span the upper layer of the convection zone
to the lower corona and include horizontal magnetic flux emergence. We
use the state of the art Bifrost code to solve the full MHD equations
with non-grey and non-LTE radiative transfer and thermal conduction
along the magnetic field line. Here, we perform a detailed study of
the various physical, dynamical and observational processes that can
lead to spectral line asymmetries at the transition region footpoints
of loops in 3D radiative MHD simulations of the solar atmosphere and
compare these with observations. Our models show that the spectral
asymmetries are a sensitive measure of the velocity gradient with
height in the transition region of coronal loops. In our models the
TR shows a large gradient of velocity that increases with height:
this occurs as a natural consequence of ubiquitous, episodic heating
at low heights in the model atmosphere.
Title: Forward modeling of emission in AIA passbands from advanced
radiative MHD simulations
Authors: de Pontieu, B.; Martinez-Sykora, J.; Hansteen, V. H.
Bibcode: 2010AGUFMSH11A1597D
Altcode:
The emission from many of the passbands observed with the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO)
is dominated by single or several lines from ions that are formed in a
narrow range of temperatures (under equilibrium conditions). However,
most AIA passbands contain contributions from lines of ions that
have formation temperatures that are significantly different from the
dominant ion. We investigate the importance of these lines by forward
modeling of the AIA passband emission from advanced radiative 3D MHD
simulations calculated with the state of the art Bifrost code. We
use simulations that span the upper layer of the convection zone to
the low corona and solve the full magnetohydrodynamic equations with
non-grey and non-LTE radiative transfer and thermal conduction along the
magnetic field lines. We find that several of the AIA passbands often
include significant contributions from plasma at different temperatures
than the canonical temperature values. We describe under which solar
conditions in the simulations these discrepancies can typically be
expected to occur.
Title: Quasi-periodic Propagating Signals in the Solar Corona:
The Signature of Magnetoacoustic Waves or High-velocity Upflows?
Authors: De Pontieu, Bart; McIntosh, Scott W.
Bibcode: 2010ApJ...722.1013D
Altcode: 2010arXiv1008.5300D
Since the discovery of quasi-periodic propagating oscillations
with periods of order 3-10 minutes in coronal loops with TRACE and
SOHO/EIT (and later with STEREO/EUVI and Hinode/EIS), they have been
almost universally interpreted as evidence for propagating slow-mode
magnetoacoustic waves in the low plasma β coronal environment. Here
we show that this interpretation is not unique, and that for coronal
loops associated with plage regions (as opposed to sunspots), the
presence of magnetoacoustic waves may not be the only cause for the
observed quasi-periodicities. We focus instead on the ubiquitous, faint
upflows at 50-150 km s-1 that were recently discovered as
blueward asymmetries of spectral line profiles in footpoint regions
of coronal loops, and as faint disturbances propagating along coronal
loops in EUV/X-ray imaging time series. These faint upflows are most
likely driven from below and have been associated with chromospheric
jets that are (partially) rapidly heated to coronal temperatures at
low heights. These two scenarios (waves versus flows) are difficult to
differentiate using only imaging data, but careful analysis of spectral
line profiles indicates that faint upflows are likely responsible
for some of the observed quasi-periodic oscillatory signals in the
corona. We show that recent EIS measurements of intensity and velocity
oscillations of coronal lines (which had previously been interpreted
as direct evidence for propagating waves) are actually accompanied
by significant oscillations in the line width that are driven by a
quasi-periodically varying component of emission in the blue wing of
the line. This faint additional component of blue-shifted emission
quasi-periodically modulates the peak intensity and line centroid
of a single Gaussian fit to the spectral profile with the same small
amplitudes (respectively a few percent of background intensity and a
few km s-1) that were previously used to infer the presence
of slow-mode magnetoacoustic waves. Our results indicate that it
is possible that a significant fraction of the quasi-periodicities
observed with coronal imagers and spectrographs that have previously
been interpreted as propagating magnetoacoustic waves are instead
caused by these upflows. The different physical cause for coronal
oscillations would significantly impact the prospects of successful
coronal seismology using propagating disturbances in coronal loops.
Title: On Redshifts and Blueshifts in the Transition Region and Corona
Authors: Hansteen, V. H.; Hara, H.; De Pontieu, B.; Carlsson, M.
Bibcode: 2010ApJ...718.1070H
Altcode: 2010arXiv1001.4769H
Emission lines formed in the transition region (TR) of the Sun have long
been known to show pervasive redshifts. Despite a variety of proposed
explanations, these TR downflows (and the slight upflows in the low
corona) remain poorly understood. We present results from comprehensive
three-dimensional MHD models that span the upper convection zone up to
the corona, 15 Mm above the photosphere. The TR and coronal heating
in these models is caused by the stressing of the magnetic field by
photospheric and convection "zone dynamics," but also in some models by
the injection of emerging magnetic flux. We show that rapid, episodic
heating, at low heights of the upper chromospheric plasma to coronal
temperatures naturally produces downflows in TR lines, and slight
upflows in low coronal lines, with similar amplitudes to those observed
with EUV/UV spectrographs. We find that TR redshifts naturally arise
in episodically heated models where the average volumetric heating
scale height lies between that of the chromospheric pressure scale
height of 200 km and the coronal scale height of 50 Mm.
Title: The Impact of New EUV Diagnostics on CME-Related Kinematics
Authors: McIntosh, Scott W.; De Pontieu, Bart; Leamon, Robert J.
Bibcode: 2010SoPh..265....5M
Altcode: 2010SoPh..tmp...74M; 2010arXiv1001.2022M
We present the application of novel diagnostics to the spectroscopic
observation of a Coronal Mass Ejection (CME) on disk by the Extreme
Ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. We
apply a recently developed line profile asymmetry analysis to the
spectroscopic observation of NOAA AR 10930 on 14 - 15 December 2006
to three raster observations before and during the eruption of a 1000
km s−1 halo CME. We see the impact that the observer's
line-of-sight and magnetic field geometry have on the diagnostics
used. Further, and more importantly, we identify the on-disk signature
of a high-speed outflow behind the CME in the dimming region arising
as a result of the eruption. Supported by recent coronal observations
of the STEREO spacecraft, we speculate about the momentum flux
resulting from this outflow as a secondary momentum source to the
CME. The results presented highlight the importance of spectroscopic
measurements in relation to CME kinematics, and the need for full-disk
synoptic spectroscopic observations of the coronal and chromospheric
plasmas to capture the signature of such explosive energy release as
a way of providing better constraints of CME propagation times to L1,
or any other point of interest in the heliosphere.
Title: Quasi-periodic Signatures in the Transition Region and Corona:
Waves or Flows?
Authors: McIntosh, Scott W.; De Pontieu, B.
Bibcode: 2010AAS...21630502M
Altcode:
Since the discovery of quasi-periodic oscillations with periods of order
3-10 minutes in coronal loops with TRACE and EIT (and later with EUVI
and EIS), these oscillations have mostly been interpreted as evidence
for propagating slow-mode magnetoacoustic waves in a low plasma beta
environment originating, most-likely, in the chromosphere. We show that
this interpretation is not unique, and that at least for plage-related
coronal loops, it may not be the most likely cause for the observed
quasi-periodicities. We use Monte Carlo simulations to show that current
oscillation detection methods based on wavelet analysis, and wave
tracking cannot distinguish the quasi-periodic signals of such waves
in coronal imaging timeseries with those caused by the faint signal
from upflows at 50-150 km/s that have lifetimes of order 1-2 minutes
and that occur randomly in time and occur on granular timescales. Such
upflows were recently discovered as blueward line asymmetries with
EIS and have been linked to chromospheric, spicular upflows that
are rapidly heated to coronal temperatures. We use EIS and SUMER
spectra to show that these faint upflows at the footpoints of coronal
loops sometimes occur quasi-periodically on timescales of order 5-15
minutes. Finally, we show that recent EIS measurements of intensity and
velocity oscillations, that have been interpreted as direct evidence for
propagating waves, are fully compatible with a scenario in which faint
upflows at high speed occur quasi-periodically. We show evidence from
spectral line asymmetry analysis that support this scenario. We suggest
that a significant fraction of the quasi-periodicities observed with
coronal imagers and spectrographs that have previously been interpreted
as propagating magnetoacoustic waves, may instead be caused by these
upflows. The uncertainty in the identification of the physical cause for
coronal oscillations significantly impacts the prospects of successful
coronal seismology using propagating, slow-mode magneto-acoustic waves.
Title: Comparison Of Observations And Advanced Numerical Simulations
Of Type II Spicules
Authors: Martinez-Sykora, Juan; De Pontieu, B.; Hansteen, V.;
Moreno-Insertis, F.
Bibcode: 2010AAS...21640306M
Altcode: 2010BAAS...41..878M
We have performed realistic 3D radiation MHD simulations of the
solar atmosphere. These simulations show jet-like features that
are similar to the type II spicules discovered with Hinode's Solar
Optical Telescope. These type II spicules have been associated with
so-called rapid blueshifted events (RBE's) on the solar disk, and with
significant blueward asymmetries in transition region and coronal
lines at the footpoints of coronal loops (discovered with Hinode's
EIS). These observational results and their ubiquity suggest they may
play a significant role in providing the corona with hot plasma. We
will present a detailed comparison of the properties of the simulated
jets, with those of type II spicules (observed with Hinode) and RBE's
(with ground-based instruments). We will present analysis of a wide
variety of synthetic emission lines from the simulations covering
temperatures from 10,000 K to several million K, and compare their
intensities, velocities, line widths and asymmetry with those of the
observed phenomena. We will also show how the formation mechanism of
these jets (reconnection at tangential discontinuities) complicates
efforts to establish a firm link between observations of magnetic
fields and of chromospheric flows, and suggests that magnetic field
observations at chromospheric heights may be crucial to establish from
observations how these jets are formed.
Title: Prevalence And Temperature Dependence Of Ubiquitous High
Speed Upflows In Transition Region And Corona
Authors: De Pontieu, Bart; McIntosh, S.
Bibcode: 2010AAS...21640301D
Altcode: 2010BAAS...41R.877D
Recent observations and analysis have revealed the presence of
ubiquitous rapid upflows with velocities of order 50-150 km/s in the
lower solar atmosphere. We have found signatures of these events in
data from a broad range of imaging and spectroscopic instruments in the
chromosphere, in the form of spicules, and in the transition region
(TR) and corona, in the form of blueward asymmetries of TR/coronal
spectral line profiles, and propagating disturbances in coronal
imaging. Preliminary analysis suggests that these upflows are part
of a previously undetected, but relentless transfer of mass between
the dense lower atmosphere and tenuous corona in which a potentially
significant amount of plasma may be heated to coronal temperatures
at very low heights, in the upper chromosphere, TR and low corona. There are many unresolved issues regarding the properties, formation
mechanism and impact of these rapid upflow events. How ubiquitous are
they? Do they occur at the footpoint regions of loops across whole
active regions, or only at the edges? How do the upflow speeds vary
with temperature? We perform a large sample study of active regions
observed with Hinode/EIS and study the asymmetry of the TR and coronal
lines for a large number of viewing angles (from center to limb) and
magnetic field configurations. We also use double fits of gaussians to
determine the velocity of high velocity component, and its variation
as a function of temperature. These measurements can provide direct
constraints for coronal heating models.
Title: STEREO observations of quasi-periodically driven high velocity
outflows in polar plumes
Authors: McIntosh, S. W.; Innes, D. E.; de Pontieu, B.; Leamon, R. J.
Bibcode: 2010A&A...510L...2M
Altcode: 2010arXiv1001.3377M
Context. Plumes are one of the most ubiquitous features seen at the
limb in polar coronal holes and are considered to be a source of
high density plasma streams to the fast solar wind.
Aims: We
analyze STEREO observations of plumes and aim to reinterpret and place
observations with previous generations of EUV imagers within a new
context that was recently developed from Hinode observations.
Methods: We exploit the higher signal-to-noise, spatial and temporal
resolution of the EUVI telescopes over that of SOHO/EIT to study
the temporal variation of polar plumes in high detail. We employ
recently developed insight from imaging (and spectral) diagnostics of
active region, plage, and quiet Sun plasmas to identify the presence
of apparent motions as high-speed upflows in magnetic regions as
opposed to previous interpretations of propagating waves.
Results: In almost all polar plumes observed at the limb in these
STEREO sequences, in all coronal passbands, we observe high speed
jets of plasma traveling along the structures with a mean velocity of
135 km s-1 at a range of temperatures from 0.5-1.5 MK. The
jets have an apparent brightness enhancement of ~5% above that of the
plumes they travel on and repeat quasi-periodically, with repeat-times
ranging from five to twenty-five minutes. We also notice a very
weak, fine scale, rapidly evolving, but ubiquitous companion of the
plumes that covers the entire coronal hole limb.
Conclusions:
The observed jets are remarkably similar in intensity enhancement,
periodicity and velocity to those observed in other magnetic regions
of the solar atmosphere. They are multi-thermal in nature. We infer
that the jets observed on the plumes are a source of heated mass
to the fast solar wind. Further, based on the previous results that
motivated this study, we suggest that these jets originated in the
upper chromosphere. Five movies are only available in electronic
form at http://www.aanda.org
Title: On red-shifts in the transition region and corona .
Authors: Hansteen, V. H.; Hara, H.; de Pontieu, B.; Carlsson, M.
Bibcode: 2010MmSAI..81..729H
Altcode:
We present evidence that transition region red-shifts are naturally
produced in episodically heated models where the average volumetric
heating scale height lies between that of the chromospheric
pressure scale height of 200 km and the coronal scale height of
50 Mm. In order to do so we present results from 3d MHD models
spanning the upper convection zone up to the corona, 15 Mm above the
photosphere. Transition region and coronal heating in these models
is due both the stressing of the magnetic field by photospheric and
convection `zone dynamics, but also in some models by the injection
of emerging magnetic flux.
Title: Propagating disturbances in the corona: flows or waves?
Authors: de Pontieu, Bart; McIntosh, Scott
Bibcode: 2010cosp...38.2925D
Altcode: 2010cosp.meet.2925D
Since the discovery of quasi-periodic oscillations with periods of
order 3-10 minutes in coronal loops with TRACE and EIT (and later
with STEREO/EUVI and Hinode/EIS), these oscil-lations have mostly been
interpreted as evidence for propagating slow-mode magnetoacoustic waves
in a low plasma β environment. We show that this interpretation is
not unique, and that at least for plage-related coronal loops, it may
not be the most likely cause for the ob-served quasi-periodicities. We
use Monte Carlo simulations to show that current oscillation detection
methods based on wavelet analysis, wave tracking and Bayesian statistics
cannot distinguish the quasi-periodic signals of such waves in coronal
imaging timeseries with those caused by the faint signal from upflows
at 50-150 km/s that have lifetimes of order 1-2 min-utes and that occur
randomly in time and occur on granular timescales. Such upflows were
recently discovered as blueward line asymmetries with EIS and have been
linked to chromo-spheric, spicular upflows that are rapidly heated
to coronal temperatures. We use EIS and SUMER spectra to show that
these faint upflows at the footpoints of coronal loops sometimes occur
quasi-periodically on timescales of order 5-15 minutes. Finally, we show
that recent EIS measurements of intensity and velocity oscillations,
that have been interpreted as direct evi-dence for propagating waves,
are fully compatible with a scenario in which faint upflows at high
speed occur quasi-periodically. We show evidence from spectral line
asymmetry analysis that supports this scenario. We suggest that a
significant fraction of the quasi-periodicities observed with coronal
imagers and spectrographs that have previously been interpreted as
propagating magnetoacoustic waves, may instead be caused by these
upflows. The uncertainty in the identi-fication of the physical cause
for coronal oscillations impacts the prospects of successful coronal
seismology using propagating, slow-mode magneto-acoustic waves.
Title: On the propagation of p-modes into the solar chromosphere
Authors: de Wijn, A. G.; McIntosh, S. W.; De Pontieu, B.
Bibcode: 2010MmSAI..81..588D
Altcode:
We employ tomographic observations of a small region of plage to study
the propagation of waves from the solar photosphere to the chromosphere
using a Fourier phase-difference analysis. Our results show the expected
vertical propagation for waves with periods of 3 minutes. Waves with
5-minute periods, i.e., above the acoustic cut-off period, are found to
propagate only at the periphery of the plage, and only in the direction
in which the field can be reasonably expected to expand. We conclude
that field inclination is critically important in the leakage of p-mode
oscillations from the photosphere into the chromosphere.
Title: High-Speed Transition Region and Coronal Upflows in the
Quiet Sun
Authors: McIntosh, Scott W.; De Pontieu, Bart
Bibcode: 2009ApJ...707..524M
Altcode: 2009arXiv0910.5191M
We study the line profiles of a range of transition region (TR)
emission lines observed in typical quiet-Sun regions. In magnetic
network regions, the Si IV 1402 Å, C IV 1548 Å, N V 1238 Å, O VI
1031 Å, and Ne VIII 770 Å spectral lines show significant asymmetry
in the blue wing of the emission line profiles. We interpret these
high-velocity upflows in the lower and upper TR as the quiet-Sun
equivalent of the recently discovered upflows in the low corona above
plage regions. The latter have been shown to be directly associated
with high-velocity chromospheric spicules that are (partially) heated
to coronal temperatures and play a significant role in supplying the
active region corona with hot plasma. We show that a similar process
likely dominates the quiet-Sun network. We provide a new interpretation
of the observed quiet-Sun TR emission in terms of the relentless
mass transport between the chromosphere and corona—a mixture of
emission from dynamic episodic heating and mass injection into the
corona as well as that from the previously filled, slowly cooling,
coronal plasma. Analysis of the observed upflow component shows that
it carries enough hot plasma to play a significant role in the energy
and mass balance of the quiet corona. We determine the temperature
dependence of the upflow velocities to constrain the acceleration and
heating mechanism that drives these upflows. We also show that the
temporal characteristics of these upflows suggest an episodic driver
that sometimes leads to quasi-periodic signals. We suggest that at
least some of the quasi-periodicities observed with coronal imagers
and spectrographs that have previously been interpreted as propagating
magnetoacoustic waves, may instead be caused by these upflows.
Title: The Interface Region Imaging Spectrograph (IRIS) Small Explorer
Authors: de Pontieu, B.; Title, A. M.; Schryver, C. J.; Lemen, J. R.;
Golub, L.; Kankelborg, C. C.; Carlsson, M.
Bibcode: 2009AGUFMSH33B1499D
Altcode:
The Interface Region Imaging Spectrograph (IRIS) was recently selected
as a small explorer mission by NASA. The primary goal of IRIS is to
understand how the solar atmosphere is energized. The IRIS investigation
combines advanced numerical modeling with a high resolution 20 cm UV
imaging spectrograph that will obtain spectra covering temperatures
from 4,500 to 10 MK in three wavelength ranges (1332-1358 Angstrom,
1390-1406 Angstrom and 2785-2835 Angstrom) and simultaneous images
covering temperatures from 4,500 K to 65,000 K. IRIS will obtain UV
spectra and images with high resolution in space (1/3 arcsec) and time
(1s) focused on the chromosphere and transition region of the Sun, a
complex dynamic interface region between the photosphere and corona. In
this region, all but a few percent of the non-radiative energy leaving
the Sun is converted into heat and radiation. IRIS fills a crucial gap
in our ability to advance Sun-Earth connection studies by tracing the
flow of energy and plasma through this foundation of the corona and
heliosphere. The IRIS investigation is led by PI Alan Title (LMSAL)
with major participation by the Harvard Smithsonian Astrophysical
Observatory, Montana State University, NASA Ames Research Center,
Stanford University and the University of Oslo (Norway). IRIS is
scheduled for launch in late 2012, and will have a nominal two year
mission lifetime.
Title: Interactions Between Reversed Granulation, p-Modes, and
Magnetism?
Authors: de Wijn, A. G.; McIntosh, S. W.; de Pontieu, B.
Bibcode: 2009ASPC..415...36D
Altcode: 2009arXiv0902.1966D
We investigate features that are observed in Ca II H sequences from
Hinode in places where reversed granulation seems to interact with
p-modes. These features appear ubiquitously in the quiet sun. They
are co-spatial with reversed granulation, and display similar
general properties, but have sharper edges and show fast brightness
changes. They also appear predominantly above wide intergranular
lanes, indicating a potential connection with magnetism. We report on
the appearance and dynamics of these features using high-resolution,
high-cadence observations from Hinode, and we discuss their possible
origin.
Title: What Goes Up Doesn't Necessarily Come Down! Connecting the
Dynamics of the Chromosphere and Transition Region with TRACE,
Hinode and SUMER
Authors: McIntosh, S. W.; de Pontieu, B.
Bibcode: 2009ASPC..415...24M
Altcode: 2009arXiv0901.2814M
We explore joint observations of the South-East limb made by
Hinode, TRACE and SOHO/SUMER on April 12, 2008 as part of the Whole
Heliosphere Interval (WHI) Quiet Sun Characterization targeted observing
program. During the sequence a large, 10Mm long, macro-spicule was sent
upward and crossed the line-of-sight of the SUMER slit, an event that
affords us an opportunity to study the coupling of cooler chromospheric
material to transition region emission formed as hot as 600,000K. This
short article provides preliminary results of the data analysis.
Title: Observing the Roots of Coronal Heating - in the Chromosphere
Authors: McIntosh, S. W.; de Pontieu, B.; Hansteen, V. H.; Schrjver, K.
Bibcode: 2009AGUFMSH44A..01M
Altcode:
I will discuss recent results using Hinode/SOT-EIS-XRT, SOHO/SUMER,
CRISP (at the Swedish Solar Telescope) and TRACE that provide a
direct connection between coronal dynamics and those of the lower
atmosphere. We use chromospheric measurements (H-alpha and Ca II
8542 spectral imaging, and Ca II H images), as well as UV spectra
(EIS and SUMER), and EUV/X-ray images (XRT and TRACE) to show that
faint, high-speed upflows at velocities of 50-100 km/s across a wide
range of temperatures from chromospheric (10,000 K), through lower
and upper transition region (0.1 to 0.7 MK) and coronal temperatures
(2 MK) are associated with significant mass-loading of the corona with
hot plasma. Our observations are incompatible with current models in
which coronal heating occurs as a result of nanoflares at coronal
heights. Instead we suggest that a significant fraction of heating
of plasma to coronal temperatures may occur at chromospheric heights
in association with jets driven from below (the recently discovered
type II spicules). Illustrating the mass and energy transport between
the chromosphere, transition region and corona, as deduced from Hinode
observations. Convective flows and oscillations in the convection zone
and photosphere of the Sun buffet the magnetic field of the Sun. This
leads to at least two different kinds of jets in the chromosphere:
Type I, and II spicules. Type II spicules drive matter upward violently
and likely form when magnetic field reconnects because of stresses
introduced by convective flows. A significant fraction of the plasma
in type II spicules is heated to coronal temperatures (>1MK),
providing the corona with hot plasma. The correlation between the
chromospheric and coronal parts of the spicules depends greatly on the
viewing angle between the line-of-sight and the direction of the upward
flows. Order of magnitude estimates indicate that the mass supplied
by type II spicules plays a significant role in supplying the corona
with hot plasma.
Title: Using SiC for Lightweight EUV Space Optics
Authors: Martinez-Galarce, Dennis S.; Boerner, P.; De Pontieu, B.;
Katz, N.; Title, A.; Soufli, R.; Robinson, J. C.; Baker, S. L.;
Gullikson, E. M.
Bibcode: 2009SPD....41.1813M
Altcode:
SiC technology is fast becoming a material of choice for space
systems. Herein, we present a novel design for an EUV telescope made
entirely of SiC - optics and metering structure inclusive - called the
High-resolution Lightweight Telescope for the EUV (HiLiTE). HiLiTE is a
Cassegrain telescope with multilayer coated SiC optics tuned to operate
at 465 Å, and will image Ne VII emission formed in solar transition
region plasma at 500,000 K. HiLiTE will have an aperture of 30 cm,
angular resolution of 0.2 arc seconds and operate at a cadence of 5
seconds or less, having a mass that is about ¼ that of one of the
20 cm aperture telescopes on the Atmospheric Imaging Assembly (AIA)
instrument aboard NASA's Solar Dynamics Observatory (SDO). This new
instrument technology thus serves as a path finder to a post-AIA,
Explorer-class mission.
Title: Observing Episodic Coronal Heating Events Rooted in
Chromospheric Activity
Authors: McIntosh, Scott W.; De Pontieu, Bart
Bibcode: 2009ApJ...706L..80M
Altcode: 2009arXiv0910.2452M
We present the results of a multi-wavelength study of episodic plasma
injection into the corona of active region (AR) 10942. We exploit
long-exposure images of the Hinode and Transition Region and Coronal
Explorer spacecraft to study the properties of faint, episodic,
"blobs" of plasma that are propelled upward along coronal loops
that are rooted in the AR plage. We find that the source location
and characteristic velocities of these episodic upflow events match
those expected from recent spectroscopic observations of faint coronal
upflows that are associated with upper chromospheric activity, in the
form of highly dynamic spicules. The analysis presented ties together
observations from coronal and chromospheric spectrographs and imagers,
providing more evidence of the connection of discrete coronal mass
heating and injection events with their source, dynamic spicules,
in the chromosphere.
Title: On-disk Counterparts of Type II Spicules in the Ca II 854.2
nm and Hα Lines
Authors: Rouppe van der Voort, L.; Leenaarts, J.; de Pontieu, B.;
Carlsson, M.; Vissers, G.
Bibcode: 2009ApJ...705..272R
Altcode: 2009arXiv0909.2115R
Recently, a second type of spicules was discovered at the solar
limb with the Solar Optical Telescope onboard the Japanese Hinode
spacecraft. These previously unrecognized type II spicules are thin
chromospheric jets that are shorter lived (10-60 s) and that show much
higher apparent upward velocities (of order 50-100 km s-1)
than the classical spicules. Since they have been implicated in
providing hot plasma to coronal loops, their formation, evolution,
and properties are important ingredients for a better understanding
of the mass and energy balance of the low solar atmosphere. Here, we
report on the discovery of the disk counterparts of type II spicules
using spectral imaging data in the Ca II 854.2 nm and Hα lines with
the CRisp Imaging SpectroPolarimeter at the Swedish Solar Telescope in
La Palma. We find rapid blueward excursions in the line profiles of
both chromospheric lines that correspond to thin, jet-like features
that show apparent velocities of order 50 km s-1. These
blueward excursions seem to form a separate absorbing component with
Doppler shifts of order 20 and 50 km s-1 for the Ca II 854.2
nm and Hα line, respectively. We show that the appearance, lifetimes,
longitudinal and transverse velocities, and occurrence rate of these
rapid blue excursions on the disk are very similar to those of the type
II spicules at the limb. A detailed study of the spectral line profiles
in these events suggests that plasma is accelerated along the jet,
and plasma is being heated throughout the short lifetime of the event.
Title: On the Propagation of p-Modes Into the Solar Chromosphere
Authors: de Wijn, A. G.; McIntosh, S. W.; De Pontieu, B.
Bibcode: 2009ApJ...702L.168D
Altcode: 2009arXiv0908.1383D
We employ tomographic observations of a small region of plage to study
the propagation of waves from the solar photosphere to the chromosphere
using a Fourier phase-difference analysis. Our results show the expected
vertical propagation for waves with periods of 3 minutes. Waves with
5 minute periods, i.e., above the acoustic cutoff period, are found to
propagate only at the periphery of the plage, and only in the direction
in which the field can be reasonably expected to expand. We conclude
that field inclination is critically important in the leakage of p-mode
oscillations from the photosphere into the chromosphere.
Title: Estimating the Chromospheric Absorption of Transition Region
Moss Emission
Authors: De Pontieu, Bart; Hansteen, Viggo H.; McIntosh, Scott W.;
Patsourakos, Spiros
Bibcode: 2009ApJ...702.1016D
Altcode: 2009arXiv0907.1883D
Many models for coronal loops have difficulty explaining the observed
EUV brightness of the transition region, which is often significantly
less than theoretical models predict. This discrepancy has been
addressed by a variety of approaches including filling factors and
time-dependent heating, with varying degrees of success. Here, we
focus on an effect that has been ignored so far: the absorption of
EUV light with wavelengths below 912 Å by the resonance continua
of neutral hydrogen and helium. Such absorption is expected to occur
in the low-lying transition region of hot, active region loops that
is colocated with cool chromospheric features and called "moss" as a
result of the reticulated appearance resulting from the absorption. We
use cotemporal and cospatial spectroheliograms obtained with the Solar
and Heliospheric Observatory/SUMER and Hinode/EIS of Fe XII 1242 Å,
195 Å, and 186.88 Å, and compare the density determination from
the 186/195 Å line ratio to that resulting from the 195/1242 Å line
ratio. We find that while coronal loops have compatible density values
from these two line pairs, upper transition region moss has conflicting
density determinations. This discrepancy can be resolved by taking
into account significant absorption of 195 Å emission caused by
the chromospheric inclusions in the moss. We find that the amount of
absorption is generally of the order of a factor of 2. We compare to
numerical models and show that the observed effect is well reproduced
by three-dimensional radiative MHD models of the transition region
and corona. We use STEREO A/B data of the same active region and find
that increased angles between line of sight and local vertical cause
additional absorption. Our determination of the amount of chromospheric
absorption of TR emission can be used to better constrain coronal
heating models.
Title: Observational Signatures of Simulated Reconnection Events in
the Solar Chromosphere and Transition Region
Authors: Heggland, L.; De Pontieu, B.; Hansteen, V. H.
Bibcode: 2009ApJ...702....1H
Altcode: 2009arXiv0902.0977H
We present the results of numerical simulations of wave-induced magnetic
reconnection in a model of the solar atmosphere. In the magnetic field
geometry we study in this paper, the waves, driven by a monochromatic
piston and a driver taken from Hinode observations, induce periodic
reconnection of the magnetic field, and this reconnection appears to
help drive long-period chromospheric jets. By synthesizing spectra
for a variety of wavelengths that are sensitive to a wide range of
temperatures, we shed light on the often confusing relationship between
the plethora of jet-like phenomena in the solar atmosphere, e.g.,
explosive events, spicules, and other phenomena thought to be caused by
reconnection. Our simulations produce spicule-like jets with lengths
and lifetimes that match observations, and the spectral signatures of
several reconnection events are similar to observations of explosive
events. We also find that in some cases, absorption from overlying
neutral hydrogen can hide emission from matter at coronal temperatures.
Title: Explosive Events Associated with a Surge
Authors: Madjarska, M. S.; Doyle, J. G.; de Pontieu, B.
Bibcode: 2009ApJ...701..253M
Altcode: 2009arXiv0906.2544M
The solar atmosphere contains a wide variety of small-scale transient
features. Here, we explore the interrelation between some of them such
as surges, explosive events, and blinkers via simultaneous spectral
and imaging data taken with the TRACE imager, the SUMER and Coronal
Diagnostics Spectrometer (CDS) on board SOHO, and Swedish Vacuum Solar
Telescope La Palma. The features were observed in spectral lines with
formation temperatures from 10,000 K to 1 MK and with the TRACE Fe
IX/X 171 Å filter. The Hα filtergrams were taken in the wings of
the Hα 6365 Å line at ±700 mÅ and ±350 mÅ. The alignment of all
data in both time and solar XY shows that SUMER line profiles, which
are attributed to explosive events, are due to a surge phenomenon. The
surge's up- and downflows, which often appear simultaneously, correspond
to the blue- and redshifted emission of the transition region N V
1238.82 Å and O V 629.77 Å lines as well as radiance increases of
the C I, S I, and S II and Si II chromospheric lines. Some parts of
the surge are also visible in the TRACE 171 Å images which could
suggest heating to coronal temperatures. The surge is triggered,
most probably, by one or more Elerman bombs which are best visible
in Hα ± 350 Å but were also registered by TRACE Fe IX/X 171 Å
and correspond to a strong radiance increase in the CDS Mg IX 368.07
Å line. With the present study, we demonstrate that the division of
small-scale transient events into a number of different subgroups,
for instance explosive events, blinkers, spicules, surges or just
brightenings, is ambiguous, implying that the definition of a feature
based only on either spectroscopic or imaging characteristics as well
as insufficient spectral and spatial resolution can be incomplete.
Title: Spicule-Like Structures Observed in Three-Dimensional Realistic
Magnetohydrodynamic Simulations
Authors: Martínez-Sykora, Juan; Hansteen, Viggo; De Pontieu, Bart;
Carlsson, Mats
Bibcode: 2009ApJ...701.1569M
Altcode: 2009arXiv0906.4446M
We analyze features that resemble type I spicules in two different
three-dimensional numerical simulations in which we include horizontal
magnetic flux emergence in a computational domain spanning the
upper layers of the convection zone to the lower corona. The two
simulations differ mainly in the pre-existing ambient magnetic field
strength and in the properties of the inserted flux tube. We use the
Oslo Staggered Code to solve the full magnetohydrodynamic equations
with nongray and non-LTE radiative transfer and thermal conduction
along the magnetic field lines. We find a multitude of features that
show a spatiotemporal evolution that is similar to that observed in
type I spicules, which are characterized by parabolic height versus
time profiles, and are dominated by rapid upward motion at speeds
of 10-30 km s-1, followed by downward motion at similar
velocities. We measured the parameters of the parabolic profile of the
spicules and find similar correlations between the parameters as those
found in observations. The values for height (or length) and duration
of the spicules found in the simulations are more limited in range than
those in the observations. The spicules found in the simulation with
higher pre-existing ambient field have shorter length and smaller
velocities. From the simulations, it appears that these kinds of
spicules can, in principle, be driven by a variety of mechanisms that
include p-modes, collapsing granules, magnetic energy release in the
photosphere and lower chromosphere, and convective buffeting of flux
concentrations.
Title: Observing the Roots of Solar Coronal Heating—in the
Chromosphere
Authors: De Pontieu, Bart; McIntosh, Scott W.; Hansteen, Viggo H.;
Schrijver, Carolus J.
Bibcode: 2009ApJ...701L...1D
Altcode: 2009arXiv0906.5434D
The Sun's corona is millions of degrees hotter than its 5000 K
photosphere. This heating enigma is typically addressed by invoking
the deposition at coronal heights of nonthermal energy generated
by the interplay between convection and magnetic field near the
photosphere. However, it remains unclear how and where coronal heating
occurs and how the corona is filled with hot plasma. We show that energy
deposition at coronal heights cannot be the only source of coronal
heating by revealing a significant coronal mass supply mechanism that
is driven from below, in the chromosphere. We quantify the asymmetry
of spectral lines observed with Hinode and SOHO and identify faint
but ubiquitous upflows with velocities that are similar (50-100 km
s-1) across a wide range of magnetic field configurations and
for temperatures from 100,000 to several million degrees. These upflows
are spatiotemporally correlated with and have similar upward velocities
as recently discovered, cool (10,000 K) chromospheric jets or (type II)
spicules. We find these upflows to be pervasive and universal. Order
of magnitude estimates constrained by conservation of mass and observed
emission measures indicate that the mass supplied by these spicules can
play a significant role in supplying the corona with hot plasma. The
properties of these events are incompatible with coronal loop models
that include only nanoflares at coronal heights. Our results suggest
that a significant part of the heating and energizing of the corona
occurs at chromospheric heights, in association with chromospheric jets.
Title: Reconciling Chromospheric and Coronal Observations of
Alfvenic Waves
Authors: McIntosh, Scott W.; De Pontieu, B.; Tomczyk, S.
Bibcode: 2009SPD....40.1303M
Altcode:
We review the properties of the Alfvenic waves that were discovered
with Hinode/SOT and that have been shown to permeate the upper
chromosphere. Statistical analysis shows that, if they penetrate into
the corona, these waves carry enough energy to impact the energy balance
of the solar wind and quiet Sun corona. However, CoMP observations
of Alfven waves show much smaller resolved amplitudes than would be
expected from the leakage of chromospheric waves into the corona. We
use Monte Carlo simulations to show that line-of-sight superposition
of a mix of Alfvenic waves with properties similar to those observed
with Hinode/SOT and CoMP can reproduce the low wave amplitudes and
enhanced non-thermal line broadening observed with CoMP. Our analysis
indicates that the CoMP observations are compatible with a scenario
in which low-frequency Alfvenic waves are responsible for a large
fraction of the non-thermal broadening seen in the corona although
some portion remains from the power spectrum of the wave generation
process. This suggests that the flux carried by Alfvenic waves, in the
finely structured corona, is significant enough to impact the energy
balance of the corona and solar wind.
Title: Observing the Roots of Solar Coronal Heating in the
Chromosphere
Authors: McIntosh, Scott W.; De Pontieu, B.; Hansteen, V.; Schrijver,
C. J.
Bibcode: 2009SPD....40.2602M
Altcode:
The Sun's atmosphere or corona is millions of degrees hotter than
its 5,000 K surface or photosphere. This heating enigma is typically
addressed by invoking the deposition at coronal heights of non-thermal
energy generated by the interplay between convection and magnetic field
near the photosphere. However, it remains unclear how and where coronal
heating occurs and how the corona is filled with hot plasma. Here,
we show that energy deposition at coronal heights cannot be the only
source of coronal heating, by revealing a significant coronal mass
supply mechanism that is driven from below, in the chromosphere, the
interface between photosphere and corona. We quantify the asymmetry
of spectral lines observed with Hinode and SOHO and identify faint
but ubiquitous upflows with velocities that are similar (50-100
km/s) across a wide range of magnetic field configurations and for
temperatures from 100,000 to several million degrees. These upflows
are correlated with and have similar upward velocities as the very fine
and dynamic chromospheric jets, or spicules, discovered by Hinode. As
these phenomena are incompatible with models of coronal loops that
only include nanoflare heating at coronal heights, we conclude that
a significant fraction of the energy needed to heat coronal plasma is
deposited at chromospheric heights in association with spicular jets
driven from below.
Title: The Solar Chromosphere: Old Challenges, New Frontiers
Authors: Ayres, T.; Uitenbroek, H.; Cauzzi, G.; Reardon, K.; Berger,
T.; Schrijver, C.; de Pontieu, B.; Judge, P.; McIntosh, S.; White,
S.; Solanki, S.
Bibcode: 2009astro2010S...9A
Altcode:
No abstract at ADS
Title: The Spectroscopic Footprint of the Fast Solar Wind
Authors: McIntosh, S. W.; Leamon, R. J.; de Pontieu, B.
Bibcode: 2008AGUFMSH41A1612M
Altcode:
We explore a large, complex equatorial coronal hole (ECH) and its
immediate surroundings through the temperature dependence of the
non-thermal line widths of three transition region emission lines
observed by SOHO/SUMER, placing them in context with recent studies of
the other spectroscopic measures taken. Using a recent semi-empirical
model of the solar wind as a basis, we explore the structure of the
solar wind during the observing period and seek to gain a better
understanding of the interaction of this region with the nascent
solar wind.
Title: Advancing our understanding of the chromosphere
Authors: Hansteen, V. H.; Carlsson, M.; de Pontieu, B.
Bibcode: 2008AGUFMSH51C..01H
Altcode:
Recent progress has shown the solar chromosphere to be fundamentally
dynamic, where non-linear techniques must be used to understand
its nature. It is also the region where the magnetic field grows
to dominate the plasma and where the coupling between radiation and
matter becomes becomes quite tenuous. Understanding the workings of the
chromosphere is vital if one is to understand the flow of energy between
the solar surface and its outer atmosphere and wind. Recent numerical
developments have shown that it is feasible to model the chromosphere,
even to the extent that newly available high resolution observations
sometimes can be reproduced in detail. We will discuss the challenges
facing numerical chromospheric models and the observations needed to
validate or refute them.
Title: Dynamics of the upper chromosphere
Authors: de Pontieu, B.; Carlsson, M.; McIntosh, S.; Hansteen, V.;
Tarbell, T.
Bibcode: 2008AGUFMSH51C..05D
Altcode:
In the past few years, high-resolution observations with ground-based
telescopes and the Broadband Filter Imager (BFI) and Narrowband
Filter Imager (NFI) of the Solar Optical Telescope onboard Hinode
have revolutionized our view of the dynamics and energetics of
the chromosphere. We review some of these results, including the
discovery of two different types of spicules and the finding that the
chromosphere is riddled with strong Alfvenic waves. We describe how
these observations, when combined with advanced numerical simulations,
can help address important unresolved issues regarding the connection
between the photosphere and corona, such as the role of waves and
of reconnection in driving the dynamics and energetics of the upper
chromosphere, and how chromospheric dynamics impact the transition
region and corona.
Title: A Coherence-Based Approach for Tracking Waves in the Solar
Corona
Authors: McIntosh, Scott W.; De Pontieu, Bart; Tomczyk, Steven
Bibcode: 2008SoPh..252..321M
Altcode: 2008arXiv0808.2978M; 2008SoPh..tmp..162M
We consider the problem of automatically (and robustly) isolating
and extracting information about waves and oscillations observed
in EUV image sequences of the solar corona with a view to near
real-time application to data from the Atmospheric Imaging Array
(AIA) on the Solar Dynamics Observatory (SDO). We find that a simple
coherence/travel-time based approach detects and provides a wealth
of information on transverse and longitudinal wave phenomena in the
test sequences provided by the Transition Region and Coronal Explorer
(TRACE). The results of the search are pruned (based on diagnostic
errors) to minimize false-detections such that the remainder provides
robust measurements of waves in the solar corona, with the calculated
propagation speed allowing automated distinction between various
wave modes. In this paper we discuss the technique, present results
on the TRACE test sequences, and describe how our method can be
used to automatically process the enormous flow of data (≈1 Tb
day−1) that will be provided by SDO/AIA.
Title: What do Spicules Tell us About the Chromosphere?
Authors: de Pontieu, B.; Carlsson, M.; McIntosh, S.; Hansteen, V.;
Tarbell, T.
Bibcode: 2008ESPM...12.2.15D
Altcode:
In the past few years, high-resolution observations with ground-based
telescopes and the Broadband Filter Imager (BFI) and Narrowband
Filter Imager (NFI) of the Solar Optical Telescope onboard
Hinode have revolutionized our view of spicules and their role in
the chromosphere. We review some of these results, including the
discovery of two different types of spicules with different dynamics
and formation mechanisms, as well as the finding that the chromosphere
is riddled with strong Alfvenic waves. In an effort to determine
the formation mechanism of spicules and their impact on the outer
atmosphere, we further focus on the thermal evolution and velocities
developed by spicules. We use Dopplergrams made in the Na D 589.6 nm,
H-alpha 656.3 nm and Mg B 517.3 nm passbands, as well as filtergrams in
the Ca H 396.8 nm passband to study the spatio-temporal relationship
between the various spicular features. We compare those findings with
synthesized images based on line profiles computed from high-resolution
3D MHD numerical simulations from the University of Oslo. We also use
the Dopplergram data to investigate the velocities that develop in
the two types of spicules that were reported previously. We perform
statistical analysis of apparent velocities in the plane of the sky
and line-of-sight velocities derived from Dopplergrams to disentangle
the superposition of Alfvenic wave amplitudes and field-aligned
flows. We study these properties for a variety of magnetic field
configurations (coronal holes, quiet Sun, active region). Finally,
we focus on the formation mechanism of spicules by analyzing spicular
features in Dopplergrams on the disk that were taken simultaneously
with SP magnetograms.
Title: Flux of Alfven Waves in the Solar Photosphere
Authors: Vranjes, J.; Poedts, S.; Pandey, B. P.; de Pontieu, B. P.
Bibcode: 2008ESPM...12.3.10V
Altcode:
The convective motions in the solar photosphere, resulting in the foot
point motion of different magnetic structures in the solar atmosphere,
are frequently proposed as the source for the excitation of Alfven
waves, which are assumed to propagate towards the chromosphere
and corona resulting finally in the heating of these layers by the
dissipation of this wave energy. However, the photosphere is a) very
weakly ionized, and, b) the dynamics of the plasma particles in this
region is heavily influenced by the plasma-neutral collisions. The
purpose of this work is to check the consequences of these two
facts on the above scenario and their effects on the electromagnetic
waves. Standard plasma theory is used and the wave physics of the weakly
ionized photosphere is discussed. The magnetization and the collision
frequencies of the plasma constituents are quantitatively examined. It is shown that the ions and electrons in the photosphere are
both un-magnetized; their collision frequency with neutrals is much
larger than the gyro-frequency. This implies that eventual Alfven-type
electromagnetic perturbations must involve the neutrals as well. This
has the following consequences. i) In the presence of perturbations,
the whole fluid (plasma + neutrals) moves. ii) The Alfven velocity
includes the total (plasma + neutrals) density and is thus considerably
smaller compared to the collision-less case. iii) The perturbed velocity
of a unit volume, which now includes both plasma and neutrals, becomes
much smaller compared to the ideal (collision-less) case. iv) Finally,
when the effects of partial ionization and collisions are consistently
taken into account, the corresponding wave energy flux for the given
parameters becomes orders of magnitude smaller compared to the ideal
case.
Title: The high-resolution lightweight telescope for the EUV (HiLiTE)
Authors: Martínez-Galarce, Dennis S.; Boerner, Paul; Soufli, Regina;
De Pontieu, Bart; Katz, Noah; Title, Alan; Gullikson, Eric M.;
Robinson, Jeff C.; Baker, Sherry L.
Bibcode: 2008SPIE.7011E..3KM
Altcode: 2008SPIE.7011E.105M
The High-resolution Lightweight Telescope for the EUV (HiLiTE) is
a Cassegrain telescope that will be made entirely of Silicon Carbide
(SiC), optical substrates and metering structure alike. Using multilayer
coatings, this instrument will be tuned to operate at the 465 Å Ne VII
emission line, formed in solar transition region plasma at ~500,000
K. HiLiTE will have an aperture of 30 cm, angular resolution of ~0.2
arc seconds and operate at a cadence of ~5 seconds or less, having a
mass that is about 1/4 that of one of the 20 cm aperture telescopes on
the Atmospheric Imaging Assembly (AIA) instrument aboard NASA's Solar
Dynamics Observatory (SDO). This new instrument technology thus serves
as a path finder to a post-AIA, Explorer-class missions.
Title: Search for High Velocities in the Disk Counterpart of Type
II Spicules
Authors: Langangen, Ø.; De Pontieu, B.; Carlsson, M.; Hansteen,
V. H.; Cauzzi, G.; Reardon, K.
Bibcode: 2008ApJ...679L.167L
Altcode: 2008arXiv0804.3256L
Recently, De Pontieu and coworkers discovered a class of spicules
that evolve more rapidly than previously known spicules, with rapid
apparent motions of 50-150 km s-1, thickness of a few 100
km, and lifetimes of order 10-60 s. These so-called type II spicules
have been difficult to study because of limited spatiotemporal and
thermal resolution. Here we use the IBIS instrument to search for the
high velocities in the disk counterpart of type II spicules. We have
detected rapidly evolving events, with lifetimes that are less than a
minute and often equal to the cadence of the instrument (19 s). These
events are characterized by a Doppler shift that only appears in the
blue wing of the Ca II IR line. Furthermore, the spatial extent,
lifetime, and location near network all suggest a link to type II
spicules. However, the magnitude of the measured Doppler velocity is
significantly lower than the apparent motions seen at the limb. We
use Monte Carlo simulations to show that this discrepancy can be
explained by a forward model in which the visibility on the disk of
the high-velocity flows in these events is limited by a combination
of line-of-sight projection and reduced opacity in upward propelled
plasma, especially in reconnection driven jets that are powered by a
roughly constant energy supply.
Title: Velocities and thermal evolution of chromospheric spicules
Authors: de Pontieu, B.; McIntosh, S. W.; Tarbell, T.; Carlsson,
M. P.; Hansteen, V. H.
Bibcode: 2008AGUSMSP53A..06D
Altcode:
We use the Broadband Filter Imager (BFI) and Narrowband Filter
Imager (NFI) of the Solar Optical Telescope on Hinode to study the
thermal evolution and velocities developed by chromospheric plasma in
spicules. We use Dopplergrams made in the Na D 589.6 nm, Hα 656.3 nm
and Mg B 517.3 nm passbands, as well as filtergrams in the Ca H 396.8 nm
passband to study the spatio-temporal relationship between the various
spicular features. We compare those findings with synthesized images
based on line profiles computed from high-resolution 3D MHD numerical
simulations from the University of Oslo. We also use the Dopplergram
data to investigate the velocities that develop in the two types of
spicules that were reported previously. We perform statistical analysis
of apparent velocities in the plane of the sky and line-of-sight
velocities derived from Dopplergrams to disentangle the superposition
of Alfvenic wave amplitudes and field-aligned flows. We study these
properties for a variety of magnetic field configurations (coronal
holes, quiet Sun, active region). Finally, we focus on the formation
mechanism of spicules by analyzing spicular features in Dopplergrams
on the disk that were taken simultaneously with SP magnetograms. This
work was supported by NASA contract NNM07AA01C. The Hinode mission is
operated by ISAS/JAXA, NAOJ, NASA, STFC, ESA and NSC.
Title: Chromospheric Flows in the Vicinity of Magnetic Features in
the Quiet Sun Observed with Hinode SOT
Authors: Tarbell, T.; de Pontieu, B.; Carlsson, M.; Hansteen, V.;
McIntosh, S.; Ichimoto, K.
Bibcode: 2008AGUSMSP41B..02T
Altcode:
The Narrowband Filter Imager of the Solar Optical Telescope on Hinode
can measure Doppler shifts and line-of- sight magnetic fields in two
lines with contributions from the low chromosphere: Na D 589.6 nm and
Mg b 517.3 nm. The SOT Spectro-Polarimeter also measures very accurate
vector magnetic fields and Doppler velocities in the photosphere. These
observations have diffraction-limited spatial resolution and superb
stability. We present examples of these measurements in quiet sun
at various disk positions. In addition to the expected granulation
and f- and p-modes, conspicuous longer-lived downflows are seen near
strong network flux elements. Transient upflows are also detected,
presumably the base of flows seen in spicules at the limb and H-alpha
mottles on the disk. Velocity features associated with emerging and
cancelling magnetic features are also described. The observations are
compared with synthesized images made from line profiles computed from
the University of Oslo 3-D MHD simulations. This work was supported by
NASA contract NNM07AA01C. The Hinode mission is operated by ISAS/JAXA,
NAOJ, NASA, STFC, ESA and NSC.
Title: Optical Analysis of HiLiTE (High-Resolution Lightweight
Telescope for the EUV)
Authors: Boerner, P.; Martinez-Galarce, D.; de Pontieu, B.; Soufli,
R.; Katz, N.; Title, A.; Gullikson, E.
Bibcode: 2008AGUSMSP51B..09B
Altcode:
We have completed a preliminary design of a telescope capable
of observing the 500,000 K transition region at high spatial (0.2
arcseconds) and temporal (5 seconds) resolution. The High-resolution
Lightweight Telescope for the EUV (HiLiTE) is a Cassegrain telescope
with an aperture of 30 cm, with multilayer-coated optics tuned to the
465 Å the Ne VII emission line formed in plasma at 500,000 K. The
HiLiTE instrument, including both mirrors and the metering structure,
will be constructed entirely from lightweight, thermally stable, high-
stiffness advanced silicon carbide (SiC) material. In this poster we
provide an update on the development of the HiLiTE instrument concept,
including metrology on SiC optics and model results of the instrument's
optical performance during a proposed sounding rocket flight.
Title: Reappraising Transition Region Line Widths in Light of Recent
Alfvén Wave Discoveries
Authors: McIntosh, Scott W.; De Pontieu, Bart; Tarbell, Theodore D.
Bibcode: 2008ApJ...673L.219M
Altcode: 2008arXiv0801.0671M
We provide a new interpretation of ultraviolet transition region
emission line widths observed by the SUMER instrument on the Solar
and Heliospheric Observatory (SOHO). This investigation is prompted
by observations of the chromosphere at unprecedented spatial and
temporal resolution from the Solar Optical Telescope (SOT) on Hinode
revealing that all chromospheric structures above the limb display
significant transverse (Alfvénic) perturbations. We demonstrate
that the magnitude, network sensitivity, and apparent center-to-limb
isotropy of the measured line widths (formed below 250,000 K) can be
explained by an observationally constrained forward model in which the
line width is caused by the line-of-sight superposition of longitudinal
and Alfvénic motions on the small-scale (spicular) structures that
dominate the chromosphere and low transition region.
Title: Energy flux of Alfvén waves in weakly ionized plasma
Authors: Vranjes, J.; Poedts, S.; Pandey, B. P.; de Pontieu, B.
Bibcode: 2008A&A...478..553V
Altcode: 2008arXiv0805.4591V
Context: The overshooting convective motions in the solar photosphere,
resulting in the foot point motion of different magnetic structures
in the solar atmosphere, are frequently proposed as the source for the
excitation of Alfvén waves, which are assumed to propagate towards the
chromosphere and corona resulting finally in the heating of these layers
by the dissipation of this wave energy. However, the photosphere is a)
very weakly ionized, and, b) the dynamics of the plasma particles in
this region is heavily influenced by the plasma-neutral collisions.
Aims: The purpose of this work is to check the consequences
of these two facts on the above scenario and their effects on the
electromagnetic waves.
Methods: Standard plasma theory is used
and the wave physics of the weakly ionized photosphere is discussed. The
magnetization and the collision frequencies of the plasma constituents
are quantitatively examined.
Results: It is shown that the ions
and electrons in the photosphere are both un-magnetized; their collision
frequency with neutrals is much larger than the gyro-frequency. This
implies that eventual Alfvén-type electromagnetic perturbations must
involve the neutrals as well. This has the following consequences: i)
in the presence of perturbations, the whole fluid (plasma + neutrals)
moves; ii) the Alfvén velocity includes the total (plasma + neutrals)
density and is thus considerably smaller compared to the collision-less
case; iii) the perturbed velocity of a unit volume, which now includes
both plasma and neutrals, becomes much smaller compared to the ideal
(collision-less) case; and iv) the corresponding wave energy flux
for the given parameters becomes much smaller compared to the ideal
case.
Conclusions: The wave energy flux through the photosphere
becomes orders of magnitude smaller, compared to the ideal case, when
the effects of partial ionization and collisions are consistently
taken into account.
Title: Spectroscopic Measurements of Dynamic Fibrils in the Ca II
λ8662 Line
Authors: Langangen, Øystein; Carlsson, Mats; Rouppe van der Voort,
Luc; Hansteen, Viggo; De Pontieu, Bart
Bibcode: 2008ApJ...673.1194L
Altcode: 2007arXiv0710.0247L
We present high spatial resolution spectroscopic measurements of dynamic
fibrils (DFs) in the Ca II λ8662 line. These data show clear Doppler
shifts in the identified DFs, which demonstrates that at least a subset
of DFs are actual mass motions in the chromosphere. A statistical
analysis of 26 DFs reveals a strong and statistically significant
correlation between the maximal velocity and the deceleration. The
range of the velocities and the decelerations are substantially lower,
about a factor 2, in our spectroscopic observations compared to the
earlier results based on proper motion in narrowband images. There
are fundamental differences in the different observational methods;
when DFs are observed spectroscopically, the measured Doppler shifts
are a result of the atmospheric velocity, weighted with the response
function to velocity over an extended height. When the proper motion
of DFs is observed in narrowband images, the movement of the top
of the DF is observed. This point is sharply defined because of the
high contrast between the DF and the surroundings. The observational
differences between the two methods are examined by several numerical
experiments using both numerical simulations and a time series of
narrowband Hα images. With basis in the simulations we conclude that
the lower maximal velocity is explained by the low formation height of
the Ca IR line. We conclude that the present observations support the
earlier result that DFs are driven by magnetoacoustic shocks excited
by convective flows and p-modes.
Title: Chromospheric Alfvénic Waves Strong Enough to Power the
Solar Wind
Authors: De Pontieu, B.; McIntosh, S. W.; Carlsson, M.; Hansteen,
V. H.; Tarbell, T. D.; Schrijver, C. J.; Title, A. M.; Shine, R. A.;
Tsuneta, S.; Katsukawa, Y.; Ichimoto, K.; Suematsu, Y.; Shimizu, T.;
Nagata, S.
Bibcode: 2007Sci...318.1574D
Altcode:
Alfvén waves have been invoked as a possible mechanism for the heating
of the Sun's outer atmosphere, or corona, to millions of degrees and
for the acceleration of the solar wind to hundreds of kilometers per
second. However, Alfvén waves of sufficient strength have not been
unambiguously observed in the solar atmosphere. We used images of
high temporal and spatial resolution obtained with the Solar Optical
Telescope onboard the Japanese Hinode satellite to reveal that the
chromosphere, the region sandwiched between the solar surface and
the corona, is permeated by Alfvén waves with strong amplitudes on
the order of 10 to 25 kilometers per second and periods of 100 to
500 seconds. Estimates of the energy flux carried by these waves and
comparisons with advanced radiative magnetohydrodynamic simulations
indicate that such Alfvén waves are energetic enough to accelerate
the solar wind and possibly to heat the quiet corona.
Title: Hinode and the Corona's Lower Boundary: Spicules and Alfven
Waves
Authors: de Pontieu, B.; McIntosh, S. W.; Hansteen, V.; Carlsson, M. P.
Bibcode: 2007AGUFMSH52C..08D
Altcode:
The lower boundary of the corona, or chromosphere, requires of order
100 times more energy than the corona itself, and provides the mass
to fill coronal loops. Yet the chromosphere and its coupling to the
corona is often overlooked. Recently, observations with the Solar
Optical Telescope (SOT) onboard Hinode and ground-based telescopes
combined with advanced numerical simulations have provided us with
unprecedented views and a better understanding of the (spicular)
dynamics of the chromosphere and how the lower boundary couples to
the corona and solar wind. We analyze high-resolution, high-cadence
Ca II and Hα observations of the solar chromosphere and find that the
dynamics of the magnetized chromosphere are dominated by at least two
different types of spicules. We show that the first type involves up-
and downward motion that is driven by shock waves that form when global
oscillations and convective flows leak into the chromosphere along
magnetic field lines on on 3-7 minute timescales. The second type of
spicules is much more dynamic: they form rapidly (in ~10s), are very
thin (<200km wide), have lifetimes of 10-150s (at any one height) and
seem to be rapidly heated to (at least) transition region temperatures,
sending material through the chromosphere at speeds of order 50-150
km/s. The properties of Type II spicules suggest a formation process
that is a consequence of magnetic reconnection. We discuss the impact of
both spicules types on the coronal mass and energy balance. Our analysis
of Hinode data also indicates that the chromosphere is permeated by
strong Alfvén waves. Both types of spicules are observed to carry
these Alfvén waves, which have significant amplitudes of order 20 km/s,
transverse displacements of order 500-1,000 km and periods of 150-400
s. Estimates of the energy flux carried by these Alfvén waves and
comparisons to advanced radiative MHD simulations indicate that these
waves most likely play a significant role in the acceleration of the
solar wind, and possibly the heating of the quiet Sun corona. We will
discuss the implications of these waves on the energy balance of the
lower atmosphere.
Title: Observing the Influence of Alfven Waves on the Energetics of
the Quiet Solar Corona and Solar Wind
Authors: McIntosh, S. W.; de Pontieu, B.; Tomczyk, S.
Bibcode: 2007AGUFMSH21A0288M
Altcode:
We will present and discuss recent observations of Alfvén waves in the
solar chromosphere, from the Solar Optical Telescope (SOT) on Hinode,
and in the corona, from HAO's ground-based Coronal Multi-channel
Polarimeter (CoMP). These observations unambiguously demonstrate, for
the first time, that the magnetic chromosphere and corona are riddled
with 3- and 5-minute (3-5mHz) Alfvénic oscillations predominantly
propagating outward into the heliosphere. The combined analysis of these
observations, augmented by spectroscopic data from SOHO/SUMER, provide
a compelling look at the influence and importance of ubiquitously
driven Alfvén waves in heating the quiet solar corona and driving
the solar wind. Indeed, we believe that these direct observations of
a low-frequency wave input must provoke a re-evaluation of solar wind
acceleration by high frequency (kHz) ion-cyclotron modes.
Title: The High-resolution Lightweight Telescope for the EUV (HiLiTE)
Authors: Martínez-Galarce, D.; Boerner, P.; de Pontieu, B.; Katz,
N.; Title, A.; Soufli, R.; Gullikson, E.
Bibcode: 2007AGUFMSH44B1738M
Altcode:
The highly-structured and extremely dynamic interface between the
photosphere and the corona is of crucial importance in understanding
solar activity and space weather. Recent high-resolution observations
with Hinode have shown that understanding this interface requires the
ability to study the transition region by imaging plasma around 500,000
K on spatial scales of ~0.2 arc seconds, at cadences of ~5 seconds or
less. We have completed a preliminary design of a telescope capable
of meeting all three of these requirements - thermal, spatial, and
temporal, called the High-resolution Lightweight Telescope for the EUV
(HiLiTE). HiLiTE is a Cassegrain telescope with an aperture of 30 cm,
angular resolution of ~0.2 arc seconds, and a mass that is about 1/4
that of one of the 20 cm aperture telescopes on SDO/AIA. The instrument
bandpass will be tuned to the 46.5 nm Ne VII emission line formed in
plasma at ~500,000 K. HiLiTE, including both mirrors and the metering
structure, will be constructed entirely from lightweight, thermally
stable, high-stiffness advanced Silicon Carbide (SiC) material. While
SiC is an extremely promising material for space telescopes, SiC optics
with the figure and surface finish required for normal-incidence
multilayers have not yet been demonstrated. Upon integrating this
instrument with an Advanced CMOS detector (in parallel development
at Lockheed Martin via another internally funded program) and on
board electronics, HiLiTE can easily be retrofitted to fly on board a
sounding rocket, acting as a path finder to a post-AIA, Explorer-class
mission. Herein, we give an update of the HiLiTE instrument development
program, discussing expected instrument performance as well as the
advantages of using SiC for EUV/Soft X-ray imaging in solar physics.
Title: On Connecting the Dynamics of the Chromosphere and Transition
Region with Hinode SOT and EIS
Authors: Hansteen, Viggo H.; de Pontieu, Bart; Carlsson, Mats;
McIntosh, Scott; Watanabe, Tetsuya; Warren, Harry P.; Harra, Louise K.;
Hara, Hirohisa; Tarbell, Theodore D.; Shine, Dick; Title, Alan M.;
Schrijver, Carolus J.; Tsuneta, Saku; Katsukawa, Yukio; Ichimoto,
Kiyoshi; Suematsu, Yoshinori; Shimizu, Toshifumi
Bibcode: 2007PASJ...59S.699H
Altcode: 2007arXiv0711.0487H
We use coordinated Hinode SOT/EIS observations that include
high-resolution magnetograms, chromospheric, and transition region
(TR) imaging, and TR/coronal spectra in a first test to study how
the dynamics of the TR are driven by the highly dynamic photospheric
magnetic fields and the ubiquitous chromospheric waves. Initial
analysis shows that these connections are quite subtle and require a
combination of techniques including magnetic field extrapolations,
frequency-filtered time-series, and comparisons with synthetic
chromospheric and TR images from advanced 3D numerical simulations. As a
first result, we find signatures of magnetic flux emergence as well as
3 and 5mHz wave power above regions of enhanced photospheric magnetic
field in both chromospheric, transition region, and coronal emission.
Title: Can High Frequency Acoustic Waves Heat the Quiet Sun
Chromosphere?
Authors: Carlsson, Mats; Hansteen, Viggo H.; de Pontieu, Bart;
McIntosh, Scott; Tarbell, Theodore D.; Shine, Dick; Tsuneta, Saku;
Katsukawa, Yukio; Ichimoto, Kiyoshi; Suematsu, Yoshinori; Shimizu,
Toshifumi; Nagata, Shin'ichi
Bibcode: 2007PASJ...59S.663C
Altcode: 2007arXiv0709.3462C
We use Hinode/SOT Ca II H-line and blue continuum broadband observations
to study the presence and power of high frequency acoustic waves at
high spatial resolution. We find that there is no dominant power at
small spatial scales; the integrated power using the full resolution of
Hinode (0.05'' pixels, 0.16'' resolution) is larger than the power in
the data degraded to 0.5'' pixels (TRACE pixel size) by only a factor
of 1.2. At 20 mHz the ratio is 1.6. Combining this result with the
estimates of the acoustic flux based on TRACE data of Fossum &
Carlsson (2006), we conclude that the total energy flux in acoustic
waves of frequency 5-40 mHz entering the internetwork chromosphere of
the quiet Sun is less than 800 W m$^{-2}$, inadequate to balance the
radiative losses in a static chromosphere by a factor of five.
Title: A Tale of Two Spicules: The Impact of Spicules on the Magnetic
Chromosphere
Authors: de Pontieu, Bart; McIntosh, Scott; Hansteen, Viggo H.;
Carlsson, Mats; Schrijver, Carolus J.; Tarbell, Theodore D.; Title,
Alan M.; Shine, Richard A.; Suematsu, Yoshinori; Tsuneta, Saku;
Katsukawa, Yukio; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Nagata,
Shin'ichi
Bibcode: 2007PASJ...59S.655D
Altcode: 2007arXiv0710.2934D
We use high-resolution observations of the Sun in CaIIH (3968Å)
from the Solar Optical Telescope on Hinode to show that there are
at least two types of spicules that dominate the structure of the
magnetic solar chromosphere. Both types are tied to the relentless
magnetoconvective driving in the photosphere, but have very different
dynamic properties. ``Type-I'' spicules are driven by shock waves
that form when global oscillations and convective flows leak into
the upper atmosphere along magnetic field lines on 3--7minute
timescales. ``Type-II'' spicules are much more dynamic: they form
rapidly (in ∼ 10s), are very thin (≤ 200 km wide), have lifetimes
of 10-150s (at any one height), and seem to be rapidly heated to
(at least) transition region temperatures, sending material through
the chromosphere at speeds of order 50--150kms-1. The
properties of Type II spicules suggest a formation process that is
a consequence of magnetic reconnection, typically in the vicinity
of magnetic flux concentrations in plage and network. Both types of
spicules are observed to carry Alfvén waves with significant amplitudes
of order 20kms-1.
Title: Chromospheric Dynamics: Spicules and Waves
Authors: de Pontieu, B.
Bibcode: 2007ASPC..369..231D
Altcode:
The dynamics of the chromosphere are dominated by waves and spicules,
jet-like features that are propelled upwards at speeds of 10-20 km/s
from the photosphere into the low magnetized atmosphere. Spicules
have been a significant challenge to both observers and theorists,
mostly because of their highly dynamic nature and small size, which
are close to current observational limits. The advent of Solar
B will enable the first seeing-free observations that are of high
enough spatial and temporal resolution to reveal the intricate links
between the photospheric magnetic field and elements, the photospheric
flowfield and waves and chromospheric spicules. In this paper, I focus
on the advances Solar-B will be able to make in our understanding of
the formation of spicules and their impact on transition region and
corona. To illustrate the issues and methods needed to tackle this
difficult problem, I present recent work on a synthesis of very high
resolution observations of spicule-like fibrils in active region plage
using the Swedish Solar Telescope (SST, La Palma, Spain) combined with
theoretical modelling of spicule formation.
Title: Numerical Simulations of Shock Wave-driven Chromospheric Jets
Authors: Heggland, L.; De Pontieu, B.; Hansteen, V. H.
Bibcode: 2007ApJ...666.1277H
Altcode: 2007astro.ph..3498H
We present the results of numerical simulations of shock wave-driven
jets in the solar atmosphere. The dependence of observable quantities
such as maximum velocity and deceleration on parameters such as the
period and amplitude of initial disturbances and the inclination of
the magnetic field is investigated. Our simulations show excellent
agreement with observations, and shed new light on the correlation
between velocity and deceleration and on the regional differences
found in observations.
Title: Leakage of photospheric acoustic waves into non-magnetic
solar atmosphere
Authors: Erdélyi, R.; Malins, C.; Tóth, G.; de Pontieu, B.
Bibcode: 2007A&A...467.1299E
Altcode:
Aims:This paper aims to look at the propagation of synthetic
photospheric oscillations from a point source into a two-dimensional
non-magnetic solar atmosphere. It takes a particular interest in
the leakage of 5-min global oscillations into the atmosphere, and
aims to complement efforts on the driving of chromospheric dynamics
(e.g. spicules and waves) by 5-min oscillations.
Methods: A
model solar atmosphere is constructed based on realistic temperature
and gravitational stratification. The response of this atmosphere to
a wide range of adiabatic periodic velocity drivers is numerically
investigated in the hydrodynamic approximation.
Results: The
findings of this modelling are threefold. Firstly, high-frequency waves
are shown to propagate from the lower atmosphere across the transition
region experiencing relatively low reflection and transmitting energy
into the corona. Secondly, it is demonstrated that driving the upper
solar photosphere with a harmonic piston driver at around the 5 min
period may generate three separate standing modes with similar periods
in the chromosphere and transition region. In the cavity formed
by the chromosphere and bounded by regions of low cut-off period
at the photospheric temperature minimum and the transition region
this is caused by reflection, while at either end of this region in
the lower chromosphere and transition region the standing modes are
caused by resonant excitation. Finally, the transition region becomes
a guide for horizontally propagating surface waves for a wide range
of driver periods, and in particular at those periods which support
chromospheric standing waves. Crucially, these findings are the results
of a combination of a chromospheric cavity and resonant excitation in
the lower atmosphere and transition region.
Title: Chromospheric and Transition-Region Dynamics in Plage
Authors: de Wijn, A. G.; de Pontieu, B.; Rutten, R. J.
Bibcode: 2007ASPC..368..137D
Altcode:
We study the dynamical interaction of the solar chromosphere with
the transition region in mossy and non-mossy active-region plage. We
carefully align image sequences taken with the Transition Region And
Coronal Explorer (TRACE) in the ultraviolet passbands around 1550, 1600,
and 1700 Å and the extreme ultraviolet passbands at 171 and 195 Å. We
compute Fourier phase-difference spectra that are spatially averaged
separately over mossy and non-mossy plage to study temporal modulations
as a function of temporal frequency. The 1550 versus 171 Å comparison
shows zero phase difference in non-mossy plage. In mossy plage, the
phase differences between all UV and EUV passbands show pronounced
upward trends with increasing frequency, which abruptly changes
into zero phase difference beyond 4 -- 6 mHz. The phase difference
between the 171 and 195 Å sequences exhibits a shallow dip below 3
mHz and then also turns to zero phase difference beyond this value. We
attribute the various similarities between the UV and EUV diagnostics
that are evident in the phase-difference diagrams to the contribution
of the C IV resonance lines in the 1550 and 1600 Å passbands. The
strong upward trend at the lower frequencies indicates the presence of
upward-traveling disturbances. It points to correspondence between the
lower chromosphere and the upper transition region, perhaps by slow-mode
magnetosonic disturbances, or by a connection between chromospheric and
coronal heating mechanisms. The transition from this upward trend to
zero phase difference at higher frequencies is due to the intermittent
obscuration by fibrils that occult the foot points of hot loops,
which are bright in the EUV and C IV lines, in oscillatory manner.
Title: High-Resolution Observations and Numerical Simulations of
Chromospheric Fibrils and Mottles
Authors: de Pontieu, B.; Hansteen, V. H.; Rouppe van der Voort, L.;
van Noort, M.; Carlsson, M.
Bibcode: 2007ASPC..368...65D
Altcode:
With the recent advent of the Swedish 1-m Solar Telescope (SST),
advanced image processing techniques, as well as numerical simulations
that provide a more realistic view of the chromosphere, a comprehensive
understanding of chromospheric jets such as spicules, mottles and
fibrils is now within reach. In this paper, we briefly summarize results
from a recent analysis of dynamic fibrils, short-lived jet-like features
that dominate the chromosphere (as imaged in Hα) above and about active
region plage. Using extremely high-resolution observations obtained
at the SST, and advanced numerical 2D radiative MHD simulations, we
show that fibrils are most likely formed by chromospheric shock waves
that occur when convective flows and global oscillations leak into the
chromosphere along the field lines of magnetic flux concentrations. In addition, we present some preliminary observations of quiet Sun
jets or mottles. We find that the mechanism that produces fibrils
in active regions is most likely also at work in quiet Sun regions,
although it is modified by the weaker magnetic field and the presence of
more mixed-polarity. A comparison with numerical simulations suggests
that the weaker magnetic field in quiet Sun allows for significantly
stronger (than in active regions) transverse motions that are
superposed on the field-aligned, shock-driven motions. This leads
to a more dynamic, and much more complex environment than in active
region plage. In addition, our observations of the mixed polarity
environment in quiet Sun regions suggest that other mechanisms, such
as reconnection, may well play a significant role in the formation of
some quiet Sun jets. Simultaneous high-resolution magnetograms (such
as those provided by Hinode), as well as numerical simulations that
take into account a whole variety of different magnetic configurations,
will be necessary to determine the relative importance in quiet Sun of,
respectively, the fibril-mechanism and reconnection.
Title: Chromospheric Spectrometry at High Spatial Resolution
Authors: Langangen, Ø.; Carlsson, M.; Rouppe van der Voort, L.;
Hansteen, V. H.; de Pontieu, B.
Bibcode: 2007ASPC..368..145L
Altcode:
In this summary we present spectrograms and images of the
chromosphere obtained in a co-observation campaign with the SST and
the DOT. The data are used to identify and measure the Doppler shifts
of dynamic fibrils. Quantitative comparison with the results of \citep{ol-2006ApJ...647L..73H} requires compensation for several
observational issues.
Title: Observational Evidence For The Ubiquity Of Strong Alfven
Waves In The Magnetized Chromosphere
Authors: De Pontieu, Bart; McIntosh, S. W.; Carlsson, M.; Hansteen,
V. H.; Schrijver, C. J.; Tarbell, T. D.; Title, A.; SOT Team
Bibcode: 2007AAS...210.9415D
Altcode: 2007BAAS...39R.219D
Hinode/SOT Ca II broadband observations show that Alfven waves with
significant amplitudes of order 10-20 km/s and periods of 150-300 s are
extremely ubiquitous in the magnetized middle to upper chromosphere. Our
observations focus on spicules at the limb, and straw-like features
associated with network and plage on the disk. We find that the
weak straw-like features and most spicules all undergo significant
transverse motions that are driven by Alfven waves. These waves are
seen to propagate both up- and downward, and may carry an energy flux
that is significant compared to both the local, coronal and solar wind
energy balance. We will provide estimates of the energy flux carried
by these waves, and will compare our observations with Alfven waves
that are observed in 3D numerical simulations that include advanced
radiative transfer treatment for the chromosphere. This work was
supported by NASA contract NNM07AA01C.
Title: Connecting The Dynamics Of The Chromosphere And Transition
Region With Hinode/sot And Eis
Authors: Hansteen, Viggo H.; McIntosh, S.; De Pontieu, B.; Carlsson,
M.; SOT Team
Bibcode: 2007AAS...210.9430H
Altcode: 2007BAAS...39..222H
We will use coordinated Hinode SOT/EIS observations that include
high-resolution magnetograms, chromospheric and TR imaging and
TR/coronal spectra to study how the dynamics of the TR are driven by
the higly dynamic photospheric magnetic fields and the ubiquitous
chromospheric waves. Using travel time analysis, magnetic field
extrapolations, frequency filtered timeseries and comparisons with
synthetic chromospheric and TR images from advanced 3D numerical
simulations, we will study and establish how the dynamics of the
photosphere, chromosphere and TR are connected.
Title: Magneto-acoustic Waves And Their Role In The Energetics And
Dynamics Of The Solar Chromosphere
Authors: Jefferies, Stuart; De Pontieu, B.; McIntosh, S.; Hansteen,
V. H.
Bibcode: 2007AAS...21012004J
Altcode: 2007BAAS...39..245J
We analyze a diverse set of observations obtained with SOHO and
TRACE, as well as with MOTH and the Swedish 1 m Solar Telescope to
show that sound waves play an important role in shaping the structure
and energetics of the magnetized chromosphere. Travel time analysis
of TRACE, MOTH and SST observations and comparisons with numerical
simulations show that normally evanescent 5 minute p-mode oscillations
leak into the chromosphere along flux tubes that are inclined with
the vertical. Comparisons of SST data of fibril-like jets above
active region plage and quiet Sun mottles with advanced radiative
MHD simulations show how these oscillations develop into slow mode
magnetoacoustic shocks that drive spicule-like chromospheric jets up
to coronal heights. The leaking waves not only drive much of the
dynamics of the magnetized chromosphere: Doppler measurements from the
MOTH instrument at several heights in the atmosphere show that the total
energy flux carried by these leaking waves may play a significant role
in the energy balance of the magnetized chromosphere. We describe
first approaches to determine more precisely how and where the wave
energy is deposited in the low atmosphere.
Title: Magnetoacoustic Shocks as a Driver of Quiet-Sun Mottles
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Hansteen,
V. H.; Carlsson, M.; van Noort, M.
Bibcode: 2007ApJ...660L.169R
Altcode: 2007astro.ph..3535R
We present high spatial and high temporal resolution observations of
the quiet Sun in Hα obtained with the Swedish 1-m Solar Telescope on
La Palma. We observe that many mottles, jetlike features in the quiet
Sun, display clear up- and downward motions along their main axis. In
addition, many mottles show vigorous transverse displacements. Unique
identification of the mottles throughout their lifetime is much harder
than for their active region counterpart, dynamic fibrils. This is
because many seem to lack a sharply defined edge at their top, and
significant fading often occurs throughout their lifetime. For those
mottles that can be reliably tracked, we find that the mottle tops
often undergo parabolic paths. We find a linear correlation between
the deceleration these mottles undergo and the maximum velocity they
reach, similar to what was found earlier for dynamic fibrils. Combined
with an analysis of oscillatory properties, we conclude that at least
part of the quiet-Sun mottles are driven by magnetoacoustic shocks. In
addition, the mixed-polarity environment and vigorous dynamics suggest
that reconnection may play a significant role in the formation of some
quiet-Sun jets.
Title: A Tale of Two Spicules
Authors: McIntosh, Scott W.; De Pontieu, B.; Carlsson, M.; Hansteen,
V. H.; Schrijver, C. J.; Tarbell, T. D.; Title, A. M.; SOT Team
Bibcode: 2007AAS...210.9414M
Altcode: 2007BAAS...39..219M
Hinode/SOT Ca II broadband images and movies show that there are
several different types of spicules at the limb. These different
types are distinguished by dynamics on different timescales. The
first type involves up- and downward motion on timescales of 3-5
minutes. The dynamics of these spicules are very similar to those of
fibrils and mottles as observed on the disk. Recent work suggests that
these are driven by slow-mode magnetoacoustic shocks that form when
convective flows and global oscillations leak into the chromosphere
along magnetic flux tubes. The second type is much more dynamic with
typical lifetimes of 10-60 s. These spicules are characterized by
sudden appearance and disappearance that may be indicative of rapid
heating to TR temperatures. We will describe the properties of these
spicules in various magnetic environments (coronal hole, quiet Sun,
active region) and study the possible role of reconnection in driving
the second type of spicules. In addition, we will perform detailed
comparisons of these different types of jets with synthetic Ca images
derived from advanced 3D numerical simulations that encompass the
convection zone up through the corona.
Title: Can High Frequency Acoustic Waves Heat the Quiet Sun
Chromosphere?
Authors: Carlsson, Mats P. O.; De Pontieu, B.; Tarbell, T.; Hansteen,
V. H.; McIntosh, S.; SOT Team
Bibcode: 2007AAS...210.6306C
Altcode: 2007BAAS...39..172C
We use Hinode/SOT Ca II, G-band and blue continuum broadband
observations to study the presence and power of high frequency acoustic
waves at high spatial resolution. Previous observations with TRACE,
which were limited by the 1 arcsec resolution, and 1D numerical
simulations (Fossum & Carlsson, 2005) have been used to constrain
the possible role of high frequency waves in the heating of the quiet
Sun chromosphere. We will use the higher spatial resolution Hinode
data and comparisons with both 1D and 3D numerical models to study
the amount of high frequency power at smaller scales, and whether that
power is sufficient to heat the quiet Sun chromosphere.
Title: Observations and Simulations of Fibrils and Mottles
Authors: De Pontieu, Bart; Hansteen, Viggo H.; Rouppe van der Voort,
Luc; van Noort, Michiel; Carlsson, Mats
Bibcode: 2007astro.ph..2081D
Altcode:
With the recent advent of the Swedish 1-m Solar Telescope (SST),
advanced image processing techniques, as well as numerical simulations
that provide a more realistic view of the chromosphere, a comprehensive
understanding of chromospheric jets such as spicules, mottles and
fibrils is now within reach. In this paper, we briefly summarize
results from a recent analysis of dynamic fibrils, short-lived
jet-like features that dominate the chromosphere (as imaged in
H-alpha) above and about active region plage. Using extremely
high-resolution observations obtained at the SST, and advanced
numerical 2D radiative MHD simulations, we show that fibrils are most
likely formed by chromospheric shock waves that occur when convective
flows and global oscillations leak into the chromosphere along the
field lines of magnetic flux concentrations. In addition, we present
some preliminary observations of quiet Sun jets or mottles. We find
that the mechanism that produces fibrils in active regions is most
likely also at work in quiet Sun regions, although it is modified by
the weaker magnetic field and the presence of more mixed-polarity. A
comparison with numerical simulations suggests that the weaker magnetic
field in quiet Sun allows for significantly stronger (than in active
regions) transverse motions that are superposed on the field-aligned,
shock-driven motions. This leads to a more dynamic, and much more
complex environment than in active region plage. In addition, our
observations of the mixed polarity environment in quiet Sun regions
suggest that other mechanisms, such as reconnection, may well play a
significant role in the formation of some quiet Sun jets.
Title: Fourier Analysis of Active-Region Plage
Authors: de Wijn, A. G.; De Pontieu, B.; Rutten, R. J.
Bibcode: 2007ApJ...654.1128D
Altcode: 2007arXiv0706.2014D
We study the dynamical interaction of the solar chromosphere with
the transition region in mossy and nonmossy active-region plage. We
carefully align image sequences taken with the Transition Region And
Coronal Explorer (TRACE) in the ultraviolet passbands around 1550,
1600, and 1700 Å and the extreme ultraviolet passbands at 171 and 195
Å. We compute Fourier phase-difference spectra that are spatially
averaged separately over mossy and nonmossy plage to study temporal
modulations as a function of temporal frequency. The 1550 versus 171
Å comparison shows zero phase difference in nonmossy plage. In mossy
plage, the phase differences between all UV and EUV passbands show
pronounced upward trends with increasing frequency, which abruptly
changes into zero phase difference beyond 4-6 mHz. The phase difference
between the 171 and 195 Å sequences exhibits a shallow dip below 3
mHz and then also turns to zero phase difference beyond this value. We
attribute the various similarities between the UV and EUV diagnostics
that are evident in the phase-difference diagrams to the contribution
of the C IV resonance lines in the 1550 and 1600 Å passbands. The
strong upward trend at the lower frequencies indicates the presence of
upward-traveling disturbances. It points to correspondence between the
lower chromosphere and the upper transition region, perhaps by slow-mode
magnetosonic disturbances, or by a connection between chromospheric and
coronal heating mechanisms. The transition from this upward trend to
zero phase difference at higher frequencies is due to the intermittent
obscuration by fibrils that occult the footpoints of hot loops, which
are bright in the EUV and C IV lines, in an oscillatory manner.
Title: High-Resolution Observations and Modeling of Dynamic Fibrils
Authors: De Pontieu, B.; Hansteen, V. H.; Rouppe van der Voort, L.;
van Noort, M.; Carlsson, M.
Bibcode: 2007ApJ...655..624D
Altcode: 2007astro.ph..1786D
We present unprecedented high-resolution Hα observations, obtained
with the Swedish 1 m Solar Telescope, that, for the first time,
spatially and temporally resolve dynamic fibrils in active regions on
the Sun. These jetlike features are similar to mottles or spicules in
quiet Sun. We find that most of these fibrils follow almost perfect
parabolic paths in their ascent and descent. We measure the properties
of the parabolic paths taken by 257 fibrils and present an overview
of the deceleration, maximum velocity, maximum length, and duration,
as well as their widths and the thickness of a bright ring that often
occurs above dynamic fibrils. We find that the observed deceleration
of the projected path is typically only a fraction of solar gravity
and incompatible with a ballistic path at solar gravity. We report on
significant differences of fibril properties between those occurring
above a dense plage region and those above a less dense plage region
where the magnetic field seems more inclined from the vertical. We
compare these findings to advanced numerical two-dimensional radiative
MHD simulations and find that fibrils are most likely formed by
chromospheric shock waves that occur when convective flows and global
oscillations leak into the chromosphere along the field lines of
magnetic flux concentrations. Detailed comparison of observed and
simulated fibril properties shows striking similarities of the values
for deceleration, maximum velocity, maximum length, and duration. We
compare our results with observations of mottles and find that a
similar mechanism is most likely at work in the quiet Sun.
Title: Fourier analysis of chromospheric and transition region
emission above active region plage
Authors: de Wijn, A. G.; de Pontieu, B.; Rutten, R. J.
Bibcode: 2006AGUFMSH23B0364D
Altcode:
We study the dynamical interaction of the solar chromosphere with the
transition region (TR) in mossy and non-mossy active region plage, and
find evidence for correlated brightness changes or upward travelling
disturbances between the low chromosphere and the upper transition
region. We carefully align image sequences taken with the Transition
Region and Coronal Explorer (TRACE) in the ultraviolet passbands around
1550, 1600 and 1700 Å\ (indicative of low chromosphere and low TR)
and the extreme ultraviolet passbands at 171 and 195 Å\ (indicative of
upper transition region). We compute Fourier phase-difference spectra
that are spatially averaged separately over mossy and non-mossy plage to
study temporal modulations as a function of temporal frequency. We find
that in non-mossy plage there is zero phase difference between 1550 Å\
and 171 Å. In mossy plage, the phase differences between all UV and EUV
passbands show pronounced upward trends with increasing frequency, which
abruptly changes into zero phase differences for frequencies beyond 4-6
mHz. The phase difference between the 171 and 195 Å\ sequences exhibits
a shallow dip below 3 mHz and then also turns to zero phase difference
beyond this value. We attribute some of the various similarities between
the UV and EUV diagnostics that are evident in the phase-difference
diagrams to the contribution of the C IV resonance lines in the 1550 and
1600 Å\ passbands. The strong upward trend at lower frequencies in the
phase difference between all UV passbands (including 1700 Å) and 171
Å\ indicates the presence of upward travelling disturbances. Since
1700 Å\ does not contain C IV emission (low TR), this points to a
correlation between brightness changes in the lower chromosphere and
the upper TR, perhaps by slow-mode disturbances, or by a connection
between chromospheric and coronal heating mechanisms. We find that
such correlated brightness changes first occur in the low chromosphere,
and are followed about 400 s later in the upper TR. The transition from
the upward trend in phase difference at low frequencies to zero phase
difference at higher frequencies is due to the intermittent obscuration
by fibrils. These chromospheric jets occult the footpoints of hot loops,
which are bright in the EUV and C IV lines, in oscillatory manner.
Title: Dynamic Fibrils Are Driven by Magnetoacoustic Shocks
Authors: de Pontieu, B.; Hansteen, V. H.; Rouppe van der Voort, L.;
van Noort, M.; Carlsson, M.
Bibcode: 2006AGUFMSH23B0359D
Altcode:
With the recent advent of the Swedish 1-m Solar Telescope (SST),
advanced image processing techniques, as well as numerical simulations
that provide a more realistic view of the chromosphere, a comprehensive
understanding of chromospheric jets such as spicules, mottles and
fibrils is now within reach. We will present results from a recent
analysis of dynamic fibrils, short-lived jet-like features that
dominate the chromosphere (as imaged in Hα) above and about active
region plage. These jets are similar to mottles and spicules in quiet
Sun. Our analysis is based on a time series of extremely high-resolution
(120 km) images taken in Hα linecenter at 1 second cadence, obtained by
the Oslo group at the SST in October 2005. The 78 min long time series
for the first time, spatially and temporally resolves dynamic fibrils
in active regions. Our analysis shows that most of the fibrils follow
almost perfect parabolic paths in their ascent and descent. We measure
the properties of the parabolic paths taken by 257 different dynamic
fibrils, and find that the observed deceleration of the projected
path is typically only a fraction of solar gravity, and incompatible
with a ballistic path at solar gravity. We report on significant
differences of measured fibril properties between those occurring in
association with a dense plage region, and those above a less dense
plage region where the magnetic field seems more inclined away from
the vertical. We compare these observational findings to advanced
numerical 2D radiative MHD simulations, and find that fibrils are most
likely formed by chromospheric shock waves that occur when convective
flows and global oscillations leak into the chromosphere along the
field lines of magnetic flux concentrations. Detailed comparison
of the properties of fibrils found in our observations and those in
our numerical simulations shows striking similarities of the values
for deceleration, maximum velocity, maximum length and duration. The
numerical simulations also reproduce the correlations we observe between
various fibrils properties, as well as the regional differences, taking
into account the different magnetic configuration for the various
regions. We compare our results with observations of mottles and find
that a similar mechanism is most likely at work in the quiet Sun.
Title: Dynamic fibrils in Hα and C IV
Authors: de Wijn, A. G.; De Pontieu, B.
Bibcode: 2006A&A...460..309D
Altcode: 2007arXiv0706.2011D
Aims.To study the interaction of the solar chromosphere with the
transition region, in particular active-region jets in the transition
region and their relation to chromospheric fibrils.
Methods:
.We carefully align image sequences taken simultaneously in C iv with
the Transition Region and Coronal Explorer and in Hα with the Swedish
1-m Solar Telescope. We examine the temporal evolution of "dynamic
fibrils", i.e., individual short-lived active-region chromospheric
jet-like features in Hα.
Results: .All dynamic fibrils appear
as absorption features in Hα that progress from the blue to the red
wing through the line, and often show recurrent behavior. Some of them,
but not all, appear also as bright features in C iv which develop at or
just beyond the apex of the Hα darkening. They tend to best resemble
the Hα fibril at +700 mÅ half a minute earlier.
Conclusions:
.Dynamic chromospheric fibrils observed in Hα regularly correspond to
transition-region jets observed in the ultraviolet. This correspondence
suggests that some plasma associated with dynamic fibrils is heated
to transition-region temperatures.
Title: Rapid Temporal Variability of Faculae: High-Resolution
Observations and Modeling
Authors: De Pontieu, B.; Carlsson, M.; Stein, R.; Rouppe van der Voort,
L.; Löfdahl, M.; van Noort, M.; Nordlund, Å.; Scharmer, G.
Bibcode: 2006ApJ...646.1405D
Altcode:
We present high-resolution G-band observations (obtained with the
Swedish 1 m Solar Telescope) of the rapid temporal variability of
faculae, which occurs on granular timescales. By combining these
observations with magnetoconvection simulations of a plage region, we
show that much of this variability is not intrinsic to the magnetic
field concentrations that are associated with faculae, but rather
a phenomenon associated with the normal evolution and splitting of
granules. We also show examples of facular variability caused by
changes in the magnetic field, with movies of dynamic behavior of
the striations that dominate much of the facular appearance at 0.1"
resolution. Examples of these dynamics include merging, splitting,
rapid motion, apparent fluting, and possibly swaying.
Title: Dynamic Fibrils Are Driven by Magnetoacoustic Shocks
Authors: Hansteen, V. H.; De Pontieu, B.; Rouppe van der Voort, L.;
van Noort, M.; Carlsson, M.
Bibcode: 2006ApJ...647L..73H
Altcode: 2006astro.ph..7332H
The formation of jets such as dynamic fibrils, mottles, and spicules
in the solar chromosphere is one of the most important, but also
most poorly understood, phenomena of the Sun's magnetized outer
atmosphere. We use extremely high resolution observations from the
Swedish 1 m Solar Telescope combined with advanced numerical modeling
to show that in active regions these jets are a natural consequence of
upwardly propagating slow-mode magnetoacoustic shocks. These shocks
form when waves generated by convective flows and global p-mode
oscillations in the lower lying photosphere leak upward into the
magnetized chromosphere. We find excellent agreement between observed
and simulated jet velocities, decelerations, lifetimes, and lengths. Our
findings suggest that previous observations of quiet-Sun spicules and
mottles may also be interpreted in light of a shock-driven mechanism.
Title: The nature of moss and lower atmospheric seismology
Authors: de Pontieu, B.; Erdélyi, R.
Bibcode: 2006RSPTA.364..383D
Altcode:
No abstract at ADS
Title: Simulated Solar Plages
Authors: Stein, R. F.; Carlsson, M.; de Pontieu, B.; Scharmer, G.;
Nordlund, Å.; Benson, D.
Bibcode: 2006apri.meet...30S
Altcode:
No abstract at ADS
Title: a Multi-Wavelength View on Coronal Rain
Authors: Müller, D. A. N.; de Groof, A.; de Pontieu, B.; Hansteen,
V. H.
Bibcode: 2005ESASP.600E..30M
Altcode: 2005dysu.confE..30M; 2005ESPM...11...30M
No abstract at ADS
Title: a Comparison Between Spicules in Hα and CIV
Authors: de Wijn, A. G.; de Pontieu, B.; Erdélyi, R.
Bibcode: 2005ESASP.600E..14D
Altcode: 2005ESPM...11...14D; 2005dysu.confE..14D
No abstract at ADS
Title: a Multi-Wavelength View on Coronal Rain
Authors: Müller, D. A. N.; de Groof, A.; de Pontieu, B.; Hansteen,
V. H.
Bibcode: 2005ESASP.596E..37M
Altcode: 2005ccmf.confE..37M
No abstract at ADS
Title: a Comparison Between Spicules in Hα and CIV
Authors: de Wijn, A.; de Pontieu, B.; Erdélyi, R.
Bibcode: 2005ESASP.596E..33D
Altcode: 2005ccmf.confE..33D
No abstract at ADS
Title: Tracing Coronal Waves Back to the Photosphere
Authors: De Pontieu, B.; Erdelyi, R.; De Moortel, I.; Metcalf, T.
Bibcode: 2005AGUSMSH11C..03D
Altcode:
There are now many observations of waves with periods around 5 minutes
in the outer atmosphere of the Sun. We provide an observational
overview of 5 minute periodicity in chromospheric spicules in active
region plage, upper transition region moss and the low legs of coronal
loops. Using a numerical model, we show that all of these phenomena
are connected: normally evanescent photospheric oscillations can
propagate into the low atmosphere as long as they are guided along
magnetic field lines that are inclined away from the vertical. The
leaked photospheric oscillations develop into shocks and lead to
periodic upward chromospheric flows, which we have identified as
active region spicules. These shocks continue upwards and enter
into the corona. We suggest that TRACE observations of propagating
acoustic waves in the corona are shocked and tunneled photospheric
oscillations. Using SOHO/MDI, TRACE and Imaging Vector Magnetograph
(Hawaii) data we explore how these coronal waves can be exploited to
determine the connectivity between photosphere and corona,and thus
allow seismology of the lower solar atmosphere.
Title: Spicules, mass transfer, oscillations, and the heating of
the corona
Authors: Pasachoff, J. M.; Kozarev, K. A.; Butts, D. L.; Gangestad,
J. W.; Seaton, D. B.; de Pontieu, B.; Golub, L.; Deluca, E.; Wilhelm,
K.; Dammasch, I.
Bibcode: 2005AGUSMSH13C..02P
Altcode:
The mass moving in chromospheric spicules is enough to replace the
corona in a brief time, so understanding the dynamics of spicules
is important for understanding the support and heating of the
solar corona. We have undertaken a program involving simultaneous
high-resolution observations in various chromospheric visible lines
(H-alpha, Ca II H, and G-band, as well as Dopplergrams) using the
Swedish Solar Telescope on La Palma, ultraviolet chromospheric,
transition-region, and coronal lines (Fe IX/X 171 A, Lyman-alpha
1216 A, and continuum/C I/C IV 1600 A) using NASA's TRACE, and
ultraviolet chromospheric and transition-region lines (Si II 1533,
C IV 1548, and Ne VIII 770) using SUMER on SOHO. Our first coordinated
observing run, in May 2004, yielded a variety of images that are under
study, especially for the morphological statistics and dynamics of
spicules. The energy transfer through the chromosphere is relevant to
the overlapping investigation of coronal heating through rapid (1Hz
range) oscillations of coronal loops as observed at total eclipses
by Williams College expeditions. This research is supported by NASA
grant number NNG04GK44G to Williams College. TRACE analysis at SAO
is supported by a contract from Lockheed Martin. SOHO is a project of
international cooperation between ESA and NASA.
Title: Travel Time and Phase Analysis of Waves in the Lower Solar
Chromosphere
Authors: Fleck, B.; Armstrong, J.; Cacciani, A.; de Pontieu, B.;
Finsterle, W.; Jefferies, S. M.; McIntosh, S. W.; Tarbell, T. D.
Bibcode: 2005AGUSMSH13C..04F
Altcode:
In an effort to better understand how the chromospheric plasma and
magnetic fields are guiding, converting and dissipating acoustic waves,
we analyze high-cadence time series taken in Na I D2 589.0 nm and K I
769.9 nm that were obtained with the Magneto Optical Filters at Two
Heights (MOTH) experiment at the South Pole in January 2003. These
data are complemented by a very high spatial resolution time series
taken in Na D with the Swedish Vacuum Solar Telescope in June 1992. The
travel time maps, power maps, and phase diagrams show some unexpected
behaviour, in particular in and around active regions.
Title: How to Channel Photospheric Oscillations into the Corona
Authors: De Pontieu, B.; Erdélyi, R.; De Moortel, I.
Bibcode: 2005ApJ...624L..61D
Altcode:
There are now many observations of waves in the solar corona with
periods around 5 minutes. The source of these waves is uncertain,
although global p-modes in the photosphere are an obvious candidate,
given the similarity of the dominant periods. However, p-modes are
traditionally considered evanescent in the upper photosphere, and it
has been unclear how they could propagate through the chromosphere
into the corona. Using a numerical model, we show that photospheric
oscillations with periods around 5 minutes can actually propagate into
the corona so long as they are guided along an inclined magnetic flux
tube. The nonverticality of the flux tube increases the acoustic cutoff
period to values closer to the dominant periods of the photospheric
oscillations, thus allowing tunneling or even direct propagation into
the outer atmosphere. The photospheric oscillations develop into shocks,
which drive chromospheric spicules and reach the corona. We suggest
that Transition Region and Coronal Explorer (TRACE) observations of
propagating magnetoacoustic waves in the corona represent these shocked
and tunneled photospheric oscillations. We also explore how seismology
of these waves could be exploited to determine the connectivity between
photosphere and corona.
Title: Photospheric Oscillations in the Solar Atmosphere: Driving
Chromospheric Spicules and Coronal Waves
Authors: De Pontieu, B.; Erdelyi, R.; De Moortel, I.; Metcalf, T.
Bibcode: 2004AGUFMSH13A1142D
Altcode:
There are now many observations of oscillations and waves with periods
around 5 minutes in the solar transition region and corona. We provide
an observational overview of 5 minute periodicity in upper transition
region moss, the low legs of coronal loops, and chromospheric spicules
in active region plage. The source of the 5 minute periodicity is
unclear, since photospheric p-modes are evanescent in the upper
photosphere which should prevent them from propagating into the
chromosphere, transition region and corona. Using a numerical model
we show that photospheric oscillations can propagate into the low
atmosphere as long as they are guided along a magnetic flux tube that is
inclined away from the vertical. The leaked photospheric oscillations
develop non-linearly into shocks at low chromospheric heights because
of the density decrease with height. The upward traveling shocks and
resulting rebound shocks of the chromosphere lead to periodic upward
chromospheric flows, which in a recent paper we have identified as
the periodic spicules that we observe in active region plage. After
passage through the spicule, these shocked photospheric oscillations
propagate into the corona. We suggest that TRACE observations of
propagating acoustic waves in the corona are shocked and tunneled
photospheric oscillations. We also explore whether these coronal waves
can be exploited to determine the connectivity between photosphere
and corona, and thus perform seismology of the lower solar atmosphere.
Title: Solar chromospheric spicules from the leakage of photospheric
oscillations and flows
Authors: De Pontieu, Bart; Erdélyi, Robert; James, Stewart P.
Bibcode: 2004Natur.430..536D
Altcode:
Spicules are dynamic jets propelled upwards (at speeds of
~20kms-1) from the solar `surface' (photosphere) into the
magnetized low atmosphere of the Sun. They carry a mass flux of 100
times that of the solar wind into the low solar corona. With diameters
close to observational limits (< 500km), spicules have been largely
unexplained since their discovery in 1877: none of the existing models
can account simultaneously for their ubiquity, evolution, energetics and
recently discovered periodicity. Here we report a synthesis of modelling
and high-spatial-resolution observations in which numerical simulations
driven by observed photospheric velocities directly reproduce the
observed occurrence and properties of individual spicules. Photospheric
velocities are dominated by convective granulation (which has been
considered before for spicule formation) and by p-modes (which are
solar global resonant acoustic oscillations visible in the photosphere
as quasi-sinusoidal velocity and intensity pulsations). We show that
the previously ignored p-modes are crucial: on inclined magnetic flux
tubes, the p-modes leak sufficient energy from the global resonant
cavity into the chromosphere to power shocks that drive upward flows
and form spicules.
Title: Observations and Theory of Longitudinal Waves in Coronal Loops
Authors: De Moortel, I.; Hood, A. W.; De Pontieu, B.
Bibcode: 2004ESASP.547..427D
Altcode: 2004soho...13..427D
High cadence TRACE observations show that outward propagating
intensity disturbances are a common feature in large, quiescent
coronal loops, close to active regions. An overview is given of
measured parameters of such longitudinal oscillations in coronal
loops. The observed oscillations are interpreted as propagating slow
magnetoacoustic waves and are unlikely to be flare-driven. A basic
magnetic field extrapolation is used to estimate the local geometry
of the magnetic field. A theoretical model of slow magneto-acoustic
waves, incorporating the effects of gravitational stratification, the
magnetic field geometry, thermal conduction and compressive viscosity
is presented to explain the very short observed damping lengths. The
results of these numerical simulations are compared with the TRACE
observations. Preliminary results indicate that the magnetic field
geometry plays an important role.
Title: Correlated Intensity Oscillations in the Upper Chromosphere
and Upper Transition Region above Active Region Plage
Authors: de Pontieu, B.
Bibcode: 2004ESASP.547...25D
Altcode: 2004soho...13...25D
Although there are now many observations showing the presence of
oscillations in the corona, their direct relationship to waves
or oscillations in the photosphere and chromosphere is not well
understood. We provide an overview of recent studies describing
correlations between oscillations in the lower and upper atmosphere. We
focus in particular on our recent wavelet analysis of observations
(made with TRACE, the Transition Region and Coronal Explorer) of strong
( 5 - 15%) intensity oscillations in the upper TR footpoints of hot
coronal loops. They show a range of periods from 200 to 600 seconds,
typically persisting for 4 to 7 cycles. These oscillations are not
associated with sunspots, as they usually occur at the periphery
of plage regions. A preliminary comparison to photospheric vertical
velocities (using the Michelson Doppler Imager onboard SOHO) reveals
that some upper TR oscillations show a correlation with p-modes in the
photosphere. In addition, a majority of the upper TR oscillations are
directly associated with upper chromospheric oscillations observed
in H, i.e., periodic flows in spicular structures. The presence of
such strong oscillations at low heights (of order 3,000 km) provides
an ideal opportunity to study the propagation of oscillations from
photosphere and chromosphere into the TR and corona. It can also help
us understand the magnetic connectivity in the chromosphere and TR, and
shed light on the source of chromospheric mass flows such as spicules.
Title: Intensity Oscillations in the upper transition region above
active region plage
Authors: de Pontieu, B.; Erdelyi, R.; de Wijn, A.; Loefdahl, M.
Bibcode: 2003AGUFMSH42B0540D
Altcode:
Although there are now many observations showing the presence
of oscillations in the corona, almost no observational studies have
focused on the bright upper transition region (TR) emission (so-called
moss) above active region plage. Here we report on a wavelet analysis
of observations (made with TRACE, the Transition Region and Coronal
Explorer) of strong ( ∼ 5-15%) intensity oscillations in the upper
TR footpoints of hot coronal loops. They show a range of periods from
200 to 600 seconds, typically persisting for 4 to 7 cycles. These
oscillations are not associated with sunspots, as they usually occur at
the periphery of plage regions. A majority of the upper TR oscillations
are directly associated with upper chromospheric oscillations observed
in Hα , i.e., periodic flows in spicular structures. The presence of
such strong oscillations at low heights (of order 3,000 km) provides
an ideal opportunity to study the propagation of oscillations from
photosphere and chromosphere into the TR and corona, and improve
our understanding of the magnetic connectivity in the chromosphere
and TR. In addition, we use new high resolution observations of the
photosphere and chromosphere, taken with the Swedish Solar Telescope, to
shed light on the source of chromospheric mass flows such as spicules.
Title: Intensity Oscillations in the Upper Transition Region above
Active Region Plage
Authors: De Pontieu, B.; Erdélyi, R.; de Wijn, A. G.
Bibcode: 2003ApJ...595L..63D
Altcode:
Although there are now many observations showing the presence of
oscillations in the corona, almost no observational studies have
focused on the bright upper transition region (TR) emission (the
so-called moss) above active region plage. Here we report on a wavelet
analysis of observations (made with the Transition Region and Coronal
Explorer) of strong (~5%-15%) intensity oscillations in the upper TR
footpoints of hot coronal loops. They show a range of periods from 200
to 600 s, typically persisting for 4-7 cycles. These oscillations are
not associated with sunspots, as they usually occur at the periphery
of plage regions. A preliminary comparison to photospheric vertical
velocities (using the Michelson Doppler Imager on board the Solar and
Heliospheric Observatory) reveals that some upper TR oscillations
show a correlation with p-modes in the photosphere. In addition,
a majority of the upper TR oscillations are directly associated with
upper chromospheric oscillations observed in Hα, i.e., periodic flows
in spicular structures. The presence of such strong oscillations at
low heights (of the order of 3000 km) provides an ideal opportunity to
study the propagation of oscillations from photosphere and chromosphere
into the TR and corona. It can also help us understand the magnetic
connectivity in the chromosphere and TR and shed light on the source
of chromospheric mass flows such as spicules.
Title: Can ion-neutral damping help to form spicules?
Authors: James, S. P.; Erdélyi, R.; De Pontieu, B.
Bibcode: 2003A&A...406..715J
Altcode:
The possible mechanism of generation of spicules by Alfvénic
waves is studied in dissipative MHD where dissipation is mainly
caused by ion-neutral collision damping, as suggested by Haerendel
(\cite{haerendel}). Ion-neutral damping becomes non-negligible at
the high cyclic frequencies involved, typically greater than 0.1unit
{Hz}, and the potential role played by this effect in both forming
and supporting solar spicules is investigated. The propagation of
high frequency Alfvén waves on vertically open solar magnetic flux
tubes is considered. The flux tubes are taken to be axisymmetric and
initially untwisted with the field strength declining from 1600unit {G}
in the photosphere to 10-40unit {G} in the corona. Their propagation
is investigated by numerically solving a set of fully nonlinear,
dissipative 1.5D MHD equations with the waves being generated by a
continuous sinusoidal driver introduced into the equation of angular
momentum in the low atmosphere of the Sun. Spicule-like structures with
heights of up to 7000unit {km} were formed. The formation was found
to be caused by the impact of a series of slow shocks generated by
the continuous interaction between the upward propagating driven wave
train and the downward propagating train of waves created by reflection
off the transition region and aided by the increased thermal pressure
gradient caused by Joule heating due to ion-neutral collisions. The
adiabatic results suggest that ion-neutral damping may not support
spicules as described by Haerendel (\cite{haerendel}). However, the
effect is highly sensitive to the level of ionisation and therefore
to the energy balance. Including the effects of thermal conduction
and radiation may well lead to different results and thus it would
be premature to dismiss the mechanism completely at this point. In
addition, the relatively high chromospheric temperatures obtained,
even at frequencies for which ion-neutral damping and heating might
be expected to be unimportant, suggest intriguing possibilities for
combining the mechanism with others that are better able to recreate
spicule dynamics but suffer from unrealistically low temperatures.
Title: Correlations on Arcsecond Scales between Chromospheric and
Transition Region Emission in Active Regions
Authors: De Pontieu, B.; Tarbell, T.; Erdélyi, R.
Bibcode: 2003ApJ...590..502D
Altcode:
The discovery of active region moss, i.e., dynamic and bright upper
transition region (TR) emission at chromospheric heights above active
region plage, provides a powerful diagnostic to probe the structure,
dynamics, energetics, and coupling of the magnetized solar chromosphere
and TR. Here we present an observational study of the interaction
of the chromosphere with the upper TR, by studying correlations (or
lack thereof) between emission at varying temperatures: from the low
chromosphere (Ca II K line), to the middle and upper chromosphere (Hα),
to the low TR (C IV λ1550 at 0.1 MK) and the upper TR (Fe IX/X λ171
at 1 MK and Fe XII λ195 at 1.5 MK). We use several data sets at high
cadence (24-42 s) obtained with the Swedish Vacuum Solar Telescope
(SVST, La Palma) and the Transition Region and Coronal Explorer
(TRACE). This correlation analysis from low chromosphere to upper
TR in active region plage quantifies and considerably expands on
previous studies. Our results elucidate various issues, such as (1)
how the heating mechanisms of the chromosphere and lower and upper TR
are related (if at all), (2) how important heating of spicular jets is
for the energy balance of the lower TR, (3) which timescales dominate
the dynamic behavior of the active region TR, and (4) whether the
spatial and temporal variability of moss can be used as a diagnostic
for coronal heating.
Title: A High Frequency Wave Search using TRACE
Authors: De Forest, C. E.; De Pontieu, B. D.; Hassler, D. M.
Bibcode: 2003SPD....34.0111D
Altcode: 2003BAAS...35..807D
We report on a possible detection of 100-milliHz band fast-mode waves
in the solar chromosphere, seen with TRACE. Near the end of 2002,
TRACE collected extremely high cadence images in the 1600 Å continuum;
initial studies show a possible signature of waves propagating near
the coronal Alfveń speed with periods as low as 10 seconds. Waves at
this frequency are near the high frequency limit because the period
is only 10-100 times the ion-electron collision time. We present these
initial results and the outcome of an ongoing follow-on study.
Title: Observations of the propagation and photospheric source of
waves at the upper transition region footpoints of coronal loops
Authors: de Pontieu, B.; Erdelyi, R.
Bibcode: 2003EAEJA.....5890D
Altcode:
We study the lower and upper transition region (TR) at the footpoints of
coronal loops anchored in active region plage. Using wavelet analysis,
we look for the presence of waves in images of C IV 1550 A (0.1 MK)
and Fe IX/X 171 A (1 MK) taken with the Transition Region and Coronal
Explorer (TRACE). We present several examples of strong intensity
oscillations in active region plage at varying temperatures, and
study wave power as a function of wave period, as well as propagation
effects. We also show, for the first time, an example of correlated
oscillations of the upper TR at the opposite ends of a coronal loop,
and use this to determine magnetic connectivity, propagation speed and
coronal properties. Co-aligned spectra from the SOHO/SUMER spectrometer
are used to determine whether correlated velocity oscillations
are also present. Co-aligned photospheric dopplergrams taken with
SOHO/MDI help us shed light on the possible source of these waves. We
find several examples of a correlation between photospheric and upper
TR oscillations, which has not been observed before in active region
plage. We discuss a theoretical model that can explain such coupling of
global helioseismic acoustic oscillations into the upper TR or corona
through the mechanism of resonant absorption.
Title: Prominence Motions Observed at High Cadences in Temperatures
from 10 000 to 250 000 K
Authors: Kucera, T. A.; Tovar, M.; De Pontieu, B.
Bibcode: 2003SoPh..212...81K
Altcode:
We report here for the first time observations of prominence velocities
over a wide range of temperatures and with a high time cadence. Our
study of ultraviolet movies of prominences reveals that multi-thermal
features with speeds of 5-70 km s−1 perpendicular to the
line of sight are common in the prominences which showed traceable
motions. These speeds are noticeably higher than the typical speeds of
5-20 km s−1 observed in Hα data from `quiet' prominences
and are more typical of `activated' prominences in which speeds of
up to 40 km s−1 have been reported. The observations
were performed using five separate datasets taken by the Solar and
Heliospheric Observatory's Coronal Diagnostic Spectrometer (SOHO/CDS)
in its wide slit overlappogram mode in lines from He i, O v, and Mg ix
and a separate prominence observation taken with both the Transition
Region and Coronal Explorer (TRACE) in its 1216 and 1600 Å bands and
in Hα by the Swedish Vacuum Solar Telescope (SVST) at La Palma. The
movies were taken with cadences >1 image per minute and were made
simultaneously or near-simultaneously in spectral lines formed at two
or more temperatures. We traced motion that lasted for 3 to 20 min and
went distances up to 105 km. Most, but not all, of these
were chiefly horizontal. In many cases we were able to observe the
same motions over temperature ranges from 20 000 to 250 000 K or 10
000 to 100 000 K. Observations are compared with model predictions.
Title: Correlations on Arcsecond Scales Between Chromospheric and
Transition Region Structures in Active Regions
Authors: de Pontieu, B.; Tarbell, T.
Bibcode: 2002AGUFMSH52A0439D
Altcode:
The discovery of active region moss, i.e, dynamic and bright upper
transition region emission at chromospheric heights above active
region (AR) plage, provides a powerful diagnostic to probe the
structure, dynamics, energetics and coupling of the magnetized
solar chromosphere and transition region (TR). Here we present an
observational study of the interaction of the chromosphere with the
TR moss, by studying correlations (or lack thereof) between emission
at varying temperatures: from the low chromosphere (Ca II K-line),
to the middle and upper chromosphere (wings of Hα), to the low
transition region (C IV 1550 Å~at 0.1 MK), and the upper transition
region (Fe IX/X 171 Å~at 1 MK and Fe XII 195 Å~at 1.5 MK). We use
several datasets at high cadence (24 to 42 seconds) obtained with the
Swedish Vacuum Solar Telescope (SVST, La Palma) and the Transition
Region and Coronal Explorer (TRACE). This correlation analysis from
low chromosphere to upper TR in AR plage quantifies and considerably
expands on previous studies. Our results elucidate various issues,
such as: 1. how the heating mechanisms of the chromosphere and lower
and upper transition region are related (if at all), 2. how important
heating of spicular jets is for the energy balance of the lower TR,
3. the occurrence of significant periodic activity at all levels of the
transition region and its coherence over a wide range of temperatures,
4. which time scales dominate the dynamic behavior of the AR transition
region, and, 5. whether the spatial and temporal variability of moss
can be used as a diagnostic for coronal heating.
Title: Detection of an optical transient following the 13 March 2000
short/hard gamma-ray burst
Authors: Castro-Tirado, A. J.; Castro Cerón, J. M.; Gorosabel,
J.; Páta, P.; Soldán, J.; Hudec, R.; Jelinek, M.; Topinka, M.;
Bernas, M.; Mateo Sanguino, T. J.; de Ugarte Postigo, A.; Berná,
J. Á.; Henden, A.; Vrba, F.; Canzian, B.; Harris, H.; Delfosse, X.;
de Pontieu, B.; Polcar, J.; Sánchez-Fernández, C.; de la Morena,
B. A.; Más-Hesse, J. M.; Torres Riera, J.; Barthelmy, S.
Bibcode: 2002A&A...393L..55C
Altcode: 2002astro.ph..6201C
We imaged the error box of a gamma-ray burst of the short (0.5 s),
hard type (GRB 000313), with the BOOTES-1 experiment in southern
Spain, starting 4 min after the gamma -ray event, in the I-band. A
bright optical transient (OT 000313) with I = 9.4 +/- 0.1 was found
in the BOOTES-1 image, close to the error box (3sigma ) provided by
BATSE. Late time VRIK'-band deep observations failed to
reveal an underlying host galaxy. If the OT 000313 is related to the
short, hard GRB 000313, this would be the first optical counterpart
ever found for this kind of events (all counterparts to date have been
found for bursts of the long, soft type). The fact that only prompt
optical emission has been detected (but no afterglow emission at all,
as supported by theoretical models) might explain why no optical
counterparts have ever been found for short, hard GRBs. This fact
suggests that most short bursts might occur in a low-density medium
and favours the models that relate them to binary mergers in very
low-density environments. Based in part on observations made with the
BOOTES instruments in South Spain.
Title: Transverse prominence motions from 10,000 - 250,000K
Authors: Kucera, T. A.; Tovar, M.; de Pontieu, B.
Bibcode: 2002ESASP.508..307K
Altcode: 2002soho...11..307K
We address the origin of prominence material by comparing high cadence
(30-60 s) He I and O V EUV observations from SOHO/CDS wide slit movies,
and also, for another prominence observation, observations from TRACE
at 1216 Å and 1600 Å and SVST in Hα. The EUV and UV observations
regularly show small scale structures with plane-of-the sky velocities
of 20-80 km/s. Many, although not all, of these motions are seen in
multiple wavelength bands, representing temperatures ranging from 10,000
- 100,000K or 20,000 - 250,000K, depending on the data set. The Hα
observations contain line shift information showing clearly that the
associated UV prominence intensity motions do actually represnt real
mass motions, as opposed to temperature or density waves. The results
also indicate that the "prominence-corona transition region" is not an
outside layer to the prominence as a whole, but is rather associated
with smaller scale structures all through the prominence. More
work is needed to determine what mechanism can explain these fast,
multi-temperature prominence motions.
Title: Transverse Prominence Motions from 10,000-250,000 K
Authors: Kucera, T. A.; Tovar, M.; De Pontieu, B.
Bibcode: 2002AAS...200.3718K
Altcode: 2002BAAS...34..697K
We address the origin of prominence material by comparing high cadence
(30-60 s) He I and O V EUV observations from SOHO/CDS wide slit movies,
and also, for another prominence observation, observations from TRACE
at 1216 Å and 1600 Å and SVST in Hα . The EUV and UV observations
regularly show small scale structures with plane-of-the-sky velocities
of 20-80 km/s. Many, although not all, of these motions are seen in
multiple wavelength bands, representing temperatures ranging from 10,000
-- 100,000 K or 20,000 -- 250,000 K, depending on the data set. The Hα
observations contain line shift information showing clearly that the
associated UV prominence intensity motions do actually represent real
mass motions, as opposed to temperature or density waves. The results
indicate that the ``prominence-corona transition region'' is not an
outside layer to the prominence as a whole, but is rather associated
with smaller scale structures all through the prominence. Support for
this work was provided by NASA SR&T Grant NASW-00034. SOHO is a
joint project of ESA and NASA.
Title: Active Region Moss as a Diagnostic for the Thermal Evolution
of Chromospheric Spicule-Like Jets, and for Coronal Heating.
Authors: De Pontieu, B.; Tarbell, T.
Bibcode: 2002AAS...200.8807D
Altcode: 2002BAAS...34..790D
The recent discovery of active region moss, i.e, dynamic and bright
upper transition region emission at chromospheric heights above active
region plage, provides a powerful diagnostic to probe the structure,
dynamics, energetics and coupling of the magnetized solar chromosphere
and transition region. Here we present an observational study of the
interaction of the chromosphere with the TR moss, using a 2 hour
time sequence of high-cadence (30 s) TRACE C IV 1550 Å (0.1 MK),
Fe IX/X 171 Å (1 MK) and Fe XII 195 Å (1.5 MK) images, as well as
co-aligned, simultaneous SUMER spectra, and ground-based filtergrams
from the Swedish Vacuum Solar Telescope (SVST, La Palma) in the wings
of H-alpha. Detailed comparisons of the H-alpha filtergrams (at -700,
-350, +350 and +700 mÅ) with the TRACE C IV images reveals that there
is often a significant spatial correlation of the C IV emission with
the highly redshifted fibril or spicule-like structures in H-alpha +700
mÅ. The discovery and detailed quantitative study of this correlation
promises to shed light on the long outstanding issue of what role
chromospheric spicule-like jets play in the heating and momentum
balance of the outer atmosphere. We have also quantitatively studied
the auto-correlation and cross-correlation time-scales of moss using
a time sequence of high cadence TRACE 171 Å and 195 Å images. In
most of the active region moss patch we studied, we find that the
emission of 1 and 1.5 MK plasma is highly correlated, but often with
significant negative and positive time delays. Our results indicate that
the footpoints of hot coronal loops seem to undergo frequent cooling
and heating on time-scales of order fifteen minutes. By quantifying
these variations we can shed light on the temporal variability and on
the location of coronal heating in general.
Title: High-Resolution Observations of Small-Scale Emerging Flux in
the Photosphere
Authors: De Pontieu, B.
Bibcode: 2002ApJ...569..474D
Altcode:
High-resolution observations of a quiet-Sun region made on 1998 May
23 with the Swedish Vacuum Solar Telescope (SVST) are presented. I
study the dynamics of magnetic elements on scales <=1" using Fe I
λ6302 magnetograms and cotemporal G-band λ4305, Ca II K line λ3933,
and Hα λ6563 filtergrams. This 3 hr long data set, obtained under
excellent seeing conditions, reveals several cases in which flux
concentrations that have recently emerged in the internetwork are
rapidly (within 10-15 minutes) dispersed after emergence. The magnetic
flux, initially quite concentrated (~0.5"), seems to get spread out
(to several arcseconds) and/or shredded as a result of granular action,
until it falls below the noise level in the magnetograms and becomes
undetectable. These magnetic flux concentrations are much smaller than
ephemeral regions, in both spatial extent and magnetic flux (of order
5×1017 Mx). They do not seem to get cancelled by opposite
polarity and typically are not associated with G-band bright points
or Ca II K line brightenings. These events may be related to the
horizontal internetwork fields (HIFs) described by Lites and colleagues.
Title: Transverse Oscillations in Coronal Loops Observed with TRACE
II. Measurements of Geometric and Physical Parameters
Authors: Aschwanden, Markus J.; De Pontieu, Bart; Schrijver, Carolus
J.; Title, Alan M.
Bibcode: 2002SoPh..206...99A
Altcode:
We measure geometric and physical parameters oftransverse oscillations
in 26 coronal loops, out of the 17 events described in Paper I by
Schrijver, Aschwanden, and Title (2002). These events, lasting
from 7 to 90 min, have been recorded with the Transition Region
and Coronal Explorer (TRACE) in the 171 and 195 Å wavelength
bands with a characteristic angular resolution of 1", with time
cadences of 15-75 seconds. We estimate the unprojected loop (half)
length L and orientation of the loop plane, based on a best-fit of a
circular geometry. Then we measure the amplitude A(t) of transverse
oscillations at the loop position with the largest amplitude. We
decompose the time series of the transverse loop motion into an
oscillating component Aosc(t) and a slowly-varying trend
Atrend(t). We find oscillation periods in the range of
P=2-33 min, transverse amplitudes of A=100-8800 km, loop half lengths
of L=37 000-291 000 km, and decay times of td=3.2-21 min. We
estimate a lower limit of the loop densities to be in the range of
nloop=0.13-1.7×109 cm−3. The
oscillations show (1) strong deviations from periodic pulses, (2)
spatially asymmetric oscillation amplitudes along the loops, and
(3) nonlinear transverse motions of the centroid of the oscillation
amplitude. From these properties we conclude that most of the
oscillating loops do not fit the simple model of kink eigen-mode
oscillations, but rather manifest flare-induced impulsively generated
MHD waves, which propagate forth and back in the loops and decay
quickly by wave leakage or damping. In contrast to earlier work we
find that the observed damping times are compatible with estimates of
wave leakage through the footpoints, for chromospheric density scale
heights of ≈400-2400 km. We conclude that transverse oscillations
are most likely excited in loops that (1) are located near magnetic
nullpoints or separator lines, and (2) are hit by a sufficiently
fast exciter. These two conditions may explain the relative rarity of
detected loop oscillations. We show that coronal seismology based on
measurements of oscillating loop properties is challenging due to the
uncertainties in estimating various loop parameters. We find that a
more accurate determination of loop densities and magnetic fields,
as well as advanced numerical modeling of oscillating loops, are
necessary conditions for true coronal seismology.
Title: Transverse oscillations in coronal loops observed with TRACE
Authors: Schrijver, C. J.; Aschwanden, M. J.; De Pontieu, B.; Title,
A. M.
Bibcode: 2001AGUFMSH11A0703S
Altcode:
TRACE discovered transverse oscillations in coronal loops associated
with a flare three years ago, and until recently only two such events
were known. We have now identified a total of 17 events that trigger
some form of loop oscillations. Oscillation periods are estimated to
range over a factor of ~ 15, with most values between 2 and 7 min. The
oscillations are excited by filament destabilizations or flares (in 6%\
of the 255 flares inspected, ranging from about C3 to X2). Oscillations
occur in loops that close within an active region, or in loops that
connect an active region to a neighboring region or to a patch of strong
flux in the quiet Sun. Some magnetic configurations are particularly
prone to exhibit oscillations: two active regions showed two, and
one region even three, distinct intervals with loop oscillations. The
loop oscillations are not a resonance that builds up: oscillations in
loops that are excited along their entire length are likely to be near
the fundamental resonance mode because of that excitation profile, but
asymmetrically excited oscillations clearly show propagating waves that
are damped too quickly to build up a resonance, and some cases show
multiple frequencies. We discuss evidence that all oscillating loops
lie near magnetic separatrices that outline the large-scale topology
of the field. Often the oscillations occur in conjunction with gradual
adjustments in loop positions in response to the triggering event. We
discuss the observations in the context of two models, and evaluate
the contraints on coronal properties that can be deduced from them.
>http://vestige.lmsal.com/TRACE/POD/TRACEoscillations.html</a>
Title: Solar Orbiter and ground-based observations: lessons from
SOHO/TRACE
Authors: de Pontieu, Bart
Bibcode: 2001ESASP.493..121D
Altcode: 2001sefs.work..121D
Due to the flexibility and/or superiority of ground-based observations
in spectral coverage, cadence, spatial resolution, targeting,
and especially bandwidth issues, they are often very complementary
to space-based observations. Coordinating ground-based efforts with
spacecraft data comes with specific operational issues, of which seeing
conditions, cross-instrument coordination, and co-alignment or targeting
are the most critical for success. Successful coordination has shown
promise for a much improved understanding of the connectivity between
the photosphere and the corona, because is allows the study of the
highly dynamic and finely structured intermediate layers through which
the energy transport from the photosphere to the corona takes place. I
will demonstrate these issues by taking a close look at recent results
obtained with the combination of SOHO, TRACE and the SVST (Swedish
Vacuum Tower Telescope in La Palma). I also briefly discuss how new
or future ground-based technologies and instruments will be able to
complement Solar Orbiter.
Title: Chromospheric Damping of Alfvén Waves
Authors: De Pontieu, B.; Martens, P. C. H.; Hudson, H. S.
Bibcode: 2001ApJ...558..859D
Altcode:
We analytically study the damping of Alfvén mode oscillations in the
chromosphere and in coronal loops. In the partially ionized chromosphere
the dominant damping process of Alfvén waves is due to collisions
between ions and neutrals. We calculate the damping time for Alfvén
waves of a given frequency, propagating through model chromospheres
of various solar structures such as active region plage, quiet sun,
and the penumbra and umbra of sunspots. For a given wave frequency,
the maximum damping always occurs at temperature minimum heights and
in the coldest structure(s), i.e., the umbra of sunspots. Energy
dissipation due to ion-neutral damping of Alfvén waves with an
energy flux of 107 ergs cm-3 s- 1 can
play a considerable role in the energy balance of umbrae, quiet sun,
and plage for Alfvén wave periods of the order, respectively, 50,
5, and 0.5 s. We also consider Alfvén waves in coronal loops and the
leakage of wave energy through the footpoints. We assume a three-layer
model of coronal loops with constant Alfvén speed vA
(and no damping) in the corona, vA varying exponentially
with height in the dissipative chromosphere, and vA again
constant in the photosphere at the end of the loop. We find an exact
analytical solution in the chromospheric part. Using these solutions, we
estimate the leakage of wave energy from the coronal volume through the
footpoint regions of the loop and find that the presence of a moderate
amount of chromospheric damping can enhance the footpoint leakage. We
apply this result to determine the damping time of standing waves in
coronal loops. The enhanced footpoint leakage also has implications
for theories of coronal heating based on resonant absorption. Finally,
we find exact expressions for the damping of Alfvén waves launched
in the photosphere and upward propagating through the chromosphere
and into the corona. The partially ionized chromosphere presents an
effective barrier for upward propagating Alfvén waves with periods
less than a few seconds.
Title: High Resolution Observations of Quiet Sun Magnetic Elements
Authors: De Pontieu, B.
Bibcode: 2001AGUSM..SH31D02D
Altcode:
We present high-resolution observations of a quiet sun region,
made on 23-May-1998 using the Swedish Vacuum Solar Telescope (SVST)
and the Transition Region and Coronal Explorer (TRACE). We study the
statistics and the effects on upper atmospheric layers of emergence
and cancellation of magnetic elements on scales of 0.5" using Fe I 6302
magnetograms, co-temporal G-band, Ca II K-line and H-alpha filtergrams,
and TRACE 1550, 1600, 1700, 171 and 195 Angstrom images. From our
3 hour long dataset, obtained under excellent seeing conditions,
we calculate maps of the photospheric flowfield, and study its
relationship to the dynamics of magnetic elements, the chromosphere
(spicules), and the TR/corona. For example, our study reveals several
cases in which flux concentrations that have recently emerged in the
internetwork, are apparently rapidly (within 10 minutes) dispersed
after emergence. Co-aligned G-band images show that the magnetic flux,
initially quite concentrated (0.5"), seems to get spread out (to several
arcseconds) and/or shredded due to granular action or convective flow,
until it falls below the noise levels in our magnetograms and becomes
undetectable. These magnetic flux concentrations do not seem to get
cancelled by opposite polarity, and typically do not form G-band bright
points or Ca II K-line brightenings. A significant fraction of the
flux that we see emerge undergoes this process.
Title: Prominence Plasma Motions Measured in the Ultraviolet
Authors: Kucera, T. A.; De Pontieu, B.
Bibcode: 2001AGUSM..SH41B10K
Altcode:
We present a study of velocities and trajectories of blobs visible
in UV emission in SOHO/CDS and TRACE prominence movies. It has long
been known that prominences are highly dynamic structures exhibiting
flowing material. In particular, recent observations in H-alpha indicate
that material is counter-streaming at velocities of 5-10 km/s along
the prominence spine and in the barbs.* These observations are highly
relevant to fundamental questions concerning the source of prominence
plasma. Many models of prominence flows involve heating of chromospheric
material. By investigating the properties of moving prominence plasma in
the 20,000 to 200,000 K range we will be able to provide parameters for
comparison with such models. The CDS data were taken in He I (584.33
A) and O V (629.7 A) with the wide (90 arcsec) slit which allows 30
sec cadence movies to be taken simultaneously in a few well isolated
lines. We also consider separate TRACE prominence data with Lyman-alpha
(1216 A) and C IV (1600 A) observations. Preliminary results indicate
motions in the 20-70 km/s range, with most of the observed motion
horizontal to the solar surface. Support for this work is provided by
NASA SR&T Grant NASW-00034 *Zirker et al., 1998, Nature, 396, 40
Title: Chromospheric Heating in the Late Phase of Two-Ribbon Flares
Authors: Czaykowska, A.; Alexander, D.; De Pontieu, B.
Bibcode: 2001ApJ...552..849C
Altcode:
Fast upflows observed in the late gradual phase of an M6.8 two-ribbon
flare by the Solar and Heliospheric Observatory/Coronal Diagnostic
Spectrometer have provided evidence for the presence of chromospheric
evaporation more than an hour after the impulsive phase of the
flare. The chromospheric heating necessary to generate these upflows
requires the continued injection and deposition of energy, which
we presume to be provided by magnetic reconnection in the flaring
corona. We investigate the nature of the transport of this energy from
the reconnection site to the chromosphere by comparing the observed
upflow velocities with those expected from different chromospheric
heating models. A nonthermal beam of energetic electrons (>~15
keV) that is capable of generating the observed velocities would also
generate significant hard X-ray emission that is not observed at this
stage of the flare. We conclude, therefore, that the most likely energy
transport mechanism is thermal conduction.
Title: Micro-scale Heating Blocks: SUMER-TRACE-La Palma Observations
and Their Modelling (CD-ROM Directory: contribs/erdelyi2)
Authors: Erdélyi, R.; de Pontieu, B.; Roussev, I.
Bibcode: 2001ASPC..223..619E
Altcode: 2001csss...11..619E
No abstract at ADS
Title: Chromospheric Damping of Alfvén Waves
Authors: De Pontieu, B.; Martens, P. C. H.; Hudson, H. S.
Bibcode: 2000SPD....31.0131D
Altcode: 2000BAAS...32..806D
We study the damping of Alfvén mode oscillations on coronal loops and
in the chromosphere. First we consider damping of standing waves on
coronal loops, such as those observed in the aftermath of a flare with
the Transition Region and Coronal Explorer (TRACE). We calculate the
leakage of wave energy from the coronal volume through the footpoints
of a coronal loop, assuming constant Alfvén speed vA in
the corona and vA varying exponentially with height in the
photosphere/chromosphere at both ends of the loop. We study analytically
the influence of chromospheric damping of standing waves on a coronal
loop and find that, for a moderate amount of chromospheric damping,
the footpoint leakage can be enhanced. The damping in the partially
ionized chromosphere is mostly due to collisions between ions and
neutrals. In a second part we calculate the damping time for Alfvén
waves of a given frequency, propagating through (model) chromospheres
of various solar structures such as active region plage, quiet sun
and the penumbra and umbra of sunspots. For a given wave frequency,
the maximum damping always occurs at temperature minimum heights
and in the coldest structure(s), i.e. the umbra of a sunspot. Energy
dissipation due to ion-neutral damping of Alfvén waves could play a
considerable role in the energy balance of umbrae, quiet sun and plage
for wave periods of the order, respectively, 100, 10 and 1 s.
Title: Dynamics of Transition Region `Moss' at high time resolution
Authors: De Pontieu, B.; Berger, T. E.; Schrijver, C. J.; Title, A. M.
Bibcode: 1999SoPh..190..419D
Altcode:
Recent observations of solar active regions made with the Transition
Region and Coronal Explorer (TRACE) have revealed finely textured,
low-lying extreme ultraviolet (EUV) emission, called the moss. It
appears as a bright, dynamic pattern with dark inclusions, structured
on spatial scales of 1 to 3 Mm. The moss has been interpreted as the
upper transition region above active region plage and below relatively
hot loops. Here we study the temporal variability of the morphology of
the moss using a 2-hr time sequence of high-cadence TRACE 171 Å images
and G-band, Ca ii K-line and Hα filtergrams from the Swedish Vacuum
Solar Telescope (SVST, La Palma) on 1 June 1999. The data provide a
unique view of the connections between the photosphere, chromosphere,
transition region and corona in an active region. We find that the
moss is dynamic on time scales of 10-30 s due to intrinsic changes
in brightness, obscuration by chromospheric jets and motion caused
by physical interaction with these jets. The temporal variations of
the bright moss elements occur on shorter time scales than those of
the Ca ii K-line bright points. The bright moss elements generally do
not occur directly above the G-band or Ca ii K-line bright points in
the photosphere or lower chromosphere. This suggests that the upper
transition region emission often occurs at the interface of neighboring
flux tubes. The temporal variability of the moss brightness on 30
s time scales may suggest that the energy source of these intensity
changes occurs relatively locally (height <10 000 km).
Title: SOHO/CDS Post-Flare Observations
Authors: Czaykowska, A.; de Pontieu, B.; Alexander, D.; Rank, G.
Bibcode: 1999ESASP.448..773C
Altcode: 1999ESPM....9..773C; 1999mfsp.conf..773C
No abstract at ADS
Title: Multiwavelength Observations (SOHO, TRACE, La Palma) and
Modelling of Explosive Events
Authors: Erdélyi, R.; de Pontieu, B.; Sarro, L. M.
Bibcode: 1999ESASP.448.1345E
Altcode: 1999ESPM....9.1345E; 1999mfsp.conf.1345E
No abstract at ADS
Title: What is Moss?
Authors: Berger, T. E.; De Pontieu, B.; Fletcher, L.; Schrijver,
C. J.; Tarbell, T. D.; Title, A. M.
Bibcode: 1999SoPh..190..409B
Altcode:
TRACE observations of active regions show a peculiar extreme ultraviolet
(EUV) emission over certain plage areas. Termed `moss' for its spongy,
low-lying, appearance, observations and modeling imply that the
phenomenon is caused by thermal conduction from 3-5 MKcoronal loops
overlying the plage: moss is the upper transition region emission of
hot coronal loops. The spongy appearance is due to the presence of
chromospheric jets or `spicules' interspersed with the EUV emission
elements. High cadence TRACE observations show that the moss EUV
elements interact with the chromospheric jets on 10 s time scales. The
location of EUV emission in the moss does not correlate well to the
locations of underlying magnetic elements in the chromosphere and
photosphere, implying a complex magnetic topology for coronal loop
footpoint regions. We summarize here the key observations leading to
these conclusions and discuss new implications for understanding the
structuring of the outer solar atmosphere.
Title: Filament-Prominence-Cme Magnetic Evolution Study
Authors: Bagala', L. G.; Mandrini, C. H.; Fernandez Borda, R.; de
Pontieu, B.; Rovira, M. G.; Rank, G.
Bibcode: 1999ESASP.446..149B
Altcode: 1999soho....8..149B
The first results of the SOHO Joint Observation Program JOP 99 are
outlined. JOP 99 involve several SOHO instruments (CDS, LASCO, MDI),
together with TRACE, and two new ground-based instruments: HASTA
(Hα Solar Telescope for Argentina) and MICA (Mirror Coronagraph for
Argentina). The proposed program have a new motivation in taking
advantage of the capabilities of the TRACE instrument, together
with our experience in magnetic reconnection. The objective here is
focused on the investigation of the conditions of the eruption of a
prominence, often associated with the CME. JOP 99 is running at the
moment that this abstract is submitted. It is a 5-days study of the
filament/prominence, with 3-4 days observing the disk and 1-2 days
observing the limb. While on disk, we will look for the eruption
signatures in two ways: by studying the physical conditions in the
filament and its surroundings (densities, temperature, abundances),
and by looking at the magnetic topology changes. While at the limb,
we will wait with luck for an eruption. If it does happen, LASCO and
MICA observations will study if there exists an associated CME.
Title: Chromospheric Evaporation In The Gradual Flare Phase
Authors: Czaykowska, A.; de Pontieu, B.; Alexander, D.; Rank, G.
Bibcode: 1999ESASP.446..257C
Altcode: 1999soho....8..257C
SOHO/CDS observations are used to determine relative line-of-sight
velocities and their temporal evolution in the late gradual flare
phase. The observations started about 1 hour after the M6.8 two-ribbon
flare in NOAA 8210 on April 29, 1998. Velocity maps in O V 629 A (Tmax
= 0.25 MK), Fe XVI 360 A (Tmax = 2 MK), and Fe XIX 592 A (Tmax = 6.3
MK), covering temperatures from the transition region to the corona
show strong gradients at the position of the Hα ribbons. Downflows
are observed in the footpoint regions of the post-flare loops whereas
the velocities observed further away from the magnetic neutral line
are interpreted as upflows due to chromospheric evaporation. Loops are
filled with hot plasma and their footpoints become visible later on at
the former evaporation site. At the same time the Hα ribbon is slowly
moving outward together with the location of the velocity gradient. Our
observations strongly support models in which chromospheric evaporation
driven by magnetic reconnection is responsible for the continuous
formation of loops, which are visible for several hours after the
flare's maximum in EUV and soft X-ray radiation.
Title: Plasma Diagnostics of Transition Region ``Moss'' using SOHO/CDS
and TRACE
Authors: Fletcher, Lyndsay; De Pontieu, Bart
Bibcode: 1999ApJ...520L.135F
Altcode:
Recent observations of solar active regions with the Transition Region
and Coronal Explorer (TRACE) have revealed finely textured, low-lying
EUV emission, called the ``moss,'' appearing as a bright dynamic
pattern with dark inclusions. The moss has been interpreted as the
upper transition region by Berger and coworkers. In this study we use
SOHO Coronal Diagnostic Spectrometer and TRACE observations of Active
Region 8227 on 1998 May 30 to determine the physical parameters of the
moss material. We establish that the plasma responsible for the moss
emission has a temperature range of (0.6-1.5)×106 K and
is associated with hot loops (T>2×106 K). Moss plasma
has an electron density of (2-5)×109 cm-3 at a
temperature of 1.3×106 K, giving a pressure of 0.7-1.7 dynes
cm-2 (a few times higher than in coronal loops observed in
the TRACE Fe IX/X λ171 passband). The volume filling factor of the
moss plasma is of order 0.1, and the path along which the emission
originates is of order 1000 km long.
Title: Evidence for Chromospheric Evaporation in the Late Gradual
Flare Phase from SOHO/CDS Observations
Authors: Czaykowska, A.; De Pontieu, B.; Alexander, D.; Rank, G.
Bibcode: 1999ApJ...521L..75C
Altcode:
Using extreme-ultraviolet (EUV) spectroheliograms from the first
intentional postflare observations with the Coronal Diagnostic
Spectrometer (CDS) on board SOHO, we determine relative line-of-sight
velocities and their temporal evolution during the gradual flare phase
of an M6.8 two-ribbon flare that occurred on 1998 April 29. Dopplergrams
in lines of O V, Fe XVI, and Fe XIX, with formation temperatures
Tmax of, respectively, 0.25, 2.0, and 8.0 MK show strong
velocity gradients coincident with the Hα ribbons, visible in Big Bear
Solar Observatory (BBSO) images. These gradients are perpendicular to
and moving with the Hα ribbons. Bright downflowing plasma seems to be
prevalent in the regions, between the ribbons and the magnetic neutral
line, that coincide with the ends of postflare loops seen with the
Extreme-Ultraviolet Imaging Telescope (EIT) on board SOHO. The plasma
on the outer side of the ribbons is less bright in the EUV but shows
strong relative blueshifts. This pattern of upflows and downflows
demonstrates, for the first time in transition region and coronal
lines, the existence of chromospheric evaporation during the late
gradual phase of a flare and provides evidence for ongoing reconnection.
Title: High-resolution Imaging of the Solar Chromosphere/Corona
Transition Region
Authors: Berger, T. E.; De Pontieu, B.; Schrijver, C. J.; Title, A. M.
Bibcode: 1999ApJ...519L..97B
Altcode:
The properties of a previously unresolved extreme-ultraviolet (EUV)
emission in solar active regions are examined using coordinated data
sets from the Transition Region and Coronal Explorer (TRACE) satellite,
the Michelson Doppler Imager on the Solar and Heliospheric Observatory
satellite, the Soft X-Ray Telescope (SXT) on the Yohkoh satellite, and
the ground-based Swedish Vacuum Solar Telescope (SVST) on La Palma. The
emission appears most prominently in TRACE Fe IX/Fe X 171 Å images
as a bright dynamic network surrounding dark inclusions on scales of
2-3 Mm, confined to layers approximately 1-3 Mm thick with base heights
approximately 2-4 Mm above the photosphere. It is seen only above plage
regions that underlie (3-5)×106 K coronal loops visible
in SXT images. The bright EUV elements emit at temperatures of about
106 K. Fine-scale motions and brightness variations of the
emission occur on timescales of 1 minute or less. The dark inclusions
correspond to jets of chromospheric plasma seen in simultaneous SVST
filtergrams in the wings of Hα. The combined characteristics imply
that we are at least partially resolving the structure and dynamics
of the conductively heated upper transition region between the solar
chromosphere and corona.
Title: Numerical simulations of spicules driven by weakly-damped
Alfvén waves. I. WKB approach
Authors: de Pontieu, B.
Bibcode: 1999A&A...347..696D
Altcode:
We present results of time-dependent 1.5 dimensional numerical
simulations of the effects that upward travelling Alfvén waves,
damped by ion-neutral collisions, have on the chromospheric plasma in
a vertical magnetic flux tube. Assuming a rigid flux tube, we use a
combination of hydrodynamic equations and a transport equation for the
wavelength-averaged wave action density (using the WKB assumption). We
find that the damping of a continuous train of upward travelling Alfvén
waves with a frequency of 0.5 Hz causes enough upward momentum transfer
and heating of the plasma to form structures that are similar to
chromospheric spicules in many aspects. We use a non-LTE approximative
formula for the hydrogen ionization and assume optically thin radiative
losses in the spicular environment. We find that the formed structure
reaches a maximum height of 6000 km, temperatures between 8000 to 12
000 K, electron number densities of the order 10(17) m(-3) and maximal
velocities of about 20 km s(-1) . The lifetime of our structure depends
on the lifetime of the wave source and can be brought into accordance
with observed spicular lifetimes.
Title: A new view of the solar outer atmosphere by the Transition
Region and Coronal Explorer
Authors: Schrijver, C. J.; Title, A. M.; Berger, T. E.; Fletcher, L.;
Hurlburt, N. E.; Nightingale, R. W.; Shine, R. A.; Tarbell, T. D.;
Wolfson, J.; Golub, L.; Bookbinder, J. A.; DeLuca, E. E.; McMullen,
R. A.; Warren, H. P.; Kankelborg, C. C.; Handy, B. N.; De Pontieu, B.
Bibcode: 1999SoPh..187..261S
Altcode:
The Transition Region and Coronal Explorer (TRACE) - described in the
companion paper by Handy et al. (1999) - provides an unprecedented
view of the solar outer atmosphere. In this overview, we discuss the
initial impressions gained from, and interpretations of, the first
million images taken with TRACE. We address, among other topics,
the fine structure of the corona, the larger-scale thermal trends,
the evolution of the corona over quiet and active regions, the high
incidence of chromospheric material dynamically embedded in the coronal
environment, the dynamics and structure of the conductively dominated
transition region between chromosphere and corona, loop oscillations
and flows, and sunspot coronal loops. With TRACE we observe a corona
that is extremely dynamic and full of flows and wave phenomena, in
which loops evolve rapidly in temperature, with associated changes in
density. This dynamic nature points to a high degree of spatio-temporal
variability even under conditions that traditionally have been referred
to as quiescent. This variability requires that coronal heating can
turn on and off on a time scale of minutes or less along field-line
bundles with cross sections at or below the instrumental resolution
of 700 km. Loops seen at 171 Å (∼1 MK) appear to meander through
the coronal volume, but it is unclear whether this is caused by the
evolution of the field or by the weaving of the heating through the
coronal volume, shifting around for periods of up to a few tens of
minutes and lighting up subsequent field lines. We discuss evidence
that the heating occurs predominantly within the first 10 to 20 Mm
from the loop footpoints. This causes the inner parts of active-region
coronae to have a higher average temperature than the outer domains.
Title: Dynamics of Transition Region Moss
Authors: Berger, T. E.; de Pontieu, B.; Schrijver, C. J.; Title, A. M.
Bibcode: 1999AAS...194.7901B
Altcode: 1999BAAS...31..963B
We examine the dynamics of solar transition region "moss", the 10(6)
K EUV emission at the footpoint regions of 2--3 MK active region coronal
loops. Comparisons of TRACE 171 Angstroms movies with SVST (La Palma) Ca
II K-line, Hα , and G-band movies are made. Local Correlation Tracking
(LCT) flowmapping techniques are used to establish the photospheric
flowfield in plage regions with and without associated moss. The
relation of moss emission to chromospheric spicules or fibrils is
examined in detail using Hα movies and dopplergrams. In addition,
several microflare events occuring in plage regions are analyzed using
TRACE and SVST movies. This research was supported by NASA contract
NAS5-38099 (TRACE) and NASA SR&T grant NASW-98008.
Title: Plasma Diagnostics of Transition Region ``Moss'' using SOHO/CDS
and TRACE
Authors: Fletcher, L.; de Pontieu, B.
Bibcode: 1999AAS...194.7902F
Altcode: 1999BAAS...31..963F
Recent observations of solar active regions with the Transition
Region And Coronal Explorer (TRACE) have revealed finely textured,
low-lying extreme ultraviolet (EUV) emission, called the ``moss'',
appearing as a bright dynamic pattern with dark inclusions. The moss
has been interpreted as the upper transition region by Berger et al.,
(1999). In this study we use simultaneous SOHO Coronal Diagnostic
Spectrometer (CDS) and TRACE observations of Active Region (AR)
8227 on 30-May-1998 to determine the physical parameters of the moss
material. A differential emission measure (DEM) analysis and other
diagnostic tools establish that the plasma responsible for the moss
emission has a temperature range of 0.6-1.5 * 10(6) K and is associated
with hot loops (T > 2 * 10(6) K) observed with CDS. This plasma
has an electron density of 2-5* 10(9) cm(-3) at a temperature of 1.3 *
10(6) K, giving a pressure of 0.7-1.7 dyne cm(-2) . Both the density
and pressure in the moss plasma are a few times higher than in coronal
loops observed in the TRACE Fe IX/X 171 Angstroms passband. The volume
filling factor of the moss plasma is of the order 0.1 and the path
along which the emission originates is of the order 1,000 km long.
Title: Dynamics and Plasma Diagnostics of Transition Region ``Moss''
using SOHO/CDS, TRACE and SVST (La Palma)
Authors: de Pontieu, B.; Berger, T. E.; Fletcher, L.; Schrijver,
C. J.; Title, A. M.
Bibcode: 1999AAS...194.7804D
Altcode: 1999BAAS...31..961D
Recent observations of solar active regions with the Transition
Region And Coronal Explorer (TRACE) have revealed finely textured,
low-lying extreme ultraviolet (EUV) emission, called the ``moss'',
appearing as a bright dynamic pattern with dark inclusions. The moss
has been interpreted as the upper transition region by Berger et al.,
(1999). In this poster we study the physical conditions in the moss
plasma, as well as its dynamics and connections to photosphere and
chromosphere. Using simultaneous SOHO Coronal Diagnostic Spectrometer
(CDS) and TRACE observations of Active Region (AR) 8227 on 30-May-1998
we determine the physical parameters of the moss material. We find T_e =
0.6-1.5 10(6) K and n_e = 2-5 10(9) cm(-3) at a temperature of 1.3 10(6)
K. The pressure in the moss plasma is higher than that in coronal loops
observed in the TRACE Fe IX/X 171 Angstroms passband, and moss emission
is associated with high temperature loops, observed by SXT and by CDS
in lines of T_max > 2.5 10(6) K. The volume filling factor of the
moss plasma is of the order 0.1 and the path along which the emission
originates is of the order 1,000 km long. We examine the dynamics of
the moss plasma, by making comparisons of TRACE 171 Angstroms movies
with SVST (La Palma) Ca II K-line, Hα , and G-band movies. Local
Correlation Tracking (LCT) flowmapping techniques are used to establish
the photospheric flowfield in plage regions with and without associated
moss. The relation of moss emission to chromospheric spicules or fibrils
is examined in detail using Hα movies and dopplergrams. In addition,
several miniflare events occuring in plage regions are analyzed using
TRACE and SVST movies. This research was supported by NASA contract
NAS5-38099 (TRACE) and NASA SR&T grant NASW-98008.
Title: Coordinated Observations of Transition Region Dynamics using
TRACE and the SVST
Authors: Berger, T.; de Pontieu, B.; Schrijver, C.; Title, A.;
Scharmer, G.
Bibcode: 1999ASPC..183..365B
Altcode: 1999hrsp.conf..365B
No abstract at ADS
Title: Internetwork Grains with TRACE
Authors: Rutten, R. J.; de Pontieu, B.; Lites, B.
Bibcode: 1999ASPC..183..383R
Altcode: 1999hrsp.conf..383R
No abstract at ADS
Title: Weakly damped Alfven waves as drivers for spicules
Authors: de Pontieu, B.; Haerendel, G.
Bibcode: 1998A&A...338..729D
Altcode:
We present an analytical model for the damping of Alfven waves in
the partially ionized chromosphere. The damping is due to collisions
between ions and neutrals. The ion-neutral collision frequency in this
environment is such that the ion and neutral populations are almost
perfectly collisionally coupled, leading the Alfven wave to behave as
if it acts on the whole plasma (i.e. including neutrals). The small
but finite coupling time between ions and neutrals leads to damping of
the Alfven waves. We find that this type of damping of upward traveling
Alfven waves with frequencies between 0.2 and 0.6 Hz, can cause not only
significant heating but also upward motion of the upper chromospheric
plasma. In addition the upward force and heating associated with this
type of damping can sustain, both dynamically and thermodynamically,
an already formed chromospheric spicule. The energy flux carried by
the Alfven waves needed for this type of support of a spicule does
not seem to be in contradiction with observational and theoretical
evidence for the presence of Alfven waves in the chromosphere.
Title: Simultaneous observations of spicules with SOHO/CDS and the
Fabry-Perot interferometer at the VTT
Authors: de Pontieu, B.; von der Lühe, O.; Soltau, D.; Kentisher, Th.
Bibcode: 1998ESASP.421...43D
Altcode: 1998sjcp.conf...43D
No abstract at ADS
Title: The flare of November 29, 1996 observed by SOHO/CDS
Authors: Czaykowska, A.; Rank, G.; Ruedi, I.; Solanki, S. K.; de
Pontieu, B.
Bibcode: 1998cee..workE..32C
Altcode:
We present flare and post-flare observations obtained with the Coronal
Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric
Observatory (SOHO) on November 29, 1996. On this day at around 20:40
UT, an M 1.0/1F flare occurred in the solar active region NOAA 7999 and
was accidentally observed by the Normal Incidence Spectrometer (NIS),
one of the two spectrometers of CDS (Harrison et al., 1995). The
data consist of two rasters lasting for 135 minutes each and both
cover an area of 4 times 4 arcminutes. The first raster is pointed at
the northern part of the active region during the flare whereas the
second one covers the southern part of the active region after the main
phase of the flare. The observations were part of the Joint Observing
Program (JOP) 54 which is aimed at the investigation of scaling laws in
coronal loops. Consequently the details of observations such as line
list and exposure time weren't convenient for flare observations. In
addition a flare can lead to over-exposures, i.e., saturation of the
CCD detector pixels, and a burn-in degeneration of the detector in
bright lines. Therefore observations of flares with CDS are avoided
and the flare from November 29, 1996, is so far the only noteworthy
flare observed by CDS. In our case we have remarkable saturation in
the chromospheric He I line at 584 AA and the coronal Fe XVI lines
at 335 AA and 361 AA, which are formed at an equilibrium temperature
of about 2.5 cdot 10^6 K. Another effect of illumination on the CCD
detector being too high is that the electron well of each pixel may
fill and hence bleed to adjacent pixels. This effect is clearly seen
in our data. As the flare occurred, the 2 times 240 arcseconds slit
was being rastered across the active region from west to east. We thus
have a convolution of spatial and temporal effects which are not easy
to separate. However, we have spectral information of each pixel in all
lines and exposures which are not saturated. Hence, line parameters such
as intensity and relative Doppler shifts can be calculated. Moreover,
the line list contains two density sensitive line pairs, Fe XII 338
AA/364 AA and Fe XIII 348 AA / 360 AA (see, e.g., Mason et al., 1997)
which can be used to determine the electron density. Using this data we
intend to study the temporal evolution of characteristics and geometry
of the loop during the flare.
Title: Database of photometric periods of artificial satellites
Authors: de Pontieu, B.
Bibcode: 1997AdSpR..19..229D
Altcode:
A database of photometric periods of artificial satellites (PPAS)
is presented. It contains almost 40,000 measurements of the tumbling
period of over 1,300 different artificial satellites. The measurements
were obtained from visual observations of the tumbling behavior of
artificial satellites by 140 amateur satellite observers between 1962
and now. The satellites observed include payloads and discarded third
stages, but also smaller pieces of space debris. The PPAS database
could be used to study the effects of collisions of small space
debris with larger artificial satellites on the tumbling behavior of
the latter. As an example of the possible use of the PPAS database,
we present a preliminary study of the tumbling period evolution with
time for discarded third stages. Several cases of non-typical evolution
(e.g. sudden jumps in the tumbling period) have been found, some of
which can probably be interpreted as collisions of the third stages
with small pieces of space debris. A careful analysis of the data
in the PPAS database could shed light on collision probabilities of
active payloads with space debris.