Author name code: martinez-sykora
ADS astronomy entries on 2022-09-14
author:"Martinez-Sykora, Juan"
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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: 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: Modeling of small-scale phenomena
Authors: Martinez Sykora, Juan
Bibcode: 2022cosp...44.2550M
Altcode:
Over the last years, to mention a few small-scale phenomena, substantial
progress has been made on modeling spicules, jets, surges, coronal rain,
and the local dynamo. These advances are because models have reached
smaller scales, but essential and complex physics is a key aspect of
advancing our understanding of small-scale phenomena. To cite some of
the relevant improvements: combination and interaction of even larger
and smaller dynamic structures, ion-neutral interaction effects (e.g.,
ambipolar diffusion and Hall term), or the ionization is treated in
NEQ. In this review, I will present some of these advances in the
numerical modeling of small-scale phenomena.
Title: Multilfuid Alfven wave simulations to understand the chemical
fractionation in the chromosphere and the role of the NEQ ionization.
Authors: Martinez Sykora, Juan
Bibcode: 2022cosp...44.2575M
Altcode:
We aim to study the role of Alfven waves on the first ionization
potential (FIP) effects — the enrichment of low FIP elements in
the outer solar atmosphere; this phenomenon is intimately tied to
the physics of the chromosphere and the corona. For this study, we
combine single fluid 2D radiative MHD models of the solar atmosphere
using Bifrost, with a novel multi-fluids multi-species numerical
code (Ebysus). With the former, we investigate the possible impact
of non-equilibrium ionization within the region where the FIP may
occur and its plasma properties. From the plasma properties from the
Bifrost model, we initialize our multi-fluid models to investigate
the fractionation and the role of the Ponderomotive force.
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: Thermal Instability-Induced Fundamental Magnetic Field Strands
in the Solar Corona
Authors: Antolin, Patrick; Martínez-Sykora, Juan; Şahin, Seray
Bibcode: 2022ApJ...926L..29A
Altcode:
Thermal instability is a fundamental process of astrophysical
plasmas. It is expected to occur whenever the cooling is dominated
by radiation and cannot be compensated for by heating. In this work,
we conduct 2.5D radiation MHD simulations with the Bifrost code
of an enhanced activity network in the solar atmosphere. Coronal
loops are produced self-consistently, mainly through Joule heating,
which is sufficiently stratified and symmetric to produce thermal
nonequilibrium. During the cooling and driven by thermal instability,
coronal rain is produced along the loops. Due to flux freezing,
the catastrophic cooling process leading to a rain clump produces a
local enhancement of the magnetic field, thereby generating a distinct
magnetic strand within the loop up to a few Gauss stronger than the
surrounding coronal field. These strands, which can be considered
fundamental, are a few hundred kilometers in width, span most of
the loop leg, and emit strongly in the UV and extreme UV (EUV),
thereby establishing a link between the commonly seen rain strands
in the visible spectrum with the observed EUV coronal strands at
high resolution. The compression downstream leads to an increase in
temperature that generates a plume-like structure, a strongly emitting
spicule-like feature, and short-lived brightening in the UV during
the rain impact, providing an explanation for similar phenomena seen
with IRIS. Thermal instability and nonequilibrium can therefore be
associated with localized and intermittent UV brightening in the
transition region and chromosphere, as well as contribute to the
characteristic filamentary morphology of the solar corona in the EUV.
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: Description of collisional frequencies for multifluid MHD
models with Chapman-Cowling collision integrals
Authors: Wargnier, Q.; Martinez-Sykora, Juan; Hansteen, Viggo;
Magin, Thierry
Bibcode: 2021AGUFMSH45B2362W
Altcode:
We focus on the detailed description of the collisional frequency in the
solar atmosphere based on a classical formalism with Chapman-Cowling
collision integrals, as described by Zhdanov (2002) in the context of
the 13N-moment model derived with a method of Grad (Grad 1949). 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 collisional frequencies are computed
accurately while being consistent at the kinetic level. We calculate
the collisional frequencies based on this formalism and compare them
with approaches commonly used in the literature in solar atmosphere
conditions. To calculate the collisional frequencies, we focus on
the collision integrals data provided by Bruno et al. (2010), which
is based on a multicomponent hydrogen-helium mixture used in Jupiter
atmosphere conditions. We propose a comparison with the classical
formalism of Vranjes & Krstic (2013) and Leake & Linton
(2013). We compare it with the formalism used in the three approaches
and highlight the differences obtained in the distribution of the
cross sections as functions of the temperature. Then, we quantify
the disparities obtained in postprocessed simulations of a 2.5D solar
atmosphere with the Bifrost code (see Gudiksen et al. 2011). Finally,
we assess the impact of the collisional frequency in a simulated
2.5D solar atmosphere with a single-fluid radiative MHD model with
ambipolar diffusion to consider ion-neutral interactions. Significant
disparities in the cross sections have been obtained between these
three formalisms. or instance, we note that Vranjes & Krstic 2013
did no integrate the transport cross sections. We will describe the
impact of these discrepancies from previous results and the importance
of doing these calculations properly.
Title: Multi-fluid Simulations of Small-scale Collisional Plasma
Instabilities in the Solar Chromosphere
Authors: Evans, Samuel; Oppenheim, Meers; Martinez-Sykora, Juan;
Dimant, Yakov; Xiao, Richard
Bibcode: 2021AGUFMSH25A2073E
Altcode:
The chromosphere may be the most complex region in the solar
atmosphere. The neutral flows, metal ions, magnetic field structure,
radiation, and non-local thermal equilibrium effects may all play
an important role in heating the solar atmosphere from a few thousand
Kelvin to over a million Kelvin. The chromosphere also spans temperature
ranges that cause it to transition between predominantly neutral to
predominantly ionized, and the ions to transition from demagnetized
to magnetized. The flows, densities, and temperatures of the various
species in this region, along with the electric and magnetic fields,
create conditions which can trigger the multi-species thermal plus
Farley-Buneman instability. This instability causes the plasma
to develop waves that lead to turbulence and heating, which may
help to explain the discrepancy between models and observations of
heating in the chromosphere. In this work, we present simulations
of this instability, using the multi-fluid multi-species (MFMS)
code, Ebysus. These simulations model a small piece of the coldest
regions of the chromosphere with a realistic, but externally imposed
current. We analyze the resulting heating, and compare the simulation
with results from a particle-in-cell (PIC) code. The ability to simulate
this instability in a multi-fluid code should enable simulations with
chromospheric parameters unobtainable by a PIC code. We expect the
result of this study will be to determine the effects of this type of
small-scale turbulence on heating and transport in the larger scale
solar atmosphere.
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: 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: Probing Uncertainties in Diagnostics of a Synthetic
Chromosphere
Authors: Schmit, Don; Martinez-Sykora, Juan; Pereira, Tiago; Asensio
Ramos, Andrés
Bibcode: 2021ApJ...913...71S
Altcode:
Effective spectroscopic diagnostics rely on the ability to convert a
particular flux measurement into a physical interpretation. Knowledge
of uncertainty is a central component of diagnostics. We present data
from a simulated solar-like chromosphere, where we have addressed the
question of whether degeneracy is a problem in mapping from a non-LTE
chromospheric line profile to a particular vertical stratification
of atmospheric properties along the line of sight. Our results
indicate that stratification degeneracies do exist, at least in our
simulated atmosphere. We quantify this effect through the creation
of posterior densities for atmospheric properties based on the Mg
II h line profile using the approximate Bayesian computation (ABC)
technique. We find that the predictive power of the ABC temperature
posterior systematically varies as a function of atmospheric column
mass and ground-truth temperature. The ABC posteriors more effectively
reproduce the spectral intensity in the Ca II 8542 Å line than they do
temperature stratification, although residual error in the Ca II line
core is common. Our results illustrate that some degeneracies should
be alleviated through simultaneous analysis of multiple chromospheric
lines.
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: Thermal instability-induced fundamental magnetic strands in
coronal loops
Authors: Antolin, Patrick; Martinez-Sykora, Juan
Bibcode: 2021cosp...43E.968A
Altcode:
Thermal instability is a fundamental process of astrophysical
plasmas. It is expected to occur whenever the cooling is dominated
by radiation and cannot be compensated by heating. This mechanism has
been invoked to explain structures at multiple scales in the Universe,
from the filamentary structure of the ISM to the phenomenon of coronal
rain in the solar corona. In this work we conduct 2.5-D Radiation MHD
simulations with the Bifrost code of an enhanced activity network in
the solar atmosphere. Coronal loops are produced self-consistently,
mainly through Ohmic heating, which is stratified and of a high enough
frequency as to produce thermal non-equilibrium. During the cooling
and driven by thermal instability, coronal rain is produced along the
loops. Due to flux freezing, the catastrophic cooling process leading
to a rain clump produces a local enhancement of the magnetic field,
thereby generating a distinct magnetic strand within the loop up to a
few Gauss stronger than the ambient corona. The compression downstream
leads to an increase in temperature that generates a strongly emitting
spicule-like feature in the UV during the rain impact. The stronger
magnetic field strength in the rarefied upstream region has a stronger
Ohmic heating, leading to a filamentary coronal strand with enhanced
EUV emission. Thermal instability and _x0005_non-equilibrium can
therefore be associated with localised and intermittent UV brightening
in the transition region and chromosphere, as well as contribute to
the characteristic filamentary morphology of the solar corona in the
EUV. An additional effect of a strand with enhanced magnetic field is to
serve as a waveguide, which combined with the Ohmic heating can act as a
seed to sustain the coronal loop and the thermal non-equilibrium cycle.
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: Expected spectropolarimetric observables in the lower solar
atmosphere from 3D radiative MHD models
Authors: Sainz Dalda, A.; Gosic, M.; Martinez-Sykora, J.
Bibcode: 2020AGUFMSH0010019S
Altcode:
No abstract at ADS
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: 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: Multi-Fluid Simulations of Collisional Plasma Instabilities
in the Solar Chromosphere
Authors: Evans, S.; Martínez-Sykora, J.; Dimant, Y. S.; Oppenheim,
M. M.
Bibcode: 2020AGUFMSH0010016E
Altcode:
The state-of-the-art instruments (IRIS-ALMA-DKIST) are challenging our
understanding of the thermodynamics of the solar chromosphere. The
chromosphere is the region between the solar surface and the
million-degree corona. Chromospheric physics involves complex processes
that are not well-described by the standard MHD assumptions, such as
partially ionized regions, diffusive terms becoming non-negligible
compared to collisional effects, and ion species which transition
between magnetized and demagnetized. All these ingredients are necessary
to develop thermal and Farley-Buneman instabilities in the solar
chromosphere. By using the new multi-fluid multi-species (MFMS) code
Ebysus, we work to simulate the effects of thermal and Farley-Buneman
instabilities in the solar chromosphere. Ebysus models each ion species
and ionization level as a separate fluid and tracks many fluids at
once, making it well-suited to investigate these instabilities with
a fluid-model. This paper will describe these instabilities as they
appear in the solar chromosphere using Ebysus and making comparisons to
PIC code simulations. This work is supported by NSF Grant 1903416.
Title: A Multi-Fluid Multi-Species (MFMS) numerical code for
simulating the solar atmosphere
Authors: Wargnier, Q.; Martínez-Sykora, J.; Hansteen, V. H.;
Szydlarski, M.; Evans, S.
Bibcode: 2020AGUFMSH0370007W
Altcode:
The solar atmosphere is characterized by multiple periods and sizes
involving a large spectrum of temporal and spatial scales. It is
regulated through complex interactions between different species and
chemical reactions, amongst other physical processes . Because of
this complexity, an accurate description of all of these multi-scale
phenomena in the solar atmosphere is out of the reach of standard
single-fluid MHD models (Hartlep et al. 2012). Furthermore, the
enrichment of low first ionization potential elements in the outer
layer of the solar atmosphere (the FIP effect) is not fully described
by the current theoretical models (e.g. Laming et al. 2017), since
they employ semi-empirical static atmospheres.
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: 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: Ambipolar diffusion in the Bifrost code
Authors: Nóbrega-Siverio, D.; Martínez-Sykora, J.; Moreno-Insertis,
F.; Carlsson, M.
Bibcode: 2020A&A...638A..79N
Altcode: 2020arXiv200411927N
Context. Ambipolar diffusion is a physical mechanism related to the
drift between charged and neutral particles in a partially ionized
plasma that is key to many different astrophysical systems. However,
understanding its effects is challenging due to basic uncertainties
concerning relevant microphysical aspects and the strong constraints it
imposes on the numerical modeling.
Aims: Our aim is to introduce
a numerical tool that allows us to address complex problems involving
ambipolar diffusion in which, additionally, departures from ionization
equilibrium are important or high resolution is needed. The primary
application of this tool is for solar atmosphere calculations, but the
methods and results presented here may also have a potential impact
on other astrophysical systems.
Methods: We have developed a
new module for the stellar atmosphere Bifrost code that improves its
computational capabilities of the ambipolar diffusion term in the
generalized Ohm's law. This module includes, among other things,
collision terms adequate to processes in the coolest regions in
the solar chromosphere. As the main feature of the module, we have
implemented the super time stepping (STS) technique, which allows an
important acceleration of the calculations. We have also introduced
hyperdiffusion terms to guarantee the stability of the code.
Results: We show that to have an accurate value for the ambipolar
diffusion coefficient in the solar atmosphere it is necessary to
include as atomic elements in the equation of state not only hydrogen
and helium, but also the main electron donors like sodium, silicon,
and potassium. In addition, we establish a range of criteria to set
up an automatic selection of the free parameters of the STS method
that guarantees the best performance, optimizing the stability and
speed for the ambipolar diffusion calculations. We validate the STS
implementation by comparison with a self-similar analytical solution.
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: 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: Nonequilibrium ionization and ambipolar diffusion in solar
magnetic flux emergence processes
Authors: Nóbrega-Siverio, D.; Moreno-Insertis, F.; Martínez-Sykora,
J.; Carlsson, M.; Szydlarski, M.
Bibcode: 2020A&A...633A..66N
Altcode: 2019arXiv191201015N
Context. Magnetic flux emergence from the solar interior has
been shown to be a key mechanism for unleashing a wide variety of
phenomena. However, there are still open questions concerning the
rise of the magnetized plasma through the atmosphere, mainly in
the chromosphere, where the plasma departs from local thermodynamic
equilibrium (LTE) and is partially ionized.
Aims: We aim to
investigate the impact of the nonequilibrium (NEQ) ionization and
recombination and molecule formation of hydrogen, as well as ambipolar
diffusion, on the dynamics and thermodynamics of the flux emergence
process.
Methods: Using the radiation-magnetohydrodynamic
Bifrost code, we performed 2.5D numerical experiments of magnetic flux
emergence from the convection zone up to the corona. The experiments
include the NEQ ionization and recombination of atomic hydrogen, the NEQ
formation and dissociation of H2 molecules, and the ambipolar
diffusion term of the generalized Ohm's law.
Results: Our
experiments show that the LTE assumption substantially underestimates
the ionization fraction in most of the emerged region, leading to an
artificial increase in the ambipolar diffusion and, therefore, in the
heating and temperatures as compared to those found when taking the
NEQ effects on the hydrogen ion population into account. We see that
LTE also overestimates the number density of H2 molecules
within the emerged region, thus mistakenly magnifying the exothermic
contribution of the H2 molecule formation to the thermal
energy during the flux emergence process. We find that the ambipolar
diffusion does not significantly affect the amount of total unsigned
emerged magnetic flux, but it is important in the shocks that cross
the emerged region, heating the plasma on characteristic times ranging
from 0.1 to 100 s. We also briefly discuss the importance of including
elements heavier than hydrogen in the equation of state so as not to
overestimate the role of ambipolar diffusion in the atmosphere. Movies associated to Figs. 2-5, 8, 9, and A.1 are available at https://www.aanda.org
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: Ebysus: a multi-fluid and multi-species numerical code:
on coupling between ionized species
Authors: Martínez-Sykora, J.; Szydlarski, M.; Hansteen, V. H.
Bibcode: 2019AGUFMSH33D3412M
Altcode:
The solar atmosphere is composed of many species which are populated at
different ionized/excited levels. The upper chromosphere, transition
region and corona are nearly collisionless. Consequently, ion-neutral
interaction effects or interactions between species may play a role. We
have developed a 3D multi-fluid and multi-species numerical code
(Ebysus) to investigate this scenario. Ebysus is capable of treating
species (e.g., hydrogen, helium etc) and fluids (neutrals, excited and
ionized elements) separately including non-equilibrium ionization,
momentum exchange, radiation, thermal conduction, and other complex
processes in the solar atmosphere. The development of the Ebysus
code started from the already existing and advanced 3D radiative MHD
Bifrost code designed to model the upper convection zone and outer
solar atmosphere. Treating different species as different fluids leads
to the presence of an electric coupling due to drifts on different ion
velocities. This coupling leads to anti-correlated high frequency waves
between the different ionized species. Momentum exchange can dissipate
this kinetic energy. Alfven waves and reconnection can produce such
high frequency waves and thus result in reconnection instabilities,
and in addition reduce the reconnection rate.
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: 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: 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: 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: 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: 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: Small-scale Magnetic Flux Emergence in the Quiet Sun
Authors: Moreno-Insertis, F.; Martinez-Sykora, J.; Hansteen, V. H.;
Muñoz, D.
Bibcode: 2018ApJ...859L..26M
Altcode: 2018arXiv180600489M
Small bipolar magnetic features are observed to appear in the interior
of individual granules in the quiet Sun, signaling the emergence of
tiny magnetic loops from the solar interior. We study the origin
of those features as part of the magnetoconvection process in the
top layers of the convection zone. Two quiet-Sun magnetoconvection
models, calculated with the radiation-magnetohydrodynamic (MHD)
Bifrost code and with domain stretching from the top layers of the
convection zone to the corona, are analyzed. Using 3D visualization
as well as a posteriori spectral synthesis of Stokes parameters,
we detect the repeated emergence of small magnetic elements in the
interior of granules, as in the observations. Additionally, we identify
the formation of organized horizontal magnetic sheets covering whole
granules. Our approach is twofold, calculating statistical properties
of the system, like joint probability density functions (JPDFs), and
pursuing individual events via visualization tools. We conclude that
the small magnetic loops surfacing within individual granules in the
observations may originate from sites at or near the downflows in the
granular and mesogranular levels, probably in the first 1 or 1.5 Mm
below the surface. We also document the creation of granule-covering
magnetic sheet-like structures through the sideways expansion of a
small subphotospheric magnetic concentration picked up and pulled out
of the interior by a nascent granule. The sheet-like structures that we
found in the models may match the recent observations of Centeno et al.
Title: Chromospheric Dynamics and Heating Processes Ion-Neutral
Effects in the Solar Chromosphere and Type II Spicules
Authors: Haraldson Hansteen, Viggo; Martinez-Sykora, Juan
Bibcode: 2018tess.conf40002H
Altcode:
Three-dimensional (3D) Magnetohydrodynamic (MHD) "realistic" models
of the solar chromosphere and lower corona have now progressed to
the point where meaningful comparisons of synthetic observables
and solar data can be made. These comparisons show that while much
can be understood in the context of MHD, there are also important
discrepancies. The solar chromosphere is largely neutral, this leads
to a whole range of phenomena as neutrals slip with respect to charged
particles, perhaps enough to resolve some of these issues. For example,
in the lower solar atmosphere, the chromosphere is permeated by jets
known as spicules, in which plasma is propelled at speeds of 50-150
km/s 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 Alfvén waves that help drive the solar
wind. In this talk spicules are shown to occur when magnetic tension
is amplified and transported upwards through interactions between ions
and neutrals. The tension is impulsively released to drive flows, heat
plasma and generate Alfvén waves. This talk aims to shed light on ion
neutral effects and in particular the formation and impact of type
II spicules in the chromosphere and in the corona, using novel 2.5D
radiative MHD simulations including ion-neutral interaction effects
with the Bifrost code.
Title: Tracing non-vertical acoustic shock propagation in the
chromosphere
Authors: Schmit, Don; Martinez-Sykora, Juan
Bibcode: 2018tess.conf20441S
Altcode:
We report on preliminary progress toward quantifying the energetic
impact of acoustic shocks to the chromosphere in magnetic regions. We
use the Bifrost simulation to track the evolution of shocks in
both vertical and inclined field regions in 2D and 3D radiative-MHD
simulations. It is well known that the telltale Ca II H&K shock
signature is near wing emission (grain) followed by a protracted
blue-to-red Doppler shift in absorption (sawtooth) for a vertical flux
tube. Given that the chromospheric magnetic field is highly structured
and that the formation height of chromospheric lines vary, we build off
that earlier work by identifying the signature of shocks in a broader
environmental and spectral context. In particular, we focus on the Mg
II h&k lines which are observed by IRIS and the Ca II 8542A line
which is observed by the Swedish Solar Telescope. We plan to use the
diagnostics derived from the simulations to derive an occurrence rate
and an energetic deposition rate for shocks in a plage region.
Title: On the Importance of the Nonequilibrium Ionization of Si IV
and O IV and the Line of Sight in Solar Surges
Authors: Nóbrega-Siverio, D.; Moreno-Insertis, F.; Martínez-Sykora,
J.
Bibcode: 2018ApJ...858....8N
Altcode: 2018arXiv180310251N
Surges are ubiquitous cool ejections in the solar atmosphere that often
appear associated with transient phenomena like UV bursts or coronal
jets. Recent observations from the Interface Region Imaging Spectrograph
show that surges, although traditionally related to chromospheric
lines, can exhibit enhanced emission in Si IV with brighter spectral
profiles than for the average transition region (TR). In this paper,
we explain why surges are natural sites to show enhanced emissivity
in TR lines. We performed 2.5D radiative-MHD numerical experiments
using the Bifrost code including the nonequilibrium (NEQ) ionization of
silicon and oxygen. A surge is obtained as a by-product of magnetic flux
emergence; the TR enveloping the emerged domain is strongly affected
by NEQ effects: assuming statistical equilibrium would produce an
absence of Si IV and O IV ions in most of the region. Studying the
properties of the surge plasma emitting in the Si IV λ1402.77 and O IV
λ1401.16 lines, we find that (a) the timescales for the optically thin
losses and heat conduction are very short, leading to departures from
statistical equilibrium, and (b) the surge emits in Si IV more and has
an emissivity ratio of Si IV to O IV larger than a standard TR. Using
synthetic spectra, we conclude the importance of line-of-sight effects:
given the involved geometry of the surge, the line of sight can cut the
emitting layer at small angles and/or cross it multiple times, causing
prominent, spatially intermittent brightenings in both Si IV and O IV.
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: Surges and Si IV Bursts in the Solar Atmosphere: Understanding
IRIS and SST Observations through RMHD Experiments
Authors: Nóbrega-Siverio, D.; Martínez-Sykora, J.; Moreno-Insertis,
F.; Rouppe van der Voort, L.
Bibcode: 2017ApJ...850..153N
Altcode: 2017arXiv171008928N
Surges often appear as a result of the emergence of magnetized
plasma from the solar interior. Traditionally, they are observed
in chromospheric lines such as Hα 6563 \mathringA and Ca II 8542
\mathringA . However, whether there is a response to the surge
appearance and evolution in the Si IV lines or, in fact, in many
other transition region lines has not been studied. In this paper,
we analyze a simultaneous episode of an Hα surge and a Si IV burst
that occurred on 2016 September 03 in active region AR 12585. To that
end, we use coordinated observations from the Interface Region Imaging
Spectrograph and the Swedish 1-m Solar Telescope. For the first time,
we report emission of Si IV within the surge, finding profiles that
are brighter and broader than the average. Furthermore, the brightest
Si IV patches within the domain of the surge are located mainly near
its footpoints. To understand the relation between the surges and the
emission in transition region lines like Si IV, we have carried out 2.5D
radiative MHD (RMHD) experiments of magnetic flux emergence episodes
using the Bifrost code and including the nonequilibrium ionization of
silicon. Through spectral synthesis, we explain several features of
the observations. We show that the presence of Si IV emission patches
within the surge, their location near the surge footpoints and various
observed spectral features are a natural consequence of the emergence of
magnetized plasma from the interior to the atmosphere and the ensuing
reconnection processes.
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: 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: 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: 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: 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: 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: 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: The Cool Surge Following Flux Emergence in a Radiation-MHD
Experiment
Authors: Nóbrega-Siverio; D.; Moreno-Insertis, F.; Martínez-Sykora,
J.
Bibcode: 2016usc..confE..68N
Altcode:
Cool and dense ejections, typically Hα surges, often appear alongside
EUV or X-ray coronal jets as a result of the emergence of magnetized
plasma from the solar interior. Idealized numerical experiments explain
those ejections as being indirectly associated with the magnetic
reconnection taking place between the emerging and preexisting
systems. However, those experiments miss basic elements that can
importantly affect the surge phenomenon. In this paper we study the
cool surges using a realistic treatment of the radiation transfer and
material plasma properties. To that end, the Bifrost code is used,
which has advanced modules for the equation of state of the plasma,
photospheric and chromospheric radiation transfer, heat conduction,
and optically thin radiative cooling. We carry out a 2.5D experiment of
the emergence of magnetized plasma through (meso) granular convection
cells and the low atmosphere to the corona. Through detailed Lagrange
tracing we study the formation and evolution of the cool ejection and,
in particular, the role of the entropy sources; this allows us to
discern families of evolutionary patterns for the plasma elements. In
the launch phase, many elements suffer accelerations well in excess
of gravity; when nearing the apex of their individual trajectories,
instead, the plasma elements follow quasi-parabolic trajectories with
accelerations close to the solar gravity . We show how the formation
of the cool ejection is mediated by a wedge-like structure composed
of two shocks, one of which leads to the detachment of the surge from
the original emerged plasma dome.
Title: The Cool Surge Following Flux Emergence in a Radiation-MHD
Experiment
Authors: Nóbrega-Siverio, D.; Moreno-Insertis, F.; Martínez-Sykora,
J.
Bibcode: 2016ApJ...822...18N
Altcode: 2016arXiv160104074N
Cool and dense ejections, typically Hα surges, often appear alongside
EUV or X-ray coronal jets as a result of the emergence of magnetized
plasma from the solar interior. Idealized numerical experiments explain
those ejections as being indirectly associated with the magnetic
reconnection taking place between the emerging and preexisting
systems. However, those experiments miss basic elements that can
importantly affect the surge phenomenon. In this paper we study the
cool surges using a realistic treatment of the radiation transfer and
material plasma properties. To that end, the Bifrost code is used,
which has advanced modules for the equation of state of the plasma,
photospheric and chromospheric radiation transfer, heat conduction,
and optically thin radiative cooling. We carry out a 2.5D experiment of
the emergence of magnetized plasma through (meso) granular convection
cells and the low atmosphere to the corona. Through detailed Lagrange
tracing we study the formation and evolution of the cool ejection and,
in particular, the role of the entropy sources; this allows us to
discern families of evolutionary patterns for the plasma elements. In
the launch phase, many elements suffer accelerations well in excess
of gravity; when nearing the apex of their individual trajectories,
instead, the plasma elements follow quasi-parabolic trajectories with
accelerations close to {g}⊙ . We show how the formation
of the cool ejection is mediated by a wedge-like structure composed
of two shocks, one of which leads to the detachment of the surge from
the original emerged plasma dome.
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: 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: 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: Multi-parametric Study of Rising 3D Buoyant Flux Tubes in an
Adiabatic Stratification Using AMR
Authors: Martínez-Sykora, Juan; Moreno-Insertis, Fernando; Cheung,
Mark C. M.
Bibcode: 2015ApJ...814....2M
Altcode: 2015arXiv150701506M
We study the buoyant rise of magnetic flux tubes embedded in
an adiabatic stratification using two-and three-dimensional,
magnetohydrodynamic simulations. We analyze the dependence of the tube
evolution on the field line twist and on the curvature of the tube axis
in different diffusion regimes. To be able to achieve a comparatively
high spatial resolution we use the FLASH code, which has a built-in
Adaptive Mesh Refinement (AMR) capability. Our 3D experiments reach
Reynolds numbers that permit a reasonable comparison of the results
with those of previous 2D simulations. When the experiments are run
without AMR, hence with a comparatively large diffusivity, the amount
of longitudinal magnetic flux retained inside the tube increases
with the curvature of the tube axis. However, when a low-diffusion
regime is reached by using the AMR algorithms, the magnetic twist is
able to prevent the splitting of the magnetic loop into vortex tubes
and the loop curvature does not play any significant role. We detect
the generation of vorticity in the main body of the tube of opposite
sign on the opposite sides of the apex. This is a consequence of the
inhomogeneity of the azimuthal component of the field on the flux
surfaces. The lift force associated with this global vorticity makes
the flanks of the tube move away from their initial vertical plane in
an antisymmetric fashion. The trajectories have an oscillatory motion
superimposed, due to the shedding of vortex rolls to the wake, which
creates a Von Karman street.
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: 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: 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: 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: 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: 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 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 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: 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: 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: 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: 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: 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: 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: Modeling small-scale flux emergence from the Convection Zone
into the Corona
Authors: Martinez-Sykora, Juan
Bibcode: 2013enss.confE..60M
Altcode:
High resolution telescopes reveal small-scale flux in the photosphere
and roughly 20% of these events seem to reach and impact the
chromosphere. As a result of such flux emergence, reconnection
with the ambient field or other processes that do not necessarily
involve reconnection but nevertheless impact the chromosphere and
lower corona may occur. I am going to present recent simulations
that show small-scale flux emergence in a computational domain that
captures the upper-convection zone, photosphere, chromosphere and lower
corona. As we will see, small scale activity is strongly dependent on
the physics that dominate in the various layers of the atmosphere,
such as thermo-dynamics, radiative transfer in the photosphere and
thermal conduction along field lines in the corona (we use for that
Bifrost). In addition, small scale activity is also dependent on the
ambient field which changes rapidly with height both in strength and
topology through the different layers of the solar atmosphere. Some
of these small-scale events erupts into the atmosphere destabilizes
the pre-existing magnetic field and drives it to new configurations.
Title: Small scale activity in the solar atmosphere.
Authors: Martinez-Sykora, J.
Bibcode: 2012AGUFMSH53B..01M
Altcode:
High resolution telescopes reveal a large variety of small-scale
activity in the photosphere and chromosphere. These processes can be
driven by convective motion and small scale flux emergence that in
some cases can penetrate into the chromosphere and higher layers. As
result of such flux emergence, reconnection with the ambient field,
or other processes that do not necessarily involve reconnection but
nevertheless impact the chromosphere and lower corona will occur. I
will review the most recent simulations that describe the various
small-scale processes that could impact the chromosphere and corona. As
we will see small scale activity is strongly dependent on the physics
that dominate in the various layers of the atmosphere. These processes
include radiative transfer in the photosphere and chromosphere, partial
ionization effects and time-dependent ionization in the chromosphere,
and thermal conduction along field lines in the corona. In addition,
small scale activity is also dependent on the ambient field which
changes rapidly with height both in strength and topology through the
different layers of the solar atmosphere.
Title: Coupling of the chromosphere and corona: What physics is
required?
Authors: Martinez-Sykora, J.
Bibcode: 2012AGUFMSH31B..02M
Altcode:
The chromosphere is the interface region between the solar surface
and the corona. The observations indicate that the chromosphere is
feeding the corona with mass, momentum, energy, dynamics and, of course,
magnetic flux. It is therefore crucial to implement the most important
physical processes active in these layers in order to build a coherent
physical model of their coupling. These processes include, but are not
limited to, radiative transfer, partial ionization, time-dependent
Hydrogen ionization and thermal conduction along field lines. The
Bifrost code takes these processes into account and in this talk I
will discuss the impact and the importance of the partial ionization
effects and time-dependent ionization. We find that ambipolar (Pedersen)
dissipation is important in the chromosphere in these radiative-MHD
simulations. Moreover, ambipolar dissipation is strongly dependent
on electron density, and the ionization state must be calculated by
taking the time-dependent Hydrogen ionization into account. As a result
this effect impacts the chromosphere in terms of thermal properties,
dynamics and magnetic evolution. Because of the coupling between the
chromosphere and corona, we will show that these physical processes
in the chromosphere also impact the corona.
Title: Current status of self-consistent 3D radiative-MHD simulations
of the solar atmosphere
Authors: Martinez-Sykora, J.
Bibcode: 2012IAUSS...6E.105M
Altcode:
In recent years, there has been major progress in the development of
self-consistent models of the solar atmosphere. These simulations aim to
capture the physics from the convection zone to the corona. However, the
solar chromosphere, which is an interface layer between the photosphere
and corona, has been difficult to model realistically. This is because
the chromosphere is dominated by transitions: from optically thin to
optically thick radiation, from continuum to energetically important
atomic transitions, from gas pressure to magnetic pressure dominance. In
addition, the chromosphere is where non-LTE and non-grey radiative
transport are important, hydrogen ionization is time dependent,
the plasma is partially ionized, etc. As a result, the chromosphere
is highly dynamic and complex, and filled with dynamical features
that may play a significant role in the mass and energy balance of
the corona and solar wind. I will describe the physics included in
current state-of-the-art numerical codes, and their importance for the
thermodynamics of the solar atmosphere. I will focus on recent work that
investigates the formation of spicule-like features, and the effects of
partial ionization on the dynamics and energetics of the chromosphere.
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: Two Types of Spicules ``Observed'' in 3D Realistic Models
Authors: Martínez-Sykora, J.
Bibcode: 2012ASPC..454..133M
Altcode:
Realistic numerical 3D models of the outer solar atmosphere show two
different kind of spicule-like phenomena, as also observed on the solar
limb. The numerical models are calculated using the Oslo Staggered Code
(OSC) to solve the full MHD equations with non-grey and NLTE radiative
transfer and thermal conduction along the magnetic field lines. The two
types of spicules arise as a natural result of the dynamical evolution
in the models. We discuss the different properties of these two types
of spicules, their differences from observed spicules and what needs
to be improved in the models.
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: 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: Observation, inversion and numerical simulation of single-lobed
Stokes V profiles in the quiet sun.
Authors: Sainz Dalda, A.; Martínez-Sykora, J.; Bellot Rubio, L.;
Title, A.
Bibcode: 2012decs.confE..89S
Altcode:
We have studied characteristics and statistics of strong asymmetric
profiles in Stokes V, i.e., single-lobed profiles, in quiet sun using
Hinode/SOT. These profiles require the existence of a velocity gradient
along the line-of-sight, possibly associated with gradients of magnetic
field strength, inclination and/or azimuth. For a better understanding,
observations, inversions and numerical simulations are compared. We
focus our analysis of the observations on the statistical properties
of the single-lobed Stokes V profiles and the results provided by the
inversions using SIRJUMP, which is an LTE inversion code that can
reproduce sharp discontinuities or jump in the magnetic field and
line-of-sight velocity of the atmosphere model. In the quiet sun,
magnetic field is continuously appearing and disappearing at small
scales due to the convective motions and the input of new flux from
deeper layers. From radiative MHD 3D simulations, using Bifrost code, we
note that most of these small scale processes have stratifications with
gradients of magnetic field strength, inclination and velocities. As
result, those stratifications showing jumps in the magnetic field
configuration are associated with the existence of single-lobe Stokes
V profiles in the solar photosphere, as we previously assumed for the
inversions. We show that most of these profiles come from emerging and
disappearance magnetic flux in small scales in the simulations. Finally,
we emphasize importance of the comparison between the synthetic profiles
from the simulations with the observed ones and the atmospheres that
produce them. This comparison will ultimately improve the realism of
the simulations and quantify the emerging and disappearance flux in
the quiet sun.
Title: Study of Single-lobed Circular Polarization Profiles in the
Quiet Sun
Authors: Sainz Dalda, A.; Martínez-Sykora, J.; Bellot Rubio, L.;
Title, A.
Bibcode: 2012ApJ...748...38S
Altcode: 2012arXiv1202.0593S
The existence of asymmetries in the circular polarization (Stokes V)
profiles emerging from the solar photosphere has been known since
the 1970s. These profiles require the presence of a velocity gradient
along the line of sight (LOS), possibly associated with gradients of
magnetic field strength, inclination, and/or azimuth. We have focused
our study on the Stokes V profiles showing extreme asymmetry in the
form of only one lobe. Using Hinode spectropolarimetric measurements,
we have performed a statistical study of the properties of these
profiles in the quiet Sun. We show their spatial distribution, their
main physical properties, how they are related with several physical
observables, and their behavior with respect to their position on
the solar disk. The single-lobed Stokes V profiles occupy roughly
2% of the solar surface. For the first time, we have observed their
temporal evolution and have retrieved the physical conditions of the
atmospheres from which they emerged using an inversion code implementing
discontinuities of the atmospheric parameters along the LOS. In
addition, we use synthetic Stokes profiles from three-dimensional
magnetoconvection simulations to complement the results of the
inversion. The main features of the synthetic single-lobed profiles
are in general agreement with the observed ones, lending support to
the magnetic and dynamic topologies inferred from the inversion. The
combination of all these different analyses suggests that most of the
single-lobed Stokes V profiles are signals coming from the magnetic
flux emergence and/or submergence processes taking place in small
patches in the photosphere of the quiet Sun.
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: 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: 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: 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: On the Origin of the Type II Spicules: Dynamic
Three-dimensional MHD Simulations
Authors: Martínez-Sykora, Juan; Hansteen, Viggo; Moreno-Insertis,
Fernando
Bibcode: 2011ApJ...736....9M
Altcode: 2010arXiv1011.4703M
Recent high temporal and spatial resolution observations of the
chromosphere have forced the definition of a new type of spicule, "type
II's," that are characterized by rising rapidly, having short lives,
and by fading away at the end of their lifetimes. Here, we report on
features found in realistic three-dimensional simulations of the outer
solar atmosphere that resemble the observed type II spicules. These
features evolve naturally from the simulations as a consequence of
the magnetohydrodynamical evolution of the model atmosphere. The
simulations span from the upper layer of the convection zone to
the lower corona and include the emergence of a horizontal magnetic
flux. The state-of-art Oslo Staggered Code is used to solve the full
MHD equations with non-gray and non-LTE radiative transfer and thermal
conduction along the magnetic field lines. We describe in detail the
physics involved in a process which we consider a possible candidate
for the driver mechanism that produces type II spicules. The modeled
spicule is composed of material rapidly ejected from the chromosphere
that rises into the corona while being heated. Its source lies in
a region with large field gradients and intense electric currents,
which lead to a strong Lorentz force that squeezes the chromospheric
material, resulting in a vertical pressure gradient that propels the
spicule along the magnetic field, as well as Joule heating, which
heats the jet material, forcing it to fade.
Title: The stellar atmosphere simulation code Bifrost. Code
description and validation
Authors: Gudiksen, B. V.; Carlsson, M.; Hansteen, V. H.; Hayek, W.;
Leenaarts, J.; Martínez-Sykora, J.
Bibcode: 2011A&A...531A.154G
Altcode: 2011arXiv1105.6306G
Context. Numerical simulations of stellar convection and photospheres
have been developed to the point where detailed shapes of observed
spectral lines can be explained. Stellar atmospheres are very complex,
and very different physical regimes are present in the convection zone,
photosphere, chromosphere, transition region and corona. To understand
the details of the atmosphere it is necessary to simulate the whole
atmosphere since the different layers interact strongly. These physical
regimes are very diverse and it takes a highly efficient massively
parallel numerical code to solve the associated equations.
Aims:
The design, implementation and validation of the massively parallel
numerical code Bifrost for simulating stellar atmospheres from the
convection zone to the corona.
Methods: The code is subjected
to a number of validation tests, among them the Sod shock tube test,
the Orzag-Tang colliding shock test, boundary condition tests and
tests of how the code treats magnetic field advection, chromospheric
radiation, radiative transfer in an isothermal scattering atmosphere,
hydrogen ionization and thermal conduction. Results.Bifrost completes
the tests with good results and shows near linear efficiency scaling
to thousands of computing cores.
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: 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: 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: 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: 2 types of spicules "observed" in 3D realistic models
Authors: Martínez-Sykora, Juan
Bibcode: 2010arXiv1001.1256M
Altcode:
Realistic numerical 3D models of the outer solar atmosphere show two
different kind of spicule-like phenomena, as also observed on the solar
limb. The numerical models are calculated using the 2 types of spicules
"observed" in 3D realistic models Oslo Staggered Code (OSC) to solve
the full MHD equations with non-grey and NLTE radiative transfer and
thermal conduction along the magnetic field lines. The two types of
spicules arise as a natural result of the dynamical evolution in the
models. We discuss the different properties of these two types of
spicules, their differences from observed spicules and what needs to
be improved in the models.
Title: Twisted Flux Tube Emergence from the Convection Zone to the
Corona. II. Later States
Authors: Martínez-Sykora, Juan; Hansteen, Viggo; Carlsson, Mats
Bibcode: 2009ApJ...702..129M
Altcode: 2009arXiv0906.5464M
Three-dimensional numerical simulations of magnetic flux emergence
are carried out in a computational domain spanning the upper layers
of the convection zone to the lower corona. We use the Oslo Staggered
Code to solve the full magnetohydrodynamic equations with non-gray
and non-local thermodynamic equilibrium radiative transfer and thermal
conduction along the magnetic field lines. In this paper, we concentrate
on the later stages of the simulations and study the evolution of the
structure of the rising flux in the upper chromosphere and corona, the
interaction between the emerging flux and the weak coronal magnetic
field initially present, and the associated dynamics. The flux tube
injected at the bottom boundary rises to the photosphere where it
largely remains. However, some parts of the flux tube become unstable
and expand in patches into the upper chromosphere. The flux rapidly
expands toward the corona, pushing the coronal and transition region
material aside, and lifting and maintaining the transition region at
heights greater than 5 Mm above the photosphere for extensive periods
of time. The pre-existing magnetic field in the corona and transition
region is perturbed by the incoming flux and reoriented by a series of
high Joule heating events. Low-density structures form in the corona,
while at later times a high-density filamentary structure appears in
the lower part of the expanding flux. The dynamics of these and other
structures is discussed. While Joule heating due to the expanding flux
is episodic, it increases in relative strength as fresh magnetic field
rises and becomes energetically important in the upper chromosphere and
corona at later times. Chromospheric, transition region, and coronal
lines are computed and their response to the perturbation caused by
the expanding emerging flux is discussed.
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: Flux emergence from the convection zone to the corona
Authors: Martínez-Sykora, Juan
Bibcode: 2009PhDT.......417M
Altcode:
No abstract at ADS
Title: Twisted Flux Tube Emergence From the Convection Zone to
the Corona
Authors: Martínez-Sykora, Juan; Hansteen, Viggo; Carlsson, Mats
Bibcode: 2008ApJ...679..871M
Altcode: 2007arXiv0712.3854M
Three-dimensional numerical simulations of a horizontal magnetic flux
tube emergence with different twist are carried out in a computational
domain spanning the upper layers of the convection zone to the lower
corona. We use the Oslo Stagger Code to solve the full MHD equations
with non-gray, non-LTE radiative transfer and thermal conduction along
the magnetic lines. A magnetic flux tube is input at the bottom boundary
into a weakly magnetized atmosphere. The photospheric and chromospheric
response is described with magnetograms and synthetic continuum as
well as Ca II H line images and velocity field distributions. In the
photosphere the granular size increases when the flux tube approaches
from below, as has been reported previously in the literature. In
the convective overshoot region, some 200 km above the photosphere,
adiabatic expansion produces cooling, darker regions with the structure
of granulation cells. We also find evidence of collapsed granulation
at the boundaries of the rising flux tube. Once the flux tube has
crossed the photosphere, bright points related to concentrated magnetic
field, vorticity, high vertical velocities, and heating by compressed
material are found at heights up to 500 km above the photosphere. At
greater heights, in the magnetized chromosphere, the rising flux tube
produces a large, cool, magnetized bubble that tends to expel the
usual chromospheric oscillations. In addition, the rising flux tube
dramatically increases the chromospheric scale height, pushing the
transition region and corona aside, such that the chromosphere extends
up to 6 Mm above the photosphere. We find flux tube emergence through
the photosphere to the lower corona to be a relatively slow process,
taking of order 1 hr.