explanation blue bibcodes open ADS page with paths to full text
Author name code: derosa
ADS astronomy entries on 2022-09-14
author:"DeRosa, M."
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Title: Suppression of Torus Instability on Cool Stars
Authors: Sun, Xudong; Derosa, Marc; Torok, Tibor
2022cosp...44.1389S Altcode:
Despite the frequent detection of stellar super flares, reports on
stellar coronal mass ejections (CMEs) are rare. This is in contrast with
our Sun, where almost all large flares are accompanied by a CME. Here,
we use an analytical coronal magnetic field model to demonstrate that
the torus instability, a leading mechanism for solar CMEs, tends to
be suppressed in stellar magnetic environment. Contributing factors
include larger starspots, stronger global dipole field, and more
closed magnetic geometry compared to the Sun. Suppression of the torus
instability may contribute to the low apparent CME rate on cool stars.
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Title: Coronal Dimming as a Proxy for Solar and Stellar Coronal
Mass Ejections
Authors: Jin, Meng; Nitta, Nariaki; Derosa, Marc; Cheung, Mark; Osten,
Rachel; France, Kevin; Mason, James; Kowalski, Adam; Schrijver, Carolus
2022cosp...44.1404J Altcode:
Solar coronal dimmings have been observed extensively in the past two
decades. Due to their close association with coronal mass ejections
(CMEs), there is a critical need to improve our understanding of the
physical processes that cause dimmings as well as their relationship
with CMEs. Recent study (e.g., Veronig et al. 2021) also shows promising
dimming signals from distant stars, which suggest the possibility of
using coronal dimming as a proxy to diagnose stellar CMEs. In this
study, we first conduct a comparative study of solar coronal dimming
using MHD simulations and SDO observations. A detailed analysis of
the simulation and observation data reveals how transient dimming
/ brightening are related to plasma heating processes, while the
long-lasting core and remote dimmings are caused by mass loss process
induced by the CME. Using metrics such as dimming depth and dimming
slope, we uncover a relationship between dimmings and CME properties
(e.g., CME mass, CME speed) in the simulation. We further extend the
model for simulating the stellar CMEs and dimmings and compare with
solar cases. Our result suggests that coronal dimmings encode important
information about the associated CMEs, which provides a physical basis
for detecting stellar CMEs from distant solar-like stars.
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Title: The Impact of Nonlinear Interactions Between Solar Photospheric
Magnetic Fields and Flows on the Evolution of the Polar Fields During
Recent Sunspot Cycles
Authors: Derosa, Marc; Hoeksema, J. Todd; Mahajan, Sushant; Upton,
Lisa A.
2022cosp...44.3224D Altcode:
The observed polar fields during solar activity minimum intervals
are believed to be a useful predictor of future sunspot cycle
amplitudes. Such polar fields result from the poleward transport
of magnetic flux from the many active regions that emerge onto the
photosphere at lower latitudes. Recent studies suggest that a subset of
emergent active regions have an outsized influence on the buildup and
eventual maximal amplitude of polar fields. Additionally, the nonlinear
interactions between these fields with the observed surface flows may
also affect the evolution of polar fields. In the work presented here,
we use surface-flux transport modeling, in combination with a curated
list of emergent active regions during sunspot cycles 24 and 25, to
investigate the effects of both active-region emergence properties
and inflows surrounding active regions on the buildup of polar fields,
with an eye toward the ability to constrain the polar field amplitude
following sunspot cycle 25.
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Title: Coronal Mass Ejections and Dimmings: A Comparative Study
Using MHD Simulations and SDO Observations
Authors: Jin, Meng; Cheung, Mark C. M.; DeRosa, Marc L.; Nitta,
Nariaki V.; Schrijver, Carolus J.
2022ApJ...928..154J Altcode: 2022arXiv220213034J
Solar coronal dimmings have been observed extensively in recent
years. Due to their close association with coronal mass ejections
(CMEs), there is a critical need to improve our understanding of the
physical processes that cause dimmings as well as their relationship
with CMEs. In this study, we investigate coronal dimmings by combining
simulation and observational efforts. By utilizing a data-constrained
global magnetohydrodynamics model (Alfvén-wave solar model), we
simulate coronal dimmings resulting from different CME energetics and
flux rope configurations. We synthesize the emissions of different EUV
spectral bands/lines and compare with SDO/AIA and EVE observations. A
detailed analysis of the simulation and observation data suggests
that the transient dimming/brightening are related to plasma heating
processes, while the long-lasting core and remote dimmings are caused
by mass-loss process induced by the CME. Moreover, the interaction
between the erupting flux rope with different orientations and the
global solar corona could significantly influence the coronal dimming
patterns. Using metrics such as dimming depth and dimming slope,
we investigate the relationship between dimmings and CME properties
(e.g., CME mass, CME speed) in the simulation. Our result suggests
that coronal dimmings encode important information about the associated
CMEs, which provides a physical basis for detecting stellar CMEs from
distant solar-like stars.
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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
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.
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Title: Torus-stable zone above starspots
Authors: Sun, Xudong; Török, Tibor; DeRosa, Marc L.
2022MNRAS.509.5075S Altcode: 2021arXiv211103665S; 2021MNRAS.tmp.2934S
Whilst intense solar flares are almost always accompanied by a coronal
mass ejection (CME), reports on stellar CMEs are rare, despite the
frequent detection of stellar 'super flares'. The torus instability of
magnetic flux ropes is believed to be one of the main driving mechanisms
of solar CMEs. Suppression of the torus instability, due to a confining
background coronal magnetic field that decreases sufficiently slowly
with height, may contribute to the lack of stellar CME detection. Here,
we use the solar magnetic field as a template to estimate the vertical
extent of this 'torus-stable zone' (TSZ) above a stellar active
region. For an idealized potential field model comprising the fields
of a local bipole (mimicking a pair of starspots) and a global dipole,
we show that the upper bound of the TSZ increases with the bipole
size, the dipole strength, and the source surface radius where the
coronal field becomes radial. The boundaries of the TSZ depend on the
interplay between the spots' and the dipole's magnetic fields, which
provide the local- and global-scale confinement, respectively. They
range from about half the bipole size to a significant fraction of the
stellar radius. For smaller spots and an intermediate dipole field,
a secondary TSZ arises at a higher altitude, which may increase the
likelihood of 'failed eruptions'. Our results suggest that the low
apparent CME occurrence rate on cool stars is, at least partially,
due to the presence of extended TSZs.
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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
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.
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Title: Assessing the Impact of Cross-Equatorial Surface Flows on
the Buildup of Polar Fields Using Surface Flux Transport Models
Authors: DeRosa, Marc; Mahajan, Sushant
2021AGUFMSH54A..02D Altcode:
Observed polar magnetic flux on the Sun is a useful indicator and
predictor of the sunspot cycle amplitudes. The buildup of such polar
flux is dependent on a number of factors, most prominently the tilt
angle of emergent active-region flux (Joy's Law) and the speed of
the near-surface meridional flow, as well as other factors such as
the inflows surrounding active regions. Surface-flux transport models
use such observations to model the evolution of solar polar fields,
transporting flux based on empirical prescriptions for differential
rotation, meridional flows, and convective dispersal. In the study
presented here, we illustrate the effects on the polar fields of
incorporating meridional flow profiles derived from observations into
a surface-flux transport model, and compare these effects to other
processes that are known to affect the buildup of polar fields. We
find that the cross-equatorial flows that are typically found from
observed meridional flow profiles typically enhance the resulting
polar fields. Such flows may also enhance hemispheric asymmetries.
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Title: Sun-as-a-star Spectral Irradiance Observations of Transiting
Active Regions: a Milestone for Characterization of Stellar Active
Regions
Authors: Toriumi, Shin; Airapetian, Vladimir; Hudson, Hugh; Schrijver,
Karel; Cheung, Chun Ming Mark; DeRosa, Marc
2021AGUFM.U43B..05T Altcode:
Recent observations have revealed that solar-type stars can produce
massive "superflares". The strongest flares on the Sun are almost
always associated with large, complex, rapidly-evolving active regions
(ARs) including sunspots. Therefore, to understand why and how stellar
flares and coronal eruptions occur, which may directly determine
the circumstances of exoplanets, it is critically important to gain
information on stellar ARs. One possible way to do so is to monitor the
star in multiple wavelengths. In this study, we perform multi-wavelength
irradiance monitoring of transiting solar ARs by using full-disk
observational (i.e. Sun-as-a-star) data from four satellites. We find
that the near UV light curves show strong correlations with photospheric
total magnetic flux and that there are time lags between the coronal
and photospheric light curves when ARs are close to the limb. Such time
lags result from high-arching, bright coronal loops above stellar ARs
being visible even when the AR is behind the limb. It is also found
that the EUV light curves sensitive to transition-region temperatures
are sometimes dimmed because of a reduction in the emission measure of
0.60.8 MK due to the plasma being heated to higher temperatures over a
wide area around the AR. These results indicate that, by measuring the
stellar light curves in multiple wavelengths, we may obtain information
on the structures and evolution of stellar ARs.
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Title: The Multiview Observatory for Solar Terrestrial Science (MOST)
Authors: Gopalswamy, Nat; Kucera, Therese; Leake, James; MacDowall,
Robert; Wilson, Lynn; Kanekal, Shrikanth; Shih, Albert; Christe,
Steven; Gong, Qian; Viall, Nicholeen; Tadikonda, Sivakumar; Fung,
Shing; Yashiro, Seiji; Makela, Pertti; Golub, Leon; DeLuca, Edward;
Reeves, Katharine; Seaton, Daniel; Savage, Sabrina; Winebarger, Amy;
DeForest, Craig; Desai, Mihir; Bastian, Tim; Lazio, Joseph; Jensen,
P. E., C. S. P., Elizabeth; Manchester, Ward; Wood, Brian; Kooi,
Jason; Wexler, David; Bale, Stuart; Krucker, Sam; Hurlburt, Neal;
DeRosa, Marc; Pevtsov, Alexei; Tripathy, Sushanta; Jain, Kiran;
Gosain, Sanjay; Petrie, Gordon; Kholikov, Shukirjon; Zhao, Junwei;
Scherrer, Philip; Woods, Thomas; Chamberlin, Philip; Kenny, Megan
2021AGUFMSH12A..07G Altcode:
The Multiview Observatory for Solar Terrestrial Science (MOST) is a
comprehensive mission concept targeting the magnetic coupling between
the solar interior and the heliosphere. The wide-ranging imagery and
time series data from MOST will help understand the solar drivers and
the heliospheric responses as a system, discerning and tracking 3D
magnetic field structures, both transient and quiescent in the inner
heliosphere. MOST will have seven remote-sensing and three in-situ
instruments: (1) Magnetic and Doppler Imager (MaDI) to investigate
surface and subsurface magnetism by exploiting the combination of
helioseismic and magnetic-field measurements in the photosphere; (2)
Inner Coronal Imager in EUV (ICIE) to study large-scale structures
such as active regions, coronal holes and eruptive structures by
capturing the magnetic connection between the photosphere and the
corona to about 3 solar radii; (3) Hard X-ray Imager (HXI) to image
the non-thermal flare structure; (4) White-light Coronagraph (WCOR) to
seamlessly study transient and quiescent large-scale coronal structures
extending from the ICIE field of view (FOV); (5) Faraday Effect
Tracker of Coronal and Heliospheric structures (FETCH), a novel radio
package to determine the magnetic field structure and plasma column
density, and their evolution within 0.5 au; (6) Heliospheric Imager
with Polarization (HIP) to track solar features beyond the WCOR FOV,
study their impact on Earth, and provide important context for FETCH;
(7) Radio and Plasma Wave instrument (M/WAVES) to study electron beams
and shocks propagating into the heliosphere via passive radio emission;
(8) Solar High-energy Ion Velocity Analyzer (SHIVA) to determine spectra
of electrons, and ions from H to Fe at multiple spatial locations
and use energetic particles as tracers of magnetic connectivity; (9)
Solar Wind Magnetometer (MAG) to characterize magnetic structures at
1 au; (10) Solar Wind Plasma Instrument (SWPI) to characterize plasma
structures at 1 au. MOST will have two large spacecraft with identical
payloads deployed at L4 and L5 and two smaller spacecraft ahead of L4
and behind L5 to carry additional FETCH elements. MOST will build upon
SOHO and STEREO achievements to expand the multiview observational
approach into the first half of the 21st Century.
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Title: Torus-Stable Zone Above Starspots
Authors: Sun, Xudong; Torok, Tibor; DeRosa, Marc
2021AGUFMSH32A..02S Altcode:
The torus instability (TI) of magnetic flux ropes is one of the main
driving mechanisms of solar coronal mass ejections (CMEs). If the
stabilizing background magnetic field decreases sufficiently slowly
with height, the TI will be suppressed. Here we estimate the vertical
extent of this "torus-stable zone" (TSZ) above starspots using the
solar magnetic field as a template. For a potential field comprising
a bipole as a pair of starspots and a global dipole, we show that the
upper bound of the TSZ increases with the bipole size, the dipole
strength, and the source surface radius where the coronal field
becomes radial. The values depend on the interplay between the spot
and dipole magnetic fields, which provide the local and global-scale
confinement, respectively. They range from about half the bipole size
to a significant fraction of the stellar radius. A secondary TSZ
sometimes arises at a higher altitude which may facilitate "failed
eruptions". The suppression of the TI may contribute to the lack of
CME detection on cool stars, as larger starspots, stronger dipole,
and more closed magnetic topology significantly expand the TSZ.
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Title: Coronal and Heliospheric Modeling with WSA: Recent Updates
and Applications
Authors: Jones, Shaela; Arge, Charles; Barnes, Graham; Casti, Marta;
Cheung, Chun Ming Mark; da Silva, Daniel; DeRosa, Marc; Henney, Carl;
Kirk, Michael; Simpson, David; Upton, Lisa; Wallace, Samantha
2021AGUFMSH15G2088J Altcode:
The Wang-Sheeley-Arge (WSA) model is a combined empirical and
physics-based model for the solar corona and inner heliosphere, widely
used in the heliophysics community for over two decades. In recent
years the model has been updated to allow solar wind forecasting for
satellites in non-Earth-like orbits, such as Parker Solar Probe (PSP)
and Solar Orbiter (SolO). Here we will describe subsequent improvements
to the model with the release of WSA version 5.3, including the
incorporation of additional photospheric map sources. We will also
present comparisons between coronal magnetic field models and solar
wind forecasts based on a number of different photospheric map sources
and discuss the variability of these results due to the uncertainty
in the photospheric flux. Finally, we will discuss the application of
the WSA model to forecasting for PSP and SolO.
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Title: A Comparative Study of Measurements of the Suns Axisymmetric
Flows: A COFFIES Effort
Authors: Upton, Lisa; Jain, Kiran; Komm, Rudolf; Mahajan, Sushant;
Pevtsov, Alexei; Roudier, Thierry; Tripathy, Sushanta; Ulrich, Roger;
Zhao, Junwei; Basu, Sarbani; Chen, Ruizhu; DeRosa, Marc; Hess Webber,
Shea; Hoeksema, J.
2021AGUFMSH55D1871U Altcode:
Consequence Of Fields and Flows in the Interior and Exterior of
the Sun (COFFIES) is a Phase-1 NASA DRIVE Science Center (DSC),
with the primary objective of developing a data driven model of
solar activity. One of COFFIES five primary science questions is
What drives varying large-scale motions in the Sun? To address this
question, we are developing a comprehensive catalog of the variable
differential rotation and meridional circulation flow patterns. This
catalog includes measurements of these flows as obtained by several
measurement techniques: Doppler imaging, granule tracking, magnetic
pattern tracking, magnetic feature tracking, as well as both time
distance and ring diagram helioseismology. We show a comparison of
these flows across these varied techniques, with a particular focus
on the MDI/HMI/GONG/Mount Wilson overlap period (May-July 2010). We
investigate the uncertainties and attempt to reconcile any discrepancies
(e.g., due to flow depth or systematics associated with the different
measurement techniques). This analysis will pave the way toward
accurately determining the global patterns of axisymmetric flows and
their regular and irregular variations during the cycle.
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Title: Are Potential Field Source Surface models from different
magnetic maps sufficiently robust to track the evolution of the
coronal magnetic topology?
Authors: Barnes, G.; DeRosa, M.; Jones, S.; Cheung, M.; Arge, C.;
Henney, C.
2021AAS...23821308B Altcode:
The geometry, connectivity, and topology of the large-scale coronal
magnetic field play a key role in determining whether a solar
reconnection event will result in an eruption, either by influencing
the location where magnetic reconnection releases energy for an event,
or by determining the pathways and access to open field that allow an
eruption to proceed. Knowing how reliably the coronal magnetic field
can be inferred is critical to understanding its role in energetic
events. Potential Field Source Surface (PFSS) models are a commonly
used tool for both modeling the coronal field itself, and as input
to other models. Multiple methods exist for generating the boundary
condition needed for a PFSS model. We present here results of examining
how robust the PFSS model topology is to different boundary maps, as
measured by the presence of coronal magnetic null points and solar wind
predictions from the Wang-Sheely-Arge (WSA) model, and characterize the
evolution of these null points within a given model. <P />This material
is based upon work supported by NASA under award No. 80NSSC19K0087. Any
opinions, findings, and conclusions or recommendations expressed in
this material are those of the authors and do not necessarily reflect
the views of the National Aeronautics and Space Administration.
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Title: Enhancements to Hinode/SOT-SP Vector Magnetic Field Data
Products
Authors: DeRosa, M. L.; Leka, K. D.; Barnes, G.; Wagner, E.; Centeno,
R.; De Wijn, A.; Bethge, C.
2021AAS...23821305D Altcode:
The Solar Optical Telescope Spectro-Polarimeter (SOT-SP), on board the
Hinode spacecraft (launched in 2006), is a scanning-slit spectrograph
that continues to provide polarization spectra useful for inferring the
vector (three-component) magnetic field at the solar photosphere. SOT-SP
achieves this goal by obtaining line profiles of two magnetically
sensitive lines, namely the Fe I 6302 Angstrom doublet, using a
0.16"×164" slit as it scans a region of interest. Once the data are
merged, a Milne-Eddington based spectropolarimetric inversion scheme is
used to infer multiple physical parameters in the solar photosphere,
including the vector magnetic field, from the calibrated polarization
spectra. All of these data are publicly available once the processing
has occurred. <P />As of this year, the Hinode/SOT team is also making
available the disambiguated vector magnetic field and the re-projected
heliographic components of the field. In making the disambiguated vector
field data product, the 180° ambiguity in the plane-of-sky component
of the vector magnetic field inherent in the spectropolarimetric
inversion process has been resolved. This ambiguity is resolved
using the Minimum-Energy algorithm, which is the same algorithm used
within the pipeline producing the vector-magnetogram data product
for the Helioseismic and Magnetic Imager aboard the Solar Dynamics
Observatory. The heliographic field components (B<SUB>phi</SUB>,
B<SUB>theta</SUB>, B<SUB>r</SUB>) on the same grid as the inverted data
are also now provided. This poster provides more details about these
data product enhancements, and some examples on how the scientific
community may readily obtain these data.
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Title: Sun-as-a-star Spectral Irradiance Observations: Milestone
For Characterizing The Stellar Active Regions
Authors: Toriumi, S.; Airapetian, V.; Hudson, H.; Schrijver, C.;
Cheung, M.; DeRosa, M.
2021AAS...23820503T Altcode:
For understanding the physical mechanism behind the solar flares, it
is crucial to measure the magnetic fields of active regions (ARs) from
the photosphere to the corona and investigate their scale, complexity,
and evolution. This is true for the stellar flares. However, it is
still difficult to spatially resolve the starspots, and one possible
way to probe their evolution and structure is to monitor the star in
multiple wavelengths. To test this possibility with the solar data,
we perform multi-wavelength irradiance monitoring of transiting solar
ARs by using full-disk observation data from SDO, Hinode, GOES, and
SORCE. As a result, we find, for instance, that the near UV light
curves show strong correlations with photospheric total magnetic flux
and that there are time lags between the coronal and photospheric light
curves when ARs are close to the limb, which together may enable one
to discern how high bright coronal loops extend above stellar ARs. It
is also revealed that the sub-MK (i.e. transition-region temperature)
EUV light curves are sometimes dimmed because the emission measure
is reduced owing to the heating over a wide area around the AR. These
results indicate that, by measuring the stellar light curves in multiple
wavelengths, we may obtain information on the structure and evolution
of stellar ARs.
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Title: Torus-Stable Zone Above Starspots
Authors: Sun, X.; Torok, T.; DeRosa, M.
2021AAS...23820801S Altcode:
The torus instability (TI) of current-carrying magnetic flux tubes
is thought to drive many solar coronal mass ejections (CMEs). The
background magnetic field provides the stabilizing force: if it
decreases with height at a rate (decay index) slower than a critical
value, the TI may be suppressed. Here we estimate the vertical extent
of a "torus-stable zone" above starspots using a scaled model for the
Sun. For a potential-field model comprising a bipole (as a pair of
starspots) in alignment with a global dipole, we show that the upper
bound of this zone h<SUB>c</SUB> increases with the bipole size a,
the dipole field with harmonic coefficient g<SUB>10</SUB>, and the
source surface radius R<SUB>s</SUB> where the magnetic field becomes
radial. The value of h<SUB>c</SUB>, ranging from about 0.5a to a
significant fraction of the stellar radius, depends on the interplay
between the spot and dipole magnetic fields; its upper limit is set
by R<SUB>s</SUB>. Suppression of the TI may contribute to the lack of
CME detection from active cool stars, as larger starspots, stronger
dipole, and more closed magnetic topology significantly expand the
torus-stable zone.
---------------------------------------------------------
Title: Torus-Stable Zone Above Starspots
Authors: Sun, Xudong; Török, Tibor; DeRosa, Marc
2021csss.confE..15S Altcode:
The torus instability (TI) of current-carrying magnetic flux tubes
is thought to drive many solar coronal mass ejections (CMEs). The
background magnetic field provides the stabilizing force: if it
decreases with height at a rate slower than a critical value, the
TI may be suppressed. Here we estimate the vertical extent of a
"torus-stable zone" above starspots using a scaled model for the
Sun. For a potential-field model comprising a bipole (as a pair of
starspots) in alignment with a global dipole, we show that the upper
bound of this zone h<SUB>c</SUB> increases with the bipole size a,
the dipole field with harmonic coefficient g<SUB>10</SUB>, and the
source surface radius R<SUB>s</SUB> where the magnetic field becomes
radial. The value of h<SUB>c</SUB>, ranging from about 0.5a to a
significant fraction of the stellar radius, depends on the interplay
between the spot and dipole magnetic fields; its upper limit is set
by R<SUB>s</SUB>. Suppression of the TI may contribute to the lack of
CME detection from active cool stars, as larger starspots, stronger
dipole, and more closed magnetic topology significantly expand the
torus-stable zone.
---------------------------------------------------------
Title: Sun-as-a-star Multi-wavelength Observations: A Milestone for
Characterization of Stellar Active Regions
Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.;
Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L.
2021csss.confE..46T Altcode:
It has been revealed that "superflares" can occur on solar-type
stars. The magnetic energy of the flares is likely to be stored in
active-region atmospheres. Therefore, to explain the energy storage and
occurrence of the flares, it is important to monitor the evolutions of
the active regions, not only in visible light but also in ultraviolet
(UV) and X-rays. To demonstrate this, we perform multi-wavelength
irradiance monitoring of transiting solar active regions by using
full-disk observation data. As a result of this sun-as-a-star spectral
irradiance analysis, we confirm that the visible continuum that
corresponds to the photosphere becomes darkened when the spot is at the
central meridian, whereas most of the UV, EUV and X-rays, which are
sensitive to chromospheric to coronal temperatures, are brightened,
reflecting the bright magnetic features above the starspots. The
time lags between the coronal and photospheric light curves have
the potential to probe the extent of coronal magnetic fields above
the starspots. These results indicate that, by measuring the stellar
light curves in multiple wavelengths, we may obtain information on
the structures and evolution of stellar active regions.
---------------------------------------------------------
Title: The Coronal Global Evolutionary Model: Using HMI Vector
Magnetogram and Doppler Data to Determine Coronal Magnetic Field
Evolution
Authors: Kazachenko, Maria; Abbett, Bill; Liu, Yang; Fisher, George;
Welsch, Brian; Bercik, Dave; DeRosa, Marc; Cheung, Mark; Sun, Xudong;
Hoeksema, J. Todd; Erkka Lumme, .; Hayashi, Keiji; Lynch, Benjamin
2021cosp...43E1785K Altcode:
The Coronal Global Evolutionary Model (CGEM) provides data-driven
simulations of the magnetic field in the solar corona to better
understand the build-up of magnetic energy that leads to eruptive
events. The CGEM project has developed six capabilities. CGEM modules
(1) prepare time series of full-disk vector magnetic field observations
to (2) derive the changing electric field in the solar photosphere over
active-region scales. This local electric field is (3) incorporated
into a surface flux transport model that reconstructs a global
electric field that evolves magnetic flux in a consistent way. These
electric fields drive a (4) 3D spherical magnetofrictional (SMF) model,
either at high resolution over a restricted range of solid angles or
at lower resolution over a global domain to determine the magnetic
field and current density in the low corona. An SMF-generated initial
field above an active region and the evolving electric field at the
photosphere are used to drive (5) detailed magnetohydrodynamic (MHD)
simulations of active regions in the low corona. SMF or MHD solutions
are then used to compute emissivity proxies that can be compared
with coronal observations. Finally, a lower-resolution SMF magnetic
field is used to initialize (6) a global MHD model that is driven by
an SMF electric field time series to simulate the outer corona and
heliosphere, ultimately connecting Sun to Earth. As a demonstration,
this report features results of CGEM applied to observations of the
evolution of NOAA Active Region 11158 in 2011 February.
---------------------------------------------------------
Title: Using New Acoustically-Derived Solar Far-Side Magnetic-Flux
Maps for Data Assimilation in Flux Transport Models
Authors: Hess Webber, S. A.; Chen, R.; DeRosa, M. L.; Upton, L.;
Zhao, J.
2020AGUFMSH0020005H Altcode:
The Sun's far-side magnetic field is important to space weather
forecasting and solar wind modeling, but currently it is not directly
observed. The far-side magnetic field can be approximated using
(a) flux transport models, which are incapable of predicting growth
or new emergence of active regions; (b) conversion from STEREO EUV
observations, which are only available for a limited time period; or
(c) helioseismic far-side acoustic images, which provide general active
region sizes and locations, but not magnetic flux. Recently, Zhao
et al. [2019] and Chen et al. [ in prep ] developed an approach that
calculates far-side acoustic images and calibrates them into far-side
magnetic-flux maps in near-real-time, using machine-learning and STEREO
EUV observations as a bridge. These far-side acoustically-derived
magnetic-flux maps are starting to be tested as assimilated data in
multiple flux transport models. In this work, we show examples of the
results from two different models, and discuss the implications of
the fully-assimilated global models of synchronic magnetic flux as
operational input for coronal or solar wind models.
---------------------------------------------------------
Title: Understanding Solar Cycle Magnetic Evolution with Properties
of Solar Active Regions
Authors: Liu, Y.; Hoeksema, T.; Zhao, J.; DeRosa, M. L.; Sun, X.
2020AGUFMSH0020015L Altcode:
Understanding the solar cycle is a fundamental and important objective
in solar physics. Recent studies have revealed correlations between
variations of the poleward transport of photospheric magnetic fields
with properties of both magnetic field in solar active regions as well
as their decay products. Features such as poleward surges often play
an outsized role in advecting flux away from the activity belts into
polar regions, and therefore affect solar cycle activity. This report
describes our plans and reviews preliminary results investigating the
effects of active region-modified zonal and meridional flows on flux
evolution and the solar cycle.
---------------------------------------------------------
Title: Search Tool for Retrieving Level 2 Data from Hinode's
Spectro-Polarimeter (SP)
Authors: Kam, C.; Arbolante, Q.; Frank, Z.; DeRosa, M. L.
2020AGUFMED0260056K Altcode:
A joint project between JAXA and NASA, the Hinode Solar Optical
Telescope (SOT) has observed our Sun since its launch in October
2006. Mission data has been used extensively to study solar flares,
polar magnetic fields, prominence structures, and changes over the
solar cycle. Archived databases of the SOT filtergraph (FG) images
and spectropolarimeter (SP) maps are maintained in the US, Japan,
and Norway. Many tools for accessing SOT data were developed early
in the mission timeline and are based on Harris Geospatial Solutions
Inc. Interactive Data Language (IDL). We demonstrate a new open source
Python-based search and cross referencing tool for the Hinode SOT
SP. This tool maps their associated Level 2 inversion data products
from the Heliophysics Events Knowlegebase (HEK) and enables greater
accessibility to this ongoing international mission.
---------------------------------------------------------
Title: Flux-Transport Simulations of Solar Polar Magnetic Fields
Based on Various Meridional Surface Flow Profiles
Authors: DeRosa, M. L.; Zhao, J.; Liu, Y.
2020AGUFMSH0020016D Altcode:
Magnetic fields located in the polar regions of the Sun during
solar minima appear to be a useful predictor of the amplitude of the
subsequent sunspot cycles. These polar fields are the result of flows
that move magnetic flux, on a net basis, poleward from active-region
latitudes. This process is captured well by two-dimensional global
flux-transport schemes, which use empirical prescriptions for
differential rotation, meridional flows, and convective dispersal to
kinematically advect flux. As a result, these models are useful for
investigating the evolution of solar surface flux and their effects
on the formation of the polar fields. In the study presented here,
we use a surface-flux transport model to gain intuition toward an
understanding of the importance of different meridional flow profiles
on the formation and evolution of the polar fields. The meridional flow
profiles used for this study are based on helioseismic determinations
of near-surface flows during recently activity cycles.
---------------------------------------------------------
Title: Sun-as-a-star Spectral Irradiance Observations of Transiting
Active Regions
Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.;
Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L.
2020ApJ...902...36T Altcode: 2020arXiv200804319T
Major solar flares are prone to occur in active-region (AR) atmospheres
associated with large, complex, dynamically evolving sunspots. This
points to the importance of monitoring the evolution of starspots,
not only in visible but also in ultraviolet (UV) and X-rays, in
understanding the origin and occurrence of stellar flares. To this end,
we perform spectral irradiance analysis on different types of transiting
solar ARs by using a variety of full-disk synoptic observations. The
target events are an isolated sunspot, spotless plage, and emerging flux
in prolonged quiet-Sun conditions selected from the past decade. We find
that the visible continuum and total solar irradiance become darkened
when the spot is at the central meridian, whereas it is bright near
the solar limb; UV bands sensitive to the chromosphere correlate well
with the variation of total unsigned magnetic flux in the photosphere;
amplitudes of extreme ultraviolet (EUV) and soft X-ray increase with
the characteristic temperature, whose light curves are flat-topped
due to their sensitivity to the optically thin corona; the transiting
spotless plage does not show the darkening in the visible irradiance,
while the emerging flux produces an asymmetry in all light curves about
the central meridian. The multiwavelength Sun-as-a-star study described
here indicates that the time lags between the coronal and photospheric
light curves have the potential to probe the extent of coronal magnetic
fields above the starspots. In addition, EUV wavelengths that are
sensitive to temperatures just below 1 MK sometimes show antiphased
variations, which may be used for diagnosing plasmas around starspots.
---------------------------------------------------------
Title: The Coronal Global Evolutionary Model: Using HMI Vector
Magnetogram and Doppler Data to Determine Coronal Magnetic Field
Evolution
Authors: Hoeksema, J. Todd; Abbett, William P.; Bercik, David J.;
Cheung, Mark C. M.; DeRosa, Marc L.; Fisher, George H.; Hayashi, Keiji;
Kazachenko, Maria D.; Liu, Yang; Lumme, Erkka; Lynch, Benjamin J.;
Sun, Xudong; Welsch, Brian T.
2020ApJS..250...28H Altcode: 2020arXiv200614579H
The Coronal Global Evolutionary Model (CGEM) provides data-driven
simulations of the magnetic field in the solar corona to better
understand the build-up of magnetic energy that leads to eruptive
events. The CGEM project has developed six capabilities. CGEM modules
(1) prepare time series of full-disk vector magnetic field observations
to (2) derive the changing electric field in the solar photosphere over
active-region scales. This local electric field is (3) incorporated
into a surface flux transport model that reconstructs a global
electric field that evolves magnetic flux in a consistent way. These
electric fields drive a (4) 3D spherical magnetofrictional (SMF) model,
either at high resolution over a restricted range of solid angles or
at lower resolution over a global domain to determine the magnetic
field and current density in the low corona. An SMF-generated initial
field above an active region and the evolving electric field at the
photosphere are used to drive (5) detailed magnetohydrodynamic (MHD)
simulations of active regions in the low corona. SMF or MHD solutions
are then used to compute emissivity proxies that can be compared
with coronal observations. Finally, a lower-resolution SMF magnetic
field is used to initialize (6) a global MHD model that is driven by
an SMF electric field time series to simulate the outer corona and
heliosphere, ultimately connecting Sun to Earth. As a demonstration,
this report features results of CGEM applied to observations of the
evolution of NOAA Active Region 11158 in 2011 February.
---------------------------------------------------------
Title: On Measuring Divergence for Magnetic Field Modeling
Authors: Gilchrist, S. A.; Leka, K. D.; Barnes, G.; Wheatland, M. S.;
DeRosa, M. L.
2020ApJ...900..136G Altcode: 2020arXiv200808863G
A physical magnetic field has a divergence of zero. Numerical error
in constructing a model field and computing the divergence, however,
introduces a finite divergence into these calculations. A popular metric
for measuring divergence is the average fractional flux $\left\langle
| {f}_{i}| \right\rangle $ . We show that $\left\langle | {f}_{i}|
\right\rangle $ scales with the size of the computational mesh, and
may be a poor measure of divergence because it becomes arbitrarily
small for increasing mesh resolution, without the divergence actually
decreasing. We define a modified version of this metric that does
not scale with mesh size. We apply the new metric to the results of
DeRosa et al., who measured $\left\langle | {f}_{i}| \right\rangle
$ for a series of nonlinear force-free field models of the coronal
magnetic field based on solar boundary data binned at different spatial
resolutions. We compute a number of divergence metrics for the DeRosa et
al. data and analyze the effect of spatial resolution on these metrics
using a nonparametric method. We find that some of the trends reported
by DeRosa et al. are due to the intrinsic scaling of $\left\langle |
{f}_{i}| \right\rangle $ . We also find that different metrics give
different results for the same data set and therefore there is value
in measuring divergence via several metrics.
---------------------------------------------------------
Title: The PDFI_SS Electric Field Inversion Software
Authors: Fisher, George H.; Kazachenko, Maria D.; Welsch, Brian T.;
Sun, Xudong; Lumme, Erkka; Bercik, David J.; DeRosa, Marc L.; Cheung,
Mark C. M.
2020ApJS..248....2F Altcode: 2019arXiv191208301F
We describe the PDFI_SS software library, which is designed to
find the electric field at the Sun's photosphere from a sequence of
vector magnetogram and Doppler velocity measurements and estimates of
horizontal velocities obtained from local correlation tracking using the
recently upgraded Fourier Local Correlation Tracking code. The library,
a collection of FORTRAN subroutines, uses the "PDFI" technique described
by Kazachenko et al., but modified for use in spherical, Plate Carrée
geometry on a staggered grid. The domain over which solutions are found
is a subset of the global spherical surface, defined by user-specified
limits of colatitude and longitude. Our staggered grid approach, based
on that of Yee, is more conservative and self-consistent compared to
the centered, Cartesian grid used by Kazachenko et al. The library can
be used to compute an end-to-end solution for electric fields from data
taken by the HMI instrument aboard NASA's SDO mission. This capability
has been incorporated into the HMI pipeline processing system operating
at SDO's Joint Science Operations Center. The library is written in a
general and modular way so that the calculations can be customized to
modify or delete electric field contributions, or used with other data
sets. Other applications include "nudging" numerical models of the solar
atmosphere to facilitate assimilative simulations. The library includes
an ability to compute "global" (whole-Sun) electric field solutions. The
library also includes an ability to compute potential magnetic field
solutions in spherical coordinates. This distribution includes a number
of test programs that allow the user to test the software.
---------------------------------------------------------
Title: Coronal dimming as a proxy for stellar coronal mass ejections
Authors: Jin, M.; Cheung, M. C. M.; DeRosa, M. L.; Nitta, N. V.;
Schrijver, C. J.; France, K.; Kowalski, A.; Mason, J. P.; Osten, R.
2020IAUS..354..426J Altcode: 2020arXiv200206249J
Solar coronal dimmings have been observed extensively in the past
two decades and are believed to have close association with coronal
mass ejections (CMEs). Recent study found that coronal dimming
is the only signature that could differentiate powerful flares
that have CMEs from those that do not. Therefore, dimming might be
one of the best candidates to observe the stellar CMEs on distant
Sun-like stars. In this study, we investigate the possibility of using
coronal dimming as a proxy to diagnose stellar CMEs. By simulating a
realistic solar CME event and corresponding coronal dimming using a
global magnetohydrodynamics model (AWSoM: Alfvén-wave Solar Model),
we first demonstrate the capability of the model to reproduce solar
observations. We then extend the model for simulating stellar CMEs
by modifying the input magnetic flux density as well as the initial
magnetic energy of the CME flux rope. Our result suggests that with
improved instrument sensitivity, it is possible to detect the coronal
dimming signals induced by the stellar CMEs.
---------------------------------------------------------
Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks
from the X8.2 Eruptive Flare on 2017 September 10
Authors: Jin, M.; Liu, W.; Cheung, C. M. M.; Nitta, N.; DeRosa,
M. L.; Manchester, W.; Ofman, L.; Downs, C.; Petrosian, V.; Omodei,
N.; Moschou, S. P.; Sokolov, I.
2019AGUFMSH32A..01J Altcode:
As one of the largest flare-CME eruptions during solar cycle 24, the
2017 September 10 X8.2 flare event is associated with spectacular
global EUV waves that transverse almost the entire visible solar
disk, a CME with speed > 3000 km/s, which is one of the fastest
CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for
more than 12 hours. All these unique observational features pose new
challenge on current numerical models to reproduce the multi-wavelength
observations. To take this challenge, we simulate the September 10
event using a global MHD model (AWSoM: Alfven Wave Solar Model) within
the Space Weather Modeling Framework and initiate CMEs by Gibson-Low
flux rope. We assess several important observed and physical inputs
(e.g., flux rope properties, polar magnetic field) in the model to
better reproduce the multi-wavelength observations. We find that the
simulated EUV wave morphology and kinematics are sensitive to the
orientation of the initial flux rope introduced to the source active
region. An orientation with the flux-rope axis in the north-south
direction produces the best match to the observations, which suggests
that EUV waves may potentially be used to constrain the flux-rope
geometry for such limb or behind-the-limb eruptions that lack good
magnetic field observations. By further combining with the white
light and radio observations, we demonstrate the flux rope-corona
interaction can greatly impact the early phase shock evolution (e.g.,
geometry and shock parameters) therefore plays a significant role
for particle acceleration near the Sun in this event. By propagating
the CMEs into the heliosphere and beyond the Earth and Mars orbits, we
compare the model results with the in-situ measurements and demonstrate
the importance of input polar magnetic field on the realistic CME
modeling therefore space weather forecasting.
---------------------------------------------------------
Title: Inferring the Sun's Far-Side Magnetic Flux for Operations
Using Time-Distance Helioseismic Imaging
Authors: Hess Webber, S. A.; Zhao, J.; Chen, R.; Hoeksema, J. T.;
Liu, Y.; Bobra, M.; DeRosa, M. L.
2019AGUFMSH33C3353H Altcode:
Solar wind models are highly dependent on global magnetic fields
at the solar surface as their inner boundary condition, and the
lack of global field data is a significant problem plaguing solar
wind modeling. Currently, only direct observations of the near-side
magnetic field exist and far-side approximations are incapable of
predicting growth of existing active regions or new magnetic flux
emergence. To fill this data gap, we develop a method that calibrates
far-side helioseismic images, which are calculated using near-side
Doppler observations, to far-side magnetic flux maps. The calibration
employs multiple machine-learning methods that use EUV 304 Å data as a
bridge. These algorithms determine a relation 1) between the near-side
AIA 304 Å data and HMI magnetic field data, and 2) between STEREO
304 Å data and far-side helioseismic images obtained from a newly
developed time-distance helioseismic far-side imaging method. The
resulting magnetic flux maps have been further calibrated using maps
produced by a flux transport model. The various data products from
this work — far-side acoustic maps, far-side STEREO EUV-derived
magnetic flux maps, and near-real-time acoustically-driven far-side
magnetic flux maps, along with maps of the associated uncertainties
— are being made available to enable a synchronic global magnetic
flux input into coronal and solar wind models.
---------------------------------------------------------
Title: Characterizing the Magnetic Environment of Exoplanet Stellar
Systems
Authors: Farrish, Alison O.; Alexander, David; Maruo, Mei; DeRosa,
Marc; Toffoletto, Frank; Sciola, Anthony M.
2019ApJ...885...51F Altcode:
We employ a flux transport model incorporating observed stellar
activity relations to characterize stellar interplanetary fields
on cycle timescales for a range of stellar activity defined by the
Rossby number. This framework allows us to examine the asterospheric
environments of exoplanetary systems and yields references against
which exoplanetary observations can be compared. We examine several
quantitative measures of star-exoplanet interaction: the ratio of open
to total stellar magnetic flux, the location of the stellar Alfvén
surface, and the strength of interplanetary magnetic field polarity
inversions, all of which influence planetary magnetic environments. For
simulations in the range of Rossby numbers considered (0.1-5
Ro<SUB>Sun</SUB>), we find that (1) the fraction of open magnetic flux
available to interplanetary space increases with Rossby number, with a
maximum of around 40% at stellar minimum for low-activity stars, while
the open flux for very active stars (Ro ∼ 0.1-0.25 Ro<SUB>Sun</SUB>)
is ∼1-5% (2) the mean Alfvén surface radius, R <SUB>A</SUB>,
varies between 0.7 and 1.3 R <SUB>A,Sun</SUB> and is larger for
lower stellar activity; and (3) at high activity, the asterospheric
current sheet becomes more complex with stronger inversions, possibly
resulting in more frequent reconnection events (e.g., magnetic storms)
at the planetary magnetosphere. The simulations presented here serve to
bound a range of asterospheric magnetic environments within which we
can characterize the conditions impacting any exoplanets present. We
relate these results to several known exoplanets and discuss how they
might be affected by changes in asterospheric magnetic field topologies.
---------------------------------------------------------
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.
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 systems<SUP>1,2</SUP>. On
the Sun, strong flares are usually found in newly emerging sunspot
regions<SUP>3</SUP>. 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 corona<SUP>4</SUP>
and on how three-dimensional magnetic reconnection allows for rapid
energy release<SUP>5,6</SUP>, 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 flares<SUP>7</SUP>,
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 plasmas<SUP>8</SUP> up to and beyond 100 million K.
---------------------------------------------------------
Title: Coronal Magnetic Field Topologies of Solar Active Regions
Authors: DeRosa, Marc L.; Barnes, Graham
2019AAS...23430504D Altcode:
The magnetic field overlying the coronae of solar active regions
displays many complex configurations. In this work, we show renderings
of the important topological surfaces corresponding to potential
fields above solar active regions. Common geometries are identified,
such as nested domains of connectivity, and the presence of narrow
channels of open flux having high expansion factors. Additionally, a
sequence of magnetic field topologies is used to demonstrate null-point
creation and annihilation. Due to the presence of electric currents,
the real coronal magnetic field topology is expected to be even more
complex than that found in these potential fields.
---------------------------------------------------------
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.
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: Reliably Inferring the Sun's Far-Side Magnetic Flux for
Operations Using Time-Distance Helioseismic Imaging - Updates
Authors: Hess Webber, Shea A.; Zhao, Junwei; Chen, Ruizhu; Hoeksema,
Jon Todd; Liu, Yang; Bobra, Monica; DeRosa, Marc L.
2019AAS...23411805H Altcode:
Solar wind models are highly dependent on global magnetic fields at
the solar surface as their inner boundary condition, and the lack
of global field data is a significant problem plaguing solar wind
modeling. Currently, only near-side magnetic field observations exist
and far-side approximations are incapable of predicting growth of
existing active regions or new magnetic flux emergence. We therefore
plan to develop a method that calibrates far-side helioseismic
images, calculated using near-side Doppler observations, to far-side
magnetic flux maps to fill this data gap. The calibration will employ
machine-learning methods that use EUV 304 Å data as a bridge: a
relation will be sought 1) between the near-side AIA 304 Å data and
HMI magnetic field data, and 2) between STEREO 304 Å data and far-side
helioseismic images obtained from a newly developed time-distance
helioseismic far-side imaging method. As an update, progress has been
made in establishing the relation between the near-side 304 Å data
and magnetic flux data, and some previously-unknown systematics were
identified and corrected in the helioseismic far-side images. These
systematic-effect-corrected far-side images will then be used to
establish a relation with the far-side EUV data.
---------------------------------------------------------
Title: Simulating the Inner Asterospheric Magnetic Fields of Exoplanet
Host Stars
Authors: Farrish, Alison; Alexander, David; Maruo, Mei; Sciola,
Anthony; Toffoletto, Frank; DeRosa, Marc L.
2019AAS...23430305F Altcode:
We study magnetic and energetic activity across a range of stellar
behavior via the application of an observationally-based heliophysics
modeling framework. We simulate the inner asterospheric magnetic fields
of host stars with the aim of better understanding and constraining the
space weather environments of exoplanets, and improving our knowledge of
the solar-stellar connection. As astronomy instrumentation has improved,
Earth-like exoplanets are increasingly being found orbiting in the
habitable zones of a variety of stars, ranging from the smallest
and coolest M dwarfs to larger and more solar-like stars. We are
therefore interested in characterizing a broad range of stellar magnetic
activity and the resulting impacts on asterospheric environments. We
will present our work simulating stellar magnetic activity on cycle
timescales via the integration of modeled magnetic flux emergence,
coronal field structure and related plasma emission, and stellar
winds. We use this self-consistent framework of heliophysics-based
models to simulate stellar and asterospheric evolution, in order
to better understand the dynamic connections between host stars and
potential impacts on planetary space weather and habitability. We also
remark on the comparative heliophysics approach which we plan to extend
to star-planet interactions via coupling to models of magnetospheric
activity and dynamo-driven stellar flux emergence.
---------------------------------------------------------
Title: The Global EUV Wave Associated with the SOL2017-09-10 X8.2
Flare: SDO/AIA Observations and Data-constrained MHD Simulations
Authors: Liu, Wei; Jin, Meng; Ofman, Leon; DeRosa, Marc L.
2019AAS...23430701L Altcode:
While large-scale extreme ultraviolet (EUV) waves associated with
coronal mass ejections (CMEs) and solar flares are common, the EUV
wave triggered by the X8 flare-CME eruption on 2017 September 10
was an extreme. This was, to the best of our knowledge, the first
detection of an EUV wave traversing the full-Sun corona over the entire
visible disk and off-limb circumference, manifesting a truly global
nature. In addition to commonly observed reflections, it had strong
transmissions in and out of both polar coronal holes, at elevated
wave speeds of >2000 km/s within them. With an exceptionally large
wave amplitude, it produced significant compressional heating to local
coronal plasma. We present detailed analysis of SDO/AIA observations,
global magnetic field extrapolations with the potential-field source
surface (PFSS) model, and data-constrained MHD simulations of this
event using the University of Michigan Alfven Wave Solar Model
(AWSoM). By comparing the observations and simulations, we benchmark
diagnostics of the magnetic field strengths and thermal properties of
the solar corona on global scales. We discuss the future prospects of
using such extreme EUV waves as probes for global coronal seismology,
an area yet to be fully exploited.
---------------------------------------------------------
Title: Magnetic Properties of Asterospheres of Exoplanet Systems
Authors: Farrish, Alison; Alexander, David; Maruo, Mei; Sciola,
Anthony; Toffoletto, Frank; DeRosa, Marc
2019shin.confE.152F Altcode:
We study magnetic and energetic activity across a range of stellar
behavior via the application of an observationally-based heliophysics
modeling framework. We simulate the inner asterospheric magnetic fields
of host stars with the aim of better understanding and constraining the
space weather environments of exoplanets, and improving our knowledge of
the solar-stellar connection. As astronomy instrumentation has improved,
Earth-like exoplanets are increasingly being found orbiting in the
habitable zones of a variety of stars, ranging from the smallest
and coolest M dwarfs to larger and more solar-like stars. We are
therefore interested in characterizing a broad range of stellar magnetic
activity and the resulting impacts on asterospheric environments. We
will present our work simulating stellar magnetic activity on cycle
timescales via the integration of modeled magnetic flux emergence,
coronal field structure and related plasma emission, and stellar
winds. We use this self-consistent framework of heliophysics-based
models to simulate stellar and asterospheric evolution, in order
to better understand the dynamic connections between host stars and
potential impacts on planetary space weather and habitability. We also
remark on the comparative heliophysics approach which we plan to extend
to star-planet interactions via coupling to models of magnetospheric
activity and dynamo-driven stellar flux emergence.
---------------------------------------------------------
Title: Reliably Inferring the Sun's Far-Side Magnetic Flux for
Operations Using Time-Distance Helioseismic Imaging
Authors: Hess Webber, Shea A.; Zhao, Junwei; Chen, Ruizhu; Hoeksema,
J. Todd; Liu, Yang; Bobra, Monica; DeRosa, Marc
2019spwe.confE...1H Altcode:
Solar wind models are highly dependent on global magnetic fields at
the solar surface as their inner boundary condition, and the lack
of global field data is a significant problem plaguing solar wind
modeling. Currently, only near-side magnetic field observations exist
and far-side approximations are incapable of predicting growth of
existing active regions or new magnetic flux emergence. We therefore
plan to develop a method that calibrates far-side helioseismic
images, calculated using near-side Doppler observations, to far-side
magnetic flux maps to fill this data gap. The calibration will
employ machine-learning methods that use EUV 304 Angstrom data as a
bridge: a relation will be sought 1) between the near-side AIA 304
Angstrom data and HMI magnetic field data, and 2) between STEREO 304
Angstrom data and far-side helioseismic images obtained from a newly
developed time-distance helioseismic far-side imaging method. As an
update, progress has been made in establishing the relation between
the near-side 304 Angstrom data and magnetic flux data, and some
previously-unknown systematics were identified and corrected in
the helioseismic far-side images. These systematic-effect-corrected
far-side images will then be used to establish a relation with the
far-side EUV data.
---------------------------------------------------------
Title: To what degree do regions of open flux located near active
regions affect their eruptivity?
Authors: DeRosa, Marc; Barnes, Graham
2019EGUGA..21.4673D Altcode:
Most, but not all, X-class flares are associated with CMEs. The
conventional wisdom likely ascribes this association to the large
amount of energy released during the flare reconnection process that
then becomes available for accelerating matter upward. For those
X-class flares that are non-eruptive, what properties set these
apart such that there is no discernible eruption? In this study, we
investigate whether active regions that produce non-eruptive X-class
flares are correlated with the lack of a nearby channel of open flux
in the overlying global coronal magnetic field configuration. We
analyze PFSS models of the coronal magnetic field associated with 56
X-class flares (in 37 flaring active regions) occurring during Cycles
23 and 24, and evaluate whether properties the field configuration
are associated with the properties of the associated flares. We find
a positive correlation between whether a region is non-eruptive and
the absence of nearby open magnetic field lines in the PFSS models,
however the confidence we assign to this result is limited by the
small number of non-eruptive X-class flares in the sample.
---------------------------------------------------------
Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth
System
Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan;
Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao,
Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa,
Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale;
Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland,
Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander;
Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens,
Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent;
Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet,
Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth,
Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha
2018arXiv181008728N Altcode:
The authors of this report met on 28-30 March 2018 at the New Jersey
Institute of Technology, Newark, New Jersey, for a 3-day workshop
that brought together a group of data providers, expert modelers, and
computer and data scientists, in the solar discipline. Their objective
was to identify challenges in the path towards building an effective
framework to achieve transformative advances in the understanding
and forecasting of the Sun-Earth system from the upper convection
zone of the Sun to the Earth's magnetosphere. The workshop aimed to
develop a research roadmap that targets the scientific challenge
of coupling observations and modeling with emerging data-science
research to extract knowledge from the large volumes of data (observed
and simulated) while stimulating computer science with new research
applications. The desire among the attendees was to promote future
trans-disciplinary collaborations and identify areas of convergence
across disciplines. The workshop combined a set of plenary sessions
featuring invited introductory talks and workshop progress reports,
interleaved with a set of breakout sessions focused on specific topics
of interest. Each breakout group generated short documents, listing
the challenges identified during their discussions in addition to
possible ways of attacking them collectively. These documents were
combined into this report-wherein a list of prioritized activities
have been collated, shared and endorsed.
---------------------------------------------------------
Title: Simulation of Exoplanet Host Star Magnetic Activity on Stellar
Cycle Timescales
Authors: Farrish, A. O.; Maruo, M.; Barnes, W. T.; Alexander, D.;
Bradshaw, S.; DeRosa, M.
2018LPICo2065.2043F Altcode:
We apply solar physics modeling tools to the study of star-exoplanet
interaction, with a focus on how variations in stellar magnetic
field and energetic emission on cycle timescales may impact planetary
habitability.
---------------------------------------------------------
Title: Using Sun's Far-Side Images Inferred by the Time-Distance
Helioseismic Imaging to Improve Synoptic Maps of Magnetic Field:
Importance and Methodology
Authors: Liu, Yang; Zhao, Junwei; Hoeksema, J. T.; Chen, Ruizhu;
Bobra, Monica; Hess Webber, Shea; DeRosa, M.; Sun, X.
2018shin.confE.147L Altcode:
Synoptic map of magnetic field is an important piece of data used
for many space weather models. Currently solar observation can only
provide magnetic field measurement on the earth-side surface. To
generate magnetic field synoptic maps, the magnetic field measured
about 13 days ago is used for the far-side surface when it was at
the earth-side. This kind of synoptic maps was improved later on by
evolving the measured magnetic field to the day of interest using a flux
transfer model. It takes into account of evolution of magnetic field,
but fails to include newly emerging magnetic flux, especially emerging
active regions, that start to emerge at the far-side surface. <P
/>In this presentation, we first demonstrate that the newly emerging
fluxes in the far-side change the coronal magnetic field structure,
and this change can be global, far reaching to the earth-side. Because
coronal magnetic field is related to the solar wind property and CMEs'
speed, this change has potential to impact space weather forecast. We
then present examples that convert far-side images into magnetic flux
distribution using deep learning. The far-side images are inferred by
the time-distance helioseismic method. Finally we propose to improve
the synoptic maps of magnetic field by combining the far-size images
and the machine learning technique.
---------------------------------------------------------
Title: Simulation of Exoplanet Host Star Magnetic Activity on Stellar
Cycle Timescales
Authors: Farrish, Alison; Maruo, M.; Barnes, W.; Alexander, D.;
Bradshaw, S.; DeRosa, M.
2018shin.confE...4F Altcode:
We apply an empirical photospheric magnetic flux transport
model, derived from solar behavior, and a magnetically-driven
stellar atmosphere model to explore the range of stellar effects on
habitability of Earth-size exoplanets around M dwarf stars. We create
detailed, dynamic simulations of stellar activity and its variability
over stellar cycle timescales. In particular, we examine how the
asterospheric magnetic field and related extreme ultraviolet (EUV)
and X-ray emission vary in time and consider the potential impact on
exoplanet habitability.
---------------------------------------------------------
Title: Do Topological Features of the Solar Corona Affect EUV
Wave Events?
Authors: DeRosa, Marc; Barnes, Graham; Sun, Xudong
2018shin.confE.142D Altcode:
We present visualizations of the topology of the coronal magnetic
field associated with an EUV wave event. This case study will be used
to evaluate whether topological features of interest, such as null
points, separatrix surfaces, domains of high Q (squashing factor),
play any role in determining the morphology of the EUV wave propagation.
---------------------------------------------------------
Title: Does Nearby Open Flux Affect the Eruptivity of Solar Active
Regions?
Authors: DeRosa, Marc L.; Barnes, Graham
2018ApJ...861..131D Altcode: 2018arXiv180201199D
The most energetic solar flares are typically associated with the
ejection of a cloud of coronal material into the heliosphere in the
form of a coronal mass ejection (CME). However, large flares exist that
are not accompanied by a CME. The existence of these noneruptive flares
raises the question of whether such flares suffer from a lack of access
to nearby open fields in the vicinity above the flare (reconnection)
site. In this study, we use a sample of 56 flares from sunspot Cycles
23 and 24 to test whether active regions that produce eruptive X-class
flares are preferentially located near coronal magnetic field domains
that are open to the heliosphere, as inferred from a potential field
source-surface model. The study shows that X-class flares with access
to open fields are eruptive at a higher rate than those for which
access is lacking. The significance of this result should be moderated
due to the small number of noneruptive X-class flares in the sample,
based on the associated Bayes factor.
---------------------------------------------------------
Title: Modeling the Global Coronal Field with Simulated Synoptic
Magnetograms from Earth and the Lagrange Points L<SUB>3</SUB>,
L<SUB>4</SUB>, and L<SUB>5</SUB>
Authors: Petrie, Gordon; Pevtsov, Alexei; Schwarz, Andrew; DeRosa, Marc
2018SoPh..293...88P Altcode:
The solar photospheric magnetic flux distribution is key to structuring
the global solar corona and heliosphere. Regular full-disk photospheric
magnetogram data are therefore essential to our ability to model
and forecast heliospheric phenomena such as space weather. However,
our spatio-temporal coverage of the photospheric field is currently
limited by our single vantage point at/near Earth. In particular,
the polar fields play a leading role in structuring the large-scale
corona and heliosphere, but each pole is unobservable for >6 months
per year. Here we model the possible effect of full-disk magnetogram
data from the Lagrange points L<SUB>4</SUB> and L<SUB>5</SUB>, each
extending longitude coverage by 60<SUP>∘</SUP>. Adding data also from
the more distant point L<SUB>3</SUB> extends the longitudinal coverage
much further. The additional vantage points also improve the visibility
of the globally influential polar fields. Using a flux-transport model
for the solar photospheric field, we model full-disk observations from
Earth/L<SUB>1</SUB>, L<SUB>3</SUB>, L<SUB>4</SUB>, and L<SUB>5</SUB>
over a solar cycle, construct synoptic maps using a novel weighting
scheme adapted for merging magnetogram data from multiple viewpoints,
and compute potential-field models for the global coronal field. Each
additional viewpoint brings the maps and models into closer agreement
with the reference field from the flux-transport simulation, with
particular improvement at polar latitudes, the main source of the fast
solar wind.
---------------------------------------------------------
Title: What Happens to Coronal Field Models when Fake East-Limb
Active Regions are Inserted into Real Synoptic Charts?
Authors: DeRosa, Marc L.
2018tess.conf41603D Altcode:
Global coronal magnetic field models and solar wind models make use of
synoptic maps of the photospheric magnetic field as a lower boundary
condition. These maps have historically been constructed using observed
magnetograms, such that a full-sun map is assembled over the course
of a full solar rotation. As a result of this process, a single maps
contains observations made at different times over the course of a
month, with east-limb longitudes being the most out-of-date. However,
there are many instances where significant missing flux located on
the east limb of the sun has been shown to affect the configuration
of coronal magnetic fields on the Earth-facing side, and in many cases
significant downstream effects occur when predicting solar wind speeds
and other quantities related to space weather. Here, the same fictitious
east-limb active region is inserted into a series of synoptic charts
spanning sunspot cycles 23 and 24 as a way to approximate magnetic flux
located at east-limb longitudes that would be missing from a synoptic
chart. The resulting ensemble of photospheric magnetic maps allows
us to evaluate how often and much of an effect such "hidden flux"
affects potential-field models of the global coronal field.
---------------------------------------------------------
Title: Simulated Coronal EUV Emission from Exoplanet Host Stars
Authors: Farrish, Alison; Barnes, Will; Alexander, David; Bradshaw,
Stephen J.; DeRosa, Mark L.
2018tess.conf40649F Altcode:
We apply a modified solar flux transport (SFT) model, developed
by Schrijver and colleagues, to emulate the magnetic activity of
the host stars of recently discovered habitable-zone planets. The
magnetic flux distributions produced by the SFT simulations serve
as a first-order proxy for the expected magnetic behavior of an
exoplanet host star. We couple the simulated magnetic structure
to a coronal heating model and simulate the expected EUV and X-ray
emission of the target star. The EUV emission is a key energetic input
to the exoplanetary atmosphere, governing ionospheric conductance and
therefore influencing the magnetospheric response to stellar activity -
a key factor in determining the overall atmospheric loss and ultimately
the potential of the planet for habitation. In addition, the simulated
stellar coronal emission may provide signatures for comparison with
astronomical observations. We consider the simulated activity over a
number of stellar cycles to explore the long-term impact of the star
on the exo-planetary environment.
---------------------------------------------------------
Title: Modeling the Global Coronal Field with Simulated Synoptic
Magnetograms from Earth and the Lagrange points L3, L4 and L5
Authors: Petrie, Gordon J. D.; Pevtsov, Alexei A.; Schwarz, Andrew
Michael; DeRosa, Marc
2018tess.conf40132P Altcode:
The solar photospheric magnetic flux distribution determines the
global structure of the solar corona and heliosphere. Regular
full-disk photospheric magnetogram data are therefore essential to
our ability to model and forecast heliospheric phenomena such as space
weather. However, our spatio-temporal coverage of the photospheric field
is currently limited by our single vantage point at/near Earth. In
particular, the polar fields define the large-scale structure of the
corona and heliosphere but each pole is unobservable for > 6 months
per year. Here we model the possible effect of full-disk magnetogram
data from the Lagrange points L4 and L5, each extending longitude
coverage by 60 degrees. Adding data also from the more distant point
L3 extends longitudinal coverage much further. The additional vantage
points also improve the visibility of the globally influential polar
fields. Using a flux-transport model for the solar photospheric field
we model full-disk observations from Earth/L1, L3, L4 and L5 over a
solar cycle, construct synoptic maps using a novel weighting scheme
adapted for merging magnetogram data from multiple viewpoints, and
compute potential-field models for the global coronal field. Each
additional viewpoint significantly improves the performance of the
maps and models with particular improvement at polar latitudes, the
main source of the fast solar wind.
---------------------------------------------------------
Title: The Application of Solar Flux Transport Modeling to Exoplanet
Systems
Authors: Alexander, David; Farrish, Alison; Maruo, Mei; De Rosa,
Marc L.
2018tess.conf40648A Altcode:
Earth-size exoplanets are preferentially detected close-in around small
stars; Proxima Centauri b, Ross 128 b, and the TRAPPIST-1 planets are
newly discovered exoplanets in this class. The effects of magnetic
interactions between the host star and such close-in exoplanets are
still not well-constrained. We utilize an empirical solar magnetic flux
transport model, first developed by Schrijver and colleagues, to explore
the possible relationships between stellar properties (e.g. rotation
period, radius, flux emergence rate, and meridional and differential
flow rates) and the expected surface magnetic flux distributions,
along with their evolution over the stellar cycle. The surface field
then provides key information about the interplanetary magnetic fields,
stellar winds, dynamic activity, and coronal emission, all of which
influence the star-planet interactions. We present simulated magnetic
flux patterns representing a range of possible exoplanet host stars,
including potential observables such as starspots, active regions,
and stellar cycle variations. The magnetic and energetic environment at
an exoplanet and its impact on the magnetospheric-atmospheric coupling
are important components of a planet's habitability that we expect to
constrain further with this application of simulated stellar magnetic
activity.
---------------------------------------------------------
Title: Coronal Mass Ejections and Dimmings: A Comparative Study
using MHD Simulations and SDO Observations
Authors: Jin, M.; Cheung, C. M. M.; DeRosa, M. L.; Nitta, N.;
Schrijver, K.
2017AGUFMSH41A2758J Altcode:
Solar coronal dimmings have been observed extensively in the past two
decades. Due to their close association with coronal mass ejections
(CMEs), there is a critical need to improve our understanding of the
physical processes that cause dimmings and determine their relationship
with CMEs. In this study, we investigate coronal dimmings by combining
simulation and observational efforts. By utilizing a data-driven global
magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we simulate
coronal dimmings resulting from different CME energetics and flux rope
configurations. We synthesize the emissions of different EUV spectral
bands/lines and compare with SDO/AIA and EVE observations. A detailed
analysis of simulation and observation data suggests that although
the transient dimming / brightening patterns could relate to plasma
heating processes (either by adiabatic compression or reconnection),
the long-lasting "core" and "remote" (also known as "secondary")
dimmings both originate from regions with open/quasi-open fields and
are caused by mass loss process. The mass loss in the remote dimming
region is induced by CME-driven shock. Using metrics such as dimming
depth, dimming slope, and recovery time, we investigate the relationship
between dimmings and CME properties (e.g., CME mass, CME speed) in the
simulation. Our result suggests that coronal dimmings encode important
information about CME energetics, CME-driven shock properties, and
magnetic configuration of erupting flux ropes. We also discuss how our
knowledge about solar coronal dimmings could be extended to the study
of stellar CMEs, which may prove important for exoplanet atmospheres
and habitability but which are currently not observable.
---------------------------------------------------------
Title: The Open Flux Problem
Authors: Linker, J. A.; Caplan, R. M.; Downs, C.; Riley, P.; Mikic,
Z.; Lionello, R.; Henney, C. J.; Arge, C. N.; Liu, Y.; Derosa, M. L.;
Yeates, A.; Owens, M. J.
2017ApJ...848...70L Altcode: 2017arXiv170802342L
The heliospheric magnetic field is of pivotal importance in solar
and space physics. The field is rooted in the Sun’s photosphere,
where it has been observed for many years. Global maps of the solar
magnetic field based on full-disk magnetograms are commonly used as
boundary conditions for coronal and solar wind models. Two primary
observational constraints on the models are (1) the open field regions
in the model should approximately correspond to coronal holes (CHs)
observed in emission and (2) the magnitude of the open magnetic
flux in the model should match that inferred from in situ spacecraft
measurements. In this study, we calculate both magnetohydrodynamic and
potential field source surface solutions using 14 different magnetic
maps produced from five different types of observatory magnetograms,
for the time period surrounding 2010 July. We have found that for
all of the model/map combinations, models that have CH areas close
to observations underestimate the interplanetary magnetic flux, or,
conversely, for models to match the interplanetary flux, the modeled
open field regions are larger than CHs observed in EUV emission. In
an alternative approach, we estimate the open magnetic flux entirely
from solar observations by combining automatically detected CHs for
Carrington rotation 2098 with observatory synoptic magnetic maps. This
approach also underestimates the interplanetary magnetic flux. Our
results imply that either typical observatory maps underestimate the
Sun’s magnetic flux, or a significant portion of the open magnetic
flux is not rooted in regions that are obviously dark in EUV and
X-ray emission.
---------------------------------------------------------
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.
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 3x10<SUP>11</SUP>
erg/cm<SUP>2</SUP>/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: Global Evolving Models of Photospheric Flux as Driven by
Electric Fields
Authors: DeRosa, Marc L.; Cheung, Mark; Kazachenko, Maria D.; Fisher,
George H.
2017SPD....4811105D Altcode:
We present a novel method for modeling the global radial magnetic field
that is based on the incorporation of time series of photospheric
electric fields. The determination of the electric fields is the
result of a recently developed method that uses as input various data
products from SDO/HMI, namely vector magnetic fields and line-of-sight
Doppler images. For locations on the sphere where electric field data
are unavailable, we instead use electric fields that are consistent
with measurements of the mean differential rotation, meridional flow,
and flux dispersal profiles. By combining these electric fields,
a full-Sun model of the photospheric radial magnetic field can be
advanced forward in time via Faraday's Law.
---------------------------------------------------------
Title: Coronal Mass Ejections and Dimmings: A Comparative Study
using MHD Simulations and SDO Observations
Authors: Jin, Meng; Cheung, Mark; DeRosa, Marc L.; Nitta, Nariaki;
Schrijver, Karel
2017SPD....4820602J Altcode:
Solar coronal dimmings have been observed extensively in the past two
decades. Due to their close association with coronal mass ejections
(CMEs), there is a critical need to improve our understanding of the
physical processes that cause dimmings and determine their relationship
with CMEs. In this study, we investigate coronal dimmings by combining
simulation and observational efforts. By utilizing a data-driven
global magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we
simulate coronal dimmings resulting from different CME energetics and
flux rope configurations. We synthesize the emissions of different EUV
spectral bands/lines and compare with SDO/AIA and EVE observations. A
detailed analysis of simulation and observation data suggests that the
“core” dimming is mainly caused by the mass loss from the CME, while
the “remote” dimming could have a different origin (e.g., plasma
heating). Moreover, the interaction between the erupting flux rope with
different orientations and the global solar corona could significantly
influence the coronal dimming patterns. Using metrics such as dimming
depth, dimming slope, and recovery time, we investigate the relationship
between dimmings and CME properties (e.g., CME mass, CME speed) in the
simulation. Our result suggests that coronal dimmings encode important
information about CMEs. We also discuss how our knowledge about solar
coronal dimmings could be extended to the study of stellar CMEs.
---------------------------------------------------------
Title: Does erupting material in flaring active regions always have
access to open flux?
Authors: DeRosa, Marc; Barnes, Graham
2017shin.confE..46D Altcode:
Most, but not all, X-class flares are associated with CMEs. The
conventional wisdom likely ascribes this association to the large
amount of energy released during the flare reconnection process that
then becomes available for accelerating matter upward. Of the class of
X flares that are non-eruptive, what properties set these apart such
that there is no discernible eruption? In this study, we investigate
whether active regions that produce non-eruptive X-class flares
are correlated with the lack of a nearby channel of open flux in the
overlying global coronal magnetic field configuration. We analyze PFSS
models of the coronal magnetic field associated with 36 flaring active
regions spanning Cycles 23 and 24, and evaluate whether properties
the field configuration are correlated with the properties of the
associated flares. We find only a weak correlation between whether a
region is eruptive and the presence of overlying open magnetic fields,
suggesting the involvement of other factors in determining whether
X-class flaring regions produce CMEs.
---------------------------------------------------------
Title: A study of the long term evolution in active region upflows
Authors: Harra, Louise K.; Ugarte-Urra, Ignacio; De Rosa, Marc;
Mandrini, Cristina; van Driel-Gesztelyi, Lidia; Baker, Deborah;
Culhane, J. Leonard; Démoulin, Pascal
2017PASJ...69...47H Altcode:
Since their discovery, upflows at the edges of active regions have
attracted a lot of interest, primarily as they could potentially
contribute to the slow solar wind. One aspect that has not been studied
yet is how the long term evolution of active regions impacts the
upflows. In this work, we analyze one active region that survives three
solar rotations. We track how the flows change with time. We use local
and global modeling of the decaying active region to determine how the
age of the active region will impact the extent of the open magnetic
fields, and then how some of the upflows could become outflows. We
finish with a discussion of how these results, set in a broader context,
can be further developed with the Solar Orbiter mission.
---------------------------------------------------------
Title: Magnetic Nulls and Super-radial Expansion in the Solar Corona
Authors: Gibson, Sarah E.; Dalmasse, Kevin; Rachmeler, Laurel A.;
De Rosa, Marc L.; Tomczyk, Steven; de Toma, Giuliana; Burkepile,
Joan; Galloy, Michael
2017ApJ...840L..13G Altcode: 2017arXiv170407470G
Magnetic fields in the Sun’s outer atmosphere—the corona—control
both solar-wind acceleration and the dynamics of solar eruptions. We
present the first clear observational evidence of coronal magnetic
nulls in off-limb linearly polarized observations of pseudostreamers,
taken by the Coronal Multichannel Polarimeter (CoMP) telescope. These
nulls represent regions where magnetic reconnection is likely to act
as a catalyst for solar activity. CoMP linear-polarization observations
also provide an independent, coronal proxy for magnetic expansion into
the solar wind, a quantity often used to parameterize and predict the
solar wind speed at Earth. We introduce a new method for explicitly
calculating expansion factors from CoMP coronal linear-polarization
observations, which does not require photospheric extrapolations. We
conclude that linearly polarized light is a powerful new diagnostic
of critical coronal magnetic topologies and the expanding magnetic
flux tubes that channel the solar wind.
---------------------------------------------------------
Title: Deriving the Properties of Coronal Pressure Fronts in 3D:
Application to the 2012 May 17 Ground Level Enhancement
Authors: Rouillard, A. P.; Plotnikov, I.; Pinto, R. F.; Tirole, M.;
Lavarra, M.; Zucca, P.; Vainio, R.; Tylka, A. J.; Vourlidas, A.;
De Rosa, M. L.; Linker, J.; Warmuth, A.; Mann, G.; Cohen, C. M. S.;
Mewaldt, R. A.
2016ApJ...833...45R Altcode: 2016arXiv160505208R
We study the link between an expanding coronal shock and the energetic
particles measured near Earth during the ground level enhancement of
2012 May 17. We developed a new technique based on multipoint imaging to
triangulate the three-dimensional (3D) expansion of the shock forming
in the corona. It uses images from three vantage points by mapping
the outermost extent of the coronal region perturbed by the pressure
front. We derive for the first time the 3D velocity vector and the
distribution of Mach numbers, M <SUB>FM</SUB>, of the entire front as
a function of time. Our approach uses magnetic field reconstructions
of the coronal field, full magnetohydrodynamic simulations and imaging
inversion techniques. We find that the highest M <SUB>FM</SUB> values
appear near the coronal neutral line within a few minutes of the
coronal mass ejection onset; this neutral line is usually associated
with the source of the heliospheric current and plasma sheet. We
illustrate the variability of the shock speed, shock geometry, and
Mach number along different modeled magnetic field lines. Despite the
level of uncertainty in deriving the shock Mach numbers, all employed
reconstruction techniques show that the release time of GeV particles
occurs when the coronal shock becomes super-critical (M <SUB>FM</SUB>
> 3). Combining in situ measurements with heliospheric imagery,
we also demonstrate that magnetic connectivity between the accelerator
(the coronal shock of 2012 May 17) and the near-Earth environment is
established via a magnetic cloud that erupted from the same active
region roughly five days earlier.
---------------------------------------------------------
Title: Flare Clustering
Authors: Title, Alan; DeRosa, Marc
2016usc..confE..50T Altcode:
The continuous full disk observations provided by the Atmospheric
Imaging Assembly (AIA ) can give an observer the impression that
many flare eruptions are causally related to one another. However,
both detailed analyses of a number of events as well as several
statistical studies have provided only rare examples or weak evidence
of causal behavior. Since the mechanisms of flare triggering are not
well understood, the lack of hard evidence is not surprising. For
this study we looked instead for groups of flares (flare clusters)
in which successive flares occur within a fixed time - the selection
time. The data set used for the investigation is the flare waiting
times provided by the X-ray flare detectors on the Geostationary
Operational Environmental Satellites (GOES). We limited the study
to flares of magnitude C5 and greater obtained during cycles 21,
22, 23, and 24. The GOES field of view includes the entire visible
surface. While many flares in a cluster may come from the same active
region, the larger clusters often have origins in multiple regions. The
longest C5 cluster found with a linking window of 36 hours in cycles
21, 22, 23,and 24 was 54, 82, 42, and 18 days, respectively. X flares
also cluster. A superposed epoch analyses demonstrates that there is
a pronounced enhancement of number of C5 and and above flares that are
centered on the X flare clusters. We suggest that this behavior implies
that a component of the observed coordinated behavior originates from
the MHD processes driven by the solar dynamo that in turn creates
unstable states in the solar atmosphere. The relationship between
flare clusters and magnetic centers of activity was explored as was
the correlation between high flare rates and significant changes in
the total solar magnetic flux,
---------------------------------------------------------
Title: a Numerical Study of Long-Range Magnetic Impacts during
Coronal Mass Ejections
Authors: Jin, Meng; Schrijver, Karel; Cheung, Mark; DeRosa, Marc;
Nitta, Nariaki; Title, Alan
2016shin.confE..38J Altcode:
With the global view and high-cadence observations from SDO/AIA and
STEREO, many spatially separated solar eruptive events appear to be
coupled. However, the mechanisms for 'sympathetic' events are still
largely unknown. In this study, we investigate the impact of an erupting
flux rope on surrounding solar structures through large-scale magnetic
coupling. We build a realistic environment of the solar corona on
2011 February 15 using a global magnetohydrodynamics (MHD) model and
initiate coronal mass ejections (CMEs) in active region (AR) 11158
by inserting Gibson-Low analytical flux ropes. We show that a CME's
impact on the surrounding structures depends not only on the magnetic
strength of these structures and their distance to the source region,
but also on the interaction between the CME with the large-scale
magnetic field. Within the CME expansion domain where the flux rope
field directly interacts with the solar structures, expansion-induced
reconnection often modifies the overlying field, thereby increasing
the decay index. This effect may provide a primary coupling mechanism
underlying the sympathetic eruptions. The magnitude of the impact
is found to depend on the orientation of the erupting flux rope,
with the largest impacts occurring when the flux rope is favorably
oriented for reconnecting with the surrounding regions. Outside the
CME expansion domain, the influence of the CME is mainly through field
line compression or post-eruption relaxation. Based on our numerical
experiments, we discuss a way to quantify the eruption impact, which
could be useful for forecasting purposes.
---------------------------------------------------------
Title: Do large-scale topological features correlate with flare
properties?
Authors: DeRosa, Marc; Barnes, Graham
2016shin.confE.129D Altcode:
In this study, we aim to identify whether the presence or absence of
particular topological features in the large-scale coronal magnetic
field are correlated with whether a flare is confined or eruptive. To
this end, we first determine the locations of null points, spine lines,
and separatrix surfaces within the potential fields associated with
the locations of several strong flares from the current and previous
sunspot cycles. We then validate the topological skeletons against
large-scale features in observations, such as the locations of streamers
and pseudostreamers in coronagraph images. Finally, we characterize the
topological environment in the vicinity of the flaring active regions
and identify the trends involving their large-scale topologies and
the properties of the associated flares.
---------------------------------------------------------
Title: The Topology of Coronal Magnetic Fields, Shine Characterizing
the Properties of Coronal Magnetic Null Points
Authors: Barnes, Graham; DeRosa, Marc; Wagner, Eric
2016shin.confE.133B Altcode:
The topology of the coronal magnetic field plays a role in a wide range
of phenomena, from Coronal Mass Ejections (CMEs) through heating of
the corona. One fundamental topological feature is the null point,
where the magnetic field vanishes. These points are natural sites of
magnetic reconnection, and hence the release of energy stored in the
magnetic field. We present preliminary results of a study using data
from the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics
Observatory to characterize the properties and evolution of null points
in a Potential Field Source Surface model of the coronal field. The
main properties considered are the lifetime of the null points, their
distribution with height, and how they form and subsequently vanish. <P
/>This work is supported by NSF/SHINE grant 1357018 and by NASA/LWS
Grant NNX14AD45G.
---------------------------------------------------------
Title: Do Large-Scale Topological Features Correlate with Flare
Properties?
Authors: DeRosa, Marc L.; Barnes, Graham
2016SPD....47.1005D Altcode:
In this study, we aim to identify whether the presence or absence of
particular topological features in the large-scale coronal magnetic
field are correlated with whether a flare is confined or eruptive. To
this end, we first determine the locations of null points, spine lines,
and separatrix surfaces within the potential fields associated with
the locations of several strong flares from the current and previous
sunspot cycles. We then validate the topological skeletons against
large-scale features in observations, such as the locations of streamers
and pseudostreamers in coronagraph images. Finally, we characterize the
topological environment in the vicinity of the flaring active regions
and identify the trends involving their large-scale topologies and
the properties of the associated flares.
---------------------------------------------------------
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
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: A Numerical Study of Long-range Magnetic Impacts during
Coronal Mass Ejections
Authors: Jin, M.; Schrijver, C. J.; Cheung, M. C. M.; DeRosa, M. L.;
Nitta, N. V.; Title, A. M.
2016ApJ...820...16J Altcode: 2016arXiv160304900J
With the global view and high-cadence observations from Solar Dynamics
Observatory/Atmospheric Imaging Assembly and Solar TErrestrial RElations
Observatory, many spatially separated solar eruptive events appear
to be coupled. However, the mechanisms for “sympathetic” events
are still largely unknown. In this study, we investigate the impact
of an erupting flux rope on surrounding solar structures through
large-scale magnetic coupling. We build a realistic environment of the
solar corona on 2011 February 15 using a global magnetohydrodynamics
model and initiate coronal mass ejections (CMEs) in active region
11158 by inserting Gibson-Low analytical flux ropes. We show that a
CME’s impact on the surrounding structures depends not only on the
magnetic strength of these structures and their distance to the source
region, but also on the interaction between the CME and the large-scale
magnetic field. Within the CME expansion domain where the flux rope
field directly interacts with the solar structures, expansion-induced
reconnection often modifies the overlying field, thereby increasing
the decay index. This effect may provide a primary coupling mechanism
underlying the sympathetic eruptions. The magnitude of the impact
is found to depend on the orientation of the erupting flux rope,
with the largest impacts occurring when the flux rope is favorably
oriented for reconnecting with the surrounding regions. Outside the
CME expansion domain, the influence of the CME is mainly through field
line compression or post-eruption relaxation. Based on our numerical
experiments, we discuss a way to quantify the eruption impact, which
could be useful for forecasting purposes.
---------------------------------------------------------
Title: The Role of Large-scale Magnetic Coupling for Solar Corona
Sympathy
Authors: Jin, M.; Schrijver, K.; Cheung, C. M. M.; DeRosa, M. L.;
Nitta, N.; Title, A. M.
2015AGUFMSH23A2425J Altcode:
With the comprehensive view and high cadence observations from
SDO/AIA and STEREO in solar cycle 24, a large number of spatially
separated solar eruptive events are found to be coupled. However,
compared with the established initiation mechanisms for "isolated"
events, the mechanisms for "sympathetic" events are still largely
unknown, and nascent theories are untested. In this study, we build
a realistic environment of solar corona on 2011 February 15 using
a global MHD model and investigate how an eruption can impact the
surrounding solar structures. Our result shows that the solar eruption's
impact on the different structures can be quite different. Within
the CME expansion domain, it is possible to trigger an eruption by
overlaying field removal through expansion induced reconnection. The
magnitude of impact is found to be dependent on the orientation
of the erupting flux rope. Outside the CME expansion domain, the
post-eruption reconfiguration could play an important role for solar
sympathy. Based on the modeling results, we discuss the possibility of
using observable/estimable parameters to quantify the eruption impact
therefore providing an useful parameter for forecasting sympathy.
---------------------------------------------------------
Title: The Influence of Spatial resolution on Nonlinear Force-free
Modeling
Authors: DeRosa, M. L.; Wheatland, M. S.; Leka, K. D.; Barnes, G.;
Amari, T.; Canou, A.; Gilchrist, S. A.; Thalmann, J. K.; Valori,
G.; Wiegelmann, T.; Schrijver, C. J.; Malanushenko, A.; Sun, X.;
Régnier, S.
2015ApJ...811..107D Altcode: 2015arXiv150805455D
The nonlinear force-free field (NLFFF) model is often used to
describe the solar coronal magnetic field, however a series of
earlier studies revealed difficulties in the numerical solution of the
model in application to photospheric boundary data. We investigate
the sensitivity of the modeling to the spatial resolution of the
boundary data, by applying multiple codes that numerically solve the
NLFFF model to a sequence of vector magnetogram data at different
resolutions, prepared from a single Hinode/Solar Optical Telescope
Spectro-Polarimeter scan of NOAA Active Region 10978 on 2007 December
13. We analyze the resulting energies and relative magnetic helicities,
employ a Helmholtz decomposition to characterize divergence errors, and
quantify changes made by the codes to the vector magnetogram boundary
data in order to be compatible with the force-free model. This study
shows that NLFFF modeling results depend quantitatively on the spatial
resolution of the input boundary data, and that using more highly
resolved boundary data yields more self-consistent results. The
free energies of the resulting solutions generally trend higher
with increasing resolution, while relative magnetic helicity values
vary significantly between resolutions for all methods. All methods
require changing the horizontal components, and for some methods also
the vertical components, of the vector magnetogram boundary field in
excess of nominal uncertainties in the data. The solutions produced
by the various methods are significantly different at each resolution
level. We continue to recommend verifying agreement between the modeled
field lines and corresponding coronal loop images before any NLFFF
model is used in a scientific setting.
---------------------------------------------------------
Title: Evolving Models of Surface and Coronal Activity of Sun-Like
Stars
Authors: DeRosa, Marc; Cheung, Mark
2015IAUGA..2257506D Altcode:
Surface flux transport models have proven useful for modeling the
evolution of magnetic patterns on the solar photospheric surface on
timescales ranging from as short as a few days to as long as multiple
magnetic cycles. In the work presented here, we use surface flux
transport models to study variations in the magnetic activity of
Sun-like stars, and to explore the dependence of flux evolution on
the properties of flux emergence, large-scale flows, and dispersal
by convective turbulence. These time sequences of surface magnetic
evolution are then used to drive magnetofrictional models of stellar
coronal fields to study how coronal fields evolve. From such models,
we can begin to assess how the evolution of various stellar features,
such as interacting starspot groups, might affect the overlying
stellar coronae.
---------------------------------------------------------
Title: Characterizing the Properties of Coronal Magnetic Null Points
Authors: Barnes, Graham; DeRosa, Marc; Wagner, Eric
2015IAUGA..2258194B Altcode:
The topology of the coronal magnetic field plays a role in a wide range
of phenomena, from Coronal Mass Ejections (CMEs) through heating of
the corona. One fundamental topological feature is the null point,
where the magnetic field vanishes. These points are natural sites of
magnetic reconnection, and hence the release of energy stored in the
magnetic field. We present preliminary results of a study using data
from the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics
Observatory to characterize the properties and evolution of null points
in a Potential Field Source Surface model of the coronal field. The
main properties considered are the lifetime of the null points,
their distribution with height, and how they form and subsequently
vanish.This work is supported by NASA/LWS Grant NNX14AD45G, and by
NSF/SHINE grant 1357018.
---------------------------------------------------------
Title: Characterizing the Properties of Coronal Magnetic Null Points
Authors: Barnes, Graham; DeRosa, Marc; Wagner, Eric
2015shin.confE..79B Altcode:
The topology of the coronal magnetic field plays a role in a wide range
of phenomena, from Coronal Mass Ejections (CMEs) through heating of
the corona. One fundamental topological feature is the null point,
where the magnetic field vanishes. These points are natural sites of
magnetic reconnection, and hence the release of energy stored in the
magnetic field. We present preliminary results of a study using data
from the SOHO/Michelson Doppler Imager and SDO/Helioseismic and Magnetic
Imager to characterize the properties and evolution of null points
in a Potential Field Source Surface model of the coronal field. The
main properties considered are the lifetime of the null points, their
distribution with height, and how they form and subsequently vanish. In
addition, we look at how the distribution of null points varies with
solar cycle.
---------------------------------------------------------
Title: The Coronal Global Evolutionary Model: Using HMI Vector
Magnetogram and Doppler Data to Model the Buildup of Free Magnetic
Energy in the Solar Corona
Authors: Fisher, G. H.; Abbett, W. P.; Bercik, D. J.; Kazachenko,
M. D.; Lynch, B. J.; Welsch, B. T.; Hoeksema, J. T.; Hayashi, K.;
Liu, Y.; Norton, A. A.; Dalda, A. Sainz; Sun, X.; DeRosa, M. L.;
Cheung, M. C. M.
2015SpWea..13..369F Altcode: 2015arXiv150506018F
The most violent space weather events (eruptive solar flares and
coronal mass ejections) are driven by the release of free magnetic
energy stored in the solar corona. Energy can build up on timescales
of hours to days, and then may be suddenly released in the form of a
magnetic eruption, which then propagates through interplanetary space,
possibly impacting the Earth's space environment. Can we use the
observed evolution of the magnetic and velocity fields in the solar
photosphere to model the evolution of the overlying solar coronal
field, including the storage and release of magnetic energy in such
eruptions? The objective of CGEM, the Coronal Global Evolutionary Model,
funded by the NASA/NSF Space Weather Modeling program, is to develop
and evaluate such a model for the evolution of the coronal magnetic
field. The evolving coronal magnetic field can then be used as a
starting point for magnetohydrodynamic (MHD) models of the corona,
which can then be used to drive models of heliospheric evolution and
predictions of magnetic field and plasma density conditions at 1AU.
---------------------------------------------------------
Title: What Do EUV Dimmings Tell Us About CME Topology
Authors: Thompson, Barbara J.; DeRosa, Marc L.; Fisher, Richard R.;
Krista, Larisza D.; Kwon, Ryun Young; Mason, James P.; Mays, Mona L.;
Nitta, Nariaki V.; Webb, David F.; West, Matthew J.
2015TESS....121201T Altcode:
Large-scale coronal EUV dimmings develop on timescales of hours in
association with a flare or filament eruption, and are known to be
well correlated with coronal mass ejections (CMEs). However, it is not
clear why some CMEs have dimmings and some do not, nor is it clear how
these dimmings relate to CME topology. The inner coronal coverage of
SDO AIA and STEREO EUVI, combined with the extended field of view of
PROBA2's SWAP imager, allow us the opportunity to map the topology of
a dimming region in three dimensions into an erupting CME. Although
the location and extent of a dimming region appears to be the best
indicator of the inner "footprint" of a CME, the correlation is far
from perfect. However, dimmings can provide vital clues about the
development and 3D kinematics of CMEs. This is particularly important
as we are currently in an extended period where the STEREO coronagraph
images are not always available and are increasingly "mirroring" LASCO
images, and therefore the 3D properties of a CME will be difficult
to deduce. Thus, understanding the inner coronal manifestations of
a CME can provide clues to its structure and dynamics, even without
multi-viewpoint coronagraph observations. We present the results of
this combined analysis effort, along with a discussion of how dimmings
can be used to forecast CME trajectories.
---------------------------------------------------------
Title: Inferring the Structure of the Solar Corona and Inner
Heliosphere During the Maunder Minimum Using Global Thermodynamic
Magnetohydrodynamic Simulations
Authors: Riley, Pete; Lionello, Roberto; Linker, Jon A.; Cliver,
Ed; Balogh, Andre; Beer, Jürg; Charbonneau, Paul; Crooker, Nancy;
DeRosa, Marc; Lockwood, Mike; Owens, Matt; McCracken, Ken; Usoskin,
Ilya; Koutchmy, S.
2015ApJ...802..105R Altcode:
Observations of the Sun’s corona during the space era have led to
a picture of relatively constant, but cyclically varying solar output
and structure. Longer-term, more indirect measurements, such as from
<SUP>10</SUP>Be, coupled by other albeit less reliable contemporaneous
reports, however, suggest periods of significant departure from this
standard. The Maunder Minimum was one such epoch where: (1) sunspots
effectively disappeared for long intervals during a 70 yr period; (2)
eclipse observations suggested the distinct lack of a visible K-corona
but possible appearance of the F-corona; (3) reports of aurora were
notably reduced; and (4) cosmic ray intensities at Earth were inferred
to be substantially higher. Using a global thermodynamic MHD model,
we have constructed a range of possible coronal configurations for the
Maunder Minimum period and compared their predictions with these limited
observational constraints. We conclude that the most likely state of the
corona during—at least—the later portion of the Maunder Minimum was
not merely that of the 2008/2009 solar minimum, as has been suggested
recently, but rather a state devoid of any large-scale structure,
driven by a photospheric field composed of only ephemeral regions,
and likely substantially reduced in strength. Moreover, we suggest
that the Sun evolved from a 2008/2009-like configuration at the start
of the Maunder Minimum toward an ephemeral-only configuration by the
end of it, supporting a prediction that we may be on the cusp of a
new grand solar minimum.
---------------------------------------------------------
Title: Low-temperature Spectroscopy of the
<SUP>12</SUP>C<SUB>2</SUB>H<SUB>2</SUB> (υ<SUB>1</SUB> +
υ<SUB>3</SUB>) Band in a Helium Buffer Gas
Authors: Santamaria, L.; Di Sarno, V.; Ricciardi, I.; De Rosa, M.;
Mosca, S.; Santambrogio, G.; Maddaloni, P.; De Natale, P.
2015ApJ...801...50S Altcode: 2014arXiv1410.5310S
Buffer gas cooling with a <SUP>4</SUP>He gas is
used to perform laser-absorption spectroscopy of the
<SUP>12</SUP>C<SUB>2</SUB>H<SUB>2</SUB> (υ<SUB>1</SUB> +
υ<SUB>3</SUB>) band at cryogenic temperatures. Doppler thermometry
is first carried out to extract translational temperatures from
the recorded spectra. Then, rotational temperatures down to 20 K
are retrieved by fitting the Boltzmann distribution to the relative
intensities of several ro-vibrational lines. The potential of our
setup to tune the thermal equilibrium between translational and
rotational degrees of freedom is also demonstrated. This can be used
to reproduce in a controlled way the regime of non-local thermal
equilibrium typically encountered in the interstellar medium. The
underlying helium-acetylene collisional physics, relevant for modeling
planetary atmospheres, is also addressed. In particular, the diffusion
time of <SUP>12</SUP>C<SUB>2</SUB>H<SUB>2</SUB> in the buffer cell is
measured against the <SUP>4</SUP>He flux at two separate translational
temperatures; the observed behavior is then compared with that
predicted by a Monte Carlo simulation, thus providing an estimate for
the respective total elastic cross sections: σ<SUB>el</SUB>(100 K) =
(4 ± 1) × 10<SUP>-20</SUP> m<SUP>2</SUP> and σ<SUB>el</SUB>(25 K) =
(7 ± 2) × 10<SUP>-20</SUP> m<SUP>2</SUP>.
---------------------------------------------------------
Title: What Do EUV Dimmings Tell Us About CME Topology?
Authors: Thompson, B. J.; DeRosa, M. L.; Fisher, R. R.; Krista, L. D.;
Kwon, R. Y.; Mason, J. P.; Mays, M. L.; Nitta, N.; Savani, N.; West,
M. J.
2014AGUFMSH43B4202T Altcode:
Large-scale coronal EUV dimmings, developing on timescales of minutes
to hours in association with a flare or filament eruption, are known to
exhibit a high correlation with coronal mass ejections. However, it is
not clear why some CMEs have dimmings and some do not, nor is it clear
how these dimmings relate to CME topology. The inner coronal coverage
of SDO AIA and STEREO EUVI, combined with the extended field of view
of PROBA2's SWAP imager, allow us the opportunity to map the topology
of a dimming region in three dimensions into an erupting CME. Although
the location and extent of a dimming region appears to be the best
indicator of the inner "footprint" of a CME, the correlation is far
from perfect. However, dimmings can provide vital clues about the
development and 3D kinematics of a CME. This is particularly important
as we are entering an extended period of time where STEREO coronagraph
images will not always be available, and therefore the 3D properties of
a CME will be difficult to deduce. Therefore, understanding the inner
coronal manifestations of a CME can provide clues to its structure and
dynamics, even without multi-viewpoint coronagraph observations. We
present the results of this combined analysis effort, along with a
discussion of how dimmings can be used in forecasting CME directions.
---------------------------------------------------------
Title: Tracking Solar Active Region Outflow Plasma from Its Source
to the Near-Earth Environment
Authors: Culhane, J. L.; Brooks, D. H.; van Driel-Gesztelyi, L.;
Démoulin, P.; Baker, D.; DeRosa, M. L.; Mandrini, C. H.; Zhao, L.;
Zurbuchen, T. H.
2014SoPh..289.3799C Altcode: 2014SoPh..tmp...90C; 2014arXiv1405.2949C
Seeking to establish whether active-region upflow material contributes
to the slow solar wind, we examine in detail the plasma upflows from
Active Region (AR) 10978, which crossed the Sun's disc in the interval 8
to 16 December 2007 during Carrington rotation (CR) 2064. In previous
work, using data from the Hinode/EUV Imaging Spectrometer, upflow
velocity evolution was extensively studied as the region crossed the
disc, while a linear force-free-field magnetic extrapolation was used
to confirm aspects of the velocity evolution and to establish the
presence of quasi-separatrix layers at the upflow source areas. The
plasma properties, temperature, density, and first ionisation potential
bias [FIP-bias] were measured with the spectrometer during the disc
passage of the active region. Global potential-field source-surface
(PFSS) models showed that AR 10978 was completely covered by the
closed field of a helmet streamer that is part of the streamer
belt. Therefore it is not clear how any of the upflowing AR-associated
plasma could reach the source surface at 2.5 R<SUB>⊙</SUB> and
contribute to the slow solar wind. However, a detailed examination of
solar-wind in-situ data obtained by the Advanced Composition Explorer
(ACE) spacecraft at the L<SUB>1</SUB> point shows that increases in
O<SUP>7+</SUP>/O<SUP>6+</SUP>, C<SUP>6+</SUP>/C<SUP>5+</SUP>, and Fe/O -
a FIP-bias proxy - are present before the heliospheric current-sheet
crossing. These increases, along with an accompanying reduction in
proton velocity and an increase in density are characteristic of
both AR and slow-solar-wind plasma. Finally, we describe a two-step
reconnection process by which some of the upflowing plasma from the
AR might reach the heliosphere.
---------------------------------------------------------
Title: Characterizing the Properties of Coronal Magnetic Null Points
Authors: Barnes, Graham; Wagner, Eric; DeRosa, Marc
2014shin.confE..74B Altcode:
The topology of the coronal magnetic field plays a role in a wide range
of phenomena, from Coronal Mass Ejections to heating of the corona. One
fundamental topological feature is the null point, where the magnetic
field vanishes. These points are natural sites of magnetic reconnection,
and hence the release of energy stored in the magnetic field. We present
preliminary results of a study using data from the Helioseismic and
Magnetic Imager aboard NASA's Solar Dynamics Observatory to characterize
the properties and evolution of null points in a Potential Field Source
Surface model of the coronal field. The main properties considered
are the lifetime of the null points, their distribution with height,
and how they form and subsequently vanish.
---------------------------------------------------------
Title: Active Region Magnetic Field Modeling Guided by Coronal Loops
and Surface Fields
Authors: DeRosa, Marc L.; Malanushenko, Anna; Schrijver, Carolus J.;
Wheatland, Michael S
2014AAS...22432319D Altcode:
Dynamic events such as solar flares, filament eruptions, and mass
ejections are powered by the evolving coronal magnetic field. However,
the ways in which energy is stored in, and released from, the coronal
magnetic field are poorly understood, in large part because the field
configuration cannot be determined directly from observations and has
eluded the successful application of routine modeling based on surface
magnetograms. Recently, we have demonstrated that the Quasi-Grad-Rubin
(QGR) method for modeling the current-carrying field associated with
active regions shows promise. In Malanushenko et al. (2014, ApJ 783:102)
we have used the QGR method to construct the magnetic field at several
times during the evolution of AR11158 during February 2011. The QGR
method does not require vector magnetograms, and instead uses the
trajectories of observed coronal loops to constrain the locations
of electric currents within the modeling domain. In this study,
we continue to assess the utility of QGR by applying this method to
additional active regions from the current activity cycle, making use
of SDO/HMI line-of-sight magnetograms and imagery from the extreme
ultraviolet channels of SDO/AIA.
---------------------------------------------------------
Title: Using Coronal Loops to Reconstruct the Magnetic Field of an
Active Region before and after a Major Flare
Authors: Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland,
M. S.
2014ApJ...783..102M Altcode: 2013arXiv1312.5389M
The shapes of solar coronal loops are sensitive to the presence
of electrical currents that are the carriers of the non-potential
energy available for impulsive activity. We use this information in
a new method for modeling the coronal magnetic field of active region
(AR) 11158 as a nonlinear force-free field (NLFFF). The observations
used are coronal images around the time of major flare activity on
2011 February 15, together with the surface line-of-sight magnetic
field measurements. The data are from the Helioseismic and Magnetic
Imager and Atmospheric Imaging Assembly on board the Solar Dynamics
Observatory. The model fields are constrained to approximate the coronal
loop configurations as closely as possible, while also being subject
to the force-free constraints. The method does not use transverse
photospheric magnetic field components as input and is thereby
distinct from methods for modeling NLFFFs based on photospheric vector
magnetograms. We validate the method using observations of AR 11158
at a time well before major flaring and subsequently review the field
evolution just prior to and following an X2.2 flare and associated
eruption. The models indicate that the energy released during the
instability is about 1 × 10<SUP>32</SUP> erg, consistent with what
is needed to power such a large eruptive flare. Immediately prior to
the eruption, the model field contains a compact sigmoid bundle of
twisted flux that is not present in the post-eruption models, which
is consistent with the observations. The core of that model structure
is twisted by ≈0.9 full turns about its axis.
---------------------------------------------------------
Title: Solar Cycle Variations of the Radio Brightness of the Solar
Polar Regions as Observed by the Nobeyama Radioheliograph
Authors: Nitta, Nariaki V.; Sun, Xudong; Hoeksema, J. Todd; DeRosa,
Marc L.
2014ApJ...780L..23N Altcode:
We have analyzed daily microwave images of the Sun at 17 GHz obtained
with the Nobeyama Radioheliograph (NoRH) in order to study the solar
cycle variations of the enhanced brightness in the polar regions. Unlike
in previous works, the averaged brightness of the polar regions is
obtained from individual images rather than from synoptic maps. We
confirm that the brightness is anti-correlated with the solar cycle and
that it has generally declined since solar cycle 22. Including images
up to 2013 October, we find that the 17 GHz brightness temperature
of the south polar region has decreased noticeably since 2012. This
coincides with a significant decrease in the average magnetic field
strength around the south pole, signaling the arrival of solar maximum
conditions in the southern hemisphere more than a year after the
northern hemisphere. We do not attribute the enhanced brightness
of the polar regions at 17 GHz to the bright compact sources that
occasionally appear in synthesized NoRH images. This is because they
have no correspondence with small-scale bright regions in images
from the Atmospheric Imaging Assembly on board the Solar Dynamics
Observatory with a broad temperature coverage. Higher-quality radio
images are needed to understand the relationship between microwave
brightness and magnetic field strength in the polar regions.
---------------------------------------------------------
Title: Using coronal loops to model the coronal magnetic field before
and after major eruptive events
Authors: Malanushenko, Anna; Schrijver, Carolus; Wheatland, M. S.;
DeRosa, Marc
2014cosp...40E1960M Altcode:
Solar flares are believed to be a manifestation of major release of
magnetic energy stored in active region field. Modeling the coronal
magnetic field may enable us to evaluate the energy available for
release, as well as possible sites of the reconnection and other
relevant properties of the field. We use a new method to aid this
problem by including the observed structure of the field (manifested
in coronal loops) as additional constraints. We verify that the method
(previously shown to work on synthetic data in Malanushenko et. al.,
ApJ, 756, 153, 2012) is generally acceptable for the solar data, as
it gives self-consistent, slowly changing results for slowly evolving
structures. We further develop the potential of this method to access
changes in the coronal magnetic field triggered by major eruptive
events, and compare the results with observations.
---------------------------------------------------------
Title: Properties of Solar Flare Clustering
Authors: Title, Alan; DeRosa, Marc
2014cosp...40E3345T Altcode:
The continuous full disk observations provided by the Atmospheric
Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) give
an observer the impression that flare and filament eruptions are
related. However, both detailed analysis of a number of events as well
as a number of statistical studies have provided only rare examples of
clear causal behavior. But the mechanisms of flare triggering are not
well understood, so the lack of hard evidence is not surprising. Here
we have examined the waiting-time statistics of GOES X-ray flares of
magnitude C5 or greater during the last sunspot cycle with the aim of
assessing the degree to which flares are clustered in time. Clusters are
groups of flares in which all successive flares occur within a fixed
separation time - the linking window. While many of the flares in a
cluster may come from the same active region, the clusters that last
more than a disk passage must result from flares in multiple active
regions. The longest cluster of the last cycle lasted more than 42
days. None of the flares were separated by more than 36 hours. Since
that cluster lasted more than three disk passages, it could not have
been caused by a single region. We find that during the last maximum,
eight clusters contributed 44% of all flares. All of these clusters
spanned multiple disk passages, but occupied only 16.5% of the cycle
duration. Two of the clusters provided 34% of the flares. We suggest
that this behavior implies that a component of the observed coordinated
behavior has its origin in the solar dynamo.
---------------------------------------------------------
Title: The Perihelion Passage of Comet ISON as seen by SDO
Authors: Pesnell, W. D.; Schrijver, C. J.; Boerner, P.; DeRosa, M. L.;
Liu, W.; Thompson, B. J.
2013AGUFM.P24A..10P Altcode:
Comet ISON will fly through perihelion on November 28, 2013. It is one
of the largest sungrazing comets to be seen in the Space Age. The Solar
Dynamics Observatory (SDO) has seen two previous sungrazing comets in
the extreme ultraviolet channels of the Atmospheric Imaging Assembly
(AIA). Comet ISON will fly farther from the Sun (perihelion distance
of 2.7 Rsun compared to 1.15 for Comet Lovejoy), meaning it probes
a different part of the solar corona, but its larger size should
provide enough mass to illuminate the path of the nucleus. Based on
the latest ephemeris, SDO will be able to track Comet ISON through
the entire perihelion passage by a series of off-point maneuvers. We
will present the AIA data obtained from the Comet ISON perihelion,
discussing the differences between Comets ISON and Lovejoy. We will
then summarize what we have learned from the observations and offer
some thoughts on what sungrazing comets may reveal about comets,
the Sun, and their interaction.
---------------------------------------------------------
Title: Pathways of Large-scale Magnetic Couplings between Solar
Coronal Events
Authors: Schrijver, Carolus J.; Title, Alan M.; Yeates, Anthony R.;
DeRosa, Marc L.
2013ApJ...773...93S Altcode: 2013arXiv1305.0801S
The high-cadence, comprehensive view of the solar corona by SDO/AIA
shows many events that are widely separated in space while occurring
close together in time. In some cases, sets of coronal events are
evidently causally related, while in many other instances indirect
evidence can be found. We present case studies to highlight a variety
of coupling processes involved in coronal events. We find that physical
linkages between events do occur, but concur with earlier studies that
these couplings appear to be crucial to understanding the initiation
of major eruptive or explosive phenomena relatively infrequently. We
note that the post-eruption reconfiguration timescale of the large-scale
corona, estimated from the extreme-ultraviolet afterglow, is on average
longer than the mean time between coronal mass ejections (CMEs), so
that many CMEs originate from a corona that is still adjusting from a
previous event. We argue that the coronal field is intrinsically global:
current systems build up over days to months, the relaxation after
eruptions continues over many hours, and evolving connections easily
span much of a hemisphere. This needs to be reflected in our modeling
of the connections from the solar surface into the heliosphere to
properly model the solar wind, its perturbations, and the generation and
propagation of solar energetic particles. However, the large-scale field
cannot be constructed reliably by currently available observational
resources. We assess the potential of high-quality observations from
beyond Earth's perspective and advanced global modeling to understand
the couplings between coronal events in the context of CMEs and solar
energetic particle events. <P />.
---------------------------------------------------------
Title: On the role of asymmetries in the reversal of the solar
magnetic field
Authors: Brun, A. S.; Derosa, M. L.; Hoeksema, J. T.
2013IAUS..294...75B Altcode:
We study how the solar magnetic field evolves from antisymmetric
(dipolar) to symmetric (quadrupolar) state during the course of
its 11-yr cycle. We show that based on equatorial symmetries of the
induction equation, flux transport solar mean field dynamo models excite
mostly the antisymmetric (dipolar) family whereas a decomposition of the
solar magnetic field data reveals that both families should be excited
to similar amplitude levels. We propose an alternative solar dynamo
solution based on North-South asymmetry of the meridional circulation
to better reconcile models and observations.
---------------------------------------------------------
Title: The Coronal Global Evolutionary Model (CGEM)
Authors: Fisher, George H.; DeRosa, M. L.; Hoeksema, J. T.
2013SPD....4410102F Altcode:
The Coronal Global Evolutionary Model, or CGEM, is a collaborative
effort from the UC Berkeley Space Sciences Laboratory (SSL), Stanford
University, and Lockheed-Martin. In work that led up to the selection of
this project, the team demonstrated its capability to use sequences of
vector magnetograms and Dopplergrams from the Helioseismic and Magnetic
Imager (HMI) instrument aboard the SDO to drive a magnetofrictional
(MF) model of the coronal magnetic field in AR 11158, which produced an
X2.2 flare. We will implement this MF model in spherical coordinates
to enable real-time, long-term modeling of the non-potential coronal
magnetic field, both globally and for individual active region
(ARs). The model's Earth-facing hemisphere will be driven using
electric fields derived from the observed evolution of photospheric
line-of-sight magnetic fields and electric currents. Far-side data
inputs will be from an existing flux transport code, combined with
HMI far-side observations of new active regions, with empirical
parametrizations of orientation and flux. Because this model includes
large-scale coronal electric currents, it is a substantial improvement
over existing real-time global coronal models, which assume potential
fields. Data products available from the model will include: 1) the
evolving photospheric electric field, Poynting flux, and helicity
flux; 2) estimates of coronal free energy and non-potential geometry
and topology; 3) initial and time-dependent boundary conditions
for MHD modeling of active regions; and 4) time-dependent boundary
conditions and flux tube expansion factors for MHD and empirical
solar wind models. Unstable configurations found from MF models will
be dynamically evolved with local and global MHD codes. Modules used
to derive surface electric fields from magnetic evolution will be
incorporated into the SDO/HMI data pipeline, and data products will
be distributed through the Joint Science Operations Center (JSOC) and
directly to space weather forecasters and users. The electric field
and MF codes will be delivered to the Community Coordinated Modeling
Center (CCMC) for science analysis and use with other models. This
project is being jointly funded by NASA and NSF.
---------------------------------------------------------
Title: Some Difficulties in Determining Causality of Sympathetic
Solar Events
Authors: DeRosa, M. L.; Schrijver, C. J.; Title, A. M.; Yeates, A. R.
2013enss.confE..91D Altcode:
Much has been made regarding the occurrence of synchronous eruptive
events occurring in the solar corona. Determining the frequencies at
which they occur and understanding the causal linkages that may connect
such events (making them sympathetic in addition to synchronous) are an
area of active research. Causal linkages are observed to take the form
of (1) disturbances in magnetic fields that connect active regions,
(2) disturbances in the magnetic field configuration overlying active
regions, and/or (3) triggering by disturbances propagating from one
region to another. Here we display two types of synchronous events:
those where, using a combination of image sequences from SDO and STEREO
as well as coronal-field modeling, evidence for sympathy seems solid,
and those where evidence of sympathy is more ambiguous. We use these two
types of cases to illustrate some difficulties in establishing whether
synchronous events are in fact sympathetic. This has implications
for determining the frequency and importance of sympathetic events,
and thus for understanding of coronal field evolution and the origins
of space weather.
---------------------------------------------------------
Title: Collective Solar Behavior
Authors: Title, Alan; Schrijver, Karel; Derosa, MArc
2013enss.confE.120T Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamic Observatory
(SDO) together with the Helioseismic and Magnetic Imager (HMI) and the
Extreme Ultraviolet Variability Experiment (EVE) allow observations of
the entire Sun from 6000 K to 20,000,000 K with arcsecond resolution
and a 12 second cadence (AIA), obtain doppler and continuum images at
a 45 second cadence and Line of Sight and vector magnetograms (HMI)
every few minutes, and integrated solar spectra from 1 to 100 nm on a 2
second cadence (EVE) 24/7. Because of the enhanced thermal and temporal
coverage and the high dynamic range available with AIA, it has been
able to discovery associated behavior associated with extreme solar
events that are apparently driven by the rapid expansion of magnetic
structures. The extent of the events are recognized by using co-temporal
STEREO data. The rapidly expanding magnetic structures, speeds between
500 and 2000 km/s, can apparently trigger filament eruptions, CME's,
and other flares. These "triggered" events are sometimes larger that
the initial disturbance. The remote triggering makes flare prediction
based upon ONLY local energy build up models less valuable, but suggests
that with proper coverage prediction of solar events with potential
for Earth impact may be made more reliable. Movies of sample events
discovered in AIA together with STEREO data will be shown.
---------------------------------------------------------
Title: Photospheric Drivers of Coronal Evolution
Authors: Welsch, B. T.; Kazachenko, M.; Fisher, G. H.; Cheung,
M. C. M.; DeRosa, M. L.; CGEM Team
2013enss.confE.108W Altcode:
Flares and coronal mass ejections (CMEs) are driven by the release
of free magnetic energy stored in the coronal magnetic field. While
this energy is stored in the corona, photospheric driving must play
a central role in its injection, storage, and release, since magnetic
fields present in the corona originated within the solar interior, and
are anchored at the photosphere. Also, the corona's low diffusivity
and high Alfven speed (compared to that at the photosphere) imply
that the large-scale coronal field essentially maintains equilibrium
(outside of episodic flares and CMEs!), and therefore only evolves
due to forcing from photospheric evolution. But fundamental questions
about each stage of this "storage and release" paradigm remain open:
How does free magnetic energy build up in the corona? How is this energy
stored? And what triggers its release? The unprecedented combination of
high cadence, resolution, and duty cycle of the HMI vector magnetograph
enables modeling coronal magnetic evolution in response to photospheric
driving, a powerful approach to addressing these questions. I will
discuss our efforts to use HMI vector magneotgrams of AR 11158 to derive
time-dependent boundary conditions for a data-driven coronal magnetic
field model. These efforts will play a key role in the planned Coronal
Global Evolutionary Model (CGEM), a data-driven, time-dependent model of
the global coronal field. This work is supported by NASA's Living With
a Star program and NSF's Division of Atmospheric and Geospace Sciences.
---------------------------------------------------------
Title: Initiation of Coronal Mass Ejections: A Comparison of AR11158
with a Simulation of Flux Cancellation
Authors: Manchester, W. B.; Fang, F.; Burns, C.; Kosovichev, A. G.;
Sun, X.; DeRosa, M. L.; Cheung, C.
2012AGUFMSH53B..06M Altcode:
We present a detailed comparison of an MHD simulation of magnetic
flux emergence with observations of a large-scale active region. The
simulation (Fang et al. 2012) addresses the buoyant rise of a flux
rope through the convection zone into the corona, which spontaneously
reproduces several features found in AR11158. We focus our study on
the central part of AR11158 from which an energetic CME was observed
on 2011 February 15. We examine AIA loops, HMI vector magnetograms,
photospheric flow patterns, and convection zone flow patterns to fully
characterize the active region and relate its dynamics to basic features
found in the MHD simulation. Salient features are the convergence of
flux concentrations of opposite polarity and strong shear flows along
the polarity inversion line observed prior to and during the CME. We
will show that such shear flows are readily explained as a response to
the Lorentz force, and the convergence are associated with convective
downdrafts that form over the polarity inversion line. We also compare
the brightening of coronal loops observed with AIA to tether-cutting
reconnection observed in or simulation. Together, these mechanisms
explain the buildup, concentration and release of energy necessary
for eruptive events.
---------------------------------------------------------
Title: Tracking Solar Active Region Outflow Plasma from its Source
to the near-Earth Environment
Authors: Culhane, J. L.; Brooks, D.; Zurbuchen, T.; van
Driel-Gesztelyi, L.; Fazakerley, A. N.; DeRosa, M. L.
2012AGUFMSH53A2255C Altcode:
In a recent study of persistent active region outflow from AR 10978 in
the period 10 - 15, December, 2007, Brooks and Warren (2011), using the
Hinode EUV Imaging Spectrometer (EIS) instrument showed the presence
of a strong low-FIP element enhancement in the outflowing plasma that
was replicated three days later in the in-situ solar wind measurements
made by the ACE/SWICS instrument. In the present work, we examine the
outflowing plasma properties (Te, Ne, v, abundances) as a function
of time in greater detail as AR 10978 passes the Earth-Sun line. The
structure of the magnetic field above the two outflow regions - E and
W of the AR, is also examined. Following an assessment of the relevant
magnetic structures between Sun and Earth, the properties of the solar
wind plasma arriving at ACE approximately three days later are measured
and compared with those of the outflowing AR plasma. The relationship
of these measurements to the in-situ magnetic field observed by the
ACE magnetometer is also studied. Finally the role of persistent AR
outflows in contributing to the slow solar wind is assessed.
---------------------------------------------------------
Title: Evolution of the solar luminosity during solar cycle 23
Authors: Vieira, L. A.; Schrijver, C.; DeRosa, M. L.; Norton, A.;
Dudok de Wit, T.; Da Silva, L.; Vuets, A.
2012AGUFMSH12A..04V Altcode:
The effect of the solar activity on the solar luminosity, which is
the total electromagnetic solar output, is one of the fundamental
questions in solar physics. Changes of the solar luminosity can arise
from changes of the energy flux in the convection zone that can also
affects other solar parameters such as the surface temperature, the
apparent radius and shape, and the symmetry of the radiative field
itself. Additionally, understanding the latitudinal distribution of the
flux density is needed to compare the solar variability and its stellar
analogues. Nevertheless, our observations of the solar flux density
are limited to a region near the ecliptic plane, which have provided
just a raw estimate of the variability of the solar luminosity. Here
we present a reconstruction of the solar flux density and solar
luminosity for the solar cycle 23 and ascending phase of cycle 24. The
reconstruction is based on a combination of a state-of-art solar surface
magnetic flux transport model and a semi-empirical total and spectral
irradiance model. The flux transport model is based on assimilation
of MDI/SOHO and HMI/SDO magnetograms. The irradiance model's free
parameters are estimated by minimizing the difference between
the model's output and the PMOD Composite of TSI measurements. We
have obtained a good agreement between the model's output and the
measurements. The distribution of active regions leads to a clear
low latitude brightening during the solar maximum. This brightening
results from the balance of the contributions from bright (faculae and
network) and dark features (sunspots) located in the solar surface,
which peaks near the solar equator. As the effects of dark features
are limited to a narrower region, the variability of the flux density
at the poles is dominated by the evolution of faculae and network. The
preliminary results indicate that the heat flux blocked by sunspots
is lower than the flux leaked by bright features. Consequently, an
increase of the luminosity through the cycle is observed as previously
estimated based on near ecliptic measurements. This work also enables
an assessment of the properties of solar variability when viewed from
out of the ecliptic, i.e., such as we might be viewing other stars of
solar activity level. Finally, the limitations of the model and future
strategies to extend the reconstruction of the flux density and solar
luminosity will be presented.
---------------------------------------------------------
Title: Magnetic Topology of Active Regions and Coronal Holes:
Implications for Coronal Outflows and the Solar Wind
Authors: van Driel-Gesztelyi, L.; Culhane, J. L.; Baker, D.; Démoulin,
P.; Mandrini, C. H.; DeRosa, M. L.; Rouillard, A. P.; Opitz, A.;
Stenborg, G.; Vourlidas, A.; Brooks, D. H.
2012SoPh..281..237V Altcode: 2012SoPh..tmp..228V
During 2 - 18 January 2008 a pair of low-latitude opposite-polarity
coronal holes (CHs) were observed on the Sun with two active regions
(ARs) and the heliospheric plasma sheet located between them. We use
the Hinode/EUV Imaging Spectrometer (EIS) to locate AR-related outflows
and measure their velocities. Solar-Terrestrial Relations Observatory
(STEREO) imaging is also employed, as are the Advanced Composition
Explorer (ACE) in-situ observations, to assess the resulting impacts on
the solar wind (SW) properties. Magnetic-field extrapolations of the two
ARs confirm that AR plasma outflows observed with EIS are co-spatial
with quasi-separatrix layer locations, including the separatrix of a
null point. Global potential-field source-surface modeling indicates
that field lines in the vicinity of the null point extend up to the
source surface, enabling a part of the EIS plasma upflows access
to the SW. We find that similar upflow properties are also observed
within closed-field regions that do not reach the source surface. We
conclude that some of plasma upflows observed with EIS remain confined
along closed coronal loops, but that a fraction of the plasma may be
released into the slow SW. This suggests that ARs bordering coronal
holes can contribute to the slow SW. Analyzing the in-situ data, we
propose that the type of slow SW present depends on whether the AR is
fully or partially enclosed by an overlying streamer.
---------------------------------------------------------
Title: Modeling Magnetic Field Structure of a Solar Active Region
Corona Using Nonlinear Force-free Fields in Spherical Geometry
Authors: Guo, Y.; Ding, M. D.; Liu, Y.; Sun, X. D.; DeRosa, M. L.;
Wiegelmann, T.
2012ApJ...760...47G Altcode: 2012arXiv1210.0998G
We test a nonlinear force-free field (NLFFF) optimization code
in spherical geometry using an analytical solution from Low and
Lou. Several tests are run, ranging from idealized cases where exact
vector field data are provided on all boundaries, to cases where noisy
vector data are provided on only the lower boundary (approximating
the solar problem). Analytical tests also show that the NLFFF code
in the spherical geometry performs better than that in the Cartesian
one when the field of view of the bottom boundary is large, say, 20°
× 20°. Additionally, we apply the NLFFF model to an active region
observed by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory (SDO) both before and after an M8.7 flare. For
each observation time, we initialize the models using potential field
source surface (PFSS) extrapolations based on either a synoptic chart
or a flux-dispersal model, and compare the resulting NLFFF models. The
results show that NLFFF extrapolations using the flux-dispersal model
as the boundary condition have slightly lower, therefore better,
force-free, and divergence-free metrics, and contain larger free
magnetic energy. By comparing the extrapolated magnetic field lines with
the extreme ultraviolet (EUV) observations by the Atmospheric Imaging
Assembly on board SDO, we find that the NLFFF performs better than
the PFSS not only for the core field of the flare productive region,
but also for large EUV loops higher than 50 Mm.
---------------------------------------------------------
Title: What Are Special About Ground-Level Events?. Flares, CMEs,
Active Regions and Magnetic Field Connection
Authors: Nitta, N. V.; Liu, Y.; DeRosa, M. L.; Nightingale, R. W.
2012SSRv..171...61N Altcode: 2012arXiv1203.5777N; 2012SSRv..tmp...21N
Ground level events (GLEs) occupy the high-energy end of gradual solar
energetic particle (SEP) events. They are associated with coronal
mass ejections (CMEs) and solar flares, but we still do not clearly
understand the special conditions that produce these rare events. During
Solar Cycle 23, a total of 16 GLEs were registered, by ground-based
neutron monitors. We first ask if these GLEs are clearly distinguishable
from other SEP events observed from space. Setting aside possible
difficulties in identifying all GLEs consistently, we then try to find
observables which may unmistakably isolate these GLEs by studying the
basic properties of the associated eruptions and the active regions
(ARs) that produced them. It is found that neither the magnitudes of
the CMEs and flares nor the complexities of the ARs give sufficient
conditions for GLEs. It is possible to find CMEs, flares or ARs that
are not associated with GLEs but that have more extreme properties than
those associated with GLEs. We also try to evaluate the importance of
magnetic field connection of the AR with Earth on the detection of GLEs
and their onset times. Using the potential field source surface (PFSS)
model, a half of the GLEs are found to be well-connected. However,
the GLE onset time with respect to the onset of the associated flare
and CME does not strongly depend on how well-connected the AR is. The
GLE onset behavior may be largely determined by when and where the
CME-driven shock develops. We could not relate the shocks responsible
for the onsets of past GLEs with features in solar images, but the
combined data from the Solar TErrestrial RElations Observatory (STEREO)
and the Solar Dynamics Observatory (SDO) have the potential to change
this for GLEs that may occur in the rising phase of Solar Cycle 24.
---------------------------------------------------------
Title: A Method for Data-driven Simulations of Evolving Solar
Active Regions
Authors: Cheung, Mark C. M.; DeRosa, Marc L.
2012ApJ...757..147C Altcode: 2012arXiv1208.2954C
We present a method for performing data-driven simulations of
solar active region formation and evolution. The approach is based
on magnetofriction, which evolves the induction equation assuming
that the plasma velocity is proportional to the Lorentz force. The
simulations of active region (AR) coronal field are driven by temporal
sequences of photospheric magnetograms from the Helioseismic Magnetic
Imager instrument on board the Solar Dynamics Observatory (SDO). Under
certain conditions, the data-driven simulations produce flux ropes that
are ejected from the modeled AR due to loss of equilibrium. Following
the ejection of flux ropes, we find an enhancement of the photospheric
horizontal field near the polarity inversion line. We also present
a method for the synthesis of mock coronal images based on a proxy
emissivity calculated from the current density distribution in the
model. This method yields mock coronal images that are somewhat
reminiscent of images of ARs taken by instruments such as SDO's
Atmospheric Imaging Assembly at extreme ultraviolet wavelengths.
---------------------------------------------------------
Title: First Three-dimensional Reconstructions of Coronal Loops
with the STEREO A+B Spacecraft. IV. Magnetic Modeling with Twisted
Force-free Fields
Authors: Aschwanden, Markus J.; Wuelser, Jean-Pierre; Nitta, Nariaki
V.; Lemen, James R.; DeRosa, Marc L.; Malanushenko, Anna
2012ApJ...756..124A Altcode: 2012arXiv1207.2790A
The three-dimensional coordinates of stereoscopically triangulated
loops provide strong constraints for magnetic field models of active
regions in the solar corona. Here, we use STEREO/A and B data from some
500 stereoscopically triangulated loops observed in four active regions
(2007 April 30, May 9, May 19, and December 11), together with SOHO/MDI
line-of-sight magnetograms. We measure the average misalignment angle
between the stereoscopic loops and theoretical magnetic field models,
finding a mismatch of μ = 19°-46° for a potential field model,
which is reduced to μ = 14°-19° for a non-potential field model
parameterized by twist parameters. The residual error is commensurable
with stereoscopic measurement errors (μ<SUB>SE</SUB> ≈ 8°-12°). We
developed a potential field code that deconvolves a line-of-sight
magnetogram into three magnetic field components (B<SUB>x</SUB> ,
B<SUB>y</SUB> , B<SUB>z</SUB> ), as well as a non-potential field
forward-fitting code that determines the full length of twisted loops
(L ≈ 50-300 Mm), the number of twist turns (median N <SUB>twist</SUB>
= 0.06), the nonlinear force-free α-parameter (median α ≈ 4 ×
10<SUP>-11</SUP> cm<SUP>-1</SUP>), and the current density (median
j<SUB>z</SUB> ≈ 1500 Mx cm<SUP>-2</SUP> s<SUP>-1</SUP>). All twisted
loops are found to be far below the critical value for kink instability,
and Joule dissipation of their currents is found to be far below the
coronal heating requirement. The algorithm developed here, based on an
analytical solution of nonlinear force-free fields that is accurate to
second order (in the force-free parameter α), represents the first
code that enables fast forward fitting to photospheric magnetograms
and stereoscopically triangulated loops in the solar corona.
---------------------------------------------------------
Title: Guiding Nonlinear Force-free Modeling Using Coronal
Observations: First Results Using a Quasi-Grad-Rubin Scheme
Authors: Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland,
M. S.; Gilchrist, S. A.
2012ApJ...756..153M Altcode: 2012arXiv1202.5420M
At present, many models of the coronal magnetic field rely on
photospheric vector magnetograms, but these data have been shown
to be problematic as the sole boundary information for nonlinear
force-free field extrapolations. Magnetic fields in the corona
manifest themselves in high-energy images (X-rays and EUV) in the
shapes of coronal loops, providing an additional constraint that
is not at present used as constraints in the computational domain,
directly influencing the evolution of the model. This is in part due
to the mathematical complications of incorporating such input into
numerical models. Projection effects, confusion due to overlapping
loops (the coronal plasma is optically thin), and the limited number
of usable loops further complicate the use of information from
coronal images. We develop and test a new algorithm to use images of
coronal loops in the modeling of the solar coronal magnetic field. We
first fit projected field lines with those of constant-α force-free
fields to approximate the three-dimensional distribution of currents
in the corona along a sparse set of trajectories. We then apply a
Grad-Rubin-like iterative technique, which uses these trajectories as
volume constraints on the values of α, to obtain a volume-filling
nonlinear force-free model of the magnetic field, modifying a code
and method presented by Wheatland. We thoroughly test the technique
on known analytical and solar-like model magnetic fields previously
used for comparing different extrapolation techniques and compare the
results with those obtained by currently available methods relying
only on the photospheric data. We conclude that we have developed a
functioning method of modeling the coronal magnetic field by combining
the line-of-sight component of the photospheric magnetic field with
information from coronal images. Whereas we focus on the use of coronal
loop information in combination with line-of-sight magnetograms, the
method is readily extended to incorporate vector-magnetic data over
any part of the photospheric boundary.
---------------------------------------------------------
Title: Solar Magnetic Field Reversals and the Role of Dynamo Families
Authors: DeRosa, M. L.; Brun, A. S.; Hoeksema, J. T.
2012ApJ...757...96D Altcode: 2012arXiv1208.1768D
The variable magnetic field of the solar photosphere exhibits periodic
reversals as a result of dynamo activity occurring within the solar
interior. We decompose the surface field as observed by both the Wilcox
Solar Observatory and the Michelson Doppler Imager into its harmonic
constituents, and present the time evolution of the mode coefficients
for the past three sunspot cycles. The interplay between the various
modes is then interpreted from the perspective of general dynamo
theory, where the coupling between the primary and secondary families
of modes is found to correlate with large-scale polarity reversals
for many examples of cyclic dynamos. Mean-field dynamos based on the
solar parameter regime are then used to explore how such couplings may
result in the various long-term trends in the surface magnetic field
observed to occur in the solar case.
---------------------------------------------------------
Title: Effects of Granulation upon Larger-Scale Convection
Authors: Hurlburt, N. E.; DeRosa, M. L.; Augustson, K. C.; Toomre, J.
2012ASPC..454...13H Altcode: 2012arXiv1201.4809H
We examine the role of small-scale granulation in helping to drive
supergranulation and even larger scales of convection. The granulation
is modeled as localized cooling events introduced at the upper boundary
of a 3-D simulation of compressible convection in a rotating spherical
shell segment. With a sufficient number of stochastic cooling events
compared to uniform cooling, we find that supergranular scales are
realized, along with a differential rotation that becomes increasingly
solar-like.
---------------------------------------------------------
Title: Magnetic topology, coronal outflows, and the solar wind
Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Vourlidas,
Angelos; Demoulin, Pascal; Stenborg, Guillermo; Opitz, Andrea;
Rouillard, Alexis; Van Driel-Gesztelyi, Lidia; Baker, Deborah; DeRosa,
Marc; Brooks, David
2012cosp...39.1173M Altcode: 2012cosp.meet.1173M
During 2-18 January 2008 a pair of low-latitude opposite polarity
coronal holes were observed on the Sun flanked by two ARs with
the heliospheric plasma sheet between them. Hinode/EUV Imaging
Telescope (EIS) is used to locate AR-related outflows and measure their
velocities. The Advanced Composition Explorer (ACE) in-situ observations
are employed to assess the resulting impacts on the interplanetary solar
wind (SW). Magnetic field extrapolations of the two ARs confirm that AR
plasma outflows observed with EIS are co-spatial with quasi-separatrix
layer locations, including the separatrix of a null point. Global
potential field source-surface modeling indicates that field lines
in the vicinity of the null point extend up to the source-surface,
enabling a part of the EIS plasma upflows access to the SW. Similar
upflow magnitude is also observed within closed field regions. Though
part of the plasma upflows observed with EIS remain confined along
closed coronal loops, a subset of them are indeed able to make their
imprint in the slow SW, making ARs bordering coronal holes a slow
SW contributor.
---------------------------------------------------------
Title: Using Electric Fields to drive simulations of the solar
coronal magnetic field
Authors: Fisher, George H.; Cheung, Mark; DeRosa, Marc; Kazachenko,
Maria; Welsch, Brian; Hoeksema, Todd; Sun, Xudong
2012shin.confE..47F Altcode:
The availability of high-cadence vector magnetograms and Doppler flow
information measured from the HMI instrument on SDO make it possible to
determine the electric field at the solar photosphere. This electric
field, in turn, can be used to drive time-dependent simulations of
the magnetic field in the solar corona, employing the MHD equations,
or simpler time-dependent models such as the magneto-frictional (MF)
model. Here, we demonstrate these concepts by using electric fields
determined from HMI data to drive a time-dependent MF model of the
solar corona in the volume overlying the photosphere near NOAA AR 11158.
---------------------------------------------------------
Title: Topology of Coronal Fields from Evolving Magnetofrictional
Models
Authors: DeRosa, Marc L.; Cheung, M.
2012AAS...22041104D Altcode:
The evolving magnetofrictional (MF) scheme enables the construction
of time-dependent models of the active region coronal magnetic field
in response to photospheric driving. When advancing such models, only
the magnetic induction is solved, during which the velocity at each
point is assumed to be oriented parallel to the Lorentz force. This
leads to the field to evolve toward a force-free state. We present
results from an evolving MF model of NOAA AR11158 using driving
from time sequences of SDO/HMI data. Utilizing this simulation, we
<P />investigate changes in magnetic configurations and topology,
including the number of null points, evolution of quasi-separatrix
layers, and the time-history of total and free magnetic energies as
well as relative helicity. This work seeks to elucidate the relation(s)
between topological and energetic properties of the AR.
---------------------------------------------------------
Title: Estimate of Energy Release In a Major Flare Using Coronal
Loops Data
Authors: Malanushenko, Anna; Schrijver, C. J.; DeRosa, M. L.
2012AAS...22052115M Altcode:
Coronal loops provide with valuable source of information about coronal
magnetic field. In particular, they allow one to observe reconfiguration
of the coronal magnetic field during eruptive episodes. The changes
in the coronal field, as observed in X-rays and extreme ultraviolet,
are often dramatic in even minor eruptions. Therefore, models of
magnetic field which take coronal loops into account might provide
for new insight at changes of the field during eruptions. We use
coronal loops data (gathered from SDO/AIA images) along with the
line-of-sight magnetograms (by SDO/HMI) to model magnetic field in
AR 11158 before and after the so-called Valentine's Flare, an X-class
flare in Feb 15, 2011. This is done using the recently developed Quasi
Grad-Rubin algorithm (QGR), which allows a reconstruction of non-linear
force-free field based on information about electric currents along
a set of arbitrary tracks in the computational domain. Tests of QGR
on solar-like fields demonstrate its ability to recover over 50% of
the free energy, as well as the large-scale structure of currents and
overall shape of field lines. We analyze model magnetic fields of AR
11158 before and after the flare, demonstrate their resemblance with
the observed structure of coronal loops and analyze the changes in
the structure of currents caused by the flare, and compare our results
with existing studies of the same event.
---------------------------------------------------------
Title: Force-Free Magneto-Stereoscopy of Coronal Loops
Authors: Aschwanden, Markus J.; Malanushenko, A.; Wuelser, J.; Nitta,
N.; Lemen, J. R.; DeRosa, M.
2012AAS...22041103A Altcode:
We derive an analytical approximation of nonlinear force-free
magnetic field solutions (NLFFF) that can efficiently be used for
fast forward-fitting to solar magnetic data, constrained either by
observed line-of-sight magnetograms and stereoscopically triangulated
coronal loops, or by 3D vector-magnetograph data. We test the code by
forward-fitting to simulated data, to force-free solutions derived by
Low and Lou (1990), and to active regions observed with STEREO/EUVI and
SOHO/MDI. The forward-fitting tests demonstrate: (i) a satisfactory
convergence behavior (with typical misalignment angles of 1-10 deg),
(ii) a high fidelity of retrieved force-free alpha-parameters, and
(iii) relatively fast computation times (from seconds to minutes). The
novel feature of this NLFFF code is the derivation of a quasi-forcefree
field based on coronal constraints, which bypasses the non-forcefree
photosphere of standard magnetograms. Applications range from magnetic
modeling of loops to the determnination of electric currents, twist,
helicity, and free (non-potential) energy in active regions.
---------------------------------------------------------
Title: A First Look at Magnetic Field Data Products from SDO/HMI
Authors: Liu, Y.; Scherrer, P. H.; Hoeksema, J. T.; Schou, J.; Bai,
T.; Beck, J. G.; Bobra, M.; Bogart, R. S.; Bush, R. I.; Couvidat,
S.; Hayashi, K.; Kosovichev, A. G.; Larson, T. P.; Rabello-Soares,
C.; Sun, X.; Wachter, R.; Zhao, J.; Zhao, X. P.; Duvall, T. L., Jr.;
DeRosa, M. L.; Schrijver, C. J.; Title, A. M.; Centeno, R.; Tomczyk,
S.; Borrero, J. M.; Norton, A. A.; Barnes, G.; Crouch, A. D.; Leka,
K. D.; Abbett, W. P.; Fisher, G. H.; Welsch, B. T.; Muglach, K.;
Schuck, P. W.; Wiegelmann, T.; Turmon, M.; Linker, J. A.; Mikić,
Z.; Riley, P.; Wu, S. T.
2012ASPC..455..337L Altcode:
The Helioseismic and Magnetic Imager (HMI; Scherrer & Schou 2011)
is one of the three instruments aboard the Solar Dynamics Observatory
(SDO) that was launched on February 11, 2010 from Cape Canaveral,
Florida. The instrument began to acquire science data on March 24. The
regular operations started on May 1. HMI measures the Doppler velocity
and line-of-sight magnetic field in the photosphere at a cadence of
45 seconds, and the vector magnetic field at a 135-second cadence,
with a 4096× 4096 pixels full disk coverage. The vector magnetic
field data is usually averaged over 720 seconds to suppress the p-modes
and increase the signal-to-noise ratio. The spatial sampling is about
0".5 per pixel. HMI observes the Fe i 6173 Å absorption line, which
has a Landé factor of 2.5. These data are further used to produce
higher level data products through the pipeline at the HMI-AIA Joint
Science Operations Center (JSOC) - Science Data Processing (Scherrer et
al. 2011) at Stanford University. In this paper, we briefly describe the
data products, and demonstrate the performance of the HMI instrument. We
conclude that the HMI is working extremely well.
---------------------------------------------------------
Title: Data-Driven Modeling of the Evolution of Active Regions and
Coronal Holes
Authors: Cheung, M. C. M.; DeRosa, M. L.
2012decs.confE..83C Altcode:
We present results from numerical simulations of the evolution of
solar Active Regions (ARs) and Coronal Holes (CHs). The simulations
use the magnetofrictional method, which solves the induction equation
to drive magnetic configurations toward force-free states in response
to photospheric changes. The method is applied to modeling energy
build-up in ARs and morphological changes in CHs. Comparisons with
AIA data will be presented.
---------------------------------------------------------
Title: Non-Linear Force-Free Modeling of Solar Corona With The Aid
of Coronal Loops
Authors: Malanushenko, A.; DeRosa, M.; Schrijver, C.; Wheatland,
M. S.; Gilchrist, S.
2012decs.confE.113M Altcode:
Accurate models of the coronal magnetic field are vital for
understanding and predicting solar activity and are therefore of the
greatest interest for solar physics. As no reliable measurements of the
coronal magnetic field exists at present, the problem of constructing
field models is typically viewed as a boundary value problem. The
construction of realistic field models requires knowledge of the full
vector of magnetic field at the boundaries of the model domain; vector
magnetograms are, however, measured in the non force-free photosphere
and their horizontal components are subject to large uncertainties. Even
if an uncertainty-free vector magnetogram at the top layer of the
chromosphere was known, the problem remains an extremely challenging
non-linear problem. There are various methods for pre-processing
vector magnetograms and using them to construct models of the coronal
field. The success of these models is often judged based on how close
its field lines correspond to the observed coronal loops, which are
believed to follow lines of the coronal magnetic field. At present,
the correspondence between coronal loops and magnetic field lines
of many models based on the vector magnetograms is far from perfect
(DeRosa et. al., 2009). The estimates of free energy in the field as
well as distribution of the magnetic currents through the volume could
be dramatically different for different models used (Schrijver et. al.,
2008). This testifies to the need of a completely new approach to this
problem. We present such an approach and demonstrate its results based
on AIA and HMI data. We have developed a way to use coronal loops as a
constraint for magnetic modelling; the field is therefore constructed to
match coronal loops. We found that when tested on known magnetic fields
the new method is able to reproduce overall shape of the field lines,
large-scale spatial distribution of the electric currents and measure
up to 60% of the free energy stored in the field. This was achieved
with as little as line-of-sight magnetogram and less than hundred of
synthetic "loops", that is, lines of magnetic fields projected onto
a plane of the sky. We found that line-of-sight HMI magnetograms and
spatial resolution of the AIA instrument combined with the amount of
filters available are more than sufficient for obtaining such data. We
briefly describe this new method and demonstrate reconstructions of the
coronal magnetic field obtained using AIA and HMI data. We evaluate how
well it reproduces coronal features and how much energy and helicity
estimates fluctuate with time for a stable non-flaring active region,
thus establishing the reliability of the new method.
---------------------------------------------------------
Title: The impact of the chromosphere on magnetic fields: field
extrapolations
Authors: DeRosa, Marc L.
2012decs.confE..88D Altcode:
Because knowledge of the coronal magnetic field is the key to gaining an
understanding of the dynamics of the coronal plasma, efforts to measure
or infer coronal magnetic fields have received much attention. In
particular, many techniques for extrapolating the coronal magnetic
field from photospheric boundary data have been developed, especially
as magnetic field data at increasingly higher resolution in space and
time as well as vector magnetogram inversions have become more readily
available. However, it has become apparent that some extrapolation
methods encounter difficulties, as the resulting extrapolations often
do not provide reliable estimates of important coronal properties
such as free energy and relative helicity. In this talk, we review
some of the various difficulties associated with magnetic field
extrapolations based on photospheric magnetograms, and discuss likely
causes and solutions. We will particularly elucidate the impact of the
chromospheric layer on such extrapolations, which is likely impacting
the reliability of the extrapolation process as it lies between the
region sampled by the boundary data [the photosphere] and the region
of interest [the corona].
---------------------------------------------------------
Title: Data-driven Simulations of Evolving Active Regions
Authors: Cheung, M.; DeRosa, M. L.
2011AGUFMSH33C..04C Altcode:
We present results from numerical simulations of coronal field evolution
in response to photospheric driving. In the simulations, the coronal
field evolves according to magnetofriction, which ensures that the
model field evolves toward a non-linear force-free state. Unlike
static field extrapolation methods, this approach takes into account
the history of the photospheric field evolution. This allows for the
formation of flux ropes as well as current sheets between magnetic
domains of connectivity. Using time sequences of HMI magnetograms
as the bottom boundary condition, we apply this method to model the
emergence and evolution of various active regions. Comparisons of the
models with AIA observations and with HMI vector magnetogram inversions
will be discussed.
---------------------------------------------------------
Title: Spectropolarimetric Comparison Between SDO/HMI and
Hinode-SOT/SP Through THEMIS/MTR
Authors: Sainz Dalda, A.; Lopez Ariste, A.; Gelly, B.; Tarbell, T. D.;
Centeno, R.; DeRosa, M. L.; Hoeksema, J. T.
2011AGUFMSH31A1986S Altcode:
In the golden age of solar spacecraft observatories, the use of similar
instruments observing same targets offers us the possibility to get
more accurate information of the physical processes taking place on
them. We present a comparison between the vector magnetic field and
thermodynamic quantities obtained by three different spectropolarimetric
instruments. We have used the simultaneous multi-wavelength capabilities
of THEMIS/MTR as bridge between the observations at Fe I 6173 Å
provided by SDO/HMI and at Fe I 6301 & 6302 Å by Hinode-SOT/SP
observations. The official inversion codes for these instruments (PCA
based-on, VFISV and MERLIN respectively) have been used with the data
properly arranged for them. Therefore, we compare the final products
usually offered to the community, i.e. after the inversion, using
different codes and these different wavelengths. The cross-calibration
of these products shall allow us to go forward from one instrument
result to other one in an easy, convenient way.
---------------------------------------------------------
Title: Non-Linear Force-Free Modeling With The Aid of Coronal
Observations
Authors: Malanushenko, A. V.; DeRosa, M. L.; Schrijver, C. J.;
Gilchrist, S. A.; Wheatland, M. S.
2011AGUFMSH43B1956M Altcode:
Currently many models of coronal magnetic field rely on vector
magnetograms and other kinds of information drawn from the
photosphere. Magnetic fields in the corona, however, manifest themselves
in the shapes of coronal loops, providing a constraint that at the
present stage receives little use due to mathematical complications of
incorporating such input into the numeric models. Projection effects
and the limited number of usable loops further complicate their
use. We present a possible way to account for coronal loops in the
models of magnetic field. We first fit the observed loops with lines
of constant-alpha fields and thus approximate three-dimensional
distribution of currents in the corona along a sparse set of
trajectories. We then apply a Grad-Rubin-like averaging technique
to obtain a volume-filling non-linear force-free model of magnetic
field, modified from the method presented in Wheatland & Regnier
(2009). We present thorough tests of this technique on several known
magnetic fields that were previously used for comparing different
extrapolation techniques (Schrijver et. al., 2006; Metcalf et. al.,
2008; Schrijver et. al., 2008; DeRosa et. al., 2009), as well as on
solar data and compare the results with those obtained by the currently
developed methods that rely completely on the photospheric data.
---------------------------------------------------------
Title: Magnetic Field Modeling with Stereoscopy and Magnetograms
Authors: Aschwanden, Wuelser; Nitta, Schrijver; DeRosa, Malanushenko
2011sdmi.confE..81A Altcode:
We developed a new code to reconstruct the 3D magnetic field of solar
active regions using stereoscopically triangulated loops with STEREO/A+B
and magnetogram data from MDI or HMI. We are using potential field
models as well as non-potential field models (nonlinear quasi-force-free
fields) that can be quickly forward-fitted to observations using
parameterizations of analytical approximations of uniformly twisted
flux tubes. This method improves the misalignment angles between
theoretical models and observed magnetic fields down to 5 degrees.
---------------------------------------------------------
Title: Dipolar and Quadrupolar Magnetic Field Evolution over Solar
Cycles 21, 22, and 23
Authors: DeRosa, M. L.; Brun, A. S.; Hoeksema, J. T.
2011IAUS..271...94D Altcode:
Time series of photospheric magnetic field maps from two observatories,
along with data from an evolving surface-flux transport model,
are decomposed into their constituent spherical harmonic modes. The
evolution of these spherical harmonic spectra reflect the modulation
of bipole emergence rates through the solar activity cycle, and the
subsequent dispersal, shear, and advection of magnetic flux patterns
across the solar photosphere. In this article, we discuss the evolution
of the dipolar and quadrupolar modes throughout the past three solar
cycles (Cycles 21-23), as well as their relation to the reversal of
the polar dipole during each solar maximum, and by extension to aspects
of the operation of the global solar dynamo.
---------------------------------------------------------
Title: Topology of Coronal Fields from Potential Field Models
Authors: DeRosa, Marc L.; Schrijver, C. J.; Barnes, G.
2011SPD....42.1810D Altcode: 2011BAAS..43S.1810D
The topology of the solar coronal magnetic field has been the subject of
much recent interest, due to its apparent importance in determining (for
example) the sources of the solar wind, the evolution of coronal hole
boundaries, and whether the configurations of coronae overlying active
regions are unstable and thus possibly eruption-prone. We identify
the topological skeleton (null points, spline lines, separators, and
separatrix surfaces) for a selection of dates of interest from the
database of potential-field source-surface models available through
the “PFSS” SolarSoft package. Several features of interest have been
identified by recent studies (e.g., Antiochos et al. 2007, Parnell et
al. 2010, Titov et al. 2011), including exceedingly narrow channels of
open field or separators associated with inferred reconnection sites. We
find that these features of interest occur frequently in the topologies
of even potential-field models of the magnetic corona. The actual solar
corona is of course likely to involve even more complex topologies,
especially as its dynamics and evolution are taken into account.
---------------------------------------------------------
Title: Simulating Coronal Emission in Six AIA Channels Using
Quasi-Static Atmosphere Models and Non-Linear Magnetic Field Models
Authors: Malanushenko, Anna; Schrijver, C.; DeRosa, M.; Aschwanden,
M.; Wheatland, M. S.; van Ballegooijen, A. A.
2011SPD....42.2116M Altcode: 2011BAAS..43S.2116M
We present the results of simulations of the EUV coronal emission in
AIA channels. We use a non-linear force-free model of magnetic field
constructed in such a way that its field lines resemble the observed
coronal loops in EUV. We then solve one-dimensional quasi-steady
atmosphere model along the magnetic field lines (Schrijver &
Ballegooijen, 2005). Using coronal abundances from CHIANTI and AIA
response functions we then simulate the emission that would be observed
in AIA EUV channels. The resulting intensities are compared against the
real observations in a manner similar to that in Aschwanden et. al.,
2011. The study is similar to those by Lindquist et. al., 2008, with a
few important differences. We use a model of the coronal magnetic field
that resembles the topology observed in EUV, we study EUV emission of
cool loops (rather than SXR) and we make use of high resolution and
cadence AIA and HMI data.
---------------------------------------------------------
Title: Data-Driven Simulations of Coronal Magnetic Fields: A First
Attempt with SDO Data
Authors: Cheung, C.; Derosa, M. L.
2010AGUFMSH14A..04C Altcode:
We present results from numerical simulations of coronal field evolution
in response to photospheric driving. In the simulations, the coronal
field evolves according to magnetofriction, which ensures that the model
field evolves toward a non-linear force-free state. Unlike static field
extrapolation methods, this approach takes into account the history
of the photospheric field evolution. This allows for the formation
of flux ropes as well as current sheets between magnetic domains of
connectivity. Using time sequences of HMI magnetograms as the bottom
boundary condition, we apply this method to model the emergence and
evolution of recent active regions. For the case of AR 11066, flux
cancellation between opposite polarities within the AR leads to the
formation of a flux rope, which subsequently lifts off. Comparisons
of the models with AIA observations will be presented.
---------------------------------------------------------
Title: Uncovering Mechanisms of Coronal Magnetism via Advanced 3D
Modeling of Flares and Active Regions
Authors: Fleishman, Gregory; Gary, Dale; Nita, Gelu; Alexander,
David; Aschwanden, Markus; Bastian, Tim; Hudson, Hugh; Hurford,
Gordon; Kontar, Eduard; Longcope, Dana; Mikic, Zoran; DeRosa, Marc;
Ryan, James; White, Stephen
2010arXiv1011.2800F Altcode:
The coming decade will see the routine use of solar data of
unprecedented spatial and spectral resolution, time cadence, and
completeness. To capitalize on the new (or soon to be available)
facilities such as SDO, ATST and FASR, and the challenges they present
in the visualization and synthesis of multi-wavelength datasets,
we propose that realistic, sophisticated, 3D active region and flare
modeling is timely and critical, and will be a forefront of coronal
studies over the coming decade. To make such modeling a reality, a
broad, concerted effort is needed to capture the wealth of information
resulting from the data, develop a synergistic modeling effort, and
generate the necessary visualization, interpretation and model-data
comparison tools to accurately extract the key physics.
---------------------------------------------------------
Title: Magnetic Field Topology and the Thermal Structure of the
Corona over Solar Active Regions
Authors: Schrijver, Carolus J.; DeRosa, Marc L.; Title, Alan M.
2010ApJ...719.1083S Altcode:
Solar extreme ultraviolet (EUV) images of quiescent active-region
coronae are characterized by ensembles of bright 1-2 MK loops that fan
out from select locations. We investigate the conditions associated
with the formation of these persistent, relatively cool, loop fans
within and surrounding the otherwise 3-5 MK coronal environment by
combining EUV observations of active regions made with TRACE with
global source-surface potential-field models based on the full-sphere
photospheric field from the assimilation of magnetograms that are
obtained by the Michelson Doppler Imager (MDI) on SOHO. We find that in
the selected active regions with largely potential-field configurations
these fans are associated with (quasi-)separatrix layers (QSLs) within
the strong-field regions of magnetic plage. Based on the empirical
evidence, we argue that persistent active-region cool-loop fans are
primarily related to the pronounced change in connectivity across a QSL
to widely separated clusters of magnetic flux, and confirm earlier work
that suggested that neither a change in loop length nor in base field
strengths across such topological features are of prime importance to
the formation of the cool-loop fans. We discuss the hypothesis that
a change in the distribution of coronal heating with height may be
involved in the phenomenon of relatively cool coronal loop fans in
quiescent active regions.
---------------------------------------------------------
Title: A Spherical Harmonic Analysis of the Evolution of the
Photospheric Magnetic Field, and Consequences for the Solar Dynamo
Authors: DeRosa, Marc L.; Hoeksema, J. T.; Brun, A. S.
2010AAS...21631701D Altcode: 2010BAAS...41..898D
Time series of synoptic maps from several observatories, along with data
from an evolving surface-flux transport model, are analyzed in terms
of their spherical harmonic decomposition. The characteristics of these
spherical harmonic spectra, such as the relative amplitudes of various
harmonic modes, at different phases of the solar cycle are shown. We
illustrate how the rise and decline of the flux emergence rates, and
the associated reversal of the polar dipole, throughout a sunspot
cycle are reflected in the evolution of the various harmonic mode
coefficients. We further discuss the interplay between the low-degree
modes, in particular the dipole and quadrupole, and how such dynamics
may trigger the reversal of the polar dipole during solar maximum.
---------------------------------------------------------
Title: Erratum: "The Dependence of Ephemeral Region Emergence on
Local Flux Imbalance" <A href="/abs/2008ApJ...678..541H">(2008, ApJ,
678, 541)</A>
Authors: Hagenaar, Hermance J.; DeRosa, Marc L.; Schrijver, Carolus J.
2010ApJ...715..696H Altcode:
We have discovered an error in the labeling of Figure 5. The importance
of the figure is to indicate the dependence of flux emergence on local
flux (im-) balance. However, the scales of the figures were incorrect,
causing a discrepancy between Table 2 and Figure 5(a). The corrected
Figure 5 appears below. The change does not affect the conclusion.
---------------------------------------------------------
Title: Magnetic Field Topology and the Thermal Structure of the
Corona over Solar Active Regions
Authors: Schrijver, Carolus J.; DeRosa, M. L.; Title, A. M.
2010AAS...21631201S Altcode:
Solar extreme-ultraviolet images of active-region coronae are
characterized by ensembles of bright 1-2 MK loops that fan out from
select locations. We investigate the conditions associated with the
formation of these relatively cool loop fans within the otherwise
3-5 MK coronal environment by combining EUV observations of active
regions made with the Transition Region and Coronal Explorer (TRACE)
with global source-surface potential-field models based on the
full-sphere photospheric field from the assimilation of magnetograms
that are obtained by MDI on SOHO. We find that in the selected active
regions with largely potential field configurations these fans are
associated with (quasi-)separatrices within the strong-field regions
of magnetic plage and vice versa. We argue that the divergence of the
field lines across a (quasi-)separatrix may cause heating to happen
relatively low in the corona, resulting in a lower loop temperature
and flatter thermal profile of relatively dense (and thus EUV-bright)
loops that are surrounded by warmer, thermally more stratified loops
in field that does not straddle such topological divides.
---------------------------------------------------------
Title: Modeling the Near-Surface Shear Layer Through Coupled
Simulations of Surface and Deep Convection
Authors: Augustson, Kyle; Hurlburt, N.; DeRosa, M.; Toomre, J.
2010AAS...21640008A Altcode: 2010BAAS...41..855A
We examine the role of small-scale granulation in helping to drive
supergranulation and even larger scales of convection. The granulation
is modeled as localized plumes with statistics taken from surface
convection simulations introduced at the upper boundary of a 3-D
simulation of compressible convection in a rotating spherical shell
segment. With a sufficient number of stochastic plume events compared
to a uniform cooling, we find that supergranular scales are realized,
along with a differential rotation that becomes increasingly solar-like.
---------------------------------------------------------
Title: Direct Imaging of an Emerging Flux Rope and a Resulting
Chromospheric Jet Observed by Hinode
Authors: Liu, Wei; Berger, T.; Title, A. M.; Tarbell, T. D.; DeRosa, M.
2010AAS...21640307L Altcode: 2010BAAS...41R.878L
Magnetic flux emergence has been traditionally observed on the disk by
identifying changes in magnetograms. Observations near the limb offer
an alternative perspective and allow direct imaging of emerging flux
ropes. We present Hinode/SOT Ca II H observations of such an event in
an equatorial coronal hole on 2007 February 9. The precursor of the
event was a bundle of fine material threads that extended at an oblique
angle above the chromosphere and appeared to rotate about a common
axis. This bundle first slowly and then rapidly swung up, accompanied
by a loop that appeared at the base of the bundle and expanded at
comparable rates. During the first (slow rise) stage, the apex of the
loop ascended at 16 km/s, a velocity similar to that of H-alpha arch
filaments (e.g., Chou & Zirin) and of emerging flux ropes expanding
into the corona as found in MHD simulations (e.g., Fan & Gibson;
Martinez-Sykora). The second stage started at the onset of a GOES A5
flare and the loop expansion accelerated, reaching a velocity of 130
km/s when the loop appeared to rupture near the peak of the flare. The
material bundle then swung back in a whiplike manner and developed into
a collimated jet, exhibiting oscillatory transverse motions across its
axis, as expected from unwinding twists. Some jet material fell back
along smooth streamlines, which bypass an unseen dome and presumably
a null point in the low corona, depicting an inverted-Y shape. Some
of these observations resemble the model (e.g., Uchida & Shibata)
of the emergence of a twisted flux rope into an open field region that
leads to reconnection and formation of a jet. Some observations are,
however, not predicted in previous models and we will discuss their
implications.
---------------------------------------------------------
Title: Seismic Constraints on Interior Solar Convection
Authors: Hanasoge, Shravan M.; Duvall, Thomas L., Jr.; DeRosa, Marc L.
2010ApJ...712L..98H Altcode: 2010arXiv1001.4508H
We constrain the velocity spectral distribution of global-scale solar
convective cells at depth using techniques of local helioseismology. We
calibrate the sensitivity of helioseismic waves to large-scale
convective cells in the interior by analyzing simulations of waves
propagating through a velocity snapshot of global solar convection
via methods of time-distance helioseismology. Applying identical
analysis techniques to observations of the Sun, we are able to bound
from above the magnitudes of solar convective cells as a function of
spatial convective scale. We find that convection at a depth of r/R
<SUB>sun</SUB> = 0.95 with spatial extent ell < 20, where ell is the
spherical harmonic degree, comprises weak flow systems, on the order
of 15 m s<SUP>-1</SUP> or less. Convective features deeper than r/R
<SUB>sun</SUB> = 0.95 are more difficult to image due to the rapidly
decreasing sensitivity of helioseismic waves.
---------------------------------------------------------
Title: Non-force-free extrapolation of solar coronal magnetic field
using vector magnetograms
Authors: Hu, Qiang; Dasgupta, B.; Derosa, M. L.; Büchner, J.; Gary,
G. A.
2010JASTP..72..219H Altcode:
We report our recent improvement in non-force-free extrapolation
of coronal magnetic field, using vector magnetograms. Based on the
principle of minimum (energy) dissipation rate (MDR), a generally
non-force-free magnetic field solution is expressed as the superposition
of one potential field and two (constant-[alpha]) linear force-free
fields, with distinct [alpha] parameters. With a known potential field,
the system is reduced to a second-order one that can be solved using
one single-layer vector magnetogram. We devise an iteration procedure
to determine the potential field, by achieving satisfactory agreement
between the MDR-model computed and measured transverse magnetic
field vectors on the bottom boundary. We illustrate this approach by
applying it to real magnetograph measurement of solar active region
AR 10953. We show that the results are satisfactory as judged from
the quantitative magnetic field measurement, and the behavior of the
derived Lorentz force.
---------------------------------------------------------
Title: Comparison of STEREO/EUVI Loops with Potential Magnetic
Field Models
Authors: Sandman, A. W.; Aschwanden, M. J.; DeRosa, M. L.; Wülser,
J. P.; Alexander, D.
2009SoPh..259....1S Altcode:
The Solar Terrestrial Relations Observatory (STEREO) provides the
first opportunity to triangulate the three-dimensional coordinates of
active region loops simultaneously from two different vantage points in
space. Three-dimensional coordinates of the coronal magnetic field have
been calculated with theoretical magnetic field models for decades,
but it is only with the recent availability of STEREO data that a
rigorous, quantitative comparison between observed loop geometries and
theoretical magnetic field models can be performed. Such a comparison
provides a valuable opportunity to assess the validity of theoretical
magnetic field models. Here we measure the misalignment angles between
model magnetic fields and observed coronal loops in three active
regions, as observed with the Extreme Ultraviolet Imager (EUVI) on
STEREO on 30 April, 9 May, and 19 May 2007. We perform stereoscopic
triangulation of some 100 - 200 EUVI loops in each active region and
compute extrapolated magnetic field lines using magnetogram information
from the Michelson Doppler Imager (MDI) on the Solar and Heliospheric
Observatory (SOHO). We examine two different magnetic extrapolation
methods: (1) a potential field and (2) a radially stretched potential
field that conserves the magnetic divergence. We find considerable
disagreement between each theoretical model and the observed loop
geometries, with an average misalignment angle on the order of 20°
- 40°. We conclude that there is a need for either more suitable
(coronal rather than photospheric) magnetic field measurements or more
realistic field extrapolation models.
---------------------------------------------------------
Title: Coronal Radiation Belts
Authors: Hudson, H. S.; MacKinnon, A. L.; De Rosa, M. L.; Frewen,
S. F. N.
2009ApJ...698L..86H Altcode: 2009arXiv0905.3824H
The magnetic field of the solar corona has a large-scale dipole
character, which maps into the bipolar field in the solar wind. Using
standard representations of the coronal field, we show that high-energy
ions can be trapped stably in these large-scale closed fields. The
drift shells that describe the conservation of the third adiabatic
invariant may have complicated geometries. Particles trapped in these
zones would resemble the Van Allen belts and could have detectable
consequences. We discuss potential sources of trapped particles.
---------------------------------------------------------
Title: Nonlinear Force-Free Magnetic Field Modeling of AR 10953:
A Critical Assessment
Authors: De Rosa, Marc L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
Lites, B. W.; Aschwanden, M. J.; Amari, T.; Canou, A.; McTiernan,
J. M.; Régnier, S.; Thalmann, J. K.; Valori, G.; Wheatland, M. S.;
Wiegelmann, T.; Cheung, M. C. M.; Conlon, P. A.; Fuhrmann, M.;
Inhester, B.; Tadesse, T.
2009SPD....40.3102D Altcode:
Nonlinear force-free field (NLFFF) modeling seeks to provide accurate
representations of the structure of the magnetic field above solar
active regions, from which estimates of physical quantities of interest
(e.g., free energy and helicity) can be made. However, the suite of
NLFFF algorithms have failed to arrive at consistent solutions when
applied to (thus far, two) cases using the highest-available-resolution
vector magnetogram data from Hinode/SOT-SP (in the region of the
modeling area of interest) and line-of-sight magnetograms from
SOHO/MDI (where vector data were not available). One issue is that
NLFFF models require consistent, force-free vector magnetic boundary
data, and vector magnetogram data sampling the photosphere do not
satisfy this requirement. Consequently, several problems have arisen
that are believed to affect such modeling efforts. We use AR 10953
to illustrate these problems, namely: (1) some of the far-reaching,
current-carrying connections are exterior to the observational field
of view, (2) the solution algorithms do not (yet) incorporate the
measurement uncertainties in the vector magnetogram data, and/or (3)
a better way is needed to account for the Lorentz forces within the
layer between the photosphere and coronal base. In light of these
issues, we conclude that it remains difficult to derive useful and
significant estimates of physical quantities from NLFFF models.
---------------------------------------------------------
Title: A Critical Assessment of Nonlinear Force-Free Field Modeling
of the Solar Corona for Active Region 10953
Authors: De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham;
Leka, K. D.; Lites, Bruce W.; Aschwanden, Markus J.; Amari, Tahar;
Canou, Aurélien; McTiernan, James M.; Régnier, Stéphane; Thalmann,
Julia K.; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas;
Cheung, Mark C. M.; Conlon, Paul A.; Fuhrmann, Marcel; Inhester,
Bernd; Tadesse, Tilaye
2009ApJ...696.1780D Altcode: 2009arXiv0902.1007D
Nonlinear force-free field (NLFFF) models are thought to be viable
tools for investigating the structure, dynamics, and evolution of
the coronae of solar active regions. In a series of NLFFF modeling
studies, we have found that NLFFF models are successful in application
to analytic test cases, and relatively successful when applied
to numerically constructed Sun-like test cases, but they are less
successful in application to real solar data. Different NLFFF models
have been found to have markedly different field line configurations
and to provide widely varying estimates of the magnetic free energy in
the coronal volume, when applied to solar data. NLFFF models require
consistent, force-free vector magnetic boundary data. However,
vector magnetogram observations sampling the photosphere, which is
dynamic and contains significant Lorentz and buoyancy forces, do not
satisfy this requirement, thus creating several major problems for
force-free coronal modeling efforts. In this paper, we discuss NLFFF
modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT,
STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process
illustrate three such issues we judge to be critical to the success of
NLFFF modeling: (1) vector magnetic field data covering larger areas
are needed so that more electric currents associated with the full
active regions of interest are measured, (2) the modeling algorithms
need a way to accommodate the various uncertainties in the boundary
data, and (3) a more realistic physical model is needed to approximate
the photosphere-to-corona interface in order to better transform the
forced photospheric magnetograms into adequate approximations of nearly
force-free fields at the base of the corona. We make recommendations
for future modeling efforts to overcome these as yet unsolved problems.
---------------------------------------------------------
Title: Stochastic Effects of Granulation and Supergranulation Upon
Deep Convection
Authors: Augustson, Kyle; De Rosa, M. L.; Hurlburt, N. E.; Toomre, J.
2009SPD....40.0805A Altcode:
Vigorous fluid motions associated with the observed patterns of
supergranulation, mesogranulation, and granulation play a large
role in the turbulent transport of heat to the solar surface. The
downflows associated with these convective motions plunge from the
surface into the near-surface layers of the Sun bringing cooler,
low entropy material with them. These flow structures may provide
some stochastic effects upon the dynamics of the giant cells of deep
convection that extend into the near-surface regions. To investigate
such dynamics, we have carried out several 3-D numerical simulations of
fully compressible fluids within curved, spherical segments that, at
this stage, approximate conditions near the top of the rotating solar
convection zone. The upper boundary of the segment is stochastically
driven with cool plumes that approximate the spatial and temporal
scales of supergranular cell downflows, in essence creating a network
of supergranular cells. The segment spans 30° in latitude and 30°
in longitude, and has a radial extent of 15% of the solar radius. We
explore the formation and evolution of the boundary layer resulting
from such stochastic driving, and discuss these dynamics in the context
of the near-surface shear layer of the solar convection zone.
---------------------------------------------------------
Title: Interaction Between Emerging Magnetic Flux And The Ambient
Solar Coronal Field
Authors: Cheung, Mark; De Rosa, M.
2009SPD....40.3103C Altcode:
We study the interaction between emerging magnetic flux and
pre-existing coronal field by means of numerical simulations using
the magneto-frictional method. By advancing the induction equation,
the magneto-frictional method models the coronal magnetic field as a
quasi-static sequence of non-linear force-free field configurations
evolving in response to photospheric driving. A general feature of the
simulations is the spontaneous formation of current sheets. At these
interfaces, the field line torsional coefficient changes abruptly
across separate domains of connectivity. Since the code evolves the
vector potential, it allows us to calculate how much relative magnetic
helicity and free energy is stored in the system. By using temporal
sequences of observed vector magnetograms as the boundary condition,
this model is potentially suitable for modeling the evolution of solar
coronal fields.
---------------------------------------------------------
Title: Nonlinear Force-Free Magnetic Field Modeling of the Solar
Corona: A Critical Assessment
Authors: De Rosa, M. L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
Lites, B. W.; Aschwanden, M. J.; McTiernan, J. M.; Régnier, S.;
Thalmann, J.; Valori, G.; Wheatland, M. S.; Wiegelmann, T.; Cheung,
M.; Conlon, P. A.; Fuhrmann, M.; Inhester, B.; Tadesse, T.
2008AGUFMSH41A1604D Altcode:
Nonlinear force-free field (NLFFF) modeling promises to provide accurate
representations of the structure of the magnetic field above solar
active regions, from which estimates of physical quantities of interest
(e.g., free energy and helicity) can be made. However, the suite of
NLFFF algorithms have so far failed to arrive at consistent solutions
when applied to cases using the highest-available-resolution vector
magnetogram data from Hinode/SOT-SP (in the region of the modeling
area of interest) and line-of-sight magnetograms from SOHO/MDI (where
vector data were not been available). It is our view that the lack of
robust results indicates an endemic problem with the NLFFF modeling
process, and that this process will likely continue to fail until (1)
more of the far-reaching, current-carrying connections are within the
observational field of view, (2) the solution algorithms incorporate
the measurement uncertainties in the vector magnetogram data, and/or
(3) a better way is found to account for the Lorentz forces within
the layer between the photosphere and coronal base. In light of these
issues, we conclude that it remains difficult to derive useful and
significant estimates of physical quantities from NLFFF models.
---------------------------------------------------------
Title: Using STEREO/EUVI to Study Active Region Magnetic Fields
Authors: Sandman, A.; Aschwanden, M.; Wuelser, J.; De Rosa, M.;
Alexander, D.
2008AGUFMSH13B1523S Altcode:
We examine the effect of linear transformations on the misalignment
between model magnetic fields and coronal loops in active regions,
as observed with STEREO/EUVI on three separate occasions between
April 30 and May 19, 2007. We perform stereoscopic triangulation of
some 100 EUVI loops in each active region, and identify the tangent
vectors along every loop. Using magnetogram information from SOHO/MDI
we compute a 3D potential field and interpolate the magnetic field
vector at every position along the EUVI loops. The angle between the
loop tangent vector and the magnetic field vector provides a measure
of the misalignment angle between the observed field configuration
and the model. We then transform the field in a way that preserves
the divergence-free condition while injecting electric currents into
the system. With this modified field we repeat our calculation of the
misalignment angles between the magnetic field vectors and the EUV
loop tangent vectors, quantifying the improvement of the transformed
magnetic field model. Results of this type of magnetic modeling are
presented for three active regions.
---------------------------------------------------------
Title: The Buildup of Large-Scale Polar Magnetic Fields on the Sun:
Small Things Can Make a Difference
Authors: De Rosa, M. L.
2008AGUFMSH44A..01D Altcode:
Large-scale magnetic field patterns visible at high latitudes on the
solar photosphere are thought to form primarily from the poleward
transport of flux that has emerged at lower latitudes. It is only a
small percentage of this lower-latitude (i.e., active region) flux,
however, that makes it to the poles, as much active-region flux
cancels during its emergence and subsequent dispersal. This dispersal
is characterized by the shearing and advection caused by the surface
differential rotation and meridional flows, as well as by constant
buffeting by near-surface convection and interactions with nearby flux
concentrations. Consequently, these processes can play an important role
in the transport of flux to the poles and the buildup of the polar caps,
and their nonlinear nature implies that interactions between patterns
with differing spatial (and temporal) scales can affect the timing of
the formation of the polar cap as well as its overall amplitude. Such
possibilities are investigated using a surface flux-transport model,
and implications regarding the heliosphere are discussed.
---------------------------------------------------------
Title: Non-force Free Coronal Extrapolation Based on the Principle
of Minimum Dissipation Rate
Authors: Hu, Q.; Dasgupta, B.; Buechner, J.; De Rosa, M.
2008AGUFMSH13A1514H Altcode:
The Principle of Minimum (energy) Dissipation Rate (MDR) originates from
irreversible thermodynamics. In analogy to the Principle of Minimum
Energy, it also follows a variational approach, but is more suitable
for a complex and externally driven system like the solar corona. And
in contrast, while the former yields a force- free magnetic field, the
MDR gives a more general non-force free magnetic field with flow. The
solution to the equation describing non-force free magnetic field
resulted from MDR can be expressed as a superposition of two linear
force-free fields with distinct α parameters, and one potential
field (α≡0). Subsequently, the plasma states can also be derived,
following standard MHD theory, given necessary boundary conditions. We
present recent progress on applying the MDR theory to non-force free
extrapolation of solar active region from vector magnetograms as bottom
boundary data. We illustrate the approach of complete characterization
of 3D magnetic field and plasma states by using numerical simulation
data, and discuss its advantages and limitations.
---------------------------------------------------------
Title: Modeling of Solar Radiation Belts
Authors: Frewen, S. S.; De Rosa, M.; Hudson, H.; MacKinnon, A.
2008AGUFMSH13B1526F Altcode:
Stable particle trapping in the complicated magnetic field of the solar
corona -- "solar radiation belts" -- at first seems unlikely in the face
of the Sun's complex, variable magnetic field. By integrating particle
orbit equations in the guiding-center approximation, we investigate
the fates of energetic ions in model coronal magnetic fields. We use
both PFSS (Potential Field Source Surface) and simple analytic field
models. Contrary to naive expectation, we find that significant numbers
of particles remain trapped more than long enough to circumnavigate
the Sun, neither precipitating to the surface nor attaining open field
lines. The drift "shells" corresponding to conservation of the third
adiabatic invariant may be complicated in form. A close look at the
dependence of the cross-field drift speed on magnetic field strength
and topology accounts for this finding.
---------------------------------------------------------
Title: On the Solar Origins of Open Magnetic Fields in the Heliosphere
Authors: Rust, David M.; Haggerty, Dennis K.; Georgoulis, Manolis K.;
Sheeley, Neil R.; Wang, Yi-Ming; DeRosa, Marc L.; Schrijver, Carolus J.
2008ApJ...687..635R Altcode:
A combination of heliospheric and solar data was used to identify open
magnetic fields stretching from the lower corona to Earth orbit. 35
near-relativistic electron beams detected at the ACE spacecraft
"labeled" the heliospheric segments of the open fields. An X-ray
flare occurred <20 minutes before injection of the electrons
in 25 events. These flares labeled the solar segment of the open
fields. The flares occurred in western-hemisphere active regions (ARs)
with coronal holes whose polarity agreed with the polarity of the
beam-carrying interplanetary fields in 23 of the 25 events. We conclude
that electron beams reach 1 AU from open AR fields adjacent to flare
sites. The Wang & Sheeley implementation of the potential-field
source-surface model successfully identified the open fields in
36% of cases. Success meant that the open fields reached the source
surface within 3 heliographic deg of the interplanetary magnetic field
connected to ACE at 1 AU. Inclusion of five near misses improves
the success rate to 56%. The success rate for the Schrijver &
DeRosa PFSS implementation was 50%. Our results suggest that, even
if the input magnetic data are updated frequently, the PFSS models
succeed in only ~50% of cases to identify the coronal segment of open
fields. Development of other techniques is in its infancy.
---------------------------------------------------------
Title: On the Stability of Active Regions and Sunspots
Authors: Hurlburt, Neal; DeRosa, Marc
2008ApJ...684L.123H Altcode:
Recent helioseismic measurements of large-scale subsurface flows
indicate that systematic horizontal inflows near the photosphere
surround many active regions. Such active-region inflows are likely
to impede the dispersal of magnetic flux into the surrounding network
and thus can influence larger-scale and longer-term patterns and
evolution of the surface magnetic field throughout the course of a
solar activity cycle. We present results of numerical simulations
of compressible magnetoconvection in which an initial unipolar
magnetic field undergoes evolution resulting from convectively driven
motions. Inflows surrounding regions of concentrated magnetic flux
are driven by reducing the surface temperature as a function of
local magnetic flux. We find flow patterns that are consistent with
observations of those observed around active regions and sunspots.
---------------------------------------------------------
Title: Preprocessing of Hinode/SOT Vector Magnetograms for Nonlinear
Force-Free Coronal Magnetic Field Modeling
Authors: Wiegelmann, T.; Thalmann, J. K.; Schrijver, C. J.; De Rosa,
M. L.; Metcalf, T. R.
2008ASPC..397..198W Altcode: 2008arXiv0801.2884W
The solar magnetic field is key to understanding the physical processes
in the solar atmosphere. Nonlinear force-free codes have been shown
to be useful in extrapolating the coronal field from underlying vector
boundary data (for an overview see Schrijver et al. (2006)). However,
we can only measure the magnetic field vector routinely with high
accuracy in the photosphere with, e.g., Hinode/SOT, and unfortunately
these data do not fulfill the force-free consistency condition as
defined by Aly (1989). We must therefore apply some transformations
to these data before nonlinear force-free extrapolation codes can be
legitimately applied. To this end, we have developed a minimization
procedure that uses the measured photospheric field vectors as input
to approximate a more chromospheric like field (The method was dubbed
preprocessing. See Wiegelmann et al. (2006) for details). The procedure
includes force-free consistency integrals and spatial smoothing. The
method has been intensively tested with model active regions (see
Metcalf et al. 2008) and been applied to several ground based vector
magnetogram data before. Here we apply the preprocessing program to
photospheric magnetic field measurements with the Hinode/SOT instrument.
---------------------------------------------------------
Title: Erratum: "Tests and Comparisons of Velocity-Inversion
Techniques" (ApJ, 670, 1434 [2007])
Authors: Welsch, B. T.; Abbett, W. P.; DeRosa, M. L.; Fisher, G. H.;
Georgoulis, M. K.; Kusano, K.; Longcope, D. W.; Ravindra, B.; Schuck,
P. W.
2008ApJ...680..827W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Dependence of Ephemeral Region Emergence on Local Flux
Imbalance
Authors: Hagenaar, Hermance J.; DeRosa, Marc L.; Schrijver, Carolus J.
2008ApJ...678..541H Altcode:
We investigate the distribution and evolution of existing and emerging
magnetic network elements in the quiet-Sun photosphere. The ephemeral
region emergence rate is found to depend primarily on the imbalance of
magnetic flux in the area surrounding its emergence location, such that
the rate of flux emergence is lower within strongly unipolar regions by
at least a factor of 3 relative to flux-balanced quiet Sun. As coronal
holes occur over unipolar regions, this also means that ephemeral
regions occur less frequently there, but we show that this is an
indirect effect—independent of whether the region is located within
an open-field coronal hole or a closed-field quiet region. We discuss
the implications of this finding for near-photospheric dynamo action and
for the coupling between closed coronal and open heliospheric fields.
---------------------------------------------------------
Title: A joint search for gravitational wave bursts with AURIGA
and LIGO
Authors: Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; De Rosa,
M.; Falferi, P.; Fattori, S.; Fortini, P.; Giusfredi, G.; Inguscio, M.;
Liguori, N.; Longo, S.; Marin, F.; Mezzena, R.; Mion, A.; Ortolan, A.;
Poggi, S.; Prodi, G. A.; Re, V.; Salemi, F.; Soranzo, G.; Taffarello,
L.; Vedovato, G.; Vinante, A.; Vitale, S.; Zendri, J. P.; Abbott, B.;
Abbott, R.; Adhikari, R.; Agresti, J.; Ajith, P.; Allen, B.; Amin, R.;
Anderson, S. B.; Anderson, W. G.; Arain, M.; Araya, M.; Armandula, H.;
Ashley, M.; Aston, S.; Aufmuth, P.; Aulbert, C.; Babak, S.; Ballmer,
S.; Bantilan, H.; Barish, B. C.; Barker, C.; Barker, D.; Barr, B.;
Barriga, P.; Barton, M. A.; Bayer, K.; Belczynski, K.; Betzwieser,
J.; Beyersdorf, P. T.; Bhawal, B.; Bilenko, I. A.; Billingsley, G.;
Biswas, R.; Black, E.; Blackburn, K.; Blackburn, L.; Blair, D.; Bland,
B.; Bogenstahl, J.; Bogue, L.; Bork, R.; Boschi, V.; Bose, S.; Brady,
P. R.; Braginsky, V. B.; Brau, J. E.; Brinkmann, M.; Brooks, A.; Brown,
D. A.; Bullington, A.; Bunkowski, A.; Buonanno, A.; Burmeister, O.;
Busby, D.; Butler, W. E.; Byer, R. L.; Cadonati, L.; Cagnoli, G.; Camp,
J. B.; Cannizzo, J.; Cannon, K.; Cantley, C. A.; Cao, J.; Cardenas,
L.; Carter, K.; Casey, M. M.; Castaldi, G.; Cepeda, C.; Chalkley, E.;
Charlton, P.; Chatterji, S.; Chelkowski, S.; Chen, Y.; Chiadini, F.;
Chin, D.; Chin, E.; Chow, J.; Christensen, N.; Clark, J.; Cochrane,
P.; Cokelaer, T.; Colacino, C. N.; Coldwell, R.; Conte, R.; Cook, D.;
Corbitt, T.; Coward, D.; Coyne, D.; Creighton, J. D. E.; Creighton,
T. D.; Croce, R. P.; Crooks, D. R. M.; Cruise, A. M.; Cumming, A.;
Dalrymple, J.; D'Ambrosio, E.; Danzmann, K.; Davies, G.; DeBra, D.;
Degallaix, J.; Degree, M.; Demma, T.; Dergachev, V.; Desai, S.;
DeSalvo, R.; Dhurandhar, S.; Díaz, M.; Dickson, J.; Di Credico,
A.; Diederichs, G.; Dietz, A.; Doomes, E. E.; Drever, R. W. P.;
Dumas, J. -C.; Dupuis, R. J.; Dwyer, J. G.; Ehrens, P.; Espinoza,
E.; Etzel, T.; Evans, M.; Evans, T.; Fairhurst, S.; Fan, Y.; Fazi,
D.; Fejer, M. M.; Finn, L. S.; Fiumara, V.; Fotopoulos, N.; Franzen,
A.; Franzen, K. Y.; Freise, A.; Frey, R.; Fricke, T.; Fritschel, P.;
Frolov, V. V.; Fyffe, M.; Galdi, V.; Ganezer, K. S.; Garofoli, J.;
Gholami, I.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Goda, K.;
Goetz, E.; Goggin, L. M.; González, G.; Gossler, S.; Grant, A.; Gras,
S.; Gray, C.; Gray, M.; Greenhalgh, J.; Gretarsson, A. M.; Grosso,
R.; Grote, H.; Grunewald, S.; Guenther, M.; Gustafson, R.; Hage, B.;
Hammer, D.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G.; Harstad,
E.; Hayler, T.; Heefner, J.; Heng, I. S.; Heptonstall, A.; Heurs, M.;
Hewitson, M.; Hild, S.; Hirose, E.; Hoak, D.; Hosken, D.; Hough, J.;
Howell, E.; Hoyland, D.; Huttner, S. H.; Ingram, D.; Innerhofer, E.;
Ito, M.; Itoh, Y.; Ivanov, A.; Jackrel, D.; Johnson, B.; Johnson,
W. W.; Jones, D. I.; Jones, G.; Jones, R.; Ju, L.; Kalmus, P.;
Kalogera, V.; Kasprzyk, D.; Katsavounidis, E.; Kawabe, K.; Kawamura,
S.; Kawazoe, F.; Kells, W.; Keppel, D. G.; Khalili, F. Ya; Kim, C.;
King, P.; Kissel, J. S.; Klimenko, S.; Kokeyama, K.; Kondrashov,
V.; Kopparapu, R. K.; Kozak, D.; Krishnan, B.; Kwee, P.; Lam, P. K.;
Landry, M.; Lantz, B.; Lazzarini, A.; Lee, B.; Lei, M.; Leiner, J.;
Leonhardt, V.; Leonor, I.; Libbrecht, K.; Lindquist, P.; Lockerbie,
N. A.; Longo, M.; Lormand, M.; Lubiński, M.; Lück, H.; Machenschalk,
B.; MacInnis, M.; Mageswaran, M.; Mailand, K.; Malec, M.; Mandic, V.;
Marano, S.; Márka, S.; Markowitz, J.; Maros, E.; Martin, I.; Marx,
J. N.; Mason, K.; Matone, L.; Matta, V.; Mavalvala, N.; McCarthy, R.;
McClelland, D. E.; McGuire, S. C.; McHugh, M.; McKenzie, K.; McNabb,
J. W. C.; McWilliams, S.; Meier, T.; Melissinos, A.; Mendell, G.;
Mercer, R. A.; Meshkov, S.; Messenger, C. J.; Meyers, D.; Mikhailov,
E.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.;
Miyakawa, O.; Mohanty, S.; Moreno, G.; Mossavi, K.; Lowry, C. Mow;
Moylan, A.; Mudge, D.; Mueller, G.; Mukherjee, S.; Müller-Ebhardt,
H.; Munch, J.; Murray, P.; Myers, E.; Myers, J.; Nash, T.; Newton, G.;
Nishizawa, A.; Nocera, F.; Numata, K.; O'Reilly, B.; O'Shaughnessy,
R.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pan, Y.; Papa, M. A.;
Parameshwaraiah, V.; Parameswariah, C.; Patel, P.; Pedraza, M.;
Penn, S.; Pierro, V.; Pinto, I. M.; Pitkin, M.; Pletsch, H.; Plissi,
M. V.; Postiglione, F.; Prix, R.; Quetschke, V.; Raab, F.; Rabeling,
D.; Radkins, H.; Rahkola, R.; Rainer, N.; Rakhmanov, M.; Ramsunder,
M.; Rawlins, K.; Ray-Majumder, S.; Regimbau, T.; Rehbein, H.; Reid,
S.; Reitze, D. H.; Ribichini, L.; Riesen, R.; Riles, K.; Rivera, B.;
Robertson, N. A.; Robinson, C.; Robinson, E. L.; Roddy, S.; Rodriguez,
A.; Rogan, A. M.; Rollins, J.; Romano, J. D.; Romie, J.; Route, R.;
Rowan, S.; Rüdiger, A.; Ruet, L.; Russell, P.; Ryan, K.; Sakata, S.;
Samidi, M.; Sancho de la Jordana, L.; Sandberg, V.; Sanders, G. H.;
Sannibale, V.; Saraf, S.; Sarin, P.; Sathyaprakash, B. S.; Sato, S.;
Saulson, P. R.; Savage, R.; Savov, P.; Sazonov, A.; Schediwy, S.;
Schilling, R.; Schnabel, R.; Schofield, R.; Schutz, B. F.; Schwinberg,
P.; Scott, S. M.; Searle, A. C.; Sears, B.; Seifert, F.; Sellers, D.;
Sengupta, A. S.; Shawhan, P.; Shoemaker, D. H.; Sibley, A.; Siemens,
X.; Sigg, D.; Sinha, S.; Sintes, A. M.; Slagmolen, B. J. J.; Slutsky,
J.; Smith, J. R.; Smith, M. R.; Somiya, K.; Strain, K. A.; Strom,
D. M.; Stuver, A.; Summerscales, T. Z.; Sun, K. -X.; Sung, M.; Sutton,
P. J.; Takahashi, H.; Tanner, D. B.; Tarallo, M.; Taylor, R.; Taylor,
R.; Thacker, J.; Thorne, K. A.; Thorne, K. S.; Thüring, A.; Tinto,
M.; Tokmakov, K. V.; Torres, C.; Torrie, C.; Traylor, G.; Trias, M.;
Tyler, W.; Ugolini, D.; Ungarelli, C.; Urbanek, K.; Vahlbruch, H.;
Vallisneri, M.; Van Den Broeck, C.; van Putten, M.; Varvella, M.;
Vass, S.; Vecchio, A.; Veitch, J.; Veitch, P.; Villar, A.; Vorvick,
C.; Vyachanin, S. P.; Waldman, S. J.; Wallace, L.; Ward, H.; Ward,
R.; Watts, K.; Webber, D.; Weidner, A.; Weinert, M.; Weinstein, A.;
Weiss, R.; Wen, S.; Wette, K.; Whelan, J. T.; Whitbeck, D. M.;
Whitcomb, S. E.; Whiting, B. F.; Wiley, S.; Wilkinson, C.; Willems,
P. A.; Williams, L.; Willke, B.; Wilmut, I.; Winkler, W.; Wipf, C. C.;
Wise, S.; Wiseman, A. G.; Woan, G.; Woods, D.; Wooley, R.; Worden,
J.; Wu, W.; Yakushin, I.; Yamamoto, H.; Yan, Z.; Yoshida, S.; Yunes,
N.; Zanolin, M.; Zhang, J.; Zhang, L.; Zhao, C.; Zotov, N.; Zucker,
M.; zur Mühlen, H.; Zweizig, J.
2008CQGra..25i5004B Altcode: 2007arXiv0710.0497A
The first simultaneous operation of the AURIGA detector<A
href="http://www.auriga.lnl.infn.it">http://www.auriga.lnl.infn.it</A>
and the LIGO observatory<A
href="http://www.ligo.org">http://www.ligo.org</A> was an opportunity
to explore real data, joint analysis methods between two very
different types of gravitational wave detectors: resonant bars and
interferometers. This paper describes a coincident gravitational
wave burst search, where data from the LIGO interferometers are
cross-correlated at the time of AURIGA candidate events to identify
coincident transients. The analysis pipeline is tuned with two
thresholds, on the signal-to-noise ratio of AURIGA candidate events and
on the significance of the cross-correlation test in LIGO. The false
alarm rate is estimated by introducing time shifts between data sets
and the network detection efficiency is measured by adding simulated
gravitational wave signals to the detector output. The simulated
waveforms have a significant fraction of power in the narrower AURIGA
band. In the absence of a detection, we discuss how to set an upper
limit on the rate of gravitational waves and to interpret it according
to different source models. Due to the short amount of analyzed data
and to the high rate of non-Gaussian transients in the detectors' noise
at the time, the relevance of this study is methodological: this was
the first joint search for gravitational wave bursts among detectors
with such different spectral sensitivity and the first opportunity
for the resonant and interferometric communities to unify languages
and techniques in the pursuit of their common goal.
---------------------------------------------------------
Title: Non-Linear Force-Free Field Modeling of a Solar Active Region
Around the Time of a Major Flare and Coronal Mass Ejection
Authors: De Rosa, M. L.; Schrijver, C. J.; Metcalf, T. R.; Barnes,
G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann,
T.; Wheatland, M.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
M.; Kusano, K.; Régnier, S.; Thalmann, J.
2008AGUSMSP31A..06D Altcode:
Solar flares and coronal mass ejections are associated with rapid
changes in coronal magnetic field connectivity and are powered by
the partial dissipation of electrical currents that run through
the solar corona. A critical unanswered question is whether the
currents involved are induced by the advection along the photosphere
of pre-existing atmospheric magnetic flux, or whether these currents
are associated with newly emergent flux. We address this problem by
applying nonlinear force-free field (NLFFF) modeling to the highest
resolution and quality vector-magnetographic data observed by the
recently launched Hinode satellite on NOAA Active Region 10930 around
the time of a powerful X3.4 flare in December 2006. We compute 14
NLFFF models using 4 different codes having a variety of boundary
conditions. We find that the model fields differ markedly in geometry,
energy content, and force-freeness. We do find agreement of the best-fit
model field with the observed coronal configuration, and argue (1)
that strong electrical currents emerge together with magnetic flux
preceding the flare, (2) that these currents are carried in an ensemble
of thin strands, (3) that the global pattern of these currents and
of field lines are compatible with a large-scale twisted flux rope
topology, and (4) that the ~1032~erg change in energy associated with
the coronal electrical currents suffices to power the flare and its
associated coronal mass ejection. We discuss the relative merits of
these models in a general critique of our present abilities to model
the coronal magnetic field based on surface vector field measurements.
---------------------------------------------------------
Title: Exploring large-scale coronal magnetic field over extended
longitudes by STEREO/EUVI and its effect on solar wind prediction
Authors: Nitta, N. V.; De Rosa, M. L.; Zarro, D. M.; Wuelser, J.;
Aschwanden, M. J.; Lemen, J. R.
2008AGUSMSH23A..06N Altcode:
The potential field source surface (PFSS) model forms the basis of
a wide range of heliospheric science and applications, including
prediction of the solar wind speed near Earth. Experience shows that
the model sometimes works quite well, but not always. Possible reasons
for failure include deviation of the interplanetary magnetic field from
the nominal Parker spiral, violation of the assumptions used in the
model such as the discontinuity at the source surface, and the lack of
simultaneous full-surface magnetograms. Here we study the impact of the
lack of simultaneous full-surface magnetograms, using observations of
the corona over an extended longitude range made possible by the EUVI
on board the STEREO mission. In spite of the lack of magnetographs on
STEREO, EUVI data with a growing separation angle between spacecraft
A and B at least allow us to locate major active regions and coronal
holes in the area not seen from Earth. The PFSS extrapolations and their
input synoptic maps are compared with EUVI data to measure how well the
model fits the observations. These comparisons are discussed in terms of
the solar wind speed predicted by the model and observed at L1 by ACE.
---------------------------------------------------------
Title: Tracing the 3-D coronal structure during CMEs with
STEREO/SECCHI EUVI observations
Authors: Wuelser, J.; Aschwanden, M.; De Rosa, M.; Lee, C.; Lemen,
J.; Nitta, N.; Sandman, A.
2008AGUSMSH31A..05W Altcode:
STEREO/SECCHI EUVI observations of solar coronal loops, filaments,
and dimming regions provide unique information on the 3-D topology
of the coronal magnetic field above active regions and its evolution
during coronal mass ejections (CMEs). Active Region #10956 produced
several CMEs during its passage across the solar disk in May 2007,
some of them showing filament eruptions and dimming. The SECCHI/EUVI
instrument on STEREO obtained high cadence observations in multiple
lines simultaneously from both STEREO spacecraft. 3-D reconstructions
of coronal features over the course of a CME show significant changes
of the field topology. Comparisons with the potential field topology
from magnetic field extrapolations show the degree of non-potentiality
of the real field and changes in the vicinity of the CME onset. We
present initial results of this study.
---------------------------------------------------------
Title: Searching for Large-scale flows around Active Regions with
Hinode
Authors: Hurlburt, N.; Derosa, M.; Hagenaar, M.
2008AGUSMSP43C..08H Altcode:
Heliosiemic studies have suggested that active regions are surrounded
by large-scale inflows (Haber et al. 2004), and it has recently been
hypothesized by Hurlburt and DeRosa (2008,HD) that these are due to
the enhanced surface cooling resulting from plage and faculae. We seek
confirmation of these results using Hinode observations of Active
Regions using a variety of methods to infer inflow velocities from
of continuum images and Dopplergrams. These flow patterns are then
compared to the HD hypothesis. This work has been supported by NASA
through contracts NNM07AA01C and NNG06GD45G. References: Haber, D.,
Hindman, B., Toomre, J. and Thompson, M. 2004, ÐOrganized Subsurface
Flows near Active Regions,î Sol. Phys. 220,371. Hurlburt & DeRosa,
2008 ÐOn the longevity of Active Regions,î Ap.J. Lett., submitted
---------------------------------------------------------
Title: Nonlinear Force-free Field Modeling of a Solar Active Region
around the Time of a Major Flare and Coronal Mass Ejection
Authors: Schrijver, C. J.; DeRosa, M. L.; Metcalf, T.; Barnes, G.;
Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.;
Wheatland, M. S.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
M.; Kusano, K.; Régnier, S.; Thalmann, J. K.
2008ApJ...675.1637S Altcode: 2007arXiv0712.0023S
Solar flares and coronal mass ejections are associated with rapid
changes in field connectivity and are powered by the partial dissipation
of electrical currents in the solar atmosphere. A critical unanswered
question is whether the currents involved are induced by the motion of
preexisting atmospheric magnetic flux subject to surface plasma flows or
whether these currents are associated with the emergence of flux from
within the solar convective zone. We address this problem by applying
state-of-the-art nonlinear force-free field (NLFFF) modeling to the
highest resolution and quality vector-magnetographic data observed
by the recently launched Hinode satellite on NOAA AR 10930 around
the time of a powerful X3.4 flare. We compute 14 NLFFF models with
four different codes and a variety of boundary conditions. We find
that the model fields differ markedly in geometry, energy content,
and force-freeness. We discuss the relative merits of these models in
a general critique of present abilities to model the coronal magnetic
field based on surface vector field measurements. For our application
in particular, we find a fair agreement of the best-fit model field
with the observed coronal configuration, and argue (1) that strong
electrical currents emerge together with magnetic flux preceding the
flare, (2) that these currents are carried in an ensemble of thin
strands, (3) that the global pattern of these currents and of field
lines are compatible with a large-scale twisted flux rope topology,
and (4) that the ~10<SUP>32</SUP> erg change in energy associated with
the coronal electrical currents suffices to power the flare and its
associated coronal mass ejection.
---------------------------------------------------------
Title: A Comparison of Solar Open Field Regions Found by Type III
Radio Bursts and the Potential Field Source Surface Model
Authors: Nitta, Nariaki V.; DeRosa, Marc L.
2008ApJ...673L.207N Altcode:
For heliophysics research and applications, the potential field
source surface (PFSS) model is often employed to extrapolate the
photospheric magnetic field to the corona. In an attempt to evaluate
the performance of the PFSS model, we compare the computed footpoints
of the heliospheric magnetic field with the locations of flares
associated with type III radio bursts, which are a good indicator
of open field lines that extend to interplanetary space. Consistent
with past experiences, the agreement is not satisfactory. We discuss
possible reasons for the discrepancy, including the model's inadequacy
to reproduce the coronal magnetic field above evolving active regions
and the lack of a simultaneous full-surface magnetic map. It is argued
that the performance of the PFSS model needs to be quantified further
against solar observations, including type III bursts, before it is
applied to heliospheric models.
---------------------------------------------------------
Title: Can We Improve the Preprocessing of Photospheric Vector
Magnetograms by the Inclusion of Chromospheric Observations?
Authors: Wiegelmann, T.; Thalmann, J. K.; Schrijver, C. J.; De Rosa,
M. L.; Metcalf, T. R.
2008SoPh..247..249W Altcode: 2008arXiv0801.2707W; 2008SoPh..tmp...27W
The solar magnetic field is key to understanding the physical processes
in the solar atmosphere. Nonlinear force-free codes have been shown to
be useful in extrapolating the coronal field upward from underlying
vector boundary data. However, we can only measure the magnetic
field vector routinely with high accuracy in the photosphere, and
unfortunately these data do not fulfill the force-free condition. We
must therefore apply some transformations to these data before nonlinear
force-free extrapolation codes can be self-consistently applied. To
this end, we have developed a minimization procedure that yields a more
chromosphere-like field, using the measured photospheric field vectors
as input. The procedure includes force-free consistency integrals,
spatial smoothing, and - newly included in the version presented here
- an improved match to the field direction as inferred from fibrils
as can be observed in, for example, chromospheric Hα images. We test
the procedure using a model active-region field that included buoyancy
forces at the photospheric level. The proposed preprocessing method
allows us to approximate the chromospheric vector field to within a few
degrees and the free energy in the coronal field to within one percent.
---------------------------------------------------------
Title: Nonlinear Force-Free Modeling of Coronal Magnetic
Fields. II. Modeling a Filament Arcade and Simulated Chromospheric
and Photospheric Vector Fields
Authors: Metcalf, Thomas R.; De Rosa, Marc L.; Schrijver, Carolus J.;
Barnes, Graham; van Ballegooijen, Adriaan A.; Wiegelmann, Thomas;
Wheatland, Michael S.; Valori, Gherardo; McTtiernan, James M.
2008SoPh..247..269M Altcode: 2008SoPh..tmp...17M
We compare a variety of nonlinear force-free field (NLFFF) extrapolation
algorithms, including optimization, magneto-frictional, and Grad -
Rubin-like codes, applied to a solar-like reference model. The model
used to test the algorithms includes realistic photospheric Lorentz
forces and a complex field including a weakly twisted, right helical
flux bundle. The codes were applied to both forced "photospheric" and
more force-free "chromospheric" vector magnetic field boundary data
derived from the model. When applied to the chromospheric boundary data,
the codes are able to recover the presence of the flux bundle and the
field's free energy, though some details of the field connectivity are
lost. When the codes are applied to the forced photospheric boundary
data, the reference model field is not well recovered, indicating
that the combination of Lorentz forces and small spatial scale
structure at the photosphere severely impact the extrapolation of the
field. Preprocessing of the forced photospheric boundary does improve
the extrapolations considerably for the layers above the chromosphere,
but the extrapolations are sensitive to the details of the numerical
codes and neither the field connectivity nor the free magnetic energy in
the full volume are well recovered. The magnetic virial theorem gives
a rapid measure of the total magnetic energy without extrapolation
though, like the NLFFF codes, it is sensitive to the Lorentz forces in
the coronal volume. Both the magnetic virial theorem and the Wiegelmann
extrapolation, when applied to the preprocessed photospheric boundary,
give a magnetic energy which is nearly equivalent to the value derived
from the chromospheric boundary, but both underestimate the free
energy above the photosphere by at least a factor of two. We discuss
the interpretation of the preprocessed field in this context. When
applying the NLFFF codes to solar data, the problems associated with
Lorentz forces present in the low solar atmosphere must be recognized:
the various codes will not necessarily converge to the correct, or
even the same, solution.
---------------------------------------------------------
Title: Ephemeral Bipolar Regions in Coronal Holes
Authors: Hagenaar, H.; Schrijver, C.; De Rosa, M.
2008ASPC..383..343H Altcode:
We investigate the distribution and evolution of magnetic network
elements in quiet Sun with or without coronal holes. Ephemeral region
emergence rates are found to depend on the degree of imbalance of
magnetic flux, but independent of whether there is a coronal hole or
not. We discuss the implications of this finding for near-photospheric
dynamo action and for the coupling between closed coronal and open
heliospheric fields.
---------------------------------------------------------
Title: Structure and Evolution of Giant Cells in Global Models of
Solar Convection
Authors: Miesch, Mark S.; Brun, Allan Sacha; DeRosa, Marc L.;
Toomre, Juri
2008ApJ...673..557M Altcode: 2007arXiv0707.1460M
The global scales of solar convection are studied through
three-dimensional simulations of compressible convection carried out
in spherical shells of rotating fluid that extend from the base of
the convection zone to within 15 Mm of the photosphere. Such modeling
at the highest spatial resolution to date allows study of distinctly
turbulent convection, revealing that coherent downflow structures
associated with giant cells continue to play a significant role in
maintaining the differential rotation that is achieved. These giant
cells at lower latitudes exhibit prograde propagation relative to
the mean zonal flow, or differential rotation, that they establish,
and retrograde propagation of more isotropic structures with vortical
character at mid and high latitudes. The interstices of the downflow
networks often possess strong and compact cyclonic flows. The
evolving giant-cell downflow systems can be partly masked by the
intense smaller scales of convection driven closer to the surface,
yet they are likely to be detectable with the helioseismic probing that
is now becoming available. Indeed, the meandering streams and varying
cellular subsurface flows revealed by helioseismology must be sampling
contributions from the giant cells, yet it is difficult to separate
out these signals from those attributed to the faster horizontal flows
of supergranulation. To aid in such detection, we use our simulations
to describe how the properties of giant cells may be expected to vary
with depth and how their patterns evolve in time.
---------------------------------------------------------
Title: Tests and Comparisons of Velocity-Inversion Techniques
Authors: Welsch, B. T.; Abbett, W. P.; De Rosa, M. L.; Fisher, G. H.;
Georgoulis, M. K.; Kusano, K.; Longcope, D. W.; Ravindra, B.; Schuck,
P. W.
2007ApJ...670.1434W Altcode:
Recently, several methods that measure the velocity of magnetized
plasma from time series of photospheric vector magnetograms have been
developed. Velocity fields derived using such techniques can be used
both to determine the fluxes of magnetic energy and helicity into the
corona, which have important consequences for understanding solar
flares, coronal mass ejections, and the solar dynamo, and to drive
time-dependent numerical models of coronal magnetic fields. To date,
these methods have not been rigorously tested against realistic,
simulated data sets, in which the magnetic field evolution and
velocities are known. Here we present the results of such tests
using several velocity-inversion techniques applied to synthetic
magnetogram data sets, generated from anelastic MHD simulations of
the upper convection zone with the ANMHD code, in which the velocity
field is fully known. Broadly speaking, the MEF, DAVE, FLCT, IM, and
ILCT algorithms performed comparably in many categories. While DAVE
estimated the magnitude and direction of velocities slightly more
accurately than the other methods, MEF's estimates of the fluxes of
magnetic energy and helicity were far more accurate than any other
method's. Overall, therefore, the MEF algorithm performed best in
tests using the ANMHD data set. We note that ANMHD data simulate
fully relaxed convection in a high-β plasma, and therefore do not
realistically model photospheric evolution.
---------------------------------------------------------
Title: Can we Improve the Preprocessing of Photospheric
Vectormagnetograms by the Inclusion of Chromospheric Observations?
Authors: Wiegelmann, T.; Thalmann, J. K.; Schrijver, C. J.; De Rosa,
M. L.; Metcalf, T. R.
2007AGUFMSH51C..02W Altcode:
The solar magnetic field is key to understanding the physical
processes in the solar atmosphere. Unfortunately, we can measure
the magnetic field vector routinely with high accuracy only in the
photosphere with, e.g., Hinode/SOT and in future with SDO/HMI. These
measurements are extrapolated into the corona under the assumption
that the field is force-free. That condition is not fulfilled in the
photosphere, but is in the chromosphere and corona. In order to make
the observed boundary data consistent with the force-free assumption,
we therefore have to apply some transformations before nonlinear
force-free extrapolation codes can be legitimately applied. We develop
a minimization procedure that uses the measured photospheric field
vectors as input to approximate a more chromospheric-like field. The
procedure includes force-free consistency integrals, spatial smoothing,
and - newly included in the version presented here - an improved match
to the field direction as inferred from fibrils as can be observed in,
e.g., chromospheric H-alpha images. We test the procedure using a model
active-region field that included buoyancy forces at the photospheric
level. We apply the combined preprocessing and nonlinear force-free
extrapolation method to compute the coronal magnetic field in an active
region measured with the Hinode/SOT instrument.
---------------------------------------------------------
Title: Results of the IGEC-2 search for gravitational wave bursts
during 2005
Authors: Astone, P.; Babusci, D.; Baggio, L.; Bassan, M.; Bignotto,
M.; Bonaldi, M.; Camarda, M.; Carelli, P.; Cavallari, G.; Cerdonio,
M.; Chincarini, A.; Coccia, E.; Conti, L.; D'Antonio, S.; de Rosa,
M.; di Paolo Emilio, M.; Drago, M.; Dubath, F.; Fafone, V.; Falferi,
P.; Foffa, S.; Fortini, P.; Frasca, S.; Gemme, G.; Giordano, G.;
Giusfredi, G.; Hamilton, W. O.; Hanson, J.; Inguscio, M.; Johnson,
W. W.; Liguori, N.; Longo, S.; Maggiore, M.; Marin, F.; Marini,
A.; McHugh, M. P.; Mezzena, R.; Miller, P.; Minenkov, Y.; Mion, A.;
Modestino, G.; Moleti, A.; Nettles, D.; Ortolan, A.; Pallottino, G. V.;
Parodi, R.; Piano Mortari, G.; Poggi, S.; Prodi, G. A.; Quintieri, L.;
Re, V.; Rocchi, A.; Ronga, F.; Salemi, F.; Soranzo, G.; Sturani, R.;
Taffarello, L.; Terenzi, R.; Torrioli, G.; Vaccarone, R.; Vandoni,
G.; Vedovato, G.; Vinante, A.; Visco, M.; Vitale, S.; Weaver, J.;
Zendri, J. P.; Zhang, P.
2007PhRvD..76j2001A Altcode: 2007arXiv0705.0688I
The network of resonant bar detectors of gravitational waves resumed
coordinated observations within the International Gravitational
Event Collaboration (IGEC-2). Four detectors are taking part in this
Collaboration: ALLEGRO, AURIGA, EXPLORER and NAUTILUS. We present here
the results of the search for gravitational wave bursts over 6 months
during 2005, when IGEC-2 was the only gravitational wave observatory
in operation. The implemented network data analysis is based on a time
coincidence search among AURIGA, EXPLORER and NAUTILUS; ALLEGRO data
was reserved for follow-up studies. The network amplitude sensitivity to
bursts improved by a factor ≈3 over the 1997-2000 IGEC observations;
the wider sensitive band also allowed the analysis to be tuned over
a larger class of waveforms. Given the higher single-detector duty
factors, the analysis was based on threefold coincidence, to ensure
the identification of any single candidate of gravitational waves with
high statistical confidence. The false detection rate was as low as
1 per century. No candidates were found.
---------------------------------------------------------
Title: Can we detect convection in the Sun?
Authors: Hanasoge, Shravan M.; Duvall, T. L.; De Rosa, M. L.; Miesch,
M. S.
2007IAUS..239..364H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simulations of Large-Scale Solar Surface Inflows Surrounding
Magnetic Fields
Authors: De Rosa, Marc L.; Hurlburt, N. E.
2007AAS...210.2211D Altcode: 2007BAAS...39..126D
Recent helioseismic measurements of large-scale subsurface flows have
indicated that systematic horizontal inflows near the photosphere
surround many active regions. Such active-region inflows are likely
to impede the dispersal into the surrounding network, and thus can
influence larger-scale and longer-term patterns of magnetic field
throughout the course of a solar activity cycle. We present preliminary
results of numerical simulations of compressible magnetoconvection,
in which an initial unipolar magnetic field undergoes evolution
resulting from convectively driven motions. Inflows surrounding regions
of concentrated magnetic flux are driven by reducing the surface
temperature in regions where the magnetic flux is strong. The effects
of these resulting inflows on the dynamics are then studied.
---------------------------------------------------------
Title: Structure and Evolution of Giant Cells in Global Models of
Solar Convection
Authors: Miesch, Mark S.; Brun, A. S.; De Rosa, M. L.; Toomre, J.
2007AAS...210.2217M Altcode: 2007BAAS...39..127M
We present the highest-resolution simulations of global-scale solar
convection so far achieved, dealing with turbulent compressible
flows interacting with rotation in a full spherical shell. The
three-dimensional simulation domain extends from 0.71R-0.98R, close
enough to the photosphere to overlap with solar subsurface weather
(SSW) maps inferred from local helioseismology. The convective patterns
achieved are complex and continually evolving on a time scale of several
days. However, embedded within the intricate downflow network near
the surface are coherent downflow lanes associated with giant cells
which persist for weeks to months and which extend through much of the
convection zone. These coherent downflow lanes are generally confined
to low latitudes and are oriented in a north-south direction. The low
dissipation in these simulations permits a more realistic balance of
forces which yields differential rotation and meridional circulation
profiles in good agreement with those inferred from helioseismology.
---------------------------------------------------------
Title: Non-linear Force-free Modeling Of Coronal Magnetic Fields
Authors: Metcalf, Thomas R.; De Rosa, M. L.; Schrijver, C. J.; Barnes,
G.; van Ballegooijen, A.; Wiegelmann, T.; Wheatland, M. S.; Valori,
G.; McTiernan, J. M.
2007AAS...210.9102M Altcode: 2007BAAS...39..204M
We compare a variety of nonlinear force-free field (NLFFF)
extrapolation algorithms, including optimization, magneto-frictional,
and Grad-Rubin-like codes, applied to a solar-like reference
model. The model used to test the algorithms includes realistic
photospheric Lorentz forces and a complex field including a weakly
twisted, right helical flux bundle. The codes were applied to both
forced "photospheric” and more force-free "chromospheric” vector
magnetic field boundary data derived from the model. When applied to
the <P />chromospheric boundary data, the codes are able to recover
the presence of the flux bundle and the field's free energy, though
some details of the field connectivity are lost. When the codes are
applied to the forced photospheric boundary data, the reference
model field is not well recovered, indicating that the Lorentz
forces on the photosphere severely impact the extrapolation of the
field. Preprocessing of the photospheric boundary does improve the
extrapolations considerably, although the results depend sensitively
on the details of the numerical codes. When applying the NLFFF codes
to solar data, the problems associated with Lorentz forces present in
the low solar atmosphere must be recognized: the various codes will
not necessarily converge to the correct, or even the same, solution.
---------------------------------------------------------
Title: SEP Properties and Magnetic Field Connection of the Source
Region
Authors: Nitta, N. V.; De Rosa, M. L.
2006AGUFMSH41B..06N Altcode:
There seems to be no clear explanation as to why some CME/flare events
produce major SEP events whereas others do not. Furthermore, we still
cannot reliably predict the peak flux and rise time of an SEP event
using remote sensing data. Even though CME shocks are the primary
accelerator for gradual SEP events and they are likely to have wide
angular extensions, we suggest that the magnetic field connection of the
source region to the observer may be an important factor for determining
their occurrence and basic properties. In order to address this issue,
we need to go beyond the common assumption that the longitudes around
W60 have the strongest connection to the Earth. For a number of
SEP-productive active regions, we compare the properties of intense
flares and energetic CMEs that originated from them over their disk
passage with the peak fluxes and rise times of the associated >10 MeV
and >50 MeV protons. We perform magnetic field extrapolation with the
potential field source surface (PFSS) model to locate well-connected
field lines with respect to the source region. Once evaluated against
multiple criteria, the PFSS extrapolation would be a useful tool to
characterize the magnetic field topology in and around the active
region responsible for the intense flares and energetic CMEs. This
study is expected to partially answer the question of whether flare-
accelerated particles contribute to gradual SEP events.
---------------------------------------------------------
Title: Coronal particle trapping revisited
Authors: Hudson, H. S.; MacKinnon, A.; De Rosa, M.
2006AGUFMSH54A..07H Altcode:
We re-examine the idea of long-term particle storage in the solar
corona in the context of modern PFSS (potential-field source surface)
magnetic models. As pointed out by H. Elliot in 1964 and others since
then, such particles could be energetically important, at the level
of some large fraction of the magnetic energy density B2/8π. We
estimate the distribution and time scales of particle trapping by
using representative PFSS coronal models from the Schrijver-De Rosa
SolarSoft code. As the coronal field simplifies during solar minimum, it
approaches axisymmetry and thus contains volumes inaccessible to charged
particles under the guiding-center approximation. We conclude that time
scales can be sufficiently long, so long in fact that the azimuthal
drift time scale (third adiabatic invariant of guiding-center motion),
for the large-scale dipolar configuration characteristic of solar
minimum, can exceed one solar cycle. We discuss the possible sources
of trapped particles, starting with the basic CRAND (cosmic-ray albedo
neutron decay) mechanism, and relate their X-ray and γ-ray signatures
to future observational capabilities including the Sentinels spacecraft.
---------------------------------------------------------
Title: Consequences of large-scale flows around active regions on
the dispersal of magnetic field across the solar surface
Authors: De Rosa, M. L.; Schrijver, C. J.
2006ESASP.624E..12D Altcode: 2006soho...18E..12D
No abstract at ADS
---------------------------------------------------------
Title: Solar Sources of Impulsive Solar Energetic Particle Events
and Their Magnetic Field Connection to the Earth
Authors: Nitta, Nariaki V.; Reames, Donald V.; De Rosa, Marc L.; Liu,
Yang; Yashiro, Seiji; Gopalswamy, Natchimuthuk
2006ApJ...650..438N Altcode:
This paper investigates the solar origin of impulsive solar energetic
particle (SEP) events, often referred to as <SUP>3</SUP>He-rich flares,
by attempting to locate the source regions of 117 events as observed
at ~2-3 MeV amu<SUP>-1</SUP>. Given large uncertainties as to when
ions at these energies were injected, we use type III radio bursts
that occur within a 5 hr time window preceding the observed ion onset,
and search in EUV and X-ray full-disk images for brightenings around
the times of the type III bursts. In this way we find the solar sources
in 69 events. High cadence EUV images often reveal a jet in the source
region shortly after the type III burst. We also study magnetic field
connections between the Earth and the solar sources of impulsive SEP
events as identified above, combining the potential field source
surface (PFSS) model for the coronal field and the Parker spiral
for the interplanetary magnetic field. We find open field lines in
and around ~80% of the source regions. But only in ~40% of the cases,
can we find field lines that are both close to the source region at the
photosphere and to the Parker spiral coordinates at the source surface,
suggesting challenges in understanding the Sun-Earth magnetic field
with observations available at present and in near future.
---------------------------------------------------------
Title: Computational Acoustics in Spherical Geometry: Steps toward
Validating Helioseismology
Authors: Hanasoge, S. M.; Larsen, R. M.; Duvall, T. L., Jr.; De Rosa,
M. L.; Hurlburt, N. E.; Schou, J.; Roth, M.; Christensen-Dalsgaard,
J.; Lele, S. K.
2006ApJ...648.1268H Altcode:
Throughout the past decade, detailed helioseismic analyses of
observations of solar surface oscillations have led to advances in our
knowledge of the structure and dynamics of the solar interior. Such
analyses involve the decomposition of time series of the observed
surface oscillation pattern into its constituent wave modes, followed
by inversion procedures that yield inferences of properties of the
solar interior. While this inverse problem has been a major focus in
recent years, the corresponding forward problem has received much less
attention. We aim to rectify this situation by taking the first steps
toward validating and determining the efficacy of the helioseismic
measurement procedure. The goal of this effort is to design a means
to perform differential studies of various effects such as flows and
thermal perturbations on helioseismic observables such as resonant
frequencies, travel-time shifts, etc. Here we describe our first
efforts to simulate wave propagation within a spherical shell,
which extends from 0.2 to about 1.0004 R<SUB>solar</SUB> (where
R<SUB>solar</SUB> is the radius of the Sun) and which possesses a
solar-like stratification. We consider a model containing no flows
that will serve as a reference model for later studies. We discuss the
computational procedure, some difficulties encountered in a simulation
of this kind, and the means to overcome them. We also present techniques
used to validate the simulation.
---------------------------------------------------------
Title: Non-linear Force-free Modeling: Applications To Solar Data
Authors: De Rosa, Marc L.; Schrijver, C. J.; Metcalf, T. R.; NLFFF Team
2006SPD....37.1805D Altcode: 2006BAAS...38..247D
Understanding the conditions under which solar magnetic fields can
destabilizeto cause flares and other eruptive events requires a
quantitativeunderstanding of the coronal magnetic field and of the
currents that itcarries. Because no direct measurements of magnetic
fields and current withincoronal volumes exist, the coronal field is
typically modeled usinginformation contained in photospheric vector
magnetograms, to be compared toH-alpha images of the chromosphere
and EUV and X-ray imagery of the corona.We report on recent results
of a team effort to further understand theintricacies of non-linear
force-free extrapolations of the coronal magneticfield, presenting
results from several solar and solar-like test cases. Wealso consider
the use of such coronal field modeling in the upcoming Solar-Band
SDO missions.
---------------------------------------------------------
Title: The Consequences Of Active-region Inflows On The Large-scale
Dispersal Of Magnetic Field Across The Solar Surface.
Authors: Schrijver, Carolus J.; De Rosa, M. L.; Hurlburt, N. E.
2006SPD....37.0716S Altcode: 2006BAAS...38..230S
Helioseismic analysis of near-surface modes recently revealed horizontal
flows near the solar surface towards regions with enhanced magnetic
activity. The magnitude of these flows appears to increase with the
magnetic flux contained within them. Such flows help to confine magnetic
flux to the activity belt and perhaps even to theactive regions within
which the field emerges, and will likely slow the random-walk dispersal
of the field. We report on experiments witha surface flux dispersal
model to study the consequences of such inflows towards strong-flux
regions. We constrain the flow magnitudeby comparing results of a flux
assimilation model to solar observations over six-month intervals
throughout the last solar cycle. The best-fit model is then used to
quantify the effects of these flows on the Sun's global dipole and
quadrupole fields on time scales of multiple centuries.
---------------------------------------------------------
Title: The PFSS Model in the Context of Impulsive SEP Events
Authors: Nitta, Nariaki; De Rosa, M.
2006SPD....37.2406N Altcode: 2006BAAS...38..251N
We have located the solar sources of 67 impulsive solar energetic
particle (SEP) events, using type III bursts to narrow down the times
of particle injection in the solar corona. This information serves
as a direct means to test the model of the Sun-Earth magnetic field
connection because the particles simply trace the field lines. We
consider the standard technique to model the Sun-Earth magnetic field,
known as the potential field source surface (PFSS) model for the coronal
part and the Parker spiral for the interplanetary part. In each of
selected SEP events, we calculate the distance of the footpoint of
the well-connected field line from the observed source location. It is
found that the technique does not work as well as when it is used to
predict the solar wind speed and the polarity of the interplanetary
magnetic field. We suggest what we need to do to better understand
the Sun-Earth magnetic field connection, or, more broadly speaking,
the interplanetary magnetic field, which is an important element in
NASA's Exploration Initiative.
---------------------------------------------------------
Title: Nonlinear Force-Free Modeling of Coronal Magnetic Fields Part
I: A Quantitative Comparison of Methods
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Metcalf, Thomas R.;
Liu, Yang; McTiernan, Jim; Régnier, Stéphane; Valori, Gherardo;
Wheatland, Michael S.; Wiegelmann, Thomas
2006SoPh..235..161S Altcode:
We compare six algorithms for the computation of nonlinear force-free
(NLFF) magnetic fields (including optimization, magnetofrictional,
Grad-Rubin based, and Green's function-based methods) by evaluating
their performance in blind tests on analytical force-free-field models
for which boundary conditions are specified either for the entire
surface area of a cubic volume or for an extended lower boundary
only. Figures of merit are used to compare the input vector field to
the resulting model fields. Based on these merit functions, we argue
that all algorithms yield NLFF fields that agree best with the input
field in the lower central region of the volume, where the field and
electrical currents are strongest and the effects of boundary conditions
weakest. The NLFF vector fields in the outer domains of the volume
depend sensitively on the details of the specified boundary conditions;
best agreement is found if the field outside of the model volume is
incorporated as part of the model boundary, either as potential field
boundaries on the side and top surfaces, or as a potential field in
a skirt around the main volume of interest. For input field (B) and
modeled field (b), the best method included in our study yields an
average relative vector error E<SUB>n</SUB> = « |B−b|»/« |B|» of
only 0.02 when all sides are specified and 0.14 for the case where only
the lower boundary is specified, while the total energy in the magnetic
field is approximated to within 2%. The models converge towards the
central, strong input field at speeds that differ by a factor of one
million per iteration step. The fastest-converging, best-performing
model for these analytical test cases is the Wheatland, Sturrock, and
Roumeliotis (2000) optimization algorithm as implemented by Wiegelmann
(2004).
---------------------------------------------------------
Title: Experimental investigation of dynamic photo-thermal effect
Authors: De Rosa, M.; Marin, F.; Marino, F.; Arcizet, O.; Heidmann,
A.; Pinard, M.
2006CQGra..23S.259D Altcode:
In an optical interferometer, a part of the laser power is absorbed
by the mirrors and gives rise to surface displacements through thermal
expansion. The position measurement sensitivity is, therefore, limited
by the shot noise of the absorbed radiation. This phenomenon is called
the photo-thermal effect and its typical frequency dependence and size
can span over several orders of magnitude, depending on the mirror
material and temperature, hence it is crucial to have an accurate model
extending over such a large range. We present an extensive experimental
investigation of dynamic photo-thermal effects, covering more than
seven decades in frequency and including finite mirror size effects
(low frequency) and coating effects (high frequency) and showing the
dependence on the beam waist. A specific extension of the basic model
is being developed that can well explain the results.
---------------------------------------------------------
Title: Canard orbits in Fabry-Perot cavities induced by radiation
pressure and photothermal effects
Authors: Marino, F.; de Rosa, M.; Marin, F.
2006PhRvE..73b6217M Altcode:
A theoretical study of a high-finesse Fabry-Perot cavity considering
radiation pressure and photothermal displacement is reported. We show
that the competition between these two effects induces a different
kind of dynamic behavior in such a system, consisting of canard orbits
and excitability. The transition between the excitable regime and the
canard oscillations, occurring through a supercritical Hopf bifurcation,
appears in an order compatible with the van der Pol FitzHugh-Nagumo
equations. Besides its interest as a study of general nonlinear
dynamics, the characterization of the effects described is critical
for high sensitivity interferometric displacement measurements as
those employed for gravitational waves detection.
---------------------------------------------------------
Title: Small-Scale Surface Flows and their Implications for Solar
Activity
Authors: De Rosa, Marc L.
2006IAUS..233...25D Altcode:
The broad range of dynamics exhibited by plasma motions within the
solar interior affects many aspects of the generation and transport
of magnetic fields during the solar magnetic activity cycle. On the
photosphere, such dynamics include the differential rotation, meridional
flows, and a hierarchy of convection cells, and these fluid motions are
observed to readily advect any small-scale magnetic fields embedded
within them. While the effects of large-scale flows on the global
activity cycle are well known, it is becoming increasingly apparent
that small-scale dynamics can also affect global magnetic activity
throughout the solar cycle. Such effects include variations in the
strength of the magnetic dipole moment with time, and the timing of
the reversals of the polar-cap flux. In this article, several aspects
of this coupling between small and large scales will be illustrated,
and the implications of such coupling on the solar activity cycle will
be discussed.
---------------------------------------------------------
Title: The status of the VIRGO experiment
Authors: Acernese, F.; Amico, P.; Arnaud, N.; Babusci, D.; Ballardin,
G.; Barille, R.; Barone, F.; Barsuglia, M.; Beauville, F.; Bellachia,
F.; Bizouard, M. A.; Boccara, C.; Boget, D.; Bondu, F.; Bourgoin,
C.; Bozzi, A.; Bracci, L.; Braccini, S.; Bradaschia, C.; Brillet,
A.; Brisson, V.; Brocco, L.; Buskulic, D.; Cachenaut, J.; Calamai,
G.; Calloni, E.; Campagna, E.; Casciano, C.; Cattuto, C.; Cavalier,
F.; Cavaliere, S.; Cavalieri, R.; Cella, G.; Chassande-Mottin, E.;
Chollet, F.; Cleva, F.; Cokelaer, T.; Conforto, G.; Cortese, S.;
Coulon, J. P.; Cuoco, E.; Dattilo, V.; Davier, P. Y.; de Rosa, M.;
de Rosa, R.; di Fiore, L.; di Virgilio, A.; Dujardin, B.; Dominici,
P.; Eleuteri, A.; Enard, D.; Evangelista, G.; Fabbroni, L.; Ferrante,
I.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Forest, D.; Fournier,
J. D.; Fournier, L.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Ganau,
P.; Gennai, A.; Gennaro, G.; Giacobone, L.; Giazotto, A.; Giordano,
G.; Girard, C.; Gougoulat, G.; Guigi, G.; Heitmann, H.; Hello, P.;
Hermel, R.; Heusse, P.; Holloway, L.; Honglie, F.; Iannarelli, M.;
Journet, L.; Krecklbergh, S.; Lagrange, B.; La Penna, P.; Leliboux,
M.; Leiunard, B.; Lomtadze, T.; Loriette, V.; Losurda, G.; Loupias,
M.; Mackowski, J. M.; Majorana, E.; Man, C. N.; Marchesoni, F.; Marion,
F.; Martelli, F.; Masserot, A.; Massonnet, L.; Mataguez, S.; Menzinger,
F.; Mazzoni, M.; Michel, C.; Milano, L.; Montorio, J. L.; Moreau, F.;
Moreau, J.; Morgado, M.; Mornet, F.; Mours, B.; Mugnier, P.; Nenci,
F.; Pacheco, J.; Pai, A.; Palomba, C.; Paoletti, F.; Paoli, A.; Paoli,
L.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Perciballi, M.;
Peruzzi, S.; Perniola, B.; Pinard, L.; Poggiani, R.; Pololizio, P.;
Porter, E.; Puccinelli, S.; Punturo, M.; Puppo, P.; Qipiani, K.;
Ramonet, J.; Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.;
Richard, F.; Roger, J. P.; Ruggi, P.; Russo, G.; Solimeno, S.; Stanga,
R.; Taddei, R.; Teuler, J. M.; Tournfier, E.; Travasso, F.; Trinquet,
H.; Turri, E.; Varvella, M.; Verkind, D.; Vetran, F.; Veziant, O.;
Viceré, A.; Vilalte, S.; Vinet, J. Y.; Vocca, H.; Yvert, M.; Zhang, Z.
2006rdgp.conf..427A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Influence of Small-scale Dynamics on Large-scale Solar Activity
Authors: De Rosa, M. L.
2005ASPC..346..337D Altcode:
The range of dynamical scales of motion within the solar convection zone
is estimated to span at least six orders of magnitude in both space
and time. Despite such breadth of scales, fluid motions occurring
on the smallest spatial and temporal scales are expected to play an
important role in the establishment and maintenance of the large-scale
differential rotation and meridional flows within the turbulent
convection zone. In turn, flows on all scales affect the transport
of magnetic fields within the solar interior, causing field to be
continually regenerated and redistributed. The surface manifestation
of these magnetic fields exhibits a surprising degree of regularity,
despite such fields being embedded in an extremely turbulent medium. The
largest magnetic fields observed at the surface follow episodic patterns
of emergence and evolution that collectively form each activity cycle,
but there is also evidence that smaller-scale magnetic fields also
possess an imprint of such cyclic behavior. This article focuses on
two specific aspects of the coupling between small and large scales
on the sun. First, the maintenance of the interior differential
rotation by small-scale Reynolds stresses is addressed, followed by
an investigation into the effects of small-scale surface magnetism on
the strength of the surface dipole and the timing of its reversals.
---------------------------------------------------------
Title: Erratum: Upper Limits on Gravitational-Wave Emission
in Association with the 27 Dec 2004 Giant Flare of SGR1806-20
[Phys. Rev. Lett. 95, 081103 (2005)]
Authors: Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; Conti,
L.; de Rosa, M.; Falferi, P.; Fortini, P.; Inguscio, M.; Liguori, N.;
Marin, F.; Mezzena, R.; Mion, A.; Ortolan, A.; Prodi, G. A.; Poggi,
S.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato, G.; Vinante,
A.; Vitale, S.; Zendri, J. P.
2005PhRvL..95m9903B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Upper Limits on Gravitational-Wave Emission in Association
with the 27 Dec 2004 Giant Flare of SGR1806-20
Authors: Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; Conti,
L.; de Rosa, M.; Falferi, P.; Fortini, P.; Inguscio, M.; Liguori, N.;
Marin, F.; Mezzena, R.; Mion, A.; Ortolan, A.; Prodi, G. A.; Poggi,
S.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato, G.; Vinante,
A.; Vitale, S.; Zendri, J. P.
2005PhRvL..95h1103B Altcode: 2005astro.ph..6142B
At the time when the giant flare of SGR1806-20 occurred, the AURIGA
“bar” gravitational-wave (GW) detector was on the air with a noise
performance close to stationary Gaussian. This allows us to set relevant
upper limits, at a number of frequencies in the vicinities of 900 Hz,
on the amplitude of the damped GW wave trains, which, according to
current models, could have been emitted, due to the excitation of
normal modes of the star associated with the peak in x-ray luminosity.
---------------------------------------------------------
Title: The Nonpotentiality of Active-Region Coronae and the Dynamics
of the Photospheric Magnetic Field
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M.;
Metcalf, Thomas R.
2005ApJ...628..501S Altcode:
The magnetic field in the solar photosphere frequently carries strong
electric currents, even though the global coronal configuration often
resembles a potential field ringed by the heliospheric current sheet. To
understand this, we compare TRACE EUV images of active-region coronae
and potential-field source-surface extrapolations based on SOHO MDI
magnetograms for 95 active regions. We conclude that significant
nonpotentiality of the overall active-region coronal field occurs
(1) when new flux has emerged within or very near a region within
the last ~30 hr, resulting in complex polarity separation lines, or
(2) when rapidly evolving, opposite-polarity concentrations are in
contact at 4" resolution. If these criteria are met by more than 15%
of the region's flux, they correctly identify the (non) potentiality of
active-region coronae in 88% of the cases. Flares are found to occur
2.4 times more frequently in active regions with nonpotential coronae
than in near-potential regions, while their average X-ray peak flare
brightness is 3.3 times higher. We suggest that the currents associated
with coronal nonpotentiality have a characteristic growth and decay
timescale of ~10-30 hr. We find that shear flows drive enhanced flaring
or coronal nonpotentiality only if associated with complex and dynamic
flux emergence within the above timescale. We discuss the implications
of this finding for the modeling of the coronal-heliospheric coupling.
---------------------------------------------------------
Title: Non-linear force-free field modeling: model techniques,
boundary conditions, hares, and hounds
Authors: Schrijver, C. J.; De Rosa, M. L.; Metcalf, T.
2005AGUSMSH31A..05S Altcode:
Understanding the conditions under which solar magnetic fields can
destabilize to erupt in flares and coronal mass ejections requires
a quantitative understanding of the coronal magnetic field and of
the currents that it carries. The increased availability of vector
magnetograms, together with EUV and X-ray coronal images, should
provide adequate constraints to model the coronal field, and thus to
visualize its 3D geometry and to measure the available free energy
and helicity. Non-linear force-free fields (NLFFF) are likely a useful
model to use when extrapolating the solar surface field upward into the
coronal volume. It may even be possible to use the observed trajectories
of coronal loops, evident in EUV images of the corona, as a further
constraint. We present initial results of a team effort to understand
the intricacies of NLFFF modeling: we discuss and evaluate comparisons
of NLFFF models computed with different models and applications of
boundary conditions, and look ahead to full coronal field modeling
for the upcoming Solar-B and SDO missions.
---------------------------------------------------------
Title: Simulations Of Acoustic-Flow Interaction In Spherical Geometry:
Steps Toward Validating Helioseismology
Authors: Hanasoge, S. M.; Duvall, T. L.; De Rosa, M. L.; Hurlburt,
N. E.
2005AGUSMSP11B..11H Altcode:
We simulate acoustic wave interaction with flows in spherical geometry
with the specific intent of using them as artificial data for validation
of helioseismology. The numerical procedure is pseudo-spectral; we
employ a spherical harmonic representation of the spherical surface,
compact finite differences in the radial direction and a fourth order
Runge-Kutta time stepping scheme. We also excite surface gravity modes,
modeling all waves as linear perturbations to the background state so as
to gain further insight into wave-flow interaction. Towards validation,
we apply techniques of helioseismology to the artificial data to
determine the efficacy of the helioseismic inversion procedure. In
other words, we are attempting the forward problem.
---------------------------------------------------------
Title: Comparison of Heliospheric Magnetic Field Lines from PFSS
Models with SEP Observations
Authors: Nitta, N. V.; Liu, Y.; De Rosa, M. L.
2005AGUSMSH13A..12N Altcode:
Impulsive Solar Energetic Particle (SEP) events are thought to come
locally from solar flares, in contrast with large gradual SEP events
that are attributed to extended shocks driven by fast CMEs. For several
impulsive SEP events, we identified the possible solar sources, using
the timings of type III bursts. The solar sources thus indentified
tend to be minor brightenings, sometimes not even detectable by the
GOES X-ray Spectrometer. We found whether the source active region is
open to the heliosphere, using potential field source surface (PFSS)
models. We also traced field lines from the spacecraft observing SEPs
to the source surface assuming constant solar wind speed, and then
mapped them to the photosphere using PFSS models. In a number of cases,
these traced field lines go close to the flare site. In other cases,
their foot-points are far from the flare, or the source active region
shows no open field lines. We interpret these various results in terms
of different magnetograms for PFSS modeling, and assumptions used in
the models.
---------------------------------------------------------
Title: Numerical Simulations of Bipolar Magnetic Field Decay in
Turbulent Convection
Authors: De Rosa, M. L.; Hurlburt, N. E.
2005AGUSMSP11C..02D Altcode:
We present numerical simulations of compressible magnetoconvection
in spherical segments, seeking to examine the decay of active region
magnetic fields on the sun. It is surprising that after their emergence,
active regions are observed to persist in relative stasis for long
periods of time (weeks to months) before suddenly disintegrating. We
perform a series of calculations to investigate this process, in which
we drive turbulent convection (Rayleigh numbers of order 107) within
two- and three-dimensional spherical segments, and measure the decay
rates of the embedded bipolar magnetic fields.
---------------------------------------------------------
Title: Interferometric readout for acoustic gravitational wave
detectors
Authors: Conti, L.; de Rosa, M.; Marin, F.; Taffarello, L.; Cerdonio,
M.
2005AIPC..751...75C Altcode:
A review is given of the optical readout for acoustic gravitational
wave detectors, ranging from the working principle, to the experimental
data and to the future developments. A summary is also given of the
scientific results obtained while developing the optical readout for a
bar detector, of interest also for the broader interferometer community.
---------------------------------------------------------
Title: Coronal heating and the appearance of solar and stellar coronae
Authors: Schrijver, C. J.; Sandman, A. W.; Aschwanden, M. J.; De Rosa,
M. L.
2005ESASP.560...65S Altcode: 2005csss...13...65S
No abstract at ADS
---------------------------------------------------------
Title: Evolution of Solar Supergranulation
Authors: De Rosa, Marc L.; Toomre, Juri
2004ApJ...616.1242D Altcode:
The structure and evolution of solar supergranulation is studied using
horizontal velocity fields, deduced from applying local correlation
tracking (LCT) techniques to full-disk, line-of-sight Doppler velocity
data observed by the Michelson Doppler Imager on board the Solar
and Heliospheric Observatory spacecraft. Two 45° square regions
of photospheric plasma, one of the quiet Sun and one with increased
magnetic activity, are tracked for as long as they remain visible on
the disk of the Sun (about 6 days), enabling a determination of the
complete life histories of over 3000 supergranules in each region. With
this method, the horizontal outflows associated with the pattern of
supergranulation are revealed with clarity, even for locations near
disk center where little of the horizontal velocity field is projected
into the line of sight. The LCT flow mappings are of sufficient temporal
extent that they can be used to study the complex evolution of a broad
spectrum of supergranules, revealing that merging and fragmentation
events figure prominently in the life histories of more than half of the
supergranules in each data set. Such dynamics lead to many short-lived
supergranules (about 75% of the total population) having lifetimes of
less than 24 hr, coexisting among numerous long-lived supergranules,
many of which exist for several days. Average supergranular lifetimes
lie in the 16-23 hr range, although about 7% of all are recognizable
for time periods of 48 hr or more. The average supergranular cell
diameter lies in the 12-20 Mm range, with smaller cells more prevalent
in areas of greater magnetism. There exists a tendency for larger cells
to preferentially have longer lifetimes when embedded in a region of
increased magnetic flux.
---------------------------------------------------------
Title: The Coronal Heating Mechanism as Identified by Full-Sun
Visualizations
Authors: Schrijver, Carolus J.; Sandman, Anne W.; Aschwanden, Markus
J.; De Rosa, Marc L.
2004ApJ...615..512S Altcode:
We constrain the properties of the mechanism(s) responsible for the
bulk of the heating of the corona of the Sun by simulating, for the
first time, the appearance of the entire solar corona. Starting from
full-sphere magnetic field maps for 2000 December 1 and 8, when
the Sun was moderately active, we populate nearly 50,000 coronal
field lines with quasi-static loop atmospheres. These atmospheres
are based on heating flux densities F<SUB>H</SUB> that depend in
different ways on the loop half-length L, the field strength B at
the chromospheric base, the loop expansion with height, and the
heating scale height. The best match to X-ray and EUV observations
of the corona over active regions and their environs is found for
F<SUB>H</SUB>~4×10<SUP>14</SUP>B<SUP>1.0+/-0.3</SUP>/L<SUP>1.0+/-0.5</SUP>
(in ergs cm<SUP>-2</SUP> s<SUP>-1</SUP> for B in Mx cm<SUP>-2</SUP> and
L in cm), while allowing for substantial loop expansion with increasing
height, and for a heating scale height that is at least a sizeable
fraction of the loop length. This scaling for coronal heating points
to DC reconnection at tangential discontinuities as the most likely
coronal heating mechanism, provided that the reconnection progresses
proportional to the Alfvén velocity. The best-fit coronal filling
factor equals unity, suggesting that most of the corona is heated most
of the time. We find evidence that loops with half-lengths exceeding
~100,000 km are heated significantly more than suggested by the above
scaling, possibly commensurate with the power deposited in the open
field of coronal holes.
---------------------------------------------------------
Title: Supergranular and Larger-Scale Surface Flows Within Magnetic
Environments
Authors: De Rosa, M. L.
2004ESASP.559..404D Altcode: 2004soho...14..404D
No abstract at ADS
---------------------------------------------------------
Title: Tomographic 3D-Modeling of the Solar Corona with FASR
Authors: Aschwanden, Markus J.; Alexander, David; de Rosa, Marc L.
2004ASSL..314..243A Altcode: 2003astro.ph..9501A
The Frequency-Agile Solar Radiotelescope (FASR) literally opens up
a new dimension, in addition to the 3D Euclidian geometry—the
frequency dimension. The 3D geometry is degenerated to 2D in all
images from astronomical telescopes, but the additional frequency
dimension allows us to retrieve the missing third dimension by means of
physical modeling. We call this type of 3D reconstruction Frequency
Tomography. In this study we simulate a realistic 3D model of an
active region, composed of 500 coronal loops with the 3D geometry
[x(s), y(s), z(s)] constrained by magnetic field extrapolations and
the physical parameters of the density n<SUB>e</SUB>(s) and temperature
T<SUB>e</SUB>(s) given by hydrostatic solutions. We simulate a series
of 20 radio images in a frequency range of ν=0.1-10 GHz, anticipating
the capabilities of FASR, and investigate what physical information
can be retrieved from such a dataset. We discuss also forward-modeling
of the chromospheric and Quiet Sun density and temperature structure,
another primary goal of future FASR science.
---------------------------------------------------------
Title: Numerical Models of solar Magnetoconvection: Toward a Coupling
to the Corona
Authors: De Rosa, M. L.; Hurlburt, N. E.
2004AAS...204.3908D Altcode: 2004BAAS...36..715D
We present numerical simulations of a stratified magnetized fluid,
confined to a spherical shell, that approximates the transition from
a high- to low-beta regime, similar to the conditions present at the
solar photosphere. In these simulations, a model corona atmosphere is
situated above a convectively unstable, high-beta fluid layer. As a
result, the dynamics associated with evolving magnetic features in the
solar atmosphere can be modeled in a manner that is self-consistent
with the convective motions that provide the driving. Our simulations
exhibit arcade-like structures that undergo reconnection as a result
of the supergranular-scale fluid motions in the convective layer below,
and discuss possible observational consequences.
---------------------------------------------------------
Title: Solar Coronal Heating Inferred from Full-disk Models of
Coronal Emission
Authors: Schrijver, C. J.; Sandman, A. W.; De Rosa, M. L.; Aschwanden,
M. J.
2004AAS...204.9501S Altcode: 2004BAAS...36Q.826S
The appearance of the corona as viewed by different instruments, as
well as its global spectral irradiance, sensitively depends on how
coronal heating scales with the properties of the coronal magnetic
field. We explore a variety of scaling dependences by simulating the
appearance of the full-disk solar corona as viewed by SOHO/EIT and by
YOHKOH/SXT, based on observed photospheric magnetic fields combined with
a potential-field source-surface model. This leads us to conclude that
the best match to X-ray and EUV observations of the corona over active
regions and their environments is found for a heating flux density going
into the corona that scales linearly with the field strength at the
coronal base and roughly inversely with loop length. This scaling points
to DC reconnection at tangential discontinuities as the most likely
coronal heating mechanism, provided that the reconnection progresses
at a rate proportional to the Alfven velocity. We also find that the
best-fit coronal filling factor equals unity, suggesting that most of
the corona is heated most of the time. We find evidence that loops with
half lengths exceeding approximately 100,000 km are heated significantly
more than suggested by the above scaling, possibly commensurate with
the power deposited in the open field of coronal holes.
---------------------------------------------------------
Title: Molecular and Compound-Specific Isotopic Study of
Monocarboxylic Acids in Murchison and Antarctic Meteorites
Authors: Huang, Y.; Wang, Y.; de'Rosa, M.; Fuller, M.; Pizzarello, S.
2004LPI....35.1888H Altcode:
We studied molecular distributions and C and H isotopic ratios of
individual monocarboxylic acids in Murchison and EET96029,20 using a
new and improved sample indtroduction method (SPME), and reveal new
monoacids and isotopic characteristics.
---------------------------------------------------------
Title: An optical readout scheme for advanced acoustic GW detectors
Authors: Marin, F.; Conti, L.; De Rosa, M.
2004CQGra..21S1237M Altcode: 2004CQGra..21.1237M
We have recently proposed a large reading area, optical readout scheme
for advanced acoustic gravitational wave (GW) detectors. In this
work we focus the analysis on a dual-cylinder detector. A specific
configuration is designed and the expected performance is calculated.
---------------------------------------------------------
Title: Solar-like convective and coronal layers in a single numerical
model
Authors: Hurlburt, N.; De Rosa, M.
2004cosp...35.3551H Altcode: 2004cosp.meet.3551H
We investigate the coupling between turbulent magnetoconvection
and an atmospheric layer on the sun using numerical simulations of
compressible fluids. The model consists of a stratified MHD fluid
spanning multiple scale heights, encompassing the transition of the
plasma beta from high to low values. Although a heat flux is imposed at
the lower boundary, only the lower portion of the domain where the beta
is high is convectively unstable. The upper portions are stabilized by
a parameterized heating function and the presence of a strong magnetic
field and, similar to the solar chromosphere and corona. As a result,
the dynamics associated with evolving magnetic features in the solar
atmosphere can be modeled in a manner that is self-consistent with the
convective motions that provide the driving. We present simulations
of arcade-like reconnection in the presence of supergranular-scale
flows and discuss possible observational consequences.
---------------------------------------------------------
Title: Modeling solar magnetoconvection and coronal structures
Authors: Hurlburt, Neal E.; De Rosa, Marc L.
2004IAUS..223..253H Altcode: 2005IAUS..223..253H
We present results of an investigation into the coupling
between solar-like magnetoconvection and coronal structures using
self-consistent numerical simulations of compressible fluids. The
model consists of a stratified MHD fluid spanning multiple scale
heights, encompassing the transition of the plasma beta from high to
low values. The lower portion of the domain, where the beta is high,
is convectively unstable while the upper portion is stabilized by the
presence of a strong magnetic field and energy losses. As a result,
the dynamics associated with evolving magnetic features in the solar
atmosphere can be modelled in a manner that is self-consistent with the
convective motions that provide the driving. We present simulations of
arcade-like reconnection in the presence of supergranular-scale flows.
---------------------------------------------------------
Title: TRACE and SOHO/MDI Observations of 3 Rotating Sunspots in
AR9002 and AR9004, Along With Modeled Coronal Magnetic Fields
Authors: Nightingale, R. W.; Schrijver, C. J.; De Rosa, M. L.
2003AGUFMSH42B0511N Altcode:
The TRACE data set provides a view of the solar atmosphere from the
photosphere in white light, through the transition region in ultraviolet
wavelengths, and into the corona in extreme ultraviolet wavelengths
(EUV). From May 16-23, 2000 TRACE and MDI/SOHO observed at least 3
rotating sunspots in AR9002 and AR9004 at several wavelengths. Over this
time period several small flares, along with a CME on May 23, occurred
in these regions. In addition we have potential-field renderings of the
coronal magnetic fields for the TRACE pointings, extrapolated based on
the Virtual Starlab forecaster data, which in turn has been generated
from the MDI/SOHO observations. An analysis of the rotating sunspots,
together with images and movies, will be provided for these active
regions, accompanied by images of the extrapolated coronal magnetic
fields for comparison with images of the TRACE 1-1.5 MK EUV loops. This
work was supported by NASA, in part under the TRACE contract NAS5-38099
and in part under the MDI/SOHO contract NAG5-13261.
---------------------------------------------------------
Title: Coronal heating and the appearance of the solar corona
Authors: Schrijver, C. J.; Sandman, A.; De Rosa, M. L.; Aschwanden,
M. J.
2003AGUFMSH32A1104S Altcode:
The details of the dependence of coronal heating on the conditions
within the corona determine the appearance of the corona as viewed
by different instruments. For example, strong fields at the base of
short loops cause relatively hot, X-ray bright loops, whereas the
much weaker fields over the quiet Sun result in cooler, EUV bright
loops. Any dependence of the volume heating rates on local conditions
(such as height or field strength) has a signature in the thermal
profiles along the loops, translating into an appearance that depends
on the instrumental pass band. In this preliminary study, we explore
how such dependences of coronal heating on coronal conditions affect
the appearance of the solar corona, and investigate the consequences
for the global EUV and X-ray spectral irradiance. These results will
eventually be used to compute the solar spectral irradiance in the
EUV and X-rays for quiescent conditions throughout the solar cycle.
---------------------------------------------------------
Title: Data analysis methods for non-Gaussian, nonstationary and
nonlinear features and their application to VIRGO
Authors: Virgo Collaboration; Acernese, F.; Amico, P.; Arnaud, N.;
Babusci, D.; Ballardin, G.; Barillé, R.; Barone, F.; Barsuglia,
M.; Beauville, F.; Bellachia, F.; Bizouard, M. A.; Boccara,
C.; Boget, D.; Bondu, F.; Bourgoin, C.; Bozzi, A.; Braccini, S.;
Bradaschia, C.; Brillet, A.; Brisson, V.; Brocco, L.; Buskulic, D.;
Cachenaut, J.; Calamai, G.; Calloni, E.; Campagna, E.; Casciano,
C.; Cattuto, C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cella,
G.; Chassande-Mottin, E.; Chollet, F.; Cleva, F.; Cokelaer, T.;
Conforto, G.; Cortese, S.; Coulon, J. P.; Cuoco, E.; Dattilo, V.;
Y Davíd, P.; Davier, M.; De Rosa, M.; De Rosa, R.; Di Fiore, L.;
Di Virgilio, A.; Dujardin, B.; Dominici, P.; Eleuteri, A.; Enard,
D.; Evangelista, G.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio,
R.; Forest, D.; Fournier, J. D.; Fournier, L.; Frasca, S.; Frasconi,
F.; Gammaitoni, L.; Ganau, P.; Gennai, A.; Gennaro, G.; Giacobone,
L.; Giazotto, A.; Giordano, G.; Girard, C.; Gougoulat, G.; Guidi,
G. M.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.; Holloway,
L.; Honglie, F.; Iannarelli, M.; Journet, L.; Krecklbergh, S.;
Lagrange, B.; La Penna, P.; Leliboux, M.; Lieunard, B.; Lomtadze, T.;
Loriette, V.; Losurdo, G.; Loupias, M.; Mackowski, J. M.; Majorana,
E.; Man, C. N.; Marchesoni, F.; Marion, F.; Martelli, F.; Masserot,
A.; Massonnet, L.; Mataguez, S.; Menzinger, F.; Mazzoni, M.; Michel,
C.; Milano, L.; Montorio, J. L.; Moreau, F.; Moreau, J.; Morgado,
N.; Mornet, F.; Mours, B.; Mugnier, P.; Nenci, F.; Pacheco, J.; Pai,
A.; Palomba, C.; Paoletti, F.; Paoli, A.; Paoli, L.; Pasqualetti,
A.; Passaquieti, R.; Passuello, D.; Perciballi, M.; Peruzzi, S.;
Perniola, B.; Pinard, L.; Poggiani, R.; Popolizio, P.; Porter, E.;
Puccinelli, S.; Punturo, M.; Puppo, P.; Qipiani, K.; Ramonet, J.;
Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.; Richard, F.;
Roger, J. P.; Ruggi, P.; Russo, G.; Solimeno, S.; Stanga, R.; Taddei,
R.; Teuler, J. M.; Tournefier, E.; Travasso, F.; Trinquet, H.; Turri,
E.; Varvella, M.; Verkindt, D.; Vetrano, F.; Veziant, O.; Viceré,
A.; Vilalte, S.; Y Vinet, J.; Vocca, H.; Yvert, M.; Zhang, Z.
2003CQGra..20S.915V Altcode:
The commissioning of the VIRGO central interferometer occasioned the
implementation and tests of various algorithms for the characterization
of the non-Gaussianity, non-stationarity and non-linearity of the
dark fringe data. This library of prototypes will serve as groundwork
for the near commissioning of VIRGO (full scale). We make a summary
of the activities on that subject including the description of the
selected algorithms and some results obtained with the data of the
engineering runs.
---------------------------------------------------------
Title: Status of VIRGO
Authors: Virgo Collaboration; Acernese, F.; Amico, P.; Arnaud, N.;
Babusci, D.; Ballardin, G.; Barillé, R.; Barone, F.; Barsuglia,
M.; Beauville, F.; Bellachia, F.; Bizouard, M. A.; Boccara,
C.; Boget, D.; Bondu, F.; Bourgoin, C.; Bozzi, A.; Braccini, S.;
Bradaschia, C.; Brillet, A.; Brisson, V.; Brocco, L.; Buskulic, D.;
Cachenaut, J.; Calamai, G.; Calloni, E.; Campagna, E.; Casciano,
C.; Cattuto, C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cella,
G.; Chassande-Mottin, E.; Chollet, F.; Cleva, F.; Cokelaer, T.;
Conforto, G.; Cortese, S.; Coulon, J. P.; Cuoco, E.; Dattilo, V.;
Y Davíd, P.; Davier, M.; De Rosa, M.; De Rosa, R.; Di Fiore, L.;
Di Virgilio, A.; Dujardin, B.; Dominici, P.; Eleuteri, A.; Enard,
D.; Evangelista, G.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio,
R.; Forest, D.; Fournier, J. D.; Fournier, L.; Frasca, S.; Frasconi,
F.; Gammaitoni, L.; Ganau, P.; Gennai, A.; Gennaro, G.; Giacobone,
L.; Giazotto, A.; Giordano, G.; Girard, C.; Gougoulat, G.; Guidi,
G. M.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.; Holloway,
L.; Honglie, F.; Iannarelli, M.; Journet, L.; Krecklbergh, S.;
Lagrange, B.; La Penna, P.; Leliboux, M.; Lieunard, B.; Lomtadze, T.;
Loriette, V.; Losurdo, G.; Loupias, M.; Mackowski, J. M.; Majorana,
E.; Man, C. N.; Marchesoni, F.; Marion, F.; Martelli, F.; Masserot,
A.; Massonnet, L.; Mataguez, S.; Menzinger, F.; Mazzoni, M.; Michel,
C.; Milano, L.; Montorio, J. L.; Moreau, F.; Moreau, J.; Morgado,
N.; Mornet, F.; Mours, B.; Mugnier, P.; Nenci, F.; Pacheco, J.; Pai,
A.; Palomba, C.; Paoletti, F.; Paoli, A.; Paoli, L.; Pasqualetti,
A.; Passaquieti, R.; Passuello, D.; Perciballi, M.; Peruzzi, S.;
Perniola, B.; Pinard, L.; Poggiani, R.; Popolizio, P.; Porter, E.;
Puccinelli, S.; Punturo, M.; Puppo, P.; Qipiani, K.; Ramonet, J.;
Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.; Richard, F.;
Roger, J. P.; Ruggi, P.; Russo, G.; Solimeno, S.; Stanga, R.; Taddei,
R.; Teuler, J. M.; Tournefier, E.; Travasso, F.; Trinquet, H.; Turri,
E.; Varvella, M.; Verkindt, D.; Vetrano, F.; Veziant, O.; Viceré,
A.; Vilalte, S.; Y Vinet, J.; Vocca, H.; Yvert, M.; Zhang, Z.
2003CQGra..20S.609V Altcode:
We report on the status of the VIRGO detector as of the beginning
of 2003. In particular, we summarize the results obtained during the
commissioning of the central portion of the detector, consisting of a
power-recycled Michelson interferometer, and we outline the steps which
will lead during 2003 and 2004 to the commissioning and operation of
the full scale, 3 km long VIRGO detector.
---------------------------------------------------------
Title: Asterospheric Magnetic Fields and Winds of Cool Stars
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M.
2003ApJ...590..493S Altcode:
This study addresses the winds and magnetic fields in the inner
asterospheres of Sun-like magnetically active stars by combining
empirical relationships between rotation rate and mass loss,
angular-momentum loss, and radiative losses with models of the magnetic
fields at the surfaces of cool stars and in their inner asterospheres
based on the solar example. Our models, for mean magnetic flux densities
up to 10 times solar, suggest that the asterospheric fields of such
stars are dominated by the large-scale dipole component of the surface
field, as is the case for the Sun. Hence, most of the time a single
current sheet is expected to separate domains of opposite magnetic
polarity; the current sheets of more active stars generally have smaller
latitudinal ripples. Magnetic braking requires that the total unsigned
asterospheric magnetic flux increase linearly with the stellar angular
velocity, which is a very much weaker increase than seen for the flux at
the stellar surface. We show that this can be achieved by an increase
in the radial distance at which the coronal field is forced open as
surface activity increases. Combined with measured mass-loss rates
and the assumption that the wind velocity is largely independent of
activity, this requires the wind's Alfvén radius to be nearly constant,
decreasing with surface activity with a power of only -0.16+/-0.13. We
point out that the surface flux density of energy needed to drive a
cool-star wind scales linearly with the unsigned surface magnetic flux
density, as does that needed to heat the corona.
---------------------------------------------------------
Title: The nature of impulsive solar energetic particle events
Authors: Nitta, N. V.; Hudson, H. S.; De Rosa, M. L.
2003SPD....34.1606N Altcode: 2003BAAS...35..833N
Impulsive solar energetic particle (SEP) events, as opposed to
gradual SEP events, are usually thought to originate from flares in
the well-connected regions. In order to test this idea, we compute
the solar locations of the field lines that cross the spacecraft
encountering particles from SEP events, and compare them with
the flare locations. We combine two frequently used techniques,
i.e., the ballistic approximation for the interplanetary magnetic
field and the potential-field source-surface model for the coronal
field. Such comparisons are made for selected impulsive SEP events
during 1995-2001. We check the validity of the techniques using
Yohkoh SXT and SOHO EIT images, which often show coronal holes on
the disk. Furthermore, we study the properties of the flares that are
identified with impulsive SEP events, and compare them with those of
other flares in the well-connected areas but without impulsive SEP
events. This will give us a clue as to the importance of the flare
processes relative to the magnetic field connectivity on the detection
of impulsive SEP events.
---------------------------------------------------------
Title: MHD Simulations Spanning the Convection Zone, Chromosphere,
and Corona
Authors: De Rosa, M. L.; Hurlburt, N. E.
2003SPD....34.0407D Altcode: 2003BAAS...35..811D
The dynamics associated with evolving magnetic structures in the solar
atmosphere are ultimately driven by vigorous convective motions below
the photosphere. There, nonlinear interactions between the flows
and fields lead to the transport of energy up into the atmosphere,
which is later converted to heat in the chromosphere and corona and
radiated into space. To investigate such dynamics, we have constructed
a self-consistent model of the sun encompassing the upper layers of the
convection zone, chromosphere, transition region, and lower corona. The
fully compressible magnetized fluid comprising the convective layer is
dynamically coupled to the atmosphere through the magnetic field. These
models allow us to investigate the dynamics associated with waves,
magnetic fields, and fluid motions within the solar atmosphere.
---------------------------------------------------------
Title: Room temperature gravitational wave bar detector with
optomechanical readout
Authors: Conti, L.; De Rosa, M.; Marin, F.; Taffarello, L.; Cerdonio,
M.
2003JAP....93.3589C Altcode: 2002gr.qc.....5115C
We present the full implementation of a room-temperature gravitational
wave bar detector equipped with an optomechanical readout. The bar
mechanical vibrations are read by a Fabry-Pérot interferometer whose
length changes are compared with a stable reference optical cavity by
means of a resonant laser. The detector performance is completely
characterized in terms of spectral sensitivity and statistical
properties of the fluctuations in the system output signal. This kind
of readout technique allows for wide-band detection sensitivity and we
can accurately test the model of the coupled oscillators for thermal
noise. Our results are very promising for cryogenic operation and
represent an important step towards significant improvements in the
performance of massive gravitational wave detectors.
---------------------------------------------------------
Title: Simulations of Near-Surface Solar Magnetoconvection Within
Localized Spherical Segments
Authors: De Rosa, M. L.; Hurlburt, N. E.
2003ASPC..293..229D Altcode: 2003tdse.conf..229D
Turbulent fluid motions near the surface of the sun, such as those
associated with the observed pattern of supergranulation, are thought
to play a role in the decay of the magnetic field within plage and
active regions on the sun. To investigate such dynamics, we have
constructed two related numerical simulations of fully compressible
magnetoconvecting fluids, each contained within a curved, spherical
segment that approximates the conditions within the upper part of the
solar convection zone. The spherical segment domains span 30 degrees in
latitude and 60 degrees in longitude, and have a radial extent of 4%
of the solar radius. We find that bipolar field configurations decay
on diffusive (Ohmic) time scales, rather than on turbulent decay time
scales, despite the network of convection cells around and within the
magnetized regions.
---------------------------------------------------------
Title: Photospheric and heliospheric magnetic fields
Authors: Schrijver, Carolus J.; De Rosa, Marc L.
2003SoPh..212..165S Altcode:
The magnetic field in the heliosphere evolves in response to the
photospheric field at its base. This evolution, together with the
rotation of the Sun, drives space weather through the continually
changing conditions of the solar wind and the magnetic field embedded
within it. We combine observations and simulations to investigate the
sources of the heliospheric field from 1996 to 2001. Our algorithms
assimilate SOHO/MDI magnetograms into a flux-dispersal model,
showing the evolving field on the full sphere with an unprecedented
duration of 5.5 yr and temporal resolution of 6 hr. We demonstrate
that acoustic far-side imaging can be successfully used to estimate
the location and magnitude of large active regions well before they
become visible on the solar disk. The results from our assimilation
model, complemented with a potential-field source-surface model for the
coronal and inner-heliospheric magnetic fields, match Yohkoh/SXT and
KPNO/He 10830 Å coronal hole boundaries quite well. Even subject to the
simplification of a uniform, steady solar wind from the source surface
outward, our model matches the polarity of the interplanetary magnetic
field (IMF) at Earth ∼3% of the time during the period 1997-2001
(independent of whether far-side acoustic data are incorporated into
the simulation). We find that around cycle maximum, the IMF originates
typically in a dozen disjoint regions. Whereas active regions are
often ignored as a source for the IMF, the fraction of the IMF that
connects to magnetic plage with absolute flux densities exceeding 50 Mx
cm<SUP>−2</SUP> increases from ≲10% at cycle minimum up to 30-50%
at cycle maximum, with even direct connections between sunspots and the
heliosphere. For the overall heliospheric field, these fractions are
≲1% to 20-30%, respectively. Two case studies based on high-resolution
TRACE observations support the direct connection of the IMF to magnetic
plage, and even to sunspots. Parallel to the data assimilation,
we run a pure simulation in which active regions are injected based
on random selection from parent distribution functions derived from
solar data. The global properties inferred for the photospheric and
heliospheric fields for these two models are in remarkable agreement,
confirming earlier studies that no subtle flux-emergence patterns or
field-dispersal properties are required of the solar dynamo beyond those
that are included in the model in order to understand the large-scale
solar and heliospheric fields.
---------------------------------------------------------
Title: Active regions as sources of the heliospheric field
Authors: Schrijver, C. J.; De Rosa, M. L.; Title, A. M.
2002AGUFMSH52A0436S Altcode:
The magnetic field in the heliosphere originates from a variety
of sources on the surface of the Sun, including mature, decaying,
and decayed active regions, as well as sunspots. The emergence of new
active regions together with the dispersal of flux from older active
regions causes the coronal magnetic field topology to continually
evolve, allowing previously closed-field regions to open into the
heliosphere and previously open-field regions to close. Such evolution
of the coronal field, together with the rotation of the Sun, drive
space weather through the continually changing conditions of the solar
wind and the magnetic field embedded within it. We combine observations
and numerical simulations by assimilating SOHO/MDI magnetograms into a
surface flux transport model, in order to investigate the origins of
the heliospheric field on the solar surface through the rising phase
of the current activity cycle. We find that around cycle maximum,
the interplanetary magnetic field (IMF) is typically rooted in a
dozen disjoint regions on the solar surface. Whereas active regions
are sometimes ignored as a source for the IMF, the fraction of the
IMF that connects directly to magnetic plage is found to reach up to
30-50%\ at cycle maximum, with even direct connections between sunspots
and the heliosphere. We further compare this data assimilation model
with a pure simulation model, in which the properties of the emergent
active regions were chosen at random from parent distribution functions
measured for the sun. The two models show remarkable agreement in the
temporal behavior of the sector structure of the IMF, in the magnitude
and time-behavior of the heliospheric field, and even in such global
properties as the tilt angle of the Sun's large scale dipole. We thus
conclude that no additional flux-emergence patterns or field-dispersal
properties are required of the solar dynamo beyond those that are
included in the model in order to understand the large-scale solar
and heliospheric fields.
---------------------------------------------------------
Title: Numerical Simulations of Solar Active Region Magnetoconvection
Authors: De Rosa, M. L.; Hurlburt, N. E.
2002AGUFMSH52A0495D Altcode:
Vigorous fluid motions associated with the observed patterns of
supergranulation, mesogranulation, and granulation on the sun are
likely to play a large role in the continual emergence, evolution,
and redistribution of magnetic field within solar active regions. To
investigate such non-linear dynamics, we have constructed numerical
simulations of fully compressible magnetized fluids, each contained
within curved, spherical segments nominally located near the top of
the solar convection zone. Overturning motions having length scales
comparable to that of solar supergranulation are driven by imposing
a solar-like heat flux through the bottom of the domain. We present
recent results of several idealized active region simulations within
thin spherical segments, each spanning 60°x 30° in longitude and
latitude and extending up to 0.04~R<SUB>sun</SUB> in radius. We are able
to investigate the analogs of both plage and active regions by varying
the amount of magnetic flux that permeates the layer. Simplified
field-line extrapolations into the volume above the spherical
segments are then used to assess how the corona might respond to the
structure and evolution of magnetic field emerging through the solar
photosphere. This work was supported by NASA through grant NAG 5-3077
to Stanford University and by Lockheed Martin Independent Research
and Development funds.
---------------------------------------------------------
Title: Solar Multiscale Convection and Rotation Gradients Studied
in Shallow Spherical Shells
Authors: De Rosa, Marc L.; Gilman, Peter A.; Toomre, Juri
2002ApJ...581.1356D Altcode: 2002astro.ph..9054D
The differential rotation of the Sun, as deduced from helioseismology,
exhibits a prominent radial shear layer near the top of the convection
zone wherein negative radial gradients of angular velocity are
evident in the low- and midlatitude regions spanning the outer 5%
of the solar radius. Supergranulation and related scales of turbulent
convection are likely to play a significant role in the maintenance
of such radial gradients and may influence dynamics on a global scale
in ways that are not yet understood. To investigate such dynamics, we
have constructed a series of three-dimensional numerical simulations
of turbulent compressible convection within spherical shells, dealing
with shallow domains to make such modeling computationally tractable. In
all but one case, the lower boundary is forced to rotate differentially
in order to approximate the influence that the differential rotation
established within the bulk of the convection zone might have upon a
near-surface shearing layer. These simulations are the first models
of solar convection in a spherical geometry that can explicitly
resolve both the largest dynamical scales of the system (of order the
solar radius) as well as smaller scale convective overturning motions
comparable in size to solar supergranulation (20-40 Mm). We find that
convection within these simulations spans a large range of horizontal
scales, especially near the top of each domain, where convection
on supergranular scales is apparent. The smaller cells are advected
laterally by the larger scales of convection within the simulations,
which take the form of a connected network of narrow downflow lanes that
horizontally divide the domain into regions measuring approximately
100-200 Mm across. We also find that the radial angular velocity
gradient in these models is typically negative, especially in the low-
and midlatitude regions. Analyses of the angular momentum transport
indicate that such gradients are maintained by Reynolds stresses
associated with the convection, transporting angular momentum inward
to balance the outward transport achieved by viscous diffusion and
large-scale flows in the meridional plane, a mechanism first proposed
by Foukal & Jokipii and tested by Gilman & Foukal. We suggest
that similar mechanisms associated with smaller scale convection in
the Sun may contribute to the maintenance of the observed radial shear
layer located immediately below the solar photosphere.
---------------------------------------------------------
Title: Experimental Measurement of the Dynamic Photothermal Effect
in Fabry-Perot Cavities for Gravitational Wave Detectors
Authors: de Rosa, M.; Conti, L.; Cerdonio, M.; Pinard, M.; Marin, F.
2002PhRvL..89w7402D Altcode: 2002gr.qc.....1038D
We report the experimental observation of the frequency dependence of
the photothermal effect. The measurements are performed by modulating
the laser power absorbed by the mirrors of two high-finesse
Fabry-Perot cavities. The results are very well described by
a recently proposed theoretical model [M. Cerdonio, L. Conti,
A. Heidmann, and M. Pinard, <journal>Phys. Rev. D</journal>
<volume>63</volume>, <pages>082003</pages>
(<date>2001</date>)</citeinfo>], confirming the
correctness of such calculations. Our observations and quantitative
characterization of the dynamic photothermal effect demonstrate its
critical importance for interferometric displacement measurements
towards the quantum limit, as those necessary for gravitational wave
detection.
---------------------------------------------------------
Title: Simulations of near-photospheric magnetoconvection within
localized spherical segments
Authors: De Rosa, M. L.; Hurlburt, N. E.; Alexander, D.
2002ESASP.505..385D Altcode: 2002IAUCo.188..385D; 2002solm.conf..385D
Vigorous fluid motions associated with the observed patterns of
supergranulation, mesogranulation, and granulation are likely to play a
large role during the evolution of magnetic field within solar active
regions. To investigate such dynamics, we have constructed numerical
simulations of fully compressible, magnetized fluids, each contained
within curved, spherical segments that approximate conditions near
the top of the solar convection zone. We present recent results of
one three-dimensional simulation of an idealized bipolar active region
contained within a thin spherical segment. The segment nominally spans
30° in latitude and 60° in longitude, and has a radial extent of 4%
of the solar radius. Upon initialization, the domain is threaded by a
bipolar radial magnetic field, which subsequently cancels as the ensuing
convection advects field horizontally across the segment. We find that
the time scale at which the field decays is slower than the expected
turbulent decay time scale, and is much closer to the diffusive (Ohmic)
decay time scale, despite the network of convection cells surrounding
the magnetized regions. We suggest that this convection serves to
confine field of like polarity and thus suppresses the turbulent decay
of magnetic field.
---------------------------------------------------------
Title: The long-term variations of the solar and heliospheric fields
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M.
2002ESASP.505..253S Altcode: 2002IAUCo.188..253S; 2002solm.conf..253S
The heliospheric field is determined by the largest-scale patterns of
magnetism at the solar surface, dominated by the lower-latitude active
regions during cycle maximum, and by the circumpolar fields during
cycle minimum. To study these patterns, we simulate the evolution of
the magnetic field at the solar surface and in the heliosphere during
the last 340 years. We conclude that, contrary to current thinking,
the observed magnetic flux in the polar regions of the Sun cannot be
understood as merely a long-term accumulation of active-region decay
products from a dynamo that modulates only the rate at which flux
emerges from cycle to cycle. We suggest that simulation and observation
may be reconciled if the high-latitude solar field decays on a time
scale comparable to that of the sunspot cycle.
---------------------------------------------------------
Title: What Is Missing from Our Understanding of Long-Term Solar
and Heliospheric Activity?
Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M.
2002ApJ...577.1006S Altcode:
The heliospheric magnetic field is associated with changes in space
weather, cosmic-ray flux, and likely climate. This field is determined
by the largest scale patterns of magnetism at the solar surface,
dominated by the lower latitude active regions during cycle maximum and
by the circumpolar fields during cycle minimum. Whereas the magnetic
field in the activity belt is readily studied, the high-latitude
field is much less accessible, and its study requires a combination of
modeling and observation. Current models hold that the high-latitude
magnetic field on the Sun is determined solely by the accumulation of
field transported poleward from lower latitude active regions. We test
this hypothesis by simulating the evolution of the magnetic field at
the solar surface and in the heliosphere during the last 340 yr using a
state-of-the-art model that incorporates all processes that are known to
contribute significantly to the evolution of the large-scale patterns
in the solar field. We find that if only the emergence frequency of
magnetic bipoles is varied in accordance with observed sunspot records,
the polar-cap field reservoir does not match measurements during past
years. Based on comparisons of our simulations with observed polar
fluxes over the last few decades and with the proxy for the heliospheric
flux formed by 340 yr of <SUP>10</SUP>Be ice-core data, we suggest that
the high-latitude field may be subject to decay on a timescale of 5-10
yr. We discuss the consequences of this finding for our understanding
of the Sun-Earth connection and explore inferences for the coupling
of the Sun's internal magnetic field to the heliospheric field.
---------------------------------------------------------
Title: A neural network-based approach to noise identification of
interferometric GW antennas: the case of the 40 m Caltech laser
interferometer
Authors: Acernese, F.; Barone, F.; de Rosa, M.; De Rosa, R.; Eleuteri,
A.; Milano, L.; Tagliaferri, R.
2002CQGra..19.3293A Altcode:
In this paper, a neural network-based approach is presented for the real
time noise identification of a GW laser interferometric antenna. The
40 m Caltech laser interferometer output data provide a realistic
test bed for noise identification algorithms because of the presence
of many relevant effects: violin resonances in the suspensions,
main power harmonics, ring-down noise from servo control systems,
electronic noises, glitches and so on. These effects can be assumed to
be present in all the first interferometric long baseline GW antennas
such as VIRGO, LIGO, GEO and TAMA. For noise identification, we used
the Caltech-40 m laser interferometer data. The results we obtained are
pretty good notwithstanding the high initial computational cost. The
algorithm we propose is general and robust, taking into account that
it does not require a priori information on the data, nor a precise
model, and it constitutes a powerful tool for time series data analysis.
---------------------------------------------------------
Title: Numerical Simulations of Supergranular Magnetoconvection
Authors: De Rosa, M. L.; Hurlburt, N. E.; Alexander, D.; Rucklidge,
A. M.
2002AAS...200.0418D Altcode: 2002BAAS...34..646D
The complex interactions between the turbulent fluid motions within
the solar convection zone and the related processes of emergence,
evolution, and cancellation of magnetic field at the photosphere have
received much recent attention. It is likely that such interactions
depend on the relative magnitudes of the field and of the flows,
but the details of this coupling are not well understood. To further
investigate the magnetohydrodynamics within such turbulent convection,
we have constructed several idealized simulations of fully compressible
MHD fluids, each contained within a curved, spherical segment that
approximates a localized volume of subphotospheric convection on the
sun. In some cases, the horizontal extent of the computational volume
spans 30 heliographic degrees in both latitude and longitude, thereby
enabling the dynamics within a large field containing approximately
100 supergranular-sized cells to be studied. By varying the amount of
total (unsigned) flux permeating the domain, we are able to investigate
analogs to patches of subsurface convection that generally resemble
either quiet-sun or active regions when viewed from above. In addition,
simplified potential-field extrapolations into the volume above the
computational domain are used to illustrate how the coronal field
topology might behave in response to the continually evolving magnetic
field within the convecting layers. This work was supported by NASA
through grant NAG 5-3077 to Stanford University and by Lockheed Martin
Independent Research and Development funds.
---------------------------------------------------------
Title: Status report and near future prospects for the gravitational
wave detector AURIGA
Authors: Zendri, J. -P.; Baggio, L.; Bignotto, M.; Bonaldi, M.;
Cerdonio, M.; Conti, L.; De Rosa, M.; Falferi, P.; Fortini, P. L.;
Inguscio, M.; Marin, A.; Marin, F.; Mezzena, R.; Ortolan, A.; Prodi,
G. A.; Rocco, E.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato,
G.; Vinante, A.; Vitale, S.
2002CQGra..19.1925Z Altcode:
We describe the experimental efforts to set up the second AURIGA
run. Thanks to the upgraded capacitive readout, fully characterized
and optimized in a dedicated facility, we predict an improvement
in the detector sensitivity and bandwidth by at least one order of
magnitude. In the second run, AURIGA will also benefit from newly
designed cryogenic mechanical suspensions and the upgraded data
acquisition and data analysis.
---------------------------------------------------------
Title: First room temperature operation of the AURIGA optical readout
Authors: De Rosa, M.; Baggio, L.; Cerdonio, M.; Conti, L.; Galet,
G.; Marin, F.; Ortolan, A.; Prodi, G. A.; Taffarello, L.; Vedovato,
G.; Vitale, S.; Zendri, J. -P.
2002CQGra..19.1919D Altcode:
In the frame of the AURIGA collaboration, a readout scheme based on
an optical resonant cavity has been implemented on a room temperature
resonant bar detector of gravitational waves. The bar equipped with
the optical readout has been operating for a few weeks and we report
here the first results.
---------------------------------------------------------
Title: The present status of the VIRGO Central Interferometer*The
present status of the VIRGO Central Interferometer
Authors: Acernese, F.; Amico, P.; Arnaud, N.; Arnault, C.; Babusci,
D.; Ballardin, G.; Barone, F.; Barsuglia, M.; Bellachia, F.; Beney,
J. L.; Bilhaut, R.; Bizouard, M. A.; Boccara, C.; Boget, D.; Bondu,
F.; Bourgoin, C.; Bozzi, A.; Bracci, L.; Braccini, S.; Bradaschia,
C.; Brillet, A.; Brisson, V.; Buskulic, D.; Cachenaut, J.; Calamai,
G.; Calloni, E.; Canitrot, P.; Caron, B.; Casciano, C.; Cattuto,
C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cecchi, R.; Cella,
G.; Chiche, R.; Chollet, F.; Cleva, F.; Cokelaer, T.; Cortese, S.;
Coulon, J. P.; Cuoco, E.; Cuzon, S.; Dattilo, V.; David, P. Y.;
Davier, M.; De Rosa, M.; De Rosa, R.; Dehamme, M.; Di Fiore, L.;
Di Virgilio, A.; Dominici, P.; Dufournaud, D.; Eder, C.; Eleuteri,
A.; Enard, D.; Errico, A.; Evangelista, G.; Fabbroni, L.; Fang, H.;
Ferrante, I.; Fidecaro, F.; Flaminio, R.; Fournier, J. D.; Fournier,
L.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Ganau, P.; Garufi, F.;
Gaspard, M.; Gennaro, G.; Giacobone, L.; Giazotto, A.; Giordano, G.;
Girard, C.; Guidi, G.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.;
Holloway, L.; Iannarelli, M.; Innocent, J. M.; Jules, E.; La Penna, P.;
Lacotte, J. C.; Lagrange, B.; Leliboux, M.; Lieunard, B.; Lodygenski,
O.; Lomtadze, T.; Loriette, V.; Losurdo, G.; Loupias, M.; Mackowski,
J. M.; Majorana, E.; Man, C. N.; Mansoux, B.; Marchesoni, F.; Marin,
P.; Marion, F.; Marrucho, J. C.; Martelli, F.; Masserot, A.; Massonnet,
L.; Mataguez, S.; Mazzoni, M.; Mencik, M.; Michel, C.; Milano, L.;
Montorio, J. L.; Morgado, N.; Mours, B.; Mugnier, P.; Nicolosi, L.;
Pacheco, J.; Palomba, C.; Paoletti, F.; Paoli, A.; Pasqualetti, A.;
Passaquieti, R.; Passuello, D.; Perciballi, M.; Pinard, L.; Poggiani,
R.; Popolizio, P.; Pradier, T.; Punturo, M.; Puppo, P.; Qipiani,
K.; Ramonet, J.; Rapagnani, P.; Reboux, A.; Regimbau, T.; Reita, V.;
Remillieux, A.; Ricci, F.; Richard, F.; Ripepe, M.; Rivoirard, P.;
Roger, J. P.; Scheidecker, J. P.; Solimeno, S.; Sottile, R.; Stanga,
R.; Taddei, R.; Taurigna, M.; Teuler, J. M.; Tourrenc, P.; Trinquet,
H.; Turri, E.; Varvella, M.; Verkindt, D.; Vetrano, F.; Veziant, O.;
Viceré, A.; Vinet, J. Y.; Vocca, H.; Yvert, M.; Zhang, Z.
2002CQGra..19.1421A Altcode:
The VIRGO Central Interferometer (CITF) is a short suspended
interferometer operated with the central area elements of the
VIRGO detector. The main motivation behind the CITF is to allow
the integration and debugging of a large part of the subsystems of
VIRGO while the construction of the long arms of the antenna is being
completed. This will permit a faster commissioning of the full-size
antenna. In fact, almost all the main components of the CITF, with
the exception of the large mirrors and a few other details, are the
same as those to be used for the full-size detector. In this paper
the present status of the VIRGO CITF is reported.
---------------------------------------------------------
Title: Advanced readout configurations for the gravitational wave
detector AURIGA
Authors: Zendri, J. -P.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.;
Conti, L.; Crivelli Visconti, V.; de Rosa, M.; Falferi, P.; Marin,
A.; Marin, F.; Mezzena, R.; Prodi, G. A.; Salviato, M.; Soranzo, G.;
Taffarello, L.; Vinante, A.; Vitale, S.
2002rdgr.conf..317Z Altcode:
We report the status of the experimental effort devoted at improving
the sensitivity and widening the band of the gravitational wave
detector AURIGA. The focus is on an optimized setup of the capacitive
resonant transducer, read by an improved dc-SQUID amplifier and on
the implementation of an opto-mechanical resonant transducer. Both
techniques, which are complementary, should lead to an improvement of
the detector performances of at least two orders of magnitude in both
energy sensitivity and bandwidth.
---------------------------------------------------------
Title: Coupled modeling of photospheric and coronal dynamics
Authors: Alexander, D.; Hurlburt, N. E.; Rucklidge, A. M.; De Rosa, M.
2001AGUFMSH11C0718A Altcode:
The coupling of the motions within and below te photosphere to the
chromosphere and corona is one of the fundamental issues in solar
physics. We have developed a model coupling the simulated dynamics of
sunspots to the simulated heating of coronal loops. In this paper we
present an extension of our earlier work to the inclusion of (a) fully
three dimensional magnetoconvection, (b) new analytical representations
of hydrostatic loops with spatially-dependent heating rates and (c)
fully time-dependent hydrodynamic coronal modeling. The dynamic loop
model uses the same numerical scheme as the magnetoconvective model
used to simulate the photospheric behavior in this sunspot system,
making it possible to more fully integrate the two regimes. We present
the first results of a hybrid model utilizing a time-dependent coronal
model and a fully three-dimensional magnetoconvective model.
---------------------------------------------------------
Title: Numerical simulations of supergranular scales of convection
in shallow spherical shells
Authors: De Rosa, Marc L.; Toomre, Juri
2001ESASP.464..595D Altcode: 2001soho...10..595D
The differential rotation of the sun, as deduced from helioseismology,
exhibits a prominent radial shear layer near the top of the convection
zone. Supergranulation and related scales of turbulent convection
are likely to play a significant role in the maintenance of strong
radial gradients in angular velocity which vary with latitude near
the surface. We present results from 3-D numerical simulations of such
turbulent convection in shallow spherical shells, using the anelastic
spherical harmonic (ASH) code running on massively parallel computers
to study the effects of rotation and compressibility on the resulting
highly nonlinear convection. Convection of supergranular nature is
driven by imposing the solar heat flux at the bottom of a shallow
spherical shell located near the top of the convection zone which is
rotating at the mean solar rate. The angular momentum balance in the
shell is studied for cases where a solar-like differential rotation
profile is imposed at the lower boundary. Convection spanning a large
range of horizontal scales is driven within the shell, especially near
the top of the domain. The resulting radial angular velocity gradient
is negative for all latitudes, suggesting that fluid parcels partially
conserve their angular momentum while moving radially.
---------------------------------------------------------
Title: Turbulent Convection and Subtleties of Differential Rotation
Within the Sun
Authors: Toomre, J.; Brun, A. Sacha; De Rosa, M.; Elliott, J. R.;
Miesch, M. S.
2001IAUS..203..131T Altcode:
Differential rotation and cycles of magnetic activity are
intimately linked dynamical processes within the deep shell of
highly turbulent convection occupying the outer 200 Mm below the
solar surface. Helioseismology has shown that the angular velocity
Ω within the solar convection zone involves strong shear layers
both near the surface and especially at its base near the interface
with the radiative interior. The tachocline of radial shear there
that varies with latitude is thought to be the site of the global
magnetic dynamo. Most recent continuous helioseismic probing with
MDI on SOHO and from GONG have revealed systematic temporal changes
in Ω with the advancing solar cycle. These include propagating bands
of zonal flow speedup extending from the surface to a depth of about
70 Mm, distinctive out-of-phase vacillations in Ω above and below the
tachocline with a period of about 1.3 years near the equator, a changing
pattern of meridional circulation cells with broken symmetries in the
two hemispheres, and complex speedups and slowdowns in the bulk of
the convection zone. We review these helioseismic findings and their
implications. We also describe current 3-D numerical simulations of
anelastic rotating convection in full spherical shells used to study
the differential rotation that can be established by such turbulence
exhibiting coherent structures. These simulations enabled by massively
parallel computers are making promising contact with aspects of the
Ω profiles deduced from helioseismology, but challenges remain.
---------------------------------------------------------
Title: Dynamics in the upper solar convection zone
Authors: DeRosa, Marc Lyle
2001PhDT.........8D Altcode:
The differential rotation of the sun, as deduced from helioseismology,
exhibits a prominent layer of radial shear near the top of the
convection zone. This shearing boundary layer just below the solar
surface is composed of convection possessing a broad range of
length and time scales, including granulation, mesogranulation, and
supergranulation. Such turbulent convection is likely to influence
the dynamics of the deep convection zone in ways that are not yet
fully understood. We seek to assess the effects of this near-surface
shear layer through two complementary studies, one observational and
the other theoretical in nature. Both deal with turbulent convection
occurring on supergranular scales within the upper solar convection
zone. We characterize the horizontal outflow patterns associated with
solar supergranulation by individually identifying several thousand
supergranules from a 45°-square field of quiet sun. This region is
tracked for a duration of six days as it rotates across the disk of the
sun, using full-disk (2<SUP> '</SUP> pixels) SOI-MDI images from the
SOHO space-craft of line- of-sight Doppler velocity imaging the solar
photosphere at a cadence of one minute. This time series represents the
first study of solar supergranulation at such high combined temporal
and spatial resolution over an extended period of time. The outflow
cells in this region are observed to have a distribution of sizes,
ranging from 14-20 Mm across, while continuously evolving on time
scales of several days. Such evolution manifests itself in the form of
cell merging, fragmentation, and advection, as the supergranules and
their associated network of convergence lanes respond to the turbulent
convection occurring a short distance below the photosphere. We have
also conducted three-dimensional numerical simulations of turbulent
compressible convection within thin spherical shells located near the
top of the convection zone. Vigorous fluid motions possessing several
length and time scales are driven by imposing the solar heat flux and
differential rotation at the bottom of the domain. The convection
patterns form a connected network of downflow lanes in the surface
layers that break up into more plume-like structures with depth. The
regions delineated by this downflow network enclose broad upflows
that fragment into smaller structures near the surface. We find that a
negative radial gradient of angular velocity Ω is maintained against
diffusion in these simulations by the tendency for the convective
motions to partially conserve their angular momentum in radial
motion. This behavior suggests that similar dynamics may be responsible
for the decrease of Ω with radius as deduced from helioseismology
within the upper shear layer of the solar convection zone.
---------------------------------------------------------
Title: New Approach to Study Extended Evolution of Supergranular
Flows and Their Advection of Magnetic Elements
Authors: Lisle, Jason; De Rosa, Marc; Toomre, Juri
2000SoPh..197...21L Altcode:
Using velocity and magnetogram data extracted from the full-disk field
of view of MDI during the 1999 Dynamics Program, we have studied the
dynamics of small-scale magnetic elements (3-7 Mm in size) over time
periods as long as six days while they are readily visible on the
solar disk. By exploiting concurrent time series of magnetograms and
Doppler images, we have compared the motion of magnetic flux elements
with the supergranular velocity field inferred from the correlation
tracking of mesogranular motions. Using this new method (which combines
the results from correlation tracking of mesogranules with detailed
analysis of simultaneous magnetograms), it is now possible to correlate
the motions of the velocity field and magnetic flux for long periods of
time and at high temporal resolution. This technique can be utilized
to examine the long-term evolution of supergranulation and associated
magnetic fields, for it can be applied to data that span far longer
time durations than has been possible previously. As tests of its
efficacy, we are able to use this method to verify many results of
earlier investigations. We confirm that magnetic elements travel at
approximately 350 m s <SUP>−1</SUP> throughout the duration of their
lifetime as they are transported by supergranular outflows. We also
find that the positions of the magnetic flux elements coincide with
the supergranular network boundaries and adjust as the supergranular
network itself evolves over the six days of this data set. Thus
we conclude that this new method permits us to study the extended
evolution of the supergranular flow field and its advection of magnetic
elements. Since small-scale magnetic elements are strongly advected
by turbulent convection, their dynamics can give important insight
into the properties of the subsurface convection.
---------------------------------------------------------
Title: An optical transduction chain for the AURIGA detector
Authors: Conti, L.; Marin, F.; de Rosa, M.; Prodi, G. A.; Taffarello,
L.; Zendri, J. P.; Cerdonio, M.; Vitale, S.
2000AIPC..523..261C Altcode: 2000grwa.conf..261C
We describe the principle of operation of an opto-mechanical readout
for resonant mass gravitational wave detectors; with such a device
the AURIGA detector is expected to reach a sensitivity at the level
of S<SUB>hh</SUB>=10<SUP>-22</SUP>/Hz over a bandwidth of about
40Hz. Recent developments in the implementation of this transduction
chain are also reported. In particular we achieve quantum limited laser
power noise in the frequency range of 200Hz around the bar fundamental
frequency (about 1kHz) by means of active stabilization. We also
set up a reference cavity of finesse 40000 with optically contacted
mirrors on a 0.2m long Zerodur spacer. The cavity can be heated from
room temperature to about 100 °C and temperature stabilized with
fluctuations within 1mK over a period of several days. The cavity is
under vacuum and isolated from mechanical disturbancies by means of
a double stage cantilever system. .
---------------------------------------------------------
Title: Evolving Dynamics of the Supergranular Flow Field
Authors: De Rosa, M. L.; Lisle, J. P.; Toomre, J.
2000SPD....31.0106D Altcode: 2000BAAS...32..802D
We study several large (45-degree square) fields of supergranules
for as long as they remain visible on the solar disk (about 6 days)
to characterize the dynamics of the supergranular flow field and its
interaction with surrounding photospheric magnetic field elements. These
flow fields are determined by applying correlation tracking methods
to time series of mesogranules seen in full-disk SOI-MDI velocity
images. We have shown previously that mesogranules observed in this
way are systematically advected by the larger scale supergranular
flow field in which they are embedded. Applying correlation tracking
methods to such time series yields the positions of the supergranular
outflows quite well, even for locations close to disk center. These
long-duration datasets contain several instances where individual
supergranules are recognizable for time scales as long as 50 hours,
though most cells persist for about 25 hours that is often quoted as a
supergranular lifetime. Many supergranule merging and splitting events
are observed, as well as other evolving flow patterns such as lanes
of converging and diverging fluid. By comparing the flow fields with
the corresponding images of magnetic fields, we confirm the result
that small-scale photospheric magnetic field elements are quickly
advected to the intercellular lanes to form a network between the
supergranular outflows. In addition, we characterize the influence
of larger-scale regions of magnetic flux, such as active regions,
on the flow fields. Furthermore, we have measured even larger-scale
flows by following the motions of the supergranules, but these flow
fields contain a high noise component and are somewhat difficult to
interpret. This research was supported by NASA through grants NAG
5-8133 and NAG 5-7996, and by NSF through grant ATM-9731676.
---------------------------------------------------------
Title: Near-Surface Flow Fields Deduced Using Correlation Tracking
and Time-Distance Analyses
Authors: De Rosa, Marc; Duvall, T. L., Jr.; Toomre, Juri
2000SoPh..192..351D Altcode:
Near-photospheric flow fields on the Sun are deduced using two
independent methods applied to the same time series of velocity images
observed by SOI-MDI on SOHO. Differences in travel times between f
modes entering and leaving each pixel measured using time-distance
helioseismology are used to determine sites of supergranular
outflows. Alternatively, correlation tracking analysis of mesogranular
scales of motion applied to the same time series is used to deduce
the near-surface flow field. These two approaches provide the means to
assess the patterns and evolution of horizontal flows on supergranular
scales even near disk center, which is not feasible with direct
line-of-sight Doppler measurements. We find that the locations of the
supergranular outflows seen in flow fields generated from correlation
tracking coincide well with the locations of the outflows determined
from the time-distance analysis, with a mean correlation coefficient
after smoothing of <SUB>s</SUB>=0.890. Near-surface velocity field
measurements can be used to study the evolution of the supergranular
network, as merging and splitting events are observed to occur in these
images. The data consist of one 2048-min time series of high-resolution
(0.6” pixels) line-of-sight velocity images taken by MDI on 1997
January 16 -18 at a cadence of one minute.
---------------------------------------------------------
Title: An Optical Transducer for Bar Detectors
Authors: Marin, F.; de Rosa, M.; Conti, L.; Prodi, G.; Vitale, S.;
Cerdonio, M.; Taffarello, L.; Zendri, J. P.
2000epgw.conf..306M Altcode:
We present a new kind of transducer for gravitational waves
bar detectors. The bar vibrations are measured by means of a
mechanically coupled optical cavity whose length is compared with
that of a reference cavity by means of a laser system. We describe in
details the transduction chain, we analyze the noise sources and the
achievable sensitivity and present some experimental steps for the
system implementation.
---------------------------------------------------------
Title: Comparison Between Near-Surface Flow Fields Deduced from
Correlation Tracking and Time-Distance Helioseismology Methods
Authors: De Rosa, M. L.; Toomre, J.; Duvall, T. L., Jr.
1999AAS...194.5608D Altcode: 1999BAAS...31..913D
Near-photospheric flow fields deduced using two independent methods
applied to the same SOI-MDI time series of images from SOHO are
compared. Differences in travel times between incoming and outgoing
f modes measured using time-distance helioseismology are used to
determine the sites of supergranule outflows. Alternatively, correlation
tracking analysis is applied to granular and mesogranular structures
seen in time series of Doppler and intensity images. We find that the
locations of the supergranular outflows seen in flow fields generated
from correlation tracking coincide well with the locations of the
outflows determined from the time-distance analysis. The near-surface
flow fields provide us with insight in understanding the dyanmics
of the turbulent convection occurring below the photosphere. The data
consist of four 512-minute time series of high-resolution (0.6” pixels)
Doppler images and continuum intensity images taken by MDI on 17--18
January 1997 at a cadence of one minute.
---------------------------------------------------------
Title: Collisional broadening and shift of lines in the
2ν<SUB>1</SUB>+2ν<SUB>2</SUB>+ν<SUB>3</SUB> band of CO<SUB>2</SUB>.
Authors: de Rosa, M.; Corsi, C.; Gabrysch, M.; D'Amato, F.
1999JQSRT..61...97D Altcode:
Using a distributed feedback diode laser, pressure induced
self-broadening and shift have been measured for several transitions
in the 2ν<SUB>1</SUB>+2ν<SUB>2</SUB>+ν<SUB>3</SUB> band of
CO<SUB>2</SUB>, centered at 1.573 μm. Foreign broadening and shift,
with N<SUB>2</SUB> and O<SUB>2</SUB> as perturbing gas, have been
measured for the most intense lines. The results for broadening have
been compared with the data given by HITRAN molecular database and
some discrepancies have been found, especially for air broadening
derived from N<SUB>2</SUB> and O<SUB>2</SUB> broadening.
---------------------------------------------------------
Title: Comparison Between Near-Surface Flow Fields Deduced from
Correlation Tracking and Time-Distance Helioseismology Methods
Authors: de Rosa, Marc; Toomre, Juri; Duvall, T. L., Jr.
1999soho....9E..51D Altcode:
Near-photospheric flow fields deduced using two independent methods
applied to the same SOI-MDI time series of images from SOHO are
compared. Differences in travel times between incoming and outgoing f
modes measured using time-distance helioseismology are used to determine
the sites of supergranule outflows. Alternatively, correlation tracking
analysis is applied to granular and mesogranular structures seen in time
series of Doppler and intensity images. We find that the locations
of the supergranular outflows seen in flow fields generated from
correlation tracking coincide well with the locations of the outflows
determined from the time-distance analysis. The near-surface flow fields
provide us with insight in understanding the dynamics of the turbulent
convection occurring below the photosphere. The data consist of four
512-minute time series of high-resolution (0.6 arc-second pixels)
Doppler images and continuum intensity images taken by MDI on 17-18
January 1997 at a cadence of one minute.
---------------------------------------------------------
Title: Long-Term Dynamics of Small-Scale Magnetic Flux Elements
Embedded in the Near-Surface Velocity Field
Authors: Lisle, Jason; de Rosa, Marc; Toomre, Juri
1999soho....9E..72L Altcode:
Using velocity and magnetogram data generated by SOI-MDI during the
1999 Dynamics Program, we have studied the dynamics of small-scale
magnetic elements over time periods of several days. By exploiting
concurrent time series of MDI magnetograms and velocity images, we
have correlated the motions of the magnetic flux elements with the
supergranular velocity field inferred from tracking of mesogranular
motions. We confirm that these magnetic elements travel at approximately
200 m/s throughout the duration of their lifetime (10-20 hours) as they
are transported by supergranular outflows. We also find that boundaries
of supergranules traced by magnetic flux elements coincide with the
boundaries determined from the tracking of mesogranules. In addition,
we have studied the association between magnetic flux emergence and
destruction events and the evolution of the supergranular network. The
data consist of several tracked regions of corresponding magnetogram and
photospheric velocity images extracted from full-disk SOI-MDI images
taken during the 1999 Dynamics Program when the MDI instrument was at
best focus. Time series were created by following these individual
patches as they rotated across the solar disk. Individual magnetic
elements were identified by thresholding the magnetograms, while the
supergranular flow fields were determined by applying a correlation
tracking algorithm to time series of mesogranules. The mesogranules
were isolated by removing the signal due to solar rotation, p-mode
oscillations, and supergranulation from the velocity data.
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Title: Correlation Tracking of Mesogranules from SOI-MDI Doppler
Images to Reveal Supergranular Flow Fields
Authors: De Rosa, Marc L.; Toomre, Juri
1998ESASP.418..753D Altcode: 1998soho....6..753D
We present evidence that mesogranules on the sun are advected
horizontally by the underlying supergranular flow field. Correlation
tracking of mesogranules, as observed in full-disk SOI-MDI Doppler
images, reveal that the flow field experienced by the mesogranules is
composed of several long-lived regions of divergent fluid. These outflow
regions correlate well with the locations of supergranules present on
related Doppler images. The flow fields also contain regions where the
fluid is converging or is moving slowly, both corresponding to areas of
the related Doppler images where no organized supergranular outflows
exist. Typical velocities are of order 200 m s<SUP>-1</SUP>. The data
used in this study consist of 30-circ-square patches of the photospheric
velocity field extracted from full-disk SOI-MDI Dopplergrams. Time
series were created by tracking each patch in a frame corotating
with the surface plasma. Images of mesogranulation superimposed on
supergranulation were created by removing the velocity signals due
to rotation and acoustic oscillations. The supergranular signal is
isolated by spatially smoothing each image, while the mesogranular
signal is isolated by taking the residual of the smoothed and unsmoothed
images. The correlation tracking calculation was performed on the time
series of mesogranulation, from which the surface flow-fields analyzed
in this study were deduced.
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Title: The Nature of Supergranulation from SOI-MDI Dopplergrams
Authors: De Rosa, Marc L.; Toomre, Juri
1997SPD....28.0257D Altcode: 1997BAAS...29..903D
We discuss the distribution of supergranule cell areas and
evolutionary characteristics as determined from a series of SOI-MDI
dopplergrams. Patches of the photospheric velocity field 30(deg)
x30(deg) (heliographic) in size were tracked as they rotated across the
disk of the sun. Supergranule boundaries were identified on each tracked
image by a pattern recognition algorithm, from which supergranule area
distributions and evolutionary trends are found.
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Title: Temperature dependence of self-shift of ammonia transitions
in the ν<SUB>2</SUB> band.
Authors: Baldacchini, G.; D'Amato, F.; de Rosa, M.; Buffa, G.;
Tarrini, O.
1996JQSRT..55..745B Altcode:
Pressure-induced lineshift has been measured as a function of
temperature, in the range 200-400 K, for five transitions of the
ν<SUB>2</SUB> band of ammonia lines near 937 cm<SUP>-1</SUP>. Results
are compared with semiclassical calculations that rely on the impact
approximation. In general the theory does not agree very well with
the experimental values of the shift, but the sign and the order of
magnitude are confirmed. The present work shows that extensive and
detailed measurement of the lineshifts is feasible and reliable, even
when their absolute values in ammonia as a function of temperature
are very small.
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Title: Differential Rotation and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Toomre, J.; Anderson, E. R.; Antia, H. M.;
Berthomieu, G.; Burtonclay, D.; Chitre, S. M.; Christensen-Dalsgaard,
J.; Corbard, T.; De Rosa, M.; Genovese, C. R.; Gough, D. O.; Haber,
D. A.; Harvey, J. W.; Hill, F.; Howe, R.; Korzennik, S. G.; Kosovichev,
A. G.; Leibacher, J. W.; Pijpers, F. P.; Provost, J.; Rhodes, E. J.,
Jr.; Schou, J.; Sekii, T.; Stark, P. B.; Wilson, P. R.
1996Sci...272.1300T Altcode:
Splitting of the sun's global oscillation frequencies by large-scale
flows can be used to investigate how rotation varies with radius
and latitude within the solar interior. The nearly uninterrupted
observations by the Global Oscillation Network Group (GONG) yield
oscillation power spectra with high duty cycles and high signal-to-noise
ratios. Frequency splittings derived from GONG observations confirm
that the variation of rotation rate with latitude seen at the surface
carries through much of the convection zone, at the base of which is
an adjustment layer leading to latitudinally independent rotation at
greater depths. A distinctive shear layer just below the surface is
discernible at low to mid-latitudes.
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Title: Propagation of electromagnetic waves in inhomogeneous plasmas
Authors: Busatti, E.; Ciucci, A.; De Rosa, M.; Palleschi, V.; Rastelli,
S.; Lontano, M.; Lunin, N.
1994JPlPh..52..443B Altcode:
The reflection and transmission coefficients for an electromagnetic
beam propagating in an inhomogeneous plasma are calculated analytically
using the Magnus approximation in different physical configurations. The
theoretical predictions for such coefficients are expressed in simple
analytical form, and are compared with the exact results obtained by
numerical solution of the wave propagation equations, using the Berreman
4 × 4 matrix method. It is shown that the theoretical approach is
able to reproduce the correct results for reflection and transmission
coefficients over a wide range of physical parameters. The accuracy
of the theoretical analysis, at different orders of approximation,
is also discussed.
