fisher

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Author name code: fisher
ADS astronomy entries on 2022-09-14
author:"Fisher, George H."

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Title: Boundary Data-driven MHD Simulation of the Eruptions of Active
Region 11158
Authors: Fan, Yuhong; Fisher, George; Afanasev, Andrei; Kazachenko,
Maria
2022cosp...44.2476F Altcode:
We present data-driven MHD simulation of the evolution of Active
Region (AR) 11158, using lower boundary driving electric fields
inferred from the time sequence of vector magnetograms observed
by the SDO/HMI. The lower boundary is driven with the horizontal
component of the PDFI electric field (Fisher et al. 2020), and an
additional twisting electric field derived based on the vertical
electric current measured from the vector magnetograms. Our simulation
shows the build-up of a coronal magnetic field with significant free
magnetic energy and strongly sheared, sigmoid shaped loops above
the PIL of the central delta-sunspot, showing morphology similar to
that observed. The simulation also shows the development of a set
of homologous eruptions. We discuss the structure of the 3D coronal
magnetic field and the mechanisms for the onset of the eruptions.

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Title: How could we use observations to constrain and validate
data-driven models of solar eruptions?
Authors: Kazachenko, Maria; Fan, Yuhong; Fisher, George; Cheung,
Mark; Afanasev, Andrei; Tremblay, Benoit; Kazachenko, Maria
2022cosp...44.2464K Altcode:
Observations of vector magnetic fields, coronal loops, flare ribbons and
coronal dimmings provide observational constraints for data-constrained
and data-driven models of solar eruptions. In this talk I will review
specific observational properties that we could use to evaluate the
realism of these models: photospheric energy fluxes, reconnection
fluxes, inferred flux rope properties and future coronal field
measurements. I will also discuss possible ways to improve current
models using more realistic photospheric boundary conditions.

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Title: Data-driven, time-dependent modeling of pre-eruptive coronal
magnetic field configuration at the periphery of NOAA AR 11726
Authors: Lumme, E.; Pomoell, J.; Price, D. J.; Kilpua, E. K. J.;
Kazachenko, M. D.; Fisher, G. H.; Welsch, B. T.
2022A&A...658A.200L Altcode:
Context. Data-driven, time-dependent magnetofrictional modeling has
proved to be an efficient tool for studying the pre-eruptive build-up
of energy for solar eruptions, and sometimes even the ejection of
coronal flux ropes during eruptions. However, previous modeling works
have illustrated the sensitivity of the results on the data-driven
boundary condition, as well as the difficulty in modeling the ejections
with proper time scales. Aims: We aim to study the pre- and
post-eruptive evolution of a weak coronal mass ejection producing
eruption at the periphery of isolated NOAA active region (AR) 11726
using a data-driven, time-dependent magnetofrictional simulation,
and aim to illustrate the strengths and weaknesses of our simulation
approach. Methods: We used state-of-the-art data processing
and electric field inversion methods to provide the data-driven
boundary condition for the simulation. We analyzed the field-line
evolution, magnetic connectivity, twist, as well as the energy and
helicity budgets in the simulation to study the pre- and post-eruptive
magnetic field evolution of the observed eruption from AR11726. 
Results: We find the simulation to produce a pre-eruptive flux rope
system consistent with several features in the extreme ultraviolet and
X-ray observations of the eruption, but the simulation largely fails
to reproduce the ejection of the flux rope. We find the flux rope
formation to be likely driven by the photospheric vorticity at one of
the footpoints, although reconnection at a coronal null-point may also
feed poloidal flux to the flux rope. The accurate determination of the
non-inductive (curl-free) component of the photospheric electric field
boundary condition is found to be essential for producing the flux
rope in the simulation. Conclusions: Our results illustrate the
applicability of the data-driven, time-dependent magnetofrictional
simulations in modeling the pre-eruptive evolution and formation
process of a flux rope system, but they indicate that the modeling
output becomes problematic for the post-eruptive times. For the
studied event, the flux rope also constituted only a small part
of the related active region. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038744/olm">https://www.aanda.org</A>

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Title: Boundary Data-driven MHD Simulations of the Emergence and
Eruption of Active Region 11158
Authors: Fan, Yuhong; Kazachenko, Maria; Afanasev, Andrei; Fisher,
George
2021AGUFMSH44A..02F Altcode:
We present data-driven MHD simulations of the emergence and eruption
of Active Region (AR) 11158, using a lower boundary driving electric
field inferred from the time sequence of vector magnetograms observed
by the SDO/HMI with the PDFI-SS inversion method (developed by Fisher
et al. 2020), and an additional driving electric field that represents
sunspot rotation and shearing at the polarity inversion line (PIL). We
found that highly sheared, S-shaped sigmoid loops form above the
PIL of the central delta-sunspot, showing morphology similar to the
observation. We experiment with the additional electric field that
drives the sunspot rotation and shearing at the PIL and examine the
conditions for the development of the eruptive flares.

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Title: Validation of the PDFI_SS Method for Electric Field Inversions
Using a Magnetic Flux Emergence Simulation
Authors: Afanasyev, Andrey N.; Kazachenko, Maria D.; Fan, Yuhong;
Fisher, George H.; Tremblay, Benoit
2021ApJ...919....7A Altcode: 2021arXiv210610579A
Knowledge of electric fields in the photosphere is required to
calculate the electromagnetic energy flux through the photosphere
and set up boundary conditions for data-driven magnetohydrodynamic
(MHD) simulations of solar eruptions. Recently, the PDFI_SS method for
inversions of electric fields from a sequence of vector magnetograms
and Doppler velocity measurements was improved to incorporate spherical
geometry and a staggered-grid description of variables. The method was
previously validated using synthetic data from anelastic MHD (ANMHD)
simulations. In this paper, we further validate the PDFI_SS method,
using approximately 1 hr long MHD simulation data of magnetic flux
emergence from the upper convection zone into the solar atmosphere. We
reconstruct photospheric electric fields and calculate the Poynting
flux, and we compare those to the actual values from the simulations. We
find that the accuracy of the PDFI_SS reconstruction is quite good
during the emergence phase of the simulated ephemeral active region
evolution and decreases during the shearing phase. Analyzing our
results, we conclude that the more complex nature of the evolution
(compared to the previously studied ANMHD case) that includes the
shearing evolution phase is responsible for the obtained accuracy
decrease.

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Title: Boundary data-driven MHD simulations of the evolution of
AR 11158
Authors: Fan, Y.; Kazachenko, M.; Afanasev, A.; Fisher, G.
2021AAS...23831320F Altcode:
We have performed initial data-driven MHD simulations of the emergence
and evolution of Active Region (AR) 11158, using a lower boundary
driving electric field inferred from the time sequence of vector
magnetograms observed by the SDO/HMI with the PDFI-SS inversion method
(developed by Fisher et al. 2020), and an additional driving electric
field that represents sunspot rotation and shearing at the polarity
inversion line (PIL). We found that highly sheared, S-shaped sigmoid
loops form above the PIL of the central delta-sunspot, showing
morphology similar to that seen in the SDO/AIA observations. We
experiment with the additional electric field that drives the sunspot
rotation and shearing at the PIL and examine the conditions for the
development of the eruptive flares. Acknowledgement: This work
is supported in part by the NASA LWS grant 80NSSC19K0070 to NCAR.

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Title: Coupling a Global Heliospheric Magnetohydrodynamic Model to
a Magnetofrictional Model of the Low Corona
Authors: Hayashi, Keiji; Abbett, William P.; Cheung, Mark C. M.;
Fisher, George H.
2021ApJS..254....1H Altcode:
Recent efforts coupling our Sun-to-Earth magnetohydrodynamics (MHD)
model and lower-corona magnetofrictional (MF) model are described. Our
Global Heliospheric MHD (GHM) model uses time-dependent three-component
magnetic field data from the lower-corona MF model as time-dependent
boundary values. The MF model uses data-assimilation techniques to
introduce the vector magnetic field data from the Solar Dynamics
Observatory/Helioseismic and Magnetic Imager, hence as a whole this
simulation coupling structure is driven with actual observations. The
GHM model employs a newly developed interface boundary treatment that
is based on the concept of characteristics, and it properly treats
the interface boundary sphere set at a height of the sub-Alfvénic
lower corona (1.15 R⊙ in this work). The coupled model
framework numerically produces twisted nonpotential magnetic features
and consequent eruption events in the solar corona in response to the
time-dependent boundary values. The combination of our two originally
independently developed models presented here is a model framework
toward achieving further capabilities of modeling the nonlinear
time-dependent nature of magnetic field and plasma, from small-scale
solar active regions to large-scale solar wind structures. This work is
a part of the Coronal Global Evolutionary Model project for enhancing
our understanding of Sun-Earth physics to help improve space weather
capabilities.

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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.

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Title: Solar and Heliospheric Models at the CCMC - An Update
Authors: MacNeice, P. J.; Chulaki, A.; Mendoza, A. M. M.; Mays, M. L.;
Weigand, C.; Arge, C. N.; Jones, S. I.; Linker, J.; Downs, C.; Torok,
T.; Fisher, G. H.; Cheung, C. M. M.
2020AGUFMSH0030015M Altcode:
The Community Coordinated Modeling Center (CCMC) at NASA Goddard Space
Flight Center is the world largest repository of models dedicated to
Space Weather Research and forecasting. In this presentation we provide
an update on new additions and updates to the CCMC's inventory of Solar
and Heliospheric models. In particular, we describe the latest version
of WSA, the CORHEL TDM model, and the CGEM model suite. The latest
version of WSA is now available to users through our Runs-On-Request
websites as well as through its continuous near realtime execution. It
can use input magnetograms from an extensive list of observatories,
including maps processed using the ADAPT surface flux evolution
model, and can return results and solar wind forecasts at all inner
planets and most inner heliospheric spacecraft locations. The CORHEL
TDM model enables users to design flux ropes embedded in coronal
fields in derived from observed magnetograms, and then follow the
evolution of the flux rope using a zero-beta MHD code. A future upgrade
(currently in development at PredSci) w ill support full thermodynamic
CME simulations. Finally, the CGEM model suite supports the generation
and application of boundary conditions for realistic driving of coronal
3D field models based on times series observations of photospheric
vector magnetogram data.

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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.

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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.

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Title: The PDFI_SS Electric Field Inversion Software
Authors: Fisher, George H.; Kazachenko, Maria D.; Welsch, Brian T.;
Lumme, Erkka
2020zndo...3711571F Altcode:
This is a copy of the PDFI_SS electric field inversion software,
as described in arXiv 1912.08301.

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Title: The FLCT local correlation tracking software
Authors: Fisher, George H.; Welsch, Brian T.
2020zndo...3711569F Altcode:
FLCT consists of a library of functions, written in C, for performing
tasks associated with local correlation tracking, and the approximate
inverse operation, the warping of an image by a two-dimensional
displacement function. The library is written in such a way that it can
be called easily from either C or Fortran. The software also includes
source code for two standalone executables, flct and warp, which will
perform the correlation tracking or warping by reading input files and
then creating output files that can be read from other applications,
such as IDL.

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Title: The Simple Data Format (SDF) library
Authors: Fisher, George; Bercik, David; Vernetti, Jack
2020zndo...3711188F Altcode:
The SDF library contains the ability to read and write binary output
files in Fortran, C, and IDL.

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Title: Contribution of Doppler Velocity to Active Region Energy and
Helicity Flux Estimate
Authors: Sun, Xudong; Schuck, Peter W.; Fisher, George H.
2019AAS...23440204S Altcode:
The advent of routine photospheric vector magnetograms now allows for
realistic estimate of active region (AR) energy and helicity flux. Such
estimate requires information of the surface velocity field. Here, we
calculate the energy and helicity flux for AR 12673 where significant
Doppler flows (Vl) were observed along the magnetic polarity
inversion line. Results based on the DAVE4VM velocity estimate (without
Vl information) and the CGEM electric field inversion
(with Vl) algorithms differ significantly, mainly due to
the additional constraint from Vl. We argue that Dopper
velocity needs to be included for realistic flux estimate. We describe
an updated DAVE4VMWDV velocity estimate algorithm that incorporates
such contribution.

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Title: Probing the Effect of Cadence on the Estimates of Photospheric
Energy and Helicity Injections in Eruptive Active Region NOAA AR 11158
Authors: Lumme, E.; Kazachenko, M. D.; Fisher, G. H.; Welsch, B. T.;
Pomoell, J.; Kilpua, E. K. J.
2019SoPh..294...84L Altcode: 2019arXiv190700367L
We study how the input-data cadence affects the photospheric energy
and helicity injection estimates in eruptive NOAA Active Region
11158. We sample the novel 2.25-minute vector magnetogram and
Dopplergram data from the Helioseismic and Magnetic Imager (HMI)
instrument onboard the Solar Dynamics Observatory (SDO) spacecraft to
create input datasets of variable cadences ranging from 2.25 minutes
to 24 hours. We employ state-of-the-art data processing, velocity,
and electric-field inversion methods for deriving estimates of the
energy and helicity injections from these datasets. We find that
the electric-field inversion methods that reproduce the observed
magnetic-field evolution through the use of Faraday's law are more
stable against variable cadence: the PDFI (PTD-Doppler-FLCT-Ideal,
where PTD refers to Poloidal-Toroidal Decomposition, and FLCT to
Fourier Local Correlation Tracking) electric-field inversion method
produces consistent injection estimates for cadences from 2.25 minutes
up to two hours, implying that the photospheric processes acting on
time scales below two hours contribute little to the injections, or
that they are below the sensitivity of the input data and the PDFI
method. On other hand, the electric-field estimate derived from the
output of DAVE4VM (Differential Affine Velocity Estimator for Vector
Magnetograms), which does not fulfill Faraday's law exactly, produces
significant variations in the energy and helicity injection estimates
in the 2.25 minutes - two hours cadence range. We also present a third,
novel DAVE4VM-based electric-field estimate, which corrects the poor
inductivity of the raw DAVE4VM estimate. This method is less sensitive
to the changes of cadence, but it still faces significant issues for
the lowest of considered cadences (≥ two hours). We find several
potential problems in both PDFI- and DAVE4VM-based injection estimates
and conclude that the quality of both should be surveyed further in
controlled environments.

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Title: Erratum: “Why Is the Great Solar
Active Region 12192 Flare-rich but CME-poor?” (<A
href="http://doi.org/10.1088/2041-8205/804/2/l28">2015, ApJL, 804,
L28</A>)
Authors: Sun, Xudong; Bobra, Monica G.; Hoeksema, J. Todd; Liu, Yang;
Li, Yan; Shen, Chenglong; Couvidat, Sebastien; Norton, Aimee A.;
Fisher, George H.
2017ApJ...850L..43S Altcode:
No abstract at ADS

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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.

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Title: The Circulation and Closure of Electric Currents in the
Solar Atmosphere
Authors: Kazachenko, M.; Fisher, G. H.; Bercik, D. J.; Welsch, B. T.;
Lynch, B. J.
2016AGUFMSH31B2579K Altcode:
How much information about vertical and horizontal currents
flowing inthe solar atmosphere can we learn from a single vector
magnetogramtaken at the photosphere? It is well-known that one
can determine theradial current density by taking the curl of the
magnetic fieldcomponents parallel to an idealised photospheric
surface. Here, weinvestigate the additional information that can be
learned abouthorizontal currents flowing in the atmosphere above
the photosphere.In particular, we study the radially integrated
horizontal currentdistribution, expressed as a surface current
density. In ourformalism, this surface-current density is projected
onto thephotospheric surface, even though it represents currents flowing
atall heights in the atmosphere. Horizontal currents reflect twosources:
(1) currents flowing around radial magnetic distributions;and (2)
horizontal currents that originate as radial currents at thephotosphere,
become horizontal above it, and return to the photosphereagain as
radial currents. Our aim is to derive two-dimensional“maps” of how
currents flow through the solar atmosphere that can bederived from
vector magnetic field measurements at a single height.

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Title: A model for stealth coronal mass ejections
Authors: Lynch, B. J.; Masson, S.; Li, Y.; DeVore, C. R.; Luhmann,
J. G.; Antiochos, S. K.; Fisher, G. H.
2016JGRA..12110677L Altcode: 2016arXiv161208323L
Stealth coronal mass ejections (CMEs) are events in which there
are almost no observable signatures of the CME eruption in the low
corona but often a well-resolved slow flux rope CME observed in
the coronagraph data. We present results from a three-dimensional
numerical magnetohydrodynamics (MHD) simulation of the 1-2 June
2008 slow streamer blowout CME that Robbrecht et al. (2009) called
"the CME from nowhere." We model the global coronal structure using a
1.4 MK isothermal solar wind and a low-order potential field source
surface representation of the Carrington Rotation 2070 magnetogram
synoptic map. The bipolar streamer belt arcade is energized by simple
shearing flows applied in the vicinity of the helmet streamer's polarity
inversion line. The flows are large scale and impart a shear typical
of that expected from the differential rotation. The slow expansion
of the energized helmet streamer arcade results in the formation of a
radial current sheet. The subsequent onset of expansion-induced flare
reconnection initiates the stealth CME while gradually releasing the
stored magnetic energy. We present favorable comparisons between our
simulation results and the multiviewpoint SOHO-LASCO (Large Angle and
Spectrometric Coronagraph) and STEREO-SECCHI (Sun Earth Connection
Coronal and Heliospheric Investigation) coronagraph observations of
the preeruption streamer structure and the initiation and evolution
of the stealth streamer blowout CME.

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Title: Unexpectedly Strong Lorentz-Force Impulse Observed During a
Solar Eruption
Authors: Sun, X.; Fisher, G.; Torok, T.; Hoeksema, J. T.; Li, Y.;
CGEM Team
2016usc..confE..12S Altcode:
For fast coronal mass ejections (CMEs), the acceleration phase takes
place in the low corona; the momentum process is presumably dominated by
the Lorentz force. Using ultra-high-cadence vector magnetic data from
the Helioseismic and Magnetic Imager (HMI) and numerical simulations,
we show that the observed fast-evolving photospheric field can be used
to characterize the impulse of the Lorentz force during a CME. While the
peak Lorentz force concurs with the maximum ejecta acceleration, the
observed total force impulse surprisingly exceeds the CME momentum by
over an order of magnitude. We conjecture that most of the Lorentz force
impulse is "trapped" in the thin layer of the photosphere above the HMI
line-formation height and is counter-balanced by gravity. This implies
a consequent upward plasma motion which we coin "gentle photospheric
upwelling". The unexpected effect dominates the momentum processes,
but is negligible for the energy budget, suggesting a complex coupling
between different layers of the solar atmosphere during CMEs.

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Title: Deriving Potential Coronal Magnetic Fields from Vector
Magnetograms
Authors: Welsch, Brian T.; Fisher, George H.
2016SoPh..291.1681W Altcode: 2016SoPh..tmp..120W; 2015arXiv150308754W
The minimum-energy configuration for the magnetic field above the solar
photosphere is curl-free (hence, by Ampère's law, also current-free),
so can be represented as the gradient of a scalar potential. Since
magnetic fields are divergence free, this scalar potential obeys
Laplace's equation, given an appropriate boundary condition (BC). With
measurements of the full magnetic vector at the photosphere, it is
possible to employ either Neumann or Dirichlet BCs there. Historically,
the Neumann BC was used with available line-of-sight magnetic field
measurements, which approximate the radial field needed for the
Neumann BC. Since each BC fully determines the 3D vector magnetic
field, either choice will, in general, be inconsistent with some
aspect of the observed field on the boundary, due to the presence of
both currents and noise in the observed field. We present a method to
combine solutions from both Dirichlet and Neumann BCs to determine a
hybrid, "least-squares" potential field, which minimizes the integrated
square of the residual between the potential and actual fields. We
also explore weighting the residuals in the fit by spatially uniform
measurement uncertainties. This has advantages both in not overfitting
the radial field used for the Neumann BC, and in maximizing consistency
with the observations. We demonstrate our methods with SDO/HMI vector
magnetic field observations of active region 11158, and find that
residual discrepancies between the observed and potential fields
are significant, and they are consistent with nonzero horizontal
photospheric currents. We also analyze potential fields for two other
active regions observed with two different vector magnetographs, and
find that hybrid-potential fields have significantly less energy than
the Neumann fields in every case - by more than 1032erg
in some cases. This has major implications for estimates of free
magnetic energy in coronal field models, e.g., non-linear force-free
field extrapolations.

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Title: Unexpectedly Large Lorentz-Force Impulse Observed During a
Solar Eruption
Authors: Sun, Xudong; Fisher, George; Torok, Tibor; Hoeksema, Todd;
Li, Yan; CGEM Team
2016shin.confE.158S Altcode:
For fast coronal mass ejections (CMEs), the acceleration phase takes
place in the low corona; the momentum process is presumably dominated by
the Lorentz force. Using ultra-high-cadence vector magnetic data from
the Helioseismic and Magnetic Imager (HMI) and numerical simulations,
we show that the observed fast-evolving photospheric field can be used
to characterize the impulse of the Lorentz force during a CME. While the
peak Lorentz force concurs with the maximum ejecta acceleration, the
observed total force impulse surprisingly exceeds the CME momentum by
over an order of magnitude. We conjecture that most of the Lorentz force
impulse is "trapped" in the thin layer of the photosphere above the HMI
line-formation height and is counter-balanced by gravity. This implies
a consequent upward plasma motion which we coin "gentle photospheric
upwelling". The unexpected effect dominates the momentum processes,
but is negligible for the energy budget, suggesting a complex coupling
between different layers of the solar atmosphere during CMEs.

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Title: Streamer Blowout CME Initiation: Not Loss-of-Equilibrium,
Not Flux-Cancellation, Not the Kink Instability, and Not the Torus
Instability
Authors: Lynch, Benjamin J.; Masson, S.; Li, Y.; DeVore, C. R.;
Luhmann, J. G.; Antiochos, S. K.; Fisher, G. H.
2016shin.confE..49L Altcode:
We present results from a three-dimensional numerical
magnetohydrodynamics (MHD) simulation of the 2008 June 1-2 slow
streamer blowout CME that Robbrecht et al. [2009] called 'the CME from
nowhere.' We investigate the CME initiation mechanism in detail,
showing definitely the eruption is *not* caused by loss-of-equilibrium,
flux-cancellation, the kink instability or the torus instability,
rather, the rising sheared arcade becomes a CME in the traditional sense
only when the eruptive flare reconnection occurs at the radial current
sheet, forming a flux rope structure *during* the eruption. We
present favorable comparisons between our simulation results and the
multi-viewpoint SOHO-LASCO and STEREO-SECCHI coronagraph observations
of the pre-eruption streamer structure and the initiation and evolution
of the stealth streamer blowout CME. We also present synthetic in-situ
time series at r=15Rs of the plasma and field signatures of the flux
rope CME and show qualitative agreement to the ICME observed by STB
on 2008 June 6-7.

---------------------------------------------------------
Title: A Potential Field Model for Spherical Sub-domains
Authors: Fisher, George H.; Bercik, David; Welsch, Brian; Kazachenko,
Maria D.; CGEM Team
2016SPD....47.0308F Altcode:
Potential field models are used widely in Solar Physics to
estimate coronal magnetic field geometry and connectivity, to
provide lower limits on magnetic energies, and to provide initial
configurations for time-dependent models of magnetic fields in the
solar atmosphere. Potential field models in a spherical geometry can be
global, covering the entire Sun, or confined to localized sub-volumes
of the sphere. Here, we focus on the latter case.We describe an
efficient potential field model for localized spherical sub-volumes
(wedges consisting of upper and lower limits of radius, co-latitude, and
longitude), employing a finite-difference approach for the solution. The
solution is derived in terms of a "poloidal" potential, which can then
be used to find either the scalar potential or the vector potential for
the magnetic field (if desired), as well as all three magnetic field
components. The magnetic field components are computed on the faces of
spherical voxels, and the finite difference grid is consistent with
the well-known "Yee" grid. The inner spherical boundary is defined
by radial magnetic field measurements, and at the outer radius a
source-surface boundary condition is imposed.Potential field solutions
on active region scales, at full HMI resolution, and with the source
surface located a solar radius above the photosphere, can be obtained
on a laptop computer in just a few minutes. The three-dimensional
finite difference equations are solved using NCAR's FISHPACK elliptic
equation solver.The potential field model was developed by the Coronal
Global Evolutionary Model (CGEM) project, funded by the NASA and NSF
Strategic Capabilities program. The potential field model described
here was motivated by CGEM's need for such a model. The model will be
released as open-source code when the model details are published.

---------------------------------------------------------
Title: Unexpectedly Strong Lorentz-Force Impulse Observed During a
Solar Eruption
Authors: Sun, Xudong; Fisher, George H.; Torok, Tibor; Hoeksema,
Jon Todd; Li, Yan; CGEM Team
2016SPD....47.0628S Altcode:
For fast coronal mass ejections (CMEs), the acceleration phase takes
place in the low corona; the momentum process is presumably dominated by
the Lorentz force. Using ultra-high-cadence vector magnetic data from
the Helioseismic and Magnetic Imager (HMI) and numerical simulations,
we show that the observed fast-evolving photospheric field can be used
to characterize the impulse of the Lorentz force during a CME. While the
peak Lorentz force concurs with the maximum ejecta acceleration, the
observed total force impulse surprisingly exceeds the CME momentum by
over an order of magnitude. We conjecture that most of the Lorentz force
impulse is "trapped" in the thin layer of the photosphere above the HMI
line-formation height and is counter-balanced by gravity. This implies
a consequent upward plasma motion which we coin "gentle photospheric
upwelling". The unexpected effect dominates the momentum processes,
but is negligible for the energy budget, suggesting a complex coupling
between different layers of the solar atmosphere during CMEs.

---------------------------------------------------------
Title: A Model for Stealth Coronal Mass Ejections
Authors: Lynch, Benjamin J.; Masson, Sophie; Li, Yan; DeVore,
C. Richard; Luhmann, Janet; Antiochos, Spiro K.; Fisher, George H.
2016SPD....47.0616L Altcode:
Stealth coronal mass ejections (CMEs) are events in which there
are almost no observable signatures of the CME eruption in the low
corona but often a well-resolved slow flux rope CME observed in
the coronagraph data. We present results from a three-dimensional
numerical magnetohydrodynamics (MHD) simulation of the 2008 June 1-2
slow streamer blowout CME that Robbrecht et al. [2009] called “the
CME from nowhere.” We model the global coronal structure using a
1.4 MK isothermal solar wind and a low-order potential field source
surface representation of the Carrington Rotation 2070 magnetogram
synoptic map. The bipolar streamer belt arcade is energized by simple
shearing flows applied in the vicinity of the helmet streamer’s
polarity inversion line. The slow expansion of the energized
helmet-streamer arcade results in the formation of a radial current
sheet. The subsequent onset of expansion-driven flare reconnection
initiates the stealth CME while gradually releasing ~1.5E+30 erg of
stored magnetic energy over the 20+ hour eruption duration. We show
the energy flux available for flare heating and flare emission during
the eruption is approximately two orders of magnitude below the energy
flux required to heat the ambient background corona, thus confirming the
“stealth” character of the 2008 June 1-2 CME’s lack of observable
on disk signatures. We also present favorable comparisons between our
simulation results and the multi-viewpoint SOHO-LASCO and STEREO-SECCHI
coronagraph observations of the pre-eruption streamer structure and
the initiation and evolution of the stealth streamer blowout CME.

---------------------------------------------------------
Title: Photospheric Electric Fields and Energy Fluxes in the Eruptive
Active Region NOAA 11158
Authors: Kazachenko, Maria D.; Fisher, George H.; Welsch, Brian T.;
Liu, Yang; Sun, Xudong
2015ApJ...811...16K Altcode: 2015arXiv150505974K
How much electromagnetic energy crosses the photosphere
in evolving solar active regions (ARs)? With the advent of
high-cadence vector magnetic field observations, addressing this
fundamental question has become tractable. In this paper, we apply
the “PTD-Doppler-FLCT-Ideal” (PDFI) electric field inversion
technique of Kazachenko et al. to a 6-day vector magnetogram and Doppler
velocity sequence from the Helioseismic and Magnetic Imager on board
the Solar Dynamics Observatory to find the electric field and Poynting
flux evolution in NOAA 11158, which produced an X2.2 flare early on
2011 February 15. We find photospheric electric fields ranging up to
2 V cm-1. The Poynting fluxes range from [-0.6 to 2.3]
× {10}10 {erg} cm-2 s-1, mostly
positive, with the largest contribution to the energy budget in the
range of [{10}9-{10}10] erg cm-2
s-1. Integrating the instantaneous energy flux over space
and time, we find that the total magnetic energy accumulated above the
photosphere from the initial emergence to the moment before the X2.2
flare to be E=10.6× {10}32 {erg}, which is partitioned as
2.0×1032erg and 8.6× {10}32 {erg}, respectively,
between free and potential energies. Those estimates are consistent with
estimates from preflare nonlinear force-free field extrapolations and
the Minimum Current Corona estimates, in spite of our very different
approach. This study of photospheric electric fields demonstrates the
potential of the PDFI approach for estimating Poynting fluxes and opens
the door to more quantitative studies of the solar photosphere and more
realistic data-driven simulations of coronal magnetic field evolution.

---------------------------------------------------------
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: Why Is the Great Solar Active Region 12192 Flare-rich but
CME-poor?
Authors: Sun, Xudong; Bobra, Monica G.; Hoeksema, J. Todd; Liu, Yang;
Li, Yan; Shen, Chenglong; Couvidat, Sebastien; Norton, Aimee A.;
Fisher, George H.
2015ApJ...804L..28S Altcode: 2015arXiv150206950S; 2015ApJ...804L..28.
Solar active region (AR) 12192 of 2014 October hosts the largest sunspot
group in 24 years. It is the most prolific flaring site of Cycle 24
so far, but surprisingly produced no coronal mass ejection (CME) from
the core region during its disk passage. Here, we study the magnetic
conditions that prevented eruption and the consequences that ensued. We
find AR 12192 to be “big but mild” its core region exhibits weaker
non-potentiality, stronger overlying field, and smaller flare-related
field changes compared to two other major flare-CME-productive ARs
(11429 and 11158). These differences are present in the intensive-type
indices (e.g., means) but generally not the extensive ones (e.g.,
totals). AR 12192's large amount of magnetic free energy does not
translate into CME productivity. The unexpected behavior suggests
that AR eruptiveness is limited by some relative measure of magnetic
non-potentiality over the restriction of background field, and that
confined flares may leave weaker photospheric and coronal imprints
compared to their eruptive counterparts.

---------------------------------------------------------
Title: The Coronal Global Evolutionary Model (CGEM): Toward Routine,
Time-Dependent, Data-Driven Modeling of the Active Corona
Authors: Welsch, Brian T.; Cheung, Mark CM; Fisher, George H.;
Kazachenko, Maria D.; Sun, Xudong
2015TESS....131106W Altcode:
The Coronal Global Evolutionary Model (CGEM) is a model for the
evolution of the magnetic field in the solar corona, driven using
photospheric vector magnetic field and Doppler measurements by the
HMI instrument on NASA's Solar Dynamics Observatory. Over days-long
time scales, the coronal magnetic field configuration is determined
quasi-statically using magnetofrictional relaxation. For a configuration
that becomes unstable and erupts or undergoes rapid evolution, we
can use the magnetofrictional configuration as the initial state for
MHD simulations. The model will be run in both global configurations,
covering the entire Sun, and local configurations, designed to model
the evolution of the corona above active regions. The model uses
spherical coordinates to realistically treat the large-scale coronal
geometry. The CGEM project also includes the dissemination of other
information derivable from HMI magnetogram data, such as (i) vertical
and horizontal Lorentz forces computed over active region domains,
to facilitate easier comparisons of flare/CME behavior and observed
changes of the photospheric magnetic field, and (ii) estimates of the
photospheric electric field and Poynting flux. We describe progress
that we have made in development of both the coronal model and its
input data, and discuss magnetic evolution in (i) the well-studied
NOAA AR 11158 around the time of the 2011 February 15 X2.2 flare, and
(ii) AR 11944 around the time of the 2014 January 7 X1.2 flare.

---------------------------------------------------------
Title: On the Relationship between Solar Magnetic Forces and CME
Momenta
Authors: Li, Yan; Lynch, Ben; Sun, Xudong; Welsch, Brian T.; Bercik,
David J.; Fisher, George H.
2015TESS....130219L Altcode:
Free magnetic energy is the energy source of solar flares and CMEs. At
the initiation of a CME, the free magnetic energy converts to kinetic
energy and few other types of energy. Observable magnetic field sudden
changes have been found at the onset of flares. The Lorentz force
around the onset of a flare have been formulated in recent studies and
can be estimated using photospheric vector magnetic field data. It is
proposed that outward Lorentz force impulses could be related to CME
momenta. We analyze about 30 CMEs and their source region magnetic
fields. The best vector magnetic field data are observed for active
regions near the center of the solar disk. We first select CMEs that
appear to be halo or partial halo CMEs in the LASCO images, and then
we use STEREO SECCHI COR2 white light images to estimate CME mass
and speed. We then estimate the Lorentz forces in the source active
regions at the flare onset using SDO HMI photosheric vector magnetic
field data. We report our studies and describe our analyses.This study
is under the support of NSF grants.

---------------------------------------------------------
Title: Why Is the Great Solar Active Region 12192 CME-Poor?
Authors: Sun, Xudong; Bobra, Monica G.; Hoeksema, Todd; Liu, Yang;
Li, Yan; Shen, Chenglong; Couvidat, Sebastien; Norton, Aimee A.;
Fisher, George H.
2015TESS....140802S Altcode:
Solar active region (AR) 12192 of October 2014 hosts the largest
sunspot group in 24 years. It is the most prolific flaring site of
Cycle 24, but surprisingly produced no coronal mass ejection (CME) from
the core region during its disk passage. Here, we study the magnetic
conditions that prevented eruption and the consequences that ensued. We
find AR 12192 to be "big but mild"; its core region exhibits weaker
non-potentiality, stronger overlying field, and smaller flare-related
field changes compared to two other major flare-CME-productive ARs
(11429 and 11158). These differences are present in the intensive-type
indices (e.g., means) but generally not the extensive ones (e.g.,
totals). AR 12192's large amount of magnetic free energy does not
translate into CME productivity. The unexpected behavior suggests
that AR eruptiveness is limited by some relative measure of magnetic
non-potentiality over the restriction of background field, and that
confined flares may leave weaker photospheric and coronal imprints
compared to their eruptive counterparts.

---------------------------------------------------------
Title: Sign Singularity and Flares in Solar Active Region NOAA 11158
Authors: Sorriso-Valvo, L.; De Vita, G.; Kazachenko, M. D.; Krucker,
S.; Primavera, L.; Servidio, S.; Vecchio, A.; Welsch, B. T.; Fisher,
G. H.; Lepreti, F.; Carbone, V.
2015ApJ...801...36S Altcode: 2015arXiv150104279S
Solar Active Region NOAA 11158 has hosted a number of strong flares,
including one X2.2 event. The complexity of current density and
current helicity are studied through cancellation analysis of their
sign-singular measure, which features power-law scaling. Spectral
analysis is also performed, revealing the presence of two separate
scaling ranges with different spectral index. The time evolution of
parameters is discussed. Sudden changes of the cancellation exponents
at the time of large flares and the presence of correlation with
Extreme-Ultra-Violet and X-ray flux suggest that eruption of large
flares can be linked to the small-scale properties of the current
structures.

---------------------------------------------------------
Title: Modeling the Convection Zone-to-Corona System over Global
Spatial Scales
Authors: Abbett, W. P.; Bercik, D. J.; Fisher, G. H.
2014AGUFMSH44A..01A Altcode:
How magnetic energy and flux emerges from the turbulent convective
interior of the Sun into the solar atmosphere is of great importance
to a number of challenging problems in solar physics. With the wealth
of data from missions such as SDO, Hinode, and IRIS, it is evident that
the dynamic interaction of magnetic structures at the photosphere and in
the solar atmosphere occurs over a vast range of spatial and temporal
scales. Emerging active regions often develop magnetic connections
to other regions of activity some distance away on the solar disk,
and always emerge into a global coronal field whose structural
complexity is a function of the solar cycle. Yet even small-scale
dynamic interactions (e.g., processes at granular or supergranular
scales in the photosphere) can trigger rapid changes in the large-scale
coronal field sufficient to power eruptive events such as coronal mass
ejections, or solar flares. The challenge of modeling this system in
its entirety is that the magnetic field not only spans multiple scales,
but also regions whose physical conditions vary dramatically. We will
summarize recent progress in the effort to dynamically model the upper
convection zone-to-corona system over large spatial scales, and will
present the latest results from a new, global radiative-MHD model of the
upper convection zone-to-corona system, RADMHD2S. We will characterize
the flux of electromagnetic energy into the solar atmosphere as flux
systems of different scales dynamically interact, and discuss how
physics-based models of the convection zone-to-corona system can be
used to guide the development and testing of data-driven models.

---------------------------------------------------------
Title: A Comprehensive Method of Estimating Electric Fields from
Vector Magnetic Field and Doppler Measurements
Authors: Kazachenko, Maria D.; Fisher, George H.; Welsch, Brian T.
2014ApJ...795...17K Altcode: 2014arXiv1404.4027K
Photospheric electric fields, estimated from sequences of vector
magnetic field and Doppler measurements, can be used to estimate the
flux of magnetic energy (the Poynting flux) into the corona and as
time-dependent boundary conditions for dynamic models of the coronal
magnetic field. We have modified and extended an existing method to
estimate photospheric electric fields that combines a poloidal-toroidal
decomposition (PTD) of the evolving magnetic field vector with Doppler
and horizontal plasma velocities. Our current, more comprehensive
method, which we dub the "PTD-Doppler-FLCT Ideal" (PDFI) technique, can
now incorporate Doppler velocities from non-normal viewing angles. It
uses the FISHPACK software package to solve several two-dimensional
Poisson equations, a faster and more robust approach than our previous
implementations. Here, we describe systematic, quantitative tests of
the accuracy and robustness of the PDFI technique using synthetic data
from anelastic MHD (ANMHD) simulations, which have been used in similar
tests in the past. We find that the PDFI method has less than 1% error
in the total Poynting flux and a 10% error in the helicity flux rate
at a normal viewing angle (θ = 0) and less than 25% and 10% errors,
respectively, at large viewing angles (θ &lt; 60°). We compare our
results with other inversion methods at zero viewing angle and find
that our method's estimates of the fluxes of magnetic energy and
helicity are comparable to or more accurate than other methods. We
also discuss the limitations of the PDFI method and its uncertainties.

---------------------------------------------------------
Title: Relationship between the photospheric Poynting flux and the
active region luminosity
Authors: Kazachenko, Maria D.; Canfield, Richard C.; Fisher, George
H.; Hudson, Hugh S.; Welsch, Brian
2014AAS...22412349K Altcode:
How does energy radiated by active regions compare with magnetic energy
that propagates lower across the photosphere? This is a fundamental
question for energy storage and release in active regions, yet it is
presently poorly understood. In this work we quantify and compare
both energy terms using SDO observations of the active region (AR)
11520. To quantify the magnetic energy crossing the photosphere, or
the Poynting flux, we need to know both the magnetic field vector B and
electric field vector E as well. Our current electric field inversion
technique, PDFI, combines the Poloidal-Toroidal-Decomposition method
with information from Doppler measurements, Fourier local correlation
tracking (FLCT) results, and the ideal MHD constraint, to determine
the electric field from vector magnetic field and Doppler data. We
apply the PDFI method to a sequence of Helioseismic and Magnetic
Imager (HMI/SDO) vector magnetogram data, to find the electric-field
and hence the Poynting-flux evolution in AR 11520. We find that most
of the magnetic energy in this AR is injected in the range of $10^7$
to $10^8$ $ergs/{cm^2 s}$, with the largest fluxes reaching $10^{10}$
$ergs/{cm^2 s}$. Integrating over the active region this yields a
total energy of order $10^{28}$ ergs/s. To quantify the active region
luminosity, we use EUV Variability Experiment (EVE) and Atmospheric
Imaging Assembly (AIA) spectrally resolved observations. We find the
active region luminosity of order $10^{28}$ ergs/s. We compare derived
magnetic and radiated energy fluxes on different temporal and spatial
scales and estimate their uncertainties. We also discuss the roles
that potential/non-potential and emerging/shearing terms play in the
total magnetic energy budget.

---------------------------------------------------------
Title: The Coronal Global Evolutionary Model (CGEM): Highlights of
the First Year
Authors: Fisher, George H.
2014AAS...22432318F Altcode:
The Coronal Global Evolutionary Model (CGEM) is a model for the
evolution of the magnetic field in the solar corona, driven by
vector and line-of-sight magnetogram data, along with Doppler data,
taken from HMI instrument on NASA's SDO Mission. On long time scales,
the magnetic field evolution is computed quasi-statically using the
magnetofrictional method. For a configuration which becomes unstable and
erupts or undergoes rapid evolution, we will use the magnetofrictional
configuration as the initial state for an MHD simulation. The model
will be run in both global configurations, covering the entire
Sun, and local configurations, designed to model the evolution of
the corona above active regions. In both cases, the model will use
spherical coordinates to enable a more realistic geometry in the outer
corona. The CGEM project also includes the dissemination of other
information derivable from HMI magnetogram data, such as the vertical
and horizontal Lorentz-forces computed over active region domains,
to facilitate easier comparisons of flare/CME behavior and observed
changes of the photospheric magnetic field.We describe progress we
have made both on the development of this new model, and our continued
development of our prototype Cartesian model, which was the basis for
the CGEM proposal. We will discuss updated simulations that use our
prototype model to study the evolution of NOAA AR 11158 over the time
period that includes the 2011 February 15 X-class flare.

---------------------------------------------------------
Title: Photospheric Flows, Lorentz Forces, and Solar-Eruption
Initiation
Authors: Fisher, George; Kazachenko, Maria
2014cosp...40E.874F Altcode:
Eruptive Flares and coronal mass ejections (CMEs) are almost
certainly magnetically driven. We discuss the role that the Lorentz
force must play in driving an eruption, and how both the radial and
horizontal components of this force can be related to changes that
occur in observations of the vector magnetic field observed at the
photosphere. We then review recent observational work on observed
flows in the solar atmosphere, and how these flows might be related
to changes in the Lorentz force observed during flares. Flows in
magnetized regions of the photosphere also generate electric fields,
which can affect the flux of magnetic energy transported across the
photosphere and into the chromosphere and corona, and result in changes
to the magnetic field there as well. We will discuss how such electric
fields are incorporated into models of active-regions, to study the
buildup of electric currents and the ejection of plasma in the context
of our recently funded project, the “Coronal Global Evolutionary Model
(CGEM)”, a collaboration between UC Berkeley, Stanford University,
and the Lockheed Martin Solar and Astrophysics Laboratory.

---------------------------------------------------------
Title: Obtaining Photospheric Electric Field Maps and Poynting
Fluxes from vector magnetograms and Doppler data: Tests and Data
Driving Applications
Authors: Kazachenko, Maria; Fisher, George; Welsch, Brian
2014cosp...40E1439K Altcode:
Quantitative studies of the flow of magnetic energy through the solar
photosphere require a knowledge of the magnetic field vector B -
and knowledge of the electric field E as well. We have modified and
improved the technique Fisher et al. developed in 2012, which combines
a poloidal-toroidal decomposition (PTD) to determine contributions
to E from Faraday's law, with additional non-inductive contributions
arising from flux emergence near polarity inversion lines, determined
from Doppler measurements. The new technique, which we call the
“PTD Doppler FLCT Ideal” (or PDFI) technique, incorporates Doppler
information from non-normal viewing angles, and adopts the faster and
more robust FISHPACK software for solutions of the two-dimensional
Poisson equations. We demonstrate the performance using synthetic data
from the anelastic pseudo-spectral ANMHD simulations that were used
in the recent comparison of velocity inversion techniques (Welsch et
al. 2007) and the PTD inversion (Fisher et al. 2012). We find that the
PDFI method has roughly 10% reconstruction errors (it predicts roughly
100% of the photospheric Poynting flux and 110% of the helicity flux
rate at normal viewing angles, consistent with Fisher et al. (2012)
results, and 90% of Poynting flux and 110% helicity flux at theta=30
degrees). We conclude that the PDFI method can be routinely applied
to observed magnetic field data and, as an example, apply it to the
6-day HMI/SDO vector magnetogram sequence centered at AR11158, where an
X2.2 flare occurred. We discuss how our electric field maps are used to
drive coronal magnetic field with a global evolutionary model, or CGEM,
a collaborative effort from the UC Berkeley Space Sciences Laboratory
(SSL), Stanford University, and Lockheed-Martin.

---------------------------------------------------------
Title: Estimating active region luminosity using EVE/SDO observations
Authors: Kazachenko, Maria D.; Hudson, H. S.; Fisher, G. H.; Canfield,
R. C.
2013SPD....44...44K Altcode:
Do solar active regions typically radiate more coronal energy during
flares than the quiescent periods between them? This is a fundamental
question for storage and release models of flares and active regions,
yet it is presently poorly answered by observations. The EUV Variability
Experiment (EVE) on the Solar Dynamics Observatory (SDO) provides
spectrally resolved observations of the Sun in the "Sun-as-a-point
source" mode. It covers a wide range of temperatures and thus allows
a detailed study of thermal emissions. Here we present two approaches
for computing the active region luminosity, using EVE observations of
fourteen Fe lines (FeIX-FeXXIV). In the first approach, we analyze EVE
data in a time-series sense, when only one active region is present on
the disk; this allows us to subtract the background due to the quiet
sun and get the contribution from the active region alone. In the
second approach, we analyze correlations of the radiative signatures
with proxy indices (total solar magnetic and Poynting fluxes) during
several months of data, when multiple active regions are present
on the solar disk. We discuss capabilities of the two approaches,
and what we can learn from them.Abstract (2,250 Maximum Characters):
Do solar active regions typically radiate more coronal energy during
flares than the quiescent periods between them? This is a fundamental
question for storage and release models of flares and active regions,
yet it is presently poorly answered by observations. The EUV Variability
Experiment (EVE) on the Solar Dynamics Observatory (SDO) provides
spectrally resolved observations of the Sun in the "Sun-as-a-point
source" mode. It covers a wide range of temperatures and thus allows
a detailed study of thermal emissions. Here we present two approaches
for computing the active region luminosity, using EVE observations of
fourteen Fe lines (FeIX-FeXXIV). In the first approach, we analyze EVE
data in a time-series sense, when only one active region is present on
the disk; this allows us to subtract the background due to the quiet
sun and get the contribution from the active region alone. In the
second approach, we analyze correlations of the radiative signatures
with proxy indices (total solar magnetic and Poynting fluxes) during
several months of data, when multiple active regions are present on
the solar disk. We discuss capabilities of the two approaches, and
what we can learn from them.

---------------------------------------------------------
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: A Magnetic Calibration of Photospheric Doppler Velocities
Authors: Welsch, Brian T.; Fisher, George H.; Sun, Xudong
2013ApJ...765...98W Altcode: 2012arXiv1201.2451W
The zero point of measured photospheric Doppler shifts is uncertain
for at least two reasons: instrumental variations (from, e.g., thermal
drifts); and the convective blueshift, a known correlation between
intensity and upflows. Accurate knowledge of the zero point is,
however, useful for (1) improving estimates of the Poynting flux of
magnetic energy across the photosphere, and (2) constraining processes
underlying flux cancellation, the mutual apparent loss of magnetic flux
in closely spaced, opposite-polarity magnetogram features. We present
a method to absolutely calibrate line-of-sight (LOS) velocities in
solar active regions (ARs) near disk center using three successive
vector magnetograms and one Dopplergram coincident with the central
magnetogram. It exploits the fact that Doppler shifts measured along
polarity inversion lines (PILs) of the LOS magnetic field determine
one component of the velocity perpendicular to the magnetic field,
and optimizes consistency between changes in LOS flux near PILs and
the transport of transverse magnetic flux by LOS velocities, assuming
that ideal electric fields govern the magnetic evolution. Previous
calibrations fitted the center-to-limb variation of Doppler velocities,
but this approach cannot, by itself, account for residual convective
shifts at the limb. We apply our method to vector magnetograms of AR
11158, observed by the Helioseismic and Magnetic Imager aboard the
Solar Dynamics Observatory, and find clear evidence of offsets in
the Doppler zero point in the range of 50-550 m s-1. In
addition, we note that a simpler calibration can be determined from an
LOS magnetogram and Dopplergram pair from the median Doppler velocity
among all near-disk-center PIL pixels. We briefly discuss shortcomings
in our initial implementation, and suggest ways to address these. In
addition, as a step in our data reduction, we discuss the use of
temporal continuity in the transverse magnetic field direction to
correct apparently spurious fluctuations in resolution of the 180°
ambiguity.

---------------------------------------------------------
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: Evolution of the Photospheric Vector Magnetic Field in HMI Data
Authors: Welsch, B. T.; Fisher, G. H.
2012AGUFMSH13A2243W Altcode:
We discuss aspects of magnetic field structure and evolution in
HMI data, including artifacts of the observation procedure and data
reduction, and characterization of noise in the magnetic variables
and their rates of change.

---------------------------------------------------------
Title: The evolution of the electric field and the Poynting and
Helicity Fluxes in NOAA AR 11158
Authors: Kazachenko, Maria D.; Fisher, George H.; Welsch, Brian T.
2012shin.confE..44K Altcode:
The existence of systematic measurements of vector magnetic fields
and Doppler shifts allows us to estimate electric field in the
photosphere, by solving Faraday's law, using a Poloidal-Toroidal
Decomposition (PTD) of the magnetic field and its partial time
derivative, as well as incorporating information from Doppler
shifts (Fisher et al. 2012). The method is based on solving a set
of two-dimensional Poisson equations. We have recently modified the
method in the following two ways. First, we improvedthe speed and
accuracy of the Poisson equation solver using the FISHPACK elliptic
partial differential equation software developed at NCAR, employing
Neumann boundary conditions appropriate for zero electric fields on
the vector-magnetogram boundary. Second, we developed a more general
procedure which allows us to calculate electric fields from magnetic
fields observed at non-zero viewing angles. We apply the improved
technique to ANMHD-simulation test case with a known electric field
and find that it yields more accurate values of Electric field,
Poynting and helicity fluxes than before. We then apply our method to
three-days-long HMI data-set centered on AR 11158, which produced an
X2.2 flare. We present our first results of electric field, helicity
and Poynting flux evolutions in AR 11158.

---------------------------------------------------------
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: Global Forces in Eruptive Solar Flares: The Lorentz Force
Acting on the Solar Atmosphere and the Solar Interior
Authors: Fisher, George H.; Bercik, D. J.; Welsch, B. T.; Hudson, H. S.
2012AAS...22020440F Altcode:
We compute the change in the Lorentz force integrated over the outer
solar atmosphere implied by observed changes in vector magnetograms
that occur during large, eruptive solar flares. This force perturbation
should be balanced by an equal and opposite force perturbation acting
on the solar photosphere and solar interior. The resulting expression
for the estimated force change in the solar interior generalizes the
earlier expression presented by Hudson, Fisher, and Welsch, providing
horizontal as well as vertical force components, and provides a more
accurate result for the vertical component of the perturbed force. We
show that magnetic eruptions should result in the magnetic field at
the photosphere becoming more horizontal, and hence should result
in a downward (toward the solar interior) force change acting on the
photosphere and solar interior, as recently argued from an analysis
of magnetogram data by Wang and Liu. We suggest the existence of an
observational relationship between the force change computed from
changes in the vector magnetograms, the outward momentum carried by
the ejecta from the flare, and the properties of the helioseismic
disturbance driven by the downward force change. We use the impulse
driven by the Lorentz-force change in the outer solar atmosphere to
derive an upper limit to the mass of erupting plasma that can escape
from the Sun. Finally, we compare the expected Lorentz-force change
at the photosphere with simple estimates from flare-driven gasdynamic
disturbances and from an estimate of the perturbed pressure from
radiative backwarming of the photosphere in flaring conditions.

---------------------------------------------------------
Title: Finding Electric Fields, Poynting and Helicity Fluxes from
Vector Magnetograms
Authors: Kazachenko, Maria; Fisher, G. H.; Welsch, B. T.
2012AAS...22020210K Altcode:
Existence of systematic measurements of vector magnetic fields allows us
to estimate electric field in the photosphere, using Poloidal-Toroidal
Decomposition of the magnetic field and its partial time derivative
(Fisher et l. 2011). The PTD method is based on solving a set of
Poisson equations which in the past has been done using Fast Fourier
Transform techniques. We modify the existing PTD method by improving
the poisson solver using a package of solvers for elliptic partial
differential equations called Fishpack. We apply the PTD with a new
Poisson equation solver to several test cases with a known electric
field. We find that for the ANMHD simulation test case application of
the new poisson solver yields a more accurate values of electric field,
Poisson and helicity fluxes than before. We further investigate the
applicability of our method to other test cases using simulations of
M. Cheung and Y. Fan and also HMI vector magnetograms.

---------------------------------------------------------
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 &amp; 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: Search and study of lightnings on planets of the Solar System
Authors: Zakharenko, V.; Konovalenko, A.; Kolyadin, V.; Zarka, P.;
Grissmeier, J. -M.; Mylostna, K.; Litvinenko, G.; Sidorchuk, M.;
Rucker, H.; Cecconi, B.; Coffre, A.; Denis, L.; Shevchenko, V.;
Nikolaenko, V.; Fisher, G.
2012EGUGA..14.8341Z Altcode:
Following the recent successful identification of lightning on Saturn
recorded by ground-based radio telescope UTR-2 and spasecraft Cassini,
we continued to study and search for electrostatic discharges on other
planets of the Solar System. With the help of the receiving equipment
with high frequency and time resolution the dispersion delay of short
powerful discharges was fixed in the frequency band 16.5...33.0 MHz,
that uniquely allows as to distinguish the lightnings and terrestrial
broadband interference. We also defined other parameters of their radio
emission. Uranus, Jupiter and Venus were selected as the following
objects for searching. Observations were carried out and are currently
under processing.

---------------------------------------------------------
Title: Global Forces in Eruptive Solar Flares: The Lorentz Force
Acting on the Solar Atmosphere and the Solar Interior
Authors: Fisher, G. H.; Bercik, D. J.; Welsch, B. T.; Hudson, H. S.
2012SoPh..277...59F Altcode: 2010arXiv1006.5247F; 2011SoPh..tmp..419F; 2011SoPh..tmp..415F
We compute the change in the Lorentz force integrated over the
outer solar atmosphere implied by observed changes in vector
magnetograms that occur during large, eruptive solar flares. This
force perturbation should be balanced by an equal and opposite force
perturbation acting on the solar photosphere and solar interior. The
resulting expression for the estimated force change in the solar
interior generalizes the earlier expression presented by Hudson,
Fisher, and Welsch (Astron. Soc. Pac. CS-383, 221, 2008), providing
horizontal as well as vertical force components, and provides a more
accurate result for the vertical component of the perturbed force. We
show that magnetic eruptions should result in the magnetic field at
the photosphere becoming more horizontal, and hence should result
in a downward (toward the solar interior) force change acting on the
photosphere and solar interior, as recently argued from an analysis
of magnetogram data by Wang and Liu (Astrophys. J. Lett. 716, L195,
2010). We suggest the existence of an observational relationship between
the force change computed from changes in the vector magnetograms,
the outward momentum carried by the ejecta from the flare, and the
properties of the helioseismic disturbance driven by the downward
force change. We use the impulse driven by the Lorentz-force change
in the outer solar atmosphere to derive an upper limit to the mass of
erupting plasma that can escape from the Sun. Finally, we compare the
expected Lorentz-force change at the photosphere with simple estimates
from flare-driven gasdynamic disturbances and from an estimate of the
perturbed pressure from radiative backwarming of the photosphere in
flaring conditions.

---------------------------------------------------------
Title: Radiative Cooling in MHD Models of the Quiet Sun Convection
Zone and Corona
Authors: Abbett, W. P.; Fisher, G. H.
2012SoPh..277....3A Altcode: 2011arXiv1102.1035A
We present a series of numerical simulations of the quiet-Sun plasma
threaded by magnetic fields that extend from the upper convection zone
into the low corona. We discuss an efficient, simplified approximation
to the physics of optically thick radiative transport through the
surface layers, and investigate the effects of convective turbulence
on the magnetic structure of the Sun's atmosphere in an initially
unipolar (open field) region. We find that the net Poynting flux below
the surface is on average directed toward the interior, while in the
photosphere and chromosphere the net flow of electromagnetic energy is
outward into the solar corona. Overturning convective motions between
these layers driven by rapid radiative cooling appears to be the source
of energy for the oppositely directed fluxes of electromagnetic energy.

---------------------------------------------------------
Title: Can We Determine Electric Fields and Poynting Fluxes from
Vector Magnetograms and Doppler Measurements?
Authors: Fisher, G. H.; Welsch, B. T.; Abbett, W. P.
2012SoPh..277..153F Altcode: 2011arXiv1101.4086F
The availability of vector-magnetogram sequences with sufficient
accuracy and cadence to estimate the temporal derivative of the magnetic
field allows us to use Faraday's law to find an approximate solution
for the electric field in the photosphere, using a Poloidal-Toroidal
Decomposition (PTD) of the magnetic field and its partial time
derivative. Without additional information, however, the electric
field found from this technique is under-determined - Faraday's law
provides no information about the electric field that can be derived
from the gradient of a scalar potential. Here, we show how additional
information in the form of line-of-sight Doppler-flow measurements,
and motions transverse to the line-of-sight determined with ad-hoc
methods such as local correlation tracking, can be combined with the
PTD solutions to provide much more accurate solutions for the solar
electric field, and therefore the Poynting flux of electromagnetic
energy in the solar photosphere. Reliable, accurate maps of the Poynting
flux are essential for quantitative studies of the buildup of magnetic
energy before flares and coronal mass ejections.

---------------------------------------------------------
Title: Momentum Distribution in Solar Flare Processes
Authors: Hudson, H. S.; Fletcher, L.; Fisher, G. H.; Abbett, W. P.;
Russell, A.
2012SoPh..277...77H Altcode:
We discuss the consequences of momentum conservation in processes
related to solar flares and coronal mass ejections (CMEs), in particular
describing the relative importance of vertical impulses that could
contribute to the excitation of seismic waves ("sunquakes"). The
initial impulse associated with the primary flare energy transport
in the impulsive phase contains sufficient momentum, as do the
impulses associated with the acceleration of the evaporation flow (the
chromospheric shock) or the CME itself. We note that the deceleration
of the evaporative flow, as coronal closed fields arrest it, will tend
to produce an opposite impulse, reducing the energy coupling into
the interior. The actual mechanism of the coupling remains unclear
at present.

---------------------------------------------------------
Title: Preface
Authors: Fan, Yuhong; Fisher, George; Leibacher, John
2012SoPh..277....1F Altcode: 2011SoPh..tmp..423F
No abstract at ADS

---------------------------------------------------------
Title: Electric Fields and Poynting Fluxes from Vector Magnetograms
Authors: Fisher, G. H.; Welsch, B. T.; Abbett, W. P.
2012decs.confE..75F Altcode:
The availability of vector-magnetogram sequences with sufficient
accuracy and cadence to estimate the temporal derivative of the magnetic
field allows us to use Faraday's law to find an approximate solution
for the electric field in the photosphere, using a Poloidal-Toroidal
Decomposition (PTD) of the magnetic field and its partial time
derivative. Without additional information, however, the electric
field found from this technique is under-determined - Faraday's law
provides no information about the electric field that can be derived
from the gradient of a scalar potential. Here, we show how additional
information in the form of line-of-sight Doppler-flow measurements,
and motions transverse to the line-of-sight determined with ad-hoc
methods such as local correlation tracking, can be combined with the
PTD solutions to provide much more accurate solutions for the solar
electric field, and therefore the Poynting flux of electromagnetic
energy in the solar photosphere. Reliable, accurate maps of the Poynting
flux are essential for quantitative studies of the buildup of magnetic
energy before flares and coronal mass ejections.

---------------------------------------------------------
Title: Determining electric fields from vector magnetograms.
Authors: Kazachenko, M.; Fisher, G. H.; Welsch, B. T.
2012decs.confE..98K Altcode:
Existence of systematic measurements of vector magnetic fields allows us
to estimate electric field in the photosphere, using Poloidal-Toroidal
Decomposition of the magnetic field and its partial time derivative
(Fisher et l. 2011). The PTD method is based on solving a set of
Poisson equations which in the past has been done using Fast Fourier
Transform techniques. We modify the existing PTD method by improving
the poisson solver using a package of solvers for elliptic partial
differential equations called Fishpack. We apply the PTD with a new
Poisson equation solver to several test cases with a known electric
field. We find that for the ANMHD simulation test case application
of the new poisson solver yields a more accurate values of electric
field than before. We further investigate the applicability of our
method to other test cases using simulations of M. Cheung and Y. Fan.

---------------------------------------------------------
Title: Roles for Data Assimilation in Studying Solar Flares &amp; CMEs
Authors: Welsch, B. T.; Abbett, W. P.; Fisher, G. H.
2011AGUFMSH54A..05W Altcode:
Solar flares and coronal mass ejections (CMEs) are driven by the
sudden release of free magnetic energy stored in electric currents
the solar corona. While there is a consensus that free energy enters
the corona from the solar interior, there is ongoing debate about the
physical processes primarily responsible for transporting free energy
into the corona and / or triggering its release once there. Since
direct measurements of the coronal vector magnetic field, necessary
to quantify coronal currents, are currently not feasible, it is hoped
that modeling of the coronal field can improve our understanding
of processes that drive the corona to flare and produce CMEs. Many
coronal modeling efforts employ spectropolarimetric observations
of the photosphere, which can be used to infer magnetic fields and
flows there; the model then relates these photospheric measurements
to coronal currents. Observations of coronal emission structures
might also usefully inform coronal field models. Here, I will discuss
different approaches to modeling the coronal magnetic field, using
both photospheric and other data sets, and possible roles for data
assimilation.

---------------------------------------------------------
Title: Can we Determine Electric Fields and Poynting Fluxes from
Vector Magnetograms and Doppler Measurements?
Authors: Fisher, G. H.; Welsch, B. T.; Abbett, W. P.
2011AGUFMSH33C..07F Altcode:
The availability of vector magnetogram sequences with sufficient
accuracy and cadence to estimate the time derivative of the magnetic
field allows us to use Faraday's law to find an approximate solution
for the electric field in the photosphere, using a Poloidal-Toroidal
Decomposition (PTD) of the magnetic field and its partial time
derivative. Without additional information, however, the electric
field found from this technique is under-determined -- Faraday's law
provides no information about the electric field that can be derived the
gradient of a scalar potential. Here, we show how additional information
in the form of line-of-sight Doppler flow measurements, and motions
transverse to the line-of-sight determined with ad-hoc methods such as
local correlation tracking, can be combined with the PTD solutions to
provide much more accurate solutions for the solar electric field,
and therefore the Poynting flux of electromagnetic energy in the
solar photosphere. Reliable, accurate maps of the Poynting flux are
essential for quantitative studies of the buildup of magnetic energy
before flares and coronal mass ejections. This work was supported by the
NASA Heliophysics Theory Program, the NASA Living-With-a-Star Program,
and the NSF Geosciences Directorate

---------------------------------------------------------
Title: Decorrelation Times of Photospheric Fields and Flows
Authors: Welsch, B. T.; Kusano, K.; Yamamoto, T. T.; Fisher, G. H.
2011AGUFMSH31A1989W Altcode:
We use autocorrelation to investigate evolution in flow fields inferred
by applying Fourier Local Correlation Tracking (FLCT) to a sequence
of high-resolution (0.3”), high-cadence (≃ 2 min.) line-of-sight
magnetograms of NOAA AR 10930 recorded by SOT/NFI aboard the Hinode
satellite over 12-13 December 2006. To baseline the timescales of
flow evolution, we also autocorrelated the magnetograms, at several
spatial binnings, to characterize the lifetimes of active region
magnetic structure as a function of spatial scale. Autocorrelation of
flow maps can be used to optimize tracking parameters, to understand
tracking algorithms' susceptibility to noise, and to estimate flow
lifetimes. Tracking parameters varied include: time interval Δ t
between magnetogram pairs tracked; spatial binning applied to the
magnetograms; and windowing parameter σ used in FLCT. In addition, we
tracked both boxcar-averaged and unaveraged magnetograms. Because flow
structures are thought to vary over a range of spatial and temporal
scales in the photospheric plasma (including unresolved scales), we
suggest that estimated flows necessarily represent a local average of
the flow pattern over space and time, and argue that flow decorrelation
times should be at least as long as Δ t to meaningfully estimate
plasma velocities. When Δ t exceeds the flow decorrelation time, then
displacements inferred from tracking represent the average velocity
over more than one flow lifetime. We also analyze decorrelation times
of flow components, divergences, and curls as functions of spatial
scale and magnetic field strength.

---------------------------------------------------------
Title: Evolution and Activity of Solar Active Regions with STEREO
Full Sun Imaging
Authors: Li, Y.; Welsch, B. T.; Lynch, B. J.; Luhmann, J. G.; Fisher,
G. H.
2011AGUFMSH13A1927L Altcode:
Solar active regions emerge from the interior of the Sun. It is believed
that the solar dynamo at the shear layer at the bottom of the convection
zone generates flux ropes, which emerge to the photosphere as active
regions. The active regions emerge with stressed and concentrated
magnetic field up to a few thousand Gauss. Following the emerging phase,
the field evolves and decays. The decay process of active regions is
not fully understood. Active regions usually have multiple flares and
CMEs. Solar eruptions consume magnetic free energy in active regions
and eject field and mass away from the Sun. Solar eruptions may play a
role in the decay of the magnetic field in active regions. The lifetime
of active regions range from hours to perhaps a few months. Stronger
active regions usually live longer than the earth view pass. We had
always a single view of the Sun before STEREO. Using the full sun
imaging of the STEREO mission, we study a few recent active regions on
the rise phase of solar cycle 24. When the regions are in earth view,
we analyze HMI magnetograms for the field and energy evolution. By
observing the total number of flares and CMEs from each region using
STEREO coronal images, we estimate the released energy through the
lifetime of these active regions. We discuss the implications to active
region energy budget and active region decay.

---------------------------------------------------------
Title: Numerical Simulation of a "Stealth" CME: Why Slow and Simple
is Not Mysterious
Authors: Lynch, B. J.; Li, Y.; Antiochos, S. K.; DeVore, C. R.;
Luhmann, J. G.; Fisher, G. H.
2011AGUFMSH43A1937L Altcode:
The stereoscopic viewing and improvements in coronagraph observations
by STEREO/SECCHI and low corona EUV and X-ray observations at multiple
wavelengths by STEREO, Hinode, and SDO -- combined with this solar
minimum's exceptionally low activity -- have given rise to the
community's interest in so-called "stealth" CMEs. A "stealth" CME is
one in which there are almost no low coronal signatures of the CME
eruption but often a very well resolved slow, flux-rope like eruption
seen in the coronagraph data. The fact that the in situ observations
of "stealth" CMEs have shown many of the signatures of magnetic clouds
(including the interplanetary flux rope structure) poses the question,
"Just how different these events are from normal CMEs?" We present a
3D numerical MHD simulation of the 2008 Jun 2 gradual streamer blowout
CME which had virtually no identifiable low coronal signatures. We
energize the field by simple footpoint shearing along the source
region's polarity inversion line (PIL) and model the background solar
wind structure using an ~2MK isothermal wind and a low-order PFSS
representation of the CR2070 synoptic magnetogram. Our results will
show that the CME "initiation" is obtained by slowly disrupting the
quasi-steady-state configuration of the helmet streamer, resulting in
the standard eruptive flare picture (albeit, on a large scale) that
ejects the sheared fields and lowers the magnetic energy stored in
filament channel. We obtain a relatively slow CME eruption and argue
that these "stealth" CMEs are no different than the standard quasi-2D
picture but are simply at the low end of the CME energy distribution. We
will show preliminary comparisons between the simulation results and
the coronagraph observations of the low coronal evolution of the CME.

---------------------------------------------------------
Title: Observational Analysis of Photospheric Magnetic Field
Restructuring During Energetic Solar Flares
Authors: Alvarado, J. D.; Buitrago, J. C.; Martinez Oliveros, J.;
Lindsey, C. A.; Abbett, W. P.; Fisher, G. H.
2011AGUFMSH13B1944A Altcode:
The magnetic field has proven to be the main driver in the behavior,
dynamics and evolution of several solar atmospheric phenomena including
sunspots, plages, faculae, CME's and flares. Observational evidence of
photospheric magnetic field restructuring during energetic flares have
shown an enhancement of the transversal field component suggesting
an apparent relation between this process with the generation of
“sunquakes”, expanding ripples on the solar photosphere as a
result of the momentum-energy transfer into the solar photosphere
and subphotosphere. In this work we present a doppler and magnetic
observational study of some recent energetic flaring events (X and
M type of the 24th solar cycle) trying to find possible acoustic
signatures and make a characterization of the photospheric magnetic
field evolution during those flares, being this the observational
basis of a future numerical modeling of the field restructuring during
this phenomenon.

---------------------------------------------------------
Title: Momentum Balance in Eruptive Solar Flares: The Lorentz Force
Acting on the Solar Atmosphere and the Solar Interior
Authors: Fisher, George H.; Bercik, David J.; Welsch, Brian T.;
Hudson, Hugh S.
2011sdmi.confE...9F Altcode:
We compute the change in the Lorentz force integrated over the outer
solar atmosphere implied by observed changes in vector magnetograms
that occur during large, eruptive solar flares. This force perturbation
should be balanced by an equal and opposite force perturbation acting on
the solar photosphere and solar interior. The resulting expression for
the estimated force change in the solar interior generalizes the earlier
expression presented by Hudson, Fisher &amp; Welsch (2008), providing
horizontal as well as vertical force components, and provides a more
accurate result for the vertical component of the perturbed force. We
show that magnetic eruptions should result in the magnetic field at
the photosphere becoming more horizontal, and hence should result in
a downward (towards the solar interior) force change acting on the
photosphere and solar interior, as recently argued from an analysis
of magnetogram data by Wang &amp; Liu. We suggest that there should
be an observational relationship between the force change computed
from changes in the vector magnetograms, the outward momentum carried
by the ejecta from the flare, and the amplitude of the helioseismic
disturbance driven by the downward force change. We use the impulse
driven by the Lorentz force change in the outer solar atmosphere to
derive an upper limit to the mass of erupting plasma that can escape
from the Sun. Finally, we compare the expected Lorentz force change
at the photosphere with simple estimates from flare-driven gasdynamic
disturbances and from an estimate of the perturbed pressure from
radiative backwarming of the photosphere in flaring conditions.

---------------------------------------------------------
Title: Radiative Cooling in MHD Models of the Quiet Sun Convection
Zone and Corona
Authors: Abbett, William; Fisher, George
2011shin.confE..10A Altcode:
We present a series of numerical simulations of the quiet Sun plasma
threaded by magnetic fields that extend from the upper convection zone
into the low corona. We discuss an efficient, simplified approximation
to the physics of optically thick radiative transport through the
surface layers, and investigate the effects of convective turbulence
on the magnetic structure of the Sun's atmosphere in an initially
unipolar (open field) region. We find that the net Poynting flux below
the surface is on average directed toward the interior, while in the
photosphere and chromosphere the net flow of electromagnetic energy is
outward into the solar corona. Overturning convective motions between
these layers driven by rapid radiative cooling appears to be the source
of energy for the oppositely directed fluxes of electromagnetic energy.