welsch

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Author name code: welsch
ADS astronomy entries on 2022-09-14
author:Welsch, Brian

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Title: Reconstruction of Photospheric Velocity Fields from Highly
Corrupted Data
Authors: Rempel, Erico L.; Chertovskih, Roman; Davletshina, Kamilla
R.; Silva, Suzana S. A.; Welsch, Brian T.; Chian, Abraham C. -L.
2022ApJ...933....2R Altcode: 2022arXiv220509846R
The analysis of the photospheric velocity field is essential for
understanding plasma turbulence in the solar surface, which may be
responsible for driving processes such as magnetic reconnection, flares,
wave propagation, particle acceleration, and coronal heating. Currently,
the only available methods to estimate velocities at the solar
photosphere transverse to an observer's line of sight infer flows from
differences in image structure in successive observations. Due to data
noise, algorithms such as local correlation tracking may lead to a
vector field with wide gaps where no velocity vectors are provided. In
this paper, a novel method for image inpainting of highly corrupted data
is proposed and applied to the restoration of horizontal velocity fields
in the solar photosphere. The restored velocity field preserves all
the vector field components present in the original field. The method
shows robustness when applied to both simulated and observational data.

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Title: Invited Review: Short-term Variability with the Observations
from the Helioseismic and Magnetic Imager (HMI) Onboard the Solar
Dynamics Observatory (SDO): Insights into Flare Magnetism
Authors: Kazachenko, Maria D.; Albelo-Corchado, Marcel F.; Tamburri,
Cole A.; Welsch, Brian T.
2022SoPh..297...59K Altcode:
Continuous vector magnetic-field measurements by the Helioseismic and
Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO)
allow us to study magnetic-field properties of many flares. Here, we
review new observational aspects of flare magnetism described using
SDO data, including statistical properties of magnetic-reconnection
fluxes and their rates, magnetic fluxes of flare dimmings, and
magnetic-field changes during flares. We summarize how these results,
along with statistical studies of coronal mass ejections (CMEs),
have improved our understanding of flares and the flare/CME feedback
relationship. Finally, we highlight future directions to improve
the current state of understanding of solar-flare magnetism using
observations.

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Title: Toward Improved Understanding of Magnetic Fields Participating
in Solar Flares: Statistical Analysis of Magnetic Fields within
Flare Ribbons
Authors: Kazachenko, Maria D.; Lynch, Benjamin J.; Savcheva, Antonia;
Sun, Xudong; Welsch, Brian T.
2022ApJ...926...56K Altcode: 2021arXiv211106048K
Violent solar flares and coronal mass ejections (CMEs) are magnetic
phenomena. However, how magnetic fields reconnecting in the flare
differ from nonflaring magnetic fields remains unclear owing to the
lack of studies of the flare magnetic properties. Here we present a
first statistical study of flaring (highlighted by flare ribbons) vector
magnetic fields in the photosphere. Our systematic approach allows us to
describe the key physical properties of solar flare magnetism, including
distributions of magnetic flux, magnetic shear, vertical current, and
net current over flaring versus nonflaring parts of the active region
(AR), and compare these with flare/CME properties. Our analysis suggests
that while flares are guided by the physical properties that scale with
AR size, like the total amount of magnetic flux that participates in
the reconnection process and the total current (extensive properties),
CMEs are guided by mean properties, like the fraction of the AR magnetic
flux that participates (intensive property), with little dependence
on the amount of shear at the polarity inversion line (PIL) or the
net current. We find that the nonneutralized current is proportional
to the amount of shear at the PIL, providing direct evidence that net
vertical currents are formed as a result of any mechanism that could
generate magnetic shear along the PIL. We also find that eruptive
events tend to have smaller PIL fluxes and larger magnetic shears than
confined events. Our analysis provides a reference for more realistic
solar and stellar flare models. The database is available online and
can be used for future quantitative studies of flare magnetism.

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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: Toward Improved Understanding of Magnetic Fields Participating
in Solar Flares: Statistical Analysis of Magnetic Field within
Flare Ribbons
Authors: Kazachenko, Maria; Lynch, Benjamin; Savcheva, Antonia;
Welsch, Brian
2021AGUFMSH45B2378K Altcode:
Flares and coronal mass ejections are manifestations of magnetic
evolution in the solar corona in which magnetic reconnection is
believed to play key roles. While the properties of underlying,
photospheric line-of-sight magnetic fields of active regions (ARs)
as a whole have been analyzed in detail, properties of vector magnetic
fields that participate in the reconnection process, highlighted by the
flare ribbons, have not been described. Here we present a statistical
analysis of vector magnetic field properties in 40 ARs associated with
33 eruptive and 7 confined flares, of GOES class C9.0 and greater. For
every event in the database, we use a HMI/SDO vector magnetogram, and
AIA 1600A images to calculate various properties of the photospheric
vector magnetic field within the AR, flare ribbons and the polarity
inversion line (PIL) areas: magnetic flux, reconnection flux fraction,
magnetic shear, vertical electric current and current neutralization. We
find that while the peak X-ray flux has a strong correlation with
ribbon reconnection flux, it has only moderate correlation with the
magnetic shear within ribbon- and PIL- areas and the degree of current
neutralization. We find a new linear relationship between the amount
of non-neutralized current within the AR (or ribbon) and the amount of
shear at PIL. This scaling is consistent with earlier simulations and
case studies, of net currents being formed as a result of any mechanism
that could generate magnetic shear along PIL: flux emergence, twisting
or shearing motions. Finally, we find that the CME speed has a much
stronger correlation with the reconnection flux fraction than with
any other active region property. We also find that for a fixed peak
X-ray flux, eruptive events tend to have smaller PIL fluxes and larger
magnetic shears than confined events. To summarize, our observational
analysis, supported by MHD ARMS and magnetofrictional simulations,
suggests that flare peak X-ray fluxes and CME speeds are most strongly
guided by the total amount of magnetic flux that participates in the
reconnection process and the amount of the flux in the overlying field,
than by the amount of PIL shear or AR net current.

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Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.

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Title: Oscillations observed in umbra, plage, quiet-Sun and the
polarity inversion line of active region 11158 using Helioseismic
Magnetic Imager/Solar Dynamics Observatory data
Authors: Norton, A. A.; Stutz, R. B.; Welsch, B. T.
2021RSPTA.37900175N Altcode: 2021arXiv210101349N
Using data from the Helioseismic Magnetic Imager, we report on the
amplitudes and phase relations of oscillations in quiet-Sun, plage,
umbra and the polarity inversion line (PIL) of an active region
NOAA#11158. We employ Fourier, wavelet and cross-correlation spectra
analysis. Waves with 5 min periods are observed in umbra, PIL and plage
with common phase values of φ(v, I) = π/2, φ(v, Blos)
= -(π/2). In addition, φ(I, Blos) = π in plage are
observed. These phase values are consistent with slow standing or
fast standing surface sausage wave modes. The line width variations,
and their phase relations with intensity and magnetic oscillations,
show different values within the plage and PIL regions, which may
offer a way to further differentiate wave mode mechanics. Significant
Doppler velocity oscillations are present along the PIL, meaning
that plasma motion is perpendicular to the magnetic field lines, a
signature of Alvènic waves. A time-distance diagram along a section
of the PIL shows Eastward propagating Doppler oscillations converting
into magnetic oscillations; the propagation speeds range between 2
and 6 km s-1. Lastly, a 3 min wave is observed in select
regions of the umbra in the magnetogram data. This article is
part of the Theo Murphy meeting issue `High-resolution wave dynamics
in the lower solar atmosphere'.

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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: Extended, Kilogauss Bald Patches in the Super-Flaring Solar
Active Region 12673
Authors: Sun, Xudong; Gibson, Sarah; Welsch, Brian; Titov, Viacheslav
2021cosp...43E1730S Altcode:
Bald patch (BP) is a magnetic topological feature where U-shaped
field lines turn tangent to the photosphere. When accompanied by
shear, BPs suggest the existence of pre-eruption magnetic flux ropes
(MFRs). Previous studies often found them in young solar active regions
(ARs) with patchy flux emergence, or decaying ARs with weaker magnetic
field. Here we report on a coherent, strong-field example observed
in the super-flaring AR 12673. The central BP, located in a narrow
delta_x000E_-spot penumbral lane, extended over 10 Mm with field
strength above 2 kG. It formed over a period 10 hr, which featured fast
Doppler downflow, gradual azimuth rotation, field strength reduction,
and field gradient enhancement. It then rapidly disintegrated during
a GOES X9 flare. Coronal field extrapolation reveals a low-lying,
kilogauss MFR with over two turns of twist wrapped inside three
intersecting BP separatrices (BPSs). The early-phase flare ribbons
coincide with BPS foot prints. We discuss the BP formation mechanism
such as flux cancellation, its stability condition, and its role in
the eruption.

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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: Statistical Analysis of Solar Flare Ribbon Properties Using
Observations from Solar Dynamics Observatory
Authors: Kazachenko, M.; Lynch, B. J.; Welsch, B. T.; Sun, X.
2019AGUFMSH12B..03K Altcode:
We extend our RibbonDB database of &gt;3000 solar flare ribbon events
corresponding to every flare of GOES class C1.0 and greater within
45 degrees from the disk center, from April 2010 until April 2019,
observed by the Solar Dynamics Observatory (SDO). For every event in
the database, we compare GOES X-ray and SDO/EVE flare properties with
corresponding active-region and flare-ribbon properties, including
cumulative reconnection flux and peak reconnection flux rate. We present
the results and discuss what could be learnt from studying typical
and outlier flares to deepen our understanding of solar flare physics.

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Title: Photospheric Flows &amp; DKIST: Resolving Both Smaller Scales
And Open Questions
Authors: Welsch, Brian
2019AAS...23422602W Altcode:
The technical aim of DKIST is to resolve dynamics on spatial scales
not yet observed - an achievement that also promises to resolve
many important science questions. For instance, the characteristics
of photospheric velocity fields on currently unresolved scales -
such as the strength of vorticity present, and the lifetimes of flow
patterns - have substantial implications for theories chromospheric
and coronal heating. Parker long ago hypothesized that the braiding of
flux tubes by photospheric flows might play a role in the generation of
current sheets above the photosphere, whose dissipation should lead to
atmospheric heating. More recently, van Ballegooijen and collaborators
have proposed that photospheric flows evolving on time scales shorter
than the round-trip, photosphere-to-transition-region travel time for
Alfven waves could lead to counter-propagating waves that should induce
turbulence and subsequent dissipative heating. Using methods like
local correlation tracking (LCT) and feature tracking to infer flows
in rapid-cadence, high-resolution DKIST observations of magnetized
regions of the lower solar atmosphere should enable testing these,
and other, coronal heating models.

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Title: What is the role of flare ribbon structure on CME speeds?
Authors: Welsch, Brian; Hencheck, Michael; Kazachenko, Maria D.;
Ginsburg, David
2019AAS...23411201W Altcode:
Coronal mass ejections (CMEs) are the primary drivers of severe space
weather disturbances, but remain poorly understood. Hence, efforts
to characterize and predict their dynamics are ongoing. Many CMEs
are associated with solar flares, and, in particular, flare ribbons,
which are bright bands of strongly enhanced emission originating above
magnetized areas of the photosphere. As a solar eruption progresses,
these ribbons typically move across areas that contain fluxes of
order 1021 Mx or more. The rate at which the ribbons
sweep across photospheric flux is thought to correspond to the rate
of coronal magnetic reconnection. Previous studies found significant
correlations between CME speeds and the total amount of flux swept by
flare ribbons. Here, we investigate relationships between CME speeds
and spatial moments of their source-region photospheric magnetic fields
and flare ribbons, including spatial moments of: (i) magnetic flux in
the source region; (ii) signed and (iii) unsigned magnetic flux within
ribbon areas; and (iv) binary maps ribbon areas. Our sample consists of
N = 75 CMEs in the SOHO/LASCO CME catalog that were manually associated
with flare ribbons identified in SDO/AIA data. Vector magnetograms
obtained by SDO/HMI were used in our calculations of source-region
magnetic properties. We confirm prior results that correlations
between CME speeds and total magnetic fluxes swept by flare ribbons are
statistically significant. We also find that spatial moments of ribbon
magnetic fields are also significantly correlated with CME speeds.

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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: Flux Accretion and Coronal Mass Ejection Dynamics
Authors: Welsch, Brian T.
2018SoPh..293..113W Altcode: 2017arXiv170109082W
Coronal mass ejections (CMEs) are the primary drivers of severe
space weather disturbances in the heliosphere. Models of CME dynamics
have been proposed that do not fully include the effects of magnetic
reconnection on the forces driving the ejection. Both observations and
numerical modeling, however, suggest that reconnection likely plays
a major role in most, if not all, fast CMEs. Here, we theoretically
investigate the accretion of magnetic flux onto a rising ejection
by reconnection involving the ejection's background field. This
reconnection alters the magnetic structure of the ejection and its
environment, thereby modifying the forces acting upon the ejection,
generically increasing its upward acceleration. The modified forces,
in turn, can more strongly drive the reconnection. This feedback
process acts, effectively, as an instability, which we refer to as
a reconnective instability. Our analysis implies that CME models
that neglect the effects of reconnection cannot accurately describe
observed CME dynamics. Our ultimate aim is to understand changes in CME
acceleration in terms of observable properties of magnetic reconnection,
such as the amount of reconnected flux. This flux can be estimated
from observations of flare ribbons and photospheric magnetic fields.

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Title: Using Photospheric Vector Magnetograms to Drive Coronal
Field Models
Authors: Welsch, Brian T.; CGEM Team
2018shin.confE..89W Altcode:
Solar flares and coronal mass ejections (CMEs) are driven by the
release of free magnetic energy stored in electric currents in the
coronal magnetic field. Without photospheric forcing, the large-scale
coronal field should, in principle, maintain a nearly steady
equilibrium. Photospheric evolution must therefore play a central
role in driving the corona to produce flares and CMEs. Consequently,
observations of the photospheric vector magnetic field provide crucial
inputs for understanding this

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Title: Flux Accretion and Coronal Mass Ejection Dynamics
Authors: Welsch, Brian T.
2018shin.confE.190W Altcode:
Coronal mass ejections (CMEs) are the primary drivers of severe
space weather disturbances in the heliosphere. Models of CME dynamics
have been proposed that do not fully include the effects of magnetic
reconnection on the forces driving the ejection. Both observations and
numerical modeling, however, suggest that reconnection likely plays
a major role in most, if not all, fast CMEs. Here, we theoretically
investigate the accretion of magnetic flux onto a rising ejection
by reconnection involving the ejection's background field. This
reconnection alters the magnetic structure of the ejection and its
environment, thereby modifying the forces acting upon the ejection,
generically increasing its upward acceleration. The modified forces,
in turn, can more strongly drive the reconnection. This feedback
process acts, effectively, as an instability, which we refer to as
a reconnective instability. Our analysis implies that CME models
that neglect the effects of reconnection do not correctly describe
observed CME dynamics. Our ultimate aim is to understand changes in CME
acceleration in terms of observable properties of magnetic reconnection,
such as the amount of reconnected flux, deduced from observations of
flare ribbons and photospheric magnetic fields.

---------------------------------------------------------
Title: What are the Roles of Magnetic Field and Flare Ribbon Structure
on CME Dynamics?
Authors: Ginsburg, David E.; Welsch, Brian
2018tess.conf10420G Altcode:
Disturbances in the near-Earth space environment - known as space
weather events - can impact humanity's infrastructure. Understanding
and predicting space weather, however, remains challenging. Because
coronal mass ejections (CMEs) are the primary driver of severe space
weather disturbances, much work revolves around the characterization
and prediction of their dynamics. Some CMEs are associated with solar
flares, and, in particular, "ribbons" of strongly enhanced emission
near the base of the corona (the Sun's outer atmosphere). Previous
work demonstrated a statistical relationship between CME speeds and
the strengths of their source flares. It has been proposed that
quadrupolar magnetic regions are more unstable to eruption than
bipolar magnetic regions. Motivated by the idea that source regions'
magnetic structure might influence eruption dynamics, we investigate
relationships between CME speeds and properties of their source-region
magnetic fields and flare ribbons, including spatial moments of: (i)
the radial photospheric flux distribution; (ii) binary maps of the
flare ribbons; and (iii) flux-weighted maps of the flare-ribbons. We
first worked to associate flare ribbons in an existing database with
CMEs, by comparing the times and locations of flares as determined by
the NOAA/GOES flare catalog with CME data taken from the SOHO/LASCO
CME catalog. The N = 76 flare/CME associations that we made comprise
our dataset. Magnetic field maps of CME source regions, obtained with
the HMI satellite, were used to calculate the spatial moments that
we analyze. We have calculated correlations between these moments
and two measures of CME speeds, as well as single- and multivariable
regressions of CME speeds as functions of these moments.

---------------------------------------------------------
Title: Flux Accretion and Coronal Mass Ejection Dynamics
Authors: Welsch, Brian T.
2018tess.conf10414W Altcode:
Coronal mass ejections (CMEs) are the primary drivers of severe
space weather disturbances in the heliosphere. Models of CME dynamics
have been proposed that do not fully include the effects of magnetic
reconnection on the forces driving the ejection. Both observations and
numerical modeling, however, suggest that reconnection likely plays
a major role in most, if not all, fast CMEs. Here, we theoretically
investigate the accretion of magnetic flux onto a rising ejection
by reconnection involving the ejection's background field. This
reconnection alters the magnetic structure of the ejection and its
environment, thereby modifying the forces acting upon the ejection,
generically increasing its upward acceleration. The modified forces,
in turn, can more strongly drive the reconnection. This feedback
process acts, effectively, as an instability, which we refer to as
a reconnective instability. Our analysis implies that CME models
that neglect the effects of reconnection cannot accurately describe
observed CME dynamics. Our ultimate aim is to understand changes in CME
acceleration in terms of observable properties of magnetic reconnection,
such as the amount of reconnected flux, deduced from observations of
flare ribbons and photospheric magnetic fields. &lt;hr&gt;

---------------------------------------------------------
Title: A Database of Flare Ribbon Properties From Solar Dynamics
Observatory: Reconnection Flux
Authors: Kazachenko, Maria D.; Welsch, Brian; Lynch, Benjamin J.;
Sun, Xudong
2017SPD....4810824K Altcode:
We present a database of 3137 solar flare ribbon events corresponding to
every flare of GOES class C1.0 and greater within 45 degrees from the
disk center, from April 2010 until April 2016, observed by the Solar
Dynamics Observatory. For every event in the database, we compare the
GOES peak X-ray flux with corresponding active-region and flare-ribbon
properties. We find that while the peak X-ray flux is not correlated
with the AR unsigned magnetic flux, it is strongly correlated with the
flare ribbon reconnection flux, flare ribbon area, and the fraction of
active region flux that undergoes reconnection. We find the relationship
between the peak X-ray flux and the flare ribbon reconnection flux to
be I_{X,peak} ~ \Phi_{ribbon}^{1.3} for flares &gt;M1 and I_{X,peak}
~ \Phi_{ribbon}^{1.5} over the entire flare set (&gt;C1). This scaling
law is consistent with earlier hydrodynamic simulations of impulsively
heated flare loops. Using the flare reconnection flux as a proxy
for the total released flare energy E, we find that the occurrence
frequency of flare energies follows a power-law dependence: dN/dE ~
E^{-1.6} for E within 10^{31} to 10^{33} erg, consistent with earlier
studies of solar and stellar flares. This database is available online
and can be used for future quantitative studies of flares.

---------------------------------------------------------
Title: A Database of Flare Ribbon Properties from the Solar Dynamics
Observatory. I. Reconnection Flux
Authors: Kazachenko, Maria D.; Lynch, Benjamin J.; Welsch, Brian T.;
Sun, Xudong
2017ApJ...845...49K Altcode: 2017arXiv170405097K
We present a database of 3137 solar flare ribbon events corresponding
to every flare of GOES class C1.0 and greater within 45° from the
central meridian, from 2010 April until 2016 April, observed by the
Solar Dynamics Observatory. For every event in the database, we compare
the GOES peak X-ray flux with the corresponding active region and
flare ribbon properties. We find that while the peak X-ray flux is not
correlated with the active region unsigned magnetic flux, it is strongly
correlated with the flare ribbon reconnection flux, flare ribbon area,
and the fraction of active region flux that undergoes reconnection. We
find the relationship between the peak X-ray flux and the flare
ribbon reconnection flux to be {I}{{X},{peak}}\propto {{{Φ
}}}{ribbon}1.5. This scaling law is consistent
with earlier hydrodynamic simulations of impulsively heated flare
loops. Using the flare reconnection flux as a proxy for the total
released flare energy E, we find that the occurrence frequency of
flare energies follows a power-law dependence: {dN}/{dE}\propto
{E}-1.6 for {10}31&lt; E&lt; {10}33
{erg}, consistent with earlier studies of solar and stellar flares. The
database is available online and can be used for future quantitative
studies of flares.

---------------------------------------------------------
Title: Flux Accretion and Coronal Mass Ejection Dynamics
Authors: Welsch, Brian
2017SPD....4820607W Altcode:
Coronal mass ejections (CMEs) are the primary drivers of severe
space weather disturbances in the heliosphere. The equations of ideal
magnetohydrodynamics (MHD) have been used to model the onset and, in
some cases, the subsequent acceleration of ejections. Both observations
and numerical modeling, however, suggest that magnetic reconnection
likely plays a major role in most, if not all, fast CMEs. Here, we
theoretically investigate the dynamical effects of accretion of magnetic
flux onto a rising ejection by reconnection involving the ejection's
background field. This reconnection alters the magnetic structure
of the ejection and its environment, thereby modifying forces acting
during the eruption, generically leading to faster acceleration of the
CME. Our ultimate aim is to characterize changes in CME acceleration
in terms of observable properties of magnetic reconnection, such as
the amount of reconnected flux, deduced from observations of flare
ribbons and photospheric magnetic fields.

---------------------------------------------------------
Title: A Database of Flare Ribbon Properties From Solar Dynamics
Observatory: Reconnection Flux
Authors: Kazachenko, Maria D.; Welsch, Brian T.; Lynch, Benjamin;
Sun, Xudong
2017shin.confE..35K Altcode:
We present a database of 3137 solar flare ribbon events corresponding to
every flare of GOES class C1.0 and greater within 45 degrees from the
disk center, from April 2010 until April 2016, observed by the Solar
Dynamics Observatory. For every event in the database, we compare the
GOES peak X-ray flux with corresponding active-region and flare-ribbon
properties. We find that while the peak X-ray flux is not correlated
with the AR unsigned magnetic flux, it is strongly correlated with the
flare ribbon reconnection flux, flare ribbon area, and the fraction of
active region flux that undergoes reconnection. We find the relationship
between the peak X-ray flux and the flare ribbon reconnection flux
to be I_{X,peak} Φ_{ribbon}^{1.3} for flares &gt;M1 and I_{X,peak}
Φ_{ribbon}^{1.5} over the entire flare set (&gt;C1). This scaling
law is consistent with earlier hydrodynamic simulations of impulsively
heated flare loops. Using the flare reconnection flux as a proxy for the
total released flare energy E, we find that the occurrence frequency
of flare energies follows a power-law dependence: dN/dE E^{-1.6} for
E within 10^{31} to 10^{33} erg, consistent with earlier studies of
solar and stellar flares. This database is available online and can
be used for future quantitative studies of flares.

---------------------------------------------------------
Title: Advanced Materials Characterization of P-Rich and P-Poor
Regions Within Single-Crystal Olivine
Authors: Hammer, J. E.; Ishii, H. A.; Bradley, J. P.; Shea, T.;
Welsch, B.; Hellebrand, E.
2017LPI....48.2375H Altcode:
We are studying how P is incorporated in olivine, by resolving
differences in the abundance and geometry of defects within P-rich
and P-poor olivine.

---------------------------------------------------------
Title: Magmatic Cooling History of Troctolite 76535 Constrained by
Diffusion Modeling of Olivine and Plagioclase Compositional Zonation
Authors: Hammer, J. E.; Shea, T.; Taylor, G. J.; Hellebrand, E.;
Welsch, B.
2017LPI....48.1274H Altcode:
Rapid initial crystallization of 76535 is suggested by diffusion
modeling of olivine compositional zonation.

---------------------------------------------------------
Title: The Roles of Reconnected Flux and Overlying Fields in CME
Speeds
Authors: Deng, Minda; Welsch, Brian T.
2017SoPh..292...17D Altcode: 2015arXiv150402905D
Researchers have reported i) correlations of coronal mass ejection
(CME) speeds and the total photospheric magnetic flux swept out by
flare ribbons in flare-associated eruptive events, and, separately,
ii) correlations of CME speeds and more rapid decay, with height,
of magnetic fields in potential-field coronal models above eruption
sites. Here, we compare the roles of both ribbon fluxes and the
decay rates of overlying fields in a set of 16 eruptive events. We
confirm previous results that higher CME speeds are associated
with both higher ribbon fluxes and more rapidly decaying overlying
fields. We find the association with ribbon fluxes to be weaker than
a previous report, but stronger than the dependence on the decay rate
of overlying fields. Since the photospheric ribbon flux is thought
to approximate the amount of coronal magnetic flux reconnected during
the event, the correlation of speeds with ribbon fluxes suggests that
reconnection plays some role in accelerating CMEs. One possibility
is that reconnected fields that wrap around the rising ejection
produce an increased outward hoop force, thereby increasing CME
acceleration. The correlation of CME speeds with more rapidly decaying
overlying fields might be caused by greater downward magnetic tension
in stronger overlying fields, which could act as a source of drag on
rising ejections.

---------------------------------------------------------
Title: A Database of Flare Ribbons Observed By Solar Dynamics
Observatory
Authors: Kazachenko, M.; Lynch, B. J.; Welsch, B. T.
2016AGUFMSH34A..03K Altcode:
Flare ribbons are emission structures observed during flares in
transition-region and in chromospheric. They typically straddle a
polarity inversion line (PIL) of the radial magnetic field at the
photosphere, and move apart as the flare progresses. The ribbon flux -
the amount of unsigned photospheric magnetic flux swept out by flare
ribbons - is thought to be related to the amount coronal magnetic
reconnection, and hence provides a key diagnostic tool for understanding
the physical processes at work in flares and CMEs. Previous measurements
of the magnetic flux swept out by flare ribbons required time-consuming
co-alignment between magnetograph and intensity data from different
instruments, explaining why those studies only analyzed, at most,
a few events. The launch of the Helioseismic and Magnetic Imager
(HMI) and the Atmospheric Imaging Assembly (AIA), both aboard the
Solar Dynamics Observatory (SDO), presented a rare opportunity to
automatically compile a complete dataset of flare-ribbon events. Here
we present a dataset of both flare ribbon positions and reconnection
fluxes, as a function of time, for all C-class flares within 45 degrees
of disk center observed by the SDO.

---------------------------------------------------------
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.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: Using Two-Ribbon Flare Data Set to Constrain Flare Properties
Authors: Kazachenko, Maria D.; Lynch, Benjamin J.; Welsch, Brian T.
2016shin.confE.118K Altcode:
Flare ribbons are emission structures that are frequently observed
during flares in transition-region and chromospheric radiation. These
typically straddle a polarity inversion line (PIL) of the radial
magnetic field at the photosphere, and move apart as the flare
progresses. The ribbon flux - the amount of unsigned photospheric
magnetic flux swept out by flare ribbons - is thought to be related
to the amount coronal magnetic reconnection, and hence provides a key
diagnostic tool for understanding the physical processes at work in
flares and CMEs. Previous measurements of the magnetic flux swept
out by flare ribbons required time-consuming co-alignment between
magnetograph and intensity data from different instruments, explaining
why those studies only analyzed, at most, a few events. The launch
of the Helioseismic and Magnetic Imager (HMI) and the Atmospheric
Imaging Assembly (AIA), both aboard the Solar Dynamics Observatory
(SDO), presented a rare opportunity to compile a much larger sample of
flare-ribbon events than could readily be assembled before. We created
a dataset of 407 events of both flare ribbon positions and fluxes,
as a function of time, for all C8.-class and greater flares within
45 degrees of disk center observed by SDO from April 2010 till April
2016. For this purpose, we used vector magnetograms (2D magnetic field
maps) from HMI and UV images from AIA. A critical problem with using
unprocessed AIA data is the existence of spurious intensities in AIA
data associated with strong flare emission, most notably

---------------------------------------------------------
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: Revisiting Ribbon Fluxes and CME Speeds
Authors: Welsch, Brian; Kazachenko, Maria D.; Hencheck, Michael
2016SPD....47.0338W Altcode:
The dynamics of coronal mass ejections (CMEs) remain poorly
understood. A previous study found that the final speeds of CMEs were
strongly correlated with the amount of photospheric magnetic flux
swept out by flare ribbons. The latter quantity, which we refer to as
the ribbon flux, is thought to be directly related to the amount of
coronal magnetic flux that reconnects during an eruption. The prior
study, however, analyzed flare ribbons associated with a small sample
(N=13) of relatively fast CMEs (all &gt; 600 km/s, mean speed &gt;
1300 km/s). With the launch of the Solar Dynamics Observatory (SDO)
in 2010, automated co-registration of ribbon images observed in UV by
its Atmospheric Imaging Assembly (AIA) with line-of-sight magnetograms
observed by its Helioseismic and Magnetic Imager (HMI) enabled
compilation of a relatively large database of ribbon fluxes. Here,
we characterize relationships between ribbon fluxes and the speeds
(and other properties) of manually-associated CMEs in a sample of
several dozen events.

---------------------------------------------------------
Title: Using Two-Ribbon Flare Observations and MHD Simulations to
Constrain Flare Properties
Authors: Kazachenko, Maria D.; Lynch, Benjamin J.; Welsch, Brian
2016SPD....47.0612K Altcode:
Flare ribbons are emission structures that are frequently observed
during flares in transition-region and chromospheric radiation. These
typically straddle a polarity inversion line (PIL) of the radial
magnetic field at the photosphere, and move apart as the flare
progresses. The ribbon flux - the amount of unsigned photospheric
magnetic flux swept out by flare ribbons - is thought to be related
to the amount coronal magnetic reconnection, and hence provides a key
diagnostic tool for understanding the physical processes at work in
flares and CMEs. Previous measurements of the magnetic flux swept
out by flare ribbons required time-consuming co-alignment between
magnetograph and intensity data from different instruments, explaining
why those studies only analyzed, at most, a few events. The launch
of the Helioseismic and Magnetic Imager (HMI) and the Atmospheric
Imaging Assembly (AIA), both aboard the Solar Dynamics Observatory
(SDO), presented a rare opportunity to compile a much larger sample of
flare-ribbon events than could readily be assembled before. We created
a dataset of 363 events of both flare ribbon positions and fluxes,
as a function of time, for all C9.-class and greater flares within
45 degrees of disk center observed by SDO from June 2010 till April
2015. For this purpose, we used vector magnetograms (2D magnetic field
maps) from HMI and UV images from AIA. A critical problem with using
unprocessed AIA data is the existence of spurious intensities in AIA
data associated with strong flare emission, most notably "blooming"
(spurious smearing of saturated signal into neighboring pixels, often in
streaks). To overcome this difficulty, we have developed an algorithmic
procedure that effectively excludes artifacts like blooming. We present
our database and compare statistical properties of flare ribbons,
e.g. evolutions of ribbon reconnection fluxes, reconnection flux rates
and vertical currents with the properties from MHD simulations.

---------------------------------------------------------
Title: Active Region Emergence and Remote Flares
Authors: Fu, Yixing; Welsch, Brian T.
2016SoPh..291..383F Altcode: 2016SoPh..tmp...13F; 2015arXiv150406633F
We study the effect of new emerging solar active regions on the
large-scale magnetic environment of existing regions. We first
present a theoretical approach to quantify the "interaction energy"
between new and pre-existing regions as the difference between i) the
summed magnetic energies of their individual potential fields and ii)
the energy of their superposed potential fields. We expect that this
interaction energy can, depending upon the relative arrangements of
newly emerged and pre-existing magnetic flux, indicate the existence
of "topological" free magnetic energy in the global coronal field
that is independent of any "internal" free magnetic energy due
to coronal electric currents flowing within the newly emerged and
pre-existing flux systems. We then examine the interaction energy in
two well-studied cases of flux emergence, but find that the predicted
energetic perturbation is relatively small compared to energies released
in large solar flares. Next, we present an observational study of the
influence of the emergence of new active regions on flare statistics
in pre-existing active regions, using NOAA's Solar Region Summary and
GOES flare databases. As part of an effort to precisely determine the
emergence time of active regions in a large event sample, we find that
emergence in about half of these regions exhibits a two-stage behavior,
with an initial gradual phase followed by a more rapid phase. Regarding
flaring, we find that the emergence of new regions is associated with
a significant increase in the occurrence rate of X- and M-class flares
in pre-existing regions. This effect tends to be more significant
when pre-existing and new emerging active regions are closer. Given
the relative weakness of the interaction energy, this effect suggests
that perturbations in the large-scale magnetic field, such as topology
changes invoked in the "breakout" model of coronal mass ejections,
might play a significant role in the occurrence of some flares.

---------------------------------------------------------
Title: Data Set of Flare-Ribbon Reconnected Magnetic Fluxes: A
Critical Tool for Understanding Solar Flares and Eruptions
Authors: Kazachenko, M.; Lynch, B. J.; Welsch, B. T.
2015AGUFMSH23D..08K Altcode:
Flare ribbons are emission structures that are frequently observed
during flares in transition-region and chromospheric radiation. These
typically straddle a polarity inversion line (PIL) of the radial
magnetic field at the photosphere, and move apart as the flare
progresses. The ribbon flux - the amount of unsigned photospheric
magnetic flux swept out by flare ribbons - is thought to be related
to the amount coronal magnetic reconnection, and hence provides a key
diagnostic tool for understanding the physical processes at work in
flares and CMEs. Previous measurements of the magnetic flux swept
out by flare ribbons required time-consuming co-alignment between
magnetograph and intensity data from different instruments, explaining
why those studies only analyzed, at most, a few events. The launch
of the Helioseismic and Magnetic Imager (HMI) and the Atmospheric
Imaging Assembly (AIA), both aboard the Solar Dynamics Observatory
(SDO), presented a rare opportunity to compile a much larger sample of
flare-ribbon events than could readily be assembled before. We created
a dataset of 141 events of both flare ribbon positions and fluxes,
as a function of time, for all C9.-class and greater flares within 45
degrees of disk center observed by SDO from January 2013 till April
2015. For this purpose, we used vector magnetograms (2D magnetic field
maps) from HMI and UV images from AIA. A critical problem with using
unprocessed AIA data is the existence of spurious intensities in AIA
data associated with strong flare emission, most notably "blooming"
(spurious smearing of saturated signal into neighboring pixels,
often in streaks). To overcome this difficulty, we have developed
an algorithmic procedure that effectively excludes artifacts like
blooming. We present our database and compare statistical properties
of flare ribbons, e.g. evolutions of ribbon reconnection fluxes and
reconnection flux rates, with the properties from theoretical models.

---------------------------------------------------------
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: A Data Set of Flare-Ribbon Magnetic Fluxes: A Critical Tool
for Understanding Solar Flares &amp; Eruptions
Authors: Kazachenko, Maria D.; Lynch, Benjamin J.; Welsch, Brian T.
2015shin.confE..13K Altcode:
Flare Ribbons are emission structures that are frequently observed
during flares in transition-region and chromospheric radiation. These
typically straddle a polarity inversion line (PIL) of the radial
magnetic field at the photosphere, and move apart as the flare
progresses. The ribbon flux -- the amount of unsigned photospheric
magnetic flux swept out by flare ribbons -- is thought to be related
to the amount coronal magnetic reconnection, and hence provides a key
diagnostic tool for understanding the physical processes at work in
flares and CMEs. Previous measurements of the magnetic flux swept
out by flare ribbons required time-consuming co-alignment between
magnetograph and intensity data from different instruments, explaining
why those studies only analyzed, at most, a few events. The launch
of the Helioseismic and Magnetic Imager (HMI) and the Atmospheric
Imaging Assembly (AIA), both aboard the Solar Dynamics Observatory
(SDO), presented a rare opportunity to compile a much larger sample of
flare-ribbon events than could readily be assembled before. We created
a dataset of 141 events of both flare ribbon positions and fluxes,
as a function of time, for all C9.-class and greater flares within 45
degrees of disk center observed by SDO from January 2013 till April
2015. For this purpose, we used vector magnetograms (2D magnetic field
maps) from HMI and UV images from AIA. A critical problem with using
unprocessed AIA data is the existence of spurious intensities in AIA
data associated with strong flare emission, most notably

---------------------------------------------------------
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: Photospheric Magnetic Energy Input and the Atmospheric Response
Authors: Welsch, Brian T.
2015TESS....111105W Altcode:
How are the chromospheres and coronae of the Sun and
solar-like stars heated to much higher temperatures than their
photospheres? Understanding atmospheric heating has been a major,
unsolved problem in solar and stellar astrophysics for many decades
now. Convective motions at the photosphere acting on the footpoints
of coronal magnetic fields are presumed to inject magnetic energy
into the Sun's atmosphere, where it is later released as heat. To
investigate this hypothesis, the upward flux of magnetic energy
across the photosphere --- quantified by the Poynting flux --- can be
estimated by combining photospheric vector magnetic field measurements
with horizontal photospheric velocities inferred by local correlation
tracking (LCT) applied to magnetogram sequences. Recently published
estimates of the net upward Poynting flux were roughly consistent
with the expected energy demand required for chromospheric and coronal
heating. But how are variations in magnetic energy injected across the
photosphere related to variations in emission in the chromosphere,
transition region, and corona? Comparisons between the estimated
upward transport of magnetic energy and the atmospheric response are
an essential step toward a comprehensive understanding of the physical
processes that drive chromospheric and coronal heating. To address this
issue, we have begun efforts to compare variations in chromospheric,
transition region, and coronal emission observed by IRIS and SDO/AIA
with estimates of the photospheric Poynting flux derived from sequential
Hinode/SOT SpectroPolarimeter and Narrowband Filter Imager magnetograms
of plage magnetic fields in active regions. Here, we will present
initial results of our comparisons. This work is supported by NASA
under contract NNG09FA40C (IRIS).

---------------------------------------------------------
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: The photospheric Poynting flux and coronal heating
Authors: Welsch, Brian T.
2015PASJ...67...18W Altcode: 2015PASJ..tmp..156W; 2014arXiv1402.4794W
Some models of coronal heating suppose that convective motions at
the photosphere shuffle the footpoints of coronal magnetic fields
and thereby inject sufficient magnetic energy upward to account
for observed coronal and chromospheric energy losses in active
regions. Using high-resolution observations of plage magnetic fields
made with the Solar Optical Telescope aboard the Hinode satellite,
we investigate this idea by estimating the upward transport of
magnetic energy-the vertical Poynting flux, Sz-across the
photosphere in a plage region. To do so, we combine the following:
(i) estimates of photospheric horizontal velocities, vh,
determined by local correlation tracking applied to a sequence
of line-of-sight magnetic field maps from the Narrowband Filter
Imager, with (ii) a vector magnetic field measurement from the
SpectroPolarimeter. Plage fields are ideal observational targets for
estimating energy injection by convection, because they are (i) strong
enough to be measured with relatively small uncertainties, (ii) not
so strong that convection is heavily suppressed (as within umbrae),
and (iii) unipolar, so Sz in plage is not influenced by
mixed-polarity processes (e.g., flux emergence) unrelated to heating
in stable, active-region fields. In this plage region, we found that
the average Sz varied in space, but was positive (upward)
and sufficient to explain coronal heating, with values near (5 ± 1) ×
107 erg cm-2 s-1. We find the energy
input per unit magnetic flux to be on the order of 105 erg
s-1 Mx-1. A comparison of intensity in a Ca II
image co-registered with one plage magnetogram shows stronger spatial
correlations with both total field strength and unsigned vertical field,
|Bz|, than either Sz or horizontal flux density,
Bh. The observed Ca II brightness enhancement, however,
probably contains a strong contribution from a near-photosphere hot-wall
effect, which is unrelated to heating in the solar atmosphere.

---------------------------------------------------------
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: 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: The relationship between CME momenta and magnetic forces
Authors: Li, Y.; Lynch, B. J.; Welsch, B. T.; Bercik, D. J.
2014AGUFMSH43B4206L Altcode:
Free magnetic energy is the energy source of solar flares and CMEs. At
theinitiation of a CME, the free magnetic energy converts to kinetic
energy and few other types of energy. Observable magnetic field sudden
changes havebeen found at the onset of flares. The Lorentz force
around the onset of a flare have been formulated in recent studies and
can be estimatedusing 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 nearthe center of the solar disk. We first select CMEs that
appear to be haloor partial halo CMEs in the LASCO images, and then
we use STEREO SECCHI COR2white light images to estimate CME mass and
speed. We then estimatethe Lorentz forces in the source active regions
at the flare onset using SDO HMI photosheric vector magnetic field
data.We report our work in progress and describe our analyses.

---------------------------------------------------------
Title: The Photosheric Poynting Flux and Coronal Heating
Authors: Welsch, B. T.
2014AGUFMSH31C..08W Altcode:
Some models of coronal heating suppose that convective motions
at thephotosphere shuffle the footpoints of coronal magnetic
fields andthereby inject sufficient magnetic energy upward to
account forobserved coronal and chromospheric energy losses
in active regions.Using high-resolution observations of plage
magnetic fields made withthe Solar Optical Telescope aboard the
Hinode satellite, weinvestigate this idea by estimating the upward
transport of magneticenergy --- the vertical Poynting flux, S_z ---
across the photospherein a plage region. To do so, we combine: (i)
estimates ofphotospheric horizontal velocities, v_h, determined by
localcorrelation tracking applied to a sequence of line-of-sight
magneticfield maps from the Narrowband Filter Imager, with (ii) a
vectormagnetic field measurement from the SpectroPolarimeter. Plage
fieldsare ideal observational targets for estimating energy
injection byconvection, because they are: (i) strong enough to be
measured withrelatively small uncertainties; (ii) not so strong
that convection isheavily suppressed (as within umbrae); and (iii)
unipolar, so S_z inplage is not influenced by mixed-polarity processes
(e.g., fluxemergence) unrelated to heating in stable, active-region
fields. Inthis plage region, we found that the average S_z varied
in space, butwas positive (upward) and sufficient to explain coronal
heating, withvalues near (5 +/- 1) x 107 erg / cm2 / s. We find the
energy inputper unit magnetic flux to be on the order of 105 erg /
s / Mx. Acomparison of intensity in a Ca II image co-registered
with one plagemagnetogram shows stronger spatial correlations
with both total fieldstrength and unsigned vertical field, |B_z|,
than either S_z orhorizontal flux density, B_h. The observed Ca II
brightnessenhancement, however, probably contains a strong contribution
from anear-photosphere hot-wall effect, which is unrelated to heating
in thesolar atmosphere.

---------------------------------------------------------
Title: Do New Solar Active Regions Trigger Flares in Existing Regions?
Authors: Fu, Y.; Welsch, B. T.
2014AGUFMSH41B4133F Altcode:
We study the effect of new emerging solar active regions on the
large-scale magnetic environment of existing regions. We first present
a theoretical approach to quantify the "interaction energy" between
new and pre-existing regions by identifying the part of the magnetic
potential field energy that couples the new and old flux systems. We
then examine this energy in two well-studied cases of flux emergence,
but find that the predicted energetic perturbation is very small
compared to energies released in large solar flares. Next, we present
an observational study of the influence of the emergence new active
regions on flare statistics in pre-existing active regions. As part of
an effort to precisely determine the emergence time of active regions in
a large sample, we find that emergence in about half of these regions
exhibits a two-stage behavior, with an initial gradual phase followed
by a more rapid phase. Preliminary results regarding flaring suggest
that newly emerging regions trigger a marginally significant increase
in the occurrence rate of X- and M-class flares in pre-existing regions.

---------------------------------------------------------
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 Photospheric Poynting Flux and Coronal Heating
Authors: Welsch, Brian
2014AAS...22410305W Altcode:
Some models of coronal heating suppose that random (cf., coherent)
convective motions at the photosphere shuffle the footpoints of coronal
magnetic fields and thereby inject sufficient magnetic energy upward
to account for observed coronal and chromospheric energy losses in
active regions. Using high-resolution observations of plage magnetic
fields made with the Solar Optical Telescope aboard the Hinode
satellite, we observationally test this idea by estimating the upward
transport of magnetic energy --- the vertical Poynting flux, S_z ---
across the photosphere in a plage region. To do so, we combine: (i)
estimates of photospheric horizontal velocities, v_h, determined by
local correlation tracking applied to a sequence of line-of-sight
magnetic field maps from the Narrowband Filter Imager, with (ii) a
vector magnetic field measurement from the SpectroPolarimeter. Plage
fields are ideal observational targets for estimating energy injection
by convection, because they are: (i) strong enough to be measured with
relatively small uncertainties; (ii) not so strong that convection
is heavily suppressed (as within umbrae); and (iii) unipolar, so S_z
in plage is not influenced by mixed-polarity processes (e.g., flux
emergence) that cannot explain steady heating in stable, active-region
fields. In this and a previously analyzed plage region, we found that
the average S_z varied between the regions, but was positive (upward)
and sufficient to explain coronal heating, with values near 2 x 10^7
erg/ cm^2/ s. We find the energy input per unit magnetic flux to be on
the order of a few times 10^4 erg/ s/ Mx. A comparison of intensity in
a Ca II image co-registered with one plage magnetogram shows stronger
spatial correlation with unsigned vertical field, |B_z|, than either
S_z or horizontal flux density, |B_h|.

---------------------------------------------------------
Title: Detection of Coherent Structures in Photospheric Turbulent
Flows
Authors: Chian, Abraham C. -L.; Rempel, Erico L.; Aulanier, Guillaume;
Schmieder, Brigitte; Shadden, Shawn C.; Welsch, Brian T.; Yeates,
Anthony R.
2014ApJ...786...51C Altcode: 2013arXiv1312.2405C
We study coherent structures in solar photospheric flows in a plage in
the vicinity of the active region AR 10930 using the horizontal velocity
data derived from Hinode/Solar Optical Telescope magnetograms. Eulerian
and Lagrangian coherent structures (LCSs) are detected by computing
the Q-criterion and the finite-time Lyapunov exponents of the velocity
field, respectively. Our analysis indicates that, on average, the
deformation Eulerian coherent structures dominate over the vortical
Eulerian coherent structures in the plage region. We demonstrate the
correspondence of the network of high magnetic flux concentration to the
attracting Lagrangian coherent structures (aLCSs) in the photospheric
velocity based on both observations and numerical simulations. In
addition, the computation of aLCS provides a measure of the local rate
of contraction/expansion of the flow.

---------------------------------------------------------
Title: The coronal energy input from magnetic braiding
Authors: Yeates, A. R.; Bianchi, F.; Welsch, B. T.; Bushby, P. J.
2014A&A...564A.131Y Altcode: 2014arXiv1403.4396Y
We estimate the energy input into the solar corona from photospheric
footpoint motions, using observations of a plage region by the Hinode
Solar Optical Telescope. Assuming a perfectly ideal coronal evolution,
two alternative lower bounds for the Poynting flux are computed based
on field line footpoint trajectories, without requiring horizontal
magnetic field data. When applied to the observed velocities, a bound
based solely on displacements between the two footpoints of each
field line is tighter than a bound based on relative twist between
field lines. Depending on the assumed length of coronal magnetic field
lines, the higher bound is found to be reasonably tight compared with
a Poynting flux estimate using an available vector magnetogram. It
is also close to the energy input required to explain conductive and
radiative losses in the active region corona. Based on similar analysis
of a numerical convection simulation, we suggest that observations
with higher spatial resolution are likely to bring the bound based
on relative twist closer to the first bound, but not to increase the
first bound substantially. Finally, we put an approximate upper bound
on the magnetic energy by constructing a hypothetical "unrelaxed"
magnetic field with the correct field line connectivity.

---------------------------------------------------------
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: Solar Magnetic Tracking. IV. The Death of Magnetic Features
Authors: Lamb, D. A.; Howard, T. A.; DeForest, C. E.; Parnell, C. E.;
Welsch, B. T.
2013ApJ...774..127L Altcode: 2013arXiv1307.4019L
The removal of magnetic flux from the quiet-Sun photosphere is
important for maintaining the statistical steady state of the magnetic
field there, for determining the magnetic flux budget of the Sun,
and for estimating the rate of energy injected into the upper solar
atmosphere. Magnetic feature death is a measurable proxy for the
removal of detectable flux, either by cancellation (submerging or
rising loops, or reconnection in the photosphere) or by dispersal
of flux. We used the SWAMIS feature tracking code to understand how
nearly 2 × 104 magnetic features die in an hour-long
sequence of Hinode/SOT/NFI magnetograms of a region of the quiet
Sun. Of the feature deaths that remove visible magnetic flux from the
photosphere, the vast majority do so by a process that merely disperses
the previously detected flux so that it is too small and too weak
to be detected, rather than completely eliminating it. The behavior
of the ensemble average of these dispersals is not consistent with
a model of simple planar diffusion, suggesting that the dispersal is
constrained by the evolving photospheric velocity field. We introduce
the concept of the partial lifetime of magnetic features, and show
that the partial lifetime due to Cancellation of magnetic flux, 22 hr,
is three times slower than previous measurements of the flux turnover
time. This indicates that prior feature-based estimates of the flux
replacement time may be too short, in contrast with the tendency
for this quantity to decrease as resolution and instrumentation have
improved. This suggests that dispersal of flux to smaller scales is
more important for the replacement of magnetic fields in the quiet
Sun than observed bipolar cancellation. We conclude that processes
on spatial scales smaller than those visible to Hinode dominate the
processes of flux emergence and cancellation, and therefore also the
quantity of magnetic flux that threads the photosphere.

---------------------------------------------------------
Title: Deriving Potential Fields from Vector Magnetograms
Authors: Welsch, Brian
2013SPD....44..118W Altcode:
The minimum-energy state for the magnetic field above the solar
photosphere is current-free. Since current is proportional to the
magnetic field's curl, the minimum energy state is curl-free, and can
therefore be represented as the gradient of a scalar potential. In
addition, the divergence-free condition on the magnetic field implies
this scalar potential obeys Laplace's equation. An appropriate boundary
condition must be specified to determine the potential. Given a
measurement of the full magnetic vector at the photosphere, it is
possible to employ either Neumann or Dirichlet boundary conditions
there. Typically, the Neumann condition is applied. Since either
condition fully specifies the three-dimensional 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 derive a potential
field that minimizes the integrated square of the residual between
both boundary conditions, and show one way to incorporate weighting
by spatially uniform measurement uncertainties in the minimization. We
demonstrate each approach using HMI vector magnetic field observations
of AR 11158. Residual discrepancies between the observed and potential
fields are significantly larger than empirically determined noise
levels, and can be interpreted as evidence of horizontal photospheric
currents. The data provide clues about properties of these currents,
but determining their spatial distribution will require additional
constraints, e.g., simplifying assumptions about photospheric magnetic
structure or observational input beyond single-height magnetograms. We
also find that the energies of potential fields computed in different
ways are significantly different --- by nearly 1e+33 ergs in some
cases. This has substantial implications for estimates of the free
magnetic energy in coronal field models that is available to power
flares and coronal mass ejections (CMEs.)

---------------------------------------------------------
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: Interpreting Magmatic Processes from Clinopyroxene in
Terrestrial Ankaramite Lavas: A Procedural Blueprint for the
Nakhlites?
Authors: Jacob, S. R.; Hammer, J. E.; Welsch, B.
2013LPI....44.3084J Altcode: 2013LPICo1719.3084J
We looked at clinopyroxene crystals from a Maui ankaramite lava flow
as a possible analog to the martian nakhlites.

---------------------------------------------------------
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: Thermal History of Yamato 980459: Constraints from Mineralogy,
Crystal Morphology, and Dynamic Cooling Experiments
Authors: First, E.; Hammer, J.; Welsch, B.
2013LPI....44.2943F Altcode: 2013LPICo1719.2943F
We seek to constrain the thermal history of Y-98 through thin section
analysis of the meteorite and 1-atm dynamic cooling experiments on a
synthetic equivalent.

---------------------------------------------------------
Title: Lagrangian coherent structures in the solar magnetoconvective
turbulence
Authors: Chian, A. C.; Rempel, E. L.; Welsch, B. T.; Yeates, A. R.
2012AGUFMSH51B2244C Altcode:
Turbulence and chaos play a fundamental role in solar convection through
the transport of particles, energy, and momentum. Lagrangian coherent
structures (LCS), which are material lines or surfaces that act as
transport barriers in the plasma, provide a novel method to describe
plasma turbulent motions (ApJL 735, L9, 2011; A&amp;A 539, A1, 2012). We
report the detection of LCS in numerical simulation of turbulent dynamo
and Hinode observation of turbulent flows in the solar photosphere. In
a 3-D helical MHD dynamo simulations of an Arnold-Beltrami-Childress
flow, two dynamo regimes, a traveling wave regime and an intermittent
regime, are identified as the magnetic diffusivity is varied. The sharp
contrast between the chaotic tangle of attracting and repelling LCS
in both regimes permits a unique understanding of the impact of the
magnetic field on the velocity field. Next, we apply the LCS method
to study the photospheric flows derived from Hinode/SOT magnetograms
in the NOAA active region AR 10930. It is shown that the generation of
a network of quasi-separatrix layers in the magnetic field correspond
to LCS in the photospheric velocity. Finally, the characteristics of
LCS in numerical simulations and Hinode observations are compared.

---------------------------------------------------------
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: Global Energetics of Thirty-eight Large Solar Eruptive Events
Authors: Emslie, A. G.; Dennis, B. R.; Shih, A. Y.; Chamberlin, P. C.;
Mewaldt, R. A.; Moore, C. S.; Share, G. H.; Vourlidas, A.; Welsch,
B. T.
2012ApJ...759...71E Altcode: 2012arXiv1209.2654E
We have evaluated the energetics of 38 solar eruptive events observed
by a variety of spacecraft instruments between 2002 February
and 2006 December, as accurately as the observations allow. The
measured energetic components include: (1) the radiated energy in
the Geostationary Operational Environmental Satellite 1-8 Å band,
(2) the total energy radiated from the soft X-ray (SXR) emitting
plasma, (3) the peak energy in the SXR-emitting plasma, (4) the
bolometric radiated energy over the full duration of the event,
(5) the energy in flare-accelerated electrons above 20 keV and in
flare-accelerated ions above 1 MeV, (6) the kinetic and potential
energies of the coronal mass ejection (CME), (7) the energy in solar
energetic particles (SEPs) observed in interplanetary space, and
(8) the amount of free (non-potential) magnetic energy estimated
to be available in the pertinent active region. Major conclusions
include: (1) the energy radiated by the SXR-emitting plasma exceeds,
by about half an order of magnitude, the peak energy content of the
thermal plasma that produces this radiation; (2) the energy content
in flare-accelerated electrons and ions is sufficient to supply the
bolometric energy radiated across all wavelengths throughout the event;
(3) the energy contents of flare-accelerated electrons and ions are
comparable; (4) the energy in SEPs is typically a few percent of the
CME kinetic energy (measured in the rest frame of the solar wind);
and (5) the available magnetic energy is sufficient to power the CME,
the flare-accelerated particles, and the hot thermal plasma.

---------------------------------------------------------
Title: Are Decaying Magnetic Fields Above Active Regions Related to
Coronal Mass Ejection Onset?
Authors: Suzuki, J.; Welsch, B. T.; Li, Y.
2012ApJ...758...22S Altcode: 2012arXiv1211.4684S
Coronal mass ejections (CMEs) are powered by magnetic energy stored
in non-potential (current-carrying) coronal magnetic fields, with
the pre-CME field in balance between outward magnetic pressure of the
proto-ejecta and inward magnetic tension from overlying fields that
confine the proto-ejecta. In studies of global potential (current-free)
models of coronal magnetic fields—Potential Field Source Surface
(PFSS) models—it has been reported that model field strengths above
flare sites tend to be weaker when CMEs occur than when eruptions fail
to occur. This suggests that potential field models might be useful
to quantify magnetic confinement. One straightforward implication
of this idea is that a decrease in model field strength overlying a
possible eruption site should correspond to diminished confinement,
implying an eruption is more likely. We have searched for such an
effect by post facto investigation of the time evolution of model
field strengths above a sample of 10 eruption sites. To check if the
strengths of overlying fields were relevant only in relatively slow
CMEs, we included both slow and fast CMEs in our sample. In most
events we study, we find no statistically significant evolution in
either (1) the rate of magnetic field decay with height, (2) the
strength of overlying magnetic fields near 50 Mm, or (3) the ratio
of fluxes at low and high altitudes (below 1.1 R ⊙, and
between 1.1 and 1.5 R ⊙, respectively). We did observe a
tendency for overlying field strengths and overlying flux to increase
slightly, and their rates of decay with height to become slightly more
gradual, consistent with increased confinement. The fact that CMEs occur
regardless of whether the parameters we use to quantify confinement are
increasing or decreasing suggests that either (1) the parameters that
we derive from PFSS models do not accurately characterize the actual
large-scale field in CME source regions, (2) systematic evolution in
the large-scale magnetic environment of CME source regions is not,
by itself, a necessary condition for CMEs to occur, or both.

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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: New Directions for Improving Estimating Electric Fields
from Magnetograms
Authors: Welsch, Brian T.
2012shin.confE..43W Altcode:
Via Faraday's law, sequences of photospheric vector magnetograms can
be used to derive electric fields in the atmospheric layer imaged
bythe magnetograph. These electric field estimates have applications
for space weather prediction: they determine the Poynting flux of
energy across the area imaged by the magnetogam, and can be used to
drive time-dependent models of the coronal magnetic field. Tests of
current approaches for estimating electric fields using artificial data
from MHD simulations of photospheric magnetic evolution reveal that
electric field estimation methods are imperfect in several respects;
most notably, the estimated electric fields underestimated the fluxes
of magnetic energy and helicity in some circumstances. Here, I will
outline some speculative approaches that might improve the accuracy
of electric field estimates.

---------------------------------------------------------
Title: Global Energetics of Large Solar Eruptive Events
Authors: Dennis, Brian R.; Emslie, A. G.; Chamberlin, P. C.; Mewaldt,
R. A.; Moore, C. S.; Share, G. H.; Shih, A. Y.; Vourlidas, A.;
Welsch, B.
2012AAS...22041002D Altcode:
We have evaluated the energetics of the larger solar eruptive events
recorded with a variety of spacecraft instruments between February
2002 and December 2006. All of the energetically important components
of the flares and of the accompanying coronal mass ejections and
solar energetic particles have been evaluated as accurately as
the observations allow. These components include the following:
(1) the total energy in the high temperature plasma determined from
the RHESSI thermal X-ray observations; (2) the total energies in
accelerated electrons above 20 keV and ions above 1 MeV from RHESSI
hard X-ray and gamma-ray observations, respectively; (3) the potential
and kinetic energies of the CME from SOHO/LASCO observations; (4)
the solar energetic particle (SEP) energy estimates from in situ
measurements on ACE, GOES, and SOHO; (5) the total radiated energy
from the SORCE/TSI measurements where available, and otherwise from
the Flare Irradiance Spectral Model (FISM). The results are assimilated
and discussed relative to the probable amount of nonpotential magnetic
energy estimated to be available in the flaring active regions from
MDI line-of-sight magnetograms.

---------------------------------------------------------
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: 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: 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: 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: Decorrelation Times of Photospheric Fields and Flows
Authors: Welsch, B. T.; Kusano, K.; Yamamoto, T. T.; Muglach, K.
2012ApJ...747..130W Altcode: 2011arXiv1110.6117W
We use autocorrelation to investigate evolution in flow fields
inferred by applying Fourier local correlation tracking (FLCT) to a
sequence of high-resolution (0farcs3), high-cadence (sime 2 minute)
line-of-sight magnetograms of NOAA active region (AR) 10930 recorded
by the narrowband filter imager of the Solar Optical Telescope aboard
the Hinode satellite over 2006 December 12 and 13. To baseline the
timescales of flow evolution, we also autocorrelated the magnetograms,
at several spatial binnings, to characterize the lifetimes of active
region magnetic structures versus 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 Δt between
magnetogram pairs tracked, spatial binning applied to the magnetograms,
and windowing parameter σ used in FLCT. Flow structures vary over a
range of spatial and temporal scales (including unresolved scales), so
tracked flows represent a local average of the flow over a particular
range of space and time. We define flow lifetime to be the flow
decorrelation time, τ. For Δt &gt; τ, tracking results represent
the average velocity over one or more flow lifetimes. We analyze
lifetimes of flow components, divergences, and curls as functions
of magnetic field strength and spatial scale. We find a significant
trend of increasing lifetimes of flow components, divergences, and
curls with field strength, consistent with Lorentz forces partially
governing flows in the active photosphere, as well as strong trends
of increasing flow lifetime and decreasing magnitudes with increases
in both spatial scale and Δt.

---------------------------------------------------------
Title: Lagrangian coherent structures in photospheric flows and
their implications for coronal magnetic structure
Authors: Yeates, A. R.; Hornig, G.; Welsch, B. T.
2012A&A...539A...1Y Altcode: 2011arXiv1110.3957Y
 Aims: We show how the build-up of magnetic gradients in the
Sun's corona may be inferred directly from photospheric velocity
data. This enables computation of magnetic connectivity measures
such as the squashing factor without recourse to magnetic field
extrapolation. Methods: Assuming an ideal evolution in the
corona, and an initially uniform magnetic field, the subsequent
field line mapping is computed by integrating trajectories of the
(time-dependent) horizontal photospheric velocity field. The method
is applied to a 12 h high-resolution sequence of photospheric flows
derived from Hinode/SOT magnetograms. Results: We find the
generation of a network of quasi-separatrix layers in the magnetic
field, which correspond to Lagrangian coherent structures in the
photospheric velocity. The visual pattern of these structures arises
primarily from the diverging part of the photospheric flow, hiding
the effect of the rotational flow component: this is demonstrated by
a simple analytical model of photospheric convection. We separate the
diverging and rotational components from the observed flow and show
qualitative agreement with purely diverging and rotational models
respectively. Increasing the flow speeds in the model suggests that
our observational results are likely to give a lower bound for the
rate at which magnetic gradients are built up by real photospheric
flows. Finally, we construct a hypothetical magnetic field with
the inferred topology, that can be used for future investigations of
reconnection and energy release. Movies are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: The Global Context of Solar Activity During the Whole
Heliosphere Interval Campaign
Authors: Webb, D. F.; Cremades, H.; Sterling, A. C.; Mandrini, C. H.;
Dasso, S.; Gibson, S. E.; Haber, D. A.; Komm, R. W.; Petrie, G. J. D.;
McIntosh, P. S.; Welsch, B. T.; Plunkett, S. P.
2011SoPh..274...57W Altcode:
The Whole Heliosphere Interval (WHI) was an international observing and
modeling effort to characterize the 3-D interconnected "heliophysical"
system during this solar minimum, centered on Carrington Rotation
2068, March 20 - April 16, 2008. During the latter half of the WHI
period, the Sun presented a sunspot-free, deep solar minimum type
face. But during the first half of CR 2068 three solar active regions
flanked by two opposite-polarity, low-latitude coronal holes were
present. These departures from the quiet Sun led to both eruptive
activity and solar wind structure. Most of the eruptive activity,
i.e., flares, filament eruptions and coronal mass ejections (CMEs),
occurred during this first, active half of the interval. We determined
the source locations of the CMEs and the type of associated region,
such as active region, or quiet sun or active region prominence. To
analyze the evolution of the events in the context of the global solar
magnetic field and its evolution during the three rotations centered
on CR 2068, we plotted the CME source locations onto synoptic maps of
the photospheric magnetic field, of the magnetic and chromospheric
structure, of the white light corona, and of helioseismological
subsurface flows. Most of the CME sources were associated with the
three dominant active regions on CR 2068, particularly AR 10989. Most
of the other sources on all three CRs appear to have been associated
with either isolated filaments or filaments in the north polar crown
filament channel. Although calculations of the flux balance and
helicity of the surface magnetic features did not clearly identify a
dominance of one region over the others, helioseismological subsurface
flows beneath these active regions did reveal a pronounced difference
among them. These preliminary results suggest that the "twistedness"
(i.e., vorticity and helicity) of subsurface flows and its temporal
variation might be related to the CME productivity of active regions,
similar to the relationship between flares and subsurface flows.

---------------------------------------------------------
Title: Photospheric Magnetic Evolution in the WHI Active Regions
Authors: Welsch, B. T.; Christe, S.; McTiernan, J. M.
2011SoPh..274..131W Altcode: 2011arXiv1103.2396W
Sequences of line-of-sight (LOS) magnetograms recorded by the Michelson
Doppler Imager are used to quantitatively characterize photospheric
magnetic structure and evolution in three active regions that rotated
across the Sun's disk during the Whole Heliosphere Interval (WHI),
in an attempt to relate the photospheric magnetic properties of these
active regions to flares and coronal mass ejections (CMEs). Several
approaches are used in our analysis, on scales ranging from whole
active regions, to magnetic features, to supergranular scales, and,
finally, to individual pixels. We calculated several parameterizations
of magnetic structure and evolution that have previously been associated
with flare and CME activity, including total unsigned magnetic flux,
magnetic flux near polarity-inversion lines, amount of canceled flux,
the "proxy Poynting flux," and helicity flux. To catalog flare events,
we used flare lists derived from both GOES and RHESSI observations. By
most such measures, AR 10988 should have been the most flare- and
CME-productive active region, and AR 10989 the least. Observations,
however, were not consistent with this expectation: ARs 10988
and 10989 produced similar numbers of flares, and AR 10989 also
produced a few CMEs. These results highlight present limitations
of statistics-based flare and CME forecasting tools that rely upon
line-of-sight photospheric magnetic data alone.

---------------------------------------------------------
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

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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.

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Title: A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere
Interval
Authors: Thompson, Barbara J.; Gibson, Sarah E.; Schroeder, Peter C.;
Webb, David F.; Arge, Charles N.; Bisi, Mario M.; de Toma, Giuliana;
Emery, Barbara A.; Galvin, Antoinette B.; Haber, Deborah A.; Jackson,
Bernard V.; Jensen, Elizabeth A.; Leamon, Robert J.; Lei, Jiuhou;
Manoharan, Periasamy K.; Mays, M. Leila; McIntosh, Patrick S.; Petrie,
Gordon J. D.; Plunkett, Simon P.; Qian, Liying; Riley, Peter; Suess,
Steven T.; Tokumaru, Munetoshi; Welsch, Brian T.; Woods, Thomas N.
2011SoPh..274...29T Altcode: 2011SoPh..tmp..413T
We present an overview of the data and models collected for the
Whole Heliosphere Interval, an international campaign to study the
three-dimensional solar-heliospheric-planetary connected system near
solar minimum. The data and models correspond to solar Carrington
Rotation 2068 (20 March - 16 April 2008) extending from below the
solar photosphere, through interplanetary space, and down to Earth's
mesosphere. Nearly 200 people participated in aspects of WHI studies,
analyzing and interpreting data from nearly 100 instruments and
models in order to elucidate the physics of fundamental heliophysical
processes. The solar and inner heliospheric data showed structure
consistent with the declining phase of the solar cycle. A closely
spaced cluster of low-latitude active regions was responsible for an
increased level of magnetic activity, while a highly warped current
sheet dominated heliospheric structure. The geospace data revealed an
unusually high level of activity, driven primarily by the periodic
impingement of high-speed streams. The WHI studies traced the solar
activity and structure into the heliosphere and geospace, and provided
new insight into the nature of the interconnected heliophysical system
near solar minimum.

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Title: Are Decaying Magnetic Fields Above Active Regions Related to
CME Onset?
Authors: Suzuki, J.; Welsch, B. T.; Li, Y.
2011AGUFMSH23A1938S Altcode:
Coronal mass ejections (CMEs) are powered by magnetic energy stored in
non-potential (current-carrying) coronal magnetic fields; the pre-CME
field is thought to exhibit a balance between outward magnetic pressure
of the proto-ejecta and inward magnetic tension from overlying fields
that confine the proto-ejecta. In global potential (current-free)
models of coronal magnetic fields --- potential field source-surface
(PFSS) models --- above flare sites where CMEs originated, it has
been noted that model field strengths are larger above sites where
eruptions fail, suggesting potential field models might be useful
to quantify magnetic confinement. One straightforward implication
of this idea is that a decrease in model field strength overlying a
possible eruption site should correspond to diminished confinement,
implying an eruption is more likely. We have searched for such an
effect by post facto investigation of the time evolution of model
field strengths above a sample of 10 eruption sites. To check if the
strengths of overlying fields were relevant only in relatively slow
CMEs, we included both slow and fast CMEs in our sample.

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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.

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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.

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Title: Understanding Links Between the Interior and Atmosphere
Authors: Welsch, Brian T.
2011sdmi.confE..11W Altcode:
Magnetic coupling between the solar interior and atmosphere is
responsible for many phenomena that interest solar physicists,
including atmospheric heating, solar flares, and coronal mass ejections
(CMEs). While all these processes release magnetic energy stored in
the atmosphere, that energy originated within the solar interior, and
the magnetic fields involved are also tethered to the interior. The
precise mechanisms by which magnetic energy passes from the interior
into the atmosphere to drive such phenomena, however, remain poorly
understood. For instance, statistical relationships have been reported
between solar flares and the structure and evolution of subsurface
flows, inferred from ring diagram analysis; but we can only speculate
about the physics underlying such relationships. In addition, we
cannot yet say if or how processes in the atmosphere feed back into
the interior. For instance, does most active region magnetic flux
submerge back into the interior? Or does it escape outward into the
atmosphere? I will discuss some open questions regarding magnetic
coupling between the interior and atmosphere, and consider ways that
the HMI and AIA instruments aboard SDO might be used to address such
questions -- with input from the audience welcomed!