leka

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Author name code: leka
ADS astronomy entries on 2022-09-14
author:"Leka, Kimberly Dawn"

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Title: Multi-height Measurements Of The Solar Vector Magnetic Field:
A White Paper Submitted To The Decadal Survey For Solar And Space
Physics (Heliophysics) 2024-2033
Authors: Bertello, L.; Arge, N.; De Wijn, A. G.; Gosain, S.; Henney,
C.; Leka, K. D.; Linker, J.; Liu, Y.; Luhmann, J.; Macniece, P. J.;
Petrie, G.; Pevtsov, A.; Pevtsov, A. A.
2022arXiv220904453B Altcode:
This white paper advocates the importance of multi-height measurements
of the vector magnetic field in the solar atmosphere. As briefly
described in this document, these measurements are critical for
addressing some of the most fundamental questions in solar and
heliospheric physics today, including: (1) What is the origin
of the magnetic field observed in the solar atmosphere? (2) What
is the coupling between magnetic fields and flows throughout the
solar atmosphere? Accurate measurements of the photospheric and
chromospheric three-dimensional magnetic fields are required for
a precise determination of the emergence and evolution of active
regions. Newly emerging magnetic flux in pre-existing magnetic regions
causes an increase in the topological complexity of the magnetic field,
which leads to flares and coronal mass ejections. Measurements of the
vector magnetic field constitute also the primary product for space
weather operations, research, and modeling of the solar atmosphere
and heliosphere. The proposed next generation Ground-based solar
Observing Network Group (ngGONG), a coordinated system of multi-platform
instruments, will address these questions and provide large datasets
for statistical investigations of solar feature behavior and evolution
and continuity in monitoring for space-weather focused endeavors
both research and operational. It will also enable sun-as-a-star
investigations, crucial as we look toward understanding other
planet-hosting stars.

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Title: On Identifying and Mitigating Bias in Inferred Measurements
for Solar Vector Magnetic Field Data
Authors: Leka, K. D.; Wagner, Eric L.; Griñón-Marín, Ana Belén;
Bommier, Véronique; Higgins, Richard
2022arXiv220711572L Altcode:
The problem of bias, meaning over- or underestimation, of the component
perpendicular to the line-of-sight, Bperp, in vector magnetic field
maps is discussed. Previous works on this topic have illustrated that
the problem exists; here we perform novel investigations to quantify
the bias, fully understand its source(s), and provide mitigation
strategies. First, we develop quantitative metrics to measure the
Bperp bias and quantify the effect in both local (physical) and native
image-plane components. Second we test and evaluate different inversion
options and data sources, to systematically characterize the impacts of
choices, including explicitly accounting for the magnetic fill fraction
ff. Third we deploy a simple model to test how noise and different
models of the bias may manifest. From these three investigations we find
that while the bias is dominantly present in under-resolved structures,
it is also present in strong-field pixel-filling structures. Noise
in the magnetograms can exacerbate the problem, but it is not
the primary cause. We show that fitting ff explicitly provides
significant mitigation, but that other considerations such as choice
of chi^2 weights and optimization algorithms can impact the results
as well. Finally, we demonstrate a straightforward "quick fix" that
can be applied post-facto but prior to solving the 180deg ambiguity in
Bperp, and which may be useful when global-scale structures are, e.g.,
used for model boundary input. The conclusions of this work support
the deployment of inversion codes that explicitly fit ff or, as with
the new SyntHIA neural-net, that are trained on data that did so.

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Title: SynthIA: A Synthetic Inversion Approximation for the Stokes
Vector Fusing SDO and Hinode into a Virtual Observatory
Authors: Higgins, Richard E. L.; Fouhey, David F.; Antiochos, Spiro K.;
Barnes, Graham; Cheung, Mark C. M.; Hoeksema, J. Todd; Leka, K. D.;
Liu, Yang; Schuck, Peter W.; Gombosi, Tamas I.
2022ApJS..259...24H Altcode: 2021arXiv210812421H
Both NASA's Solar Dynamics Observatory (SDO) and the JAXA/NASA
Hinode mission include spectropolarimetric instruments designed
to measure the photospheric magnetic field. SDO's Helioseismic
and Magnetic Imager (HMI) emphasizes full-disk, high-cadence,
and good-spatial-resolution data acquisition while Hinode's Solar
Optical Telescope Spectro-Polarimeter (SOT-SP) focuses on high
spatial resolution and spectral sampling at the cost of a limited
field of view and slower temporal cadence. This work introduces a
deep-learning system, named the Synthetic Inversion Approximation
(SynthIA), that can enhance both missions by capturing the best of
each instrument's characteristics. We use SynthIA to produce a new
magnetogram data product, the Synthetic Hinode Pipeline (SynodeP),
that mimics magnetograms from the higher-spectral-resolution
Hinode/SOT-SP pipeline, but is derived from full-disk, high-cadence,
and lower-spectral-resolution SDO/HMI Stokes observations. Results
on held-out data show that SynodeP has good agreement with the
Hinode/SOT-SP pipeline inversions, including magnetic fill fraction,
which is not provided by the current SDO/HMI pipeline. SynodeP further
shows a reduction in the magnitude of the 24 hr oscillations present in
the SDO/HMI data. To demonstrate SynthIA's generality, we show the use
of SDO/Atmospheric Imaging Assembly data and subsets of the HMI data as
inputs, which enables trade-offs between fidelity to the Hinode/SOT-SP
inversions, number of observations used, and temporal artifacts. We
discuss possible generalizations of SynthIA and its implications for
space-weather modeling. This work is part of the NASA Heliophysics
DRIVE Science Center at the University of Michigan under grant NASA
80NSSC20K0600E, and will be open-sourced.

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Title: Constraining stellar CMEs by solar observations
Authors: Leitzinger, Martin; Odert, Petra; Leka, K. D.; Heinzel,
Petr; Dissauer, Karin
2021AGUFM.U43B..06L Altcode:
Stellar coronal mass ejections (CMEs) may play an important role
in star-planet interactions, such as planetary atmospheric escape,
and in stellar mass- and angular momentum loss, influencing stellar
evolution. In the last decades much effort has been put into determining
parameters of stellar CMEs. New detection methods have been developed,
but still the number of convincing events is low and far from
enabling statistical analyses. So far the methods of detections
comprise the direct signature of ejected plasma, namely Doppler
shifted emission/absorption visible in spectra (optical, UV, X-ray),
absorptions seen during flares in X-rays interpreted as obscuring
events, and CME-associated signatures known from the Sun, like radio
type II bursts and coronal dimmings, the latter being only recently
established. The first method (Doppler shifted emission/absorption
lines) has been used since decades on stars (especially in H which
well probes the eruptive filament/prominence in the CME core) and
provides a few convincing detections and a large number of candidate
events with projected velocities significantly below the stars' escape
velocities. Such events could be CMEs seen in projection but it has
been proposed that these signatures could be caused by flare related
plasma dynamics. As there is a large pool of candidate events which
cannot be unambiguously interpreted as CMEs, we propose a new approach
to distinguish between flare and CME related signtures to increase the
number of convincing CME events. What we observe from stars are disk
integrated signals, in contrast to solar observations. To constrain
stellar CMEs by solar observations, solar 2D imaging spectroscopy is
required from which spatially integrated spectra can be created for a
sufficiently large number of events (flares and CMEs). These aspects
are fulfilled by MEES CCD (MCCD) optical observations at Mees Solar
Observatory (MSO). Therefore we propose the analysis of a sample of
solar flares and filaments/prominences from MCCD/MSO and their spatially
integrated spectra which allows to separate contributions from flares
and filaments/prominences. We present preliminary results of a few
selected solar events from MCCD demonstrating how to characterize
flare and CME related signatures in stellar observations.

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Title: What do pre-event conditions of the upper solar atmosphere
tell us about potential flaring of active regions?
Authors: Dissauer, K.; Leka, K. D.; Barnes, G.; Wagner, E.
2021AAS...23812713D Altcode:
Although solar energetic events are powered by the evolution of the
underlying magnetic field, it is still impossible to deterministically
predict when an active region will flare or not solely based on this
information. Observational case studies of the solar chromosphere and
corona reveal increased levels of magnetic reorganization, dynamics and
temperature variation prior to solar energetic events, however whether
these activities play a role in event initiation is still unclear. In order to investigate this question, we statistically analyze the
coronal and chromospheric conditions prior to solar flares and during
flare-quiet periods using data from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO). We create
and use AIA Active Region Patches (AARPs), region-targeted extractions
of AIA time-series data in (extreme-) ultraviolet, matched to the HMI
Active Region Patches (HARPs), for 2010-2018. The pre-event dynamics
and heating of the upper solar atmosphere is characterized using
high-order moments to parameterize brightness images, running-difference
images as well as emission measure, temperature, and density images,
derived from Differential Emission Measure (DEM) analysis. The temporal
behavior is captured by the slope and intercept of a linear fit over
a 7hr time-series of each parameter. The NWRA Classification
Infrastructure (NCI), a well-established statistical classifier system
based on Non-Parametric Discriminant Analysis, and standard skill
scores are used to statistically evaluate if parameters describing
the pre-event conditions significantly differ for flaring-imminent
vs. flare-quiet populations. Early results and their physical
implications will be presented. We note that AARPs present a
newly developed AIA data product which will be freely available to the
scientific community later in 2021. AARPs are presently constructed
daily, from 15:48-21:48 UT in 13 min intervals each hour with a time
cadence of 72 s, suitable for DEM Analysis. AARPs will be available
with the study's publication and at www.nwra.com/AARP

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Title: On Measuring and Mitigating Bias in the Inferred Magnetic Field
in the Helioseismic and Magnetic Imager and other Vector Magnetographs
Authors: Leka, K.; Griñón-Marín, A.; Higgins, R.; Fouhey, D.
2021AAS...23821309L Altcode:
Inferring the solar photospheric magnetic field from Zeeman polarization
data involves many steps and assumptions, each with varying degree of
impact on the accuracy of the result. It has been long known that the
treatment of unresolved structures and instrumental scattered light
will influence the inferred strength and direction of the field. The
impact of chosen assumptions for the HMI Pipeline data reduction is
most visibly manifest as a sign-change in the (local) horizontal field
direction in plage areas according to East/West hemisphere location,
as presented in Pevtsov+2021. The ramifications for science are
most apparent when considering large-scale magnetic structures from
synoptic-derived vector data products. The challenge to mitigation is,
of course, that we do not know the answer — and "hare &amp; hound"
approaches using synthetic data require more than just a sunspot model,
they must include the subtle radiative transfer and instrumental
effects that are at play here. In this poster, metrics to calculate
the magnitude of these issues fairly directly from the inversion output
are presented, based on time-series analysis of presumably steady solar
features. The approach is demonstrated for SDO/HMI and Hinode/SOT-SP,
but applicable to other instruments; the impacts are quantified
for both weak- and strong-flux areas. We present some avenues being
considered for removing or at least lessening the impact of these
issues, with the goal of achieving improved time-series analysis and
synoptic vector-field maps. This work is carried out with support
from NASA grants 80NSSC19K0317, 80NSSC18K0180, Solar B FPP Phase E,
the U. Michigan SOLSTICE DRIVE Center, and NASA Contract NAS5-02139
(HMI) to Stanford University.

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Title: Enhancements to Hinode/SOT-SP Vector Magnetic Field Data
Products
Authors: DeRosa, M. L.; Leka, K. D.; Barnes, G.; Wagner, E.; Centeno,
R.; De Wijn, A.; Bethge, C.
2021AAS...23821305D Altcode:
The Solar Optical Telescope Spectro-Polarimeter (SOT-SP), on board the
Hinode spacecraft (launched in 2006), is a scanning-slit spectrograph
that continues to provide polarization spectra useful for inferring the
vector (three-component) magnetic field at the solar photosphere. SOT-SP
achieves this goal by obtaining line profiles of two magnetically
sensitive lines, namely the Fe I 6302 Angstrom doublet, using a
0.16"×164" slit as it scans a region of interest. Once the data are
merged, a Milne-Eddington based spectropolarimetric inversion scheme is
used to infer multiple physical parameters in the solar photosphere,
including the vector magnetic field, from the calibrated polarization
spectra. All of these data are publicly available once the processing
has occurred. As of this year, the Hinode/SOT team is also making
available the disambiguated vector magnetic field and the re-projected
heliographic components of the field. In making the disambiguated vector
field data product, the 180° ambiguity in the plane-of-sky component
of the vector magnetic field inherent in the spectropolarimetric
inversion process has been resolved. This ambiguity is resolved
using the Minimum-Energy algorithm, which is the same algorithm used
within the pipeline producing the vector-magnetogram data product
for the Helioseismic and Magnetic Imager aboard the Solar Dynamics
Observatory. The heliographic field components (Bphi,
Btheta, Br) on the same grid as the inverted data
are also now provided. This poster provides more details about these
data product enhancements, and some examples on how the scientific
community may readily obtain these data.

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Title: Eruptivity in Solar Flares: The Challenges of Magnetic
Flux Ropes
Authors: Lin, Pei Hsuan; Kusano, Kanya; Leka, K. D.
2021ApJ...913..124L Altcode:
Two new schemes for identifying field lines involved in eruptions,
the r-scheme and q-scheme, are proposed to analyze the eruptive
and confined nature of solar flares, as extensions to the original
rm scheme proposed in Lin et al. Motivated by three solar
flares originating from NOAA Active Region 12192 that are misclassified
by rm, we introduce refinements to the r-scheme employing
the "magnetic twist flux" to approximate the force balance acting on
a magnetic flux rope (MFR); in the q-scheme, the reconnected field is
represented by those field lines that anchor in the flare ribbons. Based
on data obtained by the Solar Dynamics Observatory/Helioseismic and
Magnetic Imager, the coronal magnetic field for 51 flares larger than
M5.0 class, from 29 distinct active regions, is constructed using a
nonlinear force-free field extrapolation model. Statistical analysis
based on linear discriminant function analysis is then performed,
revealing that despite both schemes providing moderately successful
classifications for the 51 flares, the coronal mass ejection-eruptivity
classification for the three target events can only be improved with
the q-scheme. We find that the highly twisted field lines and the
flare-ribbon field lines have equal average force-free constant α,
but all of the flare-ribbon-related field lines are shorter than 150 Mm
in length. The findings lead us to conclude that it is challenging to
distinguish the MFR from the ambient magnetic field using any quantity
based on common magnetic nonpotentiality measures.

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Title: Fast and Accurate Emulation of the SDO/HMI Stokes Inversion
with Uncertainty Quantification
Authors: Higgins, Richard E. L.; Fouhey, David F.; Zhang, Dichang;
Antiochos, Spiro K.; Barnes, Graham; Hoeksema, J. Todd; Leka, K. D.;
Liu, Yang; Schuck, Peter W.; Gombosi, Tamas I.
2021ApJ...911..130H Altcode: 2021arXiv210317273H
The Helioseismic and Magnetic Imager (HMI) on board NASA's Solar
Dynamics Observatory produces estimates of the photospheric magnetic
field, which are a critical input to many space weather modeling and
forecasting systems. The magnetogram products produced by HMI and its
analysis pipeline are the result of a per-pixel optimization that
estimates solar atmospheric parameters and minimizes disagreement
between a synthesized and observed Stokes vector. In this paper,
we introduce a deep-learning-based approach that can emulate the
existing HMI pipeline results two orders of magnitude faster than the
current pipeline algorithms. Our system is a U-Net trained on input
Stokes vectors and their accompanying optimization-based Very Fast
Inversion of the Stokes Vector (VFISV) inversions. We demonstrate
that our system, once trained, can produce high-fidelity estimates of
the magnetic field and kinematic and thermodynamic parameters while
also producing meaningful confidence intervals. We additionally show
that despite penalizing only per-pixel loss terms, our system is able
to faithfully reproduce known systematic oscillations in full-disk
statistics produced by the pipeline. This emulation system could serve
as an initialization for the full Stokes inversion or as an ultrafast
proxy inversion. This work is part of the NASA Heliophysics DRIVE
Science Center (SOLSTICE) at the University of Michigan, under grant
NASA 80NSSC20K0600E, and will be open sourced.

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Title: Magnetic Helicity Flux across Solar Active Region
Photospheres. II. Association of Hemispheric Sign Preference with
Flaring Activity during Solar Cycle 24
Authors: Park, Sung-Hong; Leka, K. D.; Kusano, Kanya
2021ApJ...911...79P Altcode: 2021arXiv210213331P
In our earlier study (Paper I) of this series, we examined the
hemispheric sign preference (HSP) of magnetic helicity flux dH/dt
across photospheric surfaces of 4802 samples of 1105 unique active
regions (ARs) observed during solar cycle 24. Here, we investigate
any association of the HSP, expressed as a degree of compliance,
with flaring activity, analyzing the same set of dH/dt estimates as
used in Paper I. The AR samples under investigation are assigned to
heliographic regions (HRs) defined in the Carrington longitude-latitude
plane with a grid spacing of 45° in longitude and 15° in latitude. For
AR samples in each of the defined HRs, we calculate the degree of HSP
compliance and the average soft X-ray flare index. The strongest flaring
activity is found to be in one distinctive HR with an extremely low-HSP
compliance of 41% as compared to the mean and standard deviation of
62% and 7%, respectively, over all HRs. This sole HR shows an anti-HSP
(i.e., &lt;50%) and includes the highly flare-productive AR NOAA 12673,
however this AR is not uniquely responsible for the HR's low HSP. We
also find that all HRs with the highest flaring activity are located
in the southern hemisphere, and they tend to have lower degrees of HSP
compliance. These findings point to the presence of localized regions
of the convection zone with enhanced turbulence, imparting a greater
magnetic complexity and a higher flaring rate to some rising magnetic
flux tubes.

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Title: On a limitation of Zeeman polarimetry and imperfect
instrumentation in representing solar magnetic fields with weaker
polarization signal
Authors: Pevtsov, A. A.; Liu, Y.; Virtanen, I.; Bertello, L.; Mursula,
K.; Leka, K. D.; Hughes, A. L. H.
2021JSWSC..11...14P Altcode: 2021arXiv210107204P
Full disk vector magnetic fields are used widely for developing better
understanding of large-scale structure, morphology, and patterns of
the solar magnetic field. The data are also important for modeling
various solar phenomena. However, observations of vector magnetic
fields have one important limitation that may affect the determination
of the true magnetic field orientation. This limitation stems from
our ability to interpret the differing character of the Zeeman
polarization signals which arise from the photospheric line-of-sight
vs. the transverse components of the solar vector magnetic field,
and is likely exacerbated by unresolved structure (non-unity fill
fraction) as well as the disambiguation of the 180° degeneracy in
the transverse-field azimuth. Here we provide a description of this
phenomenon, and discuss issues, which require additional investigation.

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Title: Modeling the Solar Corona: Testing Nonlinear Force-Free
Methods with a Magneto-Hydrostatic Test Case
Authors: Rodriguez, S.; Gilchrist, S. A.; Leka, K. D.; Dissauer, K.
2020AGUFMSH0370008R Altcode:
The solar corona is the outer atmosphere of the Sun and it is where
highly energetic solar events take place, e.g. solar flares. The
coronal magnetic field is thought to be in a force-free state, meaning
that the magnetic Lorentz force is self-balanced. Furthermore, we
cannot reliably measure the vector magnetic field in the corona. This
motivates Nonlinear Force-Free Field (NLFFF) extrapolations of the
coronal magnetic field using photospheric magnetic data as boundary
conditions. Photospheric data is not in a force-free state, which
leads to an inconsistency between the boundary conditions and the
assumptions of the model. However, by using a Linear Magneto-HydroStatic
model (LMHS), which deliberately takes into account gravity and gas
pressure forces, as boundary conditions to a force-free model we
can examine the effect of this inconsistency in the modeling. In the
LMHS model, the non-magnetic contribution to the forces is controlled
by a single parameter. We consider several test cases with different
values of this parameter. It is hypothesized that NLFFF model will not
experience much change when this parameter is set to zero, providing a
consistent control test case. Nevertheless, by increasing non-magnetic
contributions, we seek to test the limits of the NLFFF model and
determine the deviation from the original LMHS model using various
methods of comparison (point-wise comparison, field line tracings,
magnetic energy calculations, Lorentz force calculations). This
material is based upon work supported by the National Science Foundation
under Grant No. 1841962. Any opinions, findings, and conclusions or
recommendations expressed in this material are those of the authors and
do not necessarily reflect the views of the National Science Foundation.

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Title: Magnetic Helicity Flux across Solar Active Region
Photospheres. I. Hemispheric Sign Preference in Solar Cycle 24
Authors: Park, Sung-Hong; Leka, K. D.; Kusano, Kanya
2020ApJ...904....6P Altcode: 2020arXiv201006134P
A hemispheric preference in the dominant sign of magnetic helicity
has been observed in numerous features in the solar atmosphere,
i.e., left-handed/right-handed helicity in the northern/southern
hemisphere. The relative importance of different physical processes
that may contribute to the observed hemispheric sign preference (HSP)
of magnetic helicity is still under debate. Here, we estimate magnetic
helicity flux (dH/dt) across the photospheric surface for 4802 samples
of 1105 unique active regions (ARs) that appeared over an 8 yr period
from 2010 to 2017 during solar cycle 24, using photospheric vector
magnetic field observations by the Helioseismic and Magnetic Imager
(HMI) on board the Solar Dynamics Observatory (SDO). The estimates
of dH/dt show that 63% and 65% of the investigated AR samples in the
northern and southern hemispheres, respectively, follow the HSP. We
also find a trend that the HSP of dH/dt increases from ∼50%-60%
up to ∼70%-80% as ARs (1) appear at the earlier inclining phase
of the solar cycle or higher latitudes and (2) have larger values of
$| {dH}/{dt}| $ , the total unsigned magnetic flux, and the average
plasma-flow speed. These observational findings support the enhancement
of the HSP mainly by the Coriolis force acting on a buoyantly rising
and expanding flux tube through the turbulent convection zone. In
addition, the differential rotation on the solar surface as well as
the tachocline α-effect of a flux-transport dynamo may reinforce the
HSP for ARs at higher latitudes.

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Title: On Measuring Divergence for Magnetic Field Modeling
Authors: Gilchrist, S. A.; Leka, K. D.; Barnes, G.; Wheatland, M. S.;
DeRosa, M. L.
2020ApJ...900..136G Altcode: 2020arXiv200808863G
A physical magnetic field has a divergence of zero. Numerical error
in constructing a model field and computing the divergence, however,
introduces a finite divergence into these calculations. A popular metric
for measuring divergence is the average fractional flux $\left\langle
| {f}_{i}| \right\rangle $ . We show that $\left\langle | {f}_{i}|
\right\rangle $ scales with the size of the computational mesh, and
may be a poor measure of divergence because it becomes arbitrarily
small for increasing mesh resolution, without the divergence actually
decreasing. We define a modified version of this metric that does
not scale with mesh size. We apply the new metric to the results of
DeRosa et al., who measured $\left\langle | {f}_{i}| \right\rangle
$ for a series of nonlinear force-free field models of the coronal
magnetic field based on solar boundary data binned at different spatial
resolutions. We compute a number of divergence metrics for the DeRosa et
al. data and analyze the effect of spatial resolution on these metrics
using a nonparametric method. We find that some of the trends reported
by DeRosa et al. are due to the intrinsic scaling of $\left\langle |
{f}_{i}| \right\rangle $ . We also find that different metrics give
different results for the same data set and therefore there is value
in measuring divergence via several metrics.

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Title: A New Parameter of the Photospheric Magnetic Field to
Distinguish Eruptive-flare Producing Solar Active Regions
Authors: Lin, Pei Hsuan; Kusano, Kanya; Shiota, Daikou; Inoue, Satoshi;
Leka, K. D.; Mizuno, Yuta
2020ApJ...894...20L Altcode:
Solar flares and coronal mass ejections (CMEs) are eruptive phenomena
caused by coronal magnetic fields. In particular, large eruptive
events originate in active regions (AR) with strong surface magnetic
fields. However, it is still unclear what determines the capability
of an AR to specifically produce eruptive flares and CMEs, and this
hinders our knowledge of the initiation mechanism for the eruptive
component of these phenomena. In this study, we propose a new parameter
rm to measure the possibility that a flare that occurs in
an AR can be eruptive and produce a CME. The parameter rm
is defined by the ratio of the magnetic flux of twist higher than
a threshold Tc to the surrounding—and specifically,
the overlying—magnetic flux. The value of rm for each
AR can be estimated using nonlinear force-free field extrapolation
models of the coronal magnetic field. Based on the data obtained by
the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, we
calculated the values of rm for 29 ARs at 51 times prior
to flares larger than M5.0 class. We find that the footpoints of
field lines with twist higher than 0.2 can represent the subsequent
flare ribbons well, and field lines that overlie and "fence in" the
highly twisted region will work to confine the eruption, generating
confined flares. Discriminant function analysis is used to show that
rm is moderately well able to distinguish ARs that have
the capability of producing eruptive flares.

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Title: The Trigger Mechanism of Recurrent Solar Active Region Jets
Revealed by the Magnetic Properties of a Coronal Geyser Site
Authors: Paraschiv, Alin Razvan; Donea, Alina; Leka, K. D.
2020ApJ...891..149P Altcode: 2020arXiv200211819P
Solar active region jets are small-scale collimated plasma eruptions
that are triggered from magnetic sites embedded in sunspot penumbral
regions. Multiple trigger mechanisms for recurrent jets are under
debate. Vector magnetic field data from Solar Dynamics Observatory
(SDO) Helioseismic and Magnetic Imager (HMI) observations are used to
analyze a prolific photospheric configuration, identified in extreme
ultraviolet observations as a "coronal geyser," that triggered a set of
at least 10 recurrent solar active region jets. We focus on interpreting
the magnetic fields of small-scale flaring sites aiming to understand
the processes that govern recurrent jet eruptions. We perform a custom
reprocessing of the SDO-HMI products, including disambiguation and
uncertainty estimation. We scrutinized the configuration and dynamics
of the photospheric magnetic structures. The magnetic configuration
is described, via the analysis of the photospheric magnetic vertical
fields, to identify the process that is responsible for driving
the jet eruptions. We report that the two widely debated magnetic
trigger processes, namely magnetic flux cancellation and magnetic
flux emergence, appear to be responsible on a case by case basis for
generating each eruption in our set. We find that 4 out of 10 jets
were due to flux cancellation, while the rest were clearly not and
were more likely due to flux emergence.

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Title: A Comparison of Flare Forecasting Methods. IV. Evaluating
Consecutive-day Forecasting Patterns
Authors: Park, Sung-Hong; Leka, K. D.; Kusano, Kanya; Andries, Jesse;
Barnes, Graham; Bingham, Suzy; Bloomfield, D. Shaun; McCloskey,
Aoife E.; Delouille, Veronique; Falconer, David; Gallagher, Peter T.;
Georgoulis, Manolis K.; Kubo, Yuki; Lee, Kangjin; Lee, Sangwoo; Lobzin,
Vasily; Mun, JunChul; Murray, Sophie A.; Hamad Nageem, Tarek A. M.;
Qahwaji, Rami; Sharpe, Michael; Steenburgh, R. A.; Steward, Graham;
Terkildsen, Michael
2020ApJ...890..124P Altcode: 2020arXiv200102808P
A crucial challenge to successful flare prediction is
forecasting periods that transition between "flare-quiet" and
"flare-active." Building on earlier studies in this series in which we
describe the methodology, details, and results of flare forecasting
comparison efforts, we focus here on patterns of forecast outcomes
(success and failure) over multiday periods. A novel analysis is
developed to evaluate forecasting success in the context of catching
the first event of flare-active periods and, conversely, correctly
predicting declining flare activity. We demonstrate these evaluation
methods graphically and quantitatively as they provide both quick
comparative evaluations and options for detailed analysis. For the
testing interval 2016-2017, we determine the relative frequency
distribution of two-day dichotomous forecast outcomes for three
different event histories (I.e., event/event, no-event/event, and
event/no-event) and use it to highlight performance differences between
forecasting methods. A trend is identified across all forecasting
methods that a high/low forecast probability on day 1 remains high/low
on day 2, even though flaring activity is transitioning. For M-class
and larger flares, we find that explicitly including persistence or
prior flare history in computing forecasts helps to improve overall
forecast performance. It is also found that using magnetic/modern
data leads to improvement in catching the first-event/first-no-event
transitions. Finally, 15% of major (I.e., M-class or above) flare
days over the testing interval were effectively missed due to a lack
of observations from instruments away from the Earth-Sun line.

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Title: Critical Parameters of Photospheric Magnetic Field to Produce
Eruptive Flares in Solar Active Regions
Authors: Lin, P. H.; Kusano, K.; Shiota, D.; Inoue, S.; Leka, K. D.;
Mizuno, Y.
2019AGUFMSH13D3426L Altcode:
Solar flares and coronal mass ejections (CMEs) are eruptive phenomena
caused by magnetic field in the solar corona. In particular,
large eruptive events originate in active regions (AR) on the solar
surface. However, it is still unclear what determines the capability of
an AR to produce eruptive flares and CMEs, and it hinders our ability to
predict CMEs. In this study, we propose a new parameter r m
to measure the possibility that a flare on an AR can be eruptive and
produce a CME. The parameter r m is defined by the ratio
of the magnetic flux of twist higher than a threshold T c
to the overlying magnetic flux. The value of r m for each
AR can be estimated using the nonlinear force-free field (NLFFF)
extrapolation. Based on the data obtained by the Solar Dynamics
Observatory (SDO)/Helioseismic and Magnetic Imager (HMI), we calculated
the values of r m for 29 ARs at 51 times before to flares
larger than M5.0 class. We find that the foot-point of field lines with
twist larger than 0.2 can well represent the flare ribbons. Moreover,
field lines that are overlying and fencing in these highly twisted
regions will confine the eruption, resulting in confined flares. By
using T c =0.2 and including the overlying and fencing
flux in the evaluation of r m , the discriminant analysis
shows that r m is moderately able to discriminate ARs which
have capability to produce eruptive flares. Furthermore, we in detail
analyze the exceptional events, in which the eruptive flare cannot
be predicted by r m , and discuss the possible reason for
failed prediction.

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Title: Pathways to Coronal Magnetic Energy Storage in The NOAA AR11283
Authors: Cavins, A.; Barnes, G.; Leka, K. D.; Gilchrist, S. A.
2019AGUFMSH31D3332C Altcode:
At the extreme end of the variability spectrum, powerful events
we call solar flares produce orders-of-magnitude increases
in the shorter-wavelength luminosity output on millisecond
time-scales. Although it is generally accepted that solar flares
occur through the release of energy stored in the coronal magnetic
field above an active region it is not well understood how much of
the stored energy will be released in a single event. When examined
with a large sample size, solar flares generally follow a power-law
distribution in size, although it should be noted that this may not
be the case for any individual active region. Such is the case for
NOAA AR11283 (at central meridian on 2011.09.06), which produced
multiple M and X-class flares with comparatively few smaller C class
flares. The objective of the ongoing research on this region is to
compare estimates of the magnetic energy stored by individual current
systems with the region's flaring history. The investigation heavily
focuses on studying energy of sub volumes in the region, identified
from spherical nonlinear force-free modelling, rather than the whole
region in an attempt to better understand the magnitude of single
re-connection events. A small total current along shorter field
lines generally does not store a large amount of magnetic energy,
but either current along longer field lines or a larger total amount
of current present in the individual system can lead to more magnetic
energy storage. These different situations of current size versus
current loop length can produce different distributions of energy
throughout the region. This material is based upon work supported by
the US National Science Foundation under Grant No. 1630454 and the REU
Program Award No. 1659878. Any opinions, findings, and conclusions or
recommendations expressed in this material are those of the authors and
do not necessarily reflect the views of the National Science Foundation.

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Title: Realities, Challenges, and Innovation for Solar Flare
Forecasting
Authors: Leka, K. D.
2019AGUFMSH34A..02L Altcode:
In light of recent head-to-head evaluations of operational flare
forecasting facilities, some encouraging trends have been identified,
as have some specific challenges. The use of modern magnetic data, for
example, can be helpful in some situations -- but having a Forecaster in
the Loop still provides additional skill as compared to fully automated
methods. Challenges include the fact that generally speaking all
methods score below 0.5 on a 0.0--1.0 scale across numerous standard
metrics and all methods pretty much fail to correctly identify and
predict upcoming variations in flaring activity (the first flare
/ last flare challenge). As the studies have demonstrated, many
different implementation options have been tried; in the context of
human-oriented operational forecasts as they are presently defined,
perhaps we've gotten as good as we're going to? At the same time,
numerous efforts have been recently published or are underway to
establish more promising approaches and algorithms. One difficulty is
that the timescales and performance benchmarks thus far are defined
by humans: for example defining the required forecast as being for
whether or not the Sun output a minimum flux of certain-wavelength
light as detected by a human-built satellite sometime in an upcoming
human-convenient time period. But to improve forecasts, we probably
need to turn to more physics-based timescales -- yet still keep
operational requirements in mind such as data-availability reality,
the difficulties of turning super-posed epoch analysis into successful
forecasts, and how to properly (and fairly) judge performance. In this talk I will motivate the challenges and highlight some ways
forward now that we know where we really stand operationally and where
the flare-forecasting needs are the clearest. Leka, K. D., et
al 2019 a, ApJSupp in press Leka, K. D., et al 2019 b, ApJ in press
Park, S.-H, et al 2019, ApJ submitted Support for the workshops
upon which some of this talk is based is acknowledged from the Center
for International Collaborative Research (CICR), at the Institute for
Space-Earth Environmental Research (ISEE), Nagoya University, Japan.

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Title: The How and Why of Big Solar Flares
Authors: Isola, B.; Barnes, G.; Leka, K. D.; Gilchrist, S. A.
2019AGUFMSH31D3336I Altcode:
It is generally understood that the peak soft X-ray flux of solar
flares emanating from active regions follows a power-law spectrum of
magnitudes; however, it is not understood why the flares from some
active regions do not obviously exhibit this distribution. We take
here an approach to understand why this occurs, by combining modeling
and observation to study the energy reservoirs within a solar active
region and the pathway the energy takes to produce solar events. We
consider a complex active region, NOAA AR 11793 from July 19th, 2013,
that was expected to produce larger flares than the actual C-flares
observed. We modeled the coronal magnetic field using the CFITS
nonlinear force-free extrapolation code, then identified individual
current systems by starting from photospheric concentrations of current
and propagating those through the extrapolation volume. We estimated the
energy-release prospects of each current system as a measure of how much
energy might be released in a single reconnection event. We investigated
different ways of determining the current systems to investigate the
sensitivity of the results to the choice of current systems. We present
here results comparing the energy associated with the individual
current systems with the magnitude of the flares originating from
our region. This material is based upon work supported by the
US National Science Foundation REU program under Award No. 1659878,
and NSF Grant No. 1630454. Any opinions, findings, and conclusions or
recommendations expressed in this material are those of the authors and
do not necessarily reflect the views of the National Science Foundation.

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Title: Improving boundary Br maps for global coronal
magnetic field models
Authors: Hayashi, K.; Arge, C. N.; Barnes, G.; Henney, C. J.; Jones,
S. I.; Leka, K. D.
2019AGUFMSH43E3388H Altcode:
The solar-surface Br maps are one of the key input data
to the heliophysics models. In particular, the potential-field
source-surface (PFSS) model relies on the boundary Br
map, and its solutions are widely used in the field of solar physics
(for example, in the WSA solar wind speed prediction model and MHD
models). To specify the boundary condition of the PFSS model, the
so-called synoptic map is widely used. A synoptic map is constructed by
assembling the central meridian slits of full-disk line-of-sight (LoS)
observations made over one Carrington rotation period. The LoS values
are converted to the Br component through the radial-field
assumption (or mu-correction method). However, these procedures cannot
prevent some possible artifacts: The near horizontal magnetic field
at penumbra regions often appears as the false opposite polarity
in the LoS magnetogram, and this false polarity remains through the
radial-field assumption. The map simply collecting the central meridian
slits over one Carrington rotation period can hardly represent the
solar-surface condition at arbitrary instants of interest. We
recently developed a data process suite to mitigate these issues. In
this suite, the false polarity can be corrected with the assistance
from our new potential field model that yields high-resolution solution
matching the LoS magnetogram data instead of Br from the
radial-field assumption. The ADAPT model provides a theory-based
temporally seamless inference of the Br distribution over
the whole solar surface. For testing the combination of these
features, the derived time-series whole-Sun maps are input to the WSA
solar wind prediction model. We examine differences in the open field
footpoints of the PFSS solutions, and the predicted solar wind speed
at 1 AU derived from the time series of the new Br maps and
the standard synoptic maps. This work is partially supported by
NASA HSWO2R Grant 80NSSC19K0007.

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Title: A Comparison of Flare Forecasting Methods. III. Systematic
Behaviors of Operational Solar Flare Forecasting Systems
Authors: Leka, K. D.; Park, Sung-Hong; Kusano, Kanya; Andries, Jesse;
Barnes, Graham; Bingham, Suzy; Bloomfield, D. Shaun; McCloskey,
Aoife E.; Delouille, Veronique; Falconer, David; Gallagher, Peter
T.; Georgoulis, Manolis K.; Kubo, Yuki; Lee, Kangjin; Lee, Sangwoo;
Lobzin, Vasily; Mun, JunChul; Murray, Sophie A.; Hamad Nageem, Tarek
A. M.; Qahwaji, Rami; Sharpe, Michael; Steenburgh, Robert A.; Steward,
Graham; Terkildsen, Michael
2019ApJ...881..101L Altcode: 2019arXiv190702909L
A workshop was recently held at Nagoya University (2017 October
31-November 2), sponsored by the Center for International Collaborative
Research, at the Institute for Space-Earth Environmental Research,
Nagoya University, Japan, to quantitatively compare the performance
of today’s operational solar flare forecasting facilities. Building
upon Paper I of this series, in Paper II we described the participating
methods for this latest comparison effort, the evaluation methodology,
and presented quantitative comparisons. In this paper, we focus on
the behavior and performance of the methods when evaluated in the
context of broad implementation differences. Acknowledging the short
testing interval available and the small number of methods available,
we do find that forecast performance: (1) appears to improve by
including persistence or prior flare activity, region evolution,
and a human “forecaster in the loop” (2) is hurt by restricting
data to disk-center observations; (3) may benefit from long-term
statistics but mostly when then combined with modern data sources
and statistical approaches. These trends are arguably weak and must
be viewed with numerous caveats, as discussed both here and in Paper
II. Following this present work, in Paper IV (Park et al. 2019) we
will present a novel analysis method to evaluate temporal patterns of
forecasting errors of both types (i.e., misses and false alarms). Hence,
most importantly, with this series of papers, we demonstrate the
techniques for facilitating comparisons in the interest of establishing
performance-positive methodologies.

---------------------------------------------------------
Title: A Comparison of Flare Forecasting Methods. II. Benchmarks,
Metrics, and Performance Results for Operational Solar Flare
Forecasting Systems
Authors: Leka, K. D.; Park, Sung-Hong; Kusano, Kanya; Andries, Jesse;
Barnes, Graham; Bingham, Suzy; Bloomfield, D. Shaun; McCloskey,
Aoife E.; Delouille, Veronique; Falconer, David; Gallagher, Peter
T.; Georgoulis, Manolis K.; Kubo, Yuki; Lee, Kangjin; Lee, Sangwoo;
Lobzin, Vasily; Mun, JunChul; Murray, Sophie A.; Hamad Nageem, Tarek
A. M.; Qahwaji, Rami; Sharpe, Michael; Steenburgh, Robert A.; Steward,
Graham; Terkildsen, Michael
2019ApJS..243...36L Altcode: 2019arXiv190702905L
Solar flares are extremely energetic phenomena in our solar
system. Their impulsive and often drastic radiative increases,
particularly at short wavelengths, bring immediate impacts that motivate
solar physics and space weather research to understand solar flares
to the point of being able to forecast them. As data and algorithms
improve dramatically, questions must be asked concerning how well the
forecasting performs; crucially, we must ask how to rigorously measure
performance in order to critically gauge any improvements. Building
upon earlier-developed methodology of Paper I (Barnes et al. 2016),
international representatives of regional warning centers and
research facilities assembled in 2017 at the Institute for Space-Earth
Environmental Research, Nagoya University, Japan to, for the first time,
directly compare the performance of operational solar flare forecasting
methods. Multiple quantitative evaluation metrics are employed, with the
focus and discussion on evaluation methodologies given the restrictions
of operational forecasting. Numerous methods performed consistently
above the “no-skill” level, although which method scored top marks
is decisively a function of flare event definition and the metric
used; there was no single winner. Following in this paper series, we
ask why the performances differ by examining implementation details
(Leka et al. 2019), and then we present a novel analysis method to
evaluate temporal patterns of forecasting errors in Paper IV (Park
et al. 2019). With these works, this team presents a well-defined and
robust methodology for evaluating solar flare forecasting methods in
both research and operational frameworks and today’s performance
benchmarks against which improvements and new methods may be compared.

---------------------------------------------------------
Title: Application usability levels: a framework for tracking project
product progress
Authors: Halford, Alexa J.; Kellerman, Adam C.; Garcia-Sage, Katherine;
Klenzing, Jeffrey; Carter, Brett A.; McGranaghan, Ryan M.; Guild,
Timothy; Cid, Consuelo; Henney, Carl J.; Ganushkina, Natalia Yu.;
Burrell, Angeline G.; Terkildsen, Mike; Welling, Daniel T.; Murray,
Sophie A.; Leka, K. D.; McCollough, James P.; Thompson, Barbara J.;
Pulkkinen, Antti; Fung, Shing F.; Bingham, Suzy; Bisi, Mario M.;
Liemohn, Michael W.; Walsh, Brian M.; Morley, Steven K.
2019JSWSC...9A..34H Altcode: 2019arXiv190708663H
The space physics community continues to grow and become both more
interdisciplinary and more intertwined with commercial and government
operations. This has created a need for a framework to easily identify
what projects can be used for specific applications and how close
the tool is to routine autonomous or on-demand implementation and
operation. We propose the Application Usability Level (AUL) framework
and publicizing AULs to help the community quantify the progress
of successful applications, metrics, and validation efforts. This
framework will also aid the scientific community by supplying the
type of information needed to build off of previously published work
and publicizing the applications and requirements needed by the user
communities. In this paper, we define the AUL framework, outline the
milestones required for progression to higher AULs, and provide example
projects utilizing the AUL framework. This work has been completed
as part of the activities of the Assessment of Understanding and
Quantifying Progress working group which is part of the International
Forum for Space Weather Capabilities Assessment.

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Title: Effects of particular smoothing processes for global synoptic
maps on PFSS solutions
Authors: Hayashi, Keiji; Leka, K. D.; Barnes, G.
2019shin.confE.135H Altcode:
Recent space-based and ground-based solar observations produce
high-resolution synoptic maps that capture magnetic features at
various spatial scales, such as small magnetic elements, plages,
sunspot regions, as well as large-scale unipolar magnetic regions
(UMRs). Because high-resolution PFSS solutions are computationally
expensive and because the lifetimes of small-scale magnetic features
are much shorter than one Carrington rotation period, it is a common
practice to reduce the spatial resolution of synoptic maps to employ
lower-order PFSS solutions. As demonstrated in our earlier
work [Hayashi et al., 2016], different size-reducing (smoothing)
methods often alter the PFSS solution substantially. For example, a
simple box-car averaging can suffer the so-called aliasing effect: A
averaging box can contain substantially different amount of total signed
flux than would the same-sized box but shifted by a few degrees in
longitude, in particular for regions in and near pairs of strong-field
sunspots. Such small-scale systematic differences in smoothed/resized
map can cause substantial differences in the resulting global-scale
PFSS solutions, such as the position and shape of the heliospheric
current sheet (HCS). The Gaussian-type smoothing method mitigates
such differences, although it eliminates several of the advantages
gained by using high-resolution observations in the first place. In
addition, the averaging/smoothing can alter the total unsigned fluxes
and horizontal gradients, in particular, in the strong-field sunspot
regions that are crucial for studies on energy build-up processes
and data-driven modeling. We examine differences among the PFSS
solutions of the global solar corona with down-sampling methods
(primarily boxcar-averaging and Gaussian-function smoothing) and
that obtained with high-order PFSS solution using no down-sampling
or smoothing applied to the input Br map, for the target area of
the session. The advantages and disadvantages of different smoothing
methods will be evaluated and discussed. This work is partially
supported by NASA HSWO2R Grant 80NSSC19K0007.

---------------------------------------------------------
Title: A Potential Field is Unique…Right?!? Summary of Evaluation
Methodology and Initial Results
Authors: Leka, K. D.; Barnes, Graham; McAteer, R. T. James
2019shin.confE.151L Altcode:
Given the normal component of the magnetic field on a closed surface,
the lowest-energy construct is the potential field, and mathematically
it is a unique construct. In solar physics, so much of what we are
interested in - free energy, magnetic shear, magnetic topology, helicity
- is estimated relative to the potential field. However, when methods
and results for quantities of interest (e.g. the Campaign on Energy
Storage session at SHINE 2015) what quickly becomes apparent is that
the methods of computing potential fields themselves can lead to wildly
different results - so that comparisons of, for example, NLFFF-derived
free energy are all but meaningless between publications. In
this session we explore computing this all-important starting point,
asking, (1) What is the magnitude of differences between different
potential-field calculations? (2) What implementations can mitigate
some of the worst discrepancies? with the goal of establishing
community-supported potential-field methodologies to bring better
quantitative prospects to our science. We focus separately on
global and local calculations with attention to boundary treatment,
resolution, and implementation details. Participants have prepared
potential-field calculations for 2012.06.13_11:36_TAI and/or NOAA AR
11504 for comparisons, as detailed in the session description. With
this session scheduled for Friday, we summarize in a poster the
submitted solutions (as of the start of the week, more welcome through
Wednesday!), evaluation methodologies, and results. In this way, SHINE
2019 participants can be aware of these results earlier in the week,
for context to discussions in earlier relevant sessions. This work
was partially funded by NASA HSR grant 80NSSC18K0071 and supported
by the US National Science Foundation under Grant No. 1630454. Any
opinions, findings, and conclusions or recommendations expressed in
this material are those of the authors and do not necessarily reflect
the views of the National Science Foundation.

---------------------------------------------------------
Title: Understanding the Where and the How Big of Solar Flares
Authors: Barnes, Graham; Cavins, Alanna S.; Isola, Brianna; Gilchrist,
S. A.; Leka, K. D.
2019shin.confE.141B Altcode:
The approach to understanding solar flares generally characterizes
global properties of a solar active region, for example the
total magnetic flux, the total free magnetic energy, or the total
length of a sheared magnetic neutral line. We take here a different
tack, characterizing not the region as a whole, but estimating the
energy-release prospects of different sub-regions within the region. We
have considered two active regions (NOAA ARs 11283 and 11793) which
are similar in their overall size and classification, but produced
radically different distributions of flares, with AR 11793 producing
nothing larger than C-flares while AR 11283 produced a sequence of M and
X-flares, with very few smaller flares. We modeled the coronal magnetic
field using the CFITS non-linear force-free extrapolation code, and
identified individual current systems within the the extrapolation whose
energy might be released in a single reconnection event. We present
here results comparing the energy associated with the individual
current systems with the magnitude of the flares originating from
each region. This material is based upon work supported by the
US National Science Foundation under Grant No. 1630454. Any opinions,
findings, and conclusions or recommendations expressed in this material
are those of the authors and do not necessarily reflect the views of
the National Science Foundation.

---------------------------------------------------------
Title: Quantitative assessment of coronal NLFFF extrapolations as
initial conditions to coronal MHD simulations
Authors: Gilchrist, S. A.; Leka, K. D.
2019shin.confE.136G Altcode:
NonLinear Force-Free magnetic Field (NLFFF) extrapolations may be used
as initial conditions to magneto-hydrodynamic (MHD) simulations of the
coronal magnetic field. The accuracy of the MHD simulation depends on
the accuracy of the initial conditions: the NLFFF extrapolation must be
an accurate snapshot of the coronal magnetic field. We discuss the
development of metrics for performing quantitative comparisons between
NLFFF extrapolations and coronal/photospheric image/magnetic field
observations. As a case study, we present comparisons between image data
and a NLFFF extrapolation for NOAA active region AR 12158. This
material is based upon work supported by the National Science Foundation
under Grant No. 1841962. Any opinions, findings, and conclusions or
recommendations expressed in this material are those of the authors and
do not necessarily reflect the views of the National Science Foundation.

---------------------------------------------------------
Title: New HMI Data Series: temporally consistent disambiguation
for HARP vector magnetic field timeseries data
Authors: Barnes, Graham; Leka, K. D.; Wagner, Eric
2018csc..confE.116B Altcode:
The last step of the HMI pipeline removes the 180 degree ambiguity
in the direction of the field transverse to the line of sight,
enabling users to download physically meaningful components of the
photospheric vector field. However, for the pipeline, each time is
treated independently, which can lead to changes in the direction of the
transverse field from one time to the next that are unphysical. These
changes result in large values of the time derivative of the inferred
surface magnetic field vector, and hence spurious changes in quantities
such as flows and electric fields computed from it. NWRA has developed
an enhanced version of the disambiguation code that includes a temporal
consistency term. We compare the results of the new method to the
results of the pipeline code and demonstrate the improvement in temporal
stability. A new data product with the time-series disambiguation is
being made available to the community through the JSOC for selected
HARPS. This material is based upon work supported by NASA under award
Nos. 80NSSC18K0055 and 80NSSC18K0180.

---------------------------------------------------------
Title: The Unusually Flare-UnProductive region NOAA AR 10978:
Achieving Accurate Coronal Models;
Authors: Gilchrist, Stuart A.; Leka, K. D.
2018shin.confE..85G Altcode:
We present a data-constrained nonlinear force-free field (NLFFF)
extrapolation of NOAA active region AR 10978 constructed for the
purpose of estimating the region's free energy, i.e. the magnetic
energy available in the corona for release in a flare. We discuss the
influence of the transverse boundary conditions on the extrapolation
and the free energy estimates and its implications for NLFFF modeling
generally. We also present comparisons between our NLFFF results and
observations of the corona

---------------------------------------------------------
Title: Operational Flare Forecasting Benchmarks and Initial
Performance Comparisons
Authors: Leka, K. D.; Park, Sung-Hong
2018cosp...42E1978L Altcode:
We present here select preliminary results from a recent workshop,
"Benchmarks for Operational Solar Flare Forecasts" held at the
Institute for Sun-Earth Environmental Research (ISEE) in Nagoya,
Japan, in late 2017. Numerous methods were tested in a head-to-head
operational forecasting performance exercise. Results are quantified
using standard validation metrics, with a preference for metrics based
on the probabilistic forecasts (rather than categorical results which
are impacted by probability thresholds). We present here a preliminary
analysis of the performance impacts of general method attributes,
addressing questions centered on “which approaches demonstrate
improvement in operational performance, and which approaches do not?”

---------------------------------------------------------
Title: The Magnetic Needs for Understanding (and Predicting) Solar
Energetic Events
Authors: Leka, K. D.
2018cosp...42E1977L Altcode:
Energetic Solar Events - solar flares, coronal mass ejections, and
the acceleration of high-energy particles - are all believed to be
triggered at some level by the sudden reconfiguration of solar magnetic
field lines, and powered at some level by stored magnetic energy. So,
to understand and ultimately predict these events, we need to measure
the magnetic fields on the Sun at all times, in all of space (with no
uncertainty, of course). Is that even possible? No. So, what information
is really accessible about this all-important magnetic field, how
do we acquire it, and how can we best use what we've got? In this
talk I will touch upon the diversity (and limitations) of our present
resources and the wide range of questions they are being used to answer
regarding solar energetic events. I will also review some outstanding
questions and what these imply for future magnetic field observational
requirements in the quest to further extend our understanding (and
ultimately, the prediction) of these phenomena.

---------------------------------------------------------
Title: The Unusually Flare-UnProductive region NOAA AR 10978:
Energy Estimations
Authors: Barnes, Graham; Gilchrist, S. A.; Leka, K. D.
2018shin.confE..86B Altcode:
The approach to understanding solar flares typically characterizes
global properties of a solar active region, for example the total
free magnetic energy, or the total length of sheared magnetic
neutral lines. We take here a different tack, characterizing not the
region as a whole, but estimating the energy-release prospects of
different sub-volumes within the region. We focus on NOAA AR 10978,
which developed a small delta spot on 2007 Dec 12 and by other measures
might have been expected to produce major flares yet only produced small
C-flares during its disk passage. We modeled the coronal magnetic field
using a nonlinear force-free extrapolation code with boundary conditions
derived from Hinode/SpectroPolarimeter observations. We then identified
individual current systems within the extrapolation whose energy might
be released in a single reconnection event. We present here results
comparing the energy associated with the individual current systems to
the total free energy of the region to test whether the region's unusual
flaring behavior was a consequence of only being able to release a
small fraction of the total free energy in a single reconnection event.

---------------------------------------------------------
Title: Understanding the Where and the How Big of Solar Flares
Authors: Barnes, Graham; Gilchrist, Stuart A.; Leka, K. D.
2018tess.conf30495B Altcode:
The approach to understanding solar flares generally characterizes
global properties of a solar active region, for example the
total magnetic flux, the total free magnetic energy, or the total
length of a sheared magnetic neutral line. We take here a different
tack, characterizing not the region as a whole, but estimating the
energy-release prospects of different sub-regions within the region. We
have considered two active regions (NOAA ARs 10978 and 11283) which
are similar in their overall size and classification, but produced
radically different distributions of flares, with AR 10978 producing
nothing larger than C-flares while AR 11283 produced a sequence of
M and X-flares, with very few smaller flares. We modeled the coronal
magnetic field using the CFIT non-linear force-free extrapolation code,
and identified individual current systems within the the extrapolation
whose energy might be released in a single reconnection event. We
present here early results comparing the energy associated with the
individual current systems with the magnitude of the flares originating
from each region. This material is based upon work supported
by the US National Science Foundation under Grant No. 1630454. Any
opinions, findings, and conclusions or recommendations expressed in
this material are those of the authors and do not necessarily reflect
the views of the National Science Foundation.

---------------------------------------------------------
Title: Understanding and Forecasting The Solar Origins of Space
Weather
Authors: Leka, K. D.
2018tess.conf10001L Altcode:
"Would you tell me, please, which way I ought to go from here?',
said Alice. 'That depends a good deal on where you want to get to,'
said the Cheshire Cat." The solar origins of Space Weather
are at once obvious and elusive. The obvious danger from large,
magnetically complex active regions belies the elusiveness of answers
to such critical questions as "when?", "how big?", and "are we also
going to get hit with a coronal mass ejection, too?" With growing
historical and extra-solar perspective, we need to also explore
subtle factors that may contribute to extreme solar and heliospheric
events. Forecasting is the most stringent test of observations and
understanding, and the framework of forecasting science can help
elucidate just how well we understand the solar origins of space
weather. Spoiler alert: not well. Which way ought we go? The path
of pursuing the fundamental physics leads us to microscopic levels,
the limitations of numerical models, and detailed case-studies. Another
path, operational forecasting, is often empirical and most informative
when accessing huge sample sizes. Both directions suffer from trying
to measure the (presently) un-measurable. Some measurement gaps
are being filled or will soon be filled as we obtain ever higher
resolution, some in-situ sampling, and longer-lasting facilities and
observing programs. Ultimately, the goal is for all paths to re-join
and enable physics-based high-performing forecasting for the solar and
heliospheric environment. In this talk I will discuss these paths
in the context of past, present, and future observing facilities and
modeling capabilities. I will discuss the importance of quantitative
success metrics and observationally-accessible differentiating tests. I
will finally propose that, as the Cheshire Cat admonishes to Alice,
sometimes what is needed is to ask slightly different questions.

---------------------------------------------------------
Title: Operational Flare Forecasting Benchmarks and Initial
Performance Comparisons
Authors: Leka, K. D.; Park, Sung-Hong; Barnes, Graham
2018tess.conf41407L Altcode:
It is the end of a magnetic cycle, and we recently asked two questions:
(1) "How well do operational flare forecasting methods presently
work?" and (2) "What is needed to quantitatively answer that question to
begin with?" We present here select preliminary results from a recent
workshop, "Benchmarks for Operational Solar Flare Forecasts" held at
the Institute for Sun-Earth Environmental Research (ISEE) in Nagoya,
Japan, in late 2017. Numerous methods were tested in a head-to-head
operational forecasting performance exercise. Results are quantified
using standard validation metrics, with a preference for metrics based
on the probabilistic forecasts (rather than categorical results which
are impacted by probability thresholds). We discuss how to best assess
the relative performance of different methods, and present an initial
analysis of general method attributes, addressing questions centered
on "which approaches lead to improvement in operational performance,
and which approaches do not?” Support for the workshop and this
analysis is acknowledged from the Nagoya University/Institute for
Space-Earth Environmental Research (ISEE) Center for International
Collaborative Research (CICR).

---------------------------------------------------------
Title: The NWRA Classification Infrastructure: description and
extension to the Discriminant Analysis Flare Forecasting System
(DAFFS)
Authors: Leka, K. D.; Barnes, Graham; Wagner, Eric
2018JSWSC...8A..25L Altcode: 2018arXiv180206864L
A classification infrastructure built upon Discriminant Analysis
(DA) has been developed at NorthWest Research Associates for
examining the statistical differences between samples of two known
populations. Originating to examine the physical differences between
flare-quiet and flare-imminent solar active regions, we describe herein
some details of the infrastructure including: parametrization of large
datasets, schemes for handling "null" and "bad" data in multi-parameter
analysis, application of non-parametric multi-dimensional DA, an
extension through Bayes' theorem to probabilistic classification,
and methods invoked for evaluating classifier success. The classifier
infrastructure is applicable to a wide range of scientific questions
in solar physics. We demonstrate its application to the question
of distinguishing flare-imminent from flare-quiet solar active
regions, updating results from the original publications that were
based on different data and much smaller sample sizes. Finally, as a
demonstration of "Research to Operations" efforts in the space-weather
forecasting context, we present the Discriminant Analysis Flare
Forecasting System (DAFFS), a near-real-time operationally-running solar
flare forecasting tool that was developed from the research-directed
infrastructure.

---------------------------------------------------------
Title: Inferring Currents from the Zeeman Effect at the Solar Surface
Authors: Barnes, Graham; Leka, K. D.
2018GMS...235...81B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Predicting the Where and the How Big of Solar Flares
Authors: Barnes, Graham; Leka, K. D.; Gilchrist, Stuart
2017SPD....4810825B Altcode:
The approach to predicting solar flares generally characterizes global
properties of a solar active region, for example the total magnetic flux
or the total length of a sheared magnetic neutral line, and compares new
data (from which to make a prediction) to similar observations of active
regions and their associated propensity for flare production. We take
here a different tack, examining solar active regions in the context
of their energy storage capacity. Specifically, we characterize not
the region as a whole, but summarize the energy-release prospects
of different sub-regions within, using a sub-area analysis of the
photospheric boundary, the CFIT non-linear force-free extrapolation
code, and the Minimum Current Corona model. We present here early
results from this approach whose objective is to understand the
different pathways available for regions to release stored energy, thus
eventually providing better estimates of the where (what sub-areas are
storing how much energy) and the how big (how much energy is stored,
and how much is available for release) of solar flares.

---------------------------------------------------------
Title: Predicting the Where and the How Big of Solar Flares
Authors: Leka, K. D.; Barnes, G.; Gilchrist, S.; Wheatland, M.
2017shin.confE..87L Altcode:
The approach to predicting solar flares generally characterizes global
properties of a solar active region, for example the total magnetic flux
or the total length of a sheared magnetic neutral line, and compares new
data (from which to make a prediction) to similar observations of active
regions and their associated propensity for flare production. We take
here a different tack, examining solar active regions in the context
of their energy storage capacity. Specifically, we characterize not
the region as a whole, but summarize the energy-release prospects
of different sub-regions within, using a sub-area analysis of the
photospheric boundary, the CFIT non-linear force-free extrapolation
code, and the Minimum Current Corona model. We present here early
results from this approach whose objective is to understand the
different pathways available for regions to release stored energy, thus
eventually providing better estimates of the 'where' (what sub-areas
are storing how much energy) and the 'how big' (how much energy is
stored, and how much is available for release) of solar flares.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Statistical analysis of solar
active regions (Barnes+, 2014)
Authors: Barnes, G.; Birch, A. C.; Leka, K. D.; Braun, D. C.
2017yCat..17860019B Altcode:
In brief, samples from two populations are considered: "pre-emergence"
targets (PE) that track a 32°x32° patch of the Sun prior to the
emergence of a NOAA-numbered AR and "non-emergence" targets (NE)
selected for lack of emergence and lack of strong fields in the
central portions of the tracked patch. The PE sample size comprises
107 targets obtained between 2001 and 2007, matched to 107 NE targets
drawn from an initially larger sample and selected further to match
the PE distributions in time and observing location on the disk. (2 data files).

---------------------------------------------------------
Title: A Comparison of Classifiers for Solar Energetic Events
Authors: Barnes, Graham; Schanche, Nicole; Leka, K. D.; Aggarwal,
Ashna; Reeves, Kathy
2017IAUS..325..201B Altcode:
We compare the results of using a Random Forest Classifier with the
results of using Nonparametric Discriminant Analysis to classify
whether a filament channel (in the case of a filament eruption)
or an active region (in the case of a flare) is about to produce an
event. A large number of descriptors are considered in each case,
but it is found that only a small number are needed in order to get
most of the improvement in performance over always predicting the
majority class. There is little difference in performance between the
two classifiers, and neither results in substantial improvements over
simply predicting the majority class.

---------------------------------------------------------
Title: Evaluating (and Improving) Estimates of the Solar Radial
Magnetic Field Component from Line-of-Sight Magnetograms
Authors: Leka, K. D.; Barnes, G.; Wagner, E. L.
2017SoPh..292...36L Altcode: 2017arXiv170104836L
Although for many solar physics problems the desirable or meaningful
boundary is the radial component of the magnetic field Br,
the most readily available measurement is the component of the magnetic
field along the line of sight to the observer, Blos. As
this component is only equal to the radial component where the
viewing angle is exactly zero, some approximation is required to
estimate Br at all other observed locations. In this
study, a common approximation known as the "μ -correction", which
assumes all photospheric field to be radial, is compared to a method
that invokes computing a potential field that matches the observed
Blos, from which the potential field radial component,
Brpot is recovered. We demonstrate that in
regions that are truly dominated by a radially oriented field at the
resolution of the data employed, the μ -correction performs acceptably
if not better than the potential-field approach. However, it is also
shown that for any solar structure that includes horizontal fields,
i.e. active regions, the potential-field method better recovers both the
strength of the radial field and the location of magnetic neutral line.

---------------------------------------------------------
Title: Achieving Consistent Vector Magnetic Field Measurements
from SDO/HMI
Authors: Schuck, P. W.; Antiochos, S. K.; Scherrer, P. H.; Hoeksema,
J. T.; Leka, K. D.; Barnes, G.
2016AGUFMSH31B2575S Altcode:
NASA's Solar Dynamics Observatory (SDO) is delivering vector magnetic
field observations of the full solar disk with unprecedented temporal
and spatial resolution; however, the satellite is in a highly inclined
geosynchronous orbit. The relative spacecraft-Sun velocity varies by ±3
km/s over a day which introduces significant orbital artifacts in the
Helioseismic Magnetic Imager (HMI) data. We have recently demonstrated
that the orbital artifacts contaminate all spatial and temporal scales
in the data and developed a procedure for mitigating these artifacts
in the Doppler data obtained from the Milne-Eddington inversions in the
HMI Pipeline. Simultaneously, we have found that the orbital artifacts
may be introduced by inaccurate estimates for the free-spectral ranges
(FSRs) of the optical elements in HMI. We describe our approach and
attempt to minimize orbital artifacts in the hmi.V_720 Dopplergram
series by adjusting the FSRs for the optical elements of HMI within
their measurement uncertainties of ±1%.

---------------------------------------------------------
Title: Community-wide space weather Scoreboards: Facilitating the
Validation of Real-time CME, Flare, and SEP Forecasts
Authors: Mullinix, R.; Mays, M. L.; Kuznetsova, M. M.; Andries,
J.; Bingham, S.; Bloomfield, D.; Boblitt, J. M.; Crosby, N. B.;
Dierckxsens, M.; Guerra, J. A.; Leka, K. D.; Marsh, M. S.; Murray,
S.; Wiegand, C.
2016AGUFMSH11C2256M Altcode:
Confidence assessment of predictive space weather models ultimately
determines the value of forecasts for end users. Testing predictive
capabilities before event onset is important and especially relevant
for validating space weather models. This poster presents three
real-time forecast validation projects facilitated by the CCMC via
forecast collection "scoreboards": (1) CME arrival time and geomagnetic
storm strength, (2) flare occurrence probability, and (3) SEP onset,
duration, peak flux, probability, and overall profile. The CME,
Flare, and SEP scoreboards enable world-wide community involvement
in real-time predictions, foster community validation projects,
and ultimately help researchers improve their CME, flare, and
SEP forecasts. All CME, Flare, SEP forecast modelers and experts
worldwide are invited to advise or participate in this effort. The
flare and SEP systems are automated such that model developers can
routinely upload their predictions to an anonymous ftp and the data
is accessible to anyone via an API. The "CME arrival time scoreboard"
(https://kauai.ccmc.gsfc.nasa.gov/CMEscoreboard/) provides a central
location for the community to: submit their CME arrival time forecast
in real-time, quickly view all forecasts at once in real-time, and
compare forecasting methods when the event has arrived. There are
currently 19 registered CME arrival time prediction methods. The "Flare
Scoreboard" (http://ccmc.gsfc.nasa.gov/challenges/flare.php) project
is led by the UK Met Office.The full disk and active region flare
forecasts can currently be viewed on an interactive display overlaid
on an SDO/AIA or HMI image of the Sun and will be dynamically paired
with a display of flare probability time series (coming soon). The
"SEP Scoreboard" (http://ccmc.gsfc.nasa.gov/challenges/sep.php)
project is led by BIRA-IASB and the UK Met Office. SEP forecasts can
be roughly divided into three categories: continuous/Probabilistic,
solar event triggered, non near real-time. The SEP scoreboard will
focus on real-time forecasts, however the SEP scoreboard team can
also coordinate a set of historical events for a "SEP challenge" with
different models, particularly those physics-based models in the third
category that are not ready or relevant for real-time modeling.

---------------------------------------------------------
Title: A Comparison of Flare Forecasting Methods. I. Results from
the “All-Clear” Workshop
Authors: Barnes, G.; Leka, K. D.; Schrijver, C. J.; Colak, T.;
Qahwaji, R.; Ashamari, O. W.; Yuan, Y.; Zhang, J.; McAteer, R. T. J.;
Bloomfield, D. S.; Higgins, P. A.; Gallagher, P. T.; Falconer, D. A.;
Georgoulis, M. K.; Wheatland, M. S.; Balch, C.; Dunn, T.; Wagner, E. L.
2016ApJ...829...89B Altcode: 2016arXiv160806319B
Solar flares produce radiation that can have an almost immediate effect
on the near-Earth environment, making it crucial to forecast flares
in order to mitigate their negative effects. The number of published
approaches to flare forecasting using photospheric magnetic field
observations has proliferated, with varying claims about how well
each works. Because of the different analysis techniques and data
sets used, it is essentially impossible to compare the results from
the literature. This problem is exacerbated by the low event rates of
large solar flares. The challenges of forecasting rare events have long
been recognized in the meteorology community, but have yet to be fully
acknowledged by the space weather community. During the interagency
workshop on “all clear” forecasts held in Boulder, CO in 2009,
the performance of a number of existing algorithms was compared
on common data sets, specifically line-of-sight magnetic field and
continuum intensity images from the Michelson Doppler Imager, with
consistent definitions of what constitutes an event. We demonstrate
the importance of making such systematic comparisons, and of using
standard verification statistics to determine what constitutes a good
prediction scheme. When a comparison was made in this fashion, no one
method clearly outperformed all others, which may in part be due to the
strong correlations among the parameters used by different methods to
characterize an active region. For M-class flares and above, the set
of methods tends toward a weakly positive skill score (as measured
with several distinct metrics), with no participating method proving
substantially better than climatological forecasts.

---------------------------------------------------------
Title: Lessening the Effects of Projection for Line-of-Sight Magnetic
Field Data.
Authors: Leka, K. D.; Barnes, G.; Wagner, E. L.
2016shin.confE.147L Altcode:
A method for treating line-of-sight magnetic field data (B_los)
is developed for the goal of reconstructing the radially-directed
component (B_r) of the solar photospheric magnetic field. The latter
is generally the desired quantity for use as a boundary for modeling
efforts and observational interpretation of the surface field, but the
two are only equivalent where the viewing angle is exactly zero. A
common approximation known as the 'Î¼-correction', which assumes
all photospheric field to be radial, is compared to a method which
invokes a potential field constructed to match the observed B_los
(Alissandrakis 1981; Sakurai 1982), from which the potential field
radial field component is recovered.

---------------------------------------------------------
Title: Achieving Consistent Doppler Measurements from SDO/HMI Vector
Field Inversions
Authors: Schuck, Peter W.; Antiochos, S. K.; Leka, K. D.; Barnes,
Graham
2016ApJ...823..101S Altcode: 2015arXiv151106500S
NASA’s Solar Dynamics Observatory is delivering vector magnetic
field observations of the full solar disk with unprecedented temporal
and spatial resolution; however, the satellite is in a highly
inclined geosynchronous orbit. The relative spacecraft-Sun velocity
varies by ±3 km s-1 over a day, which introduces major
orbital artifacts in the Helioseismic Magnetic Imager (HMI) data. We
demonstrate that the orbital artifacts contaminate all spatial and
temporal scales in the data. We describe a newly developed three-stage
procedure for mitigating these artifacts in the Doppler data obtained
from the Milne-Eddington inversions in the HMI pipeline. The procedure
ultimately uses 32 velocity-dependent coefficients to adjust 10 million
pixels—a remarkably sparse correction model given the complexity of
the orbital artifacts. This procedure was applied to full-disk images
of AR 11084 to produce consistent Dopplergrams. The data adjustments
reduce the power in the orbital artifacts by 31 dB. Furthermore, we
analyze in detail the corrected images and show that our procedure
greatly improves the temporal and spectral properties of the data
without adding any new artifacts. We conclude that this new procedure
makes a dramatic improvement in the consistency of the HMI data and
in its usefulness for precision scientific studies.

---------------------------------------------------------
Title: Lessening the Effects of Projection for Line-of-Sight Magnetic
Field Data
Authors: Leka, K. D.; Barnes, Graham; Wagner, Eric
2016SPD....47.1008L Altcode:
A method for treating line-of-sight magnetic field data
(Blos) is developed for the goal of reconstructing the
radially-directed component (Br) of the solar photospheric
magnetic field. The latter is generally the desired quantity for use
as a boundary for modeling efforts and observational interpretation
of the surface field, but the two are only equivalent where the
viewing angle is exactly zero (μ=1.0). A common approximation
known as the "μ-correction", which assumes all photospheric field
to be radial, is compared to a method which invokes a potential field
constructed to match the observed Blos (Alissandrakis 1981;
Sakurai 1982), from which the potential field radial field component
(Brpot) is recovered.We compare this treatment
of Blos data to the radial component derived from SDO/HMI
full-disk vector magnetograms as the "ground truth", and discuss
the implications for data analysis and modeling efforts. In regions
that are truly dominated by radial field, the μ-correction performs
acceptably if not better than the potential-field approach. However,
for any solar structure which includes horizontal fields, i.e. active
regions, the potential-field method better recovers magnetic neutral
line location and the inferred strength of the radial field.This work
was made possible through contracts with NASA, NSF, and NOAA/SBIR.

---------------------------------------------------------
Title: The Discriminant Analysis Flare Forecasting System (DAFFS)
Authors: Leka, K. D.; Barnes, Graham; Wagner, Eric; Hill, Frank;
Marble, Andrew R.
2016SPD....4720701L Altcode:
The Discriminant Analysis Flare Forecasting System (DAFFS) has been
developed under NOAA/Small Business Innovative Research funds to
quantitatively improve upon the NOAA/SWPC flare prediction. In the
Phase-I of this project, it was demonstrated that DAFFS could indeed
improve by the requested 25% most of the standard flare prediction
data products from NOAA/SWPC. In the Phase-II of this project, a
prototype has been developed and is presently running autonomously
at NWRA.DAFFS uses near-real-time data from NOAA/GOES, SDO/HMI, and
the NSO/GONG network to issue both region- and full-disk forecasts
of solar flares, based on multi-variable non-parametric Discriminant
Analysis. Presently, DAFFS provides forecasts which match those provided
by NOAA/SWPC in terms of thresholds and validity periods (including
1-, 2-, and 3- day forecasts), although issued twice daily. Of
particular note regarding DAFFS capabilities are the redundant system
design, automatically-generated validation statistics and the large
range of customizable options available. As part of this poster, a
description of the data used, algorithm, performance and customizable
options will be presented, as well as a demonstration of the DAFFS
prototype.DAFFS development at NWRA is supported by NOAA/SBIR contracts
WC-133R-13-CN-0079 and WC-133R-14-CN-0103, with additional support
from NASA contract NNH12CG10C, plus acknowledgment to the SDO/HMI and
NSO/GONG facilities and NOAA/SWPC personnel for data products, support,
and feedback. DAFFS is presently ready for Phase-III development.

---------------------------------------------------------
Title: Achieving Consistent Doppler Measurements from SDO/HMI Vector
Field Inversions
Authors: Schuck, Peter W.; Antiochos, Spiro K.; Leka, K. D.; Barnes,
Graham
2016SPD....47.1207S Altcode:
NASA’s Solar Dynamics Observatory is delivering vector magnetic
field observations of the full solar disk with unprecedented temporal
and spatial resolution; however, the satellite is in a highly inclined
geosynchronous orbit. The relative spacecraft-Sun velocity varies by
±3 km/s over a day which introduces major orbital artifacts in the
Helioseismic Magnetic Imager data. We demonstrate that the orbital
artifacts contaminate all spatial and temporal scales in the data. We
describe a newly-developed three stage procedure for mitigating these
artifacts in the Doppler data obtained from the Milne-Eddington
inversions in the HMI Pipeline. The procedure ultimately uses 32
velocity dependent coefficients to adjust 10 million pixels - a
remarkably sparse correction model given the complexity of the orbital
artifacts. This procedure was applied to full disk images of AR11084 to
produce consistent Dopplergrams. The data adjustments reduce the power
in the orbital artifacts by 31dB. Furthermore, we analyze in detail
the corrected images and show that our procedure greatly improves
the temporal and spectral properties of the data without adding any
new artifacts. We conclude that this new procedure makes a dramatic
improvement in the consistency of the HMI data and in its usefulness
for precision scientific studies.

---------------------------------------------------------
Title: Searching for Missing Pieces for Solar Flare Forecasting
Authors: Leka, K. D.
2015AGUFMSH51B2446L Altcode:
Knowledge of the state of the solar photospheric magnetic field
at a single instant in time does not appear sufficient to uniquely
predict the size and timing of impending solar flares. Such knowledge
may provide necessary conditions, such as estimates of the magnetic
energy needed for a flare to occur. Given the necessary conditions,
it is often assumed that the evolution of the field, possibly by
only a small amount, may trigger the onset of a flare. We present
the results of a study using time series of photospheric vector
field data from the Helioseismic and Magnetic Imager (HMI) on NASA's
Solar Dynamics Observatory (SDO) to quantitatively parameterize both
the state and evolution of solar active regions - their complexity,
magnetic topology and energy - as related to solar flare events. We
examine both extensive and intensive parameters and their short-term
temporal behavior, in the context of predicting flares at various
thresholds. Statistical tests based on nonparametric Discriminant
Analysis are used to compare pre-flare epochs to a control group of
flare-quiet epochs and active regions. Results regarding the type of
photospheric signature examined and the efficacy of using the present
state vs. temporal evolution to predict solar flares is quantified by
standard skill scores. This work is made possible by contracts NASA
NNH12CG10C and NOAA/SBIR WC-133R-13-CN-0079.

---------------------------------------------------------
Title: The Influence of Spatial resolution on Nonlinear Force-free
Modeling
Authors: DeRosa, M. L.; Wheatland, M. S.; Leka, K. D.; Barnes, G.;
Amari, T.; Canou, A.; Gilchrist, S. A.; Thalmann, J. K.; Valori,
G.; Wiegelmann, T.; Schrijver, C. J.; Malanushenko, A.; Sun, X.;
Régnier, S.
2015ApJ...811..107D Altcode: 2015arXiv150805455D
The nonlinear force-free field (NLFFF) model is often used to
describe the solar coronal magnetic field, however a series of
earlier studies revealed difficulties in the numerical solution of the
model in application to photospheric boundary data. We investigate
the sensitivity of the modeling to the spatial resolution of the
boundary data, by applying multiple codes that numerically solve the
NLFFF model to a sequence of vector magnetogram data at different
resolutions, prepared from a single Hinode/Solar Optical Telescope
Spectro-Polarimeter scan of NOAA Active Region 10978 on 2007 December
13. We analyze the resulting energies and relative magnetic helicities,
employ a Helmholtz decomposition to characterize divergence errors, and
quantify changes made by the codes to the vector magnetogram boundary
data in order to be compatible with the force-free model. This study
shows that NLFFF modeling results depend quantitatively on the spatial
resolution of the input boundary data, and that using more highly
resolved boundary data yields more self-consistent results. The
free energies of the resulting solutions generally trend higher
with increasing resolution, while relative magnetic helicity values
vary significantly between resolutions for all methods. All methods
require changing the horizontal components, and for some methods also
the vertical components, of the vector magnetogram boundary field in
excess of nominal uncertainties in the data. The solutions produced
by the various methods are significantly different at each resolution
level. We continue to recommend verifying agreement between the modeled
field lines and corresponding coronal loop images before any NLFFF
model is used in a scientific setting.

---------------------------------------------------------
Title: Enhanced Acoustic Emission in Relation to the Acoustic Halo
Surrounding Active Region 11429
Authors: Hanson, Chris S.; Donea, Alina C.; Leka, K. D.
2015SoPh..290.2171H Altcode: 2015arXiv150703447H; 2015SoPh..tmp...93H
The use of acoustic holography in the high-frequency p -mode spectrum
can resolve the source distributions of enhanced acoustic emissions
within halo structures surrounding active regions. In doing so,
statistical methods can then be applied to ascertain relationships with
the magnetic field. This is the focus of this study. The mechanism
responsible for the detected enhancement of acoustic sources around
solar active regions has not yet been explained. Furthermore the
relationship between the magnetic field and enhanced acoustic
emission has not yet been comprehensively examined. We have used
vector magnetograms from the Helioseismic and Magnetic Imager (HMI)
onboard the Solar Dynamics Observatory (SDO) to image the magnetic-field
properties in the halo. We have studied the acoustic morphology of an
active region, with a complex halo and "glories", and we have linked
some acoustic properties to the magnetic-field configuration. In
particular, we find that acoustic sources are significantly enhanced in
regions of intermediate field strength with inclinations no different
from the distributions found in the quiet Sun. Additionally, we have
identified a transition region between the active region and the halo,
in which the acoustic-source power is hindered by inclined fields of
intermediate field strength. Finally, we have compared the results of
acoustic-emission maps, calculated from holography, and the commonly
used local acoustic maps, finding that the two types of maps have
similar properties with respect to the magnetic field but lack spatial
correlation when examining the highest-powered regions.

---------------------------------------------------------
Title: Skill Scores and Evaluation Tools for SHINE-related Phenomena
Authors: Leka, K. D.
2015shin.confE.168L Altcode:
Evaluating how well a forecast performs is crucial, but can be quite
challenging. This is especially true when attempting to compare the
forecast results for different methods applied to different datasets
- and made even worse in the context of rare events. Ever since the
'Findley Affair' generated interest in measures of merit that focused on
usefullness (rather than to simply sounding impressive), skill scores
have been developed to address the need to quantify, 'how well does
this forecast actually work?' In the context of the disparate types
of events of interest to SHINE, from solar flares to CMEs, shocks,
and geomagnetic storms, understanding and quantifying forecast failure
can be key to pushing the research forward by identifying the trends
of failure and success. In this 'scene-setting talk', I will introduce
methods for evaluating not just operational-type forecasts but also
the related underlying research, including skill scores and other
quantitative metrics, with their differing limitations and emphasis.

---------------------------------------------------------
Title: Measuring Coronal Energy and Helicity Buildup with SDO/HMI
Authors: Schuck, P. W.; Antiochos, S. K.; Barnes, G.; Leka, K. D.
2014AGUFMSH44A..08S Altcode:
Solar eruptions are driven by energy and helicity transported through
the photosphere and into the corona. However, the mechanism by which
energy and helicity emerge from the solar interior to form the observed
coronal structures is poorly understood. SDO/HMI data are the first
space-based full-disk vector field observations of the Sun with
a near 100% duty cycle and, therefore, represent an unprecedented
opportunity to quantify the energy end helicity fluxes through the
photosphere. However, because of the SDO satellite's highly inclined
geostationary orbit, the relative velocity of the instrument varies by
±3~km/s which introduces major orbital artifacts. We have developed a
procedure for mitigating these artifacts and have applied this analysis
to AR11084 to produce a cleaned data set. Our analysis procedure is
described, in detail, and the results for AR11084 presented. We have
also recast the Berger and Field (1984) helicity transport equation
in manifestly gauge invariant form and derived the terms quantifying
the injection of helicity into the corona by the emergence of closed
field, versus helicity injection by the stressing of pre-emerged
flux. The plasma velocity fields in the photosphere, necessary for
computing energy and helicity fluxes are determined using an upgraded
version of DAVE4VM that incorporates the spherical geometry of the
solar images. We find that the bulk of the helicity into the corona is
injected by twisting motions, and we discuss the implications of our
results for understanding solar activity and especially for data-driven
modeling of solar eruptions.This work was supported, in part, by NASA

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager (HMI) Vector Magnetic
Field Pipeline: Overview and Performance
Authors: Hoeksema, J. Todd; Liu, Yang; Hayashi, Keiji; Sun, Xudong;
Schou, Jesper; Couvidat, Sebastien; Norton, Aimee; Bobra, Monica;
Centeno, Rebecca; Leka, K. D.; Barnes, Graham; Turmon, Michael
2014SoPh..289.3483H Altcode: 2014SoPh..tmp...57H; 2014arXiv1404.1881H
The Helioseismic and Magnetic Imager (HMI) began near-continuous
full-disk solar measurements on 1 May 2010 from the Solar Dynamics
Observatory (SDO). An automated processing pipeline keeps pace
with observations to produce observable quantities, including the
photospheric vector magnetic field, from sequences of filtergrams. The
basic vector-field frame list cadence is 135 seconds, but to reduce
noise the filtergrams are combined to derive data products every 720
seconds. The primary 720 s observables were released in mid-2010,
including Stokes polarization parameters measured at six wavelengths,
as well as intensity, Doppler velocity, and the line-of-sight magnetic
field. More advanced products, including the full vector magnetic field,
are now available. Automatically identified HMI Active Region Patches
(HARPs) track the location and shape of magnetic regions throughout
their lifetime.

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager (HMI) Vector Magnetic
Field Pipeline: Optimization of the Spectral Line Inversion Code
Authors: Centeno, R.; Schou, J.; Hayashi, K.; Norton, A.; Hoeksema,
J. T.; Liu, Y.; Leka, K. D.; Barnes, G.
2014SoPh..289.3531C Altcode: 2014SoPh..tmp...44C; 2014arXiv1403.3677C
The Very Fast Inversion of the Stokes Vector (VFISV) is a
Milne-Eddington spectral line inversion code used to determine the
magnetic and thermodynamic parameters of the solar photosphere from
observations of the Stokes vector in the 6173 Å Fe I line by the
Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO). We report on the modifications made to the original
VFISV inversion code in order to optimize its operation within
the HMI data pipeline and provide the smoothest solution in active
regions. The changes either sped up the computation or reduced the
frequency with which the algorithm failed to converge to a satisfactory
solution. Additionally, coding bugs which were detected and fixed in
the original VFISV release are reported here.

---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager (HMI) Vector Magnetic
Field Pipeline: SHARPs - Space-Weather HMI Active Region Patches
Authors: Bobra, M. G.; Sun, X.; Hoeksema, J. T.; Turmon, M.; Liu,
Y.; Hayashi, K.; Barnes, G.; Leka, K. D.
2014SoPh..289.3549B Altcode: 2014arXiv1404.1879B; 2014SoPh..tmp...68B
A new data product from the Helioseismic and Magnetic Imager (HMI)
onboard the Solar Dynamics Observatory (SDO) called Space-weather
HMI Active Region Patches (SHARPs) is now available. SDO/HMI is the
first space-based instrument to map the full-disk photospheric vector
magnetic field with high cadence and continuity. The SHARP data series
provide maps in patches that encompass automatically tracked magnetic
concentrations for their entire lifetime; map quantities include the
photospheric vector magnetic field and its uncertainty, along with
Doppler velocity, continuum intensity, and line-of-sight magnetic
field. Furthermore, keywords in the SHARP data series provide several
parameters that concisely characterize the magnetic-field distribution
and its deviation from a potential-field configuration. These indices
may be useful for active-region event forecasting and for identifying
regions of interest. The indices are calculated per patch and are
available on a twelve-minute cadence. Quick-look data are available
within approximately three hours of observation; definitive science
products are produced approximately five weeks later. SHARP data are
available at jsoc.stanford.edu and maps are available in either of
two different coordinate systems. This article describes the SHARP
data products and presents examples of SHARP data and parameters.

---------------------------------------------------------
Title: Sunspotter: Using Citizen Science to Determine the Complexity
of Sunspots
Authors: Higgins, Paul A.; Perez-Suarez, David; Parrish, Michael;
O'Callaghan, David; Leka, K D.; Barnes, Graham; Roche, Joseph;
Gallagher, Peter T
2014AAS...22411203H Altcode:
It is well known that sunspot groups with large, complex magnetic field
configurations and strong, sheared polarity separation lines produce
the largest flares. While methods for determining certain physical
properties, such as total magnetic flux and polarity-separation-line
length have been successfully developed for characterizing sunspot
groups, a reliable automated method for determining sunspot
complexity has never been developed. Since complexity can only be
measured in a relative sense, we have used crowd-sourcing methods
to allow human observers to compare the complexity of pairs of
sunspot groups. This allows a large dataset to be ranked in terms of
complexity. Sunspotter.org uses the Zooniverse platform and allows
the general public to contribute comparisons using a web-browser
interface. The results of this project will help to establish the true
relationship between sunspot group complexity and flares, which has
been discussed in the solar physics community for many decades.

---------------------------------------------------------
Title: A Helioseismic Survey to Investigate Relationships between
Subsurface Flows beneath Large Active Regions and Solar Flares
Authors: Braun, Douglas; Leka, K D.; Barnes, Graham
2014AAS...22421815B Altcode:
A survey of the subsurface flow properties of about 120 of the largest
active regions, determined from the application of helioseismic
holography to Dopplergrams obtained with the HMI instrument onboard
the Solar Dynamics Observatory, is being carried out. The overriding
goal is to characterize differences in the subsurface flows between
active regions associated with eruptive flares and the flows observed in
relatively quiescent regions. Applications to flare forecasting comprise
only one part of this investigation, since the potential response of
the subsurface environment to eruptive events during and after their
occurrence is also of scientific interest. Other priorities include
understanding the limitations of the helioseismic methods, identifying
and correcting systematic effects, and validating the reliability of
the measurements using artificial data. While inversions to determine
the variation with depth of subsurface flows are planned, preliminary
results will be discussed which make use of proxies for near-surface
depth-integrated properties, including the horizontal component of the
flow divergence and the vertical component of the flow vorticity.This
work is supported by the Solar Terrestrial Program of the National
Science Foundation, through grant AGS-1127327, and by the National
Oceanic and Atmospheric Administration SBIR program.

---------------------------------------------------------
Title: Studies on Forecasting Solar Flares
Authors: Leka, K. D.; Barnes, G.; Braun, D. C.; Wagner, E. L.
2014shin.confE.171L Altcode:
Forecasting solar flares is a challenge from various scientific
perspectives; major solar flares are inherently rare events, and all
observations available with which to evaluate the flare-readiness of the
Sun are remote, with inferences about the physical state rather than
direct measurements. We report on efforts to improve forecasts, using
data from the Helioseismic and Magnetic Imager on the Solar Dynamics
Observatory using magnetic field and helioseismic parametrization,
magnetic charge topology and Discriminant Analysis. We report on
preliminary results of the performance, including the temporal
variations of the parametrizations. This work is supported by
NASA contract NNH12CG10C and NOAA Contract WC-133R-13-CN-0079

---------------------------------------------------------
Title: Helioseismology of Pre-emerging Active
Regions. III. Statistical Analysis
Authors: Barnes, G.; Birch, A. C.; Leka, K. D.; Braun, D. C.
2014ApJ...786...19B Altcode: 2013arXiv1307.1938B
The subsurface properties of active regions (ARs) prior to their
appearance at the solar surface may shed light on the process of
AR formation. Helioseismic holography has been applied to samples
taken from two populations of regions on the Sun (pre-emergence and
without emergence), each sample having over 100 members, that were
selected to minimize systematic bias, as described in Paper I. Paper
II showed that there are statistically significant signatures in
the average helioseismic properties that precede the formation of
an AR. This paper describes a more detailed analysis of the samples
of pre-emergence regions and regions without emergence based on
discriminant analysis. The property that is best able to distinguish
the populations is found to be the surface magnetic field, even
a day before the emergence time. However, after accounting for the
correlations between the surface field and the quantities derived from
helioseismology, there is still evidence of a helioseismic precursor
to AR emergence that is present for at least a day prior to emergence,
although the analysis presented cannot definitively determine the
subsurface properties prior to emergence due to the small sample sizes.

---------------------------------------------------------
Title: AMBIG: Automated Ambiguity-Resolution Code
Authors: Leka, K. D.; Barnes, G.; Crouch, A.
2014ascl.soft04007L Altcode:
AMBIG is a fast, automated algorithm for resolving the 180°
ambiguity in vector magnetic field data, including those data from
Hinode/Spectropolarimeter. The Fortran-based code is loosely based
on the Minimum Energy Algorithm, and is distributed to provide
ambiguity-resolved data for the general user community.

---------------------------------------------------------
Title: The Second NWRA Flare-Forecasting Comparison Workshop:
Methods Compared and Methodology
Authors: Leka, K. D.; Barnes, G.; Flare Forecasting Comparison Group
2013SPD....44...81L Altcode:
The Second NWRA Workshop to compare methods of solar flare forecasting
was held 2-4 April 2013 in Boulder, CO. This is a follow-on to the
First NWRA Workshop on Flare Forecasting Comparison, also known as the
“All-Clear Forecasting Workshop”, held in 2009 jointly with NASA/SRAG
and NOAA/SWPC. For this most recent workshop, many researchers who are
active in the field participated, and diverse methods were represented
in terms of both the characterization of the Sun and the statistical
approaches used to create a forecast. A standard dataset was created
for this investigation, using data from the Solar Dynamics Observatory/
Helioseismic and Magnetic Imager (SDO/HMI) vector magnetic field HARP
series. For each HARP on each day, 6 hours of data were used, allowing
for nominal time-series analysis to be included in the forecasts. We
present here a summary of the forecasting methods that participated
and the standardized dataset that was used. Funding for the workshop
and the data analysis was provided by NASA/Living with a Star contract
NNH09CE72C and NASA/Guest Investigator contract NNH12CG10C.

---------------------------------------------------------
Title: Solar Flare Forecasting: a "State of the Field" Report for
Researchers
Authors: Leka, K. D.; Barnes, G.
2013SPD....44...82L Altcode:
It can be argued that the most stringent test of understanding a
deterministic system is to be able to forecast an outcome based on
observable particulars. It can also be argued that (1) solar flares may
not be deterministic , and even if they were, our present understanding
is nowhere close to being able to predict the time and location of
a solar flare with any certainty. Still, solar flare prediction is a
needed component of our national space weather infrastructure, and many
groups around the world are investigating ways to improve forecasting
methods, especially in light of new observational data available,
such as from the Solar Dynamics Observatory. We present a (very) brief
report of the "state of the field", summarizing insights gained from
workshops (held in 2009 and 2013) aimed at head-to-head comparisons
of flare forecasting methods in specific contexts. In summary,
today's methods combine sophisticated data analysis with statistical
or computer-learning algorithms generally result in probabilistic
forecasts. It is unclear whether any of the presently developed
methods clearly outperforms the others, as measured using standard
skill scores applied to the careful comparisons that participating
researchers engaged in at the workshops. However, it is also clear that
new insights into flare triggering mechanisms, especially as afforded
by modern analysis of high-cadence, high-quality data such as from
SDO, have yet to be fully exploited. Funding for the workshops and
subsequent analysis was provided by NASA/Living with a Star contract
NNH09CE72C and NASA/Guest Investigator contract NNH12CG10C.

---------------------------------------------------------
Title: A Search for Pre-Emergence Helioseismic Signatures of Active
Regions: Study Design and some Average Results
Authors: Leka, K. D.; Birch, A.; Barnes, G.; Braun, D.; Javornik,
B.; Gonzalez-Hernandez, I.; Dunn, T.
2013SPD....44...91L Altcode:
Helioseismology can be an important tool for understanding the
formation of active regions. This poster describes the design of a
recently completed study, testing whether pre-appearance signatures
of solar magnetic active regions were detectable using various tools
of local helioseismology. We provide details of the data selection
and preparation of samples, each containing over 100 members, of
two populations: regions on the Sun which produced a numbered NOAA
active region, and a "control" sample of areas which did not. The
seismology is performed on data from the GONG network; accompanying
magnetic data from the Michelson Doppler Imager aboard SoHO are used
for co-temporal analysis of the surface magnetic field. Samples are
drawn from 2001--2007, and each target is analyzed for 27.7hr prior
to an objectively determined time of emergence. We describe known
sources of bias and the approaches used to mitigate them. Examining the
average ensemble differences between the two populations, we describe
significant and surprising differences between our samples in both
quantities determined from helioseismology and from surface magnetic
fields. This work was supported by NASA contract NNH07CD25C.

---------------------------------------------------------
Title: The Second NWRA Flare-Forecasting Comparison Workshop:
Preliminary Results
Authors: Barnes, Graham; Leka, K. D.; Flare Forecasting Comparison
Group
2013SPD....44...80B Altcode:
The Second NWRA Workshop to compare methods of solar flare forecasting
was held 2-4 April 2013 in Boulder, CO. Many researchers who are active
in the field participated, and provided their methods' prediction
results on standardized datasets. We discuss what is necessary to
make meaningful comparisons of methods, focusing on techniques for
removing bias and estimating random errors, and present preliminary
method comparisons based on standardized skill scores. Funding for
the workshop and the data analysis was provided by NASA/LWS contract
NNH09CE72C and NASA/GI contract NNH12CG10C.

---------------------------------------------------------
Title: Making global map of the solar surface Br from
the HMI vector magnetic field observations
Authors: Hayashi, K.; Liu, Y.; Sun, X.; Hoeksema, J. T.; Centeno,
R.; Barnes, G.; Leka, K. D.
2013JPhCS.440a2036H Altcode:
The Helioseismic Magnetic Imager (HMI) has made full-disk vector
magnetic field measurements of the Sun with cadence of 12 minutes. The
three-component solar surface magnetic field vector data are from
the HMI observations with the data process pipeline modules, VFISV
(Very Fast Inversion of the Stokes Vector, Borrero et al., 2011)
for Milne-Eddington inversion and the minimum-energy disambiguation
algorithm (Metcalf 1994, Leka et al, 2009). The models of the global
corona and solar wind, such as the PFSS (potential-field source-surface)
model and the MHD simulations, often use the maps of solar surface
magnetic field, especially the radial component (Br) as the
boundary condition. The HMI observation can provide new Br
data for these model. Because of weak magnetic signals at the quiet
regions of the Sun, the limb darkening, and geometric effects near solar
poles, we need to apply an assumption to make a whole-surface map. In
this paper, we tested two assumptions for determining Br
at weak-field regions. The coronal structures calculated by the PFSS
model with the vector-based Br are compared with those with
the magnetogram-based Br and the corona observed by the
SDO/AIA (Atmospheric Imaging Assembly). In the tested period, CR 2098,
the vector-based Br map gives better agreements than the
line-of-sight magnetogram data, though we need further investigation
for evaluation.

---------------------------------------------------------
Title: Helioseismology of Pre-emerging Active Regions. II. Average
Emergence Properties
Authors: Birch, A. C.; Braun, D. C.; Leka, K. D.; Barnes, G.;
Javornik, B.
2013ApJ...762..131B Altcode: 2013arXiv1303.1391B
We report on average subsurface properties of pre-emerging active
regions as compared to areas where no active region emergence was
detected. Helioseismic holography is applied to samples of the two
populations (pre-emergence and without emergence), each sample having
over 100 members, which were selected to minimize systematic bias,
as described in Leka et al. We find that there are statistically
significant signatures (i.e., difference in the means of more than a few
standard errors) in the average subsurface flows and the apparent wave
speed that precede the formation of an active region. The measurements
here rule out spatially extended flows of more than about 15 m
s-1 in the top 20 Mm below the photosphere over the course
of the day preceding the start of visible emergence. These measurements
place strong constraints on models of active region formation.

---------------------------------------------------------
Title: Helioseismology of Pre-emerging Active Regions. I. Overview,
Data, and Target Selection Criteria
Authors: Leka, K. D.; Barnes, G.; Birch, A. C.; Gonzalez-Hernandez,
I.; Dunn, T.; Javornik, B.; Braun, D. C.
2013ApJ...762..130L Altcode: 2013arXiv1303.1433L
This first paper in a series describes the design of a study testing
whether pre-appearance signatures of solar magnetic active regions
were detectable using various tools of local helioseismology. The
ultimate goal is to understand flux-emergence mechanisms by setting
observational constraints on pre-appearance subsurface changes, for
comparison with results from simulation efforts. This first paper
provides details of the data selection and preparation of the samples,
each containing over 100 members, of two populations: regions on
the Sun that produced a numbered NOAA active region, and a "control"
sample of areas that did not. The seismology is performed on data from
the GONG network; accompanying magnetic data from SOHO/MDI are used
for co-temporal analysis of the surface magnetic field. Samples are
drawn from 2001-2007, and each target is analyzed for 27.7 hr prior
to an objectively determined time of emergence. The results of two
analysis approaches are published separately: one based on averages of
the seismology- and magnetic-derived signals over the samples, another
based on Discriminant Analysis of these signals, for a statistical test
of detectable differences between the two populations. We include
here descriptions of a new potential-field calculation approach
and the algorithm for matching sample distributions over multiple
variables. We describe known sources of bias and the approaches used
to mitigate them. We also describe unexpected bias sources uncovered
during the course of the study and include a discussion of refinements
that should be included in future work on this topic.

---------------------------------------------------------
Title: The Imaging Vector Magnetograph at Haleakalā IV: Stokes
Polarization Spectra in the Sodium D1 589.6 nm Spectral
Line
Authors: Leka, K. D.; Mickey, Donald L.; Uitenbroek, Han; Wagner,
Eric L.; Metcalf, Thomas R.
2012SoPh..278..471L Altcode:
The Imaging Vector Magnetograph (IVM) at the Mees Solar Observatory,
Haleakalā, Maui, Hawai'i, obtained many years of vector magnetic-field
data in the photospheric Fe I 630.25 nm line. In the latter period
of its operation, the IVM was modified to allow routine observations
in the chromospheric Na I D1 line, as well as the Fe I
line. We describe the sodium observational data in detail, including the
data-reduction steps that differ from those employed for the Fe I 630.25
nm line, to obtain calibrated Stokes polarization spectra. We have
performed a systematic comparison between the observational data and
synthetic NLTE Na I D1 Stokes spectra derived for a variety
of solar-appropriate atmospheric and magnetic configurations. While
the Na I D1 Stokes polarization signals from the solar
atmosphere are expected to be weak, they should generally be within the
IVM capability. A comparison between synthetic spectra and observational
data indicates that this is indeed the case.

---------------------------------------------------------
Title: Ambiguity Resolution of Multiple Height Magnetic Field
Observations
Authors: Barnes, Graham; Leka, K.; Crouch, A.
2012AAS...22020609B Altcode:
Typical inversions of polarized radiation and the Zeeman effect,
used to infer the vector magnetic field in the photosphere or
chromosphere, suffer from an inherent degeneracy in the direction
of the transverse field. Many methods have been developed to treat
this problem, but all must make some assumption or approximation
which may not be valid. In some cases, this has led to conflicting
physical interpretations of observed solar structures. One way to
remove the need for the assumptions is to infer the magnetic field
simultaneously at multiple heights. When line of sight variations
in the vector field are available, one can use only the vanishing of
the divergence of the magnetic field to resolve the ambiguity in the
direction of the transverse field. We present examples of applying
this technique to synthetic and observed data, and discuss how it can
improve our understanding of solar magnetic structures. This work
was supported by NASA under contracts NNH09CE60C and NNH09CF22C.

---------------------------------------------------------
Title: A Search for Pre-Emergence Helioseismic Signatures of Active
Regions
Authors: Barnes, Graham; Birch, A.; Leka, K.; Braun, D.; Dunn, T.;
Javornik, B.; Gonzalez Hernandez, I.
2012AAS...22020510B Altcode:
Helioseismology can be an important tool for understanding the formation
of active regions. As a first step towards this goal, we have carried
out a search for statistically significant helioseismic precursors
of active region emergence. We used an automatic method to determine
the time of emergence based on the NOAA/NGDC active region catalog
and MDI/SOHO 96 minute magnetograms. Using GONG data, we applied
helioseismic holography to 107 pre-emergence active regions and a
control sample of 107 regions where no active region was present. We
found some significant and surprising differences between our samples
in both quantities determined from helioseismology and from surface
magnetic fields. However, we do not see a clear signature of emergence
when considering individual active regions. The results of this
investigation may shed some light on the mechanism responsible for
flux emergence, and certainly illustrate the care which must be taken
in conducting such an investigation. This work was supported by
NASA contract NNH07CD25C.

---------------------------------------------------------
Title: Spectropolarimetry in the Sodium 589.6nm D1 line: Evaluating
the Resulting Chromospheric (?) Vector Field Maps.
Authors: Leka, K. D.
2012AAS...22020305L Altcode:
Pioneering work by T. R. Metcalf almost two decades ago pointed to
the Na 589.6nm D1 line as a contender for providing chromospheric
vector magnetic field measurements (using the Zeeman effect). We
report here on a systematic examination of what can be expected from
Sodium 589.6nm spectropolarimetry, with respects to polarization-signal
amplitudes and retrieval, and the implementation of the inversion for
this line based on the Jeffries, Lites &amp; Skumanich Weak-Field
Approximation algorithm. The analysis is performed using both
synthetic data and observations from the Imaging Vector Magnetograph,
for which a large dataset of Sodium 589.6nm vector spectropolarimetry
exists. The synthetic data are based on a 3-D field extrapolated from
photospheric vector magnetograms of two active regions, four distinct
model atmospheres coupled with NLTE synthesis of the emergent NaI
D1 Stokes polarization spectra, computed for a variety of viewing
angles. In this manner, a broad representation of active-region
features, field strengths and observing angles are tested using “hare
&amp; hound” approaches, including evaluating algorithm performance in
the presence of noise and instrumental effects. We compare retrieval
algorithms for the very weak (as expected) polarization signals, and
evaluate the retrieved vector magnetic field at a range of inferred
heights. Finally, we provide an example from the IVM and discuss the
prospects for obtaining and interpreting chromospheric vector magnetic
field maps. Support for this work comes from NASA NAG5-12466, NASA
NNH09CE60C, AFOSR F49620-03-C-0019, NSF/NSWP ATM-0519107, NSF/SHINE
ATM-0454610, and NSF CRG ATM-0551055.

---------------------------------------------------------
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: Modeling and Interpreting the Effects of Spatial Resolution
on Solar Magnetic Field Maps
Authors: Leka, K. D.; Barnes, G.
2012SoPh..277...89L Altcode: 2011arXiv1106.5024L
Different methods for simulating the effects of spatial resolution on
magnetic field maps are compared, including those commonly used for
inter-instrument comparisons. The investigation first uses synthetic
data, and the results are confirmed with Hinode/SpectroPolarimeter
data. Four methods are examined, one which manipulates the Stokes
spectra to simulate spatial-resolution degradation, and three
"post-facto" methods where the magnetic field maps are manipulated
directly. Throughout, statistical comparisons of the degraded maps
with the originals serve to quantify the outcomes. Overall, we find
that areas with inferred magnetic fill fractions close to unity may
be insensitive to optical spatial resolution; areas of sub-unity fill
fractions are very sensitive. Trends with worsening spatial resolution
can include increased average field strength, lower total flux, and
a field vector oriented closer to the line of sight. Further-derived
quantities such as vertical current density show variations even in
areas of high average magnetic fill fraction. In short, unresolved maps
fail to represent the distribution of the underlying unresolved fields,
and the "post-facto" methods generally do not reproduce the effects of
a smaller telescope aperture. It is argued that selecting a method in
order to reconcile disparate spatial resolution effects should depend
on the goal, as one method may better preserve the field distribution,
while another can reproduce spatial resolution degradation. The results
presented should help direct future inter-instrument comparisons.

---------------------------------------------------------
Title: Spectropolarimetry in the Sodium 589.6nm D1 line: Evaluating
the Resulting Chromospheric (?) Vector Field Maps.
Authors: Leka, K. D.; Barnes, G.; Stockwell, R. G.; Wagner, E. L.;
Uitenbroek, H.; Derouich, M.
2012decs.confE..79L Altcode:
Pioneering work by T. R. Metcalf almost two decades ago pointed to
the Na 589.6nm D1 line as a contender for providing chromospheric
vector magnetic field measurements (using the Zeeman effect). We
report here on a systematic examination of what can be expected from
Sodium 589.6nm spectropolarimetry, with respects to polarization-signal
amplitudes and retrieval, and the implementation of the inversion for
this line based on the Jeffries, Lites &amp; Skumanich Weak-Field
Approximation algorithm. The analysis is performed using both
synthetic data and observations from the Imaging Vector Magnetograph,
for which a large dataset of Sodium 589.6nm vector spectropolarimetry
exists. The synthetic data are based on a 3-D field extrapolated from
photospheric vector magnetograms of two active regions, four distinct
model atmospheres coupled with NLTE synthesis of the emergent NaI
D1 Stokes polarization spectra, computed for a variety of viewing
angles. In this manner, a broad representation of active-region
features, field strengths and observing angles are tested using “hare
&amp; hound” approaches, including evaluating algorithm performance in
the presence of noise and instrumental effects. We compare retrieval
algorithms for the very weak (as expected) polarization signals, and
evaluate the retrieved vector magnetic field at a range of inferred
heights. Finally, we provide an example from the IVM and discuss the
prospects for obtaining and interpreting chromospheric vector magnetic
field maps. Support for this work comes from NASA NAG5-12466, NASA
NNH09CE60C, AFOSR F49620-03-C-0019, NSF/NSWP ATM-0519107, NSF/SHINE
ATM-0454610, and NSF CRG ATM-0551055.

---------------------------------------------------------
Title: The synoptic maps of Br from HMI observations
Authors: Hayashi, Keiji; Hoeksema, J. Todd; Liu, Sun; Yang, Xudong;
Centeno, Rebecca; Leka, K. D.; Barnes, Graham
2012decs.confE..69H Altcode:
The vector magnetic field measurement can, in principal, give the
"true" radial component of the magnetic field. We prepare 4 types
of synoptic maps of the radial photospheric magnetic field, from
the vector magnetic field data disambiguated by means of the minimum
energy method developed at NWRA/CoRA, the vector data determined under
the potential-field acute assumption, and the vector data determined
under the radial-acute assumption, and the standard line-of-sight
magnetogram. The models of the global corona, the MHD and the PFSS,
are applied to different types of maps. Although the three-dimensional
structures of the global coronal magnetic field with different maps are
similar and overall agreeing well the AIA full-disk images, noticeable
differences among the model outputs are found especially in the high
latitude regions. We will show details of these test maps and discuss
the issues in determining the radial component of the photospheric
magnetic field near the poles and limb.

---------------------------------------------------------
Title: The Free Energy of NOAA Solar Active Region AR 11029
Authors: Gilchrist, S. A.; Wheatland, M. S.; Leka, K. D.
2012SoPh..276..133G Altcode: 2011arXiv1110.4418G
The NOAA active region (AR) 11029 was a small but highly active
sunspot region which produced 73 GOES soft X-ray flares during
its transit of the disk in late October 2009. The flares appear
to show a departure from the well-known power law frequency-size
distribution. Specifically, too few GOES C-class and no M-class flares
were observed by comparison with a power law distribution (Wheatland,
Astrophys. J.710, 1324, 2010). This was conjectured to be due to
the region having insufficient magnetic energy to power the missing
large events. We construct nonlinear force-free extrapolations of the
coronal magnetic field of AR 11029 using data taken on 24 October by
the SOLIS Vector SpectroMagnetograph (SOLIS/VSM) and data taken on
27 October by the Hinode Solar Optical Telescope SpectroPolarimeter
(Hinode/SP). Force-free modeling with photospheric magnetogram data
encounters problems, because the magnetogram data are inconsistent with
a force-free model. We employ a recently developed "self-consistency"
procedure which addresses this problem and accommodates uncertainties
in the boundary data (Wheatland and Régnier, Astrophys. J.700,
L88, 2009). We calculate the total energy and free energy of
the self-consistent solution, which provides a model for the
coronal magnetic field of the active region. The free energy of
the region was found to be ≈ 4×1029 erg on 24 October
and ≈ 7×1031 erg on 27 October. An order of magnitude
scaling between RHESSI non-thermal energy and GOES peak X-ray flux is
established from a sample of flares from the literature and is used to
estimate flare energies from the observed GOES peak X-ray flux. Based
on the scaling, we conclude that the estimated free energy of AR
11029 on 27 October when the flaring rate peaked was sufficient to
power M-class or X-class flares; hence, the modeling does not appear
to support the hypothesis that the absence of large flares is due to
the region having limited energy.

---------------------------------------------------------
Title: Response to “Comment on `Resolving the 180° Ambiguity in
Solar Vector Magnetic Field Data: Evaluating the Effects of Noise,
Spatial Resolution, and Method Assumptions' ”
Authors: Leka, K. D.; Barnes, Graham; Gary, G. Allen; Crouch, A. D.;
Liu, Y.
2012SoPh..276..441L Altcode: 2011arXiv1110.2697L
We address points recently discussed in Georgoulis (2011, Solar Phys.,
doi:10.1007/s11207-011-9819-1) in reference to Leka et al. (2009b,
Solar Phys.260, 83). Most importantly, we find that the results of
Georgoulis (2011) support a conclusion of Leka et al. (2009b): that
limited spatial resolution and the presence of unresolved magnetic
structures can challenge ambiguity-resolution algorithms. Moreover,
the findings of both Metcalf et al. (2006, Solar Phys.237, 267) and
Leka et al. (2009b) are confirmed in Georgoulis (2011): a method's
performance can be diminished when the observed field fails to
conform to that method's assumptions. The implication of boundaries
in models of solar magnetic structures is discussed; we confirm that
the distribution of the field components in the model used in Leka
et al. (2009b) is closer to what is observed on the Sun than what is
proposed in Georgoulis (2011). It is also shown that method does matter
with regards to simulating limited spatial resolution and avoiding an
inadvertent introduction of bias. Finally, the assignment of categories
to data-analysis algorithms is revisited; we argue that assignments
are only useful and elucidating when used appropriately.

---------------------------------------------------------
Title: HMI vector magnetic field products: the long-awaited release
has come! Now what?
Authors: Centeno, R.; Barnes, G.; Borrero, J.; Couvidat, S. P.;
Hayashi, K.; Hoeksema, J. T.; Leka, K. D.; Liu, Y.; Schou, J.; Schuck,
P. W.; Sun, X.; Tomczyk, S.
2011AGUFMSH31A1985C Altcode:
HMI vector magnetic field test products will be released, alongside
with the corresponding documentation, soon after the submission of this
abstract. These data represent a stage of the project at which the HMI
vector team has a large degree of confidence in the results. However,
longer-term research topics on how to improve certain aspects of the
data pipeline in general -and the spectral line inversion code in
particular- are being pursued as we get valuable input from the user
community. I will give a brief summary of the characteristics of the
released inversion data products and an update of where we stand now.

---------------------------------------------------------
Title: Interpreting Vector Magnetic Field Data in the Context of
Modeling Results (and vice-versa)
Authors: Leka, K. D.
2011sdmi.confE..67L Altcode:
The magnetic field structures of solar phenomena as inferred from
polarimetric measurements of the solar atmosphere are invaluable to
understanding the physical reasons for the morphology and dynamics
observed. In a complementary manner, numerical models of the
solar atmosphere allow an exploration of the physics, guided by the
observables. Context, however, can be key. In this talk I will remark
on approaches, and limitations of direct comparisons between numerical
models of the solar atmosphere and remote-observations of the same,
especially in the context of HMI vector magnetic field data.

---------------------------------------------------------
Title: A Search for Pre-Emergence Helioseismic Signatures of Active
Regions
Authors: Barnes, Graham; Birch, Aaron; Leka, K. D.; Braun, Doug;
Dunn, Tera; Hernandez Gonzalez, I.
2011sdmi.confE..58B Altcode:
Helioseismology can be an important tool for understanding the formation
of active regions. As a first step towards this goal, we have carried
out a search for statistically significant helioseismic precursors
of active region emergence. We used an automatic method to determine
the time of emergence based on the NOAA/NGDC active region catalog
and MDI/SOHO 96 minute magnetograms. Using GONG data, we applied
helioseismic holography to about 100 pre-emergence active regions
and a control sample of about 300 quiet-Sun regions. A variety of
quantities were determined from helioseismic holography. Both averages
over all the times considered, as well as statistical tests based on
discriminant analysis, show different signatures for the pre-emergence
active regions compared to the quiet-Sun. However, we do not see a clear
signature of emergence when considering individual active regions. We
discuss the significance of these results.

---------------------------------------------------------
Title: A Comparison of Methods for Manipulating SpectroPolarimetric
and Magnetic Field Data for Heliospheric Models, Data Comparisons,
and Physical Interpretation
Authors: Leka, K. D.; Barnes, G.
2011shin.confE..22L Altcode:
Heliospheric modeling efforts often begin with boundary data, and
those boundary data are either observed or simulated photospheric
magnetic field maps. Oftentimes, the available boundary data just
aren't compatible with what is needed, or what can be handled by
subsequent code. But how well do rebinned/remapped/averaged magnetic
maps represent the underlying field? We address this question using
model fields, where the true field is known, but the

---------------------------------------------------------
Title: Statistical Analysis of Pre-CME Coronal Activity
Authors: Barnes, Graham; Leka, K. D.; Stockwell, R.
2011shin.confE.138B Altcode:
The trigger mechanism(s) for Coronal Mass Ejections has long been
sought, and various models predict certain behavior (or absence thereof)
in the corona prior to the CME initiation. We examine the pre-CME
behavior of the corona, combining potential field extrapolations from
MDI with EIT data of source-identified CMEs, for indications of

---------------------------------------------------------
Title: Effects of Limited Resolution on SpectroPolarimetric data,
from the Subtle to the Supreme
Authors: Leka, K. D.
2011ASPC..437..157L Altcode:
The effects of limited resolution in two domains, spatial and
temporal, is briefly demonstrated through the use of synthetic data and
manipulation of emergent Stokes polarization spectra. The importance of
modeling the effects on incoming light is demonstrated, for averaging in
the temporal or spatial dimensions is an intensity-weighted function. It
is showed that when compared to direct binning of pure polarization
states or of later products such as derived magnetic field maps, the
evaluation of resolution effects based on these simpler methods can
be misleading. The general result is presented that limited-resolution
polarization spectra may generally have smaller amplitudes than their
constituent spectra, and sometimes drastically so; this may have
implications for signal/noise-driven integration-time estimates.

---------------------------------------------------------
Title: Subsurface Vorticity of Flaring versus Flare-Quiet Active
Regions
Authors: Komm, R.; Ferguson, R.; Hill, F.; Barnes, G.; Leka, K. D.
2011SoPh..268..389K Altcode: 2010SoPh..tmp...78K
We apply discriminant analysis to 1023 active regions and their
subsurface-flow parameters, such as vorticity and kinetic helicity
density, with the goal of distinguishing between flaring and non-flaring
active regions. We derive synoptic subsurface flows by analyzing GONG
high-resolution Doppler data with ring-diagram analysis. We include
magnetic-flux values in the discriminant analysis derived from NSO
Kitt Peak and SOLIS synoptic maps binned to the same spatial scale
as the helioseismic analysis. For each active region, we determine
the flare information from GOES and include all flares within 60°
central meridian distance to match the coverage of the ring-diagram
analysis. The subsurface-flow characteristics improve the ability to
distinguish between flaring and non-flaring active regions. For the C-
and M-class flare category, the most important subsurface parameter
is the so-called structure vorticity, which estimates the horizontal
gradient of the horizontal-vorticity components. The no-event skill
score, which measures the improvement over predicting that no events
occur, reaches 0.48 for C-class flares and 0.32 for M-class flares, when
the structure vorticity at three depths combined with total magnetic
flux are used. The contributions come mainly from shallow layers within
about 2 Mm of the surface and layers deeper than about 7 Mm.

---------------------------------------------------------
Title: Achieving Self-consistent Nonlinear Force-free Modeling of
Solar Active Regions
Authors: Wheatland, M. S.; Leka, K. D.
2011ApJ...728..112W Altcode: 2010arXiv1012.3503W
A nonlinear force-free solution is constructed for the coronal magnetic
field in NOAA solar active region (AR) 10953 based on a photospheric
vector magnetogram derived from Hinode satellite observations on
2007 April 30, taking into account uncertainties in the boundary data
and using improved methods for merging multiple-instrument data. The
solution demonstrates the "self-consistency" procedure of Wheatland
&amp; Régnier, for the first time including uncertainties. The
self-consistency procedure addresses the problem that photospheric
vector magnetogram data are inconsistent with the force-free model,
and in particular that the boundary conditions on vertical electric
current density are overspecified and permit the construction of two
different nonlinear force-free solutions. The procedure modifies the
boundary conditions on current density during a sequence of cycles until
the two nonlinear force-free solutions agree. It hence constructs an
accurate single solution to the force-free model, with boundary values
close, but not matched exactly, to the vector magnetogram data. The
inclusion of uncertainties preserves the boundary conditions more
closely at points with smaller uncertainties. The self-consistent
solution obtained for AR 10953 is significantly non-potential, with
magnetic energy E/E 0 ≈ 1.08, where E 0 is the
energy of the reference potential (current-free) magnetic field. The
self-consistent solution is shown to be robust against changes in
the details of the construction of the two force-free models at each
cycle. This suggests that reliable nonlinear force-free modeling of
ARs is possible if uncertainties in vector magnetogram boundary data
are included.

---------------------------------------------------------
Title: Modelling magnetic fields in the corona using nonlinear
force-free fields
Authors: Wheatland, M. S.; Leka, K. D.
2011ASInC...2..203W Altcode:
Force-free magnetic fields, in which the magnetic or Lorentz force is
self-balancing and hence zero, provide a simple model for fields in
the Sun's corona. In principle the model may be solved using boundary
values of the field derived from observations, e.g. data from the Hinode
spectro-polarimeter. In practise the boundary data is inconsistent
with the model, because fields at the photospheric level are subject
to non-magnetic forces, and because of substantial uncertainties in the
boundary data. The `self-consistency' procedure tep{2009ApJ...700L..88W}
provides an approach to resolving the problem. This talk reports
on results achieved with the procedure, in particular new results
obtained for active region AR 10953 using Hinode data incorporating
uncertainties in the boundary conditions tep{2011ApJ...728..112W}.

---------------------------------------------------------
Title: The Role of Magnetic Topology in the Heating of Active Region
Coronal Loops
Authors: Lee, J. -Y.; Barnes, Graham; Leka, K. D.; Reeves, Katharine
K.; Korreck, K. E.; Golub, L.; DeLuca, E. E.
2010ApJ...723.1493L Altcode: 2010arXiv1009.2070L
We investigate the evolution of coronal loop emission in the context
of the coronal magnetic field topology. New modeling techniques allow
us to investigate the magnetic field structure and energy release
in active regions (ARs). Using these models and high-resolution
multi-wavelength coronal observations from the Transition Region and
Coronal Explorer and the X-ray Telescope on Hinode, we are able to
establish a relationship between the light curves of coronal loops
and their associated magnetic topologies for NOAA AR 10963. We examine
loops that show both transient and steady emission, and we find that
loops that show many transient brightenings are located in domains
associated with a high number of separators. This topology provides
an environment for continual impulsive heating events through magnetic
reconnection at the separators. A loop with relatively constant X-ray
and EUV emission, on the other hand, is located in domains that are
not associated with separators. This result implies that larger-scale
magnetic field reconnections are not involved in heating plasma in
these regions, and the heating in these loops must come from another
mechanism, such as small-scale reconnections (i.e., nanoflares) or
wave heating. Additionally, we find that loops that undergo repeated
transient brightenings are associated with separators that have enhanced
free energy. In contrast, we find one case of an isolated transient
brightening that seems to be associated with separators with a smaller
free energy.

---------------------------------------------------------
Title: The Effects of Different Implementations of Potential Field
Extrapolations
Authors: Barnes, Graham; Leka, K. D.
2010shin.confE..54B Altcode:
In a mathematical sense, the potential magnetic field is unique
when the normal component of the magnetic field is specified on a
closed boundary. In practice, however, the implementation of the
potential field calculation can result in substantially different
results. In this poster, we consider the effects of using the line of
sight component of the field on the boundary as compared to the normal
component, and the use of Green's function methods versus eigenfunction
expansions. The differences are demonstrated in the context of the
topology and connectivity of the resulting field. This material
is based upon work supported by the National Science Foundation under
SHINE Grant No. 0454610.

---------------------------------------------------------
Title: Observing and Interpreting Na D1 589.6nm Stokes Spectra with
the Imaging Vector Magnetograph II: The Magnetic Maps
Authors: Derouich, M.; Leka, K. D.; Mickey, D. L.; Uitenbroek, H.;
Metcalf, T. R.
2010shin.confE...5D Altcode:
Following Poster I (Leka et al), we focus here on recent progress
regarding the inversion algorithms and interpretation of Zeeman
Na D1 589.6nm Stokes Spectra observed using the Imaging Vector
Magnetograph. We present systematic tests of the inversion procedures
and our interpretation of the results, relying on synthetic Na D1
589.6nm Stokes Spectra generated using known magnetic and atmospheric
models described in Poster I. In this second poster, we present the
results of "hare and hound" exercises which focus on (1) the optimal
fitting and inversion algorithm for the Na D1 589.6nm Stokes spectra,
and (2), the interpretation of the resulting active magnetic field
"maps", especially as a function of inferred height of the solar
atmosphere sampled by these Zeeman-polarization spectra. This
work has been supported by AFOSR contract F49620-03-C-0019, NSF space
weather program grant ATM-0519107 and NSF SHINE grant ATM-0454610.

---------------------------------------------------------
Title: Observing and Interpreting Na D1 589.6nm Stokes Spectra with
the Imaging Vector Magnetograph I: Polarization Spectra
Authors: Leka, K. D.; Mickey, D. L.; Uitenbroek, H.; Derouich, M.;
Metcalf, T. R.
2010shin.confE...4L Altcode:
We report on progress made recently on validating and interpreting
Stokes spectra from the Na D1 589.6nm line observed using the Imaging
Vector Magnetograph at Mees Solar Observatory, Haleakala, Maui. While
preliminary results from the dataset (which comprises daily observations
of active regions spanning 2000 - 2005, plus a few additional special
observation campaigns) have been reported previously (e.g., Leka
&amp; Metcalf 2003; Metcalf Leka &amp; Mickey 2005), we focus here
on systematic tests of the observed data and our interpretation of
them. In this first poster, we present Non-LTE synthetic Na D1 589.6nm
spectra, computed using known underlying magnetic and atmospheric
models, which form the basis for various "hare and hound" exercises
to test (1) the observed degree of polarization in (2) the context
of the instrument response and photon noise. While we find generally
excellent agreement, there are some systematic differences between
the synthetic and observational data. We summarize our understandings
of these differences and attempts to mitigate their effects in the
context of the inversion to a magnetic field map (see Poster II,
Derouich et al). This work has been supported by AFOSR contract
F49620-03-C-0019, NSF space weather program grant ATM-0519107 and NSF
SHINE grant ATM-0454610.

---------------------------------------------------------
Title: Coronal Loop Evolution and Inferred Coronal Magnetic Energy
in a Quiet Active Region
Authors: Lee, Jin-Yi; Barnes, G.; Leka, K.; Reeves, K. K.; Korreck,
K. E.; Golub, L.
2010AAS...21640514L Altcode: 2010BAAS...41R.891L
We investigate changes in the properties of the coronal magnetic field
in the context of different emission of coronal loops. Observations by
the Transition Region and Coronal Explorer (TRACE), the Hinode/X-ray
Telescope (XRT), and the SOHO/Michelson Doppler Imager (MDI), the
X-ray and EUV light curves as well as the photospheric magnetic flux
of NOAA active region 10963 are utilized to compare the coronal and
photospheric magnetic fields. A Magnetic Charge Topology (MCT) model
is used to establish potential magnetic field connectivity of the
surface magnetic flux distribution. A Minimum Current Corona (MCC)
model is applied to determine the coronal currents and quantify the
energy build-up. The results of the MCC analysis are compared to the
evolution of the coronal loop brightness, comparing areas of steady
emission, transient emission, and temporal patterns of emission which
imply coronal cooling.

---------------------------------------------------------
Title: Comparison of Solar Flare Forecasting Methods
Authors: Barnes, Graham; Leka, K. D.
2010cosp...38.4173B Altcode: 2010cosp.meet.4173B
Solar flares produce X-rays which can have an almost immediate effect
on the near-Earth environment, making it crucial to forecast flares
in order to mitigate their negative effects. The energy available
for flares is believed to be stored in the magnetic fields of active
regions, and released by magnetic reconnection in the corona. Recently,
the number of published approaches to flare forecasting using
photospheric magnetic field observations has proliferated, with widely
varying claims about how well each works. Because of the different
analysis techniques and data sets used, it is essentially impossible to
compare the results from the literature. This problem is exacerbated
by the low event rates typical of large solar flares. The challenges
of forecasting when event rates are low have long been recognized in
the meteorology community, but have yet to be fully acknowledged by the
space weather community. A recent workshop compared the performance of
a number of existing algorithms on a common data set, with consistent
definitions of what constitutes an event, with a particular focus on
"all-clear" forecasts. We summarize the importance of making such
systematic comparisons, and of using standard verification statistics
to determine what actually constitutes a good prediction scheme. This
work was funded by NASA LWS TRT contract NNH09CE72C.

---------------------------------------------------------
Title: Subsurface Flow Properties of Flaring versus Flare-Quiet
Active Regions
Authors: Ferguson, R.; Komm, R.; Hill, F.; Barnes, G.; Leka, K. D.
2009ASPC..416..127F Altcode:
We apply discriminant analysis to 1009 active regions and their
subsurface flow parameters, such as vorticity and kinetic helicity
density, with the goal of distinguishing between flaring and non-flaring
active regions. Flow and flux variables lead to better classification
rates than a no-event prediction. The Heidke skill score, which measures
the improvement over predicting that no events occur, increases by
about 25% and 50% for C- and M-class flares when several subsurface
characteristics are included compared to using a single magnetic
flux measure.

---------------------------------------------------------
Title: Resolving the Azimuthal Ambiguity in Vector Magnetogram Data
with the Divergence-Free Condition: Application to Discrete Data
Authors: Crouch, A. D.; Barnes, G.; Leka, K. D.
2009SoPh..260..271C Altcode: 2009arXiv0911.0711C
We investigate how the divergence-free property of magnetic fields can
be exploited to resolve the azimuthal ambiguity present in solar vector
magnetogram data, by using line-of-sight and horizontal heliographic
derivative information as approximated from discrete measurements. Using
synthetic data we test several methods that each make different
assumptions about how the divergence-free property can be used to
resolve the ambiguity. We find that the most robust algorithm involves
the minimisation of the absolute value of the divergence summed over
the entire field of view. Away from disk centre this method requires
the sign and magnitude of the line-of-sight derivatives of all three
components of the magnetic field vector.

---------------------------------------------------------
Title: An Automated Ambiguity-Resolution Code for Hinode/SP Vector
Magnetic Field Data
Authors: Leka, K. D.; Barnes, G.; Crouch, A.
2009ASPC..415..365L Altcode:
A fast, automated algorithm is presented for use in resolving
the 180° ambiguity in vector magnetic field data, including
those data from Hinode/Spectropolarimeter. The Fortran-based
code is loosely based on the Minimum Energy Algorithm, and is
distributed to provide ambiguity-resolved data for the general user
community. Here we generally describe the released code (available
at http://www.cora.nwra.com/AMBIG), examples of its performance and
usage for Hinode/SP data.

---------------------------------------------------------
Title: Evolution of Magnetic Properties for Two Active Regions
Observed by Hinode/XRT and TRACE
Authors: Lee, J. -Y.; Leka, K. D.; Barnes, G.; Reeves, K. K.; Korreck,
K. E.; Golub, L.
2009ASPC..415..279L Altcode:
We investigate two active regions observed by the Hinode X-ray Telescope
(XRT) and the Transition Region and Coronal Explorer (TRACE). One active
region shows constant brightness in both XRT and TRACE observations. The
other active region shows a brightening in the TRACE observation
just after a decrease in X-ray brightness indicating the cooling of a
coronal loop. The coronal magnetic topology is derived using a magnetic
charge topology (MCT) model for these two active regions applied to
magnetograms from the Michelson Doppler Imager (MDI) on board the Solar
and Heliospheric Observatory (SOHO). We discuss the results of the MCT
analysis with respect to the light curves for these two active regions.

---------------------------------------------------------
Title: Magnetic energy build-up and coronal brightness evolution
Authors: Lee, J.; Barnes, G.; Leka, K. D.; Reeves, K. K.; Korreck,
K. E.; Golub, L.
2009AGUFMSH41B1664L Altcode:
We have investigated changes in the properties of the coronal magnetic
field in the context of different emission behaviors of coronal
loops. Using observations by the Transition Region and Coronal Explorer
(TRACE), the Hinode/X-ray Telescope (XRT), and the SoHO/Michelson
Doppler Imager (MDI), NOAA active region 10963 has been analyzed
in depth as to how different coronal signatures compare to inferred
coronal energy build-up. A Magnetic Charge Topology (MCT) model was
used to establish potential magnetic field connectivity of the surface
magnetic flux distribution, and a Minimum Current Corona (MCC) model was
applied to quantify the energy build-up along separator field lines. The
results of the MCC analysis are compared to the evolution of the coronal
brightness, comparing areas of steady emission, very transient emission,
and temporal patterns of emission which imply coronal cooling.

---------------------------------------------------------
Title: Resolving the 180° Ambiguity in Solar Vector Magnetic
Field Data: Evaluating the Effects of Noise, Spatial Resolution,
and Method Assumptions
Authors: Leka, K. D.; Barnes, Graham; Crouch, A. D.; Metcalf, Thomas
R.; Gary, G. Allen; Jing, Ju; Liu, Y.
2009SoPh..260...83L Altcode:
The objective testing of algorithms for performing ambiguity
resolution in vector magnetic field data is continued, with an
examination of the effects of noise in the data. Through the use
of analytic magnetic field models, two types of noise are "added"
prior to resolving: noise to simulate Poisson photon noise in the
observed polarization spectra, and a spatial binning to simulate the
effects of unresolved structure. The results are compared through
the use of quantitative metrics and performance maps. We find that
while no algorithm severely propagates the effects of Poisson noise
beyond very local influences, some algorithms are more robust against
high photon-noise levels than others. In the case of limited spatial
resolution, loss of information regarding fine-scale structure can
easily result in erroneous solutions. Our tests imply that photon
noise and limited spatial resolution can act so as to make assumptions
used in some ambiguity resolution algorithms no longer consistent
with the observed magnetogram. We confirm a finding of the earlier
comparison study that results can be very sensitive to the details of
the treatment of the observed boundary and the assumptions governing
that treatment. We discuss the implications of these findings, given the
relative sensitivities of the algorithms to the two sources of noise
tested here. We also touch on further implications for interpreting
observational vector magnetic field data for general solar physics
research.

---------------------------------------------------------
Title: Nonlinear Force-Free Magnetic Field Modeling of AR 10953:
A Critical Assessment
Authors: De Rosa, Marc L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
Lites, B. W.; Aschwanden, M. J.; Amari, T.; Canou, A.; McTiernan,
J. M.; Régnier, S.; Thalmann, J. K.; Valori, G.; Wheatland, M. S.;
Wiegelmann, T.; Cheung, M. C. M.; Conlon, P. A.; Fuhrmann, M.;
Inhester, B.; Tadesse, T.
2009SPD....40.3102D Altcode:
Nonlinear force-free field (NLFFF) modeling seeks to provide accurate
representations of the structure of the magnetic field above solar
active regions, from which estimates of physical quantities of interest
(e.g., free energy and helicity) can be made. However, the suite of
NLFFF algorithms have failed to arrive at consistent solutions when
applied to (thus far, two) cases using the highest-available-resolution
vector magnetogram data from Hinode/SOT-SP (in the region of the
modeling area of interest) and line-of-sight magnetograms from
SOHO/MDI (where vector data were not available). One issue is that
NLFFF models require consistent, force-free vector magnetic boundary
data, and vector magnetogram data sampling the photosphere do not
satisfy this requirement. Consequently, several problems have arisen
that are believed to affect such modeling efforts. We use AR 10953
to illustrate these problems, namely: (1) some of the far-reaching,
current-carrying connections are exterior to the observational field
of view, (2) the solution algorithms do not (yet) incorporate the
measurement uncertainties in the vector magnetogram data, and/or (3)
a better way is needed to account for the Lorentz forces within the
layer between the photosphere and coronal base. In light of these
issues, we conclude that it remains difficult to derive useful and
significant estimates of physical quantities from NLFFF models.

---------------------------------------------------------
Title: A Critical Assessment of Nonlinear Force-Free Field Modeling
of the Solar Corona for Active Region 10953
Authors: De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham;
Leka, K. D.; Lites, Bruce W.; Aschwanden, Markus J.; Amari, Tahar;
Canou, Aurélien; McTiernan, James M.; Régnier, Stéphane; Thalmann,
Julia K.; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas;
Cheung, Mark C. M.; Conlon, Paul A.; Fuhrmann, Marcel; Inhester,
Bernd; Tadesse, Tilaye
2009ApJ...696.1780D Altcode: 2009arXiv0902.1007D
Nonlinear force-free field (NLFFF) models are thought to be viable
tools for investigating the structure, dynamics, and evolution of
the coronae of solar active regions. In a series of NLFFF modeling
studies, we have found that NLFFF models are successful in application
to analytic test cases, and relatively successful when applied
to numerically constructed Sun-like test cases, but they are less
successful in application to real solar data. Different NLFFF models
have been found to have markedly different field line configurations
and to provide widely varying estimates of the magnetic free energy in
the coronal volume, when applied to solar data. NLFFF models require
consistent, force-free vector magnetic boundary data. However,
vector magnetogram observations sampling the photosphere, which is
dynamic and contains significant Lorentz and buoyancy forces, do not
satisfy this requirement, thus creating several major problems for
force-free coronal modeling efforts. In this paper, we discuss NLFFF
modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT,
STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process
illustrate three such issues we judge to be critical to the success of
NLFFF modeling: (1) vector magnetic field data covering larger areas
are needed so that more electric currents associated with the full
active regions of interest are measured, (2) the modeling algorithms
need a way to accommodate the various uncertainties in the boundary
data, and (3) a more realistic physical model is needed to approximate
the photosphere-to-corona interface in order to better transform the
forced photospheric magnetograms into adequate approximations of nearly
force-free fields at the base of the corona. We make recommendations
for future modeling efforts to overcome these as yet unsolved problems.

---------------------------------------------------------
Title: Detecting, Selecting, And Controlling For Emerging
ActiveRegions In The Search For Helioseismic Pre-emergence Signatures.
Authors: Leka, K. D.; Dunn, T.; Gonzalez-Hernandez, I.; Barnes, G.;
Braun, D.; Birch, A.
2009SPD....40.0708L Altcode:
Helioseismology is potentially capable of predicting the emergence of
solaractive regions. As part of a search for statistically significant
helioseismic predictors of active region emergence, we have developed
methods for the automatic determination of emergence times based on the
NOAA/NGDC active region catalog and MDI/SOHO 96 minute magnetograms. We
demonstrate the application of this method and its sister task of
selecting an appropriate control sample. We show first results from
a statistical study investigating the pre-emergence signatures of
Solar Active Regions using GONG data. This work was supported by NASA
contract NNH07CD25C.

---------------------------------------------------------
Title: A Search for Pre-Emergence Signatures of Active Regions
Authors: Birch, Aaron; Braun, D. C.; Leka, K. D.; Barnes, G.; Dunn,
T. L.; González Hernández, I.
2009SPD....40.0402B Altcode:
Prediction of solar active region emergence is an important goal
for helioseismology. As a first step towards developing prediction
methods, we are carrying out a search for helioseismic pre-emergence
signatures. Using GONG data, we have applied helioseismic holography
to about 150 pre-emergence active regions and a control sample of 450
quiet-Sun regions. We will show preliminary results of this study. This work was supported by NASA contract NNH07CD25C

---------------------------------------------------------
Title: Subsurface Flow Properties of Flaring Versus Flare-quiet
Active Regions
Authors: Ferguson, Ryan M.; Komm, R.; Hill, F.; Barnes, G.; Leka, K. D.
2009SPD....40.1908F Altcode:
Previous studies have shown that the flare activity of active regions is
intrinsically linked with the vorticity of subsurface flows on temporal
and spatial scales comparable to the size and lifetime of active
regions. We begin to address the question whether the measured vorticity
of subsurface flows associated with active regions can help to improve
flare forecasting. For this purpose, we apply statistical tests based
on discriminant analysis to several subsurface flow parameters with the
goal to differentiate between flaring and non-flaring active regions. We will present the latest results. This work is carried out through
the National Solar Observatory Research Experiences for Undergraduate
(REU) site program, which is co-funded by the Department of Defense
in partnership with the National Science Foundation REU Program.

---------------------------------------------------------
Title: Resolving the Azimuthal Ambiguity in Vector Magnetogram Data
with the Divergence-Free Condition
Authors: Crouch, Ashley D.; Leka, K.; Barnes, G.
2009SPD....40.0915C Altcode:
We demonstrate how the divergence-free property of magnetic fields can
be exploited to resolve the azimuthal ambiguity that is present in
solar vector magnetogram data by using line-of-sight and horizontal
heliographic derivative information. Using synthetic data at two
heights we objectively test several methods that each make a different
assumption about how the divergence-free property can be used to resolve
the ambiguity. We investigate how the different approaches respond to
various effects, including the presence of noise and limited spatial
resolution. This work was supported by funding from NASA under contracts
NNH05CC49C/NNH05CC75C and NNH09CE60C.

---------------------------------------------------------
Title: Magnetic Topology and Coronal Brightness Evolution: A Case
Study
Authors: Lee, Jin-Yi; Barnes, G.; Leka, K.; Reeves, K. K.; Korreck,
K. E.; Golub, L.
2009SPD....40.1209L Altcode:
We have applied a Magnetic Charge Topology model to investigate
what changes in the properties of the magnetic field are responsible
for different coronal emission behavior of the coronal loops in two
different active regions. Observations from the X-ray Telescope (XRT)
on board Hinode and the Transition Region and Coronal Expolorer (TRACE)
were used, along with time-series of magnetograms for 24 hours from
the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric
Observatory (SOHO). The magnetic connectivity and separator field
lines were established by potential field extrapolation of the observed
surface magnetic flux distribution. We present the evolution for the
two active regions in terms of the changes in both the connections and
in the separator flux, the latter indicative of locations of possible
energy deposit or release.

---------------------------------------------------------
Title: Nonlinear Force-Free Magnetic Field Modeling of the Solar
Corona: A Critical Assessment
Authors: De Rosa, M. L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
Lites, B. W.; Aschwanden, M. J.; McTiernan, J. M.; Régnier, S.;
Thalmann, J.; Valori, G.; Wheatland, M. S.; Wiegelmann, T.; Cheung,
M.; Conlon, P. A.; Fuhrmann, M.; Inhester, B.; Tadesse, T.
2008AGUFMSH41A1604D Altcode:
Nonlinear force-free field (NLFFF) modeling promises to provide accurate
representations of the structure of the magnetic field above solar
active regions, from which estimates of physical quantities of interest
(e.g., free energy and helicity) can be made. However, the suite of
NLFFF algorithms have so far failed to arrive at consistent solutions
when applied to cases using the highest-available-resolution vector
magnetogram data from Hinode/SOT-SP (in the region of the modeling
area of interest) and line-of-sight magnetograms from SOHO/MDI (where
vector data were not been available). It is our view that the lack of
robust results indicates an endemic problem with the NLFFF modeling
process, and that this process will likely continue to fail until (1)
more of the far-reaching, current-carrying connections are within the
observational field of view, (2) the solution algorithms incorporate
the measurement uncertainties in the vector magnetogram data, and/or
(3) a better way is found to account for the Lorentz forces within
the layer between the photosphere and coronal base. In light of these
issues, we conclude that it remains difficult to derive useful and
significant estimates of physical quantities from NLFFF models.

---------------------------------------------------------
Title: Evaluating the Performance of Solar Flare Forecasting Methods
Authors: Barnes, G.; Leka, K. D.
2008ApJ...688L.107B Altcode:
The number of published approaches to solar flare forecasting using
photospheric magnetic field observations has proliferated recently, with
widely varying claims about how well each works. As different analysis
techniques and data sets were used, it is essentially impossible to
directly compare the results. A systematic comparison is presented
here using three parameters based on the published literature that
characterize the photospheric magnetic field itself, plus one that
characterizes the coronal magnetic topology. Forecasts based on the
statistical method of discriminant analysis are made for each of these
parameters, and their ability to predict major flares is quantified
using skill scores. Despite widely varying statements regarding their
forecasting utility in the original studies describing these four
parameters, there is no clear distinction in their performance here,
thus demonstrating the importance of using standard verification
statistics.

---------------------------------------------------------
Title: Forward Modeling of Active Region Coronal
Emissions. II. Implications for Coronal Heating
Authors: Lundquist, L. L.; Fisher, G. H.; Metcalf, T. R.; Leka, K. D.;
McTiernan, J. M.
2008ApJ...689.1388L Altcode:
In Paper I, we introduced and tested a method for predicting solar
active region coronal emissions using magnetic field measurements and
a chosen heating relationship. Here, we apply this forward-modeling
technique to 10 active regions observed with the Mees Solar Observatory
Imaging Vector Magnetograph and the Yohkoh Soft X-ray Telescope. We
produce synthetic images of each region using four parameterized heating
relationships depending on magnetic field strength and geometry. We
find a volumetric coronal heating rate (dEH/dV, not to be
confused with dEH/dA quoted by some authors) proportional
to magnetic field and inversely proportional to field-line loop
length (BL-1) best matches observed coronal emission
morphologies. This parameterization is most similar to the steady-state
scaling of two proposed heating mechanisms: van Ballegooijen's "current
layers" theory, taken in the AC limit, and Parker's "critical angle"
mechanism, in the case where the angle of misalignment is a twist
angle. Although this parameterization best matches the observations,
it does not match well enough to make a definitive statement as
to the nature of coronal heating. Instead, we conclude that (1) the
technique requires better magnetic field measurement and extrapolation
techniques than currently available, and (2) forward-modeling methods
that incorporate properties of transiently heated loops are necessary
to make a more conclusive statement about coronal heating mechanisms.

---------------------------------------------------------
Title: Statistical Prediction of Solar Flares Using Magnetic Field
Data: A Status Report
Authors: Leka, K.; Barnes, G.; Knoll, J.; Tessein, J. A.
2008AGUFMSA51A1535L Altcode:
The energy to power solar flares is undoubtedly stored in the
concentrated magnetic field structures of solar active region
atmospheres. Exactly how to make use of observations of the solar
magnetic field for predicting the occurrence of solar energetic events
is, however, a great challenge. Building upon our prior work of "daily"
forecasts using a dataset of photospheric magnetic vector field maps,
we examine here questions of forecasting ability in light of data
source and the target temporal window. We will discuss the benefits and
problems of relying upon line-of-sight magnetic field data (vs. vector
photospheric magnetic field maps). In addition, we begin to examine
changes in forecasting ability, as measured by standard validation
statistics, that result from considering different forecasting windows.

---------------------------------------------------------
Title: A Comparison of Flare Forecasting Parameters Derived From
Photospheric Magnetograms
Authors: Barnes, G.; Leka, K.
2007AGUFMSM41A0314B Altcode:
A variety of researchers have proposed parameters for use in
forecasting of solar flares. However, the parameters have been
calculated from different data sources, and their performance has
been judged based on various different criteria. We present here a
systematic comparison of a small number of parameters which can be
derived from the photospheric magnetic field, some of which characterize
the photospheric field itself, and some which characterize the coronal
magnetic topology. We compute the parameters for a collection of
over 1200 vector magnetograms from the Imaging Vector Magnetograph
at Haleakala, and judge their ability to forecast flares based on
discriminant analysis, climatological skill scores, and the ability
to provide an "all-clear" forecast.

---------------------------------------------------------
Title: Testing a possible scenario for delta-spot formation
Authors: MacDonald, R.; Fisher, G. H.; Leka, K.
2007AGUFMSH13A1110M Altcode:
δ-spot active regions are frequently interpreted as loops of magnetic
flux which are strongly twisted. Could these twisted active-region
field configurations arise from flux loops that originate from
regions of the tachocline (the interface layer between the convection
zone and radiative zone) that are strongly sheared by differential
rotation? Helioseismic rotation inversions show that the tachocline
displays a strong radial shear in the rotation rate at latitudes
significantly less than 30 degrees. In addition, they show that the
surface variation of differential rotation with latitude persists
throughout the convection zone and into the tachocline. In many recent
solar cycle dynamo models, most of the magnetic flux participating
in the dynamo lies in the tachocline near the base of the solar
convection zone. In some of these models, amplification of solar
magnetic field from the poloidal (N-S) directions into the toroidal
component (E-W direction) occurs primarily from the variation of the
solar rotation rate with solar latitude, rather than with depth. In
any case, the combination of radial and latitude dependent rotation
rate results in shearing motions which may not only stretch magnetic
field lines in the tachocline, but may shear them as well, especially
at low latitudes. This shearing motion is a potential candidate for
generating twisted magnetic field configurations that rise to the
photosphere. This leads us to ask the question: Is there a preference
for the formation of δ-spot active regions at low latitude? In this
poster, we investigate this question observationally, by comparing
the latitude distribution of δ-spot active regions with the the
distribution of all active regions, most of which do not display
strong twist. We show the butterfly diagram of all active regions,
just δ-spot regions, and compare and contrast the distribution of the
two active region samples with time and latitude. We will use these
data to test the hypothesis that δ-spot regions form preferentially
at low latitudes, compared to the sample of all active regions.

---------------------------------------------------------
Title: Obituary: Thomas Robert Metcalf, 1961-2007
Authors: Leka, K. D.
2007BAAS...39.1074L Altcode:
The astronomy community lost a good friend when Tom Metcalf was killed
in a skiing accident on Saturday, 7 July 2007, in the mountains near
Boulder, Colorado. Tom was widely known for prolific work on solar
magnetic fields, hard-X-ray imaging of solar flares, and spectral
line diagnostics. He was often characterized as "one of the nicest
guys in science." Born October 5, 1961 in Cheverly, Maryland,
to Fred and Marilyn, Thomas R. Metcalf joined his sister, Karen, two
years his elder, in a close family that loved sailing, inquisitiveness,
and the natural world. Sibling rivalry (usually a Tonka truck intruding
on Barbie's sub-table "castle") melted when Tom and Karen collaborated
on elaborately engineered room-sized blanket-forts. Tom confidently
signed up at age of three to crew for his family's sailboat; when the
family moved to California in 1966, as Tom's father took a Professor
of Mathematics position at the University of California Riverside,
Tom's love for sailing was well-established. Week-long cruises or short
trips in the harbor were all fun; when school friends came aboard,
it was even better--if "only slightly too crowded" from the adults'
points of view. Tom's introduction to astronomy began one cold,
very clear, December night in the early 1970s, on a family camping trip
to Death Valley. The "Sidewalk Astronomers of San Francisco" had lined
the sidewalk near the visitors' center with all sorts of telescopes for
public viewing. Soon after, Tom and his boyhood friend Jim O'Linger
were building their own scopes, attending "Amateur Telescope Makers"
conferences, and Tom was setting up his scope on a sidewalk for public
viewing. In 1986, Tom set up his telescope on the bluffs above Dana
Point Harbor, and gave numerous strangers a stunning view of Halley's
Comet. His interest in physics and mathematics became evident
during Tom's last years in high school (Poly High in Riverside), and
as a senior he qualified to take freshman Physics at the University of
California-Riverside (UCR). Computers entered Tom's life then as well:
In a 1970s example of technological generation-gapping, he learned
to program his father's new desktop computer. Soon, he was exploiting
UCR's time-shared machines for that honorable endeavor, writing computer
games. Those "great games that Metcalf wrote" brought Tom's father quite
a reputation amongst the undergraduates. Tom earned his B.A. in
Physics from the University of California-San Diego (UCSD) in 1983. He
continued at his alma mater for graduate school in 1984, and joined the
"solar group" there headed by Dr. Richard C. Canfield. After earning
an M.S. in Physics in 1985, Tom moved to the Institute for Astronomy
(IfA) of the University of Hawai`I, with Dr. Canfield's group, in
1986. Tom completed his Ph.D. through UCSD in 1990, "Flare Heating and
Ionization of the Low Solar Chromosphere", then stayed at the IfA as
first a Post-Doctoral Fellow and then Associate Astronomer. While at
the IfA, his participation in Mees Solar Observatory operations and
Yohkoh mission support developed along two themes: the observation,
analysis, and interpretation of solar magnetic fields, and hard
X-ray imaging of solar flares. Tom was a key member of the group that
demonstrated the hemispheric "handedness" trend in the twist of solar
active region magnetic fields. He applied his considerable mathematical
expertise to the application of a "pixon" algorithm for hard X-ray
image reconstruction. To this day, this approach remains the algorithm
of choice for the Reuven Ramaty High Energy Solar Spectroscopic Imager
[RHESSI) mission, on which he was a Co-Investigator. Tom moved
to the Lockheed-Martin Solar and Astrophysics Laboratory (LMSAL) of
Palo Alto, California, in 1996, once again sharing an office with
Dr. Jean-Pierre Wülser, his old office-mate from the IfA. During
his tenure at LMSAL, Tom became a Co-Investigator on several space
experiments: the X-Ray Telescope (XRT) on the Japanese Hinode mission,
and the Atmospheric Imaging Assembly (AIA) and Helioseismic and
Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO). During
this time Tom continued work on interpreting solar magnetic fields,
specifically the pioneering use of the Na-D2 spectral line to map
the solar chromospheric magnetic field. In 2005, Tom joined the
growing solar group at NorthWest Research Associates' (NWRA) division
in Boulder, Colorado. Tom was an integral part of efforts comparing
algorithms for magnetic field data analysis and coronal diagnostics
afforded by the spectacular new data from Hinode. Of note were his
work on 180∘ disambiguation algorithms for vector magnetic-field
data and non-linear force-free extrapolation methods for modeling
the coronal magnetic field. Tom's professional interests were
so wide and varied that colleagues who survive him are continually
uncovering projects to try to bring to closure. Every meeting brings
new heartfelt condolences and shy inquiries, "...if you don't mind,
Tom had some data for me . . . could you . . . ???" He developed
a navigation package using Hewlett-Packard calculators, still used
by many sailors. Tom's IfA-vintage hurricane-tracking website still
sees visitation spikes when major storms threaten. At the time of his
death, Tom had 77 publications with easily over one hundred colleagues,
including his father. Tom represented NWRA/Colorado Research Associates
at the recently formed "Boulder Solar Alliance"; through it, a new
National Science Foundation Research Experience for Undergraduates
program was funded, and many Boulder-area research groups, including
NWRA, hosted students in its 2007 inaugural summer. Tom was
routinely teased as a "closet granola-head" by friends and family;
as he moved inland his interests switched to mountain bike riding,
rock climbing, and year-round skiing. Tom would eagerly join in any
new adventure that sounded interesting. He was an avid bike commuter
who relished the challenge of learning to ride in snow and ice. He
recycled everything. Tom is survived by his daughters Shanon
Brower, Alyssa Metcalf, and Keri Metcalf to whom he was a devoted
father, their mother Janet Biggs, his parents Fred and Marilyn
Metcalf, and his sister Karen (Metcalf) Swartz. A vast array of
friends, colleagues, and extended family will also sorely miss
him. To honor Tom's long-standing support for young researchers
in solar physics, Tom's family and the Solar Physics Division of the
AAS have established a travel fund for young scientists, to which
contributions are most welcome: The Thomas Metcalf SPD Travel
Fund American Astronomical Society 2000 Florida Ave., NW Suite 400
Washington, DC 20009-1231, USA https://members.aas.org/contributions/
Thomas_Metcalf_SPD_Travel_Fund.cfm

---------------------------------------------------------
Title: Probabilistic forecasting of solar flares from vector
magnetogram data
Authors: Barnes, G.; Leka, K. D.; Schumer, E. A.; Della-Rose, D. J.
2007SpWea...5.9002B Altcode:
Discriminant analysis is a statistical approach for assigning a
measurement to one of several mutually exclusive groups. Presented here
is an application of the approach to solar flare forecasting, adapted
to provide the probability that a measurement belongs to either group,
the groups in this case being solar active regions which produced
a flare within 24 hours and those that remained flare quiet. The
technique is demonstrated for a large database of vector magnetic
field measurements obtained by the University of Hawai'i Imaging Vector
Magnetograph. For a large combination of variables characterizing the
photospheric magnetic field, the results are compared to a Bayesian
approach for solar flare prediction, and to the method employed by the
U.S. Space Environment Center (SEC). Although quantitative comparison
is difficult as the present application provides active region (rather
than whole-Sun) forecasts, and the present database covers only part
of one solar cycle, the performance of the method appears comparable
to the other approaches.

---------------------------------------------------------
Title: Photospheric Magnetic Field Properties of Flaring versus
Flare-quiet Active Regions. IV. A Statistically Significant Sample
Authors: Leka, K. D.; Barnes, G.
2007ApJ...656.1173L Altcode:
Statistical tests based on linear discriminant analysis are applied
to numerous photospheric magnetic parameters, continuing toward
the goal of identifying properties important for the production of
solar flares. For this study, the vector field data are University
of Hawai`i Imaging Vector Magnetograph daily magnetograms obtained
between 2001 and 2004. Over 1200 separate magnetograms of 496
numbered active regions comprise the data set. At the soft X-ray
C1.0 level, 359 magnetograms are considered “flare productive”
in the 24 hr postobservation. Considering multiple photospheric
variables simultaneously indicates that combinations of only a few
familiar variables encompass the majority of the predictive power
available. However, the choice of which few variables is not unique,
due to strong correlations among photospheric quantities such as total
magnetic flux and total vertical current, two of the most powerful
predictors. The best discriminant functions result from combining one
of these with additional uncorrelated variables, such as measures
of the magnetic shear, and successfully classify over 80% of the
regions. By comparison, a success rate of approximately 70% is achieved
by simply classifying all regions as “flare quiet.” Redefining
“flare-productive” at the M1.0 level, parameterizations of excess
photospheric magnetic energy outperform other variables. However, the
uniform flare-quiet classification rate is approximately 90%, while
incorporating photospheric magnetic field information results in at
most a 93% success rate. Using nonparametric discriminant analysis,
we demonstrate that the results are quite robust. Thus, we conclude
that the state of the photospheric magnetic field at any given time
has limited bearing on whether that region will be flare productive.

---------------------------------------------------------
Title: Magnetohelioseismic Analysis of AR10720 Using Helioseismic
Holography
Authors: Moradi, H.; Donea, A.; Besliu-Ionescu, D.; Cally, P.; Lindsey,
C.; Leka, K.
2006ASPC..354..168M Altcode:
We report on the recent discovery of one of the most powerful sunquakes
detected to date produced by the January 15, 2005 X1.2 solar flare
in active region 10720. We used helioseismic holography to image the
acoustic source of the seismic waves produced by the flare. Egression
power maps at 6 mHz with a 2 mHz bandwidth reveal a strong, compact
acoustic source correlated with the footpoints of a coronal loop
that hosted the flare. Using data from various solar observatories,
we present a comprehensive analysis of the acoustic properties of
the sunquake and investigate the role played by the configuration of
the photospehric magnetic field in the production of flare generated
sunquakes.

---------------------------------------------------------
Title: An Overview of Existing Algorithms for Resolving the
180° Ambiguity in Vector Magnetic Fields: Quantitative
Tests with Synthetic Data
Authors: Metcalf, Thomas R.; Leka, K. D.; Barnes, Graham; Lites,
Bruce W.; Georgoulis, Manolis K.; Pevtsov, A. A.; Balasubramaniam,
K. S.; Gary, G. Allen; Jing, Ju; Li, Jing; Liu, Y.; Wang, H. N.;
Abramenko, Valentyna; Yurchyshyn, Vasyl; Moon, Y. -J.
2006SoPh..237..267M Altcode: 2006SoPh..tmp...14M
We report here on the present state-of-the-art in algorithms used
for resolving the 180° ambiguity in solar vector magnetic field
measurements. With present observations and techniques, some assumption
must be made about the solar magnetic field in order to resolve
this ambiguity. Our focus is the application of numerous existing
algorithms to test data for which the correct answer is known. In
this context, we compare the algorithms quantitatively and seek to
understand where each succeeds, where it fails, and why. We have
considered five basic approaches: comparing the observed field to a
reference field or direction, minimizing the vertical gradient of the
magnetic pressure, minimizing the vertical current density, minimizing
some approximation to the total current density, and minimizing some
approximation to the field's divergence. Of the automated methods
requiring no human intervention, those which minimize the square of
the vertical current density in conjunction with an approximation for
the vanishing divergence of the magnetic field show the most promise.

---------------------------------------------------------
Title: Estimating Active Region Free Energy and Helicity from the
Minimum Current Corona Model
Authors: Barnes, G.; Longcope, D. W.; Beveridge, C.; Ravindra, B.;
Leka, K. D.
2006IAUJD...3E..80B Altcode:
We employ the Minimum Current Corona (MCC) model to estimate the amount
of magnetic free energy and helicity injected into the coronal magnetic
field of an active region. In the MCC model, each concentration of
photospheric magnetic flux is represented by a point source, greatly
simplifying the magnetic topology. Advecting an initial partitioning
of the flux through a long time series of magnetograms results in
a persistent set of sources. We show that the centroid velocity of
a partition compares well with the flux-weighted average over the
partition of the local correlation tracking velocities. Flux domains,
bundles of field lines interconnecting pairs of sources, are surrounded
by separatrix surfaces. The intersection of two separatrices is
a separator field line, which is the site of reconnection in this
model. The evolution of the photospheric field causes the sources
to also evolve, which would lead to changes in the domain fluxes
to maintain a potential field configuration if reconnection could
proceed rapidly. However, in the absence of reconnection, currents
begin to flow to maintain the initial distribution of domain fluxes. The
minimum energy state occurs when currents flow along the separators. The
magnitude of the separator currents can be estimated and combined with
geometrical properties of the separators to give a lower bound to
the magnetic free energy of the system. The motion of sources about
one another adds braiding helicity to the system, while the internal
rotation of a partition adds spin helicity. Starting from an initial
potential field configuration, changes in the free energy are presented
for a time series of data for NOAA AR 8210 on 1 May 1998. This work
was supported by AFOSR, NSF and NASA.

---------------------------------------------------------
Title: Photospheric Magnetic Field Properties of Flaring versus
Flare-quiet Active Regions. III. Magnetic Charge Topology Models
Authors: Barnes, G.; Leka, K. D.
2006ApJ...646.1303B Altcode:
A magnetic charge topology (MCT) model is applied to time series of
photospheric vector magnetic field data for seven active regions divided
into epochs classified as flare-quiet and flare-productive. In an
approach that parallels an earlier study by the authors using quantities
describing the photospheric properties of the vector magnetic field,
we define quantities derived from the MCT analysis that quantify the
complexity and topology of the active region coronal fields. With
the goal of distinguishing between flare-quiet and flare-imminent
magnetic topology, the time series are initially displayed for three
active regions for visual inspection with few clear distinguishing
characteristics resulting. However, an analysis of all 24 epochs
using the discriminant analysis statistical approach indicates that
coronal field topology, derived from the observed photospheric vertical
field, may indeed hold relevant information for distinguishing these
populations, although the small sample size precludes a definite
conclusion. The variables derived from the characterization of coronal
topology routinely result in higher probabilities of being able to
distinguish between the two populations than the analogous variables
derived for the photospheric field.

---------------------------------------------------------
Title: Observations of The Chromospheric Magnetic Field In Solar
Active Regions
Authors: Leka, K. D.; Metcalf, T. R.; Mickey, D. L.; Barnes, G.
2006IAUJD...3E..53L Altcode:
Measuring the magnetic field in solar active regions in all spatial
and temporal dimensions is a long-standing and ambitious goal in
solar physics. As the locations of complex and rapidly evolving
magnetic fields and the source of geo-effective energetic events,
understanding active region magnetic field generation and evolution
is extremely an important goal; however, basic physics presents great
challenges to achieving it. Measuring the chromospheric magnetic field
in active regions is an important first step beyond routine photospheric
measurements; important both for basic understanding of active region
structure but also for the many ramifications coming from chromosphere
being closer to a force-free state than the photosphere. However,
it is also a very difficult measurement. In this talk I will describe
highlights of our group's on-going efforts to understand solar active
region magnetic field structure via direct observation of the vector
chromospheric magnetic field. Since late 2003, the U. Hawai`i/Mees
Solar Observatory's Imaging Vector Magnetograph has routinely
acquired spectropolarimetry measurements of active regions across
the Na-I 589.6nm line; from the polarization at the line's near-wings
approximately 0.007nm from line center we deduce the vector magnetic
field. The data are specific to active regions, specifically the
structure, free energy storage and evolution at that low-chromospheric
layer. I will present recent results from these chromospheric data with
a focus on the differences between the photosphere and chromosphere,
and the free energy storage in solar active regions.

---------------------------------------------------------
Title: Progress on Determining What Makes a Flare-Producing Active
Region
Authors: Leka, K. D.; Barnes, G.
2006SPD....37.2203L Altcode: 2006BAAS...38R.249L
We present the results of a large effort to investigate what,
if anything,can be determined from observations of solar
photospheric magnetic fieldsconcerning the flare productivity of
active regions. Different aspects ofthis work include examining the
temporal variations of the field prior toflare events, and applying the
Magnetic Charge Topology model in order toquantify the variations of the
coronal topology prior to flare events.A slightly different approach
was also investigated, by dropping thetime-sequence data and using a
statistically significant data-base of"daily" magnetograms. Throughout,
a statistical evaluation based onDiscriminant Analysis was used
to determine how the two populations inquestion (flare-producing
and flare-quiet) could best be differentiated,often using numerous
variables simultaneously. In this presentation,the results from this
project will be summarized in the context offlare-forecasting but also
in the context of applying the results tomodeling efforts.

---------------------------------------------------------
Title: Measuring the Magnetic Free Energy Available for Solar Flares
Authors: Metcalf, Thomas R.; Leka, K. D.; Mickey, D. L.; Barnes, G.
2006SPD....37.0903M Altcode: 2006BAAS...38..236M
In this poster we report on recent progress in the effort to measurethe
magnetic energy available to power solar flares. To directlymeasure the
free magnetic energy using the virial theorem, themagnetic field must
be known at an atmospheric height where it isforce-free, i.e. J x B =
0. In Metcalf, Leka &amp; Mickey (2005) the freeenergy of AR 10486
was determined just prior to the X10 flare at20:39UT on 29 October
2003, using vector magnetic field measurementsobtained in the solar
chromosphere where the field is force-free. Theresults from this study
are expanded here to a wider investigation ofthe magnetic energy storage
in flare- and CME-producing activeregions. With appropriate effort and
instrumentation, directlymeasuring the free energy and its evolution
may provide a powerfulflare-prediction capability. This research was
funded by NASAcontract NAG5-12466 and AFOSR contract F49620-03-C-0019.

---------------------------------------------------------
Title: Quantifying the Performance of Force-free Extrapolation
Methods Using Known Solutions
Authors: Barnes, G.; Leka, K. D.; Wheatland, M. S.
2006ApJ...641.1188B Altcode:
We outline a method for quantifying the performance of extrapolation
methods for magnetic fields. We extrapolate the field for two
model cases, using a linear force-free approach and a nonlinear
approach. Each case contains a different topological feature of
the field that may be of interest in solar energetic events. We are
able to determine quantitatively whether either method is capable
of reproducing the topology of the field. In one of our examples, a
subjective evaluation of the performance of the extrapolation suggests
that it has performed quite well, while our quantitative score shows
that this is not the case, indicating the importance of being able
to quantify the performance. Our method may be useful in determining
which extrapolation techniques are best able to reproduce a force-free
field and which topological features can be recovered.

---------------------------------------------------------
Title: Implementing a Magnetic Charge Topology Model for Solar
Active Regions
Authors: Barnes, G.; Longcope, D. W.; Leka, K. D.
2005ApJ...629..561B Altcode:
Information about the magnetic topology of the solar corona is
crucial to the understanding of solar energetic events. One approach to
characterizing the topology that has had some success is magnetic charge
topology, in which the topology is defined by partitioning the observed
photospheric field into a set of discrete sources and determining which
pairs are interlinked by coronal field lines. The level of topological
activity is then quantified through the transfer of flux between
regions of differing field line connectivity. We discuss in detail how
to implement such a model for a time series of vector magnetograms,
paying particular attention to distinguishing real evolution of the
photospheric magnetic flux from changes due to variations in atmospheric
seeing, as well as uncorrelated noise. We determine the reliability
of our method and estimate the uncertainties in its results. We then
demonstrate it through an application to NOAA active region 8210,
which has been the subject of extensive previous study.

---------------------------------------------------------
Title: On the Availability of Sufficient Twist in Solar Active
Regions to Trigger the Kink Instability
Authors: Leka, K. D.; Fan, Y.; Barnes, G.
2005ApJ...626.1091L Altcode:
The question of whether there is sufficient magnetic twist in solar
active regions for the onset of the kink instability is examined
using a “blind test” of analysis methods commonly used to interpret
observational data. “Photospheric magnetograms” are constructed from
a recently developed numerical simulation of a kink-unstable emerging
flux rope with nearly constant (negative) wind. The calculation of the
best-fit linear force-free parameter αbest is applied,
with the goal of recovering the model input helicity. It is shown
that for this simple magnetic structure, three effects combine to
produce an underestimation of the known helicity: (1) the influence of
horizontal fields with lower local α values within the flux rope; (2)
an assumed simple relation between αbest and the winding
rate q does not apply to nonaxis fields in a flux rope that is not
thin; and (3) the difficulty in interpreting the force-free twist
parameter measured for a field that is forced. A different method to
evaluate the magnetic twist in active region flux ropes is presented,
which is based on evaluating the peak α value at the flux rope
axis. When applied to data from the numerical simulation, the twist
component of the magnetic helicity is essentially recovered. Both
the αbest and the new αpeak methods are then
applied to observational photospheric vector magnetic field data of
NOAA AR 7201. The αbest approach is then confounded further
in NOAA AR 7201 by a distribution of α that contains both signs, as
is generally observed in active regions. The result from the proposed
αpeak approach suggests that a larger magnetic twist is
present in this active region's δ-spot than would have been inferred
from αbest, by at least a factor of 3. It is argued that
the magnetic fields in localized active region flux ropes may indeed
carry greater than 2π winds, and thus the kink instability is a
possible trigger mechanism for solar flares and coronal mass ejections.

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Title: Chromospheric Vector Magnetic Field Measurements of Active
Regions
Authors: Leka, K. D.
2005AGUSMSH53B..02L Altcode:
Active regions, as the locations of complex and rapidly evolving
magnetic fields, are also the source of many coronal mass ejections. The
chromospheric magnetic field, being force-free, should provide direct
insights into both the energy storage for solar energetic events, and
possibly their trigger mechanism as well. In this talk I will review
recent chromospheric vector field observations from the U. Hawai`i/Mees
Solar Observatory Imaging Vector Magnetograph, obtained in the Na-I
line at 589.6nm. The focus will be on the differences between the
photosphere and chromosphere, and chromospheric field measurements
relevant to CME production such as free energy storage and evolution
prior to an energetic event.

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Title: Predicting Coronal Emissions with Multiple Heating Rates
Authors: Lundquist, L. L.; Fisher, G. H.; Leka, K. D.; Metcalf, T. R.;
McTiernan, J. M.
2005AGUSMSP14A..02L Altcode:
A variety of proposed coronal heating mechanisms remain prominent
in the literature, with insufficient observational constraints to
distinguish between them. In an attempt to add further constraints, we
create predicted coronal emission maps of several active regions using
simple parametrizations of differing theoretical heating mechanisms and
compare the results to the observed coronal emissions. The results are
interpolated to a 3-d grid, convolved with instrument response function,
and integrated over line of sight to simulate satellite observation
of the modeled loops. We also discuss those factors which dominate
the differences in observed and predicted coronal emission.

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Title: Another Piece of the Elephant: Chromospheric Vector Field
Observations
Authors: Leka, K. D.; Metcalf, T. R.; Mickey, D. L.
2005AGUSMSH13C..10L Altcode:
As with most solar observational questions, investigating the
structure and role of the chromosphere is one of remote sensing: many
investigations describing their "piece of the elephant". The goal is,
of course, to form a coherent picture of the state of the magnetized
plasma which resides there (or passes through). In this presentation,
recent efforts to understand the chromospheric magnetic field structure
via direct observation, i.e. chromospheric vector magnetograms, will
be presented. Since late 2003, the U. Hawai`i/Mees Solar Observatory's
Imaging Vector Magnetograph has routinely acquired spectropolarimetry
measurements of active regions across the Na-I 589.6nm line; from the
polarization at the line's near-wings approximately 0.007nm from line
center we deduce the vector magnetic field. The data are specific
to active regions, with the focus being the structure, free energy
storage and evolution at that low-chromospheric layer. I will present
salient aspects of the observed chromospheric magnetic field structure,
to compare and contrast with the picture formed by the other methods
in this session.

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Title: Magnetic Free Energy in NOAA Active Region 10486 on 2003
October 29
Authors: Metcalf, Thomas R.; Leka, K. D.; Mickey, D. L.
2005ApJ...623L..53M Altcode:
We calculate the total and the free magnetic energy for solar NOAA
active region 10486 on 2003 October 29 using chromospheric vector
magnetograms observed with the Imaging Vector Magnetograph at Mees Solar
Observatory in the Na I λ5896 spectral line. The magnetic energy is
derived from the magnetic virial theorem using observations spanning the
X10 flare that occurred at 20:39 UT. Although poor atmospheric seeing
prevented us from discerning changes in the free energy associated
with the flare, there was an unusually large amount of free magnetic
energy in NOAA AR 10486: (5.7+/-1.9)×1033 ergs, which is
consistent with the very high level of activity observed in this active
region. It is thus plausible that the extreme activity was powered by
the magnetic free energy.

---------------------------------------------------------
Title: Photospheric Magnetic Field Properties of Flaring
vs. Flare-Quiet Active Regions III: Discriminant Analysis of a
Statistically Significant Database
Authors: Leka, K. D.; Barnes, G.
2004AAS...204.3905L Altcode: 2004BAAS...36..715L
Solar active regions are often evaluated for their potential to produce
energetic events based their magnetic morphology. Quantitatively,
this information is available using vector magnetic field information
which is (presently only) routinely gathered from photospheric
observations. Recently we demonstrated a method of parameterizing vector
field information such that variations in the magnetic morphology
and complexity were contained in the statistical description of
(as examples) the vertical current or magnetic shear angles; it was
also demonstrated that no single parameter consistently and uniquely
displayed pre-event variations (Leka &amp; Barnes 2003a). We also
showed that with Discriminant Analysis (Leka &amp; Barnes 2003b), it is
possible to distinguish between an event-imminent photospheric magnetic
state and an event-quiet state -- but only by considering multiple
variables simultaneously. The limitations of that demonstration were
primarily due to small-number statistics given the dataset used. In the present work, Discriminant Analysis is applied to a very
different dataset: the daily "survey" magnetograms obtained by the
U. Hawai`i/Mees Solar Observatory Imaging Vector Magnetograph. In
this manner, the problem of small-number statistics is relieved and
advantages available by DA are explored. However, given the daily
temporal cadence, the focus shifts toward detecting parametric
thresholds rather than pre-event-specific evolution. Nonetheless,
the central question remains how to distinguish a region which is
primed for an energetic event, with results applicable to modeling
efforts by providing empirical discriminating information as to the
pre-eruption state of the boundary magnetic field. This effort
is funded by contract F49620-03-C-0019 through the Air Force Office
of Scientific Research.

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Title: Inferring a Photospheric Velocity Field from a Sequence of
Vector Magnetograms: The Minimum Energy Fit
Authors: Longcope, D.; Leka, K. D.
2004AAS...204.3704L Altcode: 2004BAAS...36..709L
We introduce a technique for inferring a photospheric velocity
from a sequence of vector magnetograms. The technique, called The
Minimum Energy Fit, demands that the photospheric flow agree with
the observed photospheric field evolution according to the magnetic
induction equation. It selects, from all consistent flows, that with
the smallest overall flow speed by demanding that it minimize an
energy functional. Partial or imperfect velocity information may be
incorporated by demanding a velocity consistent with the induction
equation which minimizes the squared difference with flow components
otherwise known. The combination of low velocity and consistency with
the induction equation are desirable when using the magnetogram data and
associated flow as boundary conditions of a numerical simulation. The
technique is tested on synthetic magnetograms generated by specified
flow fields and shown to yield reasonable agreement. It also yields
believable flows from magnetograms of AR8210 made with the Imaging
Vector Magnetogram at the Mees Solar Observatory. This work was
supported by AFOSR under a DoD Multi-Universities Research Initiative
(MURI) grant, “Understanding Solar Eruptions and their Interplanetary
Consequences”.

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Title: Magnetic Topology, Flux Emergence/Reconnection and Velocities
from a Magnetic Charge Topology Model for Solar Active Regions
Authors: Barnes, G.; Longcope, D. W.; Leka, K. D.
2004AAS...204.3906B Altcode: 2004BAAS...36..715B
Magnetic Charge Topology (MCT) models represent the field in the solar
corona as being due to collection of point magnetic charges located at
or below the photosphere. These models have the advantage of providing a
simple quantitative description of the field topology. We apply MCT to
time series of magnetograms from the U. Hawai`i/Mees Solar Observatory
Imaging Vector Magnetograph (IVM). We first describe the evolution of
the magnetic topology of the region, by calculating such quantities
as the magnetic flux connecting each pair of point sources, and the
number and locations of magnetic separators, which are likely to be
the location of reconnection in the solar corona. Using the changes in
the magnitudes of the point sources, and in the connectivity matrix,
we estimate the rate at which flux is emerging and submerging through
the photosphere, and the rate at which reconnection is happening in
the corona. By tracking the changes in the locations of the sources,
we are also able to estimate the horizontal velocities. This work
was performed under Air Force Office of Scientific Research contracts
F49620-03-C-0019 and F49620-02-C-0191.

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Title: The Magnetic Free Energy in AR0486
Authors: Metcalf, T. R.; Leka, K. D.; Mickey, D. L.
2004AAS...204.0208M Altcode: 2004BAAS...36S.668M
During October/November 2003, the dramatic active region 0486 traversed
the solar disk and produced many large solar flares. During this time,
we obtained chromspheric vector magnetic field data for AR0486 using
the Imaging Vector Magnetograph (IVM) at Mees Solar Observatory,
Haleakala, Hawaii. We will describe these vector field data and will
use them to compute the magnetic free energy, and its time variation,
for AR0486. This large, complex active region contained an unusually
large amount of free magnetic energy, not surprising considering the
level of activity it produced. This work was supported by NASA
grant NAG5-12466.

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Title: Observational consequences of a magnetic flux rope topology
Authors: Gibson, S.; Barnes, G.; Demoulin, P.; Fan, Y.; Fisher, G.;
Leka, K.; Longcope, D.; Mandrini, C.; Metcalf, T.
2003AGUFMSH42B0516G Altcode:
We consider the implications of a magnetic flux rope topology for
the interpretation of observations of sigmoidal active regions. A
region of tangential magnetic discontinuities can be identified
using techniques that determine a bald patch (BP) and corresponding
separatrices or a quasi-separatrix layer (QSL) -- for a flux rope this
region can be S-shaped, or sigmoidal. If such a region is physically
driven, current sheets can form yielding conditions appropriate for
reconnective heating. Using a numerical simulation of an emerging
flux rope driven by the kink instability, Fan and Gibson (ApJL, 2003)
showed that current sheets indeed formed a sigmoidal surface. In this
poster we will demonstrate that the current sheets formed on the BP and
BP separatrices. Moreover, we will use the results of the numerical
simulation as proxies for observations: specifically the simulated
field at the photosphere as proxy for the magnetic boundary condition,
the sigmoidal current sheets as proxy for the X-ray active region
emission, and the location of dipped magnetic field lines as proxy
for a filament. We will then consider to what extent such observations
might be used to understand and constrain the basic properties of the
coronal field.

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Title: Photospheric Magnetic Field Properties of Flaring versus
Flare-quiet Active Regions. I. Data, General Approach, and Sample
Results
Authors: Leka, K. D.; Barnes, G.
2003ApJ...595.1277L Altcode:
Photospheric vector magnetic field data from the University of
Hawai'i Imaging Vector Magnetograph, with good spatial and temporal
sampling, are used to study the question of identifying a preflare
signature unique to flare events in parameters derived from the
magnetic vector field, B. In this first of a series of papers, we
present the data analysis procedure and sample results focusing only
on three active regions (NOAA Active Regions 8636, 8771, and 0030),
three flares (two M class and one X class), and (most importantly) a
flare-quiet epoch in a comparable flare-producing region. Quantities
such as the distribution of the field morphology, horizontal spatial
gradients of the field, vertical current, current helicity, “twist”
parameter α, and magnetic shear angles are parameterized using their
moments and appropriate summations. The time series of the resulting
parameterizations are examined one at a time for systematic differences
in overall magnitude and evolution between the flare and flare-quiet
examples. The variations expected due to atmospheric seeing changes
are explicitly included. In this qualitative approach we find (1)
no obvious flare-imminent signatures from the plain magnetic field
vector and higher moments of its horizontal gradient or from most
parameterizations of the vertical current density; (2) counterintuitive
but distinct flare-quiet implications from the inclination angle
and higher moments of the photospheric excess magnetic energy; (3)
flare-specific or flare-productivity signatures, sometimes weak,
from the lower moments of the field gradients, kurtosis of the
vertical current density, magnetic twist, current helicity density,
and magnetic shear angle. The strongest results are, however, that (4)
in ensuring a flare-unique signature, numerous candidate parameters
(considering both their variation and overall magnitude) are nullified
on account of similar behavior in a flare-quiet region, and hence (5)
considering parameters one at a time in this qualitative manner is
inadequate. To address these limitations, a quantitative statistical
approach is presented in Paper II by Leka &amp; Barnes.

---------------------------------------------------------
Title: Photospheric Magnetic Field Properties of Flaring versus
Flare-quiet Active Regions. II. Discriminant Analysis
Authors: Leka, K. D.; Barnes, G.
2003ApJ...595.1296L Altcode:
We apply statistical tests based on discriminant analysis to the wide
range of photospheric magnetic parameters described in a companion paper
by Leka &amp; Barnes, with the goal of identifying those properties
that are important for the production of energetic events such as solar
flares. The photospheric vector magnetic field data from the University
of Hawai'i Imaging Vector Magnetograph are well sampled both temporally
and spatially, and we include here data covering 24 flare-event and
flare-quiet epochs taken from seven active regions. The mean value
and rate of change of each magnetic parameter are treated as separate
variables, thus evaluating both the parameter's state and its evolution,
to determine which properties are associated with flaring. Considering
single variables first, Hotelling's T2-tests show small
statistical differences between flare-producing and flare-quiet
epochs. Even pairs of variables considered simultaneously, which do
show a statistical difference for a number of properties, have high
error rates, implying a large degree of overlap of the samples. To
better distinguish between flare-producing and flare-quiet populations,
larger numbers of variables are simultaneously considered; lower error
rates result, but no unique combination of variables is clearly the
best discriminator. The sample size is too small to directly compare the
predictive power of large numbers of variables simultaneously. Instead,
we rank all possible four-variable permutations based on Hotelling's
T2-test and look for the most frequently appearing variables
in the best permutations, with the interpretation that they are
most likely to be associated with flaring. These variables include
an increasing kurtosis of the twist parameter and a larger standard
deviation of the twist parameter, but a smaller standard deviation of
the distribution of the horizontal shear angle and a horizontal field
that has a smaller standard deviation but a larger kurtosis. To support
the “sorting all permutations” method of selecting the most frequently
occurring variables, we show that the results of a single 10-variable
discriminant analysis are consistent with the ranking. We demonstrate
that individually, the variables considered here have little ability
to differentiate between flaring and flare-quiet populations, but with
multivariable combinations, the populations may be distinguished.

---------------------------------------------------------
Title: Photospheric Magnetic Field Properties of Flaring
vs. Flare-Quiet Active Regions I: Data, General Approach, and
Statistical Results
Authors: Leka, K. D.; Barnes, G.
2003SPD....34.1615L Altcode: 2003BAAS...35R.835L
Photospheric vector magnetic field data from the U. Hawai`i Imaging
Vector Magnetograph are examined for pre-event signatures unique to
solar energetic phenomena. Parameters are constructed from B(x,y) to
describe (for example) the distributions of the field, spatial gradients
of the field, vertical current, current helicity, ”twist” parameter
α and magnetic shear angles. A quantitative statistical approach
employing discriminant analysis and Hotelling's T2-test is
applied to the magnitude and temporal evolution of parameters from
24 flare-event and flare-quiet epochs from seven active regions. We demonstrate that (1) when requiring a flare-unique signature,
numerous candidate parameters are nullified by considering flare-quiet
epochs, (2) a more robust method exists for estimating error rates
than conventional ”truth tables”, (3) flaring and flare-quiet
populations do not necessarily have low error rates for classification
even when statistically distinguishable, and that (4) simultaneous
consideration of a large number of variables is required to produce
acceptable error rates. That is, when the parameters are considered
individually, they show little ability to differentiate between the
two populations; multi-variable combinations can discriminate the
populations and/or result in perfect classification tables. In
lieu of constructing a single all-variable discriminant function to
quantify the flare-predictive power of the parameters considered,
we devise a method whereby all permutations of the four-variable
discriminant functions are ranked by Hotelling's T2. We
present those parameters (e.g. the temporal increase of the kurtosis
of the spatial distribution of the vertical current density) which
consistently appear in the best combinations, indicating that they may
play an important role in defining a pre-event photospheric state. While
no single combination is clearly the best discriminator, we demonstrate
here the requisite approach: include flare-quiet epochs as a control
group for statistical tests of the null hypothesis. This work
was performed under Air Force Office of Scientific Research contracts
F49620-00-C-0004 and F49620-03-C-0019.

---------------------------------------------------------
Title: Photospheric Magnetic Field Properties of Flaring
vs. Flare-Quiet Active Regions II: A Magnetic Charge Topology Model
and Statistical Results
Authors: Barnes, G.; Leka, K. D.; Longcope, D. W.
2003SPD....34.1616B Altcode: 2003BAAS...35..835B
The complexity of the coronal magnetic field extrapolated from a
Magnetic Charge Topology (MCT) model, is examined for pre-event
signatures unique to solar energetic phenomena. Although extensive
use has been made of quantities measured at the photosphere, it is
important to consider the magnetic field in the corona, where (for
example) the hard X-ray signatures of energy release in solar flares
are observed. By quantifying the inferred coronal magnetic topology we
are no longer limited to considering solely the magnetic state of the
photosphere. MCT is applied to temporally sampled photospheric
magnetic data from the U. Hawai`i Imaging Vector Magnetograph, for
24 flare-event and flare-quiet epochs from seven active regions. We
outline the methodology employed for automating the application of MCT
to large data sets of complex active regions: partitioning the observed
Bz at the photosphere, assigning a charge to each partition,
and using this charge distribution to extrapolate the field in the
corona. From the resulting field we compute the connectivity matrix
ψ ij, the location of null points and the intersection
of separatrix surfaces, i.e. separator field lines. Parameters are
constructed to describe, for example, the magnetic connectivities, the
magnetic flux in those connections, and the number of separators. Examining particular events results in no obvious trends in the
magnitude and temporal evolution of the parameters just prior to
flare events. Thus, we employ the same quantitative statistical
approach outlined in Leka and Barnes [this session], i.e. applying
discriminant analysis and Hotelling's T2-test, and ranking
all four-variable discriminant functions as a proxy for a single
all-variable discriminant function. We present those parameters which
consistently appear in the best combinations, indicating that they
may play an important role in defining a pre-event coronal state. This work was performed under Air Force Office of Scientific Research
contracts F49620-00-C-0004, F49620-03-C-0019 and F49620-02-C-0191.

---------------------------------------------------------
Title: Active-Region Magnetic Structure Observed in the Photosphere
and Chromosphere
Authors: Leka, K. D.; Metcalf, Thomas R.
2003SoPh..212..361L Altcode:
The full magnetic vector has been measured in both the photosphere and
chromosphere across sunspots and plage in NOAA Active Region 8299. We
investigate the vertical magnetic structure above the umbral, penumbral
and plage regions using quantitative statistical comparisons of the
photospheric and chromospheric magnetic data. The results include: (1)
a general decrease in average magnetic flux density with height; (2)
the direct detection of the superpenumbral canopy in the chromosphere;
(3) values for dB/dz which are consistent with earlier investigations
when derived from a straight difference between the two measurements,
but which are somewhat small when derived from the ∇⋅B=0 condition,
(4) a monolithic structure in the umbrae which extends well into
the upper chromosphere, with a very complex and varied structure in
penumbrae and plage, as evidenced by (5) a uniform magnetic scale height
in the umbrae with an abrupt jump to widely varying scale heights in
penumbral and plage regions. Further, we find (6) evidence that field
extrapolations using the photospheric flux as the boundary may not
agree with expectations or with observed coronal structures as well as
those which use the chromospheric magnetic flux as the extrapolation
starting point.

---------------------------------------------------------
Title: Global budget for an eruptive active region . I. Equilibrium
reconstruction approach
Authors: Bleybel, A.; Amari, T.; van Driel-Gesztelyi, L.; Leka, K. D.
2002A&A...395..685B Altcode:
We present results on the magnetic structure of NOAA Active Region
#7912 which was involved in a long duration flare on 14 October 1995,
and was the source region for a magnetic cloud observed by the WIND
spacecraft from October 18-20. Using vector magnetograms from the
Imaging Vector Magnetograph (“IVM”), we reconstruct the magnetic
field above this active region, assuming it is in a non-linear
force-free state. This reconstruction is used to determine global
properties of the active region magnetic field including topology,
magnetic energy, and relative magnetic helicity. A comparison of some
global quantities before and after the eruptive event is discussed. We
show that the magnetic energy and relative helicity of the active
region decreased after the eruption, consistent with the ejection
of a large amount of helicity (in the magnetic cloud). We also show
that the relaxed post-flare state still contains nonlinearities and is
not consistent with a linear force-free state as predicted by Taylor's
theory of relaxation. These results agree with those of recent numerical
simulations concerning plasmoid ejection and helicity redistribution in
the disruption of magnetic configurations. We propose as an explanation
that the anchoring of field lines in the photosphere prevents a full
cascade to the Taylor state, and that a variational formulation in which
the action functional would describe this constraint should be derived.

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Title: Magnetic flux ropes: Would we know one if we saw one?
Authors: Gibson, S. E.; Low, B. C.; Leka, K. D.; Fan, Y.; Fletcher, L.
2002ESASP.505..265G Altcode: 2002IAUCo.188..265G; 2002solm.conf..265G
There has been much debate lately about whether twisted magnetic flux
ropes exist in the corona. When asked for observational evidence
of them, the temptation is to show images of apparently twisted
structures. However, we must be very careful of projection effects in
interpreting these observations. Two critical aspects of understanding
how we might observe flux ropes are 1) the 3D nature of the flux rope,
and 2) physically, which bits are visible and for what reasons? In
this paper we will use a simple but physically reasonable 3D analytic
model to address these two issues, and develop techniques that can in
future be used on more general models, both analytic and numerical.

---------------------------------------------------------
Title: Photospheric Magnetic Fields Complexity Variations and
Solar Flares
Authors: Barnes, G.; Leka, K. D.; Longcope, D. W.
2002AAS...200.6808B Altcode: 2002BAAS...34..756B
Do photospheric magnetic fields show systematic changes which precede
energetic events such as solar flares? The answer has proved elusive. We
address this question by examining vector magnetic flux maps from
the U. Hawai`i Imaging Vector Magnetograph (Mickey et al. 1996),
which obtain full Stokes spectra over entire active regions every
4 minutes on average. We compare numerous parameters derived from
the vector magnetograms of flaring active regions to those from
comparable non-flaring active regions. In addition, we determine
quantitative measurements of the complexity of the field topology
using the Minimum-Current Corona analysis (Longcope 1996). The goal
is to determine quantitative measurements of the complexity of the
field topology, and determine whether variations in those measures
correlate with or precede flare events. This project was funded by
AFOSR contract F49620-00-C-0004.

---------------------------------------------------------
Title: Stokes Asymmetries In and Around Sunspots
Authors: Leka, K. D.
2002AAS...200.3802L Altcode: 2002BAAS...34..698L
In an ideal homogeneous atmosphere with minimal complications from
gradients or unresolved features, photospheric Stokes Spectra should
have a straightforward pattern that is symmetric in wavelength for
linear polarization and anti-symmetric for circular. Deviations from
these idealized shapes can indicate gradients in the magnetic field,
in the velocity of plasma flows (see, e.g., Leka &amp; Steiner 2001),
and completely different atmospheres that are unresolved within the
pixel. Using Stokes spectra from the NSO/HAO Advanced Stokes Polarimeter
of a sunspot obtained with high (sub-arcsecond) spatial resolution, we
examine the systematic patterns of asymmetries and multiple-lobes in
the spectra over the sunspot. Initial results indicate the presence
of high-velocity and even supersonic flows in and around sunspot
penumbrae, accompanied by multiple magnetic components (of the same
and/or opposite sign) throughout the sunspot structures. This work
was funded by NSF-ATM970782.

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Title: Effects of `Seeing' on Vector Magnetograph Measurements
Authors: Leka, K. D.; Rangarajan, K. E.
2001SoPh..203..239L Altcode:
We present a study of the effects of atmospheric seeing on quantities
derived from observations of solar polarized light - specifically,
the vector magnetic flux and quantities derived from its magnitude and
direction. Data from the Imaging Vector Magnetograph (`IVM') at the
U. Hawaii/Mees Solar Observatory, are degraded by various degrees by
applying a blur function to the `incoming light', simulating a range
of seeing conditions. A quantitative study of the resulting effects
on derived quantities including total magnetic flux, vertical electric
current density and magnetic shear angles, are discussed as a function
of the imposed degradation. The generality of the seeing effects is
explored by comparing the results from two different active regions;
we find that the results are comparable for those quantities directly
computed from the magnetic flux vector (e.g., summed, as in total flux)
but less so for those quantities involving higher-order calculations
(e.g., derivatives, as in vertical currents). We suggest that for
temporal series data from any instrument, a method such as that which
we outline here, be applied in order to model the uncertainties imposed
on the data (in addition to instrumental uncertainties, etc.) due to
seeing variations.

---------------------------------------------------------
Title: The Effect of “Seeing” on Imaging Vector Magnetograph
Measurements of Solar Active Regions
Authors: Leka, K. D.; Rangarajan, K. E.
2001AGUSM..SP41B06L Altcode:
All ground-based instruments are subject to atmospheric seeing;
here we attempt to quantify the effects of atmospheric seeing on
vector magnetograph observations and the parameters derived from
them. We present the results of our study on the effect of seeing
using Imaging Vector Magnetograph (IVM) raw data and subsequent
data reduction. The blurring due to seeing is modeled by convolving
a Gaussian function with various widths with raw polarization data
of good-seeing quality to simulate different seeing conditions. The
IVM data reduction procedure is carried out on all data to arrive
at vector magnetic flux and velocity images; from these are derived
commonly used parameters such as vertical current density, shear angle
and magnetic free energy. We find that poorer seeing conditions during
observations reduce the derived magnetic field strength, as expected,
and influence the other parameters in generally expected ways. Our
study results in defining the limits on uncertainties due to seeing
in parameters derived from vector magnetic flux observations.

---------------------------------------------------------
Title: A Comparison of the Active Region Magnetic Field in the
Photosphere and Chromosphere
Authors: Metcalf, T. R.; Leka, K. D.
2001AGUSM..SP41B07M Altcode:
During the Whole Sun Fortnight, the Imaging Vector Magnetograph at Mees
Solar Observatory obtained vector magnetic field maps of AR 8299 in the
Na-D line (the core of which is formed in the lower chromosphere). At
almost the same time, the HAO/NSO Advanced Stokes Polarimeter
obtained data in the Fe-I line, formed in the photosphere. We present
a comparison of the structures observed in AR 8299's main sunspots on
18 August 1998 at the different atmospheric heights. The data suggest
that the Na-D magnetic field maps are formed 2.5 Mm above the Fe-I
magnetic field maps. At this height in the atmosphere, the magnetic
field is force-free and we will explore the implications of this for
the extrapolation of the magnetic field in the corona.

---------------------------------------------------------
Title: Understanding Small Solar Magnetic Structures: Comparing
Numerical Simulations to Observations
Authors: Leka, K. D.; Steiner, O.
2001ApJ...552..354L Altcode:
We present direct comparisons of small magnetic structures observed
in the solar photosphere with the results from numerical simulations
of those structures. We compare diagnostic signatures derived
from emergent Stokes polarization spectra from both the observed
and model atmospheres, the former recorded with the National Solar
Observatory/High Altitude Observatory Advanced Stokes Polarimeter,
the latter from a fully dynamic MHD simulation of a magnetic flux
sheet in a convective atmosphere. We focus on the asymmetries in the
Stokes V spectra and find, first and foremost, that the asymmetries
from the observed Stokes I and V in and around solar pores and azimuth
centers (ACs) are quantitatively comparable to those derived from
the simulation. We also find enhanced Stokes V asymmetry on the
periphery of pores and ACs. We interpret this as a consequence of
strong downdrafts in the surroundings of these magnetic structures,
accompanied by the expansion of the magnetic field lines with height
above these field-free downdrafts (the “canopy effect”). The
magnetic canopy can be present whether or not there is a continuum
signature (i.e., a dark “pore”). Not surprisingly, the patterns
and magnitudes of asymmetries scale with the size of the magnetic
element. In the interior of the pores and ACs, we find evidence for
mixed up- and downflows, with little spatial correlation between the
zero-crossing shift of the V profile and the V amplitude. Finally,
we report on asymmetries observed in the linear polarization
Plin(λ)=[Q(λ)2+U(λ)2]1/2,
finding further support for the presence of the magnetic canopy
from those diagnostics. We additionally present expectations for
spectropolarimetric observations at significantly higher spatial
resolution.

---------------------------------------------------------
Title: Coronal Sunspot Magnetic Fields: Extrapolation vs. Direct
Observation
Authors: Leka, K. D.; White, S.; Mikic, Z.; Lee, J.
2001AGUSM..SH31D03L Altcode:
Direct observations of the coronal magnetic field strength is presently
only available using radio wavelengths. It is, however, common to
infer the morphology of coronal magnetic fields by extrapolating
in height from observations of photospheric magnetic fields. Both
methods have sources of uncertainty, and neither presently results in
the quantitative coronal vector magnetic field measurements required
to understand coronal dynamics. In this paper we combine radio (VLA)
observations of a region containing a large spot with simultaneous
highly accurate photospheric vector magnetic field measurements obtained
with the NSO/HAO Advanced Stokes Polarimeter and investigate the coronal
response to changes in the photospheric magnetic field as NOAA AR8535
(May 1999) crossed the solar disk.

---------------------------------------------------------
Title: Applying a Two-Component Inversion to Stokes Spectra from a
Sunspot Penumbra
Authors: Leka, K. D.
2001ASPC..236..571L Altcode: 2001aspt.conf..571L
No abstract at ADS

---------------------------------------------------------
Title: Untangling Sunspot Penumbrae: New Stokes Profile Analyses
Authors: Leka, K. D.; Socas-Navarro, H.
2000SPD....31.0119L Altcode: 2000BAAS...32..804L
We present preliminary analyses of Stokes [I, Q, U, V] spectra of a
sunspot penumbra using two different analysis/inversion procedures. It
has long been known that the Stokes spectra from sunspot penumbrae, even
at disk center, commonly show multiple lobes and asymmetries. Hence,
the magnetic/thermodynamic maps obtained from Stokes spectra using
Milne-Eddington approaches are good first approximations, but will not
uncover any further details of penumbral physics. Penumbrae are known to
be very structured, hence we first present the results of an inversion
using a recent augmentation to the HAO inversion routine: the ability to
model the observed spectra using two magnetic atmospheres in addition
to the non-magnetic atmosphere. Such a 'three-component' approach is
useful to interpret unresolved structures which contribute to signals
within the resolution elements. Second, we present the results of
an inversion using the new "LILIA" code, currently under development
at HAO. LILIA is the "community Stokes inversion code" component of
the Solar Magnetism Initiative (SMI), and is based on the strategy of
Ruiz Cobo and del Toro Iniesta (1992, ApJ, 398, 375). We describe the
strengths and limitations of the two approaches, with attention to
their application for the community at large to interpret data from
both current and future ground-based and space-based instruments.

---------------------------------------------------------
Title: Summary: The Sun, the stars, and total eclipses
Authors: Leka, K. D.
2000ssls.work..129L Altcode:
This diverse group of scientists has traveled from around the globe
on the event of a total solar eclipse over Szombathely, Hungary to
experience a most bedazzling spectacle. With this gathering we take
the opportunity to examine new results in solar physics and in the
physics of Sun-like stars. In this summary I will highlight pervasive
themes and connections which emerged in the talks and posters presented.

---------------------------------------------------------
Title: Non Linear Force-Free Reconstruction of a Flaring Active Region
Authors: Bleybel, A.; Amari, T.; van Driel-Gesztelyi, L.; Leka, K. D.
1999ESASP.448..709B Altcode: 1999ESPM....9..709B; 1999mfsp.conf..709B
No abstract at ADS

---------------------------------------------------------
Title: The Imaging Vector Magnetograph at Haleakalā -
II. Reconstruction of Stokes Spectra
Authors: LaBonte, Barry J.; Mickey, Donald L.; Leka, K. D.
1999SoPh..189....1L Altcode:
The Imaging Vector Magnetograph (`IVM') at Mees Solar Observatory,
Haleakalā, Maui, Hawai`i, is designed to measure the magnetic field
vector over an entire solar active region on the Sun. The first step
in that process is to correct the raw data for all known systematic
effects introduced by the instrument and Earth's atmosphere. We define
a functional model of the atmosphere/instrument system and measure the
corrections for the degradation introduced by each component of the
model. We demonstrate the feasibility of this method and assess the
accuracy of the IVM spectra with a direct comparison of the resulting
Stokes spectra to a well-described spectropolarimeter.

---------------------------------------------------------
Title: On the value of `αAR' from vector magnetograph data -
I. Methods and Caveats
Authors: Leka, K. D.; Skumanich, A.
1999SoPh..188....3L Altcode:
This investigation centers upon the quantifying
magnetic twist by the parameter α, commonly defined as
(∇×Bh)z/Bz=μ0Jz/Bz,
and its derivation from vector magnetograph data. This parameter can
be evaluated at each spatial point where the vector B is measured,
but one may also calculate a single value of α to describe the
active region as a whole, here called 'αAR'. We test
three methods to calculate such a parameter, examine the influence
of data noise on the results, and discuss the limitations associated
with assigning such a quantity. The three methods discussed are
(1) to parameterize the distribution of α(x,y) using moments
of its distribution, (2) to determine the slope of the function
Jz(x,y)=αARBz(x,y) using a
least-squares fit and (3) to determine the value of α for which
the horizontal field from a constant-α force-free solution most
closely matches the observed horizontal magnetic field. The results
are qualitatively encouraging: between methods, the resulting value
of the αARparameter is often consistent to within the
uncertainties, even though the resulting αARcan differ in
magnitude, and in some cases in sign as well. The worst discrepancies
occur when a minimal noise threshold is adopted for the data. When the
calculations are restricted to detections of 3σ or better, there is,
in fact, fair quantitative agreement between the three methods. Still,
direct comparison of different active regions using disparate methods
must be carried out with caution. The discrepancies, agreements, and
overall robustness of the different methods are discussed. The effects
of instrumental limitations (spatial resolution and a restricted
field-of-view) on an active-region αAR, and quantifying
the validity of αAR, are addressed in Paper II (Leka, 1999).

---------------------------------------------------------
Title: On the value of `αAR' from Vector Magnetograph data -
II. Spatial Resolution, Field of View, and Validity
Authors: Leka, K. D.
1999SoPh..188...21L Altcode:
This investigation is the second of two centering on the parameter
α=(∇×Bh)z/Bz=μ0Jz/Bzand
its derivation from photospheric vector magnetogram data. While α can
be evaluated at every spatial position where the vector B is measured,
for many reasons it is useful to determine a single value of α to
parameterize the magnetic complexity of an entire active region,
here called αAR(see Leka and Skumanich, 1999). As such,
the limitations in today's vector magnetograph data, e.g., finite
spatial resolution and limited field of view, may influence any
final 'αAR' value. We apply three methods of calculating
'αAR' to degraded high-spatial-resolution data and find that
in general the discrepancies worsen for decreasing resolution compared
to the original. We apply the three methods to sub-regions centered
on the constituent sunspots for AR 7815. Two of the sub-regions are
shown to have magnetic twist with significant magnitude but opposite
sign. We show by mosaicing or otherwise combining separate sunspot
observations that a measure of αARcan be calculated which
is consistent with a single large field-of-view observation. Still, the
αAR≈0 assigned for the entire active region is an average,
and does not accurately represent the magnetic morphology of this flux
system. To measure the validity of the αARparameterization,
we demonstrate that, from each method, a relevant quantity can be
calculated which describes the 'goodness of fit' of the resulting
αAR. Given the spatial variation of α(x,y) over an active
region, it is suggested that such a second parameter be used either
to indicate uncertainty in αARor as a criterion for data
selection, as appropriate.

---------------------------------------------------------
Title: Understanding Small Solar Magnetic Elements: Comparing Models
and Observations
Authors: Leka, K. D.; Steiner, O.; Grossmann-Doerth, U.
1999AAS...194.5507L Altcode: 1999BAAS...31R.911L
We perform direct comparisons of high-resolution spectropolarimetric
observations with a full MHD model of the magnetized solar
atmosphere. In this manner we investigate the evolution and dynamics of
small magnetic elements by fully utilizing the diagnostics available
with Stokes spectropolarimetry, both computed and observed. The model
is a 2-D time-dependent numerical simulation of a small (~ 600 km
diameter) magnetic feature embedded in a non-magnetized atmosphere
(Steiner et al., 1998). At select time-steps, synthetic emergent
Stokes I and V profiles are computed using a polarized radiation
transfer code. The data consist of Stokes I and V spectra from the
Advanced Stokes Polarimeter for seventeen small magnetic elements
located near disk-center. For both the observed and computed Stokes
spectra, diagnostics are computed including the emergent continuum
intensity, V-crossing shift, and amplitude and area asymmetries of
the V-profile. We find that it is possible to differentiate between
salient processes occurring in the magnetic atmosphere (strong flows,
gradients, etc.) by their spectropolarimetric signature; from this,
we determine the dominant processes present in the observed magnetic
structures. The results are extremely encouraging. We find good
qualitative agreement between the amplitude and area asymmetries
and their spatial variation. Quantitatively, the agreement is
surprisingly good in many cases. While limitations exist for both
the model and observations, this stringent test allows us to comment
on the dynamics and possible evolutionary differences present in the
observed magnetic features. This work is funded in part by NSF grant
ATM-9710782. Reference: - Steiner, O., Grossmann-Doerth, U., Knolker,
M., Schussler, M.: 1998, ApJ 495, 468

---------------------------------------------------------
Title: Stokes profile reconstruction with the imaging vector
magnetograph
Authors: Leka, K. D.; Mickey, D. L.; Labonte, B. J.
1999ASSL..243..305L Altcode: 1999sopo.conf..305L
No abstract at ADS

---------------------------------------------------------
Title: The Evolution of Pores and the Development of Penumbrae
Authors: Leka, K. D.; Skumanich, A.
1998ApJ...507..454L Altcode:
We investigate the evolution of the magnetic field in an emerging
active region near disk center using data from the Advanced Stokes
Polarimeter. Specifically, we follow the formation of a pore from
a radiatively undisturbed region and the formation of a protospot,
i.e., the appearance of a rudimentary penumbral sector for a mature
pore. Our approach is to use the temporal evolution of bivariate
distribution functions correlating continuum intensity, Ic,
magnetic field magnitude, | B |, magnetic fill fraction, f, local
inclination, γ, local azimuth, φ, and line-of-sight Doppler velocity,
vD. The highlights of our results include, (1) in the
pore-forming region, a preference for the relatively strong vertical
field points (1000-1500 G) to be redshifted (downflowing) and the
appearance of dark pore points to be at the expense of radiatively
undisturbed points; (2) an onset flux of ~2 × 1019 Mx
in a dark pore that appears in an area in which the flux increases
by ~1 × 1020 Mx prior to the pore's appearance and that
previously contained an azimuth center, i.e., a magnetic concentration
that otherwise has no continuum-intensity signature; (3) a threshold of
(1-1.5) × 1020 Mx above which a partial penumbra forms; (4)
the appearance of penumbral elements that at once having the appropriate
penumbral range of field strengths, intensities, and inclination
angles, i.e., no obvious gradual increase in the magnetic fields'
inclination with increasing flux during the formation of penumbrae;
(5) no delay between the appearance of inclined penumbral magnetic
fields and the Evershed flow; and (6) a self-similarity between the
pore, protospot, and a small mature sunspot with respect to the (|
B |, Ic), (| B |, γ), (f, γ), and the (vD,
Ic), (vD, γ) distributions.

---------------------------------------------------------
Title: The Vector Magnetic Fields and Thermodynamics of Sunspot Light
Bridges: The Case for Field-free Disruptions in Sunspots: Erratum
Authors: Leka, K. D.
1998ApJ...495..508L Altcode:
In the paper “The Vector Magnetic Fields and Thermodynamics of Sunspot
Light Bridges: The Case for Field-free Disruptions in Sunspots” by
K. D. Leka (<A href="/abs/1997ApJ...484..900">ApJ, 484, 900 [1997]</A>),
the images of the sunspots used in the study (Fig. 1) were too dark
as a result of a printer's error. The figure is reproduced here for
clarity. The variations of the width and brightness of the light
bridges analyzed should now be apparent; the regions of interest
and positions of the artificial spectrograph slit should also now be
clearly visible. No other aspect of the paper was in error, and none
of the conclusions have changed.

---------------------------------------------------------
Title: Some Questions on Emerging Flux Addressable with Synoptic
Observations
Authors: Leka, K. D.
1998ASPC..140...91L Altcode: 1998ssp..conf...91L
No abstract at ADS

---------------------------------------------------------
Title: The Vector Magnetic Fields and Thermodynamics of Sunspot
Light Bridges: The Case for Field-free Disruptions in Sunspots
Authors: Leka, K. D.
1997ApJ...484..900L Altcode:
We present observations with the Advanced Stokes Polarimeter of 11 light
bridges in sunspots of various ages and sizes, all very close to disk
center. Full vector spectropolarimetry and a nonlinear least-squares
inversion algorithm allows us to determine not only the vector magnetic
field in the bridges and host sunspots but also thermodynamic parameters
such as continuum brightness, Doppler shifts, Doppler widths, opacity
ratio, and the source function parameters. We can also separate the
magnetic and nonmagnetic components of the spectral signal within each
resolution element. We find that there is a disruption of the
magnetic fields in light bridges, relative both to neighboring umbrae
and to normal, undisturbed penumbrae. This change takes the form of
lower intrinsic field strength and sparser, more horizontal fields in
the bridges relative to umbrae. The magnetic fields in the bridges
remain more vertically oriented, however, than those in undisturbed
penumbra. There are systematic upflows observed in the bridge plasma
relative to the neighboring umbrae, and the evidence points toward a
component that is heated and departs from radiative equilibrium. In four cases, we follow a light bridge over several days and find
that as the bridges age, they grow wider and brighter, the fields
weaken and become sparser, and the heating increases. We also find
some evidence that the magnetic field begins to reorganize itself
to accommodate the (now) two azimuth centers before there are strong
signals of a light bridge in the thermodynamic parameters. This
paper presents the first systematic look at sunspot light bridges with
full vector polarimetry and thermodynamic determination. The results
show that there is an intrusion of field-free, possibly convective
material into an otherwise stable, magnetic sunspot. The departure
from stability is seen in the magnetic field orientation prior to its
appearance in continuum intensity, and the effects of this disruption
are evident beyond the immediate umbral intrusion. The results do not
unambiguously determine the physical mechanism that makes sunspots
disappear. However, it strongly points toward a ropelike magnetic
structure through which convection may penetrate when the magnetic
fibrils separate or around which field-free plasma may flow. The
appearance of field-free heated material is likely an effect, not the
cause, of the sunspot light bridges.

---------------------------------------------------------
Title: On the Development of a Sunspot Penumbra
Authors: Leka, K. D.; Skumanich, A.
1997SPD....28.1702L Altcode: 1997BAAS...29Q.921L
Using data from the Advanced Stokes Polarimeter, we follow the
development of a rudimentary penumbra around a small pore. A sub-hourly
cadence coupled with the full vector spectro-polarimetry and non-linear
least-squares inversion algorithm allows us to determine not only
the vector magnetic field around the pore, but also thermodynamic
parameters and Doppler shifts. We find that a penumbra forms not by a
gradual “tilting” of the field lines, but by the initial appearance
of weaker fields at all inclinations. The distribution of these fields
is sparse, but grows with time to where a fully-populated range of
field strengths and inclination angles is present (as is common for
fully-developed sunspots). At the same time, the range of Doppler
velocities increases in the lower-field-strength areas. This implies
that any difference between the start of the Evershed flow and the
appearance of more inclined fields is small (less than half-hour). We
will discuss these results and their relation to the flux history of
this pore, comparing it to a nearby region in which a penumbra-less
pore develops from apparent quiet-sun.

---------------------------------------------------------
Title: Erratum: "The imaging vector magnetograph at Haleakala"
[Sol. Phys., Vol. 168, No. 2, p. 229 - 250 (Oct 1996)].
Authors: Mickey, D. L.; Canfield, R. C.; Labonte, B. J.; Leka, K. D.;
Waterson, M. F.; Weber, H. M.
1997SoPh..170..455M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Imaging Vector Magnetograph at Haleakala
Authors: Mickey, D. L.; Canfield, R. C.; LaBonte, B. J.; Leka, K. D.;
Waterson, M. F.; Weber, H. M.
1996SoPh..168..229M Altcode:
We describe an instrument we have built and installed at Mees Solar
Observatory on Haleakala, Maui, to measure polarization in narrow-band
solar images. Observations in Zeemansensitive photospheric lines have
been made for nearly all solar active regions since the instrument
began operations in 1992. The magnetograph includes a 28-cm aperture
telescope, a polarization modulator, a tunable Fabry-Pérot filter,
CCD cameras and control electronics. Stokes spectra of a photospheric
line are obtained with 7 pm spectral resolution, 1 arc sec spatial
resolution over a field 4.7 arc min square, and polarimetric precision
of 0.1%. A complete vector magnetogram observation can be made every
eight minutes. The flexibility of the instrument encourages diverse
observations: besides active region magnetograms we have made, for
example, composite vector magnetograms of the full solar disk, and
Hα polarization movies of flaring regions.

---------------------------------------------------------
Title: H alpha Surges and X-Ray Jets in AR 7260
Authors: Canfield, Richard C.; Reardon, Kevin P.; Leka, K. D.; Shibata,
K.; Yokoyama, T.; Shimojo, M.
1996ApJ...464.1016C Altcode:
We discuss nine events, observed simultaneously as jets in X-rays and
surges in Hα, which are associated with moving magnetic bipoles. The
X-ray jets share many features with those discovered by Yohkoh in active
regions, emerging flux regions, and X-ray bright points (see paper by
Shibata et al.); in particular, they originate near one end of a pair of
small flaring loops. The Hα surges are adjacent to the X-ray jets. At
the bases of these surges we observe both blueshifts (initially) and
redshifts (1-2 minutes later). All the observed surges spin in a sense
consistent with the relaxation of the twist stored in the magnetic
fields of the moving magnetic bipoles. Newly discovered phenomena
include footpoint convergence and moving-blueshift features. We develop a model of the role of magnetic reconnection in these
events. This model explains the temporal and spatial relationship
between the jets and surges, the role of the moving bipoles, the
flaring X-ray loops and their converging Hα footpoints, the Hα
moving-blueshift features, the direction and amount of spin of the
surges, and the relative temporal development of the Hα redshifts
and blueshifts.

---------------------------------------------------------
Title: The New Emerging Flux Paradigm
Authors: Leka, K. D.
1996AAS...188.3301L Altcode: 1996BAAS...28..867L
A new paradigm is emerging concerning the formation, evolution,
and influence of solar magnetic features. It had long been pictured
that magnetic flux emerged with a simple potential magnetic field
structure, evolved by coalescing pores, and then finally disintegrated
and dispersed in to the surrounding photosphere. If a sunspot region
displayed 'whorls' or magnetic shear, the shear was thought to be
brought on by the turbulent surface motions, and subsequently released
during flares. In the past five years it has become necessary to dismiss
this simple picture. Building on early observations of sunspot helicity,
erupting prominences and flaring active regions, and on cartoon ideas
of twisted flux tubes, there is recent strong observational support
for a new paradigm. The notions of simple potential Omega -loops
of magnetic flux and shearing surface flows are giving way to the
idea that non-potential magnetic flux is systematically generated
in the solar interior and transported to the surface where we see it
as current-carrying sunspot groups, non-force-free magnetic fields,
helical filament structures and self-reversed magnetic clouds. Indeed,
the picture of magnetic fields being confined only to large easily
observable features such as plage fields, sunspots, and filaments has
been shifted to a view that magnetic flux is pervasive, and abundant
on small size scales. The new paradigm is coherent, but of course some
gaps in the old picture are replaced with new puzzles. There is, of
course, scatter and disagreement amongst the observational results. The
cause of the systematic helicities is now below an easily observable
regime. And the simple notion of flux dispersion now must make room
for helicity conservation, flux expulsion into the solar atmosphere,
and the conflicting results concerning magnetic field reconfiguration
in the context of solar flares. I will review the puzzle and show how
the new view of the magnetic sun has evolved. I will outline the key
new observational results as well as highlight missing pieces; and
I'll review how, with the orchestra of ground-based and space-based
instruments, we are in an unprecedented position to both fill some of
the gaps and rigorously test this new paradigm of solar physics.

---------------------------------------------------------
Title: Evidence for Current-carrying Emerging Flux
Authors: Leka, K. D.; Canfield, R. C.; McClymont, A. N.; van
Driel-Gesztelyi, L.
1996ApJ...462..547L Altcode:
To determine the relationship between electric currents and magnetic
flux in emerging sunspots, we use observations of the morphology,
proper motion, magnetic flux, and currents associated with several
well-observed growing bipoles. Our target was NOAA Active Region 7260,
which included a preexisting large spot and a fast-growing area of new
magnetic flux. Magnetic bipoles in this region are well documented
by X-ray images from the Yohkoh spacecraft and optical images and
vector magnetograms from several ground-based observatories. In
this paper we show that (1) the Hα and X-ray structures associated
with these bipoles do not agree with potential-field extrapolations
of magnetograms; (2) proper motions imply that the flux bundles that
make up these new bipoles are twisted before they emerge; (3) these
new bipoles are cospatial with significant vertical electric currents;
(4) the morphology, proper motion, and measured currents of these
bipoles all imply the same sense of twist; (5) this sense of twist
is the same as the large-scale twist of the preexisting large spot;
and (6) the increase of these currents, as new flux emerges, is not
consistent with their generation by photospheric motions. We
conclude that the new magnetic flux that emerged in this active region
carried currents generated below the photosphere.

---------------------------------------------------------
Title: Small-Scale Horizontal Magnetic Fields in the Solar Photosphere
Authors: Lites, B. W.; Leka, K. D.; Skumanich, A.; Martinez Pillet,
V.; Shimizu, T.
1996ApJ...460.1019L Altcode:
We present recent observations of quiet regions near the center
of the solar disk using the Advanced Stokes Polarimeter. These
observations reveal a component of the solar magnetic field heretofore
unobserved: isolated, small-scale (typically 1"-2" or smaller),
predominantly horizontal magnetic flux structures in the solar
photosphere. These features occur in isolation of the well-known,
nearly vertical flux concentrations usually seen in the photospheric
"network." Hence we ascribe this horizontal flux to the photospheric
"internetwork." They reveal themselves by the distinct signature
of the Stokes Q and U polarization profiles, which are symmetric
about the line center. The polarization signals are weak, with peak
amplitudes typically ∼0.1%-0.2% of the continuum intensity in the
resolved spectral profiles, but they are well above the noise level
of these observations (≍0.05%). Such magnetic fields are weak
(significantly less than 1000 G) and largely horizontal owing to
the absence, or near absence, of accompanying Stokes V polarization
when observed at the center of the solar disk. These horizontal field
elements are often associated with blueshifted Stokes line profiles,
and they often occur between regions of opposite polarity (but weak)
Stokes V profiles. The horizontal elements are short-lived, typically
lasting ∼5 minutes. Our observations suggest that we are viewing the
emergence of small, concentrated loops of flux, carried upward either
by granular convection or magnetic buoyancy. Even though these entities
show weak field strengths, they also seem to be fairly common, implying
that they could carry the order of 1024 Mx of magnetic flux
to the surface on a daily basis. However, further observational study
is needed to identify the specific nature of this phenomenon.

---------------------------------------------------------
Title: Emerging flux and flares in NOAA 7260
Authors: Nitta, N.; van Driel-Gesztelyi, L.; Leka, K. D.; Shibata, K.
1996AdSpR..17d.201N Altcode: 1996AdSpR..17..201N
We have studied the relation between flux emergence and flare
activity in the active region NOAA 7260, using images from the Soft
X-ray Telescope aboard the Yohkoh spacecraft and other supporting
ground-based data. It is found that microflares start around the time
of flux emergence as recorded in white-light data, which generally
precedes a major flare by several hours. We interpret the microflares as
due to fast reconnection that takes place intermittently in the slow
reconnection stage while more energy is accumulated in preparation
for a larger flare.

---------------------------------------------------------
Title: H alpha Surges and X-ray Jets in AR7260
Authors: Canfield, R. C.; Reardon, K. P.; Leka, K. D.; Shibata, K.;
Yokoyama, T.; Shimojo, M.
1996mpsa.conf...49C Altcode: 1996IAUCo.153...49C
No abstract at ADS

---------------------------------------------------------
Title: Active Region Evolution and Flare Activity
Authors: Nitta, N.; van Driel-Gesztelyi, L.; Leka, K. D.; Hudson, H. S.
1996mpsa.conf..515N Altcode: 1996IAUCo.153..515N
No abstract at ADS

---------------------------------------------------------
Title: Small scale horizontal magnetic fields in the solar photosphere
Authors: Leka, K. D.; Lites, B. W.; Skumanich, A.; Martínez Pillet,
V.; Shimizu, T.
1995IAUS..176P.120L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Are Solar Emerging Flux Regions Carrying Electric Current?
Authors: Leka, Kimberly Dawn
1995PhDT..........L Altcode: 1995PhDT.......274L
Flare-productive active regions exhibit non-potential magnetic field
structures, oft described as 'sheared' or 'twisted' fields. This
morphology indicates that electric currents are present. In this thesis
I test whether surface flows generate observed active-region currents,
or whether these currents are produced prior to their appearance at
the surface as sunspots, i.e., deep in the solar convection zone. To
study this question I observed emerging magnetic flux in a uniquely
rapidly growing active region. First I undertook an exhaustive study of
the more than 50 bipoles which appeared in a sunspot group visible in
August 1992. I determined the time of emergence, magnetic connectivity
and patterns of overall development of this young active region. Then,
four independent analysis methods were used to determine whether the
emerging flux was carrying the electric current prior to its appearance,
or if the observed strong currents were generated by plasma flows in
the photosphere. The four approaches gave consistent results. For
a few young bipoles, I show that the morphology of chromospheric
and coronal loops were definitively non-potential, that those same
dipoles had proper motions which reflected twisted subsurface flux
bundles, that electric current existed in greater abundance than could
be generated given the observed characteristics and finally that the
electric current increased as the magnetic flux itself increased with no
substantial delay. All evidence was also consistent with a direction of
twist defined by J_ {z}/Bz &lt; 0. This twist direction was
also present in the older flux of this active region. I conclude that
the electric currents observed in this solar active region were not
produced by plasma motions in the photosphere. Rather, the evidence
presented in this thesis supports the hypothesis that active region
electric currents are generated either deep in the convection zone or
are produced with solar magnetic fields in a dynamo process.

---------------------------------------------------------
Title: The Magnetic Evolution of the Activity Complex AR:7260 -
a Roadmap
Authors: Leka, K. D.; Canfield, R. C.; Mickey, D. L.; van
Driel-Gesztelyi, L.; Nitta, N.; Sakurai, T.; Ichimoto, K.
1994SoPh..155..301L Altcode:
The active region NOAA 7260 rotated onto the north solar hemisphere
as a mature bipole: a dominant negative-polarity sunspot with trailing
plage and scattered small spots in attendance. The dominantp spot itself
had strong magnetic fields and covered almost 400 × 10−6
of a solar hemisphere. For a period of seven days beginning 14 August,
1992 this active region displayed rapid and drastic evolution: no fewer
than 50 magnetic bipoles emerged in the area trailing the large sunspot,
increasing the region's magnetic flux by more than 1022
Mx. This new group of sunspots formed a complexβγδ configuration
with twoδ spots and a high degree of magnetic shear.

---------------------------------------------------------
Title: Flares in Active Region NOAA 7260 - Role of Emerging Flux
Authors: Nitta, N.; Driel-Gesztelyi, L. V.; Leka, K. D.; Mickey, D. L.;
Metcalf, T. R.; Wuelser, J. -P.; Ichimoto, K.; Sakurai, T.; Shibata, K.
1994kofu.symp..385N Altcode:
Active region NOAA 7260 exhibited remarkable flare activity as an
emerging flux region appeared in the following part and evolved into
the delta configuration. While it is difficult to associate an emerging
bipole with a flare both temporally and spatially, there is an overall
correlation of the total darkness integrated over of the sunspot area,
as measured in the Yohkoh/SXT white-light images, with the soft X-ray
flux and flare occurrence. It appears that the flares in the emerging
flux region occurred preferentially at locations close to the spot of
preceding polarity that emerged in the earliest evolution of the region.

---------------------------------------------------------
Title: A Purely Polarized S-Component at 17 GHz
Authors: Shibasaki, Kiyoto; Enome, Shinzo; Nakajima, Hiroshi; Nishio,
Masanori; Takano, Toshiaki; Hanaoka, Yoichiro; Torii, Chikayoshi;
Sekiguchi, Hideaki; Kawashima, Susumu; Bushimata, Takeshi; Shinohara,
Noriyuki; Koshiishi, Hideki; Shiomi, Yasuhiko; Irimajiri, Yoshihisa;
Leka, K. D.; Canfield, Richard C.
1994PASJ...46L..17S Altcode:
A purely polarized bright radio source was found at 17 GHz by the
Nobeyama Radioheliograph. This source was associated with a large
sunspot. The source structure of this S-component was resolved due to
high spatial resolution of the radioheliograph. A soft X-ray image of
this active region taken by Yohkoh Satellite shows no counterpart for
the radio source. Emission mechanism of the radio source is identified
as gyroresonance. Magnetic field of the sunspot was measured by the
Haleakala Vector Magnetograph at Mees Solar Observatory. The field
strength at the half power level of the radio source was 2000 gauss
at the photospheric level. This corresponds to the third harmonic
layer. A bright soft X-ray loop, whose footpoint is at the penumbra
of the large sunspot, can also be seen in the radio map. This loop
is strongly curved, to form a part of spiral, which reflects strong
electric current. Vector magnetogram shows strong rotation of the
transverse field in the sunspot, which also corresponds to strong
electric current. Due to this current and also to the density and the
temperature enhancement near the X-ray loop, the radio peak is shifted
toward the loop and has no dip.

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Title: Evidence for Twisted Emerging Flux in NOAA AR 7260
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Canfield, R. C.
1994ASPC...68..145L Altcode: 1994sare.conf..145L
No abstract at ADS

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Title: Diagnostics of Twisted Flux Emergence (noaa AR7260)
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Anwar, B.; Canfield,
R. C.; Hudson, H. S.; Metcalf, T. R.; Mickey, D. L.; Nitta, N.;
Kurokawa, H.
1994xspy.conf...25L Altcode:
No abstract at ADS

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Title: Flares in Active Region NOAA 7260
Authors: Nitta, N.; van Driel-Gesztelyi, L.; Leka, K. D.; Sakurai,
T.; Shibata, K.; Ichimoto, K.; Canfield, R. C.; Wülser, J. -P.;
Metcalf, T. R.; Mickey, D. L.
1994xspy.conf..111N Altcode:
No abstract at ADS

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Title: Emerging Flux Tube Geometry and Sunspot Proper Motions
Authors: van Driel-Gesztelyi, L.; Leka, K. D.
1994ASPC...68..138V Altcode: 1994sare.conf..138V
No abstract at ADS

---------------------------------------------------------
Title: The Morphology of Flare Phenomena, Magnetic Fields, and
Electric Currents in Active Regions. I. Introduction and Methods
Authors: Canfield, Richard C.; de La Beaujardiere, J. -F.; Fan,
Yuhong; Leka, K. D.; McClymont, A. N.; Metcalf, Thomas R.; Mickey,
Donald L.; Wuelser, Jean-Pierre; Lites, Bruce W.
1993ApJ...411..362C Altcode:
Electric current systems in solar active regions and their spatial
relationship to sites of electron precipitation and high-pressure
in flares were studied with the purpose of providing observational
evidence for or against the flare models commonly discussed in the
literature. The paper describes the instrumentation, the data used, and
the data analysis methods, as well as improvements made upon earlier
studies. Several flare models are overviewed, and the predictions
yielded by each model for the relationships of flares to the vertical
current systems are discussed.

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Title: The Morphology of Flare Phenomena, Magnetic Fields, and
Electric Currents in Active Regions. II. NOAA Active Region 5747
(1989 October)
Authors: Leka, K. D.; Canfield, Richard C.; McClymont, A. N.; de La
Beaujardiere, J. -F.; Fan, Yuhong; Tang, F.
1993ApJ...411..370L Altcode:
The paper describes October 1989 observations in NOAA Active Region 5747
of the morphology of energetic electron precipitation and high-pressure
coronal flare plasmas of three flares and their relation to the
vector magnetic field and vertical electric currents. The H-alpha
spectroheliograms were coaligned with the vector magnetograms using
continuum images of sunspots, enabling positional accuracy of a few
arcsec. It was found that, during the gradual phase, the regions of
the H-alpha flare that show the effects of enhanced pressure in the
overlying corona often encompass extrema of the vertical current
density, consistent with earlier work showing a close relationship
between H-alpha emission and line-of-sight currents. The data are
also consistent with the overall morphology and evolution described
by erupting-filament models such as those of Kopp and Pneuman (1976)
and Sturrock (1989).

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Title: The Morphology of Flare Phenomena, Magnetic Fields, and
Electric Currents in Active Regions. III. NOAA Active Region 6233
(1990 August)
Authors: de La Beaujardiere, J. -F.; Canfield, Richard C.; Leka, K. D.
1993ApJ...411..378D Altcode:
We investigate the spatial relationship between vertical electric
currents and flare phenomena in NOAA Active Region 6233, which
was observed 1990, August 28-31 at Mees Solar Observatory. The two
flares studied are the 1N/M1.8 flare on August 28, 22:30 UT and the
1N/M1.6 flare on August 29, 20:35 UT. Using Stokes polarimetry we
make magnetograms of the region and compute the vertical current
density. Using H-alpha imaging spectroscopy we identify sites
of intense nonthermal electron precipitation or of high coronal
pressure. The precipitation in these flares is barely strong enough
to be detectable. We find that both precipitation and high pressure
tend to occur near vertical currents, but that neither phenomenon
is cospatial with current maxima. In contrast with the conclusion
of other authors, we argue that these observations do not support a
current-interruption model for flares, unless the relevant currents are
primarily horizontal. The magnetic morphology and temporal evolution of
these flares suggest that an erupting filament model may be relevant,
but this model does not explicitly predict the relationship between
precipitation, high pressure, and vertical currents.

---------------------------------------------------------
Title: Evidence for Twisted Emerging Flux: NOAA AR 7260
Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Canfield, R. C.; Anwar,
B.; Metcalf, T. R.; Mickey, D. L.; Nitta, N.
1993BAAS...25R1187L Altcode:
No abstract at ADS

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Title: Flares in Active Region NOAA 7260 - Role of Emerging Flux
and Reconnection
Authors: Nitta, N.; Drel-Gesztelyi, L. V.; Leka, K. D.; Mickey, D. L.;
Metcalf, T. R.; Wuelser, J. -P.; Ichimoto, K.; Sakurai, T.; Shibata, K.
1993BAAS...25.1223N Altcode:
No abstract at ADS

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Title: Joint vector magnetograph observations at BBSO, Huairou
Station and Mees Solar Observatory
Authors: Wang, Haimin; Varsik, John; Zirin, Harold; Canfield, Richard
C.; Leka, K. D.; Wang, Jingxiu
1992SoPh..142...11W Altcode:
Joint vector magnetograph observations were carried out at Big Bear
Solar Observatory (BBSO), Huairou Solar Observing Station (Huairou),
and Mees Solar Observatory (MSO) in late September 1989. Comparisons of
vector magnetograms obtained at the three stations show a high degree
of consistency in the morphology of both longitudinal and transverse
fields. Quantitative comparisons show the presence of noise, cross-talk
between longitudinal field and transverse field, Faraday rotation
and signal saturation effects in the magnetograms. We have tried to
establish how the scatter in measurements from different instruments
is apportioned between these sources of error.

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Title: The X Flare of 1991 November 15: Coordinated Mees/Yohkoh
Observations
Authors: Canfield, Richard C.; Hudson, Hugh S.; Leka, K. D.; Mickey,
Donald L.; Metcalf, Thomas R.; Wuelser, Jean-Pierre; Acton, Loren W.;
Strong, Keith T.; Kosugi, Takeo; Sakao, Taro; Tsuneta, Saku; Culhane,
J. Leonard; Phillips, Andrew; Fludra, Andrzej
1992PASJ...44L.111C Altcode:
This is a preliminary report on two unique new results from coordinated
observations at Mees Solar Observatory and Yohkoh of the X1.5 flare
of 1991 November 15, using vector magnetograms, Hα imaging spectra,
X-ray images, and X-ray spectra. First, we find a close spatial
relationship between Hα redshifts and X-rays from a flare loop and
its footpoints at a time of large X-ray blueshifts. Second, we find
that impulsive-phase hard X-rays originate in regions that are near,
but not coincident with, the peaks of the vertical electrical current
density distribution in AR 6919.

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Title: The Diffuse Interstellar Bands. VIII. New Features between
6000 and 8650 Angstrom
Authors: Herbig, G. H.; Leka, K. D.
1991ApJ...382..193H Altcode:
Twenty-two new diffuse interstellar bands (DIBs) have been discovered on
high signal-to-noise Reticon scans of reddened O- and B-type stars in
the 5840-8650 A region, with special attention being given to HD 183143
(B7 Ia). Most of the new DIBs occur in regions masked by atmospheric O2
and H2O. Attempts to find DIBs at positions expected for a transition in
the (hypothetical) spectrum of interstellar H(-), and at wavelengths of
lines in the laboratory spectrum of Cr(3+):MgO, were inconclusive. A
systematic search was made in the wavenumbers of the 105 DIBs now
known for vibrational sequences of the type 0 to v-prime; none of
those found are very convincing. The large number of DIBs now known,
far more than would be expected in the spectrum of a single species
at interstellar temperatures, must mean that a substantial number of
different carriers are responsible for the DIB spectrum.

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Title: Flare Energy Release: Observational Consequences and Signatures
Authors: Canfield, Richard C.; de La Beaujardiere, J. -F.; Leka, K. D.
1991RSPTA.336..381C Altcode:
It is generally accepted, but not yet compellingly demonstrated, that
the energy released in solar flares is stored in stressed magnetic
fields. Little is known, at present, about how the most obvious
manifestations of flare energy release - heating, mass motion, magnetic
field reconfiguration and particle acceleration - are related to the
spatial distribution of free energy within those fields. To address
this issue we have underway at Mees Solar Observatory a programme of
simultaneous polarimetric and spectroscopic observations that allow
us to explore the spatial relation between active region currents,
flare particle acceleration and flare heating. In this paper we
discuss several days observations of two flare-productive active
regions. By using the Haleakala Stokes polarimeter, we observed
the spatial distribution of the Stokes profiles of two photospheric
FeI lines, from which we inferred the spatial distribution
of the vector magnetic field and the vertical current density. In
flares that were observed on the same days, we then compared the
locations of vertical currents to the sites of non-thermal electron
precipitation and high coronal pressure inferred from Hα line profiles
and spectroheliograms obtained with the Mees charge coupled device
imaging spectrograph. Without exception we found that the sites of
significant energetic electron precipitation into the chromosphere
were at the edges of regions of vertical current, not within them. In
contrast, we found that the footpoints of high-pressure flare plasmas
during the main phase of the observed flares all coincided very well
with such currents.

---------------------------------------------------------
Title: The Magnetic Morphology of High-Pressure Plasmas in Three
October 1989 (AR5747) Flares
Authors: Leka, K. D.; Canfield, R. C.
1991BAAS...23.1066L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Flare energy release: observational consequences and
signatures.
Authors: Canfield, R. C.; de La Beaujardiere, J. -F.; Leka, K. D.
1991psf..conf..381C Altcode:
At Mees Solar Observatory a programme is underway of simultaneous
polarimetric and spectroscopic observations that allow to explore
the spatial relation between active region currents, flare particle
acceleration and flare heating. The authors discuss several days
observations of two flare-productive active regions. They compared the
locations of vertical currents to the sites of non-thermal electron
precipitation and high coronal pressure inferred from Hα line profiles
and spectroheliograms. Without exception they found that the sites
of significant energetic electron precipitation into the chromosphere
were at the edges of regions of vertical current, not within them. In
contrast, they found that the footpoints of high-pressure flare plasmas
during the main phase of the observed flares all coincided very well
with such currents.

---------------------------------------------------------
Title: Magnetic Morphology of Nonthermal Electron Precipitation
During Three Flares in a Highly Nonpotential Active Region
Authors: Canfield, Richard C.; Leka, K. D.; Wülser, Jean-Pierre
1991LNP...387...96C Altcode: 1991fpsa.conf...96C
NOAA Active region 5747, during its October 1989 transit across
the solar disk, showed highly nonpotential photospheric vector
magnetic field structure and produced many solar flares, three of
which we observed at Mees Solar Observatory. After resolution of
the 180° ambiguity, we determined the photospheric distribution of
the vertical current density. We then compared the locations of the
major current systems to sites of nonthermal electron precipitation
inferred from H profiles of three flares observed using the Mees CCD
Imaging Spectrograph. We found that the sites of energetic electron
precipitation are at the edges of these currents, not at their peaks.

---------------------------------------------------------
Title: The Magnetic Morphology of Chromospheric Particle Precipitation
in Three October 1989 (AR 5747) Flares
Authors: Leka, K. D.; Canfield, R. C.; Wülser, J. -P.; Fan, Y.
1990BAAS...22..824L Altcode:
No abstract at ADS