Author name code: leka ADS astronomy entries on 2022-09-14 author:"Leka, Kimberly Dawn" ------------------------------------------------------------------------ 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. Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. Title: Constraining stellar CMEs by solar observations Authors: Leitzinger, Martin; Odert, Petra; Leka, K. D.; Heinzel, Petr; Dissauer, Karin Bibcode: 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. 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. Bibcode: 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 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. Bibcode: 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 & 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. 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. Bibcode: 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. Title: Eruptivity in Solar Flares: The Challenges of Magnetic Flux Ropes Authors: Lin, Pei Hsuan; Kusano, Kanya; Leka, K. D. Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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., <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. 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. Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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. Title: On Measuring Divergence for Magnetic Field Modeling Authors: Gilchrist, S. A.; Leka, K. D.; Barnes, G.; Wheatland, M. S.; DeRosa, M. L. Bibcode: 2020ApJ...900..136G Altcode: 2020arXiv200808863G A physical magnetic field has a divergence of zero. Numerical error in constructing a model field and computing the divergence, however, introduces a finite divergence into these calculations. A popular metric for measuring divergence is the average fractional flux $\left\langle | {f}_{i}| \right\rangle $ . We show that $\left\langle | {f}_{i}| \right\rangle $ scales with the size of the computational mesh, and may be a poor measure of divergence because it becomes arbitrarily small for increasing mesh resolution, without the divergence actually decreasing. We define a modified version of this metric that does not scale with mesh size. We apply the new metric to the results of DeRosa et al., who measured $\left\langle | {f}_{i}| \right\rangle $ for a series of nonlinear force-free field models of the coronal magnetic field based on solar boundary data binned at different spatial resolutions. We compute a number of divergence metrics for the DeRosa et al. data and analyze the effect of spatial resolution on these metrics using a nonparametric method. We find that some of the trends reported by DeRosa et al. are due to the intrinsic scaling of $\left\langle | {f}_{i}| \right\rangle $ . We also find that different metrics give different results for the same data set and therefore there is value in measuring divergence via several metrics. Title: 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 Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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. 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. Bibcode: 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. Title: Pathways to Coronal Magnetic Energy Storage in The NOAA AR11283 Authors: Cavins, A.; Barnes, G.; Leka, K. D.; Gilchrist, S. A. Bibcode: 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. Title: Realities, Challenges, and Innovation for Solar Flare Forecasting Authors: Leka, K. D. Bibcode: 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. Title: The How and Why of Big Solar Flares Authors: Isola, B.; Barnes, G.; Leka, K. D.; Gilchrist, S. A. Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Title: Effects of particular smoothing processes for global synoptic maps on PFSS solutions Authors: Hayashi, Keiji; Leka, K. D.; Barnes, G. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 '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 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 & 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 & 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. Bibcode: 2012ASPC..455..337L Altcode: The Helioseismic and Magnetic Imager (HMI; Scherrer & Schou 2011) is one of the three instruments aboard the Solar Dynamics Observatory (SDO) that was launched on February 11, 2010 from Cape Canaveral, Florida. The instrument began to acquire science data on March 24. The regular operations started on May 1. HMI measures the Doppler velocity and line-of-sight magnetic field in the photosphere at a cadence of 45 seconds, and the vector magnetic field at a 135-second cadence, with a 4096× 4096 pixels full disk coverage. The vector magnetic field data is usually averaged over 720 seconds to suppress the p-modes and increase the signal-to-noise ratio. The spatial sampling is about 0".5 per pixel. HMI observes the Fe i 6173 Å absorption line, which has a Landé factor of 2.5. These data are further used to produce higher level data products through the pipeline at the HMI-AIA Joint Science Operations Center (JSOC) - Science Data Processing (Scherrer et al. 2011) at Stanford University. In this paper, we briefly describe the data products, and demonstrate the performance of the HMI instrument. We conclude that the HMI is working extremely well. Title: Modeling and Interpreting the Effects of Spatial Resolution on Solar Magnetic Field Maps Authors: Leka, K. D.; Barnes, G. Bibcode: 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. Bibcode: 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 & 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 & 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 & 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 & Metcalf 2003; Metcalf Leka & 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 & 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Title: Chromospheric Vector Magnetic Field Measurements of Active Regions Authors: Leka, K. D. Bibcode: 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. Title: Predicting Coronal Emissions with Multiple Heating Rates Authors: Lundquist, L. L.; Fisher, G. H.; Leka, K. D.; Metcalf, T. R.; McTiernan, J. M. Bibcode: 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. Title: Another Piece of the Elephant: Chromospheric Vector Field Observations Authors: Leka, K. D.; Metcalf, T. R.; Mickey, D. L. Bibcode: 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. Title: Magnetic Free Energy in NOAA Active Region 10486 on 2003 October 29 Authors: Metcalf, Thomas R.; Leka, K. D.; Mickey, D. L. Bibcode: 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. Bibcode: 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 & Barnes 2003a). We also showed that with Discriminant Analysis (Leka & 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. Title: Inferring a Photospheric Velocity Field from a Sequence of Vector Magnetograms: The Minimum Energy Fit Authors: Longcope, D.; Leka, K. D. Bibcode: 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''. 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. Bibcode: 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. Title: The Magnetic Free Energy in AR0486 Authors: Metcalf, T. R.; Leka, K. D.; Mickey, D. L. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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 & Barnes. Title: Photospheric Magnetic Field Properties of Flaring versus Flare-quiet Active Regions. II. Discriminant Analysis Authors: Leka, K. D.; Barnes, G. Bibcode: 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 & 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 & 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. Title: Effects of `Seeing' on Vector Magnetograph Measurements Authors: Leka, K. D.; Rangarajan, K. E. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1999SoPh..188....3L Altcode: This investigation centers upon the quantifying magnetic twist by the parameter α, commonly defined as (∇×Bh)z/Bz0Jz/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. Bibcode: 1999SoPh..188...21L Altcode: This investigation is the second of two centering on the parameter α=(∇×Bh)z/Bz0Jz/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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 (ApJ, 484, 900 [1997]), 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1995IAUS..176P.120L Altcode: No abstract at ADS Title: Are Solar Emerging Flux Regions Carrying Electric Current? Authors: Leka, Kimberly Dawn Bibcode: 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 < 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Title: Evidence for Twisted Emerging Flux in NOAA AR 7260 Authors: Leka, K. D.; van Driel-Gesztelyi, L.; Canfield, R. C. Bibcode: 1994ASPC...68..145L Altcode: 1994sare.conf..145L No abstract at ADS 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. Bibcode: 1994xspy.conf...25L Altcode: No abstract at ADS 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. Bibcode: 1994xspy.conf..111N Altcode: No abstract at ADS Title: Emerging Flux Tube Geometry and Sunspot Proper Motions Authors: van Driel-Gesztelyi, L.; Leka, K. D. Bibcode: 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. Bibcode: 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. 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. Bibcode: 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). 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. Bibcode: 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. Bibcode: 1993BAAS...25R1187L Altcode: No abstract at ADS 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. Bibcode: 1993BAAS...25.1223N Altcode: No abstract at ADS 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 Bibcode: 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. 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 Bibcode: 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. Title: The Diffuse Interstellar Bands. VIII. New Features between 6000 and 8650 Angstrom Authors: Herbig, G. H.; Leka, K. D. Bibcode: 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. Title: Flare Energy Release: Observational Consequences and Signatures Authors: Canfield, Richard C.; de La Beaujardiere, J. -F.; Leka, K. D. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1990BAAS...22..824L Altcode: No abstract at ADS