Author name code: barnes ADS astronomy entries on 2022-09-14 =author:"Barnes, G." -aff:"NASA" ------------------------------------------------------------------------ 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: 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: 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: 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: 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: 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: Photospheric Magnetic Field Properties of Flaring vs. Flare-quiet active regions, V: Results from HMI Authors: Leka, KD; Barnes, G. Bibcode: 2018csc..confE..87L Altcode: What constitutes the difference between those solar active regions that produce energetic events and those that do not? The answer no doubt lies in the state and ongoing evolution of the magnetic field. Extending this series of studies of the photospheric magnetic field as related to flare imminency, we consider daily evaluations of almost all HMI Active Region Patches (HARPS), including temporal evolution. Using the NWRA Classification Infrastructure based on NonParametric Discriminant Analysis, we evaluate not only the static characterization of the photospheric field (extending well beyond the SHARP parameters) but include coronal topology and time-series considerations, as well. Additionally, we extend the analysis beyond "global" parametrizations to describe sub-area sites which may play roles in coronal energization and event triggering. We report here on those parametrizations which best distinguish imminent flaring from imminent quiet sunspot groups. 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: 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: A Fixed-point Scheme for the Numerical Construction of Magnetohydrostatic Atmospheres in Three Dimensions Authors: Gilchrist, S. A.; Braun, D. C.; Barnes, G. Bibcode: 2016SoPh..291.3583G Altcode: 2016arXiv160900733G; 2016SoPh..tmp..182G Magnetohydrostatic models of the solar atmosphere are often based on idealized analytic solutions because the underlying equations are too difficult to solve in full generality. Numerical approaches, too, are often limited in scope and have tended to focus on the two-dimensional problem. In this article we develop a numerical method for solving the nonlinear magnetohydrostatic equations in three dimensions. Our method is a fixed-point iteration scheme that extends the method of Grad and Rubin (Proc. 2nd Int. Conf. on Peaceful Uses of Atomic Energy31, 190, 1958) to include a finite gravity force. We apply the method to a test case to demonstrate the method in general and our implementation in code in particular. 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: Fractionated (Martian) Noble Gases — EFA, Experiments and Meteorites Authors: Schwenzer, S. P.; Barnes, G.; Bridges, J. C.; Bullock, M. A.; Chavez, C. L.; Filiberto, J.; Herrmann, S.; Hicks, L. J.; Kelley, S. P.; Miller, M. A.; Moore, J. M.; Ott, U.; Smith, H. D.; Steer, E. D.; Swindle, T. D.; Treiman, A. H. Bibcode: 2016LPICo1921.6099S Altcode: Noble gases are tracers for physical processes, including adsorption, dissolution and secondary mineral formation. We examine the Martian fractionated atmosphere through literature, terrestrial analogs and experiments. 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: 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: 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: 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: 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: 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: 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: Topology of Coronal Fields from Potential Field Models Authors: DeRosa, Marc L.; Schrijver, C. J.; Barnes, G. Bibcode: 2011SPD....42.1810D Altcode: 2011BAAS..43S.1810D The topology of the solar coronal magnetic field has been the subject of much recent interest, due to its apparent importance in determining (for example) the sources of the solar wind, the evolution of coronal hole boundaries, and whether the configurations of coronae overlying active regions are unstable and thus possibly eruption-prone. We identify the topological skeleton (null points, spline lines, separators, and separatrix surfaces) for a selection of dates of interest from the database of potential-field source-surface models available through the ``PFSS'' SolarSoft package. Several features of interest have been identified by recent studies (e.g., Antiochos et al. 2007, Parnell et al. 2010, Titov et al. 2011), including exceedingly narrow channels of open field or separators associated with inferred reconnection sites. We find that these features of interest occur frequently in the topologies of even potential-field models of the magnetic corona. The actual solar corona is of course likely to involve even more complex topologies, especially as its dynamics and evolution are taken into account. Title: 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: 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: 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: 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: 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: UVNS: An UVvis-NIR Spectrometer for Mars airglow. Authors: McConnell, J. C.; Barnes, G.; McDade, I.; Solheim, B.; Llewellyn, T.; Bourassa, A.; Daerden, F.; Friberg, D.; Blaxley, S.; Marchand, P.; Proulx, P.; Donovan, E.; Sioris, C.; McLinden, C.; Siskind, D.; Stevens, M.; Murtagh, D.; Smith, K.; Kabin, K. Bibcode: 2009AGUSM.P23A..01M Altcode: Airglow from a planetary atmosphere can yield important information on composition and dynamics. In this poster we examine the scientific return for the Mars Science Orbiter goals using a set of compact light instruments with a proven heritage (OSIRIS, SOIR, and SHOW) which span the UV-vis-NIR-SWIR part of the spectrum measuring scattered light and airglow from the limb and also stellar and solar occultation. A nadir viewing option is also a possibility for the UV spectrometer. The prime instruments consist of (a) a NIR- tomographic Ox imager (NTOI) (provenance OSIRIS) and (b) a high resolution IR spectrometer provenance SOIR) operating in solar and stellar occultation modes. By imaging the O2(1Δ) with the NTOI in the vertical it should be possible to derive a 2D structure for ozone during the daytime and O at night, providing chemical structure in the 50-80 km height range. The observed structure, analysed using 3D chemistry climate models, will also provide much needed information on dynamics and possibly the role of gravity waves and thermal tides. The HRIRS/SOIR occultation instrument, with a sensitivity of 2 ppbv at 3.3 microns will provide a unique opportunity to detect methane and measure any spatial variability. But other species such as CO should be detectable. A third instrument (c) uses the spatial heterodyne method of the SHOW instrument and it should be possible to measure water vapour and SO2 and perhaps tune the instrument for other species. (d) The UV-Vis spectrometer (UVS) would be based on the OSIRIS spectrometer but tuned for 200-600 nm to measure NO airglow and aurorae ∼ 200 nm, Herzberg II bands, ozone column in the Herzberg continuum at ∼ 250 nm with nadir viewing. Rayleigh scattering would provide temperature and pressure. Thus measurements of ozone column and water vapour will continue the climatology of these species initiated by MAWD on the Viking orbiters, TES on MGS and PFS on Mars Express. The unambiguous detection of methane and its distribution would be a major achievement and contribute to the question of its source. The UVNS will also measure aerosol (dust, water ice, and CO2 ice) optical depth and with the inclusion of infrared channels [SOIR] will provide improved information on the size distribution (Bourassa et al., 2008). A secondary objective would be to use the airglow data that would be observed to extend the MAVEN science mission and characterise the interaction of the solar wind with the Martian upper atmosphere by means of detailed airglow measurements. Title: Effects of Partitioning and Extrapolation on the Connectivity of Potential Magnetic Fields Authors: Longcope, D. W.; Barnes, G.; Beveridge, C. Bibcode: 2009ApJ...693...97L Altcode: 2008arXiv0811.1241L Coronal magnetic field may be characterized by how its field lines interconnect regions of opposing photospheric flux—its connectivity. Connectivity can be quantified as the net flux connecting pairs of opposing regions, once such regions are identified. One existing algorithm will partition a typical active region into a number of unipolar regions ranging from a few dozen to a few hundred, depending on algorithmic parameters. This work explores how the properties of the partitions depend on some algorithmic parameters, and how connectivity depends on the coarseness of partitioning for one particular active region magnetogram. We find the number of connections among them scales with the number of regions even as the number of possible connections scales with its square. There are several methods of generating a coronal field, even a potential field. The field may be computed inside conducting boundaries or over an infinite half-space. For computation of connectivity, the unipolar regions may be replaced by point sources or the exact magnetogram may be used as a lower boundary condition. Our investigation shows that the connectivities from these various fields differ only slightly—no more than 15%. The greatest difference is between fields within conducting walls and those in the half-space. Their connectivities grow more different as finer partitioning creates more source regions. This also gives a quantitative means of establishing how far away conducting boundaries must be placed in order not to significantly affect the extrapolation. For identical outer boundaries, the use of point sources instead of the exact magnetogram makes a smaller difference in connectivity: typically 6% independent of the number of source regions. 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: 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: Non-Linear Force-Free Field Modeling of a Solar Active Region Around the Time of a Major Flare and Coronal Mass Ejection Authors: De Rosa, M. L.; Schrijver, C. J.; Metcalf, T. R.; Barnes, G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.; Wheatland, M.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann, M.; Kusano, K.; Régnier, S.; Thalmann, J. Bibcode: 2008AGUSMSP31A..06D Altcode: Solar flares and coronal mass ejections are associated with rapid changes in coronal magnetic field connectivity and are powered by the partial dissipation of electrical currents that run through the solar corona. A critical unanswered question is whether the currents involved are induced by the advection along the photosphere of pre-existing atmospheric magnetic flux, or whether these currents are associated with newly emergent flux. We address this problem by applying nonlinear force-free field (NLFFF) modeling to the highest resolution and quality vector-magnetographic data observed by the recently launched Hinode satellite on NOAA Active Region 10930 around the time of a powerful X3.4 flare in December 2006. We compute 14 NLFFF models using 4 different codes having a variety of boundary conditions. We find that the model fields differ markedly in geometry, energy content, and force-freeness. We do find agreement of the best-fit model field with the observed coronal configuration, and argue (1) that strong electrical currents emerge together with magnetic flux preceding the flare, (2) that these currents are carried in an ensemble of thin strands, (3) that the global pattern of these currents and of field lines are compatible with a large-scale twisted flux rope topology, and (4) that the ~1032~erg change in energy associated with the coronal electrical currents suffices to power the flare and its associated coronal mass ejection. We discuss the relative merits of these models in a general critique of our present abilities to model the coronal magnetic field based on surface vector field measurements. Title: Nonlinear Force-free Field Modeling of a Solar Active Region around the Time of a Major Flare and Coronal Mass Ejection Authors: Schrijver, C. J.; DeRosa, M. L.; Metcalf, T.; Barnes, G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.; Wheatland, M. S.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann, M.; Kusano, K.; Régnier, S.; Thalmann, J. K. Bibcode: 2008ApJ...675.1637S Altcode: 2007arXiv0712.0023S Solar flares and coronal mass ejections are associated with rapid changes in field connectivity and are powered by the partial dissipation of electrical currents in the solar atmosphere. A critical unanswered question is whether the currents involved are induced by the motion of preexisting atmospheric magnetic flux subject to surface plasma flows or whether these currents are associated with the emergence of flux from within the solar convective zone. We address this problem by applying state-of-the-art nonlinear force-free field (NLFFF) modeling to the highest resolution and quality vector-magnetographic data observed by the recently launched Hinode satellite on NOAA AR 10930 around the time of a powerful X3.4 flare. We compute 14 NLFFF models with four different codes and a variety of boundary conditions. We find that the model fields differ markedly in geometry, energy content, and force-freeness. We discuss the relative merits of these models in a general critique of present abilities to model the coronal magnetic field based on surface vector field measurements. For our application in particular, we find a fair agreement of the best-fit model field with the observed coronal configuration, and argue (1) that strong electrical currents emerge together with magnetic flux preceding the flare, (2) that these currents are carried in an ensemble of thin strands, (3) that the global pattern of these currents and of field lines are compatible with a large-scale twisted flux rope topology, and (4) that the ~1032 erg change in energy associated with the coronal electrical currents suffices to power the flare and its associated coronal mass ejection. Title: Resolving the Azimuthal Ambiguity in Vector Magnetogram Data with the Divergence-Free Condition: Theoretical Examination Authors: Crouch, A. D.; Barnes, G. Bibcode: 2008SoPh..247...25C Altcode: We demonstrate that the azimuthal ambiguity that is present in solar vector magnetogram data can be resolved with line-of-sight and horizontal heliographic derivative information by using the divergence-free property of magnetic fields without additional assumptions. We discuss the specific derivative information that is sufficient to resolve the ambiguity away from disk centre, with particular emphasis on the line-of-sight derivative of the various components of the magnetic field. Conversely, we also show cases where ambiguity resolution fails because sufficient line-of-sight derivative information is not available. For example, knowledge of only the line-of-sight derivative of the line-of-sight component of the field is not sufficient to resolve the ambiguity away from disk centre. 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: On the Relationship between Coronal Magnetic Null Points and Solar Eruptive Events Authors: Barnes, G. Bibcode: 2007ApJ...670L..53B Altcode: One mechanism that has been proposed for initiating coronal mass ejections (CMEs) is the ``breakout'' model. For this model to account for CMEs, a coronal null point must be present prior to the eruption. The relationship between the existence of coronal null points and eruptive events is investigated using a collection of over 1800 vector magnetograms from the Imaging Vector Magnetograph at Haleakalā. Each magnetogram is subjected to magnetic charge topology analysis, including determining the presence of coronal null points. It is found that the majority of events originate in regions above which no null point is found. However, a much larger fraction of active regions for which a coronal null point was found were the source of an eruption than active regions for which no null was found. The implications of these results for the breakout model are discussed. Title: Determining the Source of Coronal Helicity through Measurements of Braiding and Spin Helicity Fluxes in Active Regions Authors: Longcope, D. W.; Ravindra, B.; Barnes, G. Bibcode: 2007ApJ...668..571L Altcode: Magnetic helicity has become a valuable tool for understanding the energetics and dynamics of coronal magnetic fields. Recently, long time sequences of magnetograms have been used to measure the flux of helicity into active region coronae. We demonstrate how this helicity flux can be usefully decomposed into contributions of differing origin, called ``spin'' helicity and ``braiding'' helicity. These contributions could be envisioned to come at the expense of twist and writhe helicity, respectively, of a subphotospheric flux tube anchored to the regions. In order to effect this decomposition, each magnetogram is partitioned into a set of unipolar regions. We present a method of defining such regions so that they persist through the sequences and track the photospheric flow. The spin helicity of a given region quantifies the mean rotation rate of motions internal to that region, while braiding helicity is injected by the motions of whole regions about one another. Applying the method to six active regions shows cases where either spin or braiding dominates, and where they have the same signs and opposite signs. Thus, it would seem that no general statement can be made regarding the dominance of twist or writhe in supplying helicity to the corona. In one particular case, spin and braiding helicity follow different time histories but inject equal and opposite net helicities. This suggests that the spinning and braiding are driven by a kink instability in the submerged flux tube. 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: Resolving The Azimuthal Ambiguity In Vector Magnetograms Away From Disk Centre With The Solenoidal Condition Authors: Crouch, Ashley D.; Barnes, G. Bibcode: 2007AAS...210.5304C Altcode: 2007BAAS...39..164C We employ the divergence-free property of magnetic fields to resolve the azimuthal ambiguity in solar vector magnetograms. We show that the ambiguity can be resolved away from disk centre if one knows the line-of-sight derivative of the magnetic field components in the directions parallel and transverse to the line-of-sight. However, knowing only the line-of-sight derivative of the line-of-sight component of the magnetic field is not sufficient except at disk centre. Thus, multi-height vector magnetogram data can be used to resolve the ambiguity provided that all the line-of-sight derivatives can be determined reliably. We use a simple theoretical example, consisting of two submerged magnetic point sources, to demonstrate our findings. This work was supported by funding from NASA/LWS under contract NNH05CC75C. Title: Active Region Magnetic Field Line Twist and Source of Coronal Magnetic Helicity. Authors: Belur, Ravindra; Longcope, D.; Barnes, G.; Nandy, D. Bibcode: 2007AAS...210.2401B Altcode: 2007BAAS...39..128B Magnetic helicity is an important quantity which measures how the magnetic field lines are twisted and sheared. Recently it has become possible to measure the flux of magnetic helicity in active regions using the observational data. These observed helicity fluxes may arise due to the twist in the emerging active region flux tubes or it may come from the photospheric shearing motion. Here, we decompose the helicity flux into two different contributions called spin and braiding. These components typically come from twist and writhe helicity of a sub-photospheric flux tube anchored to the regions. The spin helicity of a given region quantifies the mean rotation rate of motion internal to that region and braiding helicity is injected by the motions of whole

regions about one another. The injected helicity flux due to spin and braiding motion leads to the coronal magnetic field line twist. The twist determined from vector magnetograms can be used to estimate the total helicity content of the coronal field at one time. The rate of change of this helicity estimate can be compared to the total helicity flux as well as its spin and braiding component. We make such a comparison for several active regions. Title: Non-linear Force-free Modeling Of Coronal Magnetic Fields Authors: Metcalf, Thomas R.; De Rosa, M. L.; Schrijver, C. J.; Barnes, G.; van Ballegooijen, A.; Wiegelmann, T.; Wheatland, M. S.; Valori, G.; McTiernan, J. M. Bibcode: 2007AAS...210.9102M Altcode: 2007BAAS...39..204M We compare a variety of nonlinear force-free field (NLFFF) extrapolation algorithms, including optimization, magneto-frictional, and Grad-Rubin-like codes, applied to a solar-like reference model. The model used to test the algorithms includes realistic photospheric Lorentz forces and a complex field including a weakly twisted, right helical flux bundle. The codes were applied to both forced "photospheric'' and more force-free "chromospheric'' vector magnetic field boundary data derived from the model. When applied to the

chromospheric boundary data, the codes are able to recover the presence of the flux bundle and the field's free energy, though some details of the field connectivity are lost. When the codes are applied to the forced photospheric boundary data, the reference model field is not well recovered, indicating that the Lorentz forces on the photosphere severely impact the extrapolation of the field. Preprocessing of the photospheric boundary does improve the extrapolations considerably, although the results depend sensitively on the details of the numerical codes. When applying the NLFFF codes to solar data, the problems associated with Lorentz forces present in the low solar atmosphere must be recognized: the various codes will not necessarily converge to the correct, or even the same, solution. Title: 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: Topological Estimates of Free-Energy Build-up in Active Regions Authors: Longcope, D. W.; Barnes, G.; Ravindra, B.; Beveridge, C. Bibcode: 2006AGUFMSH31B..02L Altcode: There is a growing consensus that slow evolution of an active region's photospheric flux leads to a build-up in the energy of its coronal field. The anchoring of coronal field lines to the photosphere defines a connectivity between photospheric footpoints of opposing polarities. Due to the corona's extremely high electrical conductivity these connections remain unchanged even as the footpoints move. To estimate the energy stored this way, we group photospheric footpoints into unipolar source regions and reduce the pointwise connectivity map to a matrix of connections between regions. The flux in each such connection must remain fixed even as the source regions evolve. One coronal magnetic field, called the flux constrained equilibrium, has the minimum possible energy for a specified connectivity. The free energy in this equilibrium provides a lower bound on the free energy in the actual field. We obtain such a free-energy lower bounds for several observed active regions. Source regions are defined in a magnetogram (MDI) time sequence of an active region. As the sources evolve the connectivity in a potential field will change, however, the actual connectivity will not. The growing disparity between the two is used to estimate the free energy stored in the coronal field. Flare reconnection will release some portion of this stored energy by changing some of the connectivities. We compare these estimates with observational signatures of energy release. This work supported by NASA's Living with a Star Program and by AFOSR. 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: Modeling And Measuring The Flux Reconnected By The Two-ribbon Flare On 2004-11-07 Authors: Longcope, Dana; Beveridge, C.; Qiu, J.; Belur, R.; Barnes, G. Bibcode: 2006SPD....37.0803L Altcode: 2006BAAS...38R.230L Observations of the large two-ribbon flare on 2004-Nov-7 made using SOHO and TRACE data are interpreted in terms of a three-dimensional magnetic field model. This model predicts the amount of flux reconnected during the flare and the energy it would release. These values are compared to the flux swept up by the flare ribbons observed by TRACE in 1600 A and the energy release inferred by the GOES light curves. The helicity of the model field may be independently compared to the helicty injected by photospheric motions during the buildup to the flare. The model also predicts the sequence in which the reconnections should occur. This in turn provide insight into the conversion of mutual helicity into self-helicity during the production of a twisted flux rope.This work is supported by NASA Grant NAG5-10489 and DoD MURI grant. 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: Measuring Braiding and Spin Helicity Fluxes in Active Regions Authors: Belur, R.; Longcope, D. W.; Barnes, G. Bibcode: 2005AGUFMSH11A0248B Altcode: Magnetic helicity has become a valuable theoretical tool for understanding the dynamics of the solar corona. The free energy stored in the coronal magnetic field can be estimated based on its helicity content. Furthermore, rapid release of stored energy must be accomplished while preserving the total magnetic helicity. Recently long time-sequences of magnetograms have been used to measure the flux of helicity into active regions. We demonstrate how this helicity flux can be usefully decomposed into a sum of spin helicity terms and an overall mutual helicity term. Each magnetogram is partitioned into a set of unipolar regions. These must persist through the sequence and track the photospheric flow. The spin helicity of a given region quantifies the effects of motions internal to that region, while braiding helicity is injected by the motions of whole regions about one another. Since the terms themselves can be of different signs it is possible to re-distribute the coronal helicity by reconnection without changing the overall helicity content. This decomposition is demonstrated on active region observations. 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: The OSIRIS instrument on the Odin spacecraft Authors: Llewellyn, E.; Lloyd, N. D.; Degenstein, D. A.; Gattinger, R. L.; Petelina, S. V.; Bourassa, A. E.; Wiensz, J. T.; Ivanov, E. V.; McDade, I. C.; Solheim, B. H.; McConnell, J. C.; Haley, C. S.; von Savigny, C.; Sioris, C. E.; McLinden, C. A.; Griffioen, E.; Kaminski, J.; Evans, W. F. J.; Puckrin, E.; Strong, K.; Wehrle, V.; Hum, R. H.; Kendall, D. J. W.; Matsushita, J.; Murtagh, D. P.; Brohede, S.; Stegman, J.; Witt, G.; Barnes, G.; Payne, W. F.; Piché, L.; Smith, K.; Warshaw, G.; Deslauniers, D. L.; Marchand, P.; Richardson, E. H.; King, R. A.; Wevers, I.; McCreath, W.; Kyrölä, E.; Oikarinen, L.; Leppelmeier, G. W.; Auvinen, H.; Megie, G.; Hauchecorne, A.; Lefevre, F.; de La Nöe, J.; Ricaud, P.; Frisk, U.; Sjoberg, F.; von Schéele, F.; Nordh, L. Bibcode: 2004CaJPh..82..411L Altcode: The optical spectrograph and infrared imager system (OSIRIS) on board the Odin spacecraft is designed to retrieve altitude profiles of terrestrial atmospheric minor species by observing limb-radiance profiles. The grating optical spectrograph (OS) obtains spectra of scattered sunlight over the range 280-800 nm with a spectral resolution of approximately 1 nm. The Odin spacecraft performs a repetitive vertical limb scan to sweep the OS 1 km vertical field of view over selected altitude ranges from approximately 10 to 100 km. The terrestrial absorption features that are superimposed on the scattered solar spectrum are monitored to derive the minor species altitude profiles. The spectrograph also detects the airglow, which can be used to study the mesosphere and lower thermosphere. The other part of OSIRIS is a three-channel infrared imager (IRI) that uses linear array detectors to image the vertical limb radiance over an altitude range of approximately 100 km. The IRI observes both scattered sunlight and the airglow emissions from the oxygen infrared atmospheric band at 1.27 mum and the OH (3-1) Meinel band at 1.53 mum. A tomographic inversion technique is used with a series of these vertical images to derive the two-dimensional distribution of the emissions within the orbit plane. 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: 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: 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: 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: Frequency Dependent Ray Paths in Local Helioseismology Authors: Barnes, G.; Cally, P. S. Bibcode: 2001PASA...18..243B Altcode: The surface of the Sun is continually oscillating due to sound waves encroaching on it from the interior. Measurements of the surface velocity are used to infer some of the properties of the regions through which the sound waves have propagated. Traditionally, this has been done by using a modal decomposition of the surface disturbances. However, the use of ray descriptions, in the form of acoustic holography or time-distance helioseismology, provides an alternative approach which may reveal more detailed information about the properties of local phenomena such as sunspots and active regions. Fundamental to any such treatment is determining the correct ray paths in a given atmosphere. In the simplest approach, the ray paths are constructed to minimise the travel time between two points (Fermat's principle). However, such an approach is only valid in the high frequency limit, ω≫ωc, N, where ωc is the acoustic cut-off and N the Brunt-Väisälä frequency. Although ωc is often included in time-distance calculations, and N occasionally, the same is not true of acoustic holography. We argue that this raises concerns about image sharpness. As illustrations, representative ray paths are integrated in a realistic solar model to show that the Fermat approximation performs poorly for frequencies of helioseismic interest. We also briefly discuss the importance of the Brunt-Väisälä frequency to the time-distance diagram. Title: Mode Mixing by a Shallow Sunspot Authors: Barnes, G.; Cally, P. S. Bibcode: 2000SoPh..193..373B Altcode: Sunspots are strong absorbers of f and p modes. A possible absorption mechanism is direct conversion to slow magnetoacoustic waves. Calculations based on vertical magnetic field models show that this works well for f modes, but is inadequate for p modes. Using a very simple `shallow spot' model, in which the effects of the magnetic field are accounted for solely by a surface condition, we investigate the possibility that p modes first scatter into f modes inside the spot, which are then more susceptible to conversion to slow modes. We find that the coupling between an incident p mode and the internal f mode is unlikely to be strong enough to account for the observed absorption, but that the incident modes do couple strongly to the acoustic jacket in some cases, leading to a region immediately around the sunspot where a significant fraction of the surface velocity is due to the jacket modes. Title: Magnetic fields and light element depletion in the Sun Authors: Charbonneau, P.; Barnes, G.; MacGregor, K. B. Bibcode: 2000IAUJD...5E..14C Altcode: I will first briefly review some important similarities and differences in models for the spin-down of solar-type stars, with or without internal magnetic fields in their radiative interior. This will be followed by a presentation of some simple calculations for the main-sequence depletion of Lithium and Beryllium in the Sun, in a regime where magnetic fields provide the chief mechanism for the internal redistribution of angular momentum. In this model the transport of light elements still occurs in response to shear-induced small-scale turbulence, following various commonly used prescriptions for the transport coefficients. For some (physically reasonable) values of model parameters, both internal differential rotation and light element abundances end up solar-like at 4.5Gyr. Within this framework light element depletion is a sensitive function of the strength of the assumed internal magnetic field. Title: On the magnetohydrodynamics of a conducting fluid between two flat plates Authors: Barnes, G.; MacGregor, K. B. Bibcode: 1999PhPl....6.3030B Altcode: The time-dependent flow of a viscous, electrically conducting fluid contained within the space between two parallel, semi-infinite, perfectly conducting plates is considered. A uniform magnetic field directed perpendicular to the plate surfaces is assumed to pervade the fluid. Oscillatory motion of one of the plates in its own plane is induced through the application of a prescribed acceleration, the magnitude and direction of which vary sinusoidally in time. For a system forced in this manner, the resulting flow and transverse field component are solved for, as well as for the motion of the plate as a function of time. The magnetic and viscous stresses exerted on the boundary plate by the contiguous field and fluid are explicitly incorporated into the treatment of its motion. The physical properties and behavior of this system are investigated by examining analytic and numerical solutions obtained for a range of forcing periods, Reynolds numbers, and plate mass column densities. The relevance of these results to the interpretation of a model for Alfvénic torsional oscillations in the solar interior are discussed. Title: Mode Mixing by a Shallow Sunspot Authors: Barnes, G.; Cally, P. S. Bibcode: 1999soho....9E..35B Altcode: In a polytropic atmosphere, the oscillation modes are described by well-known special functions. However, the presence of a magnetic field inside a sunspot makes the mode structure much more complex, so that analytic expressions are not available. Recent observations of sunspots suggest that most of the scattering and absorption due to the spots occurs in a layer immediately below the surface of the sun. We have therefore modelled the acoustic modes inside a sunspot by assuming that the effect of the magnetic field is concentrated right at the surface. Instead of imposing the conventional upper boundary condition, that the divergence of the velocity vanish, we require that the horizontal component of the velocity vanish, which allows us to write down analytic expressions for the acoustic modes inside the spot. This may be justified by arguing that a vertical magnetic field will tend to inhibit horizontal fluid motions. In effect, we are introducing a purely scattering disk to the surface of the sun. More realistic models, in which the disk both scatters and absorbs energy are also possible. We consider the scattering of an incident p-mode off our "sunspot," matching the pressure and horizontal velocity across the boundary. The result is a mixing of the incident mode into outgoing external p-modes and internal p-modes, as well as jacket modes both inside and outside the spot. We find that the inclusion of the jacket modes is crucial to satisfying the matching conditions, and we present results indicating the spectrum of outgoing and internal modes that are present. Title: Angular Momentum Transport in Magnetized Stellar Radiative Zones. III. The Solar Light-Element Abundances Authors: Barnes, G.; Charbonneau, P.; MacGregor, K. B. Bibcode: 1999ApJ...511..466B Altcode: We calculate the depletion of the trace elements lithium and beryllium within a solar-mass star during the course of its evolution from the zero-age main sequence to the age of the present-day Sun. In the radiative layers beneath the convection zone, we assume that these elements are transported by the turbulent fluid motions that result from instability of the shear flow associated with internal differential rotation. This turbulent mixing is modeled as a diffusion process, using a diffusion coefficient that is taken to be proportional to the gradient of the angular velocity distribution inside the star. We study the evolution of the light-element abundances produced by rotational mixing for models in which internal angular momentum redistribution takes place either by hydrodynamic or by hydromagnetic means. Since models based on these alternative mechanisms for angular-momentum transport predict similar surface rotation rates late in the evolution, we explore the extent to which light-element abundances make it possible to distinguish between them. In the case of an internally magnetized star, our computations indicate that both the details of the surface abundance evolution and the magnitude of the depletion at solar age can depend sensitively on the assumed strength and configuration of the poloidal magnetic field inside the star. For a configuration with no direct magnetic coupling between the radiative and convective portions of the stellar interior, the depletion of lithium calibrated to the solar lithium depletion at the solar age is similar at all ages to the lithium depletion of a model in which angular-momentum transport occurs solely by hydrodynamical processes. However, the two models can be distinguished on the basis of their respective beryllium depletions, with the depletion of the magnetic model being significantly smaller than that of the nonmagnetic model. Title: Gravity Waves in a Magnetized Shear Layer Authors: Barnes, G.; MacGregor, K. B.; Charbonneau, P. Bibcode: 1998ApJ...498L.169B Altcode: We use the equations governing the propagation of a gravity wave in the presence of a background flow and magnetic field to derive, in the Boussinesq approximation, dispersion relations for plane wave solutions in certain special cases. We show how, under conditions typical of the interior of the Sun, the addition of a magnetic field may prevent certain wavevectors from propagating and alter the existence and position of any critical layer that might absorb the gravity wave. Title: Angular Momentum Transport in Magnetized Stellar Radiative Zones: The Solar Light Element Abundances Authors: Barnes, G.; Charbonneau, P.; MacGregor, K. B. Bibcode: 1998ASPC..154..886B Altcode: 1998csss...10..886B We calculate the depletion of the trace elements lithium and beryllium within a solar mass star, during the course of its evolution from the zero-age main sequence to the age of the present-day Sun. In the radiative layers beneath the convection zone, we assume that these elements are transported by the turbulent fluid motions that result from the instability of the shear flow associated with internal differential rotation. This turbulent mixing is modeled as a diffusive process, using a diffusion coefficient that is taken to be proportional to the gradient of the angular velocity distribution inside the star. We study the evolution of the light element abundances produced by rotational mixing for models in which internal angular momentum redistribution takes place either by hydrodynamic or by hydromagnetic means. Since models based on these alternative mechanisms for angular momentum transport predict similar surface rotation rates late in the evolution, we explore the extent to which light element abundances make it possible to distinguish between them. In the case of an internally magnetized star, our computations indicate that both the details of the surface abundance evolution and the magnitude of the depletion at solar age can depend sensitively on the assumed strength and configuration of the poloidal magnetic field inside the star. For a configuration with no direct magnetic coupling between the radiative and convective portions of the stellar interior, the depletion of lithium as a function of age is similar to that of a model in which angular momentum transport occurs solely by hydrodynamical processes. However, the two models can be distinguished on the basis of their respective beryllium depletions, with the depletion of the magnetic model being significantly smaller than that of the non-magnetic model. Title: Mixing in Low-Mass Stars: The Lithium-Rotation Connection Authors: Balachandran, Suchitra C.; Garcia Lopez, R. J.; Kraft, R. P.; MacGregor, K. B.; Barnes, G.; Martin, E. L.; Pinsonneault, Marc H. Bibcode: 1998ASPC..154..111B Altcode: 1998csss...10..111B We have known for over three decades that the Sun has depleted its surface lithium. During this period it has become increasingly evident that mixing, unaccounted for by the standard models, occurs in the stellar interior. There is some conjecture that this mixing may be driven by rotation and thus be dependent upon the rotational history of the star. In this discussion session, we will examine the observational connection between mixing and rotation and critically evaluate current models.