Author name code: derosa ADS astronomy entries on 2022-09-14 author:"DeRosa, M." ------------------------------------------------------------------------ Title: Suppression of Torus Instability on Cool Stars Authors: Sun, Xudong; Derosa, Marc; Torok, Tibor Bibcode: 2022cosp...44.1389S Altcode: Despite the frequent detection of stellar super flares, reports on stellar coronal mass ejections (CMEs) are rare. This is in contrast with our Sun, where almost all large flares are accompanied by a CME. Here, we use an analytical coronal magnetic field model to demonstrate that the torus instability, a leading mechanism for solar CMEs, tends to be suppressed in stellar magnetic environment. Contributing factors include larger starspots, stronger global dipole field, and more closed magnetic geometry compared to the Sun. Suppression of the torus instability may contribute to the low apparent CME rate on cool stars. Title: Coronal Dimming as a Proxy for Solar and Stellar Coronal Mass Ejections Authors: Jin, Meng; Nitta, Nariaki; Derosa, Marc; Cheung, Mark; Osten, Rachel; France, Kevin; Mason, James; Kowalski, Adam; Schrijver, Carolus Bibcode: 2022cosp...44.1404J Altcode: Solar coronal dimmings have been observed extensively in the past two decades. Due to their close association with coronal mass ejections (CMEs), there is a critical need to improve our understanding of the physical processes that cause dimmings as well as their relationship with CMEs. Recent study (e.g., Veronig et al. 2021) also shows promising dimming signals from distant stars, which suggest the possibility of using coronal dimming as a proxy to diagnose stellar CMEs. In this study, we first conduct a comparative study of solar coronal dimming using MHD simulations and SDO observations. A detailed analysis of the simulation and observation data reveals how transient dimming / brightening are related to plasma heating processes, while the long-lasting core and remote dimmings are caused by mass loss process induced by the CME. Using metrics such as dimming depth and dimming slope, we uncover a relationship between dimmings and CME properties (e.g., CME mass, CME speed) in the simulation. We further extend the model for simulating the stellar CMEs and dimmings and compare with solar cases. Our result suggests that coronal dimmings encode important information about the associated CMEs, which provides a physical basis for detecting stellar CMEs from distant solar-like stars. Title: The Impact of Nonlinear Interactions Between Solar Photospheric Magnetic Fields and Flows on the Evolution of the Polar Fields During Recent Sunspot Cycles Authors: Derosa, Marc; Hoeksema, J. Todd; Mahajan, Sushant; Upton, Lisa A. Bibcode: 2022cosp...44.3224D Altcode: The observed polar fields during solar activity minimum intervals are believed to be a useful predictor of future sunspot cycle amplitudes. Such polar fields result from the poleward transport of magnetic flux from the many active regions that emerge onto the photosphere at lower latitudes. Recent studies suggest that a subset of emergent active regions have an outsized influence on the buildup and eventual maximal amplitude of polar fields. Additionally, the nonlinear interactions between these fields with the observed surface flows may also affect the evolution of polar fields. In the work presented here, we use surface-flux transport modeling, in combination with a curated list of emergent active regions during sunspot cycles 24 and 25, to investigate the effects of both active-region emergence properties and inflows surrounding active regions on the buildup of polar fields, with an eye toward the ability to constrain the polar field amplitude following sunspot cycle 25. Title: Coronal Mass Ejections and Dimmings: A Comparative Study Using MHD Simulations and SDO Observations Authors: Jin, Meng; Cheung, Mark C. M.; DeRosa, Marc L.; Nitta, Nariaki V.; Schrijver, Carolus J. Bibcode: 2022ApJ...928..154J Altcode: 2022arXiv220213034J Solar coronal dimmings have been observed extensively in recent years. Due to their close association with coronal mass ejections (CMEs), there is a critical need to improve our understanding of the physical processes that cause dimmings as well as their relationship with CMEs. In this study, we investigate coronal dimmings by combining simulation and observational efforts. By utilizing a data-constrained global magnetohydrodynamics model (Alfvén-wave solar model), we simulate coronal dimmings resulting from different CME energetics and flux rope configurations. We synthesize the emissions of different EUV spectral bands/lines and compare with SDO/AIA and EVE observations. A detailed analysis of the simulation and observation data suggests that the transient dimming/brightening are related to plasma heating processes, while the long-lasting core and remote dimmings are caused by mass-loss process induced by the CME. Moreover, the interaction between the erupting flux rope with different orientations and the global solar corona could significantly influence the coronal dimming patterns. Using metrics such as dimming depth and dimming slope, we investigate the relationship between dimmings and CME properties (e.g., CME mass, CME speed) in the simulation. Our result suggests that coronal dimmings encode important information about the associated CMEs, which provides a physical basis for detecting stellar CMEs from distant solar-like stars. Title: Probing the Physics of the Solar Atmosphere with the Multi-slit Solar Explorer (MUSE). II. Flares and Eruptions Authors: Cheung, Mark C. M.; Martínez-Sykora, Juan; Testa, Paola; De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito, Vanessa; Kerr, Graham S.; Reeves, Katharine K.; Fletcher, Lyndsay; Jin, Meng; Nóbrega-Siverio, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc L.; Boerner, Paul; Jaeggli, Sarah; Nitta, Nariaki V.; Daw, Adrian; Carlsson, Mats; Golub, Leon; The Bibcode: 2022ApJ...926...53C Altcode: 2021arXiv210615591C Current state-of-the-art spectrographs cannot resolve the fundamental spatial (subarcseconds) and temporal (less than a few tens of seconds) scales of the coronal dynamics of solar flares and eruptive phenomena. The highest-resolution coronal data to date are based on imaging, which is blind to many of the processes that drive coronal energetics and dynamics. As shown by the Interface Region Imaging Spectrograph for the low solar atmosphere, we need high-resolution spectroscopic measurements with simultaneous imaging to understand the dominant processes. In this paper: (1) we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne observatory to fill this observational gap by providing high-cadence (<20 s), subarcsecond-resolution spectroscopic rasters over an active region size of the solar transition region and corona; (2) using advanced numerical models, we demonstrate the unique diagnostic capabilities of MUSE for exploring solar coronal dynamics and for constraining and discriminating models of solar flares and eruptions; (3) we discuss the key contributions MUSE would make in addressing the science objectives of the Next Generation Solar Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope (and other ground-based observatories) can operate as a distributed implementation of the NGSPM. This is a companion paper to De Pontieu et al., which focuses on investigating coronal heating with MUSE. Title: Torus-stable zone above starspots Authors: Sun, Xudong; Török, Tibor; DeRosa, Marc L. Bibcode: 2022MNRAS.509.5075S Altcode: 2021arXiv211103665S; 2021MNRAS.tmp.2934S Whilst intense solar flares are almost always accompanied by a coronal mass ejection (CME), reports on stellar CMEs are rare, despite the frequent detection of stellar 'super flares'. The torus instability of magnetic flux ropes is believed to be one of the main driving mechanisms of solar CMEs. Suppression of the torus instability, due to a confining background coronal magnetic field that decreases sufficiently slowly with height, may contribute to the lack of stellar CME detection. Here, we use the solar magnetic field as a template to estimate the vertical extent of this 'torus-stable zone' (TSZ) above a stellar active region. For an idealized potential field model comprising the fields of a local bipole (mimicking a pair of starspots) and a global dipole, we show that the upper bound of the TSZ increases with the bipole size, the dipole strength, and the source surface radius where the coronal field becomes radial. The boundaries of the TSZ depend on the interplay between the spots' and the dipole's magnetic fields, which provide the local- and global-scale confinement, respectively. They range from about half the bipole size to a significant fraction of the stellar radius. For smaller spots and an intermediate dipole field, a secondary TSZ arises at a higher altitude, which may increase the likelihood of 'failed eruptions'. Our results suggest that the low apparent CME occurrence rate on cool stars is, at least partially, due to the presence of extended TSZs. Title: Probing the Physics of the Solar Atmosphere with the Multi-slit Solar Explorer (MUSE): II. Flares and Eruptions Authors: Cheung, Chun Ming Mark; Martinez-Sykora, Juan; Testa, Paola; De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito, Vanessa; Kerr, Graham; Reeves, Katharine; Fletcher, Lyndsay; Jin, Meng; Nobrega, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc; Boerner, Paul; Jaeggli, Sarah; Nitta, Nariaki; Daw, Adrian; Carlsson, Mats; Golub, Leon Bibcode: 2021AGUFMSH51A..08C Altcode: Current state-of-the-art spectrographs cannot resolve the fundamental spatial (sub-arcseconds) and temporal scales (less than a few tens of seconds) of the coronal dynamics of solar flares and eruptive phenomena. The highest resolution coronal data to date are based on imaging, which is blind to many of the processes that drive coronal energetics and dynamics. As shown by IRIS for the low solar atmosphere, we need high-resolution spectroscopic measurements with simultaneous imaging to understand the dominant processes. In this paper: (1) we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne observatory to fill this observational gap by providing high-cadence (<20 s), sub-arcsecond resolution spectroscopic rasters over an active region size of the solar transition region and corona; (2) using advanced numerical models, we demonstrate the unique diagnostic capabilities of MUSE for exploring solar coronal dynamics, and for constraining and discriminating models of solar flares and eruptions; (3) we discuss the key contributions MUSE would make in addressing the science objectives of the Next Generation Solar Physics Mission (NGSPM), and how MUSE, the high-throughput EUV Solar Telescope (EUVST) and the Daniel K Inouye Solar Telescope (and other ground-based observatories) can operate as a distributed implementation of the NGSPM. This is a companion paper to De Pontieu et al. (2021, also submitted to SH-17), which focuses on investigating coronal heating with MUSE. Title: Assessing the Impact of Cross-Equatorial Surface Flows on the Buildup of Polar Fields Using Surface Flux Transport Models Authors: DeRosa, Marc; Mahajan, Sushant Bibcode: 2021AGUFMSH54A..02D Altcode: Observed polar magnetic flux on the Sun is a useful indicator and predictor of the sunspot cycle amplitudes. The buildup of such polar flux is dependent on a number of factors, most prominently the tilt angle of emergent active-region flux (Joy's Law) and the speed of the near-surface meridional flow, as well as other factors such as the inflows surrounding active regions. Surface-flux transport models use such observations to model the evolution of solar polar fields, transporting flux based on empirical prescriptions for differential rotation, meridional flows, and convective dispersal. In the study presented here, we illustrate the effects on the polar fields of incorporating meridional flow profiles derived from observations into a surface-flux transport model, and compare these effects to other processes that are known to affect the buildup of polar fields. We find that the cross-equatorial flows that are typically found from observed meridional flow profiles typically enhance the resulting polar fields. Such flows may also enhance hemispheric asymmetries. Title: Sun-as-a-star Spectral Irradiance Observations of Transiting Active Regions: a Milestone for Characterization of Stellar Active Regions Authors: Toriumi, Shin; Airapetian, Vladimir; Hudson, Hugh; Schrijver, Karel; Cheung, Chun Ming Mark; DeRosa, Marc Bibcode: 2021AGUFM.U43B..05T Altcode: Recent observations have revealed that solar-type stars can produce massive "superflares". The strongest flares on the Sun are almost always associated with large, complex, rapidly-evolving active regions (ARs) including sunspots. Therefore, to understand why and how stellar flares and coronal eruptions occur, which may directly determine the circumstances of exoplanets, it is critically important to gain information on stellar ARs. One possible way to do so is to monitor the star in multiple wavelengths. In this study, we perform multi-wavelength irradiance monitoring of transiting solar ARs by using full-disk observational (i.e. Sun-as-a-star) data from four satellites. We find that the near UV light curves show strong correlations with photospheric total magnetic flux and that there are time lags between the coronal and photospheric light curves when ARs are close to the limb. Such time lags result from high-arching, bright coronal loops above stellar ARs being visible even when the AR is behind the limb. It is also found that the EUV light curves sensitive to transition-region temperatures are sometimes dimmed because of a reduction in the emission measure of 0.60.8 MK due to the plasma being heated to higher temperatures over a wide area around the AR. These results indicate that, by measuring the stellar light curves in multiple wavelengths, we may obtain information on the structures and evolution of stellar ARs. Title: The Multiview Observatory for Solar Terrestrial Science (MOST) Authors: Gopalswamy, Nat; Kucera, Therese; Leake, James; MacDowall, Robert; Wilson, Lynn; Kanekal, Shrikanth; Shih, Albert; Christe, Steven; Gong, Qian; Viall, Nicholeen; Tadikonda, Sivakumar; Fung, Shing; Yashiro, Seiji; Makela, Pertti; Golub, Leon; DeLuca, Edward; Reeves, Katharine; Seaton, Daniel; Savage, Sabrina; Winebarger, Amy; DeForest, Craig; Desai, Mihir; Bastian, Tim; Lazio, Joseph; Jensen, P. E., C. S. P., Elizabeth; Manchester, Ward; Wood, Brian; Kooi, Jason; Wexler, David; Bale, Stuart; Krucker, Sam; Hurlburt, Neal; DeRosa, Marc; Pevtsov, Alexei; Tripathy, Sushanta; Jain, Kiran; Gosain, Sanjay; Petrie, Gordon; Kholikov, Shukirjon; Zhao, Junwei; Scherrer, Philip; Woods, Thomas; Chamberlin, Philip; Kenny, Megan Bibcode: 2021AGUFMSH12A..07G Altcode: The Multiview Observatory for Solar Terrestrial Science (MOST) is a comprehensive mission concept targeting the magnetic coupling between the solar interior and the heliosphere. The wide-ranging imagery and time series data from MOST will help understand the solar drivers and the heliospheric responses as a system, discerning and tracking 3D magnetic field structures, both transient and quiescent in the inner heliosphere. MOST will have seven remote-sensing and three in-situ instruments: (1) Magnetic and Doppler Imager (MaDI) to investigate surface and subsurface magnetism by exploiting the combination of helioseismic and magnetic-field measurements in the photosphere; (2) Inner Coronal Imager in EUV (ICIE) to study large-scale structures such as active regions, coronal holes and eruptive structures by capturing the magnetic connection between the photosphere and the corona to about 3 solar radii; (3) Hard X-ray Imager (HXI) to image the non-thermal flare structure; (4) White-light Coronagraph (WCOR) to seamlessly study transient and quiescent large-scale coronal structures extending from the ICIE field of view (FOV); (5) Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH), a novel radio package to determine the magnetic field structure and plasma column density, and their evolution within 0.5 au; (6) Heliospheric Imager with Polarization (HIP) to track solar features beyond the WCOR FOV, study their impact on Earth, and provide important context for FETCH; (7) Radio and Plasma Wave instrument (M/WAVES) to study electron beams and shocks propagating into the heliosphere via passive radio emission; (8) Solar High-energy Ion Velocity Analyzer (SHIVA) to determine spectra of electrons, and ions from H to Fe at multiple spatial locations and use energetic particles as tracers of magnetic connectivity; (9) Solar Wind Magnetometer (MAG) to characterize magnetic structures at 1 au; (10) Solar Wind Plasma Instrument (SWPI) to characterize plasma structures at 1 au. MOST will have two large spacecraft with identical payloads deployed at L4 and L5 and two smaller spacecraft ahead of L4 and behind L5 to carry additional FETCH elements. MOST will build upon SOHO and STEREO achievements to expand the multiview observational approach into the first half of the 21st Century. Title: Torus-Stable Zone Above Starspots Authors: Sun, Xudong; Torok, Tibor; DeRosa, Marc Bibcode: 2021AGUFMSH32A..02S Altcode: The torus instability (TI) of magnetic flux ropes is one of the main driving mechanisms of solar coronal mass ejections (CMEs). If the stabilizing background magnetic field decreases sufficiently slowly with height, the TI will be suppressed. Here we estimate the vertical extent of this "torus-stable zone" (TSZ) above starspots using the solar magnetic field as a template. For a potential field comprising a bipole as a pair of starspots and a global dipole, we show that the upper bound of the TSZ increases with the bipole size, the dipole strength, and the source surface radius where the coronal field becomes radial. The values depend on the interplay between the spot and dipole magnetic fields, which provide the local and global-scale confinement, respectively. They range from about half the bipole size to a significant fraction of the stellar radius. A secondary TSZ sometimes arises at a higher altitude which may facilitate "failed eruptions". The suppression of the TI may contribute to the lack of CME detection on cool stars, as larger starspots, stronger dipole, and more closed magnetic topology significantly expand the TSZ. Title: Coronal and Heliospheric Modeling with WSA: Recent Updates and Applications Authors: Jones, Shaela; Arge, Charles; Barnes, Graham; Casti, Marta; Cheung, Chun Ming Mark; da Silva, Daniel; DeRosa, Marc; Henney, Carl; Kirk, Michael; Simpson, David; Upton, Lisa; Wallace, Samantha Bibcode: 2021AGUFMSH15G2088J Altcode: The Wang-Sheeley-Arge (WSA) model is a combined empirical and physics-based model for the solar corona and inner heliosphere, widely used in the heliophysics community for over two decades. In recent years the model has been updated to allow solar wind forecasting for satellites in non-Earth-like orbits, such as Parker Solar Probe (PSP) and Solar Orbiter (SolO). Here we will describe subsequent improvements to the model with the release of WSA version 5.3, including the incorporation of additional photospheric map sources. We will also present comparisons between coronal magnetic field models and solar wind forecasts based on a number of different photospheric map sources and discuss the variability of these results due to the uncertainty in the photospheric flux. Finally, we will discuss the application of the WSA model to forecasting for PSP and SolO. Title: A Comparative Study of Measurements of the Suns Axisymmetric Flows: A COFFIES Effort Authors: Upton, Lisa; Jain, Kiran; Komm, Rudolf; Mahajan, Sushant; Pevtsov, Alexei; Roudier, Thierry; Tripathy, Sushanta; Ulrich, Roger; Zhao, Junwei; Basu, Sarbani; Chen, Ruizhu; DeRosa, Marc; Hess Webber, Shea; Hoeksema, J. Bibcode: 2021AGUFMSH55D1871U Altcode: Consequence Of Fields and Flows in the Interior and Exterior of the Sun (COFFIES) is a Phase-1 NASA DRIVE Science Center (DSC), with the primary objective of developing a data driven model of solar activity. One of COFFIES five primary science questions is What drives varying large-scale motions in the Sun? To address this question, we are developing a comprehensive catalog of the variable differential rotation and meridional circulation flow patterns. This catalog includes measurements of these flows as obtained by several measurement techniques: Doppler imaging, granule tracking, magnetic pattern tracking, magnetic feature tracking, as well as both time distance and ring diagram helioseismology. We show a comparison of these flows across these varied techniques, with a particular focus on the MDI/HMI/GONG/Mount Wilson overlap period (May-July 2010). We investigate the uncertainties and attempt to reconcile any discrepancies (e.g., due to flow depth or systematics associated with the different measurement techniques). This analysis will pave the way toward accurately determining the global patterns of axisymmetric flows and their regular and irregular variations during the cycle. Title: Are Potential Field Source Surface models from different magnetic maps sufficiently robust to track the evolution of the coronal magnetic topology? Authors: Barnes, G.; DeRosa, M.; Jones, S.; Cheung, M.; Arge, C.; Henney, C. Bibcode: 2021AAS...23821308B Altcode: The geometry, connectivity, and topology of the large-scale coronal magnetic field play a key role in determining whether a solar reconnection event will result in an eruption, either by influencing the location where magnetic reconnection releases energy for an event, or by determining the pathways and access to open field that allow an eruption to proceed. Knowing how reliably the coronal magnetic field can be inferred is critical to understanding its role in energetic events. Potential Field Source Surface (PFSS) models are a commonly used tool for both modeling the coronal field itself, and as input to other models. Multiple methods exist for generating the boundary condition needed for a PFSS model. We present here results of examining how robust the PFSS model topology is to different boundary maps, as measured by the presence of coronal magnetic null points and solar wind predictions from the Wang-Sheely-Arge (WSA) model, and characterize the evolution of these null points within a given model.

This material is based upon work supported by NASA under award No. 80NSSC19K0087. 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 Aeronautics and Space Administration. 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: Sun-as-a-star Spectral Irradiance Observations: Milestone For Characterizing The Stellar Active Regions Authors: Toriumi, S.; Airapetian, V.; Hudson, H.; Schrijver, C.; Cheung, M.; DeRosa, M. Bibcode: 2021AAS...23820503T Altcode: For understanding the physical mechanism behind the solar flares, it is crucial to measure the magnetic fields of active regions (ARs) from the photosphere to the corona and investigate their scale, complexity, and evolution. This is true for the stellar flares. However, it is still difficult to spatially resolve the starspots, and one possible way to probe their evolution and structure is to monitor the star in multiple wavelengths. To test this possibility with the solar data, we perform multi-wavelength irradiance monitoring of transiting solar ARs by using full-disk observation data from SDO, Hinode, GOES, and SORCE. As a result, we find, for instance, that the near UV light curves show strong correlations with photospheric total magnetic flux and that there are time lags between the coronal and photospheric light curves when ARs are close to the limb, which together may enable one to discern how high bright coronal loops extend above stellar ARs. It is also revealed that the sub-MK (i.e. transition-region temperature) EUV light curves are sometimes dimmed because the emission measure is reduced owing to the heating over a wide area around the AR. These results indicate that, by measuring the stellar light curves in multiple wavelengths, we may obtain information on the structure and evolution of stellar ARs. Title: Torus-Stable Zone Above Starspots Authors: Sun, X.; Torok, T.; DeRosa, M. Bibcode: 2021AAS...23820801S Altcode: The torus instability (TI) of current-carrying magnetic flux tubes is thought to drive many solar coronal mass ejections (CMEs). The background magnetic field provides the stabilizing force: if it decreases with height at a rate (decay index) slower than a critical value, the TI may be suppressed. Here we estimate the vertical extent of a "torus-stable zone" above starspots using a scaled model for the Sun. For a potential-field model comprising a bipole (as a pair of starspots) in alignment with a global dipole, we show that the upper bound of this zone hc increases with the bipole size a, the dipole field with harmonic coefficient g10, and the source surface radius Rs where the magnetic field becomes radial. The value of hc, ranging from about 0.5a to a significant fraction of the stellar radius, depends on the interplay between the spot and dipole magnetic fields; its upper limit is set by Rs. Suppression of the TI may contribute to the lack of CME detection from active cool stars, as larger starspots, stronger dipole, and more closed magnetic topology significantly expand the torus-stable zone. Title: Torus-Stable Zone Above Starspots Authors: Sun, Xudong; Török, Tibor; DeRosa, Marc Bibcode: 2021csss.confE..15S Altcode: The torus instability (TI) of current-carrying magnetic flux tubes is thought to drive many solar coronal mass ejections (CMEs). The background magnetic field provides the stabilizing force: if it decreases with height at a rate slower than a critical value, the TI may be suppressed. Here we estimate the vertical extent of a "torus-stable zone" above starspots using a scaled model for the Sun. For a potential-field model comprising a bipole (as a pair of starspots) in alignment with a global dipole, we show that the upper bound of this zone hc increases with the bipole size a, the dipole field with harmonic coefficient g10, and the source surface radius Rs where the magnetic field becomes radial. The value of hc, ranging from about 0.5a to a significant fraction of the stellar radius, depends on the interplay between the spot and dipole magnetic fields; its upper limit is set by Rs. Suppression of the TI may contribute to the lack of CME detection from active cool stars, as larger starspots, stronger dipole, and more closed magnetic topology significantly expand the torus-stable zone. Title: Sun-as-a-star Multi-wavelength Observations: A Milestone for Characterization of Stellar Active Regions Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.; Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L. Bibcode: 2021csss.confE..46T Altcode: It has been revealed that "superflares" can occur on solar-type stars. The magnetic energy of the flares is likely to be stored in active-region atmospheres. Therefore, to explain the energy storage and occurrence of the flares, it is important to monitor the evolutions of the active regions, not only in visible light but also in ultraviolet (UV) and X-rays. To demonstrate this, we perform multi-wavelength irradiance monitoring of transiting solar active regions by using full-disk observation data. As a result of this sun-as-a-star spectral irradiance analysis, we confirm that the visible continuum that corresponds to the photosphere becomes darkened when the spot is at the central meridian, whereas most of the UV, EUV and X-rays, which are sensitive to chromospheric to coronal temperatures, are brightened, reflecting the bright magnetic features above the starspots. The time lags between the coronal and photospheric light curves have the potential to probe the extent of coronal magnetic fields above the starspots. These results indicate that, by measuring the stellar light curves in multiple wavelengths, we may obtain information on the structures and evolution of stellar active regions. Title: The Coronal Global Evolutionary Model: Using HMI Vector Magnetogram and Doppler Data to Determine Coronal Magnetic Field Evolution Authors: Kazachenko, Maria; Abbett, Bill; Liu, Yang; Fisher, George; Welsch, Brian; Bercik, Dave; DeRosa, Marc; Cheung, Mark; Sun, Xudong; Hoeksema, J. Todd; Erkka Lumme, .; Hayashi, Keiji; Lynch, Benjamin Bibcode: 2021cosp...43E1785K Altcode: The Coronal Global Evolutionary Model (CGEM) provides data-driven simulations of the magnetic field in the solar corona to better understand the build-up of magnetic energy that leads to eruptive events. The CGEM project has developed six capabilities. CGEM modules (1) prepare time series of full-disk vector magnetic field observations to (2) derive the changing electric field in the solar photosphere over active-region scales. This local electric field is (3) incorporated into a surface flux transport model that reconstructs a global electric field that evolves magnetic flux in a consistent way. These electric fields drive a (4) 3D spherical magnetofrictional (SMF) model, either at high resolution over a restricted range of solid angles or at lower resolution over a global domain to determine the magnetic field and current density in the low corona. An SMF-generated initial field above an active region and the evolving electric field at the photosphere are used to drive (5) detailed magnetohydrodynamic (MHD) simulations of active regions in the low corona. SMF or MHD solutions are then used to compute emissivity proxies that can be compared with coronal observations. Finally, a lower-resolution SMF magnetic field is used to initialize (6) a global MHD model that is driven by an SMF electric field time series to simulate the outer corona and heliosphere, ultimately connecting Sun to Earth. As a demonstration, this report features results of CGEM applied to observations of the evolution of NOAA Active Region 11158 in 2011 February. Title: Using New Acoustically-Derived Solar Far-Side Magnetic-Flux Maps for Data Assimilation in Flux Transport Models Authors: Hess Webber, S. A.; Chen, R.; DeRosa, M. L.; Upton, L.; Zhao, J. Bibcode: 2020AGUFMSH0020005H Altcode: The Sun's far-side magnetic field is important to space weather forecasting and solar wind modeling, but currently it is not directly observed. The far-side magnetic field can be approximated using (a) flux transport models, which are incapable of predicting growth or new emergence of active regions; (b) conversion from STEREO EUV observations, which are only available for a limited time period; or (c) helioseismic far-side acoustic images, which provide general active region sizes and locations, but not magnetic flux. Recently, Zhao et al. [2019] and Chen et al. [ in prep ] developed an approach that calculates far-side acoustic images and calibrates them into far-side magnetic-flux maps in near-real-time, using machine-learning and STEREO EUV observations as a bridge. These far-side acoustically-derived magnetic-flux maps are starting to be tested as assimilated data in multiple flux transport models. In this work, we show examples of the results from two different models, and discuss the implications of the fully-assimilated global models of synchronic magnetic flux as operational input for coronal or solar wind models. Title: Understanding Solar Cycle Magnetic Evolution with Properties of Solar Active Regions Authors: Liu, Y.; Hoeksema, T.; Zhao, J.; DeRosa, M. L.; Sun, X. Bibcode: 2020AGUFMSH0020015L Altcode: Understanding the solar cycle is a fundamental and important objective in solar physics. Recent studies have revealed correlations between variations of the poleward transport of photospheric magnetic fields with properties of both magnetic field in solar active regions as well as their decay products. Features such as poleward surges often play an outsized role in advecting flux away from the activity belts into polar regions, and therefore affect solar cycle activity. This report describes our plans and reviews preliminary results investigating the effects of active region-modified zonal and meridional flows on flux evolution and the solar cycle. Title: Search Tool for Retrieving Level 2 Data from Hinode's Spectro-Polarimeter (SP) Authors: Kam, C.; Arbolante, Q.; Frank, Z.; DeRosa, M. L. Bibcode: 2020AGUFMED0260056K Altcode: A joint project between JAXA and NASA, the Hinode Solar Optical Telescope (SOT) has observed our Sun since its launch in October 2006. Mission data has been used extensively to study solar flares, polar magnetic fields, prominence structures, and changes over the solar cycle. Archived databases of the SOT filtergraph (FG) images and spectropolarimeter (SP) maps are maintained in the US, Japan, and Norway. Many tools for accessing SOT data were developed early in the mission timeline and are based on Harris Geospatial Solutions Inc. Interactive Data Language (IDL). We demonstrate a new open source Python-based search and cross referencing tool for the Hinode SOT SP. This tool maps their associated Level 2 inversion data products from the Heliophysics Events Knowlegebase (HEK) and enables greater accessibility to this ongoing international mission. Title: Flux-Transport Simulations of Solar Polar Magnetic Fields Based on Various Meridional Surface Flow Profiles Authors: DeRosa, M. L.; Zhao, J.; Liu, Y. Bibcode: 2020AGUFMSH0020016D Altcode: Magnetic fields located in the polar regions of the Sun during solar minima appear to be a useful predictor of the amplitude of the subsequent sunspot cycles. These polar fields are the result of flows that move magnetic flux, on a net basis, poleward from active-region latitudes. This process is captured well by two-dimensional global flux-transport schemes, which use empirical prescriptions for differential rotation, meridional flows, and convective dispersal to kinematically advect flux. As a result, these models are useful for investigating the evolution of solar surface flux and their effects on the formation of the polar fields. In the study presented here, we use a surface-flux transport model to gain intuition toward an understanding of the importance of different meridional flow profiles on the formation and evolution of the polar fields. The meridional flow profiles used for this study are based on helioseismic determinations of near-surface flows during recently activity cycles. Title: Sun-as-a-star Spectral Irradiance Observations of Transiting Active Regions Authors: Toriumi, Shin; Airapetian, Vladimir S.; Hudson, Hugh S.; Schrijver, Carolus J.; Cheung, Mark C. M.; DeRosa, Marc L. Bibcode: 2020ApJ...902...36T Altcode: 2020arXiv200804319T Major solar flares are prone to occur in active-region (AR) atmospheres associated with large, complex, dynamically evolving sunspots. This points to the importance of monitoring the evolution of starspots, not only in visible but also in ultraviolet (UV) and X-rays, in understanding the origin and occurrence of stellar flares. To this end, we perform spectral irradiance analysis on different types of transiting solar ARs by using a variety of full-disk synoptic observations. The target events are an isolated sunspot, spotless plage, and emerging flux in prolonged quiet-Sun conditions selected from the past decade. We find that the visible continuum and total solar irradiance become darkened when the spot is at the central meridian, whereas it is bright near the solar limb; UV bands sensitive to the chromosphere correlate well with the variation of total unsigned magnetic flux in the photosphere; amplitudes of extreme ultraviolet (EUV) and soft X-ray increase with the characteristic temperature, whose light curves are flat-topped due to their sensitivity to the optically thin corona; the transiting spotless plage does not show the darkening in the visible irradiance, while the emerging flux produces an asymmetry in all light curves about the central meridian. The multiwavelength Sun-as-a-star study described here indicates that the time lags between the coronal and photospheric light curves have the potential to probe the extent of coronal magnetic fields above the starspots. In addition, EUV wavelengths that are sensitive to temperatures just below 1 MK sometimes show antiphased variations, which may be used for diagnosing plasmas around starspots. Title: The Coronal Global Evolutionary Model: Using HMI Vector Magnetogram and Doppler Data to Determine Coronal Magnetic Field Evolution Authors: Hoeksema, J. Todd; Abbett, William P.; Bercik, David J.; Cheung, Mark C. M.; DeRosa, Marc L.; Fisher, George H.; Hayashi, Keiji; Kazachenko, Maria D.; Liu, Yang; Lumme, Erkka; Lynch, Benjamin J.; Sun, Xudong; Welsch, Brian T. Bibcode: 2020ApJS..250...28H Altcode: 2020arXiv200614579H The Coronal Global Evolutionary Model (CGEM) provides data-driven simulations of the magnetic field in the solar corona to better understand the build-up of magnetic energy that leads to eruptive events. The CGEM project has developed six capabilities. CGEM modules (1) prepare time series of full-disk vector magnetic field observations to (2) derive the changing electric field in the solar photosphere over active-region scales. This local electric field is (3) incorporated into a surface flux transport model that reconstructs a global electric field that evolves magnetic flux in a consistent way. These electric fields drive a (4) 3D spherical magnetofrictional (SMF) model, either at high resolution over a restricted range of solid angles or at lower resolution over a global domain to determine the magnetic field and current density in the low corona. An SMF-generated initial field above an active region and the evolving electric field at the photosphere are used to drive (5) detailed magnetohydrodynamic (MHD) simulations of active regions in the low corona. SMF or MHD solutions are then used to compute emissivity proxies that can be compared with coronal observations. Finally, a lower-resolution SMF magnetic field is used to initialize (6) a global MHD model that is driven by an SMF electric field time series to simulate the outer corona and heliosphere, ultimately connecting Sun to Earth. As a demonstration, this report features results of CGEM applied to observations of the evolution of NOAA Active Region 11158 in 2011 February. 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: The PDFI_SS Electric Field Inversion Software Authors: Fisher, George H.; Kazachenko, Maria D.; Welsch, Brian T.; Sun, Xudong; Lumme, Erkka; Bercik, David J.; DeRosa, Marc L.; Cheung, Mark C. M. Bibcode: 2020ApJS..248....2F Altcode: 2019arXiv191208301F We describe the PDFI_SS software library, which is designed to find the electric field at the Sun's photosphere from a sequence of vector magnetogram and Doppler velocity measurements and estimates of horizontal velocities obtained from local correlation tracking using the recently upgraded Fourier Local Correlation Tracking code. The library, a collection of FORTRAN subroutines, uses the "PDFI" technique described by Kazachenko et al., but modified for use in spherical, Plate Carrée geometry on a staggered grid. The domain over which solutions are found is a subset of the global spherical surface, defined by user-specified limits of colatitude and longitude. Our staggered grid approach, based on that of Yee, is more conservative and self-consistent compared to the centered, Cartesian grid used by Kazachenko et al. The library can be used to compute an end-to-end solution for electric fields from data taken by the HMI instrument aboard NASA's SDO mission. This capability has been incorporated into the HMI pipeline processing system operating at SDO's Joint Science Operations Center. The library is written in a general and modular way so that the calculations can be customized to modify or delete electric field contributions, or used with other data sets. Other applications include "nudging" numerical models of the solar atmosphere to facilitate assimilative simulations. The library includes an ability to compute "global" (whole-Sun) electric field solutions. The library also includes an ability to compute potential magnetic field solutions in spherical coordinates. This distribution includes a number of test programs that allow the user to test the software. Title: Coronal dimming as a proxy for stellar coronal mass ejections Authors: Jin, M.; Cheung, M. C. M.; DeRosa, M. L.; Nitta, N. V.; Schrijver, C. J.; France, K.; Kowalski, A.; Mason, J. P.; Osten, R. Bibcode: 2020IAUS..354..426J Altcode: 2020arXiv200206249J Solar coronal dimmings have been observed extensively in the past two decades and are believed to have close association with coronal mass ejections (CMEs). Recent study found that coronal dimming is the only signature that could differentiate powerful flares that have CMEs from those that do not. Therefore, dimming might be one of the best candidates to observe the stellar CMEs on distant Sun-like stars. In this study, we investigate the possibility of using coronal dimming as a proxy to diagnose stellar CMEs. By simulating a realistic solar CME event and corresponding coronal dimming using a global magnetohydrodynamics model (AWSoM: Alfvén-wave Solar Model), we first demonstrate the capability of the model to reproduce solar observations. We then extend the model for simulating stellar CMEs by modifying the input magnetic flux density as well as the initial magnetic energy of the CME flux rope. Our result suggests that with improved instrument sensitivity, it is possible to detect the coronal dimming signals induced by the stellar CMEs. Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks from the X8.2 Eruptive Flare on 2017 September 10 Authors: Jin, M.; Liu, W.; Cheung, C. M. M.; Nitta, N.; DeRosa, M. L.; Manchester, W.; Ofman, L.; Downs, C.; Petrosian, V.; Omodei, N.; Moschou, S. P.; Sokolov, I. Bibcode: 2019AGUFMSH32A..01J Altcode: As one of the largest flare-CME eruptions during solar cycle 24, the 2017 September 10 X8.2 flare event is associated with spectacular global EUV waves that transverse almost the entire visible solar disk, a CME with speed > 3000 km/s, which is one of the fastest CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for more than 12 hours. All these unique observational features pose new challenge on current numerical models to reproduce the multi-wavelength observations. To take this challenge, we simulate the September 10 event using a global MHD model (AWSoM: Alfven Wave Solar Model) within the Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux rope. We assess several important observed and physical inputs (e.g., flux rope properties, polar magnetic field) in the model to better reproduce the multi-wavelength observations. We find that the simulated EUV wave morphology and kinematics are sensitive to the orientation of the initial flux rope introduced to the source active region. An orientation with the flux-rope axis in the north-south direction produces the best match to the observations, which suggests that EUV waves may potentially be used to constrain the flux-rope geometry for such limb or behind-the-limb eruptions that lack good magnetic field observations. By further combining with the white light and radio observations, we demonstrate the flux rope-corona interaction can greatly impact the early phase shock evolution (e.g., geometry and shock parameters) therefore plays a significant role for particle acceleration near the Sun in this event. By propagating the CMEs into the heliosphere and beyond the Earth and Mars orbits, we compare the model results with the in-situ measurements and demonstrate the importance of input polar magnetic field on the realistic CME modeling therefore space weather forecasting. Title: Inferring the Sun's Far-Side Magnetic Flux for Operations Using Time-Distance Helioseismic Imaging Authors: Hess Webber, S. A.; Zhao, J.; Chen, R.; Hoeksema, J. T.; Liu, Y.; Bobra, M.; DeRosa, M. L. Bibcode: 2019AGUFMSH33C3353H Altcode: Solar wind models are highly dependent on global magnetic fields at the solar surface as their inner boundary condition, and the lack of global field data is a significant problem plaguing solar wind modeling. Currently, only direct observations of the near-side magnetic field exist and far-side approximations are incapable of predicting growth of existing active regions or new magnetic flux emergence. To fill this data gap, we develop a method that calibrates far-side helioseismic images, which are calculated using near-side Doppler observations, to far-side magnetic flux maps. The calibration employs multiple machine-learning methods that use EUV 304 Å data as a bridge. These algorithms determine a relation 1) between the near-side AIA 304 Å data and HMI magnetic field data, and 2) between STEREO 304 Å data and far-side helioseismic images obtained from a newly developed time-distance helioseismic far-side imaging method. The resulting magnetic flux maps have been further calibrated using maps produced by a flux transport model. The various data products from this work — far-side acoustic maps, far-side STEREO EUV-derived magnetic flux maps, and near-real-time acoustically-driven far-side magnetic flux maps, along with maps of the associated uncertainties — are being made available to enable a synchronic global magnetic flux input into coronal and solar wind models. Title: Characterizing the Magnetic Environment of Exoplanet Stellar Systems Authors: Farrish, Alison O.; Alexander, David; Maruo, Mei; DeRosa, Marc; Toffoletto, Frank; Sciola, Anthony M. Bibcode: 2019ApJ...885...51F Altcode: We employ a flux transport model incorporating observed stellar activity relations to characterize stellar interplanetary fields on cycle timescales for a range of stellar activity defined by the Rossby number. This framework allows us to examine the asterospheric environments of exoplanetary systems and yields references against which exoplanetary observations can be compared. We examine several quantitative measures of star-exoplanet interaction: the ratio of open to total stellar magnetic flux, the location of the stellar Alfvén surface, and the strength of interplanetary magnetic field polarity inversions, all of which influence planetary magnetic environments. For simulations in the range of Rossby numbers considered (0.1-5 RoSun), we find that (1) the fraction of open magnetic flux available to interplanetary space increases with Rossby number, with a maximum of around 40% at stellar minimum for low-activity stars, while the open flux for very active stars (Ro ∼ 0.1-0.25 RoSun) is ∼1-5% (2) the mean Alfvén surface radius, R A, varies between 0.7 and 1.3 R A,Sun and is larger for lower stellar activity; and (3) at high activity, the asterospheric current sheet becomes more complex with stronger inversions, possibly resulting in more frequent reconnection events (e.g., magnetic storms) at the planetary magnetosphere. The simulations presented here serve to bound a range of asterospheric magnetic environments within which we can characterize the conditions impacting any exoplanets present. We relate these results to several known exoplanets and discuss how they might be affected by changes in asterospheric magnetic field topologies. Title: A comprehensive three-dimensional radiative magnetohydrodynamic simulation of a solar flare Authors: Cheung, M. C. M.; Rempel, M.; Chintzoglou, G.; Chen, F.; Testa, P.; Martínez-Sykora, J.; Sainz Dalda, A.; DeRosa, M. L.; Malanushenko, A.; Hansteen, V.; De Pontieu, B.; Carlsson, M.; Gudiksen, B.; McIntosh, S. W. Bibcode: 2019NatAs...3..160C Altcode: 2018NatAs...3..160C Solar and stellar flares are the most intense emitters of X-rays and extreme ultraviolet radiation in planetary systems1,2. On the Sun, strong flares are usually found in newly emerging sunspot regions3. The emergence of these magnetic sunspot groups leads to the accumulation of magnetic energy in the corona. When the magnetic field undergoes abrupt relaxation, the energy released powers coronal mass ejections as well as heating plasma to temperatures beyond tens of millions of kelvins. While recent work has shed light on how magnetic energy and twist accumulate in the corona4 and on how three-dimensional magnetic reconnection allows for rapid energy release5,6, a self-consistent model capturing how such magnetic changes translate into observable diagnostics has remained elusive. Here, we present a comprehensive radiative magnetohydrodynamics simulation of a solar flare capturing the process from emergence to eruption. The simulation has sufficient realism for the synthesis of remote sensing measurements to compare with observations at visible, ultraviolet and X-ray wavelengths. This unifying model allows us to explain a number of well-known features of solar flares7, including the time profile of the X-ray flux during flares, origin and temporal evolution of chromospheric evaporation and condensation, and sweeping of flare ribbons in the lower atmosphere. Furthermore, the model reproduces the apparent non-thermal shape of coronal X-ray spectra, which is the result of the superposition of multi-component super-hot plasmas8 up to and beyond 100 million K. Title: Coronal Magnetic Field Topologies of Solar Active Regions Authors: DeRosa, Marc L.; Barnes, Graham Bibcode: 2019AAS...23430504D Altcode: The magnetic field overlying the coronae of solar active regions displays many complex configurations. In this work, we show renderings of the important topological surfaces corresponding to potential fields above solar active regions. Common geometries are identified, such as nested domains of connectivity, and the presence of narrow channels of open flux having high expansion factors. Additionally, a sequence of magnetic field topologies is used to demonstrate null-point creation and annihilation. Due to the presence of electric currents, the real coronal magnetic field topology is expected to be even more complex than that found in these potential fields. Title: Radiative MHD Simulation of a Solar Flare Authors: Cheung, Mark; Rempel, Matthias D.; Chintzoglou, Georgios; Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto; DeRosa, Marc L.; Malanushenko, Anna; Hansteen, Viggo; Carlsson, Mats; De Pontieu, Bart; Gudiksen, Boris; McIntosh, Scott W. Bibcode: 2019AAS...23431005C Altcode: We present a radiative MHD simulation of a solar flare. The computational domain captures the near-surface layers of the convection zone and overlying atmosphere. Inspired by the observed evolution of NOAA Active Region (AR) 12017, a parasitic bipolar region is imposed to emerge in the vicinity of a pre-existing sunspot. The emergence of twisted magnetic flux generates shear flows that create a pre-existing flux rope underneath the canopy field of the sunspot. Following erosion of the overlying bootstrapping field, the flux rope erupts. Rapid release of magnetic energy results in multi-wavelength synthetic observables (including X-ray spectra, narrowband EUV images, Doppler shifts of EUV lines) that are consistent with flare observations. This works suggests the super-position of multi-thermal, superhot (up to 100 MK) plasma may be partially responsible for the apparent non-thermal shape of coronal X-ray sources in flares. Implications for remote sensing observations of other astrophysical objects is also discussed. This work is an important stepping stone toward high-fidelity data-driven MHD models. Title: Reliably Inferring the Sun's Far-Side Magnetic Flux for Operations Using Time-Distance Helioseismic Imaging - Updates Authors: Hess Webber, Shea A.; Zhao, Junwei; Chen, Ruizhu; Hoeksema, Jon Todd; Liu, Yang; Bobra, Monica; DeRosa, Marc L. Bibcode: 2019AAS...23411805H Altcode: Solar wind models are highly dependent on global magnetic fields at the solar surface as their inner boundary condition, and the lack of global field data is a significant problem plaguing solar wind modeling. Currently, only near-side magnetic field observations exist and far-side approximations are incapable of predicting growth of existing active regions or new magnetic flux emergence. We therefore plan to develop a method that calibrates far-side helioseismic images, calculated using near-side Doppler observations, to far-side magnetic flux maps to fill this data gap. The calibration will employ machine-learning methods that use EUV 304 Å data as a bridge: a relation will be sought 1) between the near-side AIA 304 Å data and HMI magnetic field data, and 2) between STEREO 304 Å data and far-side helioseismic images obtained from a newly developed time-distance helioseismic far-side imaging method. As an update, progress has been made in establishing the relation between the near-side 304 Å data and magnetic flux data, and some previously-unknown systematics were identified and corrected in the helioseismic far-side images. These systematic-effect-corrected far-side images will then be used to establish a relation with the far-side EUV data. Title: Simulating the Inner Asterospheric Magnetic Fields of Exoplanet Host Stars Authors: Farrish, Alison; Alexander, David; Maruo, Mei; Sciola, Anthony; Toffoletto, Frank; DeRosa, Marc L. Bibcode: 2019AAS...23430305F Altcode: We study magnetic and energetic activity across a range of stellar behavior via the application of an observationally-based heliophysics modeling framework. We simulate the inner asterospheric magnetic fields of host stars with the aim of better understanding and constraining the space weather environments of exoplanets, and improving our knowledge of the solar-stellar connection. As astronomy instrumentation has improved, Earth-like exoplanets are increasingly being found orbiting in the habitable zones of a variety of stars, ranging from the smallest and coolest M dwarfs to larger and more solar-like stars. We are therefore interested in characterizing a broad range of stellar magnetic activity and the resulting impacts on asterospheric environments. We will present our work simulating stellar magnetic activity on cycle timescales via the integration of modeled magnetic flux emergence, coronal field structure and related plasma emission, and stellar winds. We use this self-consistent framework of heliophysics-based models to simulate stellar and asterospheric evolution, in order to better understand the dynamic connections between host stars and potential impacts on planetary space weather and habitability. We also remark on the comparative heliophysics approach which we plan to extend to star-planet interactions via coupling to models of magnetospheric activity and dynamo-driven stellar flux emergence. Title: The Global EUV Wave Associated with the SOL2017-09-10 X8.2 Flare: SDO/AIA Observations and Data-constrained MHD Simulations Authors: Liu, Wei; Jin, Meng; Ofman, Leon; DeRosa, Marc L. Bibcode: 2019AAS...23430701L Altcode: While large-scale extreme ultraviolet (EUV) waves associated with coronal mass ejections (CMEs) and solar flares are common, the EUV wave triggered by the X8 flare-CME eruption on 2017 September 10 was an extreme. This was, to the best of our knowledge, the first detection of an EUV wave traversing the full-Sun corona over the entire visible disk and off-limb circumference, manifesting a truly global nature. In addition to commonly observed reflections, it had strong transmissions in and out of both polar coronal holes, at elevated wave speeds of >2000 km/s within them. With an exceptionally large wave amplitude, it produced significant compressional heating to local coronal plasma. We present detailed analysis of SDO/AIA observations, global magnetic field extrapolations with the potential-field source surface (PFSS) model, and data-constrained MHD simulations of this event using the University of Michigan Alfven Wave Solar Model (AWSoM). By comparing the observations and simulations, we benchmark diagnostics of the magnetic field strengths and thermal properties of the solar corona on global scales. We discuss the future prospects of using such extreme EUV waves as probes for global coronal seismology, an area yet to be fully exploited. Title: Magnetic Properties of Asterospheres of Exoplanet Systems Authors: Farrish, Alison; Alexander, David; Maruo, Mei; Sciola, Anthony; Toffoletto, Frank; DeRosa, Marc Bibcode: 2019shin.confE.152F Altcode: We study magnetic and energetic activity across a range of stellar behavior via the application of an observationally-based heliophysics modeling framework. We simulate the inner asterospheric magnetic fields of host stars with the aim of better understanding and constraining the space weather environments of exoplanets, and improving our knowledge of the solar-stellar connection. As astronomy instrumentation has improved, Earth-like exoplanets are increasingly being found orbiting in the habitable zones of a variety of stars, ranging from the smallest and coolest M dwarfs to larger and more solar-like stars. We are therefore interested in characterizing a broad range of stellar magnetic activity and the resulting impacts on asterospheric environments. We will present our work simulating stellar magnetic activity on cycle timescales via the integration of modeled magnetic flux emergence, coronal field structure and related plasma emission, and stellar winds. We use this self-consistent framework of heliophysics-based models to simulate stellar and asterospheric evolution, in order to better understand the dynamic connections between host stars and potential impacts on planetary space weather and habitability. We also remark on the comparative heliophysics approach which we plan to extend to star-planet interactions via coupling to models of magnetospheric activity and dynamo-driven stellar flux emergence. Title: Reliably Inferring the Sun's Far-Side Magnetic Flux for Operations Using Time-Distance Helioseismic Imaging Authors: Hess Webber, Shea A.; Zhao, Junwei; Chen, Ruizhu; Hoeksema, J. Todd; Liu, Yang; Bobra, Monica; DeRosa, Marc Bibcode: 2019spwe.confE...1H Altcode: Solar wind models are highly dependent on global magnetic fields at the solar surface as their inner boundary condition, and the lack of global field data is a significant problem plaguing solar wind modeling. Currently, only near-side magnetic field observations exist and far-side approximations are incapable of predicting growth of existing active regions or new magnetic flux emergence. We therefore plan to develop a method that calibrates far-side helioseismic images, calculated using near-side Doppler observations, to far-side magnetic flux maps to fill this data gap. The calibration will employ machine-learning methods that use EUV 304 Angstrom data as a bridge: a relation will be sought 1) between the near-side AIA 304 Angstrom data and HMI magnetic field data, and 2) between STEREO 304 Angstrom data and far-side helioseismic images obtained from a newly developed time-distance helioseismic far-side imaging method. As an update, progress has been made in establishing the relation between the near-side 304 Angstrom data and magnetic flux data, and some previously-unknown systematics were identified and corrected in the helioseismic far-side images. These systematic-effect-corrected far-side images will then be used to establish a relation with the far-side EUV data. Title: To what degree do regions of open flux located near active regions affect their eruptivity? Authors: DeRosa, Marc; Barnes, Graham Bibcode: 2019EGUGA..21.4673D Altcode: Most, but not all, X-class flares are associated with CMEs. The conventional wisdom likely ascribes this association to the large amount of energy released during the flare reconnection process that then becomes available for accelerating matter upward. For those X-class flares that are non-eruptive, what properties set these apart such that there is no discernible eruption? In this study, we investigate whether active regions that produce non-eruptive X-class flares are correlated with the lack of a nearby channel of open flux in the overlying global coronal magnetic field configuration. We analyze PFSS models of the coronal magnetic field associated with 56 X-class flares (in 37 flaring active regions) occurring during Cycles 23 and 24, and evaluate whether properties the field configuration are associated with the properties of the associated flares. We find a positive correlation between whether a region is non-eruptive and the absence of nearby open magnetic field lines in the PFSS models, however the confidence we assign to this result is limited by the small number of non-eruptive X-class flares in the sample. Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth System Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan; Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao, Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa, Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale; Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland, Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander; Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens, Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent; Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet, Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth, Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha Bibcode: 2018arXiv181008728N Altcode: The authors of this report met on 28-30 March 2018 at the New Jersey Institute of Technology, Newark, New Jersey, for a 3-day workshop that brought together a group of data providers, expert modelers, and computer and data scientists, in the solar discipline. Their objective was to identify challenges in the path towards building an effective framework to achieve transformative advances in the understanding and forecasting of the Sun-Earth system from the upper convection zone of the Sun to the Earth's magnetosphere. The workshop aimed to develop a research roadmap that targets the scientific challenge of coupling observations and modeling with emerging data-science research to extract knowledge from the large volumes of data (observed and simulated) while stimulating computer science with new research applications. The desire among the attendees was to promote future trans-disciplinary collaborations and identify areas of convergence across disciplines. The workshop combined a set of plenary sessions featuring invited introductory talks and workshop progress reports, interleaved with a set of breakout sessions focused on specific topics of interest. Each breakout group generated short documents, listing the challenges identified during their discussions in addition to possible ways of attacking them collectively. These documents were combined into this report-wherein a list of prioritized activities have been collated, shared and endorsed. Title: Simulation of Exoplanet Host Star Magnetic Activity on Stellar Cycle Timescales Authors: Farrish, A. O.; Maruo, M.; Barnes, W. T.; Alexander, D.; Bradshaw, S.; DeRosa, M. Bibcode: 2018LPICo2065.2043F Altcode: We apply solar physics modeling tools to the study of star-exoplanet interaction, with a focus on how variations in stellar magnetic field and energetic emission on cycle timescales may impact planetary habitability. Title: Using Sun's Far-Side Images Inferred by the Time-Distance Helioseismic Imaging to Improve Synoptic Maps of Magnetic Field: Importance and Methodology Authors: Liu, Yang; Zhao, Junwei; Hoeksema, J. T.; Chen, Ruizhu; Bobra, Monica; Hess Webber, Shea; DeRosa, M.; Sun, X. Bibcode: 2018shin.confE.147L Altcode: Synoptic map of magnetic field is an important piece of data used for many space weather models. Currently solar observation can only provide magnetic field measurement on the earth-side surface. To generate magnetic field synoptic maps, the magnetic field measured about 13 days ago is used for the far-side surface when it was at the earth-side. This kind of synoptic maps was improved later on by evolving the measured magnetic field to the day of interest using a flux transfer model. It takes into account of evolution of magnetic field, but fails to include newly emerging magnetic flux, especially emerging active regions, that start to emerge at the far-side surface.

In this presentation, we first demonstrate that the newly emerging fluxes in the far-side change the coronal magnetic field structure, and this change can be global, far reaching to the earth-side. Because coronal magnetic field is related to the solar wind property and CMEs' speed, this change has potential to impact space weather forecast. We then present examples that convert far-side images into magnetic flux distribution using deep learning. The far-side images are inferred by the time-distance helioseismic method. Finally we propose to improve the synoptic maps of magnetic field by combining the far-size images and the machine learning technique. Title: Simulation of Exoplanet Host Star Magnetic Activity on Stellar Cycle Timescales Authors: Farrish, Alison; Maruo, M.; Barnes, W.; Alexander, D.; Bradshaw, S.; DeRosa, M. Bibcode: 2018shin.confE...4F Altcode: We apply an empirical photospheric magnetic flux transport model, derived from solar behavior, and a magnetically-driven stellar atmosphere model to explore the range of stellar effects on habitability of Earth-size exoplanets around M dwarf stars. We create detailed, dynamic simulations of stellar activity and its variability over stellar cycle timescales. In particular, we examine how the asterospheric magnetic field and related extreme ultraviolet (EUV) and X-ray emission vary in time and consider the potential impact on exoplanet habitability. Title: Do Topological Features of the Solar Corona Affect EUV Wave Events? Authors: DeRosa, Marc; Barnes, Graham; Sun, Xudong Bibcode: 2018shin.confE.142D Altcode: We present visualizations of the topology of the coronal magnetic field associated with an EUV wave event. This case study will be used to evaluate whether topological features of interest, such as null points, separatrix surfaces, domains of high Q (squashing factor), play any role in determining the morphology of the EUV wave propagation. Title: Does Nearby Open Flux Affect the Eruptivity of Solar Active Regions? Authors: DeRosa, Marc L.; Barnes, Graham Bibcode: 2018ApJ...861..131D Altcode: 2018arXiv180201199D The most energetic solar flares are typically associated with the ejection of a cloud of coronal material into the heliosphere in the form of a coronal mass ejection (CME). However, large flares exist that are not accompanied by a CME. The existence of these noneruptive flares raises the question of whether such flares suffer from a lack of access to nearby open fields in the vicinity above the flare (reconnection) site. In this study, we use a sample of 56 flares from sunspot Cycles 23 and 24 to test whether active regions that produce eruptive X-class flares are preferentially located near coronal magnetic field domains that are open to the heliosphere, as inferred from a potential field source-surface model. The study shows that X-class flares with access to open fields are eruptive at a higher rate than those for which access is lacking. The significance of this result should be moderated due to the small number of noneruptive X-class flares in the sample, based on the associated Bayes factor. Title: Modeling the Global Coronal Field with Simulated Synoptic Magnetograms from Earth and the Lagrange Points L3, L4, and L5 Authors: Petrie, Gordon; Pevtsov, Alexei; Schwarz, Andrew; DeRosa, Marc Bibcode: 2018SoPh..293...88P Altcode: The solar photospheric magnetic flux distribution is key to structuring the global solar corona and heliosphere. Regular full-disk photospheric magnetogram data are therefore essential to our ability to model and forecast heliospheric phenomena such as space weather. However, our spatio-temporal coverage of the photospheric field is currently limited by our single vantage point at/near Earth. In particular, the polar fields play a leading role in structuring the large-scale corona and heliosphere, but each pole is unobservable for >6 months per year. Here we model the possible effect of full-disk magnetogram data from the Lagrange points L4 and L5, each extending longitude coverage by 60∘. Adding data also from the more distant point L3 extends the longitudinal coverage much further. The additional vantage points also improve the visibility of the globally influential polar fields. Using a flux-transport model for the solar photospheric field, we model full-disk observations from Earth/L1, L3, L4, and L5 over a solar cycle, construct synoptic maps using a novel weighting scheme adapted for merging magnetogram data from multiple viewpoints, and compute potential-field models for the global coronal field. Each additional viewpoint brings the maps and models into closer agreement with the reference field from the flux-transport simulation, with particular improvement at polar latitudes, the main source of the fast solar wind. Title: What Happens to Coronal Field Models when Fake East-Limb Active Regions are Inserted into Real Synoptic Charts? Authors: DeRosa, Marc L. Bibcode: 2018tess.conf41603D Altcode: Global coronal magnetic field models and solar wind models make use of synoptic maps of the photospheric magnetic field as a lower boundary condition. These maps have historically been constructed using observed magnetograms, such that a full-sun map is assembled over the course of a full solar rotation. As a result of this process, a single maps contains observations made at different times over the course of a month, with east-limb longitudes being the most out-of-date. However, there are many instances where significant missing flux located on the east limb of the sun has been shown to affect the configuration of coronal magnetic fields on the Earth-facing side, and in many cases significant downstream effects occur when predicting solar wind speeds and other quantities related to space weather. Here, the same fictitious east-limb active region is inserted into a series of synoptic charts spanning sunspot cycles 23 and 24 as a way to approximate magnetic flux located at east-limb longitudes that would be missing from a synoptic chart. The resulting ensemble of photospheric magnetic maps allows us to evaluate how often and much of an effect such "hidden flux" affects potential-field models of the global coronal field. Title: Simulated Coronal EUV Emission from Exoplanet Host Stars Authors: Farrish, Alison; Barnes, Will; Alexander, David; Bradshaw, Stephen J.; DeRosa, Mark L. Bibcode: 2018tess.conf40649F Altcode: We apply a modified solar flux transport (SFT) model, developed by Schrijver and colleagues, to emulate the magnetic activity of the host stars of recently discovered habitable-zone planets. The magnetic flux distributions produced by the SFT simulations serve as a first-order proxy for the expected magnetic behavior of an exoplanet host star. We couple the simulated magnetic structure to a coronal heating model and simulate the expected EUV and X-ray emission of the target star. The EUV emission is a key energetic input to the exoplanetary atmosphere, governing ionospheric conductance and therefore influencing the magnetospheric response to stellar activity - a key factor in determining the overall atmospheric loss and ultimately the potential of the planet for habitation. In addition, the simulated stellar coronal emission may provide signatures for comparison with astronomical observations. We consider the simulated activity over a number of stellar cycles to explore the long-term impact of the star on the exo-planetary environment. Title: Modeling the Global Coronal Field with Simulated Synoptic Magnetograms from Earth and the Lagrange points L3, L4 and L5 Authors: Petrie, Gordon J. D.; Pevtsov, Alexei A.; Schwarz, Andrew Michael; DeRosa, Marc Bibcode: 2018tess.conf40132P Altcode: The solar photospheric magnetic flux distribution determines the global structure of the solar corona and heliosphere. Regular full-disk photospheric magnetogram data are therefore essential to our ability to model and forecast heliospheric phenomena such as space weather. However, our spatio-temporal coverage of the photospheric field is currently limited by our single vantage point at/near Earth. In particular, the polar fields define the large-scale structure of the corona and heliosphere but each pole is unobservable for > 6 months per year. Here we model the possible effect of full-disk magnetogram data from the Lagrange points L4 and L5, each extending longitude coverage by 60 degrees. Adding data also from the more distant point L3 extends longitudinal coverage much further. The additional vantage points also improve the visibility of the globally influential polar fields. Using a flux-transport model for the solar photospheric field we model full-disk observations from Earth/L1, L3, L4 and L5 over a solar cycle, construct synoptic maps using a novel weighting scheme adapted for merging magnetogram data from multiple viewpoints, and compute potential-field models for the global coronal field. Each additional viewpoint significantly improves the performance of the maps and models with particular improvement at polar latitudes, the main source of the fast solar wind. Title: The Application of Solar Flux Transport Modeling to Exoplanet Systems Authors: Alexander, David; Farrish, Alison; Maruo, Mei; De Rosa, Marc L. Bibcode: 2018tess.conf40648A Altcode: Earth-size exoplanets are preferentially detected close-in around small stars; Proxima Centauri b, Ross 128 b, and the TRAPPIST-1 planets are newly discovered exoplanets in this class. The effects of magnetic interactions between the host star and such close-in exoplanets are still not well-constrained. We utilize an empirical solar magnetic flux transport model, first developed by Schrijver and colleagues, to explore the possible relationships between stellar properties (e.g. rotation period, radius, flux emergence rate, and meridional and differential flow rates) and the expected surface magnetic flux distributions, along with their evolution over the stellar cycle. The surface field then provides key information about the interplanetary magnetic fields, stellar winds, dynamic activity, and coronal emission, all of which influence the star-planet interactions. We present simulated magnetic flux patterns representing a range of possible exoplanet host stars, including potential observables such as starspots, active regions, and stellar cycle variations. The magnetic and energetic environment at an exoplanet and its impact on the magnetospheric-atmospheric coupling are important components of a planet's habitability that we expect to constrain further with this application of simulated stellar magnetic activity. Title: Coronal Mass Ejections and Dimmings: A Comparative Study using MHD Simulations and SDO Observations Authors: Jin, M.; Cheung, C. M. M.; DeRosa, M. L.; Nitta, N.; Schrijver, K. Bibcode: 2017AGUFMSH41A2758J Altcode: Solar coronal dimmings have been observed extensively in the past two decades. Due to their close association with coronal mass ejections (CMEs), there is a critical need to improve our understanding of the physical processes that cause dimmings and determine their relationship with CMEs. In this study, we investigate coronal dimmings by combining simulation and observational efforts. By utilizing a data-driven global magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we simulate coronal dimmings resulting from different CME energetics and flux rope configurations. We synthesize the emissions of different EUV spectral bands/lines and compare with SDO/AIA and EVE observations. A detailed analysis of simulation and observation data suggests that although the transient dimming / brightening patterns could relate to plasma heating processes (either by adiabatic compression or reconnection), the long-lasting "core" and "remote" (also known as "secondary") dimmings both originate from regions with open/quasi-open fields and are caused by mass loss process. The mass loss in the remote dimming region is induced by CME-driven shock. Using metrics such as dimming depth, dimming slope, and recovery time, we investigate the relationship between dimmings and CME properties (e.g., CME mass, CME speed) in the simulation. Our result suggests that coronal dimmings encode important information about CME energetics, CME-driven shock properties, and magnetic configuration of erupting flux ropes. We also discuss how our knowledge about solar coronal dimmings could be extended to the study of stellar CMEs, which may prove important for exoplanet atmospheres and habitability but which are currently not observable. Title: The Open Flux Problem Authors: Linker, J. A.; Caplan, R. M.; Downs, C.; Riley, P.; Mikic, Z.; Lionello, R.; Henney, C. J.; Arge, C. N.; Liu, Y.; Derosa, M. L.; Yeates, A.; Owens, M. J. Bibcode: 2017ApJ...848...70L Altcode: 2017arXiv170802342L The heliospheric magnetic field is of pivotal importance in solar and space physics. The field is rooted in the Sun’s photosphere, where it has been observed for many years. Global maps of the solar magnetic field based on full-disk magnetograms are commonly used as boundary conditions for coronal and solar wind models. Two primary observational constraints on the models are (1) the open field regions in the model should approximately correspond to coronal holes (CHs) observed in emission and (2) the magnitude of the open magnetic flux in the model should match that inferred from in situ spacecraft measurements. In this study, we calculate both magnetohydrodynamic and potential field source surface solutions using 14 different magnetic maps produced from five different types of observatory magnetograms, for the time period surrounding 2010 July. We have found that for all of the model/map combinations, models that have CH areas close to observations underestimate the interplanetary magnetic flux, or, conversely, for models to match the interplanetary flux, the modeled open field regions are larger than CHs observed in EUV emission. In an alternative approach, we estimate the open magnetic flux entirely from solar observations by combining automatically detected CHs for Carrington rotation 2098 with observatory synoptic magnetic maps. This approach also underestimates the interplanetary magnetic flux. Our results imply that either typical observatory maps underestimate the Sun’s magnetic flux, or a significant portion of the open magnetic flux is not rooted in regions that are obviously dark in EUV and X-ray emission. Title: Realistic radiative MHD simulation of a solar flare Authors: Rempel, Matthias D.; Cheung, Mark; Chintzoglou, Georgios; Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto; DeRosa, Marc L.; Viktorovna Malanushenko, Anna; Hansteen, Viggo H.; De Pontieu, Bart; Carlsson, Mats; Gudiksen, Boris; McIntosh, Scott W. Bibcode: 2017SPD....4840001R Altcode: We present a recently developed version of the MURaM radiative MHD code that includes coronal physics in terms of optically thin radiative loss and field aligned heat conduction. The code employs the "Boris correction" (semi-relativistic MHD with a reduced speed of light) and a hyperbolic treatment of heat conduction, which allow for efficient simulations of the photosphere/corona system by avoiding the severe time-step constraints arising from Alfven wave propagation and heat conduction. We demonstrate that this approach can be used even in dynamic phases such as a flare. We consider a setup in which a flare is triggered by flux emergence into a pre-existing bipolar active region. After the coronal energy release, efficient transport of energy along field lines leads to the formation of flare ribbons within seconds. In the flare ribbons we find downflows for temperatures lower than ~5 MK and upflows at higher temperatures. The resulting soft X-ray emission shows a fast rise and slow decay, reaching a peak corresponding to a mid C-class flare. The post reconnection energy release in the corona leads to average particle energies reaching 50 keV (500 MK under the assumption of a thermal plasma). We show that hard X-ray emission from the corona computed under the assumption of thermal bremsstrahlung can produce a power-law spectrum due to the multi-thermal nature of the plasma. The electron energy flux into the flare ribbons (classic heat conduction with free streaming limit) is highly inhomogeneous and reaches peak values of about 3x1011 erg/cm2/s in a small fraction of the ribbons, indicating regions that could potentially produce hard X-ray footpoint sources. We demonstrate that these findings are robust by comparing simulations computed with different values of the saturation heat flux as well as the "reduced speed of light". Title: Global Evolving Models of Photospheric Flux as Driven by Electric Fields Authors: DeRosa, Marc L.; Cheung, Mark; Kazachenko, Maria D.; Fisher, George H. Bibcode: 2017SPD....4811105D Altcode: We present a novel method for modeling the global radial magnetic field that is based on the incorporation of time series of photospheric electric fields. The determination of the electric fields is the result of a recently developed method that uses as input various data products from SDO/HMI, namely vector magnetic fields and line-of-sight Doppler images. For locations on the sphere where electric field data are unavailable, we instead use electric fields that are consistent with measurements of the mean differential rotation, meridional flow, and flux dispersal profiles. By combining these electric fields, a full-Sun model of the photospheric radial magnetic field can be advanced forward in time via Faraday's Law. Title: Coronal Mass Ejections and Dimmings: A Comparative Study using MHD Simulations and SDO Observations Authors: Jin, Meng; Cheung, Mark; DeRosa, Marc L.; Nitta, Nariaki; Schrijver, Karel Bibcode: 2017SPD....4820602J Altcode: Solar coronal dimmings have been observed extensively in the past two decades. Due to their close association with coronal mass ejections (CMEs), there is a critical need to improve our understanding of the physical processes that cause dimmings and determine their relationship with CMEs. In this study, we investigate coronal dimmings by combining simulation and observational efforts. By utilizing a data-driven global magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we simulate coronal dimmings resulting from different CME energetics and flux rope configurations. We synthesize the emissions of different EUV spectral bands/lines and compare with SDO/AIA and EVE observations. A detailed analysis of simulation and observation data suggests that the “core” dimming is mainly caused by the mass loss from the CME, while the “remote” dimming could have a different origin (e.g., plasma heating). Moreover, the interaction between the erupting flux rope with different orientations and the global solar corona could significantly influence the coronal dimming patterns. Using metrics such as dimming depth, dimming slope, and recovery time, we investigate the relationship between dimmings and CME properties (e.g., CME mass, CME speed) in the simulation. Our result suggests that coronal dimmings encode important information about CMEs. We also discuss how our knowledge about solar coronal dimmings could be extended to the study of stellar CMEs. Title: Does erupting material in flaring active regions always have access to open flux? Authors: DeRosa, Marc; Barnes, Graham Bibcode: 2017shin.confE..46D Altcode: Most, but not all, X-class flares are associated with CMEs. The conventional wisdom likely ascribes this association to the large amount of energy released during the flare reconnection process that then becomes available for accelerating matter upward. Of the class of X flares that are non-eruptive, what properties set these apart such that there is no discernible eruption? In this study, we investigate whether active regions that produce non-eruptive X-class flares are correlated with the lack of a nearby channel of open flux in the overlying global coronal magnetic field configuration. We analyze PFSS models of the coronal magnetic field associated with 36 flaring active regions spanning Cycles 23 and 24, and evaluate whether properties the field configuration are correlated with the properties of the associated flares. We find only a weak correlation between whether a region is eruptive and the presence of overlying open magnetic fields, suggesting the involvement of other factors in determining whether X-class flaring regions produce CMEs. Title: A study of the long term evolution in active region upflows Authors: Harra, Louise K.; Ugarte-Urra, Ignacio; De Rosa, Marc; Mandrini, Cristina; van Driel-Gesztelyi, Lidia; Baker, Deborah; Culhane, J. Leonard; Démoulin, Pascal Bibcode: 2017PASJ...69...47H Altcode: Since their discovery, upflows at the edges of active regions have attracted a lot of interest, primarily as they could potentially contribute to the slow solar wind. One aspect that has not been studied yet is how the long term evolution of active regions impacts the upflows. In this work, we analyze one active region that survives three solar rotations. We track how the flows change with time. We use local and global modeling of the decaying active region to determine how the age of the active region will impact the extent of the open magnetic fields, and then how some of the upflows could become outflows. We finish with a discussion of how these results, set in a broader context, can be further developed with the Solar Orbiter mission. Title: Magnetic Nulls and Super-radial Expansion in the Solar Corona Authors: Gibson, Sarah E.; Dalmasse, Kevin; Rachmeler, Laurel A.; De Rosa, Marc L.; Tomczyk, Steven; de Toma, Giuliana; Burkepile, Joan; Galloy, Michael Bibcode: 2017ApJ...840L..13G Altcode: 2017arXiv170407470G Magnetic fields in the Sun’s outer atmosphere—the corona—control both solar-wind acceleration and the dynamics of solar eruptions. We present the first clear observational evidence of coronal magnetic nulls in off-limb linearly polarized observations of pseudostreamers, taken by the Coronal Multichannel Polarimeter (CoMP) telescope. These nulls represent regions where magnetic reconnection is likely to act as a catalyst for solar activity. CoMP linear-polarization observations also provide an independent, coronal proxy for magnetic expansion into the solar wind, a quantity often used to parameterize and predict the solar wind speed at Earth. We introduce a new method for explicitly calculating expansion factors from CoMP coronal linear-polarization observations, which does not require photospheric extrapolations. We conclude that linearly polarized light is a powerful new diagnostic of critical coronal magnetic topologies and the expanding magnetic flux tubes that channel the solar wind. Title: Deriving the Properties of Coronal Pressure Fronts in 3D: Application to the 2012 May 17 Ground Level Enhancement Authors: Rouillard, A. P.; Plotnikov, I.; Pinto, R. F.; Tirole, M.; Lavarra, M.; Zucca, P.; Vainio, R.; Tylka, A. J.; Vourlidas, A.; De Rosa, M. L.; Linker, J.; Warmuth, A.; Mann, G.; Cohen, C. M. S.; Mewaldt, R. A. Bibcode: 2016ApJ...833...45R Altcode: 2016arXiv160505208R We study the link between an expanding coronal shock and the energetic particles measured near Earth during the ground level enhancement of 2012 May 17. We developed a new technique based on multipoint imaging to triangulate the three-dimensional (3D) expansion of the shock forming in the corona. It uses images from three vantage points by mapping the outermost extent of the coronal region perturbed by the pressure front. We derive for the first time the 3D velocity vector and the distribution of Mach numbers, M FM, of the entire front as a function of time. Our approach uses magnetic field reconstructions of the coronal field, full magnetohydrodynamic simulations and imaging inversion techniques. We find that the highest M FM values appear near the coronal neutral line within a few minutes of the coronal mass ejection onset; this neutral line is usually associated with the source of the heliospheric current and plasma sheet. We illustrate the variability of the shock speed, shock geometry, and Mach number along different modeled magnetic field lines. Despite the level of uncertainty in deriving the shock Mach numbers, all employed reconstruction techniques show that the release time of GeV particles occurs when the coronal shock becomes super-critical (M FM > 3). Combining in situ measurements with heliospheric imagery, we also demonstrate that magnetic connectivity between the accelerator (the coronal shock of 2012 May 17) and the near-Earth environment is established via a magnetic cloud that erupted from the same active region roughly five days earlier. Title: Flare Clustering Authors: Title, Alan; DeRosa, Marc Bibcode: 2016usc..confE..50T Altcode: The continuous full disk observations provided by the Atmospheric Imaging Assembly (AIA ) can give an observer the impression that many flare eruptions are causally related to one another. However, both detailed analyses of a number of events as well as several statistical studies have provided only rare examples or weak evidence of causal behavior. Since the mechanisms of flare triggering are not well understood, the lack of hard evidence is not surprising. For this study we looked instead for groups of flares (flare clusters) in which successive flares occur within a fixed time - the selection time. The data set used for the investigation is the flare waiting times provided by the X-ray flare detectors on the Geostationary Operational Environmental Satellites (GOES). We limited the study to flares of magnitude C5 and greater obtained during cycles 21, 22, 23, and 24. The GOES field of view includes the entire visible surface. While many flares in a cluster may come from the same active region, the larger clusters often have origins in multiple regions. The longest C5 cluster found with a linking window of 36 hours in cycles 21, 22, 23,and 24 was 54, 82, 42, and 18 days, respectively. X flares also cluster. A superposed epoch analyses demonstrates that there is a pronounced enhancement of number of C5 and and above flares that are centered on the X flare clusters. We suggest that this behavior implies that a component of the observed coordinated behavior originates from the MHD processes driven by the solar dynamo that in turn creates unstable states in the solar atmosphere. The relationship between flare clusters and magnetic centers of activity was explored as was the correlation between high flare rates and significant changes in the total solar magnetic flux, Title: a Numerical Study of Long-Range Magnetic Impacts during Coronal Mass Ejections Authors: Jin, Meng; Schrijver, Karel; Cheung, Mark; DeRosa, Marc; Nitta, Nariaki; Title, Alan Bibcode: 2016shin.confE..38J Altcode: With the global view and high-cadence observations from SDO/AIA and STEREO, many spatially separated solar eruptive events appear to be coupled. However, the mechanisms for 'sympathetic' events are still largely unknown. In this study, we investigate the impact of an erupting flux rope on surrounding solar structures through large-scale magnetic coupling. We build a realistic environment of the solar corona on 2011 February 15 using a global magnetohydrodynamics (MHD) model and initiate coronal mass ejections (CMEs) in active region (AR) 11158 by inserting Gibson-Low analytical flux ropes. We show that a CME's impact on the surrounding structures depends not only on the magnetic strength of these structures and their distance to the source region, but also on the interaction between the CME with the large-scale magnetic field. Within the CME expansion domain where the flux rope field directly interacts with the solar structures, expansion-induced reconnection often modifies the overlying field, thereby increasing the decay index. This effect may provide a primary coupling mechanism underlying the sympathetic eruptions. The magnitude of the impact is found to depend on the orientation of the erupting flux rope, with the largest impacts occurring when the flux rope is favorably oriented for reconnecting with the surrounding regions. Outside the CME expansion domain, the influence of the CME is mainly through field line compression or post-eruption relaxation. Based on our numerical experiments, we discuss a way to quantify the eruption impact, which could be useful for forecasting purposes. Title: Do large-scale topological features correlate with flare properties? Authors: DeRosa, Marc; Barnes, Graham Bibcode: 2016shin.confE.129D Altcode: In this study, we aim to identify whether the presence or absence of particular topological features in the large-scale coronal magnetic field are correlated with whether a flare is confined or eruptive. To this end, we first determine the locations of null points, spine lines, and separatrix surfaces within the potential fields associated with the locations of several strong flares from the current and previous sunspot cycles. We then validate the topological skeletons against large-scale features in observations, such as the locations of streamers and pseudostreamers in coronagraph images. Finally, we characterize the topological environment in the vicinity of the flaring active regions and identify the trends involving their large-scale topologies and the properties of the associated flares. Title: The Topology of Coronal Magnetic Fields, Shine Characterizing the Properties of Coronal Magnetic Null Points Authors: Barnes, Graham; DeRosa, Marc; Wagner, Eric Bibcode: 2016shin.confE.133B Altcode: The topology of the coronal magnetic field plays a role in a wide range of phenomena, from Coronal Mass Ejections (CMEs) through heating of the corona. One fundamental topological feature is the null point, where the magnetic field vanishes. These points are natural sites of magnetic reconnection, and hence the release of energy stored in the magnetic field. We present preliminary results of a study using data from the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics Observatory to characterize the properties and evolution of null points in a Potential Field Source Surface model of the coronal field. The main properties considered are the lifetime of the null points, their distribution with height, and how they form and subsequently vanish.

This work is supported by NSF/SHINE grant 1357018 and by NASA/LWS Grant NNX14AD45G. Title: Do Large-Scale Topological Features Correlate with Flare Properties? Authors: DeRosa, Marc L.; Barnes, Graham Bibcode: 2016SPD....47.1005D Altcode: In this study, we aim to identify whether the presence or absence of particular topological features in the large-scale coronal magnetic field are correlated with whether a flare is confined or eruptive. To this end, we first determine the locations of null points, spine lines, and separatrix surfaces within the potential fields associated with the locations of several strong flares from the current and previous sunspot cycles. We then validate the topological skeletons against large-scale features in observations, such as the locations of streamers and pseudostreamers in coronagraph images. Finally, we characterize the topological environment in the vicinity of the flaring active regions and identify the trends involving their large-scale topologies and the properties of the associated flares. Title: Physics & Diagnostics of the Drivers of Solar Eruptions Authors: Cheung, Mark; Rempel, Matthias D.; Martinez-Sykora, Juan; Testa, Paola; Hansteen, Viggo H.; Viktorovna Malanushenko, Anna; Sainz Dalda, Alberto; DeRosa, Marc L.; De Pontieu, Bart; Carlsson, Mats; Chen, Feng; McIntosh, Scott W.; Gudiksen, Boris Bibcode: 2016SPD....47.0607C Altcode: We provide an update on our NASA Heliophysics Grand Challenges Research (HGCR) project on the ‘Physics & Diagnostics of the Drivers of Solar Eruptions’. This presentation will focus on results from a data-inspired, 3D radiative MHD model of a solar flare. The model flare results from the interaction of newly emerging flux with a pre-existing active region. Synthetic observables from the model reproduce observational features compatible with actual flares. These include signatures of coronal magnetic reconnection, chromospheric evaporation, EUV flare arcades, sweeping motion of flare ribbons and sunquakes. Title: A Numerical Study of Long-range Magnetic Impacts during Coronal Mass Ejections Authors: Jin, M.; Schrijver, C. J.; Cheung, M. C. M.; DeRosa, M. L.; Nitta, N. V.; Title, A. M. Bibcode: 2016ApJ...820...16J Altcode: 2016arXiv160304900J With the global view and high-cadence observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly and Solar TErrestrial RElations Observatory, many spatially separated solar eruptive events appear to be coupled. However, the mechanisms for “sympathetic” events are still largely unknown. In this study, we investigate the impact of an erupting flux rope on surrounding solar structures through large-scale magnetic coupling. We build a realistic environment of the solar corona on 2011 February 15 using a global magnetohydrodynamics model and initiate coronal mass ejections (CMEs) in active region 11158 by inserting Gibson-Low analytical flux ropes. We show that a CME’s impact on the surrounding structures depends not only on the magnetic strength of these structures and their distance to the source region, but also on the interaction between the CME and the large-scale magnetic field. Within the CME expansion domain where the flux rope field directly interacts with the solar structures, expansion-induced reconnection often modifies the overlying field, thereby increasing the decay index. This effect may provide a primary coupling mechanism underlying the sympathetic eruptions. The magnitude of the impact is found to depend on the orientation of the erupting flux rope, with the largest impacts occurring when the flux rope is favorably oriented for reconnecting with the surrounding regions. Outside the CME expansion domain, the influence of the CME is mainly through field line compression or post-eruption relaxation. Based on our numerical experiments, we discuss a way to quantify the eruption impact, which could be useful for forecasting purposes. Title: The Role of Large-scale Magnetic Coupling for Solar Corona Sympathy Authors: Jin, M.; Schrijver, K.; Cheung, C. M. M.; DeRosa, M. L.; Nitta, N.; Title, A. M. Bibcode: 2015AGUFMSH23A2425J Altcode: With the comprehensive view and high cadence observations from SDO/AIA and STEREO in solar cycle 24, a large number of spatially separated solar eruptive events are found to be coupled. However, compared with the established initiation mechanisms for "isolated" events, the mechanisms for "sympathetic" events are still largely unknown, and nascent theories are untested. In this study, we build a realistic environment of solar corona on 2011 February 15 using a global MHD model and investigate how an eruption can impact the surrounding solar structures. Our result shows that the solar eruption's impact on the different structures can be quite different. Within the CME expansion domain, it is possible to trigger an eruption by overlaying field removal through expansion induced reconnection. The magnitude of impact is found to be dependent on the orientation of the erupting flux rope. Outside the CME expansion domain, the post-eruption reconfiguration could play an important role for solar sympathy. Based on the modeling results, we discuss the possibility of using observable/estimable parameters to quantify the eruption impact therefore providing an useful parameter for forecasting sympathy. 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: Evolving Models of Surface and Coronal Activity of Sun-Like Stars Authors: DeRosa, Marc; Cheung, Mark Bibcode: 2015IAUGA..2257506D Altcode: Surface flux transport models have proven useful for modeling the evolution of magnetic patterns on the solar photospheric surface on timescales ranging from as short as a few days to as long as multiple magnetic cycles. In the work presented here, we use surface flux transport models to study variations in the magnetic activity of Sun-like stars, and to explore the dependence of flux evolution on the properties of flux emergence, large-scale flows, and dispersal by convective turbulence. These time sequences of surface magnetic evolution are then used to drive magnetofrictional models of stellar coronal fields to study how coronal fields evolve. From such models, we can begin to assess how the evolution of various stellar features, such as interacting starspot groups, might affect the overlying stellar coronae. Title: Characterizing the Properties of Coronal Magnetic Null Points Authors: Barnes, Graham; DeRosa, Marc; Wagner, Eric Bibcode: 2015IAUGA..2258194B Altcode: The topology of the coronal magnetic field plays a role in a wide range of phenomena, from Coronal Mass Ejections (CMEs) through heating of the corona. One fundamental topological feature is the null point, where the magnetic field vanishes. These points are natural sites of magnetic reconnection, and hence the release of energy stored in the magnetic field. We present preliminary results of a study using data from the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics Observatory to characterize the properties and evolution of null points in a Potential Field Source Surface model of the coronal field. The main properties considered are the lifetime of the null points, their distribution with height, and how they form and subsequently vanish.This work is supported by NASA/LWS Grant NNX14AD45G, and by NSF/SHINE grant 1357018. Title: Characterizing the Properties of Coronal Magnetic Null Points Authors: Barnes, Graham; DeRosa, Marc; Wagner, Eric Bibcode: 2015shin.confE..79B Altcode: The topology of the coronal magnetic field plays a role in a wide range of phenomena, from Coronal Mass Ejections (CMEs) through heating of the corona. One fundamental topological feature is the null point, where the magnetic field vanishes. These points are natural sites of magnetic reconnection, and hence the release of energy stored in the magnetic field. We present preliminary results of a study using data from the SOHO/Michelson Doppler Imager and SDO/Helioseismic and Magnetic Imager to characterize the properties and evolution of null points in a Potential Field Source Surface model of the coronal field. The main properties considered are the lifetime of the null points, their distribution with height, and how they form and subsequently vanish. In addition, we look at how the distribution of null points varies with solar cycle. Title: The Coronal Global Evolutionary Model: Using HMI Vector Magnetogram and Doppler Data to Model the Buildup of Free Magnetic Energy in the Solar Corona Authors: Fisher, G. H.; Abbett, W. P.; Bercik, D. J.; Kazachenko, M. D.; Lynch, B. J.; Welsch, B. T.; Hoeksema, J. T.; Hayashi, K.; Liu, Y.; Norton, A. A.; Dalda, A. Sainz; Sun, X.; DeRosa, M. L.; Cheung, M. C. M. Bibcode: 2015SpWea..13..369F Altcode: 2015arXiv150506018F The most violent space weather events (eruptive solar flares and coronal mass ejections) are driven by the release of free magnetic energy stored in the solar corona. Energy can build up on timescales of hours to days, and then may be suddenly released in the form of a magnetic eruption, which then propagates through interplanetary space, possibly impacting the Earth's space environment. Can we use the observed evolution of the magnetic and velocity fields in the solar photosphere to model the evolution of the overlying solar coronal field, including the storage and release of magnetic energy in such eruptions? The objective of CGEM, the Coronal Global Evolutionary Model, funded by the NASA/NSF Space Weather Modeling program, is to develop and evaluate such a model for the evolution of the coronal magnetic field. The evolving coronal magnetic field can then be used as a starting point for magnetohydrodynamic (MHD) models of the corona, which can then be used to drive models of heliospheric evolution and predictions of magnetic field and plasma density conditions at 1AU. Title: What Do EUV Dimmings Tell Us About CME Topology Authors: Thompson, Barbara J.; DeRosa, Marc L.; Fisher, Richard R.; Krista, Larisza D.; Kwon, Ryun Young; Mason, James P.; Mays, Mona L.; Nitta, Nariaki V.; Webb, David F.; West, Matthew J. Bibcode: 2015TESS....121201T Altcode: Large-scale coronal EUV dimmings develop on timescales of hours in association with a flare or filament eruption, and are known to be well correlated with coronal mass ejections (CMEs). However, it is not clear why some CMEs have dimmings and some do not, nor is it clear how these dimmings relate to CME topology. The inner coronal coverage of SDO AIA and STEREO EUVI, combined with the extended field of view of PROBA2's SWAP imager, allow us the opportunity to map the topology of a dimming region in three dimensions into an erupting CME. Although the location and extent of a dimming region appears to be the best indicator of the inner "footprint" of a CME, the correlation is far from perfect. However, dimmings can provide vital clues about the development and 3D kinematics of CMEs. This is particularly important as we are currently in an extended period where the STEREO coronagraph images are not always available and are increasingly "mirroring" LASCO images, and therefore the 3D properties of a CME will be difficult to deduce. Thus, understanding the inner coronal manifestations of a CME can provide clues to its structure and dynamics, even without multi-viewpoint coronagraph observations. We present the results of this combined analysis effort, along with a discussion of how dimmings can be used to forecast CME trajectories. Title: Inferring the Structure of the Solar Corona and Inner Heliosphere During the Maunder Minimum Using Global Thermodynamic Magnetohydrodynamic Simulations Authors: Riley, Pete; Lionello, Roberto; Linker, Jon A.; Cliver, Ed; Balogh, Andre; Beer, Jürg; Charbonneau, Paul; Crooker, Nancy; DeRosa, Marc; Lockwood, Mike; Owens, Matt; McCracken, Ken; Usoskin, Ilya; Koutchmy, S. Bibcode: 2015ApJ...802..105R Altcode: Observations of the Sun’s corona during the space era have led to a picture of relatively constant, but cyclically varying solar output and structure. Longer-term, more indirect measurements, such as from 10Be, coupled by other albeit less reliable contemporaneous reports, however, suggest periods of significant departure from this standard. The Maunder Minimum was one such epoch where: (1) sunspots effectively disappeared for long intervals during a 70 yr period; (2) eclipse observations suggested the distinct lack of a visible K-corona but possible appearance of the F-corona; (3) reports of aurora were notably reduced; and (4) cosmic ray intensities at Earth were inferred to be substantially higher. Using a global thermodynamic MHD model, we have constructed a range of possible coronal configurations for the Maunder Minimum period and compared their predictions with these limited observational constraints. We conclude that the most likely state of the corona during—at least—the later portion of the Maunder Minimum was not merely that of the 2008/2009 solar minimum, as has been suggested recently, but rather a state devoid of any large-scale structure, driven by a photospheric field composed of only ephemeral regions, and likely substantially reduced in strength. Moreover, we suggest that the Sun evolved from a 2008/2009-like configuration at the start of the Maunder Minimum toward an ephemeral-only configuration by the end of it, supporting a prediction that we may be on the cusp of a new grand solar minimum. Title: Low-temperature Spectroscopy of the 12C2H2 (υ1 + υ3) Band in a Helium Buffer Gas Authors: Santamaria, L.; Di Sarno, V.; Ricciardi, I.; De Rosa, M.; Mosca, S.; Santambrogio, G.; Maddaloni, P.; De Natale, P. Bibcode: 2015ApJ...801...50S Altcode: 2014arXiv1410.5310S Buffer gas cooling with a 4He gas is used to perform laser-absorption spectroscopy of the 12C2H2 (υ1 + υ3) band at cryogenic temperatures. Doppler thermometry is first carried out to extract translational temperatures from the recorded spectra. Then, rotational temperatures down to 20 K are retrieved by fitting the Boltzmann distribution to the relative intensities of several ro-vibrational lines. The potential of our setup to tune the thermal equilibrium between translational and rotational degrees of freedom is also demonstrated. This can be used to reproduce in a controlled way the regime of non-local thermal equilibrium typically encountered in the interstellar medium. The underlying helium-acetylene collisional physics, relevant for modeling planetary atmospheres, is also addressed. In particular, the diffusion time of 12C2H2 in the buffer cell is measured against the 4He flux at two separate translational temperatures; the observed behavior is then compared with that predicted by a Monte Carlo simulation, thus providing an estimate for the respective total elastic cross sections: σel(100 K) = (4 ± 1) × 10-20 m2 and σel(25 K) = (7 ± 2) × 10-20 m2. Title: What Do EUV Dimmings Tell Us About CME Topology? Authors: Thompson, B. J.; DeRosa, M. L.; Fisher, R. R.; Krista, L. D.; Kwon, R. Y.; Mason, J. P.; Mays, M. L.; Nitta, N.; Savani, N.; West, M. J. Bibcode: 2014AGUFMSH43B4202T Altcode: Large-scale coronal EUV dimmings, developing on timescales of minutes to hours in association with a flare or filament eruption, are known to exhibit a high correlation with coronal mass ejections. However, it is not clear why some CMEs have dimmings and some do not, nor is it clear how these dimmings relate to CME topology. The inner coronal coverage of SDO AIA and STEREO EUVI, combined with the extended field of view of PROBA2's SWAP imager, allow us the opportunity to map the topology of a dimming region in three dimensions into an erupting CME. Although the location and extent of a dimming region appears to be the best indicator of the inner "footprint" of a CME, the correlation is far from perfect. However, dimmings can provide vital clues about the development and 3D kinematics of a CME. This is particularly important as we are entering an extended period of time where STEREO coronagraph images will not always be available, and therefore the 3D properties of a CME will be difficult to deduce. Therefore, understanding the inner coronal manifestations of a CME can provide clues to its structure and dynamics, even without multi-viewpoint coronagraph observations. We present the results of this combined analysis effort, along with a discussion of how dimmings can be used in forecasting CME directions. Title: Tracking Solar Active Region Outflow Plasma from Its Source to the Near-Earth Environment Authors: Culhane, J. L.; Brooks, D. H.; van Driel-Gesztelyi, L.; Démoulin, P.; Baker, D.; DeRosa, M. L.; Mandrini, C. H.; Zhao, L.; Zurbuchen, T. H. Bibcode: 2014SoPh..289.3799C Altcode: 2014SoPh..tmp...90C; 2014arXiv1405.2949C Seeking to establish whether active-region upflow material contributes to the slow solar wind, we examine in detail the plasma upflows from Active Region (AR) 10978, which crossed the Sun's disc in the interval 8 to 16 December 2007 during Carrington rotation (CR) 2064. In previous work, using data from the Hinode/EUV Imaging Spectrometer, upflow velocity evolution was extensively studied as the region crossed the disc, while a linear force-free-field magnetic extrapolation was used to confirm aspects of the velocity evolution and to establish the presence of quasi-separatrix layers at the upflow source areas. The plasma properties, temperature, density, and first ionisation potential bias [FIP-bias] were measured with the spectrometer during the disc passage of the active region. Global potential-field source-surface (PFSS) models showed that AR 10978 was completely covered by the closed field of a helmet streamer that is part of the streamer belt. Therefore it is not clear how any of the upflowing AR-associated plasma could reach the source surface at 2.5 R⊙ and contribute to the slow solar wind. However, a detailed examination of solar-wind in-situ data obtained by the Advanced Composition Explorer (ACE) spacecraft at the L1 point shows that increases in O7+/O6+, C6+/C5+, and Fe/O - a FIP-bias proxy - are present before the heliospheric current-sheet crossing. These increases, along with an accompanying reduction in proton velocity and an increase in density are characteristic of both AR and slow-solar-wind plasma. Finally, we describe a two-step reconnection process by which some of the upflowing plasma from the AR might reach the heliosphere. Title: Characterizing the Properties of Coronal Magnetic Null Points Authors: Barnes, Graham; Wagner, Eric; DeRosa, Marc Bibcode: 2014shin.confE..74B Altcode: The topology of the coronal magnetic field plays a role in a wide range of phenomena, from Coronal Mass Ejections to heating of the corona. One fundamental topological feature is the null point, where the magnetic field vanishes. These points are natural sites of magnetic reconnection, and hence the release of energy stored in the magnetic field. We present preliminary results of a study using data from the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics Observatory to characterize the properties and evolution of null points in a Potential Field Source Surface model of the coronal field. The main properties considered are the lifetime of the null points, their distribution with height, and how they form and subsequently vanish. Title: Active Region Magnetic Field Modeling Guided by Coronal Loops and Surface Fields Authors: DeRosa, Marc L.; Malanushenko, Anna; Schrijver, Carolus J.; Wheatland, Michael S Bibcode: 2014AAS...22432319D Altcode: Dynamic events such as solar flares, filament eruptions, and mass ejections are powered by the evolving coronal magnetic field. However, the ways in which energy is stored in, and released from, the coronal magnetic field are poorly understood, in large part because the field configuration cannot be determined directly from observations and has eluded the successful application of routine modeling based on surface magnetograms. Recently, we have demonstrated that the Quasi-Grad-Rubin (QGR) method for modeling the current-carrying field associated with active regions shows promise. In Malanushenko et al. (2014, ApJ 783:102) we have used the QGR method to construct the magnetic field at several times during the evolution of AR11158 during February 2011. The QGR method does not require vector magnetograms, and instead uses the trajectories of observed coronal loops to constrain the locations of electric currents within the modeling domain. In this study, we continue to assess the utility of QGR by applying this method to additional active regions from the current activity cycle, making use of SDO/HMI line-of-sight magnetograms and imagery from the extreme ultraviolet channels of SDO/AIA. Title: Using Coronal Loops to Reconstruct the Magnetic Field of an Active Region before and after a Major Flare Authors: Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland, M. S. Bibcode: 2014ApJ...783..102M Altcode: 2013arXiv1312.5389M The shapes of solar coronal loops are sensitive to the presence of electrical currents that are the carriers of the non-potential energy available for impulsive activity. We use this information in a new method for modeling the coronal magnetic field of active region (AR) 11158 as a nonlinear force-free field (NLFFF). The observations used are coronal images around the time of major flare activity on 2011 February 15, together with the surface line-of-sight magnetic field measurements. The data are from the Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The model fields are constrained to approximate the coronal loop configurations as closely as possible, while also being subject to the force-free constraints. The method does not use transverse photospheric magnetic field components as input and is thereby distinct from methods for modeling NLFFFs based on photospheric vector magnetograms. We validate the method using observations of AR 11158 at a time well before major flaring and subsequently review the field evolution just prior to and following an X2.2 flare and associated eruption. The models indicate that the energy released during the instability is about 1 × 1032 erg, consistent with what is needed to power such a large eruptive flare. Immediately prior to the eruption, the model field contains a compact sigmoid bundle of twisted flux that is not present in the post-eruption models, which is consistent with the observations. The core of that model structure is twisted by ≈0.9 full turns about its axis. Title: Solar Cycle Variations of the Radio Brightness of the Solar Polar Regions as Observed by the Nobeyama Radioheliograph Authors: Nitta, Nariaki V.; Sun, Xudong; Hoeksema, J. Todd; DeRosa, Marc L. Bibcode: 2014ApJ...780L..23N Altcode: We have analyzed daily microwave images of the Sun at 17 GHz obtained with the Nobeyama Radioheliograph (NoRH) in order to study the solar cycle variations of the enhanced brightness in the polar regions. Unlike in previous works, the averaged brightness of the polar regions is obtained from individual images rather than from synoptic maps. We confirm that the brightness is anti-correlated with the solar cycle and that it has generally declined since solar cycle 22. Including images up to 2013 October, we find that the 17 GHz brightness temperature of the south polar region has decreased noticeably since 2012. This coincides with a significant decrease in the average magnetic field strength around the south pole, signaling the arrival of solar maximum conditions in the southern hemisphere more than a year after the northern hemisphere. We do not attribute the enhanced brightness of the polar regions at 17 GHz to the bright compact sources that occasionally appear in synthesized NoRH images. This is because they have no correspondence with small-scale bright regions in images from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory with a broad temperature coverage. Higher-quality radio images are needed to understand the relationship between microwave brightness and magnetic field strength in the polar regions. Title: Using coronal loops to model the coronal magnetic field before and after major eruptive events Authors: Malanushenko, Anna; Schrijver, Carolus; Wheatland, M. S.; DeRosa, Marc Bibcode: 2014cosp...40E1960M Altcode: Solar flares are believed to be a manifestation of major release of magnetic energy stored in active region field. Modeling the coronal magnetic field may enable us to evaluate the energy available for release, as well as possible sites of the reconnection and other relevant properties of the field. We use a new method to aid this problem by including the observed structure of the field (manifested in coronal loops) as additional constraints. We verify that the method (previously shown to work on synthetic data in Malanushenko et. al., ApJ, 756, 153, 2012) is generally acceptable for the solar data, as it gives self-consistent, slowly changing results for slowly evolving structures. We further develop the potential of this method to access changes in the coronal magnetic field triggered by major eruptive events, and compare the results with observations. Title: Properties of Solar Flare Clustering Authors: Title, Alan; DeRosa, Marc Bibcode: 2014cosp...40E3345T Altcode: The continuous full disk observations provided by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) give an observer the impression that flare and filament eruptions are related. However, both detailed analysis of a number of events as well as a number of statistical studies have provided only rare examples of clear causal behavior. But the mechanisms of flare triggering are not well understood, so the lack of hard evidence is not surprising. Here we have examined the waiting-time statistics of GOES X-ray flares of magnitude C5 or greater during the last sunspot cycle with the aim of assessing the degree to which flares are clustered in time. Clusters are groups of flares in which all successive flares occur within a fixed separation time - the linking window. While many of the flares in a cluster may come from the same active region, the clusters that last more than a disk passage must result from flares in multiple active regions. The longest cluster of the last cycle lasted more than 42 days. None of the flares were separated by more than 36 hours. Since that cluster lasted more than three disk passages, it could not have been caused by a single region. We find that during the last maximum, eight clusters contributed 44% of all flares. All of these clusters spanned multiple disk passages, but occupied only 16.5% of the cycle duration. Two of the clusters provided 34% of the flares. We suggest that this behavior implies that a component of the observed coordinated behavior has its origin in the solar dynamo. Title: The Perihelion Passage of Comet ISON as seen by SDO Authors: Pesnell, W. D.; Schrijver, C. J.; Boerner, P.; DeRosa, M. L.; Liu, W.; Thompson, B. J. Bibcode: 2013AGUFM.P24A..10P Altcode: Comet ISON will fly through perihelion on November 28, 2013. It is one of the largest sungrazing comets to be seen in the Space Age. The Solar Dynamics Observatory (SDO) has seen two previous sungrazing comets in the extreme ultraviolet channels of the Atmospheric Imaging Assembly (AIA). Comet ISON will fly farther from the Sun (perihelion distance of 2.7 Rsun compared to 1.15 for Comet Lovejoy), meaning it probes a different part of the solar corona, but its larger size should provide enough mass to illuminate the path of the nucleus. Based on the latest ephemeris, SDO will be able to track Comet ISON through the entire perihelion passage by a series of off-point maneuvers. We will present the AIA data obtained from the Comet ISON perihelion, discussing the differences between Comets ISON and Lovejoy. We will then summarize what we have learned from the observations and offer some thoughts on what sungrazing comets may reveal about comets, the Sun, and their interaction. Title: Pathways of Large-scale Magnetic Couplings between Solar Coronal Events Authors: Schrijver, Carolus J.; Title, Alan M.; Yeates, Anthony R.; DeRosa, Marc L. Bibcode: 2013ApJ...773...93S Altcode: 2013arXiv1305.0801S The high-cadence, comprehensive view of the solar corona by SDO/AIA shows many events that are widely separated in space while occurring close together in time. In some cases, sets of coronal events are evidently causally related, while in many other instances indirect evidence can be found. We present case studies to highlight a variety of coupling processes involved in coronal events. We find that physical linkages between events do occur, but concur with earlier studies that these couplings appear to be crucial to understanding the initiation of major eruptive or explosive phenomena relatively infrequently. We note that the post-eruption reconfiguration timescale of the large-scale corona, estimated from the extreme-ultraviolet afterglow, is on average longer than the mean time between coronal mass ejections (CMEs), so that many CMEs originate from a corona that is still adjusting from a previous event. We argue that the coronal field is intrinsically global: current systems build up over days to months, the relaxation after eruptions continues over many hours, and evolving connections easily span much of a hemisphere. This needs to be reflected in our modeling of the connections from the solar surface into the heliosphere to properly model the solar wind, its perturbations, and the generation and propagation of solar energetic particles. However, the large-scale field cannot be constructed reliably by currently available observational resources. We assess the potential of high-quality observations from beyond Earth's perspective and advanced global modeling to understand the couplings between coronal events in the context of CMEs and solar energetic particle events.

. Title: On the role of asymmetries in the reversal of the solar magnetic field Authors: Brun, A. S.; Derosa, M. L.; Hoeksema, J. T. Bibcode: 2013IAUS..294...75B Altcode: We study how the solar magnetic field evolves from antisymmetric (dipolar) to symmetric (quadrupolar) state during the course of its 11-yr cycle. We show that based on equatorial symmetries of the induction equation, flux transport solar mean field dynamo models excite mostly the antisymmetric (dipolar) family whereas a decomposition of the solar magnetic field data reveals that both families should be excited to similar amplitude levels. We propose an alternative solar dynamo solution based on North-South asymmetry of the meridional circulation to better reconcile models and observations. Title: The Coronal Global Evolutionary Model (CGEM) Authors: Fisher, George H.; DeRosa, M. L.; Hoeksema, J. T. Bibcode: 2013SPD....4410102F Altcode: The Coronal Global Evolutionary Model, or CGEM, is a collaborative effort from the UC Berkeley Space Sciences Laboratory (SSL), Stanford University, and Lockheed-Martin. In work that led up to the selection of this project, the team demonstrated its capability to use sequences of vector magnetograms and Dopplergrams from the Helioseismic and Magnetic Imager (HMI) instrument aboard the SDO to drive a magnetofrictional (MF) model of the coronal magnetic field in AR 11158, which produced an X2.2 flare. We will implement this MF model in spherical coordinates to enable real-time, long-term modeling of the non-potential coronal magnetic field, both globally and for individual active region (ARs). The model's Earth-facing hemisphere will be driven using electric fields derived from the observed evolution of photospheric line-of-sight magnetic fields and electric currents. Far-side data inputs will be from an existing flux transport code, combined with HMI far-side observations of new active regions, with empirical parametrizations of orientation and flux. Because this model includes large-scale coronal electric currents, it is a substantial improvement over existing real-time global coronal models, which assume potential fields. Data products available from the model will include: 1) the evolving photospheric electric field, Poynting flux, and helicity flux; 2) estimates of coronal free energy and non-potential geometry and topology; 3) initial and time-dependent boundary conditions for MHD modeling of active regions; and 4) time-dependent boundary conditions and flux tube expansion factors for MHD and empirical solar wind models. Unstable configurations found from MF models will be dynamically evolved with local and global MHD codes. Modules used to derive surface electric fields from magnetic evolution will be incorporated into the SDO/HMI data pipeline, and data products will be distributed through the Joint Science Operations Center (JSOC) and directly to space weather forecasters and users. The electric field and MF codes will be delivered to the Community Coordinated Modeling Center (CCMC) for science analysis and use with other models. This project is being jointly funded by NASA and NSF. Title: Some Difficulties in Determining Causality of Sympathetic Solar Events Authors: DeRosa, M. L.; Schrijver, C. J.; Title, A. M.; Yeates, A. R. Bibcode: 2013enss.confE..91D Altcode: Much has been made regarding the occurrence of synchronous eruptive events occurring in the solar corona. Determining the frequencies at which they occur and understanding the causal linkages that may connect such events (making them sympathetic in addition to synchronous) are an area of active research. Causal linkages are observed to take the form of (1) disturbances in magnetic fields that connect active regions, (2) disturbances in the magnetic field configuration overlying active regions, and/or (3) triggering by disturbances propagating from one region to another. Here we display two types of synchronous events: those where, using a combination of image sequences from SDO and STEREO as well as coronal-field modeling, evidence for sympathy seems solid, and those where evidence of sympathy is more ambiguous. We use these two types of cases to illustrate some difficulties in establishing whether synchronous events are in fact sympathetic. This has implications for determining the frequency and importance of sympathetic events, and thus for understanding of coronal field evolution and the origins of space weather. Title: Collective Solar Behavior Authors: Title, Alan; Schrijver, Karel; Derosa, MArc Bibcode: 2013enss.confE.120T Altcode: The Atmospheric Imaging Assembly (AIA) on the Solar Dynamic Observatory (SDO) together with the Helioseismic and Magnetic Imager (HMI) and the Extreme Ultraviolet Variability Experiment (EVE) allow observations of the entire Sun from 6000 K to 20,000,000 K with arcsecond resolution and a 12 second cadence (AIA), obtain doppler and continuum images at a 45 second cadence and Line of Sight and vector magnetograms (HMI) every few minutes, and integrated solar spectra from 1 to 100 nm on a 2 second cadence (EVE) 24/7. Because of the enhanced thermal and temporal coverage and the high dynamic range available with AIA, it has been able to discovery associated behavior associated with extreme solar events that are apparently driven by the rapid expansion of magnetic structures. The extent of the events are recognized by using co-temporal STEREO data. The rapidly expanding magnetic structures, speeds between 500 and 2000 km/s, can apparently trigger filament eruptions, CME's, and other flares. These "triggered" events are sometimes larger that the initial disturbance. The remote triggering makes flare prediction based upon ONLY local energy build up models less valuable, but suggests that with proper coverage prediction of solar events with potential for Earth impact may be made more reliable. Movies of sample events discovered in AIA together with STEREO data will be shown. Title: Photospheric Drivers of Coronal Evolution Authors: Welsch, B. T.; Kazachenko, M.; Fisher, G. H.; Cheung, M. C. M.; DeRosa, M. L.; CGEM Team Bibcode: 2013enss.confE.108W Altcode: Flares and coronal mass ejections (CMEs) are driven by the release of free magnetic energy stored in the coronal magnetic field. While this energy is stored in the corona, photospheric driving must play a central role in its injection, storage, and release, since magnetic fields present in the corona originated within the solar interior, and are anchored at the photosphere. Also, the corona's low diffusivity and high Alfven speed (compared to that at the photosphere) imply that the large-scale coronal field essentially maintains equilibrium (outside of episodic flares and CMEs!), and therefore only evolves due to forcing from photospheric evolution. But fundamental questions about each stage of this "storage and release" paradigm remain open: How does free magnetic energy build up in the corona? How is this energy stored? And what triggers its release? The unprecedented combination of high cadence, resolution, and duty cycle of the HMI vector magnetograph enables modeling coronal magnetic evolution in response to photospheric driving, a powerful approach to addressing these questions. I will discuss our efforts to use HMI vector magneotgrams of AR 11158 to derive time-dependent boundary conditions for a data-driven coronal magnetic field model. These efforts will play a key role in the planned Coronal Global Evolutionary Model (CGEM), a data-driven, time-dependent model of the global coronal field. This work is supported by NASA's Living With a Star program and NSF's Division of Atmospheric and Geospace Sciences. Title: Initiation of Coronal Mass Ejections: A Comparison of AR11158 with a Simulation of Flux Cancellation Authors: Manchester, W. B.; Fang, F.; Burns, C.; Kosovichev, A. G.; Sun, X.; DeRosa, M. L.; Cheung, C. Bibcode: 2012AGUFMSH53B..06M Altcode: We present a detailed comparison of an MHD simulation of magnetic flux emergence with observations of a large-scale active region. The simulation (Fang et al. 2012) addresses the buoyant rise of a flux rope through the convection zone into the corona, which spontaneously reproduces several features found in AR11158. We focus our study on the central part of AR11158 from which an energetic CME was observed on 2011 February 15. We examine AIA loops, HMI vector magnetograms, photospheric flow patterns, and convection zone flow patterns to fully characterize the active region and relate its dynamics to basic features found in the MHD simulation. Salient features are the convergence of flux concentrations of opposite polarity and strong shear flows along the polarity inversion line observed prior to and during the CME. We will show that such shear flows are readily explained as a response to the Lorentz force, and the convergence are associated with convective downdrafts that form over the polarity inversion line. We also compare the brightening of coronal loops observed with AIA to tether-cutting reconnection observed in or simulation. Together, these mechanisms explain the buildup, concentration and release of energy necessary for eruptive events. Title: Tracking Solar Active Region Outflow Plasma from its Source to the near-Earth Environment Authors: Culhane, J. L.; Brooks, D.; Zurbuchen, T.; van Driel-Gesztelyi, L.; Fazakerley, A. N.; DeRosa, M. L. Bibcode: 2012AGUFMSH53A2255C Altcode: In a recent study of persistent active region outflow from AR 10978 in the period 10 - 15, December, 2007, Brooks and Warren (2011), using the Hinode EUV Imaging Spectrometer (EIS) instrument showed the presence of a strong low-FIP element enhancement in the outflowing plasma that was replicated three days later in the in-situ solar wind measurements made by the ACE/SWICS instrument. In the present work, we examine the outflowing plasma properties (Te, Ne, v, abundances) as a function of time in greater detail as AR 10978 passes the Earth-Sun line. The structure of the magnetic field above the two outflow regions - E and W of the AR, is also examined. Following an assessment of the relevant magnetic structures between Sun and Earth, the properties of the solar wind plasma arriving at ACE approximately three days later are measured and compared with those of the outflowing AR plasma. The relationship of these measurements to the in-situ magnetic field observed by the ACE magnetometer is also studied. Finally the role of persistent AR outflows in contributing to the slow solar wind is assessed. Title: Evolution of the solar luminosity during solar cycle 23 Authors: Vieira, L. A.; Schrijver, C.; DeRosa, M. L.; Norton, A.; Dudok de Wit, T.; Da Silva, L.; Vuets, A. Bibcode: 2012AGUFMSH12A..04V Altcode: The effect of the solar activity on the solar luminosity, which is the total electromagnetic solar output, is one of the fundamental questions in solar physics. Changes of the solar luminosity can arise from changes of the energy flux in the convection zone that can also affects other solar parameters such as the surface temperature, the apparent radius and shape, and the symmetry of the radiative field itself. Additionally, understanding the latitudinal distribution of the flux density is needed to compare the solar variability and its stellar analogues. Nevertheless, our observations of the solar flux density are limited to a region near the ecliptic plane, which have provided just a raw estimate of the variability of the solar luminosity. Here we present a reconstruction of the solar flux density and solar luminosity for the solar cycle 23 and ascending phase of cycle 24. The reconstruction is based on a combination of a state-of-art solar surface magnetic flux transport model and a semi-empirical total and spectral irradiance model. The flux transport model is based on assimilation of MDI/SOHO and HMI/SDO magnetograms. The irradiance model's free parameters are estimated by minimizing the difference between the model's output and the PMOD Composite of TSI measurements. We have obtained a good agreement between the model's output and the measurements. The distribution of active regions leads to a clear low latitude brightening during the solar maximum. This brightening results from the balance of the contributions from bright (faculae and network) and dark features (sunspots) located in the solar surface, which peaks near the solar equator. As the effects of dark features are limited to a narrower region, the variability of the flux density at the poles is dominated by the evolution of faculae and network. The preliminary results indicate that the heat flux blocked by sunspots is lower than the flux leaked by bright features. Consequently, an increase of the luminosity through the cycle is observed as previously estimated based on near ecliptic measurements. This work also enables an assessment of the properties of solar variability when viewed from out of the ecliptic, i.e., such as we might be viewing other stars of solar activity level. Finally, the limitations of the model and future strategies to extend the reconstruction of the flux density and solar luminosity will be presented. Title: Magnetic Topology of Active Regions and Coronal Holes: Implications for Coronal Outflows and the Solar Wind Authors: van Driel-Gesztelyi, L.; Culhane, J. L.; Baker, D.; Démoulin, P.; Mandrini, C. H.; DeRosa, M. L.; Rouillard, A. P.; Opitz, A.; Stenborg, G.; Vourlidas, A.; Brooks, D. H. Bibcode: 2012SoPh..281..237V Altcode: 2012SoPh..tmp..228V During 2 - 18 January 2008 a pair of low-latitude opposite-polarity coronal holes (CHs) were observed on the Sun with two active regions (ARs) and the heliospheric plasma sheet located between them. We use the Hinode/EUV Imaging Spectrometer (EIS) to locate AR-related outflows and measure their velocities. Solar-Terrestrial Relations Observatory (STEREO) imaging is also employed, as are the Advanced Composition Explorer (ACE) in-situ observations, to assess the resulting impacts on the solar wind (SW) properties. Magnetic-field extrapolations of the two ARs confirm that AR plasma outflows observed with EIS are co-spatial with quasi-separatrix layer locations, including the separatrix of a null point. Global potential-field source-surface modeling indicates that field lines in the vicinity of the null point extend up to the source surface, enabling a part of the EIS plasma upflows access to the SW. We find that similar upflow properties are also observed within closed-field regions that do not reach the source surface. We conclude that some of plasma upflows observed with EIS remain confined along closed coronal loops, but that a fraction of the plasma may be released into the slow SW. This suggests that ARs bordering coronal holes can contribute to the slow SW. Analyzing the in-situ data, we propose that the type of slow SW present depends on whether the AR is fully or partially enclosed by an overlying streamer. Title: Modeling Magnetic Field Structure of a Solar Active Region Corona Using Nonlinear Force-free Fields in Spherical Geometry Authors: Guo, Y.; Ding, M. D.; Liu, Y.; Sun, X. D.; DeRosa, M. L.; Wiegelmann, T. Bibcode: 2012ApJ...760...47G Altcode: 2012arXiv1210.0998G We test a nonlinear force-free field (NLFFF) optimization code in spherical geometry using an analytical solution from Low and Lou. Several tests are run, ranging from idealized cases where exact vector field data are provided on all boundaries, to cases where noisy vector data are provided on only the lower boundary (approximating the solar problem). Analytical tests also show that the NLFFF code in the spherical geometry performs better than that in the Cartesian one when the field of view of the bottom boundary is large, say, 20° × 20°. Additionally, we apply the NLFFF model to an active region observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (SDO) both before and after an M8.7 flare. For each observation time, we initialize the models using potential field source surface (PFSS) extrapolations based on either a synoptic chart or a flux-dispersal model, and compare the resulting NLFFF models. The results show that NLFFF extrapolations using the flux-dispersal model as the boundary condition have slightly lower, therefore better, force-free, and divergence-free metrics, and contain larger free magnetic energy. By comparing the extrapolated magnetic field lines with the extreme ultraviolet (EUV) observations by the Atmospheric Imaging Assembly on board SDO, we find that the NLFFF performs better than the PFSS not only for the core field of the flare productive region, but also for large EUV loops higher than 50 Mm. Title: What Are Special About Ground-Level Events?. Flares, CMEs, Active Regions and Magnetic Field Connection Authors: Nitta, N. V.; Liu, Y.; DeRosa, M. L.; Nightingale, R. W. Bibcode: 2012SSRv..171...61N Altcode: 2012arXiv1203.5777N; 2012SSRv..tmp...21N Ground level events (GLEs) occupy the high-energy end of gradual solar energetic particle (SEP) events. They are associated with coronal mass ejections (CMEs) and solar flares, but we still do not clearly understand the special conditions that produce these rare events. During Solar Cycle 23, a total of 16 GLEs were registered, by ground-based neutron monitors. We first ask if these GLEs are clearly distinguishable from other SEP events observed from space. Setting aside possible difficulties in identifying all GLEs consistently, we then try to find observables which may unmistakably isolate these GLEs by studying the basic properties of the associated eruptions and the active regions (ARs) that produced them. It is found that neither the magnitudes of the CMEs and flares nor the complexities of the ARs give sufficient conditions for GLEs. It is possible to find CMEs, flares or ARs that are not associated with GLEs but that have more extreme properties than those associated with GLEs. We also try to evaluate the importance of magnetic field connection of the AR with Earth on the detection of GLEs and their onset times. Using the potential field source surface (PFSS) model, a half of the GLEs are found to be well-connected. However, the GLE onset time with respect to the onset of the associated flare and CME does not strongly depend on how well-connected the AR is. The GLE onset behavior may be largely determined by when and where the CME-driven shock develops. We could not relate the shocks responsible for the onsets of past GLEs with features in solar images, but the combined data from the Solar TErrestrial RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) have the potential to change this for GLEs that may occur in the rising phase of Solar Cycle 24. Title: A Method for Data-driven Simulations of Evolving Solar Active Regions Authors: Cheung, Mark C. M.; DeRosa, Marc L. Bibcode: 2012ApJ...757..147C Altcode: 2012arXiv1208.2954C We present a method for performing data-driven simulations of solar active region formation and evolution. The approach is based on magnetofriction, which evolves the induction equation assuming that the plasma velocity is proportional to the Lorentz force. The simulations of active region (AR) coronal field are driven by temporal sequences of photospheric magnetograms from the Helioseismic Magnetic Imager instrument on board the Solar Dynamics Observatory (SDO). Under certain conditions, the data-driven simulations produce flux ropes that are ejected from the modeled AR due to loss of equilibrium. Following the ejection of flux ropes, we find an enhancement of the photospheric horizontal field near the polarity inversion line. We also present a method for the synthesis of mock coronal images based on a proxy emissivity calculated from the current density distribution in the model. This method yields mock coronal images that are somewhat reminiscent of images of ARs taken by instruments such as SDO's Atmospheric Imaging Assembly at extreme ultraviolet wavelengths. Title: First Three-dimensional Reconstructions of Coronal Loops with the STEREO A+B Spacecraft. IV. Magnetic Modeling with Twisted Force-free Fields Authors: Aschwanden, Markus J.; Wuelser, Jean-Pierre; Nitta, Nariaki V.; Lemen, James R.; DeRosa, Marc L.; Malanushenko, Anna Bibcode: 2012ApJ...756..124A Altcode: 2012arXiv1207.2790A The three-dimensional coordinates of stereoscopically triangulated loops provide strong constraints for magnetic field models of active regions in the solar corona. Here, we use STEREO/A and B data from some 500 stereoscopically triangulated loops observed in four active regions (2007 April 30, May 9, May 19, and December 11), together with SOHO/MDI line-of-sight magnetograms. We measure the average misalignment angle between the stereoscopic loops and theoretical magnetic field models, finding a mismatch of μ = 19°-46° for a potential field model, which is reduced to μ = 14°-19° for a non-potential field model parameterized by twist parameters. The residual error is commensurable with stereoscopic measurement errors (μSE ≈ 8°-12°). We developed a potential field code that deconvolves a line-of-sight magnetogram into three magnetic field components (Bx , By , Bz ), as well as a non-potential field forward-fitting code that determines the full length of twisted loops (L ≈ 50-300 Mm), the number of twist turns (median N twist = 0.06), the nonlinear force-free α-parameter (median α ≈ 4 × 10-11 cm-1), and the current density (median jz ≈ 1500 Mx cm-2 s-1). All twisted loops are found to be far below the critical value for kink instability, and Joule dissipation of their currents is found to be far below the coronal heating requirement. The algorithm developed here, based on an analytical solution of nonlinear force-free fields that is accurate to second order (in the force-free parameter α), represents the first code that enables fast forward fitting to photospheric magnetograms and stereoscopically triangulated loops in the solar corona. Title: Guiding Nonlinear Force-free Modeling Using Coronal Observations: First Results Using a Quasi-Grad-Rubin Scheme Authors: Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland, M. S.; Gilchrist, S. A. Bibcode: 2012ApJ...756..153M Altcode: 2012arXiv1202.5420M At present, many models of the coronal magnetic field rely on photospheric vector magnetograms, but these data have been shown to be problematic as the sole boundary information for nonlinear force-free field extrapolations. Magnetic fields in the corona manifest themselves in high-energy images (X-rays and EUV) in the shapes of coronal loops, providing an additional constraint that is not at present used as constraints in the computational domain, directly influencing the evolution of the model. This is in part due to the mathematical complications of incorporating such input into numerical models. Projection effects, confusion due to overlapping loops (the coronal plasma is optically thin), and the limited number of usable loops further complicate the use of information from coronal images. We develop and test a new algorithm to use images of coronal loops in the modeling of the solar coronal magnetic field. We first fit projected field lines with those of constant-α force-free fields to approximate the three-dimensional distribution of currents in the corona along a sparse set of trajectories. We then apply a Grad-Rubin-like iterative technique, which uses these trajectories as volume constraints on the values of α, to obtain a volume-filling nonlinear force-free model of the magnetic field, modifying a code and method presented by Wheatland. We thoroughly test the technique on known analytical and solar-like model magnetic fields previously used for comparing different extrapolation techniques and compare the results with those obtained by currently available methods relying only on the photospheric data. We conclude that we have developed a functioning method of modeling the coronal magnetic field by combining the line-of-sight component of the photospheric magnetic field with information from coronal images. Whereas we focus on the use of coronal loop information in combination with line-of-sight magnetograms, the method is readily extended to incorporate vector-magnetic data over any part of the photospheric boundary. Title: Solar Magnetic Field Reversals and the Role of Dynamo Families Authors: DeRosa, M. L.; Brun, A. S.; Hoeksema, J. T. Bibcode: 2012ApJ...757...96D Altcode: 2012arXiv1208.1768D The variable magnetic field of the solar photosphere exhibits periodic reversals as a result of dynamo activity occurring within the solar interior. We decompose the surface field as observed by both the Wilcox Solar Observatory and the Michelson Doppler Imager into its harmonic constituents, and present the time evolution of the mode coefficients for the past three sunspot cycles. The interplay between the various modes is then interpreted from the perspective of general dynamo theory, where the coupling between the primary and secondary families of modes is found to correlate with large-scale polarity reversals for many examples of cyclic dynamos. Mean-field dynamos based on the solar parameter regime are then used to explore how such couplings may result in the various long-term trends in the surface magnetic field observed to occur in the solar case. Title: Effects of Granulation upon Larger-Scale Convection Authors: Hurlburt, N. E.; DeRosa, M. L.; Augustson, K. C.; Toomre, J. Bibcode: 2012ASPC..454...13H Altcode: 2012arXiv1201.4809H We examine the role of small-scale granulation in helping to drive supergranulation and even larger scales of convection. The granulation is modeled as localized cooling events introduced at the upper boundary of a 3-D simulation of compressible convection in a rotating spherical shell segment. With a sufficient number of stochastic cooling events compared to uniform cooling, we find that supergranular scales are realized, along with a differential rotation that becomes increasingly solar-like. Title: Magnetic topology, coronal outflows, and the solar wind Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Vourlidas, Angelos; Demoulin, Pascal; Stenborg, Guillermo; Opitz, Andrea; Rouillard, Alexis; Van Driel-Gesztelyi, Lidia; Baker, Deborah; DeRosa, Marc; Brooks, David Bibcode: 2012cosp...39.1173M Altcode: 2012cosp.meet.1173M During 2-18 January 2008 a pair of low-latitude opposite polarity coronal holes were observed on the Sun flanked by two ARs with the heliospheric plasma sheet between them. Hinode/EUV Imaging Telescope (EIS) is used to locate AR-related outflows and measure their velocities. The Advanced Composition Explorer (ACE) in-situ observations are employed to assess the resulting impacts on the interplanetary solar wind (SW). Magnetic field extrapolations of the two ARs confirm that AR plasma outflows observed with EIS are co-spatial with quasi-separatrix layer locations, including the separatrix of a null point. Global potential field source-surface modeling indicates that field lines in the vicinity of the null point extend up to the source-surface, enabling a part of the EIS plasma upflows access to the SW. Similar upflow magnitude is also observed within closed field regions. Though part of the plasma upflows observed with EIS remain confined along closed coronal loops, a subset of them are indeed able to make their imprint in the slow SW, making ARs bordering coronal holes a slow SW contributor. Title: Using Electric Fields to drive simulations of the solar coronal magnetic field Authors: Fisher, George H.; Cheung, Mark; DeRosa, Marc; Kazachenko, Maria; Welsch, Brian; Hoeksema, Todd; Sun, Xudong Bibcode: 2012shin.confE..47F Altcode: The availability of high-cadence vector magnetograms and Doppler flow information measured from the HMI instrument on SDO make it possible to determine the electric field at the solar photosphere. This electric field, in turn, can be used to drive time-dependent simulations of the magnetic field in the solar corona, employing the MHD equations, or simpler time-dependent models such as the magneto-frictional (MF) model. Here, we demonstrate these concepts by using electric fields determined from HMI data to drive a time-dependent MF model of the solar corona in the volume overlying the photosphere near NOAA AR 11158. Title: Topology of Coronal Fields from Evolving Magnetofrictional Models Authors: DeRosa, Marc L.; Cheung, M. Bibcode: 2012AAS...22041104D Altcode: The evolving magnetofrictional (MF) scheme enables the construction of time-dependent models of the active region coronal magnetic field in response to photospheric driving. When advancing such models, only the magnetic induction is solved, during which the velocity at each point is assumed to be oriented parallel to the Lorentz force. This leads to the field to evolve toward a force-free state. We present results from an evolving MF model of NOAA AR11158 using driving from time sequences of SDO/HMI data. Utilizing this simulation, we

investigate changes in magnetic configurations and topology, including the number of null points, evolution of quasi-separatrix layers, and the time-history of total and free magnetic energies as well as relative helicity. This work seeks to elucidate the relation(s) between topological and energetic properties of the AR. Title: Estimate of Energy Release In a Major Flare Using Coronal Loops Data Authors: Malanushenko, Anna; Schrijver, C. J.; DeRosa, M. L. Bibcode: 2012AAS...22052115M Altcode: Coronal loops provide with valuable source of information about coronal magnetic field. In particular, they allow one to observe reconfiguration of the coronal magnetic field during eruptive episodes. The changes in the coronal field, as observed in X-rays and extreme ultraviolet, are often dramatic in even minor eruptions. Therefore, models of magnetic field which take coronal loops into account might provide for new insight at changes of the field during eruptions. We use coronal loops data (gathered from SDO/AIA images) along with the line-of-sight magnetograms (by SDO/HMI) to model magnetic field in AR 11158 before and after the so-called Valentine's Flare, an X-class flare in Feb 15, 2011. This is done using the recently developed Quasi Grad-Rubin algorithm (QGR), which allows a reconstruction of non-linear force-free field based on information about electric currents along a set of arbitrary tracks in the computational domain. Tests of QGR on solar-like fields demonstrate its ability to recover over 50% of the free energy, as well as the large-scale structure of currents and overall shape of field lines. We analyze model magnetic fields of AR 11158 before and after the flare, demonstrate their resemblance with the observed structure of coronal loops and analyze the changes in the structure of currents caused by the flare, and compare our results with existing studies of the same event. Title: Force-Free Magneto-Stereoscopy of Coronal Loops Authors: Aschwanden, Markus J.; Malanushenko, A.; Wuelser, J.; Nitta, N.; Lemen, J. R.; DeRosa, M. Bibcode: 2012AAS...22041103A Altcode: We derive an analytical approximation of nonlinear force-free magnetic field solutions (NLFFF) that can efficiently be used for fast forward-fitting to solar magnetic data, constrained either by observed line-of-sight magnetograms and stereoscopically triangulated coronal loops, or by 3D vector-magnetograph data. We test the code by forward-fitting to simulated data, to force-free solutions derived by Low and Lou (1990), and to active regions observed with STEREO/EUVI and SOHO/MDI. The forward-fitting tests demonstrate: (i) a satisfactory convergence behavior (with typical misalignment angles of 1-10 deg), (ii) a high fidelity of retrieved force-free alpha-parameters, and (iii) relatively fast computation times (from seconds to minutes). The novel feature of this NLFFF code is the derivation of a quasi-forcefree field based on coronal constraints, which bypasses the non-forcefree photosphere of standard magnetograms. Applications range from magnetic modeling of loops to the determnination of electric currents, twist, helicity, and free (non-potential) energy in active regions. 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: Data-Driven Modeling of the Evolution of Active Regions and Coronal Holes Authors: Cheung, M. C. M.; DeRosa, M. L. Bibcode: 2012decs.confE..83C Altcode: We present results from numerical simulations of the evolution of solar Active Regions (ARs) and Coronal Holes (CHs). The simulations use the magnetofrictional method, which solves the induction equation to drive magnetic configurations toward force-free states in response to photospheric changes. The method is applied to modeling energy build-up in ARs and morphological changes in CHs. Comparisons with AIA data will be presented. Title: Non-Linear Force-Free Modeling of Solar Corona With The Aid of Coronal Loops Authors: Malanushenko, A.; DeRosa, M.; Schrijver, C.; Wheatland, M. S.; Gilchrist, S. Bibcode: 2012decs.confE.113M Altcode: Accurate models of the coronal magnetic field are vital for understanding and predicting solar activity and are therefore of the greatest interest for solar physics. As no reliable measurements of the coronal magnetic field exists at present, the problem of constructing field models is typically viewed as a boundary value problem. The construction of realistic field models requires knowledge of the full vector of magnetic field at the boundaries of the model domain; vector magnetograms are, however, measured in the non force-free photosphere and their horizontal components are subject to large uncertainties. Even if an uncertainty-free vector magnetogram at the top layer of the chromosphere was known, the problem remains an extremely challenging non-linear problem. There are various methods for pre-processing vector magnetograms and using them to construct models of the coronal field. The success of these models is often judged based on how close its field lines correspond to the observed coronal loops, which are believed to follow lines of the coronal magnetic field. At present, the correspondence between coronal loops and magnetic field lines of many models based on the vector magnetograms is far from perfect (DeRosa et. al., 2009). The estimates of free energy in the field as well as distribution of the magnetic currents through the volume could be dramatically different for different models used (Schrijver et. al., 2008). This testifies to the need of a completely new approach to this problem. We present such an approach and demonstrate its results based on AIA and HMI data. We have developed a way to use coronal loops as a constraint for magnetic modelling; the field is therefore constructed to match coronal loops. We found that when tested on known magnetic fields the new method is able to reproduce overall shape of the field lines, large-scale spatial distribution of the electric currents and measure up to 60% of the free energy stored in the field. This was achieved with as little as line-of-sight magnetogram and less than hundred of synthetic "loops", that is, lines of magnetic fields projected onto a plane of the sky. We found that line-of-sight HMI magnetograms and spatial resolution of the AIA instrument combined with the amount of filters available are more than sufficient for obtaining such data. We briefly describe this new method and demonstrate reconstructions of the coronal magnetic field obtained using AIA and HMI data. We evaluate how well it reproduces coronal features and how much energy and helicity estimates fluctuate with time for a stable non-flaring active region, thus establishing the reliability of the new method. Title: The impact of the chromosphere on magnetic fields: field extrapolations Authors: DeRosa, Marc L. Bibcode: 2012decs.confE..88D Altcode: Because knowledge of the coronal magnetic field is the key to gaining an understanding of the dynamics of the coronal plasma, efforts to measure or infer coronal magnetic fields have received much attention. In particular, many techniques for extrapolating the coronal magnetic field from photospheric boundary data have been developed, especially as magnetic field data at increasingly higher resolution in space and time as well as vector magnetogram inversions have become more readily available. However, it has become apparent that some extrapolation methods encounter difficulties, as the resulting extrapolations often do not provide reliable estimates of important coronal properties such as free energy and relative helicity. In this talk, we review some of the various difficulties associated with magnetic field extrapolations based on photospheric magnetograms, and discuss likely causes and solutions. We will particularly elucidate the impact of the chromospheric layer on such extrapolations, which is likely impacting the reliability of the extrapolation process as it lies between the region sampled by the boundary data [the photosphere] and the region of interest [the corona]. Title: Data-driven Simulations of Evolving Active Regions Authors: Cheung, M.; DeRosa, M. L. Bibcode: 2011AGUFMSH33C..04C Altcode: We present results from numerical simulations of coronal field evolution in response to photospheric driving. In the simulations, the coronal field evolves according to magnetofriction, which ensures that the model field evolves toward a non-linear force-free state. Unlike static field extrapolation methods, this approach takes into account the history of the photospheric field evolution. This allows for the formation of flux ropes as well as current sheets between magnetic domains of connectivity. Using time sequences of HMI magnetograms as the bottom boundary condition, we apply this method to model the emergence and evolution of various active regions. Comparisons of the models with AIA observations and with HMI vector magnetogram inversions will be discussed. Title: Spectropolarimetric Comparison Between SDO/HMI and Hinode-SOT/SP Through THEMIS/MTR Authors: Sainz Dalda, A.; Lopez Ariste, A.; Gelly, B.; Tarbell, T. D.; Centeno, R.; DeRosa, M. L.; Hoeksema, J. T. Bibcode: 2011AGUFMSH31A1986S Altcode: In the golden age of solar spacecraft observatories, the use of similar instruments observing same targets offers us the possibility to get more accurate information of the physical processes taking place on them. We present a comparison between the vector magnetic field and thermodynamic quantities obtained by three different spectropolarimetric instruments. We have used the simultaneous multi-wavelength capabilities of THEMIS/MTR as bridge between the observations at Fe I 6173 Å provided by SDO/HMI and at Fe I 6301 & 6302 Å by Hinode-SOT/SP observations. The official inversion codes for these instruments (PCA based-on, VFISV and MERLIN respectively) have been used with the data properly arranged for them. Therefore, we compare the final products usually offered to the community, i.e. after the inversion, using different codes and these different wavelengths. The cross-calibration of these products shall allow us to go forward from one instrument result to other one in an easy, convenient way. Title: Non-Linear Force-Free Modeling With The Aid of Coronal Observations Authors: Malanushenko, A. V.; DeRosa, M. L.; Schrijver, C. J.; Gilchrist, S. A.; Wheatland, M. S. Bibcode: 2011AGUFMSH43B1956M Altcode: Currently many models of coronal magnetic field rely on vector magnetograms and other kinds of information drawn from the photosphere. Magnetic fields in the corona, however, manifest themselves in the shapes of coronal loops, providing a constraint that at the present stage receives little use due to mathematical complications of incorporating such input into the numeric models. Projection effects and the limited number of usable loops further complicate their use. We present a possible way to account for coronal loops in the models of magnetic field. We first fit the observed loops with lines of constant-alpha fields and thus approximate three-dimensional distribution of currents in the corona along a sparse set of trajectories. We then apply a Grad-Rubin-like averaging technique to obtain a volume-filling non-linear force-free model of magnetic field, modified from the method presented in Wheatland & Regnier (2009). We present thorough tests of this technique on several known magnetic fields that were previously used for comparing different extrapolation techniques (Schrijver et. al., 2006; Metcalf et. al., 2008; Schrijver et. al., 2008; DeRosa et. al., 2009), as well as on solar data and compare the results with those obtained by the currently developed methods that rely completely on the photospheric data. Title: Magnetic Field Modeling with Stereoscopy and Magnetograms Authors: Aschwanden, Wuelser; Nitta, Schrijver; DeRosa, Malanushenko Bibcode: 2011sdmi.confE..81A Altcode: We developed a new code to reconstruct the 3D magnetic field of solar active regions using stereoscopically triangulated loops with STEREO/A+B and magnetogram data from MDI or HMI. We are using potential field models as well as non-potential field models (nonlinear quasi-force-free fields) that can be quickly forward-fitted to observations using parameterizations of analytical approximations of uniformly twisted flux tubes. This method improves the misalignment angles between theoretical models and observed magnetic fields down to 5 degrees. Title: Dipolar and Quadrupolar Magnetic Field Evolution over Solar Cycles 21, 22, and 23 Authors: DeRosa, M. L.; Brun, A. S.; Hoeksema, J. T. Bibcode: 2011IAUS..271...94D Altcode: Time series of photospheric magnetic field maps from two observatories, along with data from an evolving surface-flux transport model, are decomposed into their constituent spherical harmonic modes. The evolution of these spherical harmonic spectra reflect the modulation of bipole emergence rates through the solar activity cycle, and the subsequent dispersal, shear, and advection of magnetic flux patterns across the solar photosphere. In this article, we discuss the evolution of the dipolar and quadrupolar modes throughout the past three solar cycles (Cycles 21-23), as well as their relation to the reversal of the polar dipole during each solar maximum, and by extension to aspects of the operation of the global solar dynamo. 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: Simulating Coronal Emission in Six AIA Channels Using Quasi-Static Atmosphere Models and Non-Linear Magnetic Field Models Authors: Malanushenko, Anna; Schrijver, C.; DeRosa, M.; Aschwanden, M.; Wheatland, M. S.; van Ballegooijen, A. A. Bibcode: 2011SPD....42.2116M Altcode: 2011BAAS..43S.2116M We present the results of simulations of the EUV coronal emission in AIA channels. We use a non-linear force-free model of magnetic field constructed in such a way that its field lines resemble the observed coronal loops in EUV. We then solve one-dimensional quasi-steady atmosphere model along the magnetic field lines (Schrijver & Ballegooijen, 2005). Using coronal abundances from CHIANTI and AIA response functions we then simulate the emission that would be observed in AIA EUV channels. The resulting intensities are compared against the real observations in a manner similar to that in Aschwanden et. al., 2011. The study is similar to those by Lindquist et. al., 2008, with a few important differences. We use a model of the coronal magnetic field that resembles the topology observed in EUV, we study EUV emission of cool loops (rather than SXR) and we make use of high resolution and cadence AIA and HMI data. Title: Data-Driven Simulations of Coronal Magnetic Fields: A First Attempt with SDO Data Authors: Cheung, C.; Derosa, M. L. Bibcode: 2010AGUFMSH14A..04C Altcode: We present results from numerical simulations of coronal field evolution in response to photospheric driving. In the simulations, the coronal field evolves according to magnetofriction, which ensures that the model field evolves toward a non-linear force-free state. Unlike static field extrapolation methods, this approach takes into account the history of the photospheric field evolution. This allows for the formation of flux ropes as well as current sheets between magnetic domains of connectivity. Using time sequences of HMI magnetograms as the bottom boundary condition, we apply this method to model the emergence and evolution of recent active regions. For the case of AR 11066, flux cancellation between opposite polarities within the AR leads to the formation of a flux rope, which subsequently lifts off. Comparisons of the models with AIA observations will be presented. Title: Uncovering Mechanisms of Coronal Magnetism via Advanced 3D Modeling of Flares and Active Regions Authors: Fleishman, Gregory; Gary, Dale; Nita, Gelu; Alexander, David; Aschwanden, Markus; Bastian, Tim; Hudson, Hugh; Hurford, Gordon; Kontar, Eduard; Longcope, Dana; Mikic, Zoran; DeRosa, Marc; Ryan, James; White, Stephen Bibcode: 2010arXiv1011.2800F Altcode: The coming decade will see the routine use of solar data of unprecedented spatial and spectral resolution, time cadence, and completeness. To capitalize on the new (or soon to be available) facilities such as SDO, ATST and FASR, and the challenges they present in the visualization and synthesis of multi-wavelength datasets, we propose that realistic, sophisticated, 3D active region and flare modeling is timely and critical, and will be a forefront of coronal studies over the coming decade. To make such modeling a reality, a broad, concerted effort is needed to capture the wealth of information resulting from the data, develop a synergistic modeling effort, and generate the necessary visualization, interpretation and model-data comparison tools to accurately extract the key physics. Title: Magnetic Field Topology and the Thermal Structure of the Corona over Solar Active Regions Authors: Schrijver, Carolus J.; DeRosa, Marc L.; Title, Alan M. Bibcode: 2010ApJ...719.1083S Altcode: Solar extreme ultraviolet (EUV) images of quiescent active-region coronae are characterized by ensembles of bright 1-2 MK loops that fan out from select locations. We investigate the conditions associated with the formation of these persistent, relatively cool, loop fans within and surrounding the otherwise 3-5 MK coronal environment by combining EUV observations of active regions made with TRACE with global source-surface potential-field models based on the full-sphere photospheric field from the assimilation of magnetograms that are obtained by the Michelson Doppler Imager (MDI) on SOHO. We find that in the selected active regions with largely potential-field configurations these fans are associated with (quasi-)separatrix layers (QSLs) within the strong-field regions of magnetic plage. Based on the empirical evidence, we argue that persistent active-region cool-loop fans are primarily related to the pronounced change in connectivity across a QSL to widely separated clusters of magnetic flux, and confirm earlier work that suggested that neither a change in loop length nor in base field strengths across such topological features are of prime importance to the formation of the cool-loop fans. We discuss the hypothesis that a change in the distribution of coronal heating with height may be involved in the phenomenon of relatively cool coronal loop fans in quiescent active regions. Title: A Spherical Harmonic Analysis of the Evolution of the Photospheric Magnetic Field, and Consequences for the Solar Dynamo Authors: DeRosa, Marc L.; Hoeksema, J. T.; Brun, A. S. Bibcode: 2010AAS...21631701D Altcode: 2010BAAS...41..898D Time series of synoptic maps from several observatories, along with data from an evolving surface-flux transport model, are analyzed in terms of their spherical harmonic decomposition. The characteristics of these spherical harmonic spectra, such as the relative amplitudes of various harmonic modes, at different phases of the solar cycle are shown. We illustrate how the rise and decline of the flux emergence rates, and the associated reversal of the polar dipole, throughout a sunspot cycle are reflected in the evolution of the various harmonic mode coefficients. We further discuss the interplay between the low-degree modes, in particular the dipole and quadrupole, and how such dynamics may trigger the reversal of the polar dipole during solar maximum. Title: Erratum: "The Dependence of Ephemeral Region Emergence on Local Flux Imbalance" (2008, ApJ, 678, 541) Authors: Hagenaar, Hermance J.; DeRosa, Marc L.; Schrijver, Carolus J. Bibcode: 2010ApJ...715..696H Altcode: We have discovered an error in the labeling of Figure 5. The importance of the figure is to indicate the dependence of flux emergence on local flux (im-) balance. However, the scales of the figures were incorrect, causing a discrepancy between Table 2 and Figure 5(a). The corrected Figure 5 appears below. The change does not affect the conclusion. Title: Magnetic Field Topology and the Thermal Structure of the Corona over Solar Active Regions Authors: Schrijver, Carolus J.; DeRosa, M. L.; Title, A. M. Bibcode: 2010AAS...21631201S Altcode: Solar extreme-ultraviolet images of active-region coronae are characterized by ensembles of bright 1-2 MK loops that fan out from select locations. We investigate the conditions associated with the formation of these relatively cool loop fans within the otherwise 3-5 MK coronal environment by combining EUV observations of active regions made with the Transition Region and Coronal Explorer (TRACE) with global source-surface potential-field models based on the full-sphere photospheric field from the assimilation of magnetograms that are obtained by MDI on SOHO. We find that in the selected active regions with largely potential field configurations these fans are associated with (quasi-)separatrices within the strong-field regions of magnetic plage and vice versa. We argue that the divergence of the field lines across a (quasi-)separatrix may cause heating to happen relatively low in the corona, resulting in a lower loop temperature and flatter thermal profile of relatively dense (and thus EUV-bright) loops that are surrounded by warmer, thermally more stratified loops in field that does not straddle such topological divides. Title: Modeling the Near-Surface Shear Layer Through Coupled Simulations of Surface and Deep Convection Authors: Augustson, Kyle; Hurlburt, N.; DeRosa, M.; Toomre, J. Bibcode: 2010AAS...21640008A Altcode: 2010BAAS...41..855A We examine the role of small-scale granulation in helping to drive supergranulation and even larger scales of convection. The granulation is modeled as localized plumes with statistics taken from surface convection simulations introduced at the upper boundary of a 3-D simulation of compressible convection in a rotating spherical shell segment. With a sufficient number of stochastic plume events compared to a uniform cooling, we find that supergranular scales are realized, along with a differential rotation that becomes increasingly solar-like. Title: Direct Imaging of an Emerging Flux Rope and a Resulting Chromospheric Jet Observed by Hinode Authors: Liu, Wei; Berger, T.; Title, A. M.; Tarbell, T. D.; DeRosa, M. Bibcode: 2010AAS...21640307L Altcode: 2010BAAS...41R.878L Magnetic flux emergence has been traditionally observed on the disk by identifying changes in magnetograms. Observations near the limb offer an alternative perspective and allow direct imaging of emerging flux ropes. We present Hinode/SOT Ca II H observations of such an event in an equatorial coronal hole on 2007 February 9. The precursor of the event was a bundle of fine material threads that extended at an oblique angle above the chromosphere and appeared to rotate about a common axis. This bundle first slowly and then rapidly swung up, accompanied by a loop that appeared at the base of the bundle and expanded at comparable rates. During the first (slow rise) stage, the apex of the loop ascended at 16 km/s, a velocity similar to that of H-alpha arch filaments (e.g., Chou & Zirin) and of emerging flux ropes expanding into the corona as found in MHD simulations (e.g., Fan & Gibson; Martinez-Sykora). The second stage started at the onset of a GOES A5 flare and the loop expansion accelerated, reaching a velocity of 130 km/s when the loop appeared to rupture near the peak of the flare. The material bundle then swung back in a whiplike manner and developed into a collimated jet, exhibiting oscillatory transverse motions across its axis, as expected from unwinding twists. Some jet material fell back along smooth streamlines, which bypass an unseen dome and presumably a null point in the low corona, depicting an inverted-Y shape. Some of these observations resemble the model (e.g., Uchida & Shibata) of the emergence of a twisted flux rope into an open field region that leads to reconnection and formation of a jet. Some observations are, however, not predicted in previous models and we will discuss their implications. Title: Seismic Constraints on Interior Solar Convection Authors: Hanasoge, Shravan M.; Duvall, Thomas L., Jr.; DeRosa, Marc L. Bibcode: 2010ApJ...712L..98H Altcode: 2010arXiv1001.4508H We constrain the velocity spectral distribution of global-scale solar convective cells at depth using techniques of local helioseismology. We calibrate the sensitivity of helioseismic waves to large-scale convective cells in the interior by analyzing simulations of waves propagating through a velocity snapshot of global solar convection via methods of time-distance helioseismology. Applying identical analysis techniques to observations of the Sun, we are able to bound from above the magnitudes of solar convective cells as a function of spatial convective scale. We find that convection at a depth of r/R sun = 0.95 with spatial extent ell < 20, where ell is the spherical harmonic degree, comprises weak flow systems, on the order of 15 m s-1 or less. Convective features deeper than r/R sun = 0.95 are more difficult to image due to the rapidly decreasing sensitivity of helioseismic waves. Title: Non-force-free extrapolation of solar coronal magnetic field using vector magnetograms Authors: Hu, Qiang; Dasgupta, B.; Derosa, M. L.; Büchner, J.; Gary, G. A. Bibcode: 2010JASTP..72..219H Altcode: We report our recent improvement in non-force-free extrapolation of coronal magnetic field, using vector magnetograms. Based on the principle of minimum (energy) dissipation rate (MDR), a generally non-force-free magnetic field solution is expressed as the superposition of one potential field and two (constant-[alpha]) linear force-free fields, with distinct [alpha] parameters. With a known potential field, the system is reduced to a second-order one that can be solved using one single-layer vector magnetogram. We devise an iteration procedure to determine the potential field, by achieving satisfactory agreement between the MDR-model computed and measured transverse magnetic field vectors on the bottom boundary. We illustrate this approach by applying it to real magnetograph measurement of solar active region AR 10953. We show that the results are satisfactory as judged from the quantitative magnetic field measurement, and the behavior of the derived Lorentz force. Title: Comparison of STEREO/EUVI Loops with Potential Magnetic Field Models Authors: Sandman, A. W.; Aschwanden, M. J.; DeRosa, M. L.; Wülser, J. P.; Alexander, D. Bibcode: 2009SoPh..259....1S Altcode: The Solar Terrestrial Relations Observatory (STEREO) provides the first opportunity to triangulate the three-dimensional coordinates of active region loops simultaneously from two different vantage points in space. Three-dimensional coordinates of the coronal magnetic field have been calculated with theoretical magnetic field models for decades, but it is only with the recent availability of STEREO data that a rigorous, quantitative comparison between observed loop geometries and theoretical magnetic field models can be performed. Such a comparison provides a valuable opportunity to assess the validity of theoretical magnetic field models. Here we measure the misalignment angles between model magnetic fields and observed coronal loops in three active regions, as observed with the Extreme Ultraviolet Imager (EUVI) on STEREO on 30 April, 9 May, and 19 May 2007. We perform stereoscopic triangulation of some 100 - 200 EUVI loops in each active region and compute extrapolated magnetic field lines using magnetogram information from the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO). We examine two different magnetic extrapolation methods: (1) a potential field and (2) a radially stretched potential field that conserves the magnetic divergence. We find considerable disagreement between each theoretical model and the observed loop geometries, with an average misalignment angle on the order of 20° - 40°. We conclude that there is a need for either more suitable (coronal rather than photospheric) magnetic field measurements or more realistic field extrapolation models. Title: Coronal Radiation Belts Authors: Hudson, H. S.; MacKinnon, A. L.; De Rosa, M. L.; Frewen, S. F. N. Bibcode: 2009ApJ...698L..86H Altcode: 2009arXiv0905.3824H The magnetic field of the solar corona has a large-scale dipole character, which maps into the bipolar field in the solar wind. Using standard representations of the coronal field, we show that high-energy ions can be trapped stably in these large-scale closed fields. The drift shells that describe the conservation of the third adiabatic invariant may have complicated geometries. Particles trapped in these zones would resemble the Van Allen belts and could have detectable consequences. We discuss potential sources of trapped particles. Title: Nonlinear Force-Free Magnetic Field Modeling of AR 10953: A Critical Assessment Authors: De Rosa, Marc L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.; Lites, B. W.; Aschwanden, M. J.; Amari, T.; Canou, A.; McTiernan, J. M.; Régnier, S.; Thalmann, J. K.; Valori, G.; Wheatland, M. S.; Wiegelmann, T.; Cheung, M. C. M.; Conlon, P. A.; Fuhrmann, M.; Inhester, B.; Tadesse, T. Bibcode: 2009SPD....40.3102D Altcode: Nonlinear force-free field (NLFFF) modeling seeks to provide accurate representations of the structure of the magnetic field above solar active regions, from which estimates of physical quantities of interest (e.g., free energy and helicity) can be made. However, the suite of NLFFF algorithms have failed to arrive at consistent solutions when applied to (thus far, two) cases using the highest-available-resolution vector magnetogram data from Hinode/SOT-SP (in the region of the modeling area of interest) and line-of-sight magnetograms from SOHO/MDI (where vector data were not available). One issue is that NLFFF models require consistent, force-free vector magnetic boundary data, and vector magnetogram data sampling the photosphere do not satisfy this requirement. Consequently, several problems have arisen that are believed to affect such modeling efforts. We use AR 10953 to illustrate these problems, namely: (1) some of the far-reaching, current-carrying connections are exterior to the observational field of view, (2) the solution algorithms do not (yet) incorporate the measurement uncertainties in the vector magnetogram data, and/or (3) a better way is needed to account for the Lorentz forces within the layer between the photosphere and coronal base. In light of these issues, we conclude that it remains difficult to derive useful and significant estimates of physical quantities from NLFFF models. Title: A Critical Assessment of Nonlinear Force-Free Field Modeling of the Solar Corona for Active Region 10953 Authors: De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham; Leka, K. D.; Lites, Bruce W.; Aschwanden, Markus J.; Amari, Tahar; Canou, Aurélien; McTiernan, James M.; Régnier, Stéphane; Thalmann, Julia K.; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas; Cheung, Mark C. M.; Conlon, Paul A.; Fuhrmann, Marcel; Inhester, Bernd; Tadesse, Tilaye Bibcode: 2009ApJ...696.1780D Altcode: 2009arXiv0902.1007D Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics, and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically constructed Sun-like test cases, but they are less successful in application to real solar data. Different NLFFF models have been found to have markedly different field line configurations and to provide widely varying estimates of the magnetic free energy in the coronal volume, when applied to solar data. NLFFF models require consistent, force-free vector magnetic boundary data. However, vector magnetogram observations sampling the photosphere, which is dynamic and contains significant Lorentz and buoyancy forces, do not satisfy this requirement, thus creating several major problems for force-free coronal modeling efforts. In this paper, we discuss NLFFF modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT, STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process illustrate three such issues we judge to be critical to the success of NLFFF modeling: (1) vector magnetic field data covering larger areas are needed so that more electric currents associated with the full active regions of interest are measured, (2) the modeling algorithms need a way to accommodate the various uncertainties in the boundary data, and (3) a more realistic physical model is needed to approximate the photosphere-to-corona interface in order to better transform the forced photospheric magnetograms into adequate approximations of nearly force-free fields at the base of the corona. We make recommendations for future modeling efforts to overcome these as yet unsolved problems. Title: Stochastic Effects of Granulation and Supergranulation Upon Deep Convection Authors: Augustson, Kyle; De Rosa, M. L.; Hurlburt, N. E.; Toomre, J. Bibcode: 2009SPD....40.0805A Altcode: Vigorous fluid motions associated with the observed patterns of supergranulation, mesogranulation, and granulation play a large role in the turbulent transport of heat to the solar surface. The downflows associated with these convective motions plunge from the surface into the near-surface layers of the Sun bringing cooler, low entropy material with them. These flow structures may provide some stochastic effects upon the dynamics of the giant cells of deep convection that extend into the near-surface regions. To investigate such dynamics, we have carried out several 3-D numerical simulations of fully compressible fluids within curved, spherical segments that, at this stage, approximate conditions near the top of the rotating solar convection zone. The upper boundary of the segment is stochastically driven with cool plumes that approximate the spatial and temporal scales of supergranular cell downflows, in essence creating a network of supergranular cells. The segment spans 30° in latitude and 30° in longitude, and has a radial extent of 15% of the solar radius. We explore the formation and evolution of the boundary layer resulting from such stochastic driving, and discuss these dynamics in the context of the near-surface shear layer of the solar convection zone. Title: Interaction Between Emerging Magnetic Flux And The Ambient Solar Coronal Field Authors: Cheung, Mark; De Rosa, M. Bibcode: 2009SPD....40.3103C Altcode: We study the interaction between emerging magnetic flux and pre-existing coronal field by means of numerical simulations using the magneto-frictional method. By advancing the induction equation, the magneto-frictional method models the coronal magnetic field as a quasi-static sequence of non-linear force-free field configurations evolving in response to photospheric driving. A general feature of the simulations is the spontaneous formation of current sheets. At these interfaces, the field line torsional coefficient changes abruptly across separate domains of connectivity. Since the code evolves the vector potential, it allows us to calculate how much relative magnetic helicity and free energy is stored in the system. By using temporal sequences of observed vector magnetograms as the boundary condition, this model is potentially suitable for modeling the evolution of solar coronal fields. 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: Using STEREO/EUVI to Study Active Region Magnetic Fields Authors: Sandman, A.; Aschwanden, M.; Wuelser, J.; De Rosa, M.; Alexander, D. Bibcode: 2008AGUFMSH13B1523S Altcode: We examine the effect of linear transformations on the misalignment between model magnetic fields and coronal loops in active regions, as observed with STEREO/EUVI on three separate occasions between April 30 and May 19, 2007. We perform stereoscopic triangulation of some 100 EUVI loops in each active region, and identify the tangent vectors along every loop. Using magnetogram information from SOHO/MDI we compute a 3D potential field and interpolate the magnetic field vector at every position along the EUVI loops. The angle between the loop tangent vector and the magnetic field vector provides a measure of the misalignment angle between the observed field configuration and the model. We then transform the field in a way that preserves the divergence-free condition while injecting electric currents into the system. With this modified field we repeat our calculation of the misalignment angles between the magnetic field vectors and the EUV loop tangent vectors, quantifying the improvement of the transformed magnetic field model. Results of this type of magnetic modeling are presented for three active regions. Title: The Buildup of Large-Scale Polar Magnetic Fields on the Sun: Small Things Can Make a Difference Authors: De Rosa, M. L. Bibcode: 2008AGUFMSH44A..01D Altcode: Large-scale magnetic field patterns visible at high latitudes on the solar photosphere are thought to form primarily from the poleward transport of flux that has emerged at lower latitudes. It is only a small percentage of this lower-latitude (i.e., active region) flux, however, that makes it to the poles, as much active-region flux cancels during its emergence and subsequent dispersal. This dispersal is characterized by the shearing and advection caused by the surface differential rotation and meridional flows, as well as by constant buffeting by near-surface convection and interactions with nearby flux concentrations. Consequently, these processes can play an important role in the transport of flux to the poles and the buildup of the polar caps, and their nonlinear nature implies that interactions between patterns with differing spatial (and temporal) scales can affect the timing of the formation of the polar cap as well as its overall amplitude. Such possibilities are investigated using a surface flux-transport model, and implications regarding the heliosphere are discussed. Title: Non-force Free Coronal Extrapolation Based on the Principle of Minimum Dissipation Rate Authors: Hu, Q.; Dasgupta, B.; Buechner, J.; De Rosa, M. Bibcode: 2008AGUFMSH13A1514H Altcode: The Principle of Minimum (energy) Dissipation Rate (MDR) originates from irreversible thermodynamics. In analogy to the Principle of Minimum Energy, it also follows a variational approach, but is more suitable for a complex and externally driven system like the solar corona. And in contrast, while the former yields a force- free magnetic field, the MDR gives a more general non-force free magnetic field with flow. The solution to the equation describing non-force free magnetic field resulted from MDR can be expressed as a superposition of two linear force-free fields with distinct α parameters, and one potential field (α≡0). Subsequently, the plasma states can also be derived, following standard MHD theory, given necessary boundary conditions. We present recent progress on applying the MDR theory to non-force free extrapolation of solar active region from vector magnetograms as bottom boundary data. We illustrate the approach of complete characterization of 3D magnetic field and plasma states by using numerical simulation data, and discuss its advantages and limitations. Title: Modeling of Solar Radiation Belts Authors: Frewen, S. S.; De Rosa, M.; Hudson, H.; MacKinnon, A. Bibcode: 2008AGUFMSH13B1526F Altcode: Stable particle trapping in the complicated magnetic field of the solar corona -- "solar radiation belts" -- at first seems unlikely in the face of the Sun's complex, variable magnetic field. By integrating particle orbit equations in the guiding-center approximation, we investigate the fates of energetic ions in model coronal magnetic fields. We use both PFSS (Potential Field Source Surface) and simple analytic field models. Contrary to naive expectation, we find that significant numbers of particles remain trapped more than long enough to circumnavigate the Sun, neither precipitating to the surface nor attaining open field lines. The drift "shells" corresponding to conservation of the third adiabatic invariant may be complicated in form. A close look at the dependence of the cross-field drift speed on magnetic field strength and topology accounts for this finding. Title: On the Solar Origins of Open Magnetic Fields in the Heliosphere Authors: Rust, David M.; Haggerty, Dennis K.; Georgoulis, Manolis K.; Sheeley, Neil R.; Wang, Yi-Ming; DeRosa, Marc L.; Schrijver, Carolus J. Bibcode: 2008ApJ...687..635R Altcode: A combination of heliospheric and solar data was used to identify open magnetic fields stretching from the lower corona to Earth orbit. 35 near-relativistic electron beams detected at the ACE spacecraft "labeled" the heliospheric segments of the open fields. An X-ray flare occurred <20 minutes before injection of the electrons in 25 events. These flares labeled the solar segment of the open fields. The flares occurred in western-hemisphere active regions (ARs) with coronal holes whose polarity agreed with the polarity of the beam-carrying interplanetary fields in 23 of the 25 events. We conclude that electron beams reach 1 AU from open AR fields adjacent to flare sites. The Wang & Sheeley implementation of the potential-field source-surface model successfully identified the open fields in 36% of cases. Success meant that the open fields reached the source surface within 3 heliographic deg of the interplanetary magnetic field connected to ACE at 1 AU. Inclusion of five near misses improves the success rate to 56%. The success rate for the Schrijver & DeRosa PFSS implementation was 50%. Our results suggest that, even if the input magnetic data are updated frequently, the PFSS models succeed in only ~50% of cases to identify the coronal segment of open fields. Development of other techniques is in its infancy. Title: On the Stability of Active Regions and Sunspots Authors: Hurlburt, Neal; DeRosa, Marc Bibcode: 2008ApJ...684L.123H Altcode: Recent helioseismic measurements of large-scale subsurface flows indicate that systematic horizontal inflows near the photosphere surround many active regions. Such active-region inflows are likely to impede the dispersal of magnetic flux into the surrounding network and thus can influence larger-scale and longer-term patterns and evolution of the surface magnetic field throughout the course of a solar activity cycle. We present results of numerical simulations of compressible magnetoconvection in which an initial unipolar magnetic field undergoes evolution resulting from convectively driven motions. Inflows surrounding regions of concentrated magnetic flux are driven by reducing the surface temperature as a function of local magnetic flux. We find flow patterns that are consistent with observations of those observed around active regions and sunspots. Title: Preprocessing of Hinode/SOT Vector Magnetograms for Nonlinear Force-Free Coronal Magnetic Field Modeling Authors: Wiegelmann, T.; Thalmann, J. K.; Schrijver, C. J.; De Rosa, M. L.; Metcalf, T. R. Bibcode: 2008ASPC..397..198W Altcode: 2008arXiv0801.2884W The solar magnetic field is key to understanding the physical processes in the solar atmosphere. Nonlinear force-free codes have been shown to be useful in extrapolating the coronal field from underlying vector boundary data (for an overview see Schrijver et al. (2006)). However, we can only measure the magnetic field vector routinely with high accuracy in the photosphere with, e.g., Hinode/SOT, and unfortunately these data do not fulfill the force-free consistency condition as defined by Aly (1989). We must therefore apply some transformations to these data before nonlinear force-free extrapolation codes can be legitimately applied. To this end, we have developed a minimization procedure that uses the measured photospheric field vectors as input to approximate a more chromospheric like field (The method was dubbed preprocessing. See Wiegelmann et al. (2006) for details). The procedure includes force-free consistency integrals and spatial smoothing. The method has been intensively tested with model active regions (see Metcalf et al. 2008) and been applied to several ground based vector magnetogram data before. Here we apply the preprocessing program to photospheric magnetic field measurements with the Hinode/SOT instrument. Title: Erratum: "Tests and Comparisons of Velocity-Inversion Techniques" (ApJ, 670, 1434 [2007]) Authors: Welsch, B. T.; Abbett, W. P.; DeRosa, M. L.; Fisher, G. H.; Georgoulis, M. K.; Kusano, K.; Longcope, D. W.; Ravindra, B.; Schuck, P. W. Bibcode: 2008ApJ...680..827W Altcode: No abstract at ADS Title: The Dependence of Ephemeral Region Emergence on Local Flux Imbalance Authors: Hagenaar, Hermance J.; DeRosa, Marc L.; Schrijver, Carolus J. Bibcode: 2008ApJ...678..541H Altcode: We investigate the distribution and evolution of existing and emerging magnetic network elements in the quiet-Sun photosphere. The ephemeral region emergence rate is found to depend primarily on the imbalance of magnetic flux in the area surrounding its emergence location, such that the rate of flux emergence is lower within strongly unipolar regions by at least a factor of 3 relative to flux-balanced quiet Sun. As coronal holes occur over unipolar regions, this also means that ephemeral regions occur less frequently there, but we show that this is an indirect effect—independent of whether the region is located within an open-field coronal hole or a closed-field quiet region. We discuss the implications of this finding for near-photospheric dynamo action and for the coupling between closed coronal and open heliospheric fields. Title: A joint search for gravitational wave bursts with AURIGA and LIGO Authors: Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; De Rosa, M.; Falferi, P.; Fattori, S.; Fortini, P.; Giusfredi, G.; Inguscio, M.; Liguori, N.; Longo, S.; Marin, F.; Mezzena, R.; Mion, A.; Ortolan, A.; Poggi, S.; Prodi, G. A.; Re, V.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato, G.; Vinante, A.; Vitale, S.; Zendri, J. P.; Abbott, B.; Abbott, R.; Adhikari, R.; Agresti, J.; Ajith, P.; Allen, B.; Amin, R.; Anderson, S. B.; Anderson, W. G.; Arain, M.; Araya, M.; Armandula, H.; Ashley, M.; Aston, S.; Aufmuth, P.; Aulbert, C.; Babak, S.; Ballmer, S.; Bantilan, H.; Barish, B. C.; Barker, C.; Barker, D.; Barr, B.; Barriga, P.; Barton, M. A.; Bayer, K.; Belczynski, K.; Betzwieser, J.; Beyersdorf, P. T.; Bhawal, B.; Bilenko, I. A.; Billingsley, G.; Biswas, R.; Black, E.; Blackburn, K.; Blackburn, L.; Blair, D.; Bland, B.; Bogenstahl, J.; Bogue, L.; Bork, R.; Boschi, V.; Bose, S.; Brady, P. R.; Braginsky, V. B.; Brau, J. E.; Brinkmann, M.; Brooks, A.; Brown, D. A.; Bullington, A.; Bunkowski, A.; Buonanno, A.; Burmeister, O.; Busby, D.; Butler, W. E.; Byer, R. L.; Cadonati, L.; Cagnoli, G.; Camp, J. B.; Cannizzo, J.; Cannon, K.; Cantley, C. A.; Cao, J.; Cardenas, L.; Carter, K.; Casey, M. M.; Castaldi, G.; Cepeda, C.; Chalkley, E.; Charlton, P.; Chatterji, S.; Chelkowski, S.; Chen, Y.; Chiadini, F.; Chin, D.; Chin, E.; Chow, J.; Christensen, N.; Clark, J.; Cochrane, P.; Cokelaer, T.; Colacino, C. N.; Coldwell, R.; Conte, R.; Cook, D.; Corbitt, T.; Coward, D.; Coyne, D.; Creighton, J. D. E.; Creighton, T. D.; Croce, R. P.; Crooks, D. R. M.; Cruise, A. M.; Cumming, A.; Dalrymple, J.; D'Ambrosio, E.; Danzmann, K.; Davies, G.; DeBra, D.; Degallaix, J.; Degree, M.; Demma, T.; Dergachev, V.; Desai, S.; DeSalvo, R.; Dhurandhar, S.; Díaz, M.; Dickson, J.; Di Credico, A.; Diederichs, G.; Dietz, A.; Doomes, E. E.; Drever, R. W. P.; Dumas, J. -C.; Dupuis, R. J.; Dwyer, J. G.; Ehrens, P.; Espinoza, E.; Etzel, T.; Evans, M.; Evans, T.; Fairhurst, S.; Fan, Y.; Fazi, D.; Fejer, M. M.; Finn, L. S.; Fiumara, V.; Fotopoulos, N.; Franzen, A.; Franzen, K. Y.; Freise, A.; Frey, R.; Fricke, T.; Fritschel, P.; Frolov, V. V.; Fyffe, M.; Galdi, V.; Ganezer, K. S.; Garofoli, J.; Gholami, I.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Goda, K.; Goetz, E.; Goggin, L. M.; González, G.; Gossler, S.; Grant, A.; Gras, S.; Gray, C.; Gray, M.; Greenhalgh, J.; Gretarsson, A. M.; Grosso, R.; Grote, H.; Grunewald, S.; Guenther, M.; Gustafson, R.; Hage, B.; Hammer, D.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G.; Harstad, E.; Hayler, T.; Heefner, J.; Heng, I. S.; Heptonstall, A.; Heurs, M.; Hewitson, M.; Hild, S.; Hirose, E.; Hoak, D.; Hosken, D.; Hough, J.; Howell, E.; Hoyland, D.; Huttner, S. H.; Ingram, D.; Innerhofer, E.; Ito, M.; Itoh, Y.; Ivanov, A.; Jackrel, D.; Johnson, B.; Johnson, W. W.; Jones, D. I.; Jones, G.; Jones, R.; Ju, L.; Kalmus, P.; Kalogera, V.; Kasprzyk, D.; Katsavounidis, E.; Kawabe, K.; Kawamura, S.; Kawazoe, F.; Kells, W.; Keppel, D. G.; Khalili, F. Ya; Kim, C.; King, P.; Kissel, J. S.; Klimenko, S.; Kokeyama, K.; Kondrashov, V.; Kopparapu, R. K.; Kozak, D.; Krishnan, B.; Kwee, P.; Lam, P. K.; Landry, M.; Lantz, B.; Lazzarini, A.; Lee, B.; Lei, M.; Leiner, J.; Leonhardt, V.; Leonor, I.; Libbrecht, K.; Lindquist, P.; Lockerbie, N. A.; Longo, M.; Lormand, M.; Lubiński, M.; Lück, H.; Machenschalk, B.; MacInnis, M.; Mageswaran, M.; Mailand, K.; Malec, M.; Mandic, V.; Marano, S.; Márka, S.; Markowitz, J.; Maros, E.; Martin, I.; Marx, J. N.; Mason, K.; Matone, L.; Matta, V.; Mavalvala, N.; McCarthy, R.; McClelland, D. E.; McGuire, S. C.; McHugh, M.; McKenzie, K.; McNabb, J. W. C.; McWilliams, S.; Meier, T.; Melissinos, A.; Mendell, G.; Mercer, R. A.; Meshkov, S.; Messenger, C. J.; Meyers, D.; Mikhailov, E.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Miyakawa, O.; Mohanty, S.; Moreno, G.; Mossavi, K.; Lowry, C. Mow; Moylan, A.; Mudge, D.; Mueller, G.; Mukherjee, S.; Müller-Ebhardt, H.; Munch, J.; Murray, P.; Myers, E.; Myers, J.; Nash, T.; Newton, G.; Nishizawa, A.; Nocera, F.; Numata, K.; O'Reilly, B.; O'Shaughnessy, R.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pan, Y.; Papa, M. A.; Parameshwaraiah, V.; Parameswariah, C.; Patel, P.; Pedraza, M.; Penn, S.; Pierro, V.; Pinto, I. M.; Pitkin, M.; Pletsch, H.; Plissi, M. V.; Postiglione, F.; Prix, R.; Quetschke, V.; Raab, F.; Rabeling, D.; Radkins, H.; Rahkola, R.; Rainer, N.; Rakhmanov, M.; Ramsunder, M.; Rawlins, K.; Ray-Majumder, S.; Regimbau, T.; Rehbein, H.; Reid, S.; Reitze, D. H.; Ribichini, L.; Riesen, R.; Riles, K.; Rivera, B.; Robertson, N. A.; Robinson, C.; Robinson, E. L.; Roddy, S.; Rodriguez, A.; Rogan, A. M.; Rollins, J.; Romano, J. D.; Romie, J.; Route, R.; Rowan, S.; Rüdiger, A.; Ruet, L.; Russell, P.; Ryan, K.; Sakata, S.; Samidi, M.; Sancho de la Jordana, L.; Sandberg, V.; Sanders, G. H.; Sannibale, V.; Saraf, S.; Sarin, P.; Sathyaprakash, B. S.; Sato, S.; Saulson, P. R.; Savage, R.; Savov, P.; Sazonov, A.; Schediwy, S.; Schilling, R.; Schnabel, R.; Schofield, R.; Schutz, B. F.; Schwinberg, P.; Scott, S. M.; Searle, A. C.; Sears, B.; Seifert, F.; Sellers, D.; Sengupta, A. S.; Shawhan, P.; Shoemaker, D. H.; Sibley, A.; Siemens, X.; Sigg, D.; Sinha, S.; Sintes, A. M.; Slagmolen, B. J. J.; Slutsky, J.; Smith, J. R.; Smith, M. R.; Somiya, K.; Strain, K. A.; Strom, D. M.; Stuver, A.; Summerscales, T. Z.; Sun, K. -X.; Sung, M.; Sutton, P. J.; Takahashi, H.; Tanner, D. B.; Tarallo, M.; Taylor, R.; Taylor, R.; Thacker, J.; Thorne, K. A.; Thorne, K. S.; Thüring, A.; Tinto, M.; Tokmakov, K. V.; Torres, C.; Torrie, C.; Traylor, G.; Trias, M.; Tyler, W.; Ugolini, D.; Ungarelli, C.; Urbanek, K.; Vahlbruch, H.; Vallisneri, M.; Van Den Broeck, C.; van Putten, M.; Varvella, M.; Vass, S.; Vecchio, A.; Veitch, J.; Veitch, P.; Villar, A.; Vorvick, C.; Vyachanin, S. P.; Waldman, S. J.; Wallace, L.; Ward, H.; Ward, R.; Watts, K.; Webber, D.; Weidner, A.; Weinert, M.; Weinstein, A.; Weiss, R.; Wen, S.; Wette, K.; Whelan, J. T.; Whitbeck, D. M.; Whitcomb, S. E.; Whiting, B. F.; Wiley, S.; Wilkinson, C.; Willems, P. A.; Williams, L.; Willke, B.; Wilmut, I.; Winkler, W.; Wipf, C. C.; Wise, S.; Wiseman, A. G.; Woan, G.; Woods, D.; Wooley, R.; Worden, J.; Wu, W.; Yakushin, I.; Yamamoto, H.; Yan, Z.; Yoshida, S.; Yunes, N.; Zanolin, M.; Zhang, J.; Zhang, L.; Zhao, C.; Zotov, N.; Zucker, M.; zur Mühlen, H.; Zweizig, J. Bibcode: 2008CQGra..25i5004B Altcode: 2007arXiv0710.0497A The first simultaneous operation of the AURIGA detectorhttp://www.auriga.lnl.infn.it and the LIGO observatoryhttp://www.ligo.org was an opportunity to explore real data, joint analysis methods between two very different types of gravitational wave detectors: resonant bars and interferometers. This paper describes a coincident gravitational wave burst search, where data from the LIGO interferometers are cross-correlated at the time of AURIGA candidate events to identify coincident transients. The analysis pipeline is tuned with two thresholds, on the signal-to-noise ratio of AURIGA candidate events and on the significance of the cross-correlation test in LIGO. The false alarm rate is estimated by introducing time shifts between data sets and the network detection efficiency is measured by adding simulated gravitational wave signals to the detector output. The simulated waveforms have a significant fraction of power in the narrower AURIGA band. In the absence of a detection, we discuss how to set an upper limit on the rate of gravitational waves and to interpret it according to different source models. Due to the short amount of analyzed data and to the high rate of non-Gaussian transients in the detectors' noise at the time, the relevance of this study is methodological: this was the first joint search for gravitational wave bursts among detectors with such different spectral sensitivity and the first opportunity for the resonant and interferometric communities to unify languages and techniques in the pursuit of their common goal. 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: Exploring large-scale coronal magnetic field over extended longitudes by STEREO/EUVI and its effect on solar wind prediction Authors: Nitta, N. V.; De Rosa, M. L.; Zarro, D. M.; Wuelser, J.; Aschwanden, M. J.; Lemen, J. R. Bibcode: 2008AGUSMSH23A..06N Altcode: The potential field source surface (PFSS) model forms the basis of a wide range of heliospheric science and applications, including prediction of the solar wind speed near Earth. Experience shows that the model sometimes works quite well, but not always. Possible reasons for failure include deviation of the interplanetary magnetic field from the nominal Parker spiral, violation of the assumptions used in the model such as the discontinuity at the source surface, and the lack of simultaneous full-surface magnetograms. Here we study the impact of the lack of simultaneous full-surface magnetograms, using observations of the corona over an extended longitude range made possible by the EUVI on board the STEREO mission. In spite of the lack of magnetographs on STEREO, EUVI data with a growing separation angle between spacecraft A and B at least allow us to locate major active regions and coronal holes in the area not seen from Earth. The PFSS extrapolations and their input synoptic maps are compared with EUVI data to measure how well the model fits the observations. These comparisons are discussed in terms of the solar wind speed predicted by the model and observed at L1 by ACE. Title: Tracing the 3-D coronal structure during CMEs with STEREO/SECCHI EUVI observations Authors: Wuelser, J.; Aschwanden, M.; De Rosa, M.; Lee, C.; Lemen, J.; Nitta, N.; Sandman, A. Bibcode: 2008AGUSMSH31A..05W Altcode: STEREO/SECCHI EUVI observations of solar coronal loops, filaments, and dimming regions provide unique information on the 3-D topology of the coronal magnetic field above active regions and its evolution during coronal mass ejections (CMEs). Active Region #10956 produced several CMEs during its passage across the solar disk in May 2007, some of them showing filament eruptions and dimming. The SECCHI/EUVI instrument on STEREO obtained high cadence observations in multiple lines simultaneously from both STEREO spacecraft. 3-D reconstructions of coronal features over the course of a CME show significant changes of the field topology. Comparisons with the potential field topology from magnetic field extrapolations show the degree of non-potentiality of the real field and changes in the vicinity of the CME onset. We present initial results of this study. Title: Searching for Large-scale flows around Active Regions with Hinode Authors: Hurlburt, N.; Derosa, M.; Hagenaar, M. Bibcode: 2008AGUSMSP43C..08H Altcode: Heliosiemic studies have suggested that active regions are surrounded by large-scale inflows (Haber et al. 2004), and it has recently been hypothesized by Hurlburt and DeRosa (2008,HD) that these are due to the enhanced surface cooling resulting from plage and faculae. We seek confirmation of these results using Hinode observations of Active Regions using a variety of methods to infer inflow velocities from of continuum images and Dopplergrams. These flow patterns are then compared to the HD hypothesis. This work has been supported by NASA through contracts NNM07AA01C and NNG06GD45G. References: Haber, D., Hindman, B., Toomre, J. and Thompson, M. 2004, ÐOrganized Subsurface Flows near Active Regions,î Sol. Phys. 220,371. Hurlburt & DeRosa, 2008 ÐOn the longevity of Active Regions,î Ap.J. Lett., submitted 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: A Comparison of Solar Open Field Regions Found by Type III Radio Bursts and the Potential Field Source Surface Model Authors: Nitta, Nariaki V.; DeRosa, Marc L. Bibcode: 2008ApJ...673L.207N Altcode: For heliophysics research and applications, the potential field source surface (PFSS) model is often employed to extrapolate the photospheric magnetic field to the corona. In an attempt to evaluate the performance of the PFSS model, we compare the computed footpoints of the heliospheric magnetic field with the locations of flares associated with type III radio bursts, which are a good indicator of open field lines that extend to interplanetary space. Consistent with past experiences, the agreement is not satisfactory. We discuss possible reasons for the discrepancy, including the model's inadequacy to reproduce the coronal magnetic field above evolving active regions and the lack of a simultaneous full-surface magnetic map. It is argued that the performance of the PFSS model needs to be quantified further against solar observations, including type III bursts, before it is applied to heliospheric models. Title: Can We Improve the Preprocessing of Photospheric Vector Magnetograms by the Inclusion of Chromospheric Observations? Authors: Wiegelmann, T.; Thalmann, J. K.; Schrijver, C. J.; De Rosa, M. L.; Metcalf, T. R. Bibcode: 2008SoPh..247..249W Altcode: 2008arXiv0801.2707W; 2008SoPh..tmp...27W The solar magnetic field is key to understanding the physical processes in the solar atmosphere. Nonlinear force-free codes have been shown to be useful in extrapolating the coronal field upward from underlying vector boundary data. However, we can only measure the magnetic field vector routinely with high accuracy in the photosphere, and unfortunately these data do not fulfill the force-free condition. We must therefore apply some transformations to these data before nonlinear force-free extrapolation codes can be self-consistently applied. To this end, we have developed a minimization procedure that yields a more chromosphere-like field, using the measured photospheric field vectors as input. The procedure includes force-free consistency integrals, spatial smoothing, and - newly included in the version presented here - an improved match to the field direction as inferred from fibrils as can be observed in, for example, chromospheric Hα images. We test the procedure using a model active-region field that included buoyancy forces at the photospheric level. The proposed preprocessing method allows us to approximate the chromospheric vector field to within a few degrees and the free energy in the coronal field to within one percent. Title: Nonlinear Force-Free Modeling of Coronal Magnetic Fields. II. Modeling a Filament Arcade and Simulated Chromospheric and Photospheric Vector Fields Authors: Metcalf, Thomas R.; De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham; van Ballegooijen, Adriaan A.; Wiegelmann, Thomas; Wheatland, Michael S.; Valori, Gherardo; McTtiernan, James M. Bibcode: 2008SoPh..247..269M Altcode: 2008SoPh..tmp...17M 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 combination of Lorentz forces and small spatial scale structure at the photosphere severely impact the extrapolation of the field. Preprocessing of the forced photospheric boundary does improve the extrapolations considerably for the layers above the chromosphere, but the extrapolations are sensitive to the details of the numerical codes and neither the field connectivity nor the free magnetic energy in the full volume are well recovered. The magnetic virial theorem gives a rapid measure of the total magnetic energy without extrapolation though, like the NLFFF codes, it is sensitive to the Lorentz forces in the coronal volume. Both the magnetic virial theorem and the Wiegelmann extrapolation, when applied to the preprocessed photospheric boundary, give a magnetic energy which is nearly equivalent to the value derived from the chromospheric boundary, but both underestimate the free energy above the photosphere by at least a factor of two. We discuss the interpretation of the preprocessed field in this context. 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: Ephemeral Bipolar Regions in Coronal Holes Authors: Hagenaar, H.; Schrijver, C.; De Rosa, M. Bibcode: 2008ASPC..383..343H Altcode: We investigate the distribution and evolution of magnetic network elements in quiet Sun with or without coronal holes. Ephemeral region emergence rates are found to depend on the degree of imbalance of magnetic flux, but independent of whether there is a coronal hole or not. We discuss the implications of this finding for near-photospheric dynamo action and for the coupling between closed coronal and open heliospheric fields. Title: Structure and Evolution of Giant Cells in Global Models of Solar Convection Authors: Miesch, Mark S.; Brun, Allan Sacha; DeRosa, Marc L.; Toomre, Juri Bibcode: 2008ApJ...673..557M Altcode: 2007arXiv0707.1460M The global scales of solar convection are studied through three-dimensional simulations of compressible convection carried out in spherical shells of rotating fluid that extend from the base of the convection zone to within 15 Mm of the photosphere. Such modeling at the highest spatial resolution to date allows study of distinctly turbulent convection, revealing that coherent downflow structures associated with giant cells continue to play a significant role in maintaining the differential rotation that is achieved. These giant cells at lower latitudes exhibit prograde propagation relative to the mean zonal flow, or differential rotation, that they establish, and retrograde propagation of more isotropic structures with vortical character at mid and high latitudes. The interstices of the downflow networks often possess strong and compact cyclonic flows. The evolving giant-cell downflow systems can be partly masked by the intense smaller scales of convection driven closer to the surface, yet they are likely to be detectable with the helioseismic probing that is now becoming available. Indeed, the meandering streams and varying cellular subsurface flows revealed by helioseismology must be sampling contributions from the giant cells, yet it is difficult to separate out these signals from those attributed to the faster horizontal flows of supergranulation. To aid in such detection, we use our simulations to describe how the properties of giant cells may be expected to vary with depth and how their patterns evolve in time. Title: Tests and Comparisons of Velocity-Inversion Techniques Authors: Welsch, B. T.; Abbett, W. P.; De Rosa, M. L.; Fisher, G. H.; Georgoulis, M. K.; Kusano, K.; Longcope, D. W.; Ravindra, B.; Schuck, P. W. Bibcode: 2007ApJ...670.1434W Altcode: Recently, several methods that measure the velocity of magnetized plasma from time series of photospheric vector magnetograms have been developed. Velocity fields derived using such techniques can be used both to determine the fluxes of magnetic energy and helicity into the corona, which have important consequences for understanding solar flares, coronal mass ejections, and the solar dynamo, and to drive time-dependent numerical models of coronal magnetic fields. To date, these methods have not been rigorously tested against realistic, simulated data sets, in which the magnetic field evolution and velocities are known. Here we present the results of such tests using several velocity-inversion techniques applied to synthetic magnetogram data sets, generated from anelastic MHD simulations of the upper convection zone with the ANMHD code, in which the velocity field is fully known. Broadly speaking, the MEF, DAVE, FLCT, IM, and ILCT algorithms performed comparably in many categories. While DAVE estimated the magnitude and direction of velocities slightly more accurately than the other methods, MEF's estimates of the fluxes of magnetic energy and helicity were far more accurate than any other method's. Overall, therefore, the MEF algorithm performed best in tests using the ANMHD data set. We note that ANMHD data simulate fully relaxed convection in a high-β plasma, and therefore do not realistically model photospheric evolution. Title: Can we Improve the Preprocessing of Photospheric Vectormagnetograms by the Inclusion of Chromospheric Observations? Authors: Wiegelmann, T.; Thalmann, J. K.; Schrijver, C. J.; De Rosa, M. L.; Metcalf, T. R. Bibcode: 2007AGUFMSH51C..02W Altcode: The solar magnetic field is key to understanding the physical processes in the solar atmosphere. Unfortunately, we can measure the magnetic field vector routinely with high accuracy only in the photosphere with, e.g., Hinode/SOT and in future with SDO/HMI. These measurements are extrapolated into the corona under the assumption that the field is force-free. That condition is not fulfilled in the photosphere, but is in the chromosphere and corona. In order to make the observed boundary data consistent with the force-free assumption, we therefore have to apply some transformations before nonlinear force-free extrapolation codes can be legitimately applied. We develop a minimization procedure that uses the measured photospheric field vectors as input to approximate a more chromospheric-like field. The procedure includes force-free consistency integrals, spatial smoothing, and - newly included in the version presented here - an improved match to the field direction as inferred from fibrils as can be observed in, e.g., chromospheric H-alpha images. We test the procedure using a model active-region field that included buoyancy forces at the photospheric level. We apply the combined preprocessing and nonlinear force-free extrapolation method to compute the coronal magnetic field in an active region measured with the Hinode/SOT instrument. Title: Results of the IGEC-2 search for gravitational wave bursts during 2005 Authors: Astone, P.; Babusci, D.; Baggio, L.; Bassan, M.; Bignotto, M.; Bonaldi, M.; Camarda, M.; Carelli, P.; Cavallari, G.; Cerdonio, M.; Chincarini, A.; Coccia, E.; Conti, L.; D'Antonio, S.; de Rosa, M.; di Paolo Emilio, M.; Drago, M.; Dubath, F.; Fafone, V.; Falferi, P.; Foffa, S.; Fortini, P.; Frasca, S.; Gemme, G.; Giordano, G.; Giusfredi, G.; Hamilton, W. O.; Hanson, J.; Inguscio, M.; Johnson, W. W.; Liguori, N.; Longo, S.; Maggiore, M.; Marin, F.; Marini, A.; McHugh, M. P.; Mezzena, R.; Miller, P.; Minenkov, Y.; Mion, A.; Modestino, G.; Moleti, A.; Nettles, D.; Ortolan, A.; Pallottino, G. V.; Parodi, R.; Piano Mortari, G.; Poggi, S.; Prodi, G. A.; Quintieri, L.; Re, V.; Rocchi, A.; Ronga, F.; Salemi, F.; Soranzo, G.; Sturani, R.; Taffarello, L.; Terenzi, R.; Torrioli, G.; Vaccarone, R.; Vandoni, G.; Vedovato, G.; Vinante, A.; Visco, M.; Vitale, S.; Weaver, J.; Zendri, J. P.; Zhang, P. Bibcode: 2007PhRvD..76j2001A Altcode: 2007arXiv0705.0688I The network of resonant bar detectors of gravitational waves resumed coordinated observations within the International Gravitational Event Collaboration (IGEC-2). Four detectors are taking part in this Collaboration: ALLEGRO, AURIGA, EXPLORER and NAUTILUS. We present here the results of the search for gravitational wave bursts over 6 months during 2005, when IGEC-2 was the only gravitational wave observatory in operation. The implemented network data analysis is based on a time coincidence search among AURIGA, EXPLORER and NAUTILUS; ALLEGRO data was reserved for follow-up studies. The network amplitude sensitivity to bursts improved by a factor ≈3 over the 1997-2000 IGEC observations; the wider sensitive band also allowed the analysis to be tuned over a larger class of waveforms. Given the higher single-detector duty factors, the analysis was based on threefold coincidence, to ensure the identification of any single candidate of gravitational waves with high statistical confidence. The false detection rate was as low as 1 per century. No candidates were found. Title: Can we detect convection in the Sun? Authors: Hanasoge, Shravan M.; Duvall, T. L.; De Rosa, M. L.; Miesch, M. S. Bibcode: 2007IAUS..239..364H Altcode: No abstract at ADS Title: Simulations of Large-Scale Solar Surface Inflows Surrounding Magnetic Fields Authors: De Rosa, Marc L.; Hurlburt, N. E. Bibcode: 2007AAS...210.2211D Altcode: 2007BAAS...39..126D Recent helioseismic measurements of large-scale subsurface flows have indicated that systematic horizontal inflows near the photosphere surround many active regions. Such active-region inflows are likely to impede the dispersal into the surrounding network, and thus can influence larger-scale and longer-term patterns of magnetic field throughout the course of a solar activity cycle. We present preliminary results of numerical simulations of compressible magnetoconvection, in which an initial unipolar magnetic field undergoes evolution resulting from convectively driven motions. Inflows surrounding regions of concentrated magnetic flux are driven by reducing the surface temperature in regions where the magnetic flux is strong. The effects of these resulting inflows on the dynamics are then studied. Title: Structure and Evolution of Giant Cells in Global Models of Solar Convection Authors: Miesch, Mark S.; Brun, A. S.; De Rosa, M. L.; Toomre, J. Bibcode: 2007AAS...210.2217M Altcode: 2007BAAS...39..127M We present the highest-resolution simulations of global-scale solar convection so far achieved, dealing with turbulent compressible flows interacting with rotation in a full spherical shell. The three-dimensional simulation domain extends from 0.71R-0.98R, close enough to the photosphere to overlap with solar subsurface weather (SSW) maps inferred from local helioseismology. The convective patterns achieved are complex and continually evolving on a time scale of several days. However, embedded within the intricate downflow network near the surface are coherent downflow lanes associated with giant cells which persist for weeks to months and which extend through much of the convection zone. These coherent downflow lanes are generally confined to low latitudes and are oriented in a north-south direction. The low dissipation in these simulations permits a more realistic balance of forces which yields differential rotation and meridional circulation profiles in good agreement with those inferred from helioseismology. 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: SEP Properties and Magnetic Field Connection of the Source Region Authors: Nitta, N. V.; De Rosa, M. L. Bibcode: 2006AGUFMSH41B..06N Altcode: There seems to be no clear explanation as to why some CME/flare events produce major SEP events whereas others do not. Furthermore, we still cannot reliably predict the peak flux and rise time of an SEP event using remote sensing data. Even though CME shocks are the primary accelerator for gradual SEP events and they are likely to have wide angular extensions, we suggest that the magnetic field connection of the source region to the observer may be an important factor for determining their occurrence and basic properties. In order to address this issue, we need to go beyond the common assumption that the longitudes around W60 have the strongest connection to the Earth. For a number of SEP-productive active regions, we compare the properties of intense flares and energetic CMEs that originated from them over their disk passage with the peak fluxes and rise times of the associated >10 MeV and >50 MeV protons. We perform magnetic field extrapolation with the potential field source surface (PFSS) model to locate well-connected field lines with respect to the source region. Once evaluated against multiple criteria, the PFSS extrapolation would be a useful tool to characterize the magnetic field topology in and around the active region responsible for the intense flares and energetic CMEs. This study is expected to partially answer the question of whether flare- accelerated particles contribute to gradual SEP events. Title: Coronal particle trapping revisited Authors: Hudson, H. S.; MacKinnon, A.; De Rosa, M. Bibcode: 2006AGUFMSH54A..07H Altcode: We re-examine the idea of long-term particle storage in the solar corona in the context of modern PFSS (potential-field source surface) magnetic models. As pointed out by H. Elliot in 1964 and others since then, such particles could be energetically important, at the level of some large fraction of the magnetic energy density B2/8π. We estimate the distribution and time scales of particle trapping by using representative PFSS coronal models from the Schrijver-De Rosa SolarSoft code. As the coronal field simplifies during solar minimum, it approaches axisymmetry and thus contains volumes inaccessible to charged particles under the guiding-center approximation. We conclude that time scales can be sufficiently long, so long in fact that the azimuthal drift time scale (third adiabatic invariant of guiding-center motion), for the large-scale dipolar configuration characteristic of solar minimum, can exceed one solar cycle. We discuss the possible sources of trapped particles, starting with the basic CRAND (cosmic-ray albedo neutron decay) mechanism, and relate their X-ray and γ-ray signatures to future observational capabilities including the Sentinels spacecraft. Title: Consequences of large-scale flows around active regions on the dispersal of magnetic field across the solar surface Authors: De Rosa, M. L.; Schrijver, C. J. Bibcode: 2006ESASP.624E..12D Altcode: 2006soho...18E..12D No abstract at ADS Title: Solar Sources of Impulsive Solar Energetic Particle Events and Their Magnetic Field Connection to the Earth Authors: Nitta, Nariaki V.; Reames, Donald V.; De Rosa, Marc L.; Liu, Yang; Yashiro, Seiji; Gopalswamy, Natchimuthuk Bibcode: 2006ApJ...650..438N Altcode: This paper investigates the solar origin of impulsive solar energetic particle (SEP) events, often referred to as 3He-rich flares, by attempting to locate the source regions of 117 events as observed at ~2-3 MeV amu-1. Given large uncertainties as to when ions at these energies were injected, we use type III radio bursts that occur within a 5 hr time window preceding the observed ion onset, and search in EUV and X-ray full-disk images for brightenings around the times of the type III bursts. In this way we find the solar sources in 69 events. High cadence EUV images often reveal a jet in the source region shortly after the type III burst. We also study magnetic field connections between the Earth and the solar sources of impulsive SEP events as identified above, combining the potential field source surface (PFSS) model for the coronal field and the Parker spiral for the interplanetary magnetic field. We find open field lines in and around ~80% of the source regions. But only in ~40% of the cases, can we find field lines that are both close to the source region at the photosphere and to the Parker spiral coordinates at the source surface, suggesting challenges in understanding the Sun-Earth magnetic field with observations available at present and in near future. Title: Computational Acoustics in Spherical Geometry: Steps toward Validating Helioseismology Authors: Hanasoge, S. M.; Larsen, R. M.; Duvall, T. L., Jr.; De Rosa, M. L.; Hurlburt, N. E.; Schou, J.; Roth, M.; Christensen-Dalsgaard, J.; Lele, S. K. Bibcode: 2006ApJ...648.1268H Altcode: Throughout the past decade, detailed helioseismic analyses of observations of solar surface oscillations have led to advances in our knowledge of the structure and dynamics of the solar interior. Such analyses involve the decomposition of time series of the observed surface oscillation pattern into its constituent wave modes, followed by inversion procedures that yield inferences of properties of the solar interior. While this inverse problem has been a major focus in recent years, the corresponding forward problem has received much less attention. We aim to rectify this situation by taking the first steps toward validating and determining the efficacy of the helioseismic measurement procedure. The goal of this effort is to design a means to perform differential studies of various effects such as flows and thermal perturbations on helioseismic observables such as resonant frequencies, travel-time shifts, etc. Here we describe our first efforts to simulate wave propagation within a spherical shell, which extends from 0.2 to about 1.0004 Rsolar (where Rsolar is the radius of the Sun) and which possesses a solar-like stratification. We consider a model containing no flows that will serve as a reference model for later studies. We discuss the computational procedure, some difficulties encountered in a simulation of this kind, and the means to overcome them. We also present techniques used to validate the simulation. Title: Non-linear Force-free Modeling: Applications To Solar Data Authors: De Rosa, Marc L.; Schrijver, C. J.; Metcalf, T. R.; NLFFF Team Bibcode: 2006SPD....37.1805D Altcode: 2006BAAS...38..247D Understanding the conditions under which solar magnetic fields can destabilizeto cause flares and other eruptive events requires a quantitativeunderstanding of the coronal magnetic field and of the currents that itcarries. Because no direct measurements of magnetic fields and current withincoronal volumes exist, the coronal field is typically modeled usinginformation contained in photospheric vector magnetograms, to be compared toH-alpha images of the chromosphere and EUV and X-ray imagery of the corona.We report on recent results of a team effort to further understand theintricacies of non-linear force-free extrapolations of the coronal magneticfield, presenting results from several solar and solar-like test cases. Wealso consider the use of such coronal field modeling in the upcoming Solar-Band SDO missions. Title: The Consequences Of Active-region Inflows On The Large-scale Dispersal Of Magnetic Field Across The Solar Surface. Authors: Schrijver, Carolus J.; De Rosa, M. L.; Hurlburt, N. E. Bibcode: 2006SPD....37.0716S Altcode: 2006BAAS...38..230S Helioseismic analysis of near-surface modes recently revealed horizontal flows near the solar surface towards regions with enhanced magnetic activity. The magnitude of these flows appears to increase with the magnetic flux contained within them. Such flows help to confine magnetic flux to the activity belt and perhaps even to theactive regions within which the field emerges, and will likely slow the random-walk dispersal of the field. We report on experiments witha surface flux dispersal model to study the consequences of such inflows towards strong-flux regions. We constrain the flow magnitudeby comparing results of a flux assimilation model to solar observations over six-month intervals throughout the last solar cycle. The best-fit model is then used to quantify the effects of these flows on the Sun's global dipole and quadrupole fields on time scales of multiple centuries. Title: The PFSS Model in the Context of Impulsive SEP Events Authors: Nitta, Nariaki; De Rosa, M. Bibcode: 2006SPD....37.2406N Altcode: 2006BAAS...38..251N We have located the solar sources of 67 impulsive solar energetic particle (SEP) events, using type III bursts to narrow down the times of particle injection in the solar corona. This information serves as a direct means to test the model of the Sun-Earth magnetic field connection because the particles simply trace the field lines. We consider the standard technique to model the Sun-Earth magnetic field, known as the potential field source surface (PFSS) model for the coronal part and the Parker spiral for the interplanetary part. In each of selected SEP events, we calculate the distance of the footpoint of the well-connected field line from the observed source location. It is found that the technique does not work as well as when it is used to predict the solar wind speed and the polarity of the interplanetary magnetic field. We suggest what we need to do to better understand the Sun-Earth magnetic field connection, or, more broadly speaking, the interplanetary magnetic field, which is an important element in NASA's Exploration Initiative. Title: Nonlinear Force-Free Modeling of Coronal Magnetic Fields Part I: A Quantitative Comparison of Methods Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Metcalf, Thomas R.; Liu, Yang; McTiernan, Jim; Régnier, Stéphane; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas Bibcode: 2006SoPh..235..161S Altcode: We compare six algorithms for the computation of nonlinear force-free (NLFF) magnetic fields (including optimization, magnetofrictional, Grad-Rubin based, and Green's function-based methods) by evaluating their performance in blind tests on analytical force-free-field models for which boundary conditions are specified either for the entire surface area of a cubic volume or for an extended lower boundary only. Figures of merit are used to compare the input vector field to the resulting model fields. Based on these merit functions, we argue that all algorithms yield NLFF fields that agree best with the input field in the lower central region of the volume, where the field and electrical currents are strongest and the effects of boundary conditions weakest. The NLFF vector fields in the outer domains of the volume depend sensitively on the details of the specified boundary conditions; best agreement is found if the field outside of the model volume is incorporated as part of the model boundary, either as potential field boundaries on the side and top surfaces, or as a potential field in a skirt around the main volume of interest. For input field (B) and modeled field (b), the best method included in our study yields an average relative vector error En = « |B−b|»/« |B|» of only 0.02 when all sides are specified and 0.14 for the case where only the lower boundary is specified, while the total energy in the magnetic field is approximated to within 2%. The models converge towards the central, strong input field at speeds that differ by a factor of one million per iteration step. The fastest-converging, best-performing model for these analytical test cases is the Wheatland, Sturrock, and Roumeliotis (2000) optimization algorithm as implemented by Wiegelmann (2004). Title: Experimental investigation of dynamic photo-thermal effect Authors: De Rosa, M.; Marin, F.; Marino, F.; Arcizet, O.; Heidmann, A.; Pinard, M. Bibcode: 2006CQGra..23S.259D Altcode: In an optical interferometer, a part of the laser power is absorbed by the mirrors and gives rise to surface displacements through thermal expansion. The position measurement sensitivity is, therefore, limited by the shot noise of the absorbed radiation. This phenomenon is called the photo-thermal effect and its typical frequency dependence and size can span over several orders of magnitude, depending on the mirror material and temperature, hence it is crucial to have an accurate model extending over such a large range. We present an extensive experimental investigation of dynamic photo-thermal effects, covering more than seven decades in frequency and including finite mirror size effects (low frequency) and coating effects (high frequency) and showing the dependence on the beam waist. A specific extension of the basic model is being developed that can well explain the results. Title: Canard orbits in Fabry-Perot cavities induced by radiation pressure and photothermal effects Authors: Marino, F.; de Rosa, M.; Marin, F. Bibcode: 2006PhRvE..73b6217M Altcode: A theoretical study of a high-finesse Fabry-Perot cavity considering radiation pressure and photothermal displacement is reported. We show that the competition between these two effects induces a different kind of dynamic behavior in such a system, consisting of canard orbits and excitability. The transition between the excitable regime and the canard oscillations, occurring through a supercritical Hopf bifurcation, appears in an order compatible with the van der Pol FitzHugh-Nagumo equations. Besides its interest as a study of general nonlinear dynamics, the characterization of the effects described is critical for high sensitivity interferometric displacement measurements as those employed for gravitational waves detection. Title: Small-Scale Surface Flows and their Implications for Solar Activity Authors: De Rosa, Marc L. Bibcode: 2006IAUS..233...25D Altcode: The broad range of dynamics exhibited by plasma motions within the solar interior affects many aspects of the generation and transport of magnetic fields during the solar magnetic activity cycle. On the photosphere, such dynamics include the differential rotation, meridional flows, and a hierarchy of convection cells, and these fluid motions are observed to readily advect any small-scale magnetic fields embedded within them. While the effects of large-scale flows on the global activity cycle are well known, it is becoming increasingly apparent that small-scale dynamics can also affect global magnetic activity throughout the solar cycle. Such effects include variations in the strength of the magnetic dipole moment with time, and the timing of the reversals of the polar-cap flux. In this article, several aspects of this coupling between small and large scales will be illustrated, and the implications of such coupling on the solar activity cycle will be discussed. Title: The status of the VIRGO experiment Authors: Acernese, F.; Amico, P.; Arnaud, N.; Babusci, D.; Ballardin, G.; Barille, R.; Barone, F.; Barsuglia, M.; Beauville, F.; Bellachia, F.; Bizouard, M. A.; Boccara, C.; Boget, D.; Bondu, F.; Bourgoin, C.; Bozzi, A.; Bracci, L.; Braccini, S.; Bradaschia, C.; Brillet, A.; Brisson, V.; Brocco, L.; Buskulic, D.; Cachenaut, J.; Calamai, G.; Calloni, E.; Campagna, E.; Casciano, C.; Cattuto, C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cella, G.; Chassande-Mottin, E.; Chollet, F.; Cleva, F.; Cokelaer, T.; Conforto, G.; Cortese, S.; Coulon, J. P.; Cuoco, E.; Dattilo, V.; Davier, P. Y.; de Rosa, M.; de Rosa, R.; di Fiore, L.; di Virgilio, A.; Dujardin, B.; Dominici, P.; Eleuteri, A.; Enard, D.; Evangelista, G.; Fabbroni, L.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Forest, D.; Fournier, J. D.; Fournier, L.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Ganau, P.; Gennai, A.; Gennaro, G.; Giacobone, L.; Giazotto, A.; Giordano, G.; Girard, C.; Gougoulat, G.; Guigi, G.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.; Holloway, L.; Honglie, F.; Iannarelli, M.; Journet, L.; Krecklbergh, S.; Lagrange, B.; La Penna, P.; Leliboux, M.; Leiunard, B.; Lomtadze, T.; Loriette, V.; Losurda, G.; Loupias, M.; Mackowski, J. M.; Majorana, E.; Man, C. N.; Marchesoni, F.; Marion, F.; Martelli, F.; Masserot, A.; Massonnet, L.; Mataguez, S.; Menzinger, F.; Mazzoni, M.; Michel, C.; Milano, L.; Montorio, J. L.; Moreau, F.; Moreau, J.; Morgado, M.; Mornet, F.; Mours, B.; Mugnier, P.; Nenci, F.; Pacheco, J.; Pai, A.; Palomba, C.; Paoletti, F.; Paoli, A.; Paoli, L.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Perciballi, M.; Peruzzi, S.; Perniola, B.; Pinard, L.; Poggiani, R.; Pololizio, P.; Porter, E.; Puccinelli, S.; Punturo, M.; Puppo, P.; Qipiani, K.; Ramonet, J.; Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.; Richard, F.; Roger, J. P.; Ruggi, P.; Russo, G.; Solimeno, S.; Stanga, R.; Taddei, R.; Teuler, J. M.; Tournfier, E.; Travasso, F.; Trinquet, H.; Turri, E.; Varvella, M.; Verkind, D.; Vetran, F.; Veziant, O.; Viceré, A.; Vilalte, S.; Vinet, J. Y.; Vocca, H.; Yvert, M.; Zhang, Z. Bibcode: 2006rdgp.conf..427A Altcode: No abstract at ADS Title: Influence of Small-scale Dynamics on Large-scale Solar Activity Authors: De Rosa, M. L. Bibcode: 2005ASPC..346..337D Altcode: The range of dynamical scales of motion within the solar convection zone is estimated to span at least six orders of magnitude in both space and time. Despite such breadth of scales, fluid motions occurring on the smallest spatial and temporal scales are expected to play an important role in the establishment and maintenance of the large-scale differential rotation and meridional flows within the turbulent convection zone. In turn, flows on all scales affect the transport of magnetic fields within the solar interior, causing field to be continually regenerated and redistributed. The surface manifestation of these magnetic fields exhibits a surprising degree of regularity, despite such fields being embedded in an extremely turbulent medium. The largest magnetic fields observed at the surface follow episodic patterns of emergence and evolution that collectively form each activity cycle, but there is also evidence that smaller-scale magnetic fields also possess an imprint of such cyclic behavior. This article focuses on two specific aspects of the coupling between small and large scales on the sun. First, the maintenance of the interior differential rotation by small-scale Reynolds stresses is addressed, followed by an investigation into the effects of small-scale surface magnetism on the strength of the surface dipole and the timing of its reversals. Title: Erratum: Upper Limits on Gravitational-Wave Emission in Association with the 27 Dec 2004 Giant Flare of SGR1806-20 [Phys. Rev. Lett. 95, 081103 (2005)] Authors: Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; Conti, L.; de Rosa, M.; Falferi, P.; Fortini, P.; Inguscio, M.; Liguori, N.; Marin, F.; Mezzena, R.; Mion, A.; Ortolan, A.; Prodi, G. A.; Poggi, S.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato, G.; Vinante, A.; Vitale, S.; Zendri, J. P. Bibcode: 2005PhRvL..95m9903B Altcode: No abstract at ADS Title: Upper Limits on Gravitational-Wave Emission in Association with the 27 Dec 2004 Giant Flare of SGR1806-20 Authors: Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; Conti, L.; de Rosa, M.; Falferi, P.; Fortini, P.; Inguscio, M.; Liguori, N.; Marin, F.; Mezzena, R.; Mion, A.; Ortolan, A.; Prodi, G. A.; Poggi, S.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato, G.; Vinante, A.; Vitale, S.; Zendri, J. P. Bibcode: 2005PhRvL..95h1103B Altcode: 2005astro.ph..6142B At the time when the giant flare of SGR1806-20 occurred, the AURIGA “bar” gravitational-wave (GW) detector was on the air with a noise performance close to stationary Gaussian. This allows us to set relevant upper limits, at a number of frequencies in the vicinities of 900 Hz, on the amplitude of the damped GW wave trains, which, according to current models, could have been emitted, due to the excitation of normal modes of the star associated with the peak in x-ray luminosity. Title: The Nonpotentiality of Active-Region Coronae and the Dynamics of the Photospheric Magnetic Field Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M.; Metcalf, Thomas R. Bibcode: 2005ApJ...628..501S Altcode: The magnetic field in the solar photosphere frequently carries strong electric currents, even though the global coronal configuration often resembles a potential field ringed by the heliospheric current sheet. To understand this, we compare TRACE EUV images of active-region coronae and potential-field source-surface extrapolations based on SOHO MDI magnetograms for 95 active regions. We conclude that significant nonpotentiality of the overall active-region coronal field occurs (1) when new flux has emerged within or very near a region within the last ~30 hr, resulting in complex polarity separation lines, or (2) when rapidly evolving, opposite-polarity concentrations are in contact at 4" resolution. If these criteria are met by more than 15% of the region's flux, they correctly identify the (non) potentiality of active-region coronae in 88% of the cases. Flares are found to occur 2.4 times more frequently in active regions with nonpotential coronae than in near-potential regions, while their average X-ray peak flare brightness is 3.3 times higher. We suggest that the currents associated with coronal nonpotentiality have a characteristic growth and decay timescale of ~10-30 hr. We find that shear flows drive enhanced flaring or coronal nonpotentiality only if associated with complex and dynamic flux emergence within the above timescale. We discuss the implications of this finding for the modeling of the coronal-heliospheric coupling. Title: Non-linear force-free field modeling: model techniques, boundary conditions, hares, and hounds Authors: Schrijver, C. J.; De Rosa, M. L.; Metcalf, T. Bibcode: 2005AGUSMSH31A..05S Altcode: Understanding the conditions under which solar magnetic fields can destabilize to erupt in flares and coronal mass ejections requires a quantitative understanding of the coronal magnetic field and of the currents that it carries. The increased availability of vector magnetograms, together with EUV and X-ray coronal images, should provide adequate constraints to model the coronal field, and thus to visualize its 3D geometry and to measure the available free energy and helicity. Non-linear force-free fields (NLFFF) are likely a useful model to use when extrapolating the solar surface field upward into the coronal volume. It may even be possible to use the observed trajectories of coronal loops, evident in EUV images of the corona, as a further constraint. We present initial results of a team effort to understand the intricacies of NLFFF modeling: we discuss and evaluate comparisons of NLFFF models computed with different models and applications of boundary conditions, and look ahead to full coronal field modeling for the upcoming Solar-B and SDO missions. Title: Simulations Of Acoustic-Flow Interaction In Spherical Geometry: Steps Toward Validating Helioseismology Authors: Hanasoge, S. M.; Duvall, T. L.; De Rosa, M. L.; Hurlburt, N. E. Bibcode: 2005AGUSMSP11B..11H Altcode: We simulate acoustic wave interaction with flows in spherical geometry with the specific intent of using them as artificial data for validation of helioseismology. The numerical procedure is pseudo-spectral; we employ a spherical harmonic representation of the spherical surface, compact finite differences in the radial direction and a fourth order Runge-Kutta time stepping scheme. We also excite surface gravity modes, modeling all waves as linear perturbations to the background state so as to gain further insight into wave-flow interaction. Towards validation, we apply techniques of helioseismology to the artificial data to determine the efficacy of the helioseismic inversion procedure. In other words, we are attempting the forward problem. Title: Comparison of Heliospheric Magnetic Field Lines from PFSS Models with SEP Observations Authors: Nitta, N. V.; Liu, Y.; De Rosa, M. L. Bibcode: 2005AGUSMSH13A..12N Altcode: Impulsive Solar Energetic Particle (SEP) events are thought to come locally from solar flares, in contrast with large gradual SEP events that are attributed to extended shocks driven by fast CMEs. For several impulsive SEP events, we identified the possible solar sources, using the timings of type III bursts. The solar sources thus indentified tend to be minor brightenings, sometimes not even detectable by the GOES X-ray Spectrometer. We found whether the source active region is open to the heliosphere, using potential field source surface (PFSS) models. We also traced field lines from the spacecraft observing SEPs to the source surface assuming constant solar wind speed, and then mapped them to the photosphere using PFSS models. In a number of cases, these traced field lines go close to the flare site. In other cases, their foot-points are far from the flare, or the source active region shows no open field lines. We interpret these various results in terms of different magnetograms for PFSS modeling, and assumptions used in the models. Title: Numerical Simulations of Bipolar Magnetic Field Decay in Turbulent Convection Authors: De Rosa, M. L.; Hurlburt, N. E. Bibcode: 2005AGUSMSP11C..02D Altcode: We present numerical simulations of compressible magnetoconvection in spherical segments, seeking to examine the decay of active region magnetic fields on the sun. It is surprising that after their emergence, active regions are observed to persist in relative stasis for long periods of time (weeks to months) before suddenly disintegrating. We perform a series of calculations to investigate this process, in which we drive turbulent convection (Rayleigh numbers of order 107) within two- and three-dimensional spherical segments, and measure the decay rates of the embedded bipolar magnetic fields. Title: Interferometric readout for acoustic gravitational wave detectors Authors: Conti, L.; de Rosa, M.; Marin, F.; Taffarello, L.; Cerdonio, M. Bibcode: 2005AIPC..751...75C Altcode: A review is given of the optical readout for acoustic gravitational wave detectors, ranging from the working principle, to the experimental data and to the future developments. A summary is also given of the scientific results obtained while developing the optical readout for a bar detector, of interest also for the broader interferometer community. Title: Coronal heating and the appearance of solar and stellar coronae Authors: Schrijver, C. J.; Sandman, A. W.; Aschwanden, M. J.; De Rosa, M. L. Bibcode: 2005ESASP.560...65S Altcode: 2005csss...13...65S No abstract at ADS Title: Evolution of Solar Supergranulation Authors: De Rosa, Marc L.; Toomre, Juri Bibcode: 2004ApJ...616.1242D Altcode: The structure and evolution of solar supergranulation is studied using horizontal velocity fields, deduced from applying local correlation tracking (LCT) techniques to full-disk, line-of-sight Doppler velocity data observed by the Michelson Doppler Imager on board the Solar and Heliospheric Observatory spacecraft. Two 45° square regions of photospheric plasma, one of the quiet Sun and one with increased magnetic activity, are tracked for as long as they remain visible on the disk of the Sun (about 6 days), enabling a determination of the complete life histories of over 3000 supergranules in each region. With this method, the horizontal outflows associated with the pattern of supergranulation are revealed with clarity, even for locations near disk center where little of the horizontal velocity field is projected into the line of sight. The LCT flow mappings are of sufficient temporal extent that they can be used to study the complex evolution of a broad spectrum of supergranules, revealing that merging and fragmentation events figure prominently in the life histories of more than half of the supergranules in each data set. Such dynamics lead to many short-lived supergranules (about 75% of the total population) having lifetimes of less than 24 hr, coexisting among numerous long-lived supergranules, many of which exist for several days. Average supergranular lifetimes lie in the 16-23 hr range, although about 7% of all are recognizable for time periods of 48 hr or more. The average supergranular cell diameter lies in the 12-20 Mm range, with smaller cells more prevalent in areas of greater magnetism. There exists a tendency for larger cells to preferentially have longer lifetimes when embedded in a region of increased magnetic flux. Title: The Coronal Heating Mechanism as Identified by Full-Sun Visualizations Authors: Schrijver, Carolus J.; Sandman, Anne W.; Aschwanden, Markus J.; De Rosa, Marc L. Bibcode: 2004ApJ...615..512S Altcode: We constrain the properties of the mechanism(s) responsible for the bulk of the heating of the corona of the Sun by simulating, for the first time, the appearance of the entire solar corona. Starting from full-sphere magnetic field maps for 2000 December 1 and 8, when the Sun was moderately active, we populate nearly 50,000 coronal field lines with quasi-static loop atmospheres. These atmospheres are based on heating flux densities FH that depend in different ways on the loop half-length L, the field strength B at the chromospheric base, the loop expansion with height, and the heating scale height. The best match to X-ray and EUV observations of the corona over active regions and their environs is found for FH~4×1014B1.0+/-0.3/L1.0+/-0.5 (in ergs cm-2 s-1 for B in Mx cm-2 and L in cm), while allowing for substantial loop expansion with increasing height, and for a heating scale height that is at least a sizeable fraction of the loop length. This scaling for coronal heating points to DC reconnection at tangential discontinuities as the most likely coronal heating mechanism, provided that the reconnection progresses proportional to the Alfvén velocity. The best-fit coronal filling factor equals unity, suggesting that most of the corona is heated most of the time. We find evidence that loops with half-lengths exceeding ~100,000 km are heated significantly more than suggested by the above scaling, possibly commensurate with the power deposited in the open field of coronal holes. Title: Supergranular and Larger-Scale Surface Flows Within Magnetic Environments Authors: De Rosa, M. L. Bibcode: 2004ESASP.559..404D Altcode: 2004soho...14..404D No abstract at ADS Title: Tomographic 3D-Modeling of the Solar Corona with FASR Authors: Aschwanden, Markus J.; Alexander, David; de Rosa, Marc L. Bibcode: 2004ASSL..314..243A Altcode: 2003astro.ph..9501A The Frequency-Agile Solar Radiotelescope (FASR) literally opens up a new dimension, in addition to the 3D Euclidian geometry—the frequency dimension. The 3D geometry is degenerated to 2D in all images from astronomical telescopes, but the additional frequency dimension allows us to retrieve the missing third dimension by means of physical modeling. We call this type of 3D reconstruction Frequency Tomography. In this study we simulate a realistic 3D model of an active region, composed of 500 coronal loops with the 3D geometry [x(s), y(s), z(s)] constrained by magnetic field extrapolations and the physical parameters of the density ne(s) and temperature Te(s) given by hydrostatic solutions. We simulate a series of 20 radio images in a frequency range of ν=0.1-10 GHz, anticipating the capabilities of FASR, and investigate what physical information can be retrieved from such a dataset. We discuss also forward-modeling of the chromospheric and Quiet Sun density and temperature structure, another primary goal of future FASR science. Title: Numerical Models of solar Magnetoconvection: Toward a Coupling to the Corona Authors: De Rosa, M. L.; Hurlburt, N. E. Bibcode: 2004AAS...204.3908D Altcode: 2004BAAS...36..715D We present numerical simulations of a stratified magnetized fluid, confined to a spherical shell, that approximates the transition from a high- to low-beta regime, similar to the conditions present at the solar photosphere. In these simulations, a model corona atmosphere is situated above a convectively unstable, high-beta fluid layer. As a result, the dynamics associated with evolving magnetic features in the solar atmosphere can be modeled in a manner that is self-consistent with the convective motions that provide the driving. Our simulations exhibit arcade-like structures that undergo reconnection as a result of the supergranular-scale fluid motions in the convective layer below, and discuss possible observational consequences. Title: Solar Coronal Heating Inferred from Full-disk Models of Coronal Emission Authors: Schrijver, C. J.; Sandman, A. W.; De Rosa, M. L.; Aschwanden, M. J. Bibcode: 2004AAS...204.9501S Altcode: 2004BAAS...36Q.826S The appearance of the corona as viewed by different instruments, as well as its global spectral irradiance, sensitively depends on how coronal heating scales with the properties of the coronal magnetic field. We explore a variety of scaling dependences by simulating the appearance of the full-disk solar corona as viewed by SOHO/EIT and by YOHKOH/SXT, based on observed photospheric magnetic fields combined with a potential-field source-surface model. This leads us to conclude that the best match to X-ray and EUV observations of the corona over active regions and their environments is found for a heating flux density going into the corona that scales linearly with the field strength at the coronal base and roughly inversely with loop length. This scaling points to DC reconnection at tangential discontinuities as the most likely coronal heating mechanism, provided that the reconnection progresses at a rate proportional to the Alfven velocity. We also find that the best-fit coronal filling factor equals unity, suggesting that most of the corona is heated most of the time. We find evidence that loops with half lengths exceeding approximately 100,000 km are heated significantly more than suggested by the above scaling, possibly commensurate with the power deposited in the open field of coronal holes. Title: Molecular and Compound-Specific Isotopic Study of Monocarboxylic Acids in Murchison and Antarctic Meteorites Authors: Huang, Y.; Wang, Y.; de'Rosa, M.; Fuller, M.; Pizzarello, S. Bibcode: 2004LPI....35.1888H Altcode: We studied molecular distributions and C and H isotopic ratios of individual monocarboxylic acids in Murchison and EET96029,20 using a new and improved sample indtroduction method (SPME), and reveal new monoacids and isotopic characteristics. Title: An optical readout scheme for advanced acoustic GW detectors Authors: Marin, F.; Conti, L.; De Rosa, M. Bibcode: 2004CQGra..21S1237M Altcode: 2004CQGra..21.1237M We have recently proposed a large reading area, optical readout scheme for advanced acoustic gravitational wave (GW) detectors. In this work we focus the analysis on a dual-cylinder detector. A specific configuration is designed and the expected performance is calculated. Title: Solar-like convective and coronal layers in a single numerical model Authors: Hurlburt, N.; De Rosa, M. Bibcode: 2004cosp...35.3551H Altcode: 2004cosp.meet.3551H We investigate the coupling between turbulent magnetoconvection and an atmospheric layer on the sun using numerical simulations of compressible fluids. The model consists of a stratified MHD fluid spanning multiple scale heights, encompassing the transition of the plasma beta from high to low values. Although a heat flux is imposed at the lower boundary, only the lower portion of the domain where the beta is high is convectively unstable. The upper portions are stabilized by a parameterized heating function and the presence of a strong magnetic field and, similar to the solar chromosphere and corona. As a result, the dynamics associated with evolving magnetic features in the solar atmosphere can be modeled in a manner that is self-consistent with the convective motions that provide the driving. We present simulations of arcade-like reconnection in the presence of supergranular-scale flows and discuss possible observational consequences. Title: Modeling solar magnetoconvection and coronal structures Authors: Hurlburt, Neal E.; De Rosa, Marc L. Bibcode: 2004IAUS..223..253H Altcode: 2005IAUS..223..253H We present results of an investigation into the coupling between solar-like magnetoconvection and coronal structures using self-consistent numerical simulations of compressible fluids. The model consists of a stratified MHD fluid spanning multiple scale heights, encompassing the transition of the plasma beta from high to low values. The lower portion of the domain, where the beta is high, is convectively unstable while the upper portion is stabilized by the presence of a strong magnetic field and energy losses. As a result, the dynamics associated with evolving magnetic features in the solar atmosphere can be modelled in a manner that is self-consistent with the convective motions that provide the driving. We present simulations of arcade-like reconnection in the presence of supergranular-scale flows. Title: TRACE and SOHO/MDI Observations of 3 Rotating Sunspots in AR9002 and AR9004, Along With Modeled Coronal Magnetic Fields Authors: Nightingale, R. W.; Schrijver, C. J.; De Rosa, M. L. Bibcode: 2003AGUFMSH42B0511N Altcode: The TRACE data set provides a view of the solar atmosphere from the photosphere in white light, through the transition region in ultraviolet wavelengths, and into the corona in extreme ultraviolet wavelengths (EUV). From May 16-23, 2000 TRACE and MDI/SOHO observed at least 3 rotating sunspots in AR9002 and AR9004 at several wavelengths. Over this time period several small flares, along with a CME on May 23, occurred in these regions. In addition we have potential-field renderings of the coronal magnetic fields for the TRACE pointings, extrapolated based on the Virtual Starlab forecaster data, which in turn has been generated from the MDI/SOHO observations. An analysis of the rotating sunspots, together with images and movies, will be provided for these active regions, accompanied by images of the extrapolated coronal magnetic fields for comparison with images of the TRACE 1-1.5 MK EUV loops. This work was supported by NASA, in part under the TRACE contract NAS5-38099 and in part under the MDI/SOHO contract NAG5-13261. Title: Coronal heating and the appearance of the solar corona Authors: Schrijver, C. J.; Sandman, A.; De Rosa, M. L.; Aschwanden, M. J. Bibcode: 2003AGUFMSH32A1104S Altcode: The details of the dependence of coronal heating on the conditions within the corona determine the appearance of the corona as viewed by different instruments. For example, strong fields at the base of short loops cause relatively hot, X-ray bright loops, whereas the much weaker fields over the quiet Sun result in cooler, EUV bright loops. Any dependence of the volume heating rates on local conditions (such as height or field strength) has a signature in the thermal profiles along the loops, translating into an appearance that depends on the instrumental pass band. In this preliminary study, we explore how such dependences of coronal heating on coronal conditions affect the appearance of the solar corona, and investigate the consequences for the global EUV and X-ray spectral irradiance. These results will eventually be used to compute the solar spectral irradiance in the EUV and X-rays for quiescent conditions throughout the solar cycle. Title: Data analysis methods for non-Gaussian, nonstationary and nonlinear features and their application to VIRGO Authors: Virgo Collaboration; Acernese, F.; Amico, P.; Arnaud, N.; Babusci, D.; Ballardin, G.; Barillé, R.; Barone, F.; Barsuglia, M.; Beauville, F.; Bellachia, F.; Bizouard, M. A.; Boccara, C.; Boget, D.; Bondu, F.; Bourgoin, C.; Bozzi, A.; Braccini, S.; Bradaschia, C.; Brillet, A.; Brisson, V.; Brocco, L.; Buskulic, D.; Cachenaut, J.; Calamai, G.; Calloni, E.; Campagna, E.; Casciano, C.; Cattuto, C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cella, G.; Chassande-Mottin, E.; Chollet, F.; Cleva, F.; Cokelaer, T.; Conforto, G.; Cortese, S.; Coulon, J. P.; Cuoco, E.; Dattilo, V.; Y Davíd, P.; Davier, M.; De Rosa, M.; De Rosa, R.; Di Fiore, L.; Di Virgilio, A.; Dujardin, B.; Dominici, P.; Eleuteri, A.; Enard, D.; Evangelista, G.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Forest, D.; Fournier, J. D.; Fournier, L.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Ganau, P.; Gennai, A.; Gennaro, G.; Giacobone, L.; Giazotto, A.; Giordano, G.; Girard, C.; Gougoulat, G.; Guidi, G. M.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.; Holloway, L.; Honglie, F.; Iannarelli, M.; Journet, L.; Krecklbergh, S.; Lagrange, B.; La Penna, P.; Leliboux, M.; Lieunard, B.; Lomtadze, T.; Loriette, V.; Losurdo, G.; Loupias, M.; Mackowski, J. M.; Majorana, E.; Man, C. N.; Marchesoni, F.; Marion, F.; Martelli, F.; Masserot, A.; Massonnet, L.; Mataguez, S.; Menzinger, F.; Mazzoni, M.; Michel, C.; Milano, L.; Montorio, J. L.; Moreau, F.; Moreau, J.; Morgado, N.; Mornet, F.; Mours, B.; Mugnier, P.; Nenci, F.; Pacheco, J.; Pai, A.; Palomba, C.; Paoletti, F.; Paoli, A.; Paoli, L.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Perciballi, M.; Peruzzi, S.; Perniola, B.; Pinard, L.; Poggiani, R.; Popolizio, P.; Porter, E.; Puccinelli, S.; Punturo, M.; Puppo, P.; Qipiani, K.; Ramonet, J.; Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.; Richard, F.; Roger, J. P.; Ruggi, P.; Russo, G.; Solimeno, S.; Stanga, R.; Taddei, R.; Teuler, J. M.; Tournefier, E.; Travasso, F.; Trinquet, H.; Turri, E.; Varvella, M.; Verkindt, D.; Vetrano, F.; Veziant, O.; Viceré, A.; Vilalte, S.; Y Vinet, J.; Vocca, H.; Yvert, M.; Zhang, Z. Bibcode: 2003CQGra..20S.915V Altcode: The commissioning of the VIRGO central interferometer occasioned the implementation and tests of various algorithms for the characterization of the non-Gaussianity, non-stationarity and non-linearity of the dark fringe data. This library of prototypes will serve as groundwork for the near commissioning of VIRGO (full scale). We make a summary of the activities on that subject including the description of the selected algorithms and some results obtained with the data of the engineering runs. Title: Status of VIRGO Authors: Virgo Collaboration; Acernese, F.; Amico, P.; Arnaud, N.; Babusci, D.; Ballardin, G.; Barillé, R.; Barone, F.; Barsuglia, M.; Beauville, F.; Bellachia, F.; Bizouard, M. A.; Boccara, C.; Boget, D.; Bondu, F.; Bourgoin, C.; Bozzi, A.; Braccini, S.; Bradaschia, C.; Brillet, A.; Brisson, V.; Brocco, L.; Buskulic, D.; Cachenaut, J.; Calamai, G.; Calloni, E.; Campagna, E.; Casciano, C.; Cattuto, C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cella, G.; Chassande-Mottin, E.; Chollet, F.; Cleva, F.; Cokelaer, T.; Conforto, G.; Cortese, S.; Coulon, J. P.; Cuoco, E.; Dattilo, V.; Y Davíd, P.; Davier, M.; De Rosa, M.; De Rosa, R.; Di Fiore, L.; Di Virgilio, A.; Dujardin, B.; Dominici, P.; Eleuteri, A.; Enard, D.; Evangelista, G.; Ferrante, I.; Fidecaro, F.; Fiori, I.; Flaminio, R.; Forest, D.; Fournier, J. D.; Fournier, L.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Ganau, P.; Gennai, A.; Gennaro, G.; Giacobone, L.; Giazotto, A.; Giordano, G.; Girard, C.; Gougoulat, G.; Guidi, G. M.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.; Holloway, L.; Honglie, F.; Iannarelli, M.; Journet, L.; Krecklbergh, S.; Lagrange, B.; La Penna, P.; Leliboux, M.; Lieunard, B.; Lomtadze, T.; Loriette, V.; Losurdo, G.; Loupias, M.; Mackowski, J. M.; Majorana, E.; Man, C. N.; Marchesoni, F.; Marion, F.; Martelli, F.; Masserot, A.; Massonnet, L.; Mataguez, S.; Menzinger, F.; Mazzoni, M.; Michel, C.; Milano, L.; Montorio, J. L.; Moreau, F.; Moreau, J.; Morgado, N.; Mornet, F.; Mours, B.; Mugnier, P.; Nenci, F.; Pacheco, J.; Pai, A.; Palomba, C.; Paoletti, F.; Paoli, A.; Paoli, L.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Perciballi, M.; Peruzzi, S.; Perniola, B.; Pinard, L.; Poggiani, R.; Popolizio, P.; Porter, E.; Puccinelli, S.; Punturo, M.; Puppo, P.; Qipiani, K.; Ramonet, J.; Rapagnani, P.; Reita, V.; Remillieux, A.; Ricci, F.; Richard, F.; Roger, J. P.; Ruggi, P.; Russo, G.; Solimeno, S.; Stanga, R.; Taddei, R.; Teuler, J. M.; Tournefier, E.; Travasso, F.; Trinquet, H.; Turri, E.; Varvella, M.; Verkindt, D.; Vetrano, F.; Veziant, O.; Viceré, A.; Vilalte, S.; Y Vinet, J.; Vocca, H.; Yvert, M.; Zhang, Z. Bibcode: 2003CQGra..20S.609V Altcode: We report on the status of the VIRGO detector as of the beginning of 2003. In particular, we summarize the results obtained during the commissioning of the central portion of the detector, consisting of a power-recycled Michelson interferometer, and we outline the steps which will lead during 2003 and 2004 to the commissioning and operation of the full scale, 3 km long VIRGO detector. Title: Asterospheric Magnetic Fields and Winds of Cool Stars Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M. Bibcode: 2003ApJ...590..493S Altcode: This study addresses the winds and magnetic fields in the inner asterospheres of Sun-like magnetically active stars by combining empirical relationships between rotation rate and mass loss, angular-momentum loss, and radiative losses with models of the magnetic fields at the surfaces of cool stars and in their inner asterospheres based on the solar example. Our models, for mean magnetic flux densities up to 10 times solar, suggest that the asterospheric fields of such stars are dominated by the large-scale dipole component of the surface field, as is the case for the Sun. Hence, most of the time a single current sheet is expected to separate domains of opposite magnetic polarity; the current sheets of more active stars generally have smaller latitudinal ripples. Magnetic braking requires that the total unsigned asterospheric magnetic flux increase linearly with the stellar angular velocity, which is a very much weaker increase than seen for the flux at the stellar surface. We show that this can be achieved by an increase in the radial distance at which the coronal field is forced open as surface activity increases. Combined with measured mass-loss rates and the assumption that the wind velocity is largely independent of activity, this requires the wind's Alfvén radius to be nearly constant, decreasing with surface activity with a power of only -0.16+/-0.13. We point out that the surface flux density of energy needed to drive a cool-star wind scales linearly with the unsigned surface magnetic flux density, as does that needed to heat the corona. Title: The nature of impulsive solar energetic particle events Authors: Nitta, N. V.; Hudson, H. S.; De Rosa, M. L. Bibcode: 2003SPD....34.1606N Altcode: 2003BAAS...35..833N Impulsive solar energetic particle (SEP) events, as opposed to gradual SEP events, are usually thought to originate from flares in the well-connected regions. In order to test this idea, we compute the solar locations of the field lines that cross the spacecraft encountering particles from SEP events, and compare them with the flare locations. We combine two frequently used techniques, i.e., the ballistic approximation for the interplanetary magnetic field and the potential-field source-surface model for the coronal field. Such comparisons are made for selected impulsive SEP events during 1995-2001. We check the validity of the techniques using Yohkoh SXT and SOHO EIT images, which often show coronal holes on the disk. Furthermore, we study the properties of the flares that are identified with impulsive SEP events, and compare them with those of other flares in the well-connected areas but without impulsive SEP events. This will give us a clue as to the importance of the flare processes relative to the magnetic field connectivity on the detection of impulsive SEP events. Title: MHD Simulations Spanning the Convection Zone, Chromosphere, and Corona Authors: De Rosa, M. L.; Hurlburt, N. E. Bibcode: 2003SPD....34.0407D Altcode: 2003BAAS...35..811D The dynamics associated with evolving magnetic structures in the solar atmosphere are ultimately driven by vigorous convective motions below the photosphere. There, nonlinear interactions between the flows and fields lead to the transport of energy up into the atmosphere, which is later converted to heat in the chromosphere and corona and radiated into space. To investigate such dynamics, we have constructed a self-consistent model of the sun encompassing the upper layers of the convection zone, chromosphere, transition region, and lower corona. The fully compressible magnetized fluid comprising the convective layer is dynamically coupled to the atmosphere through the magnetic field. These models allow us to investigate the dynamics associated with waves, magnetic fields, and fluid motions within the solar atmosphere. Title: Room temperature gravitational wave bar detector with optomechanical readout Authors: Conti, L.; De Rosa, M.; Marin, F.; Taffarello, L.; Cerdonio, M. Bibcode: 2003JAP....93.3589C Altcode: 2002gr.qc.....5115C We present the full implementation of a room-temperature gravitational wave bar detector equipped with an optomechanical readout. The bar mechanical vibrations are read by a Fabry-Pérot interferometer whose length changes are compared with a stable reference optical cavity by means of a resonant laser. The detector performance is completely characterized in terms of spectral sensitivity and statistical properties of the fluctuations in the system output signal. This kind of readout technique allows for wide-band detection sensitivity and we can accurately test the model of the coupled oscillators for thermal noise. Our results are very promising for cryogenic operation and represent an important step towards significant improvements in the performance of massive gravitational wave detectors. Title: Simulations of Near-Surface Solar Magnetoconvection Within Localized Spherical Segments Authors: De Rosa, M. L.; Hurlburt, N. E. Bibcode: 2003ASPC..293..229D Altcode: 2003tdse.conf..229D Turbulent fluid motions near the surface of the sun, such as those associated with the observed pattern of supergranulation, are thought to play a role in the decay of the magnetic field within plage and active regions on the sun. To investigate such dynamics, we have constructed two related numerical simulations of fully compressible magnetoconvecting fluids, each contained within a curved, spherical segment that approximates the conditions within the upper part of the solar convection zone. The spherical segment domains span 30 degrees in latitude and 60 degrees in longitude, and have a radial extent of 4% of the solar radius. We find that bipolar field configurations decay on diffusive (Ohmic) time scales, rather than on turbulent decay time scales, despite the network of convection cells around and within the magnetized regions. Title: Photospheric and heliospheric magnetic fields Authors: Schrijver, Carolus J.; De Rosa, Marc L. Bibcode: 2003SoPh..212..165S Altcode: The magnetic field in the heliosphere evolves in response to the photospheric field at its base. This evolution, together with the rotation of the Sun, drives space weather through the continually changing conditions of the solar wind and the magnetic field embedded within it. We combine observations and simulations to investigate the sources of the heliospheric field from 1996 to 2001. Our algorithms assimilate SOHO/MDI magnetograms into a flux-dispersal model, showing the evolving field on the full sphere with an unprecedented duration of 5.5 yr and temporal resolution of 6 hr. We demonstrate that acoustic far-side imaging can be successfully used to estimate the location and magnitude of large active regions well before they become visible on the solar disk. The results from our assimilation model, complemented with a potential-field source-surface model for the coronal and inner-heliospheric magnetic fields, match Yohkoh/SXT and KPNO/He 10830 Å coronal hole boundaries quite well. Even subject to the simplification of a uniform, steady solar wind from the source surface outward, our model matches the polarity of the interplanetary magnetic field (IMF) at Earth ∼3% of the time during the period 1997-2001 (independent of whether far-side acoustic data are incorporated into the simulation). We find that around cycle maximum, the IMF originates typically in a dozen disjoint regions. Whereas active regions are often ignored as a source for the IMF, the fraction of the IMF that connects to magnetic plage with absolute flux densities exceeding 50 Mx cm−2 increases from ≲10% at cycle minimum up to 30-50% at cycle maximum, with even direct connections between sunspots and the heliosphere. For the overall heliospheric field, these fractions are ≲1% to 20-30%, respectively. Two case studies based on high-resolution TRACE observations support the direct connection of the IMF to magnetic plage, and even to sunspots. Parallel to the data assimilation, we run a pure simulation in which active regions are injected based on random selection from parent distribution functions derived from solar data. The global properties inferred for the photospheric and heliospheric fields for these two models are in remarkable agreement, confirming earlier studies that no subtle flux-emergence patterns or field-dispersal properties are required of the solar dynamo beyond those that are included in the model in order to understand the large-scale solar and heliospheric fields. Title: Active regions as sources of the heliospheric field Authors: Schrijver, C. J.; De Rosa, M. L.; Title, A. M. Bibcode: 2002AGUFMSH52A0436S Altcode: The magnetic field in the heliosphere originates from a variety of sources on the surface of the Sun, including mature, decaying, and decayed active regions, as well as sunspots. The emergence of new active regions together with the dispersal of flux from older active regions causes the coronal magnetic field topology to continually evolve, allowing previously closed-field regions to open into the heliosphere and previously open-field regions to close. Such evolution of the coronal field, together with the rotation of the Sun, drive space weather through the continually changing conditions of the solar wind and the magnetic field embedded within it. We combine observations and numerical simulations by assimilating SOHO/MDI magnetograms into a surface flux transport model, in order to investigate the origins of the heliospheric field on the solar surface through the rising phase of the current activity cycle. We find that around cycle maximum, the interplanetary magnetic field (IMF) is typically rooted in a dozen disjoint regions on the solar surface. Whereas active regions are sometimes ignored as a source for the IMF, the fraction of the IMF that connects directly to magnetic plage is found to reach up to 30-50%\ at cycle maximum, with even direct connections between sunspots and the heliosphere. We further compare this data assimilation model with a pure simulation model, in which the properties of the emergent active regions were chosen at random from parent distribution functions measured for the sun. The two models show remarkable agreement in the temporal behavior of the sector structure of the IMF, in the magnitude and time-behavior of the heliospheric field, and even in such global properties as the tilt angle of the Sun's large scale dipole. We thus conclude that no additional flux-emergence patterns or field-dispersal properties are required of the solar dynamo beyond those that are included in the model in order to understand the large-scale solar and heliospheric fields. Title: Numerical Simulations of Solar Active Region Magnetoconvection Authors: De Rosa, M. L.; Hurlburt, N. E. Bibcode: 2002AGUFMSH52A0495D Altcode: Vigorous fluid motions associated with the observed patterns of supergranulation, mesogranulation, and granulation on the sun are likely to play a large role in the continual emergence, evolution, and redistribution of magnetic field within solar active regions. To investigate such non-linear dynamics, we have constructed numerical simulations of fully compressible magnetized fluids, each contained within curved, spherical segments nominally located near the top of the solar convection zone. Overturning motions having length scales comparable to that of solar supergranulation are driven by imposing a solar-like heat flux through the bottom of the domain. We present recent results of several idealized active region simulations within thin spherical segments, each spanning 60°x 30° in longitude and latitude and extending up to 0.04~Rsun in radius. We are able to investigate the analogs of both plage and active regions by varying the amount of magnetic flux that permeates the layer. Simplified field-line extrapolations into the volume above the spherical segments are then used to assess how the corona might respond to the structure and evolution of magnetic field emerging through the solar photosphere. This work was supported by NASA through grant NAG 5-3077 to Stanford University and by Lockheed Martin Independent Research and Development funds. Title: Solar Multiscale Convection and Rotation Gradients Studied in Shallow Spherical Shells Authors: De Rosa, Marc L.; Gilman, Peter A.; Toomre, Juri Bibcode: 2002ApJ...581.1356D Altcode: 2002astro.ph..9054D The differential rotation of the Sun, as deduced from helioseismology, exhibits a prominent radial shear layer near the top of the convection zone wherein negative radial gradients of angular velocity are evident in the low- and midlatitude regions spanning the outer 5% of the solar radius. Supergranulation and related scales of turbulent convection are likely to play a significant role in the maintenance of such radial gradients and may influence dynamics on a global scale in ways that are not yet understood. To investigate such dynamics, we have constructed a series of three-dimensional numerical simulations of turbulent compressible convection within spherical shells, dealing with shallow domains to make such modeling computationally tractable. In all but one case, the lower boundary is forced to rotate differentially in order to approximate the influence that the differential rotation established within the bulk of the convection zone might have upon a near-surface shearing layer. These simulations are the first models of solar convection in a spherical geometry that can explicitly resolve both the largest dynamical scales of the system (of order the solar radius) as well as smaller scale convective overturning motions comparable in size to solar supergranulation (20-40 Mm). We find that convection within these simulations spans a large range of horizontal scales, especially near the top of each domain, where convection on supergranular scales is apparent. The smaller cells are advected laterally by the larger scales of convection within the simulations, which take the form of a connected network of narrow downflow lanes that horizontally divide the domain into regions measuring approximately 100-200 Mm across. We also find that the radial angular velocity gradient in these models is typically negative, especially in the low- and midlatitude regions. Analyses of the angular momentum transport indicate that such gradients are maintained by Reynolds stresses associated with the convection, transporting angular momentum inward to balance the outward transport achieved by viscous diffusion and large-scale flows in the meridional plane, a mechanism first proposed by Foukal & Jokipii and tested by Gilman & Foukal. We suggest that similar mechanisms associated with smaller scale convection in the Sun may contribute to the maintenance of the observed radial shear layer located immediately below the solar photosphere. Title: Experimental Measurement of the Dynamic Photothermal Effect in Fabry-Perot Cavities for Gravitational Wave Detectors Authors: de Rosa, M.; Conti, L.; Cerdonio, M.; Pinard, M.; Marin, F. Bibcode: 2002PhRvL..89w7402D Altcode: 2002gr.qc.....1038D We report the experimental observation of the frequency dependence of the photothermal effect. The measurements are performed by modulating the laser power absorbed by the mirrors of two high-finesse Fabry-Perot cavities. The results are very well described by a recently proposed theoretical model [M. Cerdonio, L. Conti, A. Heidmann, and M. Pinard, <journal>Phys. Rev. D</journal> <volume>63</volume>, <pages>082003</pages> (<date>2001</date>)</citeinfo>], confirming the correctness of such calculations. Our observations and quantitative characterization of the dynamic photothermal effect demonstrate its critical importance for interferometric displacement measurements towards the quantum limit, as those necessary for gravitational wave detection. Title: Simulations of near-photospheric magnetoconvection within localized spherical segments Authors: De Rosa, M. L.; Hurlburt, N. E.; Alexander, D. Bibcode: 2002ESASP.505..385D Altcode: 2002IAUCo.188..385D; 2002solm.conf..385D Vigorous fluid motions associated with the observed patterns of supergranulation, mesogranulation, and granulation are likely to play a large role during the evolution of magnetic field within solar active regions. To investigate such dynamics, we have constructed numerical simulations of fully compressible, magnetized fluids, each contained within curved, spherical segments that approximate conditions near the top of the solar convection zone. We present recent results of one three-dimensional simulation of an idealized bipolar active region contained within a thin spherical segment. The segment nominally spans 30° in latitude and 60° in longitude, and has a radial extent of 4% of the solar radius. Upon initialization, the domain is threaded by a bipolar radial magnetic field, which subsequently cancels as the ensuing convection advects field horizontally across the segment. We find that the time scale at which the field decays is slower than the expected turbulent decay time scale, and is much closer to the diffusive (Ohmic) decay time scale, despite the network of convection cells surrounding the magnetized regions. We suggest that this convection serves to confine field of like polarity and thus suppresses the turbulent decay of magnetic field. Title: The long-term variations of the solar and heliospheric fields Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M. Bibcode: 2002ESASP.505..253S Altcode: 2002IAUCo.188..253S; 2002solm.conf..253S The heliospheric field is determined by the largest-scale patterns of magnetism at the solar surface, dominated by the lower-latitude active regions during cycle maximum, and by the circumpolar fields during cycle minimum. To study these patterns, we simulate the evolution of the magnetic field at the solar surface and in the heliosphere during the last 340 years. We conclude that, contrary to current thinking, the observed magnetic flux in the polar regions of the Sun cannot be understood as merely a long-term accumulation of active-region decay products from a dynamo that modulates only the rate at which flux emerges from cycle to cycle. We suggest that simulation and observation may be reconciled if the high-latitude solar field decays on a time scale comparable to that of the sunspot cycle. Title: What Is Missing from Our Understanding of Long-Term Solar and Heliospheric Activity? Authors: Schrijver, Carolus J.; De Rosa, Marc L.; Title, Alan M. Bibcode: 2002ApJ...577.1006S Altcode: The heliospheric magnetic field is associated with changes in space weather, cosmic-ray flux, and likely climate. This field is determined by the largest scale patterns of magnetism at the solar surface, dominated by the lower latitude active regions during cycle maximum and by the circumpolar fields during cycle minimum. Whereas the magnetic field in the activity belt is readily studied, the high-latitude field is much less accessible, and its study requires a combination of modeling and observation. Current models hold that the high-latitude magnetic field on the Sun is determined solely by the accumulation of field transported poleward from lower latitude active regions. We test this hypothesis by simulating the evolution of the magnetic field at the solar surface and in the heliosphere during the last 340 yr using a state-of-the-art model that incorporates all processes that are known to contribute significantly to the evolution of the large-scale patterns in the solar field. We find that if only the emergence frequency of magnetic bipoles is varied in accordance with observed sunspot records, the polar-cap field reservoir does not match measurements during past years. Based on comparisons of our simulations with observed polar fluxes over the last few decades and with the proxy for the heliospheric flux formed by 340 yr of 10Be ice-core data, we suggest that the high-latitude field may be subject to decay on a timescale of 5-10 yr. We discuss the consequences of this finding for our understanding of the Sun-Earth connection and explore inferences for the coupling of the Sun's internal magnetic field to the heliospheric field. Title: A neural network-based approach to noise identification of interferometric GW antennas: the case of the 40 m Caltech laser interferometer Authors: Acernese, F.; Barone, F.; de Rosa, M.; De Rosa, R.; Eleuteri, A.; Milano, L.; Tagliaferri, R. Bibcode: 2002CQGra..19.3293A Altcode: In this paper, a neural network-based approach is presented for the real time noise identification of a GW laser interferometric antenna. The 40 m Caltech laser interferometer output data provide a realistic test bed for noise identification algorithms because of the presence of many relevant effects: violin resonances in the suspensions, main power harmonics, ring-down noise from servo control systems, electronic noises, glitches and so on. These effects can be assumed to be present in all the first interferometric long baseline GW antennas such as VIRGO, LIGO, GEO and TAMA. For noise identification, we used the Caltech-40 m laser interferometer data. The results we obtained are pretty good notwithstanding the high initial computational cost. The algorithm we propose is general and robust, taking into account that it does not require a priori information on the data, nor a precise model, and it constitutes a powerful tool for time series data analysis. Title: Numerical Simulations of Supergranular Magnetoconvection Authors: De Rosa, M. L.; Hurlburt, N. E.; Alexander, D.; Rucklidge, A. M. Bibcode: 2002AAS...200.0418D Altcode: 2002BAAS...34..646D The complex interactions between the turbulent fluid motions within the solar convection zone and the related processes of emergence, evolution, and cancellation of magnetic field at the photosphere have received much recent attention. It is likely that such interactions depend on the relative magnitudes of the field and of the flows, but the details of this coupling are not well understood. To further investigate the magnetohydrodynamics within such turbulent convection, we have constructed several idealized simulations of fully compressible MHD fluids, each contained within a curved, spherical segment that approximates a localized volume of subphotospheric convection on the sun. In some cases, the horizontal extent of the computational volume spans 30 heliographic degrees in both latitude and longitude, thereby enabling the dynamics within a large field containing approximately 100 supergranular-sized cells to be studied. By varying the amount of total (unsigned) flux permeating the domain, we are able to investigate analogs to patches of subsurface convection that generally resemble either quiet-sun or active regions when viewed from above. In addition, simplified potential-field extrapolations into the volume above the computational domain are used to illustrate how the coronal field topology might behave in response to the continually evolving magnetic field within the convecting layers. This work was supported by NASA through grant NAG 5-3077 to Stanford University and by Lockheed Martin Independent Research and Development funds. Title: Status report and near future prospects for the gravitational wave detector AURIGA Authors: Zendri, J. -P.; Baggio, L.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; Conti, L.; De Rosa, M.; Falferi, P.; Fortini, P. L.; Inguscio, M.; Marin, A.; Marin, F.; Mezzena, R.; Ortolan, A.; Prodi, G. A.; Rocco, E.; Salemi, F.; Soranzo, G.; Taffarello, L.; Vedovato, G.; Vinante, A.; Vitale, S. Bibcode: 2002CQGra..19.1925Z Altcode: We describe the experimental efforts to set up the second AURIGA run. Thanks to the upgraded capacitive readout, fully characterized and optimized in a dedicated facility, we predict an improvement in the detector sensitivity and bandwidth by at least one order of magnitude. In the second run, AURIGA will also benefit from newly designed cryogenic mechanical suspensions and the upgraded data acquisition and data analysis. Title: First room temperature operation of the AURIGA optical readout Authors: De Rosa, M.; Baggio, L.; Cerdonio, M.; Conti, L.; Galet, G.; Marin, F.; Ortolan, A.; Prodi, G. A.; Taffarello, L.; Vedovato, G.; Vitale, S.; Zendri, J. -P. Bibcode: 2002CQGra..19.1919D Altcode: In the frame of the AURIGA collaboration, a readout scheme based on an optical resonant cavity has been implemented on a room temperature resonant bar detector of gravitational waves. The bar equipped with the optical readout has been operating for a few weeks and we report here the first results. Title: The present status of the VIRGO Central Interferometer*The present status of the VIRGO Central Interferometer Authors: Acernese, F.; Amico, P.; Arnaud, N.; Arnault, C.; Babusci, D.; Ballardin, G.; Barone, F.; Barsuglia, M.; Bellachia, F.; Beney, J. L.; Bilhaut, R.; Bizouard, M. A.; Boccara, C.; Boget, D.; Bondu, F.; Bourgoin, C.; Bozzi, A.; Bracci, L.; Braccini, S.; Bradaschia, C.; Brillet, A.; Brisson, V.; Buskulic, D.; Cachenaut, J.; Calamai, G.; Calloni, E.; Canitrot, P.; Caron, B.; Casciano, C.; Cattuto, C.; Cavalier, F.; Cavaliere, S.; Cavalieri, R.; Cecchi, R.; Cella, G.; Chiche, R.; Chollet, F.; Cleva, F.; Cokelaer, T.; Cortese, S.; Coulon, J. P.; Cuoco, E.; Cuzon, S.; Dattilo, V.; David, P. Y.; Davier, M.; De Rosa, M.; De Rosa, R.; Dehamme, M.; Di Fiore, L.; Di Virgilio, A.; Dominici, P.; Dufournaud, D.; Eder, C.; Eleuteri, A.; Enard, D.; Errico, A.; Evangelista, G.; Fabbroni, L.; Fang, H.; Ferrante, I.; Fidecaro, F.; Flaminio, R.; Fournier, J. D.; Fournier, L.; Frasca, S.; Frasconi, F.; Gammaitoni, L.; Ganau, P.; Garufi, F.; Gaspard, M.; Gennaro, G.; Giacobone, L.; Giazotto, A.; Giordano, G.; Girard, C.; Guidi, G.; Heitmann, H.; Hello, P.; Hermel, R.; Heusse, P.; Holloway, L.; Iannarelli, M.; Innocent, J. M.; Jules, E.; La Penna, P.; Lacotte, J. C.; Lagrange, B.; Leliboux, M.; Lieunard, B.; Lodygenski, O.; Lomtadze, T.; Loriette, V.; Losurdo, G.; Loupias, M.; Mackowski, J. M.; Majorana, E.; Man, C. N.; Mansoux, B.; Marchesoni, F.; Marin, P.; Marion, F.; Marrucho, J. C.; Martelli, F.; Masserot, A.; Massonnet, L.; Mataguez, S.; Mazzoni, M.; Mencik, M.; Michel, C.; Milano, L.; Montorio, J. L.; Morgado, N.; Mours, B.; Mugnier, P.; Nicolosi, L.; Pacheco, J.; Palomba, C.; Paoletti, F.; Paoli, A.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Perciballi, M.; Pinard, L.; Poggiani, R.; Popolizio, P.; Pradier, T.; Punturo, M.; Puppo, P.; Qipiani, K.; Ramonet, J.; Rapagnani, P.; Reboux, A.; Regimbau, T.; Reita, V.; Remillieux, A.; Ricci, F.; Richard, F.; Ripepe, M.; Rivoirard, P.; Roger, J. P.; Scheidecker, J. P.; Solimeno, S.; Sottile, R.; Stanga, R.; Taddei, R.; Taurigna, M.; Teuler, J. M.; Tourrenc, P.; Trinquet, H.; Turri, E.; Varvella, M.; Verkindt, D.; Vetrano, F.; Veziant, O.; Viceré, A.; Vinet, J. Y.; Vocca, H.; Yvert, M.; Zhang, Z. Bibcode: 2002CQGra..19.1421A Altcode: The VIRGO Central Interferometer (CITF) is a short suspended interferometer operated with the central area elements of the VIRGO detector. The main motivation behind the CITF is to allow the integration and debugging of a large part of the subsystems of VIRGO while the construction of the long arms of the antenna is being completed. This will permit a faster commissioning of the full-size antenna. In fact, almost all the main components of the CITF, with the exception of the large mirrors and a few other details, are the same as those to be used for the full-size detector. In this paper the present status of the VIRGO CITF is reported. Title: Advanced readout configurations for the gravitational wave detector AURIGA Authors: Zendri, J. -P.; Bignotto, M.; Bonaldi, M.; Cerdonio, M.; Conti, L.; Crivelli Visconti, V.; de Rosa, M.; Falferi, P.; Marin, A.; Marin, F.; Mezzena, R.; Prodi, G. A.; Salviato, M.; Soranzo, G.; Taffarello, L.; Vinante, A.; Vitale, S. Bibcode: 2002rdgr.conf..317Z Altcode: We report the status of the experimental effort devoted at improving the sensitivity and widening the band of the gravitational wave detector AURIGA. The focus is on an optimized setup of the capacitive resonant transducer, read by an improved dc-SQUID amplifier and on the implementation of an opto-mechanical resonant transducer. Both techniques, which are complementary, should lead to an improvement of the detector performances of at least two orders of magnitude in both energy sensitivity and bandwidth. Title: Coupled modeling of photospheric and coronal dynamics Authors: Alexander, D.; Hurlburt, N. E.; Rucklidge, A. M.; De Rosa, M. Bibcode: 2001AGUFMSH11C0718A Altcode: The coupling of the motions within and below te photosphere to the chromosphere and corona is one of the fundamental issues in solar physics. We have developed a model coupling the simulated dynamics of sunspots to the simulated heating of coronal loops. In this paper we present an extension of our earlier work to the inclusion of (a) fully three dimensional magnetoconvection, (b) new analytical representations of hydrostatic loops with spatially-dependent heating rates and (c) fully time-dependent hydrodynamic coronal modeling. The dynamic loop model uses the same numerical scheme as the magnetoconvective model used to simulate the photospheric behavior in this sunspot system, making it possible to more fully integrate the two regimes. We present the first results of a hybrid model utilizing a time-dependent coronal model and a fully three-dimensional magnetoconvective model. Title: Numerical simulations of supergranular scales of convection in shallow spherical shells Authors: De Rosa, Marc L.; Toomre, Juri Bibcode: 2001ESASP.464..595D Altcode: 2001soho...10..595D The differential rotation of the sun, as deduced from helioseismology, exhibits a prominent radial shear layer near the top of the convection zone. Supergranulation and related scales of turbulent convection are likely to play a significant role in the maintenance of strong radial gradients in angular velocity which vary with latitude near the surface. We present results from 3-D numerical simulations of such turbulent convection in shallow spherical shells, using the anelastic spherical harmonic (ASH) code running on massively parallel computers to study the effects of rotation and compressibility on the resulting highly nonlinear convection. Convection of supergranular nature is driven by imposing the solar heat flux at the bottom of a shallow spherical shell located near the top of the convection zone which is rotating at the mean solar rate. The angular momentum balance in the shell is studied for cases where a solar-like differential rotation profile is imposed at the lower boundary. Convection spanning a large range of horizontal scales is driven within the shell, especially near the top of the domain. The resulting radial angular velocity gradient is negative for all latitudes, suggesting that fluid parcels partially conserve their angular momentum while moving radially. Title: Turbulent Convection and Subtleties of Differential Rotation Within the Sun Authors: Toomre, J.; Brun, A. Sacha; De Rosa, M.; Elliott, J. R.; Miesch, M. S. Bibcode: 2001IAUS..203..131T Altcode: Differential rotation and cycles of magnetic activity are intimately linked dynamical processes within the deep shell of highly turbulent convection occupying the outer 200 Mm below the solar surface. Helioseismology has shown that the angular velocity Ω within the solar convection zone involves strong shear layers both near the surface and especially at its base near the interface with the radiative interior. The tachocline of radial shear there that varies with latitude is thought to be the site of the global magnetic dynamo. Most recent continuous helioseismic probing with MDI on SOHO and from GONG have revealed systematic temporal changes in Ω with the advancing solar cycle. These include propagating bands of zonal flow speedup extending from the surface to a depth of about 70 Mm, distinctive out-of-phase vacillations in Ω above and below the tachocline with a period of about 1.3 years near the equator, a changing pattern of meridional circulation cells with broken symmetries in the two hemispheres, and complex speedups and slowdowns in the bulk of the convection zone. We review these helioseismic findings and their implications. We also describe current 3-D numerical simulations of anelastic rotating convection in full spherical shells used to study the differential rotation that can be established by such turbulence exhibiting coherent structures. These simulations enabled by massively parallel computers are making promising contact with aspects of the Ω profiles deduced from helioseismology, but challenges remain. Title: Dynamics in the upper solar convection zone Authors: DeRosa, Marc Lyle Bibcode: 2001PhDT.........8D Altcode: The differential rotation of the sun, as deduced from helioseismology, exhibits a prominent layer of radial shear near the top of the convection zone. This shearing boundary layer just below the solar surface is composed of convection possessing a broad range of length and time scales, including granulation, mesogranulation, and supergranulation. Such turbulent convection is likely to influence the dynamics of the deep convection zone in ways that are not yet fully understood. We seek to assess the effects of this near-surface shear layer through two complementary studies, one observational and the other theoretical in nature. Both deal with turbulent convection occurring on supergranular scales within the upper solar convection zone. We characterize the horizontal outflow patterns associated with solar supergranulation by individually identifying several thousand supergranules from a 45°-square field of quiet sun. This region is tracked for a duration of six days as it rotates across the disk of the sun, using full-disk (2 ' pixels) SOI-MDI images from the SOHO space-craft of line- of-sight Doppler velocity imaging the solar photosphere at a cadence of one minute. This time series represents the first study of solar supergranulation at such high combined temporal and spatial resolution over an extended period of time. The outflow cells in this region are observed to have a distribution of sizes, ranging from 14-20 Mm across, while continuously evolving on time scales of several days. Such evolution manifests itself in the form of cell merging, fragmentation, and advection, as the supergranules and their associated network of convergence lanes respond to the turbulent convection occurring a short distance below the photosphere. We have also conducted three-dimensional numerical simulations of turbulent compressible convection within thin spherical shells located near the top of the convection zone. Vigorous fluid motions possessing several length and time scales are driven by imposing the solar heat flux and differential rotation at the bottom of the domain. The convection patterns form a connected network of downflow lanes in the surface layers that break up into more plume-like structures with depth. The regions delineated by this downflow network enclose broad upflows that fragment into smaller structures near the surface. We find that a negative radial gradient of angular velocity Ω is maintained against diffusion in these simulations by the tendency for the convective motions to partially conserve their angular momentum in radial motion. This behavior suggests that similar dynamics may be responsible for the decrease of Ω with radius as deduced from helioseismology within the upper shear layer of the solar convection zone. Title: New Approach to Study Extended Evolution of Supergranular Flows and Their Advection of Magnetic Elements Authors: Lisle, Jason; De Rosa, Marc; Toomre, Juri Bibcode: 2000SoPh..197...21L Altcode: Using velocity and magnetogram data extracted from the full-disk field of view of MDI during the 1999 Dynamics Program, we have studied the dynamics of small-scale magnetic elements (3-7 Mm in size) over time periods as long as six days while they are readily visible on the solar disk. By exploiting concurrent time series of magnetograms and Doppler images, we have compared the motion of magnetic flux elements with the supergranular velocity field inferred from the correlation tracking of mesogranular motions. Using this new method (which combines the results from correlation tracking of mesogranules with detailed analysis of simultaneous magnetograms), it is now possible to correlate the motions of the velocity field and magnetic flux for long periods of time and at high temporal resolution. This technique can be utilized to examine the long-term evolution of supergranulation and associated magnetic fields, for it can be applied to data that span far longer time durations than has been possible previously. As tests of its efficacy, we are able to use this method to verify many results of earlier investigations. We confirm that magnetic elements travel at approximately 350 m s −1 throughout the duration of their lifetime as they are transported by supergranular outflows. We also find that the positions of the magnetic flux elements coincide with the supergranular network boundaries and adjust as the supergranular network itself evolves over the six days of this data set. Thus we conclude that this new method permits us to study the extended evolution of the supergranular flow field and its advection of magnetic elements. Since small-scale magnetic elements are strongly advected by turbulent convection, their dynamics can give important insight into the properties of the subsurface convection. Title: An optical transduction chain for the AURIGA detector Authors: Conti, L.; Marin, F.; de Rosa, M.; Prodi, G. A.; Taffarello, L.; Zendri, J. P.; Cerdonio, M.; Vitale, S. Bibcode: 2000AIPC..523..261C Altcode: 2000grwa.conf..261C We describe the principle of operation of an opto-mechanical readout for resonant mass gravitational wave detectors; with such a device the AURIGA detector is expected to reach a sensitivity at the level of Shh=10-22/Hz over a bandwidth of about 40Hz. Recent developments in the implementation of this transduction chain are also reported. In particular we achieve quantum limited laser power noise in the frequency range of 200Hz around the bar fundamental frequency (about 1kHz) by means of active stabilization. We also set up a reference cavity of finesse 40000 with optically contacted mirrors on a 0.2m long Zerodur spacer. The cavity can be heated from room temperature to about 100 °C and temperature stabilized with fluctuations within 1mK over a period of several days. The cavity is under vacuum and isolated from mechanical disturbancies by means of a double stage cantilever system. . Title: Evolving Dynamics of the Supergranular Flow Field Authors: De Rosa, M. L.; Lisle, J. P.; Toomre, J. Bibcode: 2000SPD....31.0106D Altcode: 2000BAAS...32..802D We study several large (45-degree square) fields of supergranules for as long as they remain visible on the solar disk (about 6 days) to characterize the dynamics of the supergranular flow field and its interaction with surrounding photospheric magnetic field elements. These flow fields are determined by applying correlation tracking methods to time series of mesogranules seen in full-disk SOI-MDI velocity images. We have shown previously that mesogranules observed in this way are systematically advected by the larger scale supergranular flow field in which they are embedded. Applying correlation tracking methods to such time series yields the positions of the supergranular outflows quite well, even for locations close to disk center. These long-duration datasets contain several instances where individual supergranules are recognizable for time scales as long as 50 hours, though most cells persist for about 25 hours that is often quoted as a supergranular lifetime. Many supergranule merging and splitting events are observed, as well as other evolving flow patterns such as lanes of converging and diverging fluid. By comparing the flow fields with the corresponding images of magnetic fields, we confirm the result that small-scale photospheric magnetic field elements are quickly advected to the intercellular lanes to form a network between the supergranular outflows. In addition, we characterize the influence of larger-scale regions of magnetic flux, such as active regions, on the flow fields. Furthermore, we have measured even larger-scale flows by following the motions of the supergranules, but these flow fields contain a high noise component and are somewhat difficult to interpret. This research was supported by NASA through grants NAG 5-8133 and NAG 5-7996, and by NSF through grant ATM-9731676. Title: Near-Surface Flow Fields Deduced Using Correlation Tracking and Time-Distance Analyses Authors: De Rosa, Marc; Duvall, T. L., Jr.; Toomre, Juri Bibcode: 2000SoPh..192..351D Altcode: Near-photospheric flow fields on the Sun are deduced using two independent methods applied to the same time series of velocity images observed by SOI-MDI on SOHO. Differences in travel times between f modes entering and leaving each pixel measured using time-distance helioseismology are used to determine sites of supergranular outflows. Alternatively, correlation tracking analysis of mesogranular scales of motion applied to the same time series is used to deduce the near-surface flow field. These two approaches provide the means to assess the patterns and evolution of horizontal flows on supergranular scales even near disk center, which is not feasible with direct line-of-sight Doppler measurements. We find that the locations of the supergranular outflows seen in flow fields generated from correlation tracking coincide well with the locations of the outflows determined from the time-distance analysis, with a mean correlation coefficient after smoothing of s=0.890. Near-surface velocity field measurements can be used to study the evolution of the supergranular network, as merging and splitting events are observed to occur in these images. The data consist of one 2048-min time series of high-resolution (0.6'' pixels) line-of-sight velocity images taken by MDI on 1997 January 16 -18 at a cadence of one minute. Title: An Optical Transducer for Bar Detectors Authors: Marin, F.; de Rosa, M.; Conti, L.; Prodi, G.; Vitale, S.; Cerdonio, M.; Taffarello, L.; Zendri, J. P. Bibcode: 2000epgw.conf..306M Altcode: We present a new kind of transducer for gravitational waves bar detectors. The bar vibrations are measured by means of a mechanically coupled optical cavity whose length is compared with that of a reference cavity by means of a laser system. We describe in details the transduction chain, we analyze the noise sources and the achievable sensitivity and present some experimental steps for the system implementation. Title: Comparison Between Near-Surface Flow Fields Deduced from Correlation Tracking and Time-Distance Helioseismology Methods Authors: De Rosa, M. L.; Toomre, J.; Duvall, T. L., Jr. Bibcode: 1999AAS...194.5608D Altcode: 1999BAAS...31..913D Near-photospheric flow fields deduced using two independent methods applied to the same SOI-MDI time series of images from SOHO are compared. Differences in travel times between incoming and outgoing f modes measured using time-distance helioseismology are used to determine the sites of supergranule outflows. Alternatively, correlation tracking analysis is applied to granular and mesogranular structures seen in time series of Doppler and intensity images. We find that the locations of the supergranular outflows seen in flow fields generated from correlation tracking coincide well with the locations of the outflows determined from the time-distance analysis. The near-surface flow fields provide us with insight in understanding the dyanmics of the turbulent convection occurring below the photosphere. The data consist of four 512-minute time series of high-resolution (0.6'' pixels) Doppler images and continuum intensity images taken by MDI on 17--18 January 1997 at a cadence of one minute. Title: Collisional broadening and shift of lines in the 2ν1+2ν2+ν3 band of CO2. Authors: de Rosa, M.; Corsi, C.; Gabrysch, M.; D'Amato, F. Bibcode: 1999JQSRT..61...97D Altcode: Using a distributed feedback diode laser, pressure induced self-broadening and shift have been measured for several transitions in the 2ν1+2ν2+ν3 band of CO2, centered at 1.573 μm. Foreign broadening and shift, with N2 and O2 as perturbing gas, have been measured for the most intense lines. The results for broadening have been compared with the data given by HITRAN molecular database and some discrepancies have been found, especially for air broadening derived from N2 and O2 broadening. Title: Comparison Between Near-Surface Flow Fields Deduced from Correlation Tracking and Time-Distance Helioseismology Methods Authors: de Rosa, Marc; Toomre, Juri; Duvall, T. L., Jr. Bibcode: 1999soho....9E..51D Altcode: Near-photospheric flow fields deduced using two independent methods applied to the same SOI-MDI time series of images from SOHO are compared. Differences in travel times between incoming and outgoing f modes measured using time-distance helioseismology are used to determine the sites of supergranule outflows. Alternatively, correlation tracking analysis is applied to granular and mesogranular structures seen in time series of Doppler and intensity images. We find that the locations of the supergranular outflows seen in flow fields generated from correlation tracking coincide well with the locations of the outflows determined from the time-distance analysis. The near-surface flow fields provide us with insight in understanding the dynamics of the turbulent convection occurring below the photosphere. The data consist of four 512-minute time series of high-resolution (0.6 arc-second pixels) Doppler images and continuum intensity images taken by MDI on 17-18 January 1997 at a cadence of one minute. Title: Long-Term Dynamics of Small-Scale Magnetic Flux Elements Embedded in the Near-Surface Velocity Field Authors: Lisle, Jason; de Rosa, Marc; Toomre, Juri Bibcode: 1999soho....9E..72L Altcode: Using velocity and magnetogram data generated by SOI-MDI during the 1999 Dynamics Program, we have studied the dynamics of small-scale magnetic elements over time periods of several days. By exploiting concurrent time series of MDI magnetograms and velocity images, we have correlated the motions of the magnetic flux elements with the supergranular velocity field inferred from tracking of mesogranular motions. We confirm that these magnetic elements travel at approximately 200 m/s throughout the duration of their lifetime (10-20 hours) as they are transported by supergranular outflows. We also find that boundaries of supergranules traced by magnetic flux elements coincide with the boundaries determined from the tracking of mesogranules. In addition, we have studied the association between magnetic flux emergence and destruction events and the evolution of the supergranular network. The data consist of several tracked regions of corresponding magnetogram and photospheric velocity images extracted from full-disk SOI-MDI images taken during the 1999 Dynamics Program when the MDI instrument was at best focus. Time series were created by following these individual patches as they rotated across the solar disk. Individual magnetic elements were identified by thresholding the magnetograms, while the supergranular flow fields were determined by applying a correlation tracking algorithm to time series of mesogranules. The mesogranules were isolated by removing the signal due to solar rotation, p-mode oscillations, and supergranulation from the velocity data. Title: Correlation Tracking of Mesogranules from SOI-MDI Doppler Images to Reveal Supergranular Flow Fields Authors: De Rosa, Marc L.; Toomre, Juri Bibcode: 1998ESASP.418..753D Altcode: 1998soho....6..753D We present evidence that mesogranules on the sun are advected horizontally by the underlying supergranular flow field. Correlation tracking of mesogranules, as observed in full-disk SOI-MDI Doppler images, reveal that the flow field experienced by the mesogranules is composed of several long-lived regions of divergent fluid. These outflow regions correlate well with the locations of supergranules present on related Doppler images. The flow fields also contain regions where the fluid is converging or is moving slowly, both corresponding to areas of the related Doppler images where no organized supergranular outflows exist. Typical velocities are of order 200 m s-1. The data used in this study consist of 30-circ-square patches of the photospheric velocity field extracted from full-disk SOI-MDI Dopplergrams. Time series were created by tracking each patch in a frame corotating with the surface plasma. Images of mesogranulation superimposed on supergranulation were created by removing the velocity signals due to rotation and acoustic oscillations. The supergranular signal is isolated by spatially smoothing each image, while the mesogranular signal is isolated by taking the residual of the smoothed and unsmoothed images. The correlation tracking calculation was performed on the time series of mesogranulation, from which the surface flow-fields analyzed in this study were deduced. Title: The Nature of Supergranulation from SOI-MDI Dopplergrams Authors: De Rosa, Marc L.; Toomre, Juri Bibcode: 1997SPD....28.0257D Altcode: 1997BAAS...29..903D We discuss the distribution of supergranule cell areas and evolutionary characteristics as determined from a series of SOI-MDI dopplergrams. Patches of the photospheric velocity field 30(deg) x30(deg) (heliographic) in size were tracked as they rotated across the disk of the sun. Supergranule boundaries were identified on each tracked image by a pattern recognition algorithm, from which supergranule area distributions and evolutionary trends are found. Title: Temperature dependence of self-shift of ammonia transitions in the ν2 band. Authors: Baldacchini, G.; D'Amato, F.; de Rosa, M.; Buffa, G.; Tarrini, O. Bibcode: 1996JQSRT..55..745B Altcode: Pressure-induced lineshift has been measured as a function of temperature, in the range 200-400 K, for five transitions of the ν2 band of ammonia lines near 937 cm-1. Results are compared with semiclassical calculations that rely on the impact approximation. In general the theory does not agree very well with the experimental values of the shift, but the sign and the order of magnitude are confirmed. The present work shows that extensive and detailed measurement of the lineshifts is feasible and reliable, even when their absolute values in ammonia as a function of temperature are very small. Title: Differential Rotation and Dynamics of the Solar Interior Authors: Thompson, M. J.; Toomre, J.; Anderson, E. R.; Antia, H. M.; Berthomieu, G.; Burtonclay, D.; Chitre, S. M.; Christensen-Dalsgaard, J.; Corbard, T.; De Rosa, M.; Genovese, C. R.; Gough, D. O.; Haber, D. A.; Harvey, J. W.; Hill, F.; Howe, R.; Korzennik, S. G.; Kosovichev, A. G.; Leibacher, J. W.; Pijpers, F. P.; Provost, J.; Rhodes, E. J., Jr.; Schou, J.; Sekii, T.; Stark, P. B.; Wilson, P. R. Bibcode: 1996Sci...272.1300T Altcode: Splitting of the sun's global oscillation frequencies by large-scale flows can be used to investigate how rotation varies with radius and latitude within the solar interior. The nearly uninterrupted observations by the Global Oscillation Network Group (GONG) yield oscillation power spectra with high duty cycles and high signal-to-noise ratios. Frequency splittings derived from GONG observations confirm that the variation of rotation rate with latitude seen at the surface carries through much of the convection zone, at the base of which is an adjustment layer leading to latitudinally independent rotation at greater depths. A distinctive shear layer just below the surface is discernible at low to mid-latitudes. Title: Propagation of electromagnetic waves in inhomogeneous plasmas Authors: Busatti, E.; Ciucci, A.; De Rosa, M.; Palleschi, V.; Rastelli, S.; Lontano, M.; Lunin, N. Bibcode: 1994JPlPh..52..443B Altcode: The reflection and transmission coefficients for an electromagnetic beam propagating in an inhomogeneous plasma are calculated analytically using the Magnus approximation in different physical configurations. The theoretical predictions for such coefficients are expressed in simple analytical form, and are compared with the exact results obtained by numerical solution of the wave propagation equations, using the Berreman 4 × 4 matrix method. It is shown that the theoretical approach is able to reproduce the correct results for reflection and transmission coefficients over a wide range of physical parameters. The accuracy of the theoretical analysis, at different orders of approximation, is also discussed.