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Does Nearby Open Flux Affect the Eruptivity of Solar Active Regions?  

Marc DeRosa   Submitted: 2018-05-30 14:29

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, there exist large flares which are not accompanied by a CME. The existence of these non-eruptive 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 having 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 non-eruptive X-class flares in the sample, based on the associated Bayes factor.

Authors: Marc L. DeRosa, Graham Barnes

Publication Status: ApJ (in press)
Last Modified: 2018-06-03 13:00
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The Influence of Spatial Resolution on Nonlinear Force-Free Modeling  

Marc DeRosa   Submitted: 2015-08-25 12:25

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/SOT-SP 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.

Authors: M. L. DeRosa, M. S. Wheatland, K. D. Leka, G. Barnes, T. Amari, A. Canou, S. A. Gilchrist, J. K. Thalmann, G. Valori, T. Wiegelmann, C. J. Schrijver, A. Malanushenko, X. Sun, S. Régnier
Projects: Hinode/SOT

Publication Status: ApJ (in press)
Last Modified: 2015-08-25 16:45
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A Method for Data-Driven Simulations of Evolving Solar Active Regions  

Marc DeRosa   Submitted: 2012-08-14 18:20

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 the plasma velocity is proportional to the Lorentz force. The simulations of active region coronal field are driven by temporal sequences of photospheric magnetograms from the Helioseismic Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO). Under certain conditions, the data-driven simulations produce flux ropes that are ejected from the modeled active region 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 active regions taken by instruments such as SDO?s Atmospheric Imaging Assembly (AIA) at extreme ultraviolet wavelengths.

Authors: Mark C. M. Cheung & Marc L. DeRosa
Projects: SDO-HMI

Publication Status: ApJ (2012) 757 147
Last Modified: 2015-08-21 23:31
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A Critical Assessment of Nonlinear Force-Free Field Modeling of the Solar Corona for Active Region 10953  

Marc DeRosa   Submitted: 2009-02-05 19:26

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 article, 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 the 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.

Authors: Marc L. DeRosa, Carolus J. Schrijver, Graham Barnes, K. D. Leka, Bruce W. Lites, Markus J. Aschwanden, Tahar Amari, Aurelien Canou, James M. McTiernan, Stephane Regnier, Julia K. Thalmann, Gherardo Valori, Michael S. Wheatland, Thomas Wiegelmann, Mark C. M. Cheung, Paul A. Conlon, Marcel Fuhrmann, Bernd Inhester, Tilaye Tadesse
Projects: Hinode/SOT

Publication Status: ApJ (2009) 696 1780
Last Modified: 2015-08-21 23:30
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Abstracts by Author
Does Nearby Open Flux Affect the Eruptivity of Solar Active Regions?
The Influence of Spatial Resolution on Nonlinear Force-Free Modeling
A Method for Data-Driven Simulations of Evolving Solar Active Regions
A Critical Assessment of Nonlinear Force-Free Field Modeling of the Solar Corona for Active Region 10953

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