The Influence of Spatial Resolution on Nonlinear ForceFree Modeling 

Marc DeRosa Submitted: 20150825 12:25
The nonlinear forcefree 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/SOTSP 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 forcefree 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 selfconsistent 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: 20150825 16:45



A Critical Assessment of Nonlinear ForceFree Field Modeling of the Solar Corona for Active Region 10953 

Marc DeRosa Submitted: 20090205 19:26
Nonlinear forcefree 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 Sunlike 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 forcefree coronal modeling efforts. In this article, we discuss NLFFF modeling of NOAA Active
Region 10953 using Hinode/SOTSP, Hinode/XRT, STEREO/SECCHIEUVI, 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 photospheretocorona interface in order to better
transform the forced photospheric magnetograms into adequate approximations of nearly forcefree 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: 20150821 23:30




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