Temporal Evolution of Free Magnetic Energy Associated with Four X-class Flares
Ju Jing Submitted: 2009-02-23 07:06
We study the temporal variation of free magnetic energy Efree
around the time of four X-class flares. The high-cadence
photospheric vector magnetograms obtained by the digital vector
magnegograph (DVMG) system at the Big Bear Solar Observatory
(BBSO) are used as the boundary conditions to reconstruct the
three-dimensional (3D) non-linear force-free (NLFF) coronal field.
In order to remove the effect of the net Lorentz force and torque
acting in the photosphere, the vector magnetograms are
preprocessed using the method devised by Wiegelmann et al. (2006).
Then a well-tested multigrid-like optimization code by Wiegelmann
(2004) is applied to the preprocessed boundary data to extrapolate
the NLFF coronal field with which we are able to estimate the free
energy Efree. In all the four events, we find a significant
drop of Efree starting ~15 min before the peak time of
the associated non-thermal flare emission, although long term
trend varies from event to event. We discuss the physical
implication of the result, i.e., the magnetic relaxation is
already going on in the corona well before the flare reconnection.
Authors: Ju Jing, P. F. Chen, Thomas Wiegelmann, Yan Xu, Sung-Hong Park, Haimin Wang
Publication Status: accepted by Ap.J.
Last Modified: 2010-07-12 08:48