AN IMPROVED APPROACH TO NONFORCE FREE CORONAL MAGNETIC FIELD EXTRAPOLATION 

qiang hu Submitted: 20061122 15:28
We develop an approach to deriving threedimensional nonforce free coronal
magnetic field from vector magnetograms. Based on the principle of Minimum Dissipation
Rate, a general nonforce free magnetic field is expressed as superposition of one potential
field, and two constantα (linear) force free fields. Each is extrapolated from their bottom
boundary data, providing the normal component only. The constant α parameters are
distinct, and determined by minimizing the deviations between the numerically computed
and measured transverse magnetic field at the bottom boundary. The boundary conditions
required are at least two layers of vector magnetograms, one at the photospheric level and
the other the chromospheric level, presumably. We apply it to a few analytic test cases,
especially to two nonlinear force free cases examined by Schrijver et al. (2006). We find
that for one case with small α parameters, the quantitative measures of the quality of
our result are better than the median values of those from a set of nonlinear force free
methods. The reconstructed magnetic field configuration is valid up to a vertical height of
the transverse scale. For the other cases, the results remain valid to a lower vertical height
due to the limitations of the linear force free field solver. As based on the Fast Fourier
Transform algorithm, our method is much faster and easy to implement. We discuss the
potential usefulness of our method and its limitations.
Authors: QIANG HU, and BRAHMANANDA DASGUPTA
Projects:

Publication Status: Solar Physics (submitted; under revision)
Last Modified: 20061201 12:06


