Study on Two Methods for Nonlinear Force-Free Extrapolation Based on Semi-Analytical Field |
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Authors: | S Liu H Q Zhang J T Su M T Song |
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Institution: | (1) School of Science, Xidian University, Xi’an, Shaanxi, China;(2) School of Applied Science, Taiyuan University of Science and Technology, Taiyuan, Shanxi, China |
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Abstract: | In this paper, two semi-analytical solutions of force-free fields (Low and Lou, Astrophys. J.
352, 343, 1990) have been used to test two nonlinear force-free extrapolation methods. One is the boundary integral equation (BIE) method
developed by Yan and Sakurai (Solar Phys.
195, 89, 2000), and the other is the approximate vertical integration (AVI) method developed by Song et al. (Astrophys. J.
649, 1084, 2006). Some improvements have been made to the AVI method to avoid the singular points in the process of calculation. It is found
that the correlation coefficients between the first semi-analytical field and extrapolated field using the BIE method, and
also that obtained by the improved AVI method, are greater than 90% below a height 10 of the 64×64 lower boundary. For the
second semi-analytical field, these correlation coefficients are greater than 80% below the same relative height. Although
differences between the semi-analytical solutions and the extrapolated fields exist for both the BIE and AVI methods, these
two methods can give reliable results for heights of about 15% of the extent of the lower boundary. |
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