THE 3-D BOUNDARY-ELEMENT FORMULATION OF LINEAR FORCE-FREE MAGNETIC-FIELDS WITH FINITE-ENERGY CONTENT IN SEMIINFINITE SPACE

In this paper, a formulation describing a force-free magnetic field wi th constant alpha, either alpha not equal O or alpha = O, with finite energy content in semi-infinite space, z > O, above the Sun is propose d and solved uniquely by a numerical method: the boundary element meth od (BEM). The method is effective and convenient in extrapolating the magnetic field above the solar surface, Gamma, directly from the measu red magnetogram. Meanwhile, no additional data treatment is needed. Ba sed on the existence of such a field, the uniqueness of the solution i n the present formulation is proved and some useful properties are obt ained. The validity is also demonstrated by its application to the mag netic field computation in the chromosphere from observed magnetogram data. The practical feasibility is thus discussed and further confirme d.