RECONSTRUCTION OF CORONAL MAGNETIC CONFIGURATIONS - THE CASE OF STRONGLY NONLINEAR FORCE-FREE FIELDS

A method for the reconstruction of force-free field (FFF) coronal magnetic configurations above active regions is proposed. It is based on the mapping of the entire space surrounding the Sun onto a rectangular box of dimensions (1,2,2pi), inside which the FFF Maxwell's equations are solved. The boundary conditions used are the field components observed at the photosphere, their vanishing at infinity and finiteness of the magnetic potential components along the poles. The solution is based on relaxation techniques and is illustrated for the 2 1/2D case, that is the case in which all three field components B(r), B(theta) and B(phi) are finite and depend only on the polar coordinates r and theta. The equilibrium state is considered to be reached when the mean relative change in any of the field components, from one time step to another, is smaller than a prescribed infinitesimal number.