Modeling of magnetic loops on the west solar limb observed during the total solar eclipse of October 24, 1995

Abstract

The coronal magnetic loop structure of the Sun can be observed during a total solar eclipse or using special instruments in space. We simulate the coronal magnetic loop structure by considering a constant-alpha force-free field model and using fast Fourier transforms (FFT) in a method generalized from that of Alissandrakis (1981). We use magnetogram data from the National Optical Astronomy Observatories (NOAO) as a boundary condition and derive a force-free coronal magnetic field in three dimensions. When comparing our simulation results with X-ray observations from the Yohkoth satellite, we find that alpha - 0.1 arc second -1 gives the appropriate S-shape for loops on the disk. We compare our field model with the photograph of Fe +9 line emission taken by a Chulalongkorn University expedition during the total solar eclipse of October 24th, 1995, which yields a high resolution image of the discontinuity of loop structures. We conclude that the discontinuity is indeed in large (~10x10x10x10x10 km) loop structures and did not occur from small magnetic loops at the footpoints. Our best explanation of this apparent discontinuity is that solar activity involving these loops occurred some days before our observation, so the loops were not in thermodynamic equilibrium, in accordance with our observation.