A Possible Solar Cycle Dependence to the Hemispheric Pattern of Filament Magnetic Fields?

Abstract

The origin of the observed hemispheric pattern of filament magnetic fields is considered. Using a magnetic flux transport model, we simulate the interactions of magnetic bipoles with each other and with polar magnetic fields in the rising and declining phases of the solar activity cycle. In contrast to previous studies, the nonpotential character of the initial coronal fields is taken into account, and the dependence of the hemispheric pattern on the initial tilt and helicity of the bipoles is considered. For the rising phase of the cycle, a range of initial bipole twists and tilt angles can be found that reproduce the observed hemispheric pattern. However, for the declining phase no such range can be found: the predicted fields on the return arms at the rear of switchbacks are consistent with filament observations, but those on the high-latitude east-west arms are not. It is argued that existing observations of the hemispheric pattern are weighted toward the rising phase of the solar activity cycle and may give us a biased view of the Sun. New observations of filament magnetic fields are needed to determine whether there is a cycle dependence of the observed hemispheric pattern.