Solar magnetic fields: triple arcade structures

Abstract

Recent observation with the LASCO coronagraph on board the SOHO spacecraft have shown that helmet streamers may have an internal triple arcade structure. The observations suggest that this triple structure might be important for the initiation of coronal mass ejections (CME's). In this paper we undertake a first step towards the theoretical description of such triple structures by calculating self-consistent solutions of the magnetohydrostatic equations in two dimensions. For simplicity, we start with the investigations of current-free structures, leading to potential magnetic fields. We then go on to investigate the case of linear currents. These two cases have the disadvantage of being linearly stable in the framework of MHD, which makes it difficult to take them as starting-points for further investigations. Therefore, we also investigate special exact solutions of a nonlinear case and apply the method of asymptotic expansion to another nonlinear problem to obtain approximate elongated solutions, which might be useful for linear or nonlinear stability checks.