Alfvén wave dynamics at the neighbourhood of a 2.5D magnetic null-point

Abstract

The aim of the present study is to highlight the energy transfer via the interaction of magnetohydrodynamic waves with a 2.5D magnetic null-point in a finite plasma-β regime of the solar corona. An initially symmetric Alfvén pulse at a specific distance from a magnetic null-point is kicked towards the isothermal null-point. A shock-capturing Godunov-type pluto code is used to solve the ideal magnetohydrodynamic set equations in the context of wave-plasma energy transfer. As the Alfvén wave propagates towards the magnetic null-point, it experiences speed lowering which ends up in releasing energy along the separatrices. In this line owing to the Alfvén wave, a series of events take place that contribute towards coronal heating. Non-linear-induced waves are by-products of the torsional Alfvén interaction with magnetic null-points. The energy of these induced waves which are fast magnetoacoustic (transverse) and slow magnetoacoustic (longitudinal) waves is supplied by the Alfvén wave. The non-linearly induced density perturbations are proportional to the Alfvén wave energy loss. This supplies energy for the propagation of fast and slow magnetoacoustic waves, where in contrast to the fast wave the slow wave experiences a continuous energy increase. As such, the slow wave may transfer its energy to the medium at later times, maintaining a continuous heating mechanism at the neighbourhood of a magnetic null-point.