ESPOS: Generation of Alfvén Wave Packet by Mode Conversion at the Coronal Null and Its Phase Mixing (Akash Bairagi)

For many decades, Alfvén waves have been considered to be a source of energy in the solar coronal plasma and supersonic wind. Understanding the possible dissipation mechanisms of Alfvén waves in the heterogeneously structured corona is important. Magnetic singularities enable mode conversion of MHD waves near the equipartition layer (Cs≈CA). In our study, we performed a 2.5D MHD numerical simulation of Alfvén wave packet generation through mode conversion when a fast wave interacts with a localised magnetic null in the corona. Subsequently, the out-of-plane velocity (i.e., Vz) and magnetic field fluctuations (i.e., bz) are generated in the equipartition layer (Cs≈CA) and propagate toward the large-scale heterogeneous corona. Also, the Alfvén wave packet decays in amplitude on the curved magnetic field due to phase mixing from the gradient of the local Alfvén speed across the magnetic field. Moreover, the strength of phase mixing depends on the amplitude of the local transverse gradient of bz, which helps form localised current layers. Thus, our results show that Alfvén waves can be generated from the magnetic null through MHD mode conversion, which then damps due to phase mixing and propagates toward another nearby null. We conclude that realistic physical conditions are needed to determine the extent of phase mixing and dissipation in the structured solar corona.