Interaction of Fast Magnetoacoustic Wave with the Localized Coronal Null and Generation of the Energetic Alfv\'en Wave Packet

In the present paper, we have performed 2.5D resistive magnetohydrodynamic simulations of the interaction of a fast magnetoacoustic wave with a localized coronal magnetic null point. As a result, an Alfv\'en wave packet is generated by the mode conversion when a fast magnetoacoustic perturbation interacts with the null point. The field-aligned plasma flows are also generated due to the non-linear effects. When the fast mode wavefront interacts with the null, some parts of this wavefront get refracted around it, while some other part is trapped at the null region. Subsequently, the velocity fluctuation out of the plane and in-phase magnetic field fluctuations have evolved and propagated with the local Alfv\'en speed along the separatrixes at one side of the coronal null region. The resulting disturbance behaves as an incompressible and energetic Alfv\'en wave packet. A secondary fast magnetoacoustic wave is also produced and propagates. In the synthetic SDO/AIA observations, no intensity fluctuations are evident in the region where the Alfv\'en wave packet propagates, while the fast magnetoacoustic wave fronts are clearly evident. Our results suggest that given the appropriate physical conditions at the null, when the fast mode wave is incident, Alfv\'en packets can be excited due to the mode conversion, further carrying substantial momentum and energy flux in the solar corona.