Poloidal field line resonances driven by a fast wave

Abstract

We present numerical simulations of the excitation of resonant poloidal Alfvén waves. The resulting Alfvén waves could be loosely described as “high‐m” (m is the azimuthal wave number) in as much as the azimuthal scale of the wave is much less than the scale in the direction normal to L‐shells. Such waves are generally excited by wave‐particle interactions. In this article we show how resonant poloidal Alfvén waves can be excited by a fast mode (of large azimuthal scale) in a cold plasma. The key property that enables this is a three‐dimensional equilibrium, which facilitates the process of phasemixing in the azimuthal direction. We show that the classification of resonant Alfvén waves as high‐m and low‐m has limited applicability in 3D inhomogeneous media and suggest an alternative classification be based on the excitation mechanism.