Wave fields of electromagnetic ion cyclotron and whistler waves in a two dimensional dipole magnetosphere and associated particle acceleration and pitch angle scattering

Abstract:

Radiation belt particles are thought to be strongly affected by inner magnetospheric waves. Here, we consider electromagnetic ion cyclotron (EMIC) and whistler waves driven by anisotropic pressure in a two dimensional (axisymmetric) dipole magnetosphere. We use a hybrid code with a population of cold inertialess electrons to simulate these waves within a range of L shells. First, we present the properties of the waves. For both types of waves, the waves refract outward as they propagate away from the magnetic equator. Whistler waves lead to diffusion in both energy and pitch angle, whereas EMIC waves only affect the pitch angle. The whistler waves scatter the particles through the cyclotron or Landau resonance. The Landau resonance is effective, even though there is no parallel electric field in our system of equations, because of a self-induced cyclotron resonance with oblique waves. EMIC waves can cause large pitch angle diffusion, even at the lower energies. Nonresonant scattering appear to occur due to irregularities in the magnetic field and to wobbling of the field due to the gyromotion.