Effect of magnetic field distortions on gyroresonance at low L values

Abstract

From fully relativistic test particle simulations of the gyroresonance interaction between energetic electrons and whistler mode waves in the magnetosphere it is known that pitch angle diffusion due to this interaction becomes less and less effective at low L values, requiring very large wave amplitudes (∼100 nT) for significant pitch angle changes (Δα>1°). Such pitch angle changes are needed to produce the wave‐induced electron precipitation as observed through the Trimpi events which have been reported at low latitudes. Our computer simulation has been extended to model background field distortions which may alter the curvature of the field lines in such a way as to enhance the interaction efficiency. In general, “flattening” of the field line in the region near resonance enhances the interaction considerably, with a possible best case threefold increase in interaction time when compared to a undisturbed (dipole) field configuration. Our results indicate that pitch angle diffusion due to gyroresonance can only be significant at low L during periods of field line distortion, such as dayside compression or in the presence of Pc 4 or Pc 5 pulsations and various cavity mode oscillations.