Evidence of Small Scale Plasma Irregularity Effects on Whistler Mode Chorus Propagation

Abstract

The impact of randomly distributed field aligned density irregularities on whistler mode wave propagation is investigated using full wave simulations and multipoint spacecraft observations. The irregularities are modeled as randomized density perturbations between 1% and 10% of the nominal background density value with scales of ∼10-60 km transverse and ∼50-500 km along the background magnetic field. The density irregularities affect whistler wave propagation and lead to spatial modulation of wave average power density accompanied by spreading of the wave normal angle distribution. Wave power variation is shown to statistically increase with the depth of density irregularities. The simulation results are in good agreement with the observed correlations of chorus power and variation of the plasma density from multipoint observations by the four Magnetosphere MultiScale spacecraft. The change in fundamental wave properties from scattering from these irregularities affects the efficiency of wave particle interactions in the radiation belts and needs to be incorporated into large scale energetic particle flux models.