Influence of wave normal angles on hiss‐electron interaction in Earth's slot region

Abstract

AbstractWave‐particle interaction which occurs in the radiation belts is generally determined by variations in wave normal angles. Using the Gaussian wave normal angle ( ) distribution, we study the influence of peak wave normal angle ( ) on gyroresonance between plasmaspheric hiss waves and energetic electrons in the slot regions L = 2.5, 3.0, and 3.5. The bounce‐averaged diffusion coefficients are calculated for different Xm = 0,1,3,5, and then the phase space density (PSD) evolutions of energetic electrons driven by hiss waves are simulated over a continuous energy range 0.2–5 MeV. As Xm increases, diffusion coefficients basically decrease mainly from the medium to a critical pitch angle αc for Ek≤1.0 MeV but increase at lower pitch angles for Ek>1.0 MeV. Differences of diffusion coefficients between Xm = 0 and 1 are close but become substantial as Xm≥3. Hiss can cause substantial drops in electron PSDs for Ek≤0.5 MeV and Xm≤1 from the loss cone αL to αc. For Ek≥1.0 MeV, such PSD drops become much smaller and confined in the lower pitch angles close to αL for each Xm. In contrast, electron PSD increases for Ek≤1.0 MeV above αc at L = 2.5 and 3.0, probably because momentum diffusion coefficients increase steeply above αc. The current results demonstrate that gyroresonance between plasmaspheric hiss and energetic electrons in the slot region is strongly associated with variations of peak wave normal angles, which should be integrated into future global modeling of radiation belt dynamics.