Influence of wave normal angle on gyroresonance between chorus waves and outer radiation belt electrons

Abstract

In this paper, using a Gaussian distribution of wave normal angle X=tanθ, and considering contributions of harmonic resonances n up to ±5, we analyze the effect of normal angle on diffusion coefficients induced by gyroresonance between chorus waves and electrons with energies 0.1 and 1.0 MeV on the dayside and nightside at L=4.5. When pitch angle α e>10°, for 0.1 and 1.0 MeV electrons on the dayside and nightside, diffusion coefficients of five orders (−2,−1, 0, 1, 2) decrease with increasing normal angle peak, leading to the total diffusion coefficients decreasing with increasing peak. When α e<10°, for 1.0 MeV electrons on the dayside and 0.1 MeV electrons on the dayside and nightside, the positive order diffusion coefficients are generally smaller than the same negative order ones; in the meanwhile, diffusion coefficients of orders (−2, 1, 2) are very small, the dominant order n=−1 diffusion coefficients change very little, hence the total diffusion coefficients almost remain unchanged. However, for 1.0 MeV electrons on the nightside, diffusion coefficients of orders (−2, 1, 2) which are larger than those of the order (−1) resonance increase with increasing peak, hence the total diffusion coefficients increase with increasing peak. The current results show that the wave normal angle plays an important role in the quantitative analysis of gyroresonance between chorus waves and electrons in the outer radiation belt.