Wave Normal Angle Influence Of Chorus And Hiss On Dynamic Evolution Of Radiation Belt Energetic Electrons

Since the 1958 discovery by US scientific satellite the radiation belts surrounding Earth region 1-7 Earth radii has been widely concerned because of trapped geomagnetic energetic charged particles, which mainly consist of high-energy electrons and protons, and a small amount of alpha particles and heavy nuclei components. They can be divided into inner radiation belt and outer radiation belt. Their shape looks like a set of two rings outside the Earth. Charged particles in the radiation belts have three adiabatic invariants and can be present for a longer period of time. Currently most of spacecrafts are operating in the outer radiation belt region. High energy charged particles can cause damage to the material and the human body, and also a threat to astronauts. Therefore, it is important to study and predict the outer radiation belt energetic electrons dynamical evolution.Gyroresonance between chorus 、 hiss waves and radiation belt electrons is usually evaluated by using the Gaussian wave normal angle(X = tanθ) distribution. In this study, we examine the influence of peak wave normal angle(X m = tanθ m) on chorus-electron and hiss-electron interaction at locations L = 4.5 and 6.0. By varying X m = 0,2,4,6, we calculate the bounce-averaged diffusion coefficients, and then simulate the phase space density(PSD)evolution of radiation belt energetic electrons induced by both dayside and nightside chorus and hiss waves. Numerical simulations show that diffusion coefficients for the chorus move to the low pitch angle region and drop rapidly by a factor of ~10 as Xm increases by 2 each time.Meanwhile, diffusion coefficients for the hiss move to the low pitch angle region but drop slowly as Xm increases by 2 each time. This will consequently leads to the smaller amplitude and narrower pitch angle region in electron PSD evolution. The peak effect on the PSD by chorus+hiss and chorus at L=6 is similar to that at L=4.5. PSD evolution by chorus alone at L=6 is slightly larger than that at L=4.5, but PSD evolution by chorus+hiss at L=6 is slightly smaller than that at L=4.5 at low energy.