Precipitation Rates of Electrons Interacting With Lower-Band Chorus Emissions in the Inner Magnetosphere

Abstract

Electrons trapped in the Earth's magnetic field can be scattered by whistler mode chorus emissions and precipitate into the Earth's upper atmosphere. Whistler mode chorus waves propagating in the Earth's inner magnetic field are usually observed with oblique wave normal angles (WNAs). In this study, we apply 12 chorus wave models with four various WNA sets (the maximum WNA are 0°, 20°, 60°, and 90% of resonance cone angles) and three wave amplitude sets (the maximum wave magnetic fields are 2.1 nT, 307 pT, and 49.4 pT) at L = 4.5. We use test-particle simulations to trace electrons interacting with the waves and create Green's function sets for electrons initially at kinetic energies (K) 10–6, 000 keV and equatorial pitch angles (α) 5°–89°. The simulation results show that in the 2.1 nT cases, the very oblique chorus waves contribute to more electron precipitation than the other three chorus wave models, especially at energies 50–100 keV. Checking the highest initial equatorial pitch angle of the precipitated electrons, we find that the very oblique chorus waves can precipitate electrons with α > 45°. In contrast, the other chorus waves can only precipitate electrons with α < 30°. Furthermore, the precipitation rates reveal that the anomalous trapping effect, which moves low equatorial pitch angle electrons away from the loss cone, in the oblique cases is much weaker than in the parallel case, resulting in higher precipitation rates. Finally, we derive the pitch angle scattering rates and verify the precipitation by nth cyclotron resonances with oblique chorus.