The Correlation Between Whistler Mode Waves and Electron Beam-Like Distribution: Test Particle Simulations and THEMIS Observations

The beam-like electron population is often observed along with whistler mode waves in the Earth's magnetosphere, but its generation mechanism is still under debate. In this study, we use a test particle simulation model to study the Landau resonance between whistler mode waves and electrons, and quantify the proportion (Formula presented.) of beam-like electrons. There is a trend that the (Formula presented.) first increases and then decreases with the increasing temperature of hot electrons or ratio of plasma frequency to electron gyrofrequency. While the (Formula presented.) is positively correlated with the parallel electric field, magnetic amplitude, wave normal angle, or frequency of whistler mode waves if other parameters are fixed. Essentially the parallel electric field is the key parameter in determining (Formula presented.). Furthermore, we have also compared simulation results with THEMIS observations for one year. The results suggest the observed beam-like population could be generated by simultaneously observed whistler mode waves for 44.5% quasi-parallel cases. But the beam-like population is unlikely to be generated by simultaneously observed waves for the remaining 55.5% of quasi-parallel cases and nearly all oblique cases. Our study provides a better understanding of the formation of beam-like electron distribution in the Earth's magnetosphere.