A numerical study of the excitation of rising-tone chorus using the DAWN code

摘要

Chorus waves play a controlling role in radiation belt electron dynamics. However, its excitation mechanism remains to be fully understood. Because of the complex nonlinear dynamics involved, numerical simulations are normally used to study the detailed excitation process and properties of chorus. In this work, we present a new hybrid code, DAWN, to simulate the generation of chorus waves. The DAWN code is unique in that it models cold electrons using linearized fluid equations and hot electrons using particle-in-cell techniques. The simplified fluid equations can be solved with robust and simple algorithms. We demonstrate that discrete chorus elements can be generated from broadband whistler waves using this code. Waveforms of the generated elements show amplitude modulation or “subpackets”. Also frequency sweep rates of the generated elements are compared with a chorus generation theory by Helliwell. We then investigate the relationship between the starting frequency of chorus elements and properties of background whistler waves using the DAWN code. This work should be helpful to further understand the generation mechanism of chorus waves.