Nonlinear Signatures of VLF-Triggered Emissions: A Simulation Study

We conduct a particle-in-cell simulation reproducing triggering process of whistler-mode rising-tone emissions by injecting a wave with a fixed frequency at the equator. Rising-tone elements with multiple subpackets with monotonically increasing frequencies are generated from the triggering wave. Generation regions of the subpackets move upstream or downstream depending on the group velocities and resonance velocities for different frequencies. Because of the motion of a source region to the upstream, a long rising-tone subpacket is generated self-sustainingly through formation of an electron hole in velocity phase space stretched over the generation region. The long rising-tone subpacket is modulated with increasing magnitude, splitting into smaller subpackets through propagation. The amplitude modulations in the subpacket arise from two different processes; resonant trapping oscillation of electrons at the equatorial region and enhancement of amplitude variations through propagation in the downstream.

Automated summary

We conducted a particle-in-cell simulation to reproduce the triggering process of whistler-mode rising-tone emissions. We found that the rising-tone elements with increasing frequencies are generated through the self-sustaining formation of a long subpacket in the upstream region, which then splits into smaller subpackets during propagation.