Connection Between Chorus Wave Amplitude and Background Magnetic Field Inhomogeneity: A Parametric Study

Whistler mode chorus waves frequently appear as discrete, repetitive, and quasi-monochromatic emissions with frequency chirping. With different wave amplitude and frequency chirping rate, chorus waves have been observed not only in the magnetosphere of the Earth but also in the magnetospheres of other planets, such as Saturn and Jupiter. Motivated by understanding different properties of chorus waves at these planets using the recently proposed Trap-Release-Amplify (TaRA) model, we perform a parametric study using Particle-In-Cell simulations by varying background magnetic field inhomogeneity and the corresponding threshold hot electron number density. We show the consistency between simulation results and theoretical predictions for threshold hot electron number density, chorus chirping rate, and wave amplitude. Our results suggest the significant role of the background magnetic field inhomogeneity in affecting chorus wave properties, including its amplitude at different planets as predicted by the TaRA model. As an electromagnetic wave in planetary magnetospheres, whistler mode chorus waves play essential roles in energetic electron dynamics. These waves have the distinct feature of rapid frequency variation with time, or frequency chirping, when observed. Chorus waves show different wave properties, such as wave strength and frequency chirping rate, in the magnetospheres of different planets. To understand this, we use first-principle computer simulations to investigate chorus wave generation and establish a theoretical connection between wave strength and background magnetic field nonuniformity using a recently proposed theoretical model called the Trap-Release-Amplify (TaRA) model. To simulate the magnetic field environment of different planets, we vary the background magnetic field nonuniformity between simulations. Our simulation results show good consistency with TaRA model predictions and point to a strong impact of background magnetic field nonuniformity on chorus wave properties, including both its strength and frequency chirping rate at various planets. A theoretical connection between chorus wave amplitude and background magnetic field inhomogeneity is establishedThe relation between chorus wave amplitude and chirping rate from simulation shows good agreement with the model predictionBackground magnetic field plays a significant role in shaping chorus wave properties including its amplitude

Automated summary

This study investigates the properties of whistler mode chorus waves using Particle-In-Cell simulations and a theoretical model. The results show that the background magnetic field nonuniformity plays a significant role in determining the amplitude and frequency chirping rate of chorus waves.