The research team led by Prof. TAO Xin from the University of Science and Technology of China (USTC), collaborating with Prof. Fulvio Zonca from the National Agency for New Technology, Energy and Sustainable Economic Development (ENEA), Italy, and Prof. CHEN Liu from Zhejiang University, proposed a “Trap-Release-Amplify” (TaRA) model to elucidate how and where chirping occurs. This work was published in JGR Space Physics.

The chirping mechanism of chorus waves has been studied for more than half a century, and many theoretical models have been put forward. There are two chorus wave models explaining the existence and rate of chirping. One model demonstrates that the chirping rate is proportional to the background magnetic field inhomogeneity. The other model suggests that the rate is proportional to the amplitude of chorus waves. However, there are questions about the chirping process that remain to be elucidated.

The researchers in this study proposed the TaRA model based on a particle-in-cell (PIC) simulation for the rising-tone chorus with a dipole-type background magnetic field to help understand different properties of chorus.

Through computer simulations, they evaluated this model, and they elaborated fine structures of chorus waves including subpackets and bandwidth and their evolution through dynamics of phase-trapped electrons.

The results showed that TaRA could encompass both the background magnetic field inhomogeneity and wave amplitude models mentioned above, making it possible to explain various chirping phenomena reported previously.

This quantitative approach sets the stage for the future research in different properties of chorus, and can simplify the measurement of various phases in the chorus generation.

Illustration of the TaRA model. (Image by TAO Xin et al)

Paper link: https://doi.org/10.1029/2021JA029585

(Written by CAI Bohan, edited by HOU Luyao, USTC News Center)