TaRA model unifies two seemingly contradictory hypotheses

The research team led by Prof. TAO Xin from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), 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, jointly proposed a “Trap-Release-Amplify” (TaRA) model to elucidate how and where chirping occurs. This work was published in JGR Space Physics.

Researchers have studied the chirping mechanism of chorus waves for more than half a century, during which many theoretical models were put forward. But so far there is not a recognized one.

There are two chorus wave models explaining the existence and rate of chirping. One demonstrates that the chirping rate is proportional to the background magnetic field inhomogeneity. Another one suggests that the rate is proportional to the amplitude of chorus waves. However, despite the success of different models, there are still questions remain to be elucidated about the chirping process.

Based on a particle-in-cell (PIC) simulation for the rising-tone chorus with a dipole-type background magnetic field, this work proposed the TaRA model to help understand different properties of chorus. In the experiment, computer simulations were conducted to evaluate this model, further elaborating fine structures of chorus waves, including subpackets and bandwidth, and their evolution through dynamics of phase-trapped electrons.

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

This innovative quantitative approach sets the stage for the future research in different properties of chorus, which can also simplify the measurement of various phases in the chorus generation. This work is also recommended as a research spotlight of the American Geophysical Union.

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