Simulation of Chorus Wave Excitation in the Compressed/Stretched Dipole Magnetic Field

The properties of chorus waves have been extensively studied, which are important to understand chorus generation and wave‐particle interactions between chorus and energetic electrons. Observations reveal that there exists a distinct day‐night asymmetry for the properties of chorus waves, such as the sweep rate and duration, which is predicted to be relevant to the asymmetric configuration of Earth's background magnetic field. In this paper, using the one‐dimensional (1‐D) particle‐in‐cell (PIC) simulation model with a compressed/stretched dipole magnetic field, we study the dependences of the properties of rising‐tone chorus waves on the background magnetic field. It is demonstrated that the saturated amplitude and the chorus sweep rate increase while the chorus duration decreases with an increase of the compression factor ξ, which represents the compression/stretch degree of the field line. Moreover, the threshold of exciting chorus waves in the compressed dipole field is generally lower than that in the stretched dipole field. These results are useful to understand the chorus excitation and the day‐night asymmetry of chorus properties. Key Points A one‐dimensional particle‐in‐cell model is used to study how the configuration of the magnetic field controls the properties of chorus waves The amplitude and frequency sweep rate increase with increasing compression factor ξ, while the duration varies oppositely The threshold of exciting chorus waves is lowered by a large compression factor or a large field curvature