资源环境科技发展态势分析平台

Chorus waves are coherent electromagnetic emissions in the inner magnetosphere, generally composed of a series of discrete and repetitive elements. These elements usually have rising frequency chirpings, which are occasionally mingled with one or several elements with a hooked spectrogram. In this letter, we perform a one-dimensional general curvilinear particle-in-cell (gcPIC)- simulation of chorus waves excited by temperature anisotropic electrons in a dipole magnetic field, and identify one chorus element with a hooked spectrogram, which is embedded in several chorus elements with a rising frequency chirping. In the hooked chorus element, the frequency increases firstly, and then decreases. Interestingly, we find that there are clear electron holes in the electron velocity space, no matter whether the chorus element has a rising-tone or hooked-tone spectrogram. Our study presents an important clue for the theoretical analysis of the frequency chirping in the chorus waves.