Fig. 4
From: Origin of two-band chorus in the radiation belt of Earth
Simulation of chorus wave excitation and the concurrent electron PSD variation. a The initial electron PSD versus energy at selected pitch angles, showing a cold isotropic population extending to ~100 eV and a warm anisotropic population above ~ 300 eV. b The wave magnetic spectral intensity for each (ω, k) mode obtained by Fourier transformation of the magnetic field over T = 50–100 τgyro (electron gyro-period), showing a continuous one-band spectral structure, while the excitation of upper-band chorus is faster. c The electron PSD at T = 150 τgyro, showing a notable parallel acceleration at ~2–3 keV, which is around the Landau resonant energies of the chorus waves. d As the chorus waves at both bands continues to grow, the wave intensity at 0.5 fce is notably weaker than the two bands, due to the reduce anisotropy at ~2–3 keV. e At T = 800 τgyro, the electron PSD exhibits two distinct anisotropic components, separated by the electrons that have undergone parallel acceleration by chorus waves. f The resultant two-band chorus waves with a gap at 0.5 fce. The upper-band chorus grows from the ~1 keV anisotropic component, and the lower-band chorus grows from tens of keV anisotropic component
