Triggering of Whistler‐Mode Rising and Falling Tone Emissions in a Homogeneous Magnetic Field. Issue 2 (26th January 2023)

• Record Type: Journal Article
• Authors: Fujiwara, Yuya; Omura, Yoshiharu; Nogi, Takeshi
• Is Part Of: Journal of geophysical research. Volume 128:Issue 2(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-01-26
• Subjects: whistler‐mode wave -- chorus -- particle simulation -- nonlinear process -- wave‐particle interaction -- homogeneous field; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2022JA030967
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: We perform a self‐consistent one‐dimensional electromagnetic particle simulation with a uniform magnetic field and open boundaries. The plasma environment consists of cold isotropic electrons, energetic electrons, and immobile ions. The energetic electrons are initialized with a subtracted‐Maxwellian distribution with temperature anisotropy. By oscillating external currents with a constant frequency 0.2 f ce, where f ce is the electron cyclotron frequency, a whistler‐mode wave is injected as a triggering wave from the center of the simulation system, and we investigated the process of interactions between the triggering wave and energetic electrons. We find that both rising‐tone and falling‐tone emissions are triggered through the formation of an electron hole and an electron hill in the velocity phase space consisting of a parallel velocity and the gyro‐phase angle of the perpendicular velocities. The rising‐tone emission varies from 0.2 f ce to 0.4 f ce, while the falling‐tone varies from 0.2 f ce to 0.15 f ce . The generation region of the rising‐tone triggered emission starts near the injection point of the triggering wave and moves upstream generating new subpackets. The generation region of the falling‐tone triggered emission also moves upstream generating new subpackets. The simultaneous formation of the electron hole and hill is identified by separating small and large wavenumber components corresponding to lower and higher frequencies, respectively, by applying the discrete Fourier transformation to the waveforms in space. Based on the simulation results of the whistler‐mode triggered emissions, we conclude that the mechanism of frequency variation of whistler‐mode chorus emissions works even in a uniform magnetic field. Plain Language Summary: We perform a particle‐in‐cell simulation for the generation of whistler‐mode waves in a homogeneous magnetized plasma. In addition to cold electrons supporting the propagation of whistler‐mode waves, we assume energetic electrons that can interact with the waves through cyclotron resonance. We find both rising‐tone and falling‐tone waves are excited from a triggering wave with a constant frequency. We analyze the velocity distribution function of energetic electrons and find the formation of both electron holes and hills in the velocity phase space. The mechanism of frequency variation and nonlinear wave growth of whistler‐mode chorus emissions works even in a uniform magnetic field. Key Points: Rising‐tone and falling‐tone emissions are generated simultaneously in a homogeneous magnetic field Electron holes and hills are formed in velocity phase space during the generation of rising and falling tone emissions, respectively Generation points of both emissions move upstream from the triggering wave