Abstract
Abstract We study frequency variation of a coherent whistler-mode wave in a homogeneous magnetic field by a selfconsistent simulation model. Simulation results show that an injected whistler-mode wave packet grows due to an instability driven by temperature anisotropy and the amplified wave packet triggers emissions with frequency shift during its propagation. We clarify that the resonant currents J E and J B due to the nonlinear wave-particle interaction play significant roles in both wave growth and frequency variation. Based on the simulation results, we show that the range of the frequency shift in a homogeneous system is quantitatively estimated by the trapping frequency V T of trapped electrons; in a case that the original frequency of the wave packet is 0.62Ωe and V T=4.05 × 10−2 c, the lower and upper frequencies are estimated to be 0.565Ωe and 0.685Ωe, respectively. The results of the present study reveal that the role of nonlinear trapping is significant in the elementary process of VLF triggered emissions in the equatorial region of the magnetosphere.
Highlights
We often realize that the Earth’s magnetosphere is a natural laboratory for studying plasma physics
We study frequency variation of a coherent whistler-mode wave in a homogeneous magnetic field by a selfconsistent simulation model
Based on the simulation results, we show that the range of the frequency shift in a homogeneous system is quantitatively estimated by the trapping frequency VT of trapped electrons; in a case that the original frequency of the wave packet is 0.62 e and VT = 4.05 × 10−2c, the lower and upper frequencies are estimated to be 0.565 e and 0.685 e, respectively
Summary
We often realize that the Earth’s magnetosphere is a natural laboratory for studying plasma physics. We study frequency variation of a coherent whistler-mode wave in a homogeneous magnetic field by a selfconsistent simulation model. Omura and Matsumoto (1985) performed a simulation study on the frequency variation of a wave packet in a uniform magnetic field and showed that the frequency rising of a triggered emission occurs after slight decrease of wave frequency due to the positive resonant currents JB formed by trapped electrons.
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