Gap Formation Around 0.5Ω<sub><i>e</i></sub> of Whistler‐Mode Waves Excited by Electron Temperature Anisotropy
Huayue Chen, Xinliang Gao, Quanming Lu, K. Sauer, Rui Chen, Jiansheng Yao, Shui Wang
Abstract
Abstract With a one‐dimensional particle‐in‐cell simulation model, we have investigated the gap formation around 0.5 of the quasi‐parallel whistler‐mode waves excited by an electron temperature anisotropy. When the frequencies of excited waves in the linear stage cross 0.5 , or when they are slightly larger than 0.5 but then drift to lower values, the Landau resonance can make the electron distribution form a beam‐like/plateau population. Such an electron distribution only slightly changes the dispersion relation of whistler‐mode waves, but can cause severe damping around 0.5 via cyclotron resonance. At last, the wave spectrum is separated into two bands with a power gap around 0.5 . The condition under different electron temperature anisotropy and plasma beta is also surveyed for such kind of power gap. Besides, when only the waves with frequencies lower than 0.5 are excited in the linear stage, a power gap can also be formed due to the wave‐wave interactions, i.e., lower band cascade. Our study provides a clue to reveal the well‐known 0.5 power gap of whistler‐mode waves ubiquitously observed in the inner magnetosphere.