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Abstract:
With a one‐dimensional particle‐in‐cell simulation model, we have investigated the gap formation around 0.5Ωe of the quasi‐parallel whistler‐mode waves excited by an electron temperature anisotropy. When the frequencies of excited waves in the linear stage cross 0.5Ωe, or when they are slightly larger than 0.5Ωe 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 0.5Ωe via cyclotron resonance. At last, the wave spectrum is separated into two bands with a power gap around 0.5Ωe. 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 0.5Ωe 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 0.5Ωe power gap of whistler‐mode waves ubiquitously observed in the inner magnetosphere.
