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Whistler Mode Waves Excited by Anisotropic Hot Electrons With a Drift Velocity in Earth's Magnetosphere: Linear Theory
Journal of Geophysical Research: Space Physics ( IF 2.8 ) Pub Date : 2020-08-06 , DOI: 10.1029/2020ja028149
Kai Fan 1, 2 , Jicheng Sun 3 , Jun Guo 4
Affiliation  

With a linear theoretical model, we have investigated the properties of whistler waves excited by anisotropic hot electrons with a drift velocity parallel to the background magnetic field, which is usually neglected in previous studies. It is found that a finite drift velocity can significantly change the properties of excited whistler waves, resulting in distinct properties for parallel and antiparallel propagating waves. In the high‐beta regime, as the drift velocity increases, the frequency of parallel propagating whistler waves increases, while that of antiparallel propagating waves is found to decline. So parallel and antiparallel propagating whistler waves appear in different frequency bands. However, the growth rate of parallel wave is always smaller than that of antiparallel wave and falls below 10−2Ωe for large drift velocities (vd/vth > 1.5), in which case the parallel wave may be too weak to be observed. Generally, the growth rate of whistler waves in both directions is enhanced with the increasing anisotropy or proportion of hot electrons. In the low‐beta regime, the trends of the frequency and linear growth rate of excited whistler waves are quite similar to those in the high‐beta regime. But with the increase of the drift velocity, the wave normal angle of parallel propagating whistler waves gradually declines until reaching 0, while that of antiparallel propagating waves continues to increase. Our study may be helpful to understand various whistler mode spectra observed in the Earth's magnetosphere.

中文翻译:

地球磁层中具有漂移速度的各向异性热电子激发的惠斯勒模式波:线性理论

利用线性理论模型,我们研究了各向异性热电子激发的哨声波的特性,其漂移速度平行于背景磁场,而这在以前的研究中通常被忽略。发现有限的漂移速度可以显着改变激发的惠斯勒波的特性,从而导致平行传播波和反平行传播波具有明显的特性。在高贝塔状态下,随着漂移速度的增加,平行传播的哨声波的频率增加,而反平行传播的哨声波的频率下降。因此,平行和反平行传播的惠斯勒波出现在不同的频带中。但是,平行波的增长率始终小于反平行波的增长率,并且低于10 -2Ω Ë对于大漂移速度(v d / v > 1.5被观察到的),在这种情况下,平行波可能太弱。通常,随着各向异性或热电子比例的增加,双向吹哨声的增长率会提高。在低β状态下,激发的哨声波的频率和线性增长率的趋势与高β状态下的趋势十分相似。但是随着漂移速度的增加,平行传播的惠斯勒波的波法向角逐渐减小直至达到0,反平行传播的惠斯勒波的波法向角继续增大。我们的研究可能有助于理解在地球磁层中观察到的各种惠斯模式频谱。
更新日期:2020-08-14
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