Occurrence Rates and Variability of Whistler-Mode Waves in the Plasma Trough

IF 2.9 2区 地球科学 Q2 ASTRONOMY & ASTROPHYSICS
C. E. J. Watt, N. P. Meredith, J. Wong, K. R. Murphy, I. J. Rae, S. Chakraborty, S. N. Bentley, O. Allanson, C. J. Rodger
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Abstract

Numerical models of energetic electron behavior in the outer radiation belt require descriptions of the wave-particle interactions across the inner magnetosphere. Quasilinear diffusion coefficients describe gyro-resonant wave-particle interactions over large time- and length-scales but these must be constrained by observations to construct realistic radiation belt models. Recent work indicates the importance of identifying and including realistic spatiotemporal variation of diffusion coefficients. In this paper, we study the spatiotemporal variability of whistler-mode waves outside the plasmasphere, typically referred to as whistler-mode chorus. We separately consider the probability of (a) parts of the model domain being outside the plasmasphere, and (b) the probability of detecting wave activity should that part of the model domain be outside the plasmasphere. We discover that the spatiotemporal variability of whistler-mode waves significantly differs across the model domain; we propose that wave power variability in short wave intervals ( 5 ${\sim} 5$ min) is a useful characteristic to distinguish between two types of whistler-mode waves, especially where their frequency ranges overlap. Our novel spatiotemporal variability analysis indicates that low variability waves are dayside exohiss whose typically high occurrence rate ( 0.8 ${\sim} 0.8$ ) decreases with substorm activity, and high variability waves are sporadic post-midnight/dawn sector substorm-driven chorus with a typical occurrence rate of 0.2. Further, although previous studies often combine the occurrence rates and wave characteristics into climatological averages of chorus wave power, this study highlights the importance of separating the study of occurrence rates and power of the waves, since each can have a different relationship with driving factors.

Abstract Image

等离子体槽中哨声模式波的发生率和变异性
外辐射带高能电子行为的数值模型需要描述波粒在内磁层的相互作用。准线性扩散系数描述了大时间和长度尺度上的回旋共振波粒相互作用,但这些必须受到观测结果的约束才能构建真实的辐射带模型。最近的工作表明,识别和包括扩散系数的现实时空变化的重要性。在本文中,我们研究了等离子体层外哨声模式波的时空变异性,通常被称为哨声模式合唱。我们分别考虑(a)部分模型域在等离子体层外的概率,以及(b)当该部分模型域在等离子体层外时探测到波活动的概率。我们发现哨声模波的时空变异性在不同的模式域中有显著差异;我们提出,短波间隔(~ 5$ {\sim} 5$ min)的波能变化是区分两种类型的哨声模式波的有用特征,特别是在它们的频率范围重叠的地方。我们的新时空变异性分析表明,低变异性波是白天侧的逸出波,其典型的高发生率(~ 0.8$ {\sim} 0.8$)随着亚暴活动而降低,而高变异性波是子夜/黎明扇区亚暴驱动的零星齐声波,典型的发生率为0.2。此外,尽管以前的研究经常将发生率和波浪特征结合到合唱波浪功率的气候平均值中,但本研究强调了将波浪的发生率和功率研究分开的重要性,因为两者与驱动因素之间可能存在不同的关系。
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来源期刊
Journal of Geophysical Research: Space Physics
Journal of Geophysical Research: Space Physics Earth and Planetary Sciences-Geophysics
CiteScore
5.30
自引率
35.70%
发文量
570
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