Reflection and absorption of Alfvénic power in the low‐altitude magnetosphere
Reflection and absorption of Alfvénic power in the low‐altitude magnetosphere
复制标题
低空磁层中阿尔芬尼克能量的反射和吸收
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
W. Lotko
中科院分区：
文献类型：
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作者：
A. Streltsov;W. Lotko
本文给出了大振幅Alfven波与低空极光磁层和电离层非线性相互作用的数值研究结果。在该模型中，当携带波场定向电流密度的电子的有效平行漂移超过与电流驱动的微不稳定性开始相对应的临界阈值时，Alfven波遇到无碰撞电阻耗散。由此产生的平行电场和平行电位降引入频率、幅度和垂直长度尺度依赖于阿尔芬波能的吸收。功率流分析表明：(1)磁层中恒流源产生的、由相对小振幅、高频、短横波长Alfven波携带的大部分功率在低空被波致无碰撞电阻层（RL）反射；(2) Alfven波能主要在RL中被吸收，除非受到恒压发生器的刺激，其中电离层焦耳加热在大横向长度尺度上占主导地位；(3)恒压源条件下，在10 ~ 20 km（电离层投影）长度尺度上吸收率高（≈0.8）；(4)波致平行电位降与波场对准电流之间的关系是线性的，在大部分感兴趣的范围内，比例常数为109阶Ω-m2。证明了预测性质与卫星观测之间的对应关系。
[1] Results from a numerical study of the nonlinear interaction between large-amplitude Alfven waves and the low-altitude auroral magnetosphere and ionosphere are presented. In the model the Alfven wave encounters collisionless resistive dissipation when and where the effective parallel drift of electrons carrying the wave field-aligned current density exceeds a critical threshold corresponding to onset of current-driven microinstability. The resulting parallel electric field and parallel potential drop introduce frequency, amplitude, and perpendicular length-scale dependence in the absorption of Alfven wave power. Analysis of the power flow shows that (1) most of the power generated by a constant-current source in the magnetosphere and carried by relatively small-amplitude, high-frequency, and short transverse wavelength Alfven waves is reflected at low altitudes by the wave-induced collisionless resistive layer (RL); (2) Alfven wave power is absorbed primarily in the RL except when stimulated by a constant-voltage generator, wherein ionospheric Joule heating dominates the absorption at large transverse length scales; (3) the absorption is high (≈0.8) at length scales of 10–20 km (ionospheric projection) for constant voltage source conditions; and (4) the relation between the wave-induced parallel potential drop and wave field-aligned current is linear with proportionality constant of order 109 Ω-m2 over much of the range of interest. Correspondence between predicted properties and satellite observations is demonstrated.