Hybrid Kelvin‐Helmholtz/Rayleigh‐Taylor instability in the plasma sheet
Hybrid Kelvin‐Helmholtz/Rayleigh‐Taylor instability in the plasma sheet
复制标题
等离子体片中的混合开尔文-亥姆霍兹/瑞利-泰勒不稳定性
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
Tetsuya T. Yamamoto
中科院分区：
文献类型：
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作者：
Tetsuya T. Yamamoto
[1]本文推广了磁层-电离层（M-I）耦合系统中混合Kelvin-Helmholtz/Rayleigh-Taylor（KH/RT）不稳定性的线性分析，该线性分析在Lky = 2的长波极限下是有效的，其中ky是方位波数，L是方位速度或能量密度的纬向剖面的标度长度.对于第一次，混合波的线性增长率分布可以揭示在一个基本上整个范围内的ky。当能量密度的梯度指向内部（朝向内部磁壳层）时，在ky：0 < Lky < m的一定范围内，混合生长速率是正的（意味着生长）。当惯性弛豫速率v接近零时，增长速率曲线接近于m = 2时的KH“谱”，其中v = P/Cm，即磁层等离子体的惯性电容与电离层中高度积分的彼得森电导率之间的比值。在背景流中没有速度切变时，谱大大展宽，即出现RT谱。的混合增长率示出有相应的KH和RT的“根”不稳定性的两个之间的光谱中间。还发现，静电KH不稳定性完全抑制时，KH增长率，估计不包括M-I耦合，小于v，这是一个简单的扩展，以前的工作。在Tsyganenko模型中Cm的评估的基础上，静电波（在电离层高度波长大于几十公里）是不可能增长的KH不稳定性单独在夜间等离子体片。相反，混合波可以在粒子能量密度具有向内梯度的地方生长。这一事实可以解释为什么在夜间椭圆的高纬度部分经常出现周期性的极光光度，以及通常在亚暴的恢复阶段形成欧米茄带。
[1] This paper is to generalize the previous linear analysis of the hybrid Kelvin-Helmholtz/Rayleigh-Taylor (KH/RT) instability in a system of the magnetosphere-ionosphere (M-I) coupling, which is valid in the long-wavelength limit of Lky ≪ 2, where ky is the azimuthal wave number and L stands for the scale length of a latitudinal profile in azimuthal velocity or energy density. For the first time, the linear growth rate profile of a hybrid wave can be revealed in an essentially overall range of ky. When the gradient of the energy density is directed inward (toward inner magnetic shells), the hybrid growth rate is positive (meaning growth) in a certain range of ky: 0 < Lky < m. As the inertial relaxation rate v approaches zero, the growth rate curve is close to the KH “spectrum” with m = 2, where v ≡ ΣP/Cm, the ratio between the inertial capacitance of the magnetospheric plasma and the height-integrated Pedersen conductivity in the ionosphere. Without a velocity shear in the background flow, the spectrum much broadens, namely, the RT spectrum appears. The hybrid growth rate is shown to have a spectrum intermediate between the two ones of the corresponding KH and RT “root” instabilities. It is also found that the electrostatic KH instability is completely suppressed when the KH growth rate, estimated excluding the M-I coupling, is less than v, which is a straightforward extension of that previous work. On the basis of the evaluation of Cm in the Tsyganenko model, electrostatic waves (with wavelengths greater than a few tens of kilometers at the ionospheric height) are unlikely to grow by the KH instability alone in the nighttime plasma sheet. Instead, hybrid waves can grow at the places where the particle energy density has an inward gradient. This fact may account for the frequent appearance of periodic auroral luminosity in a high-latitude part of the nighttime oval as well as the formation of omega bands typically in the recovery phase of a substorm.