Toward an Integrated View of Ionospheric Plasma Instabilities: 4. Behavior in the Transitional Valley Region
Toward an Integrated View of Ionospheric Plasma Instabilities: 4. Behavior in the Transitional Valley Region
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DOI：
10.1029/2019ja027303
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发表时间：
2019-11
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影响因子：
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通讯作者：
R. Makarevich
中科院分区：
文献类型：
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作者：
R. Makarevich
分析了法利-布尼曼不稳定性（FBI）和梯度漂移不稳定性（GDI）产生的不稳定等离子体波在海拔120 km附近的过渡谷区的行为。该分析基于FBI/GDI增长率γ的表达式，该表达式最近被推广到在流体和局部方法所施加的限制范围内，包括任意高度和波长的离子惯性效应。当对流分量介于由离子声速Cs和离子碰撞与陀螺频率之比ri决定的两个临界值之间时，离子惯性导致了不同的不稳定行为。最有趣的情况发生在120公里附近，就在ri=1的下面。从电子密度梯度G=∇n/n导致的边缘不稳定条件γ=0（即临界梯度G0）的分析可知，存在一个G0=0的临界尺度，在该尺度下所有波对FBI都是不稳定的。在这个尺度以上，梯度需要足够强才能使等离子体通过GDI变得不稳定。依赖性也存在最大值G0λ，即最小的不稳定尺度和梯度。对于规定范围以外的对流，不存在临界尺度或最小不稳定尺度，这是过渡谷区以外的典型情况。总体而言，分析表明，离子惯性对FBI对流阈值和GDI临界梯度有一定的影响，且在120 km附近的过渡谷区影响最为明显。
Behavior of unstable plasma waves generated by the Farley‐Buneman instability (FBI) and the gradient drift instability (GDI) is analyzed in the transitional valley region near 120 km in altitude. The analysis is based on the expression for the FBI/GDI growth rate γ that has been recently generalized to include ion inertia effects for arbitrary altitude and wavelength, within the limits imposed by the fluid and local approaches. It is found that the ion inertia leads to a different instability behavior when the convection component is between the two critical values determined by the ion acoustic speed Cs and the ratio ri between the ion collision and gyrofrequency. The most interesting case occurs near 120 km, just below where ri=1. From analysis of electron density gradients G=∇n/n that result in marginal instability condition γ=0 (i.e., critical gradients G0), there exists a critical scale where G0=0 and below which all waves are unstable to FBI. Above this scale, G0>0 and gradients need to be sufficiently strong G>G0 for the plasma to become unstable through GDI. There also exists a maximum in dependence G0λ , which refers to the least unstable scale and gradient. For convection outside of the specified range, no critical or least unstable scale exists, which is a typical situation outside of the transitional valley region. Overall, this analysis shows that the FBI convection thresholds and the GDI critical gradients are modified by the ion inertia and that the effects are most pronounced in the transitional valley region near 120 km.