Magnetospheric waves and the atmosphere‐ionosphere layer
Magnetospheric waves and the atmosphere‐ionosphere layer
复制标题
磁层波和大气电离层
DOI：
10.1029/91ja02129
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发表时间：
1991
影响因子：
--
通讯作者：
M. Kivelson
中科院分区：
文献类型：
--
作者：
E. Hameiri;M. Kivelson
磁层中的磁流体波受邻近导电电离层和绝缘大气的影响。在假设磁层波长远大于电离层或大气层高度的条件下，导出了电离层的边界条件。与以前的作品，我们的边界条件表示的形式，既适用于纯阿尔芬或磁声波和完全耦合波。使用这些新的条件证明了一个精确的解决方案，在盒子模型，磁层微脉动的激发的特殊情况下。结果表明，与众所周知的观测结果相一致，共振激发的微脉动的振幅是在昼侧磁层比在夜侧大得多，因为更大的昼侧电离层电导率。我们认为，波阻尼的低电导率的夜侧电离层的效率是不是一个令人信服的解释这种现象。我们的另一种解释是，阿尔芬共振没有有效地激发电离层电导率低，因为边界条件施加不同的磁场对齐结构的压缩和横向部分的信号。这种差异随着电导率的增加而减小，从而使谐振耦合变得有效。
Hydromagnetic waves in the magnetosphere are affected by the presence of the adjacent conducting ionosphere and insulating atmosphere. Boundary conditions at the ionosphere are derived under the assumption that the magnetospheric wavelength is much larger than the height of the ionosphere or atmosphere. Unlike earlier works, our boundary conditions are expressed in a form that applies both to pure Alfven or magnetosonic waves and to fully coupled waves. The use of these new conditions is demonstrated by giving an exact solution, within the box model, to a special case of excitation of magnetospheric micropulsations. It is shown that, consistent with well-known observations, the amplitude of resonantly excited micropulsations is much larger in the dayside magnetosphere than in the nightside because of the larger dayside ionospheric conductivity. We argue that the efficiency of wave damping by the low-conductivity nightside ionosphere is not a convincing explanation of this phenomenon. Our alternative interpretation is that the Alfven resonances are not efficiently excited where the ionospheric conductivity is low because boundary conditions impose different field-aligned structure on the compressional and transverse parts of a signal. The differences diminish as the conductivity increases, allowing resonant coupling to become efficient.