On the spectrum of magnetosonic eigenoscillations of an axisymmetric magnetosphere
On the spectrum of magnetosonic eigenoscillations of an axisymmetric magnetosphere
复制标题
轴对称磁层磁声本征振荡频谱
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
V. A. Mazur
中科院分区：
文献类型：
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作者：
A. Leonovich;V. A. Mazur
在WKB近似下，确定了轴对称磁层沿磁壳方向的磁声本征振荡结构。数值研究了它们的本征频率谱。介质模型假定为偶极磁场，并考虑了等离子体层顶和磁层顶的阿尔芬速度突变，介质的本征频率为复值。频率的虚部是本征振荡的阻尼衰减，与它们的一些能量逃逸到太阳风有关。结果表明，在磁力线向坐标原点集中的类偶极地磁场中，磁声振荡的振幅从磁层顶到电离层逐渐增大。虽然从太阳风穿透到磁层深处或在磁层边界产生的振荡在磁层顶附近的振幅相对较小，但随着接近地球，由于几何原因，其振幅可达到相当大的值。
The structure of magnetosonic eigenoscillations of an axisymmetric magnetosphere in the direction across magnetic shells was determined within the WKB approximation. The spectrum of their eigenfrequencies was investigated numerically. The model of the medium assumes a dipole magnetic field and a two-dimensional Alfven velocity distribution in the meridional plane which takes into account abrupt changes of the Alfven velocity at the plasmapause and magnetopause, It is shown that eigenfrequencies are complex valued. The imaginary part of the frequency is a damping decrement of the eigenoscillations associated with the escape of some of their energy to the solar wind. It is shown that in a dipole-like geomagnetic field in which field lines concentrated toward the origin of coordinates, the amplitude of magnetosonic oscillations increases from the magnetopause to the ionosphere. While the oscillations penetrating deep into the magnetosphere from the solar wind or generated at the magnetospheric boundary have near the magnetopause a relatively small amplitude, as the Earth is approached, their amplitude can reach a significant value for geometrical reasons.