A strong dawn/dusk asymmetry in Pc5 pulsation occurrence observed by the DE‐1 satellite
A strong dawn/dusk asymmetry in Pc5 pulsation occurrence observed by the DE‐1 satellite
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DE-1 卫星观测到的 Pc5 脉动出现强烈的黎明/黄昏不对称性
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
J. Slavin
中科院分区：
文献类型：
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作者：
M. Nosé;T. Iyemori;M. Sugiura;J. Slavin
本文利用DE-1极轨卫星的磁场观测资料，研究了内磁层横向Pc 5脉动的统计特征。发生分布被发现有很强的黎明/黄昏不对称性。在0800 - 1000 MLT之间的72°不变纬度（ILAT）附近的区域中，这种现象最常见。分布转移到较低的ILAT无论是在上午和下午部门。我们的结果是一般与以前的研究所获得的发生分布一致，除了明显的差异，在当地时间的峰值发生。横向Pc 5发生太阳风速度的依赖关系也进行了研究。结果表明，太阳风风速越大，Pc 5的出现频率越高。这一事实表明，这些Pc 5的能量来源是在磁层顶的开尔文-亥姆霍兹不稳定性（KHI）。为了解释强烈的黎明/黄昏不对称性，Pc 5发生在黄道平面上的太阳风速度和IMF之间的角度的依赖性进行了研究。发现当太阳风速度较小时，这个角度控制着Pc 5出现的磁地方时。这种依赖性可以解释的低阈值KHI由于准平行弓激波的影响。
Using the magnetic field data obtained by the DE-1 polar orbiting satellite, statistical characteristics of transverse Pc5 pulsations in the inner magnetosphere are examined. The occurrence distribution is found to have a strong dawn/dusk asymmetry. The occurrence is most frequent in the region around 72° invariant latitude (ILAT) between 0800 and 1000MLT. The distribution shifts to lower ILAT both in the early morning and in the afternoon sectors. Our results are generally consistent with the occurrence distributions obtained by previous studies except for appreciable differences in the local time of the peak occurrence. The dependence of the transverse Pc5 occurrence on solar wind velocity is also investigated. Results show that the higher the solar wind velocity, the more frequent the Pc5 occurrence. This fact suggests that the energy source of these Pc5's is in the Kelvin-Helmholtz instability (KHI) on the magnetopause. To explain the strong dawn/dusk asymmetry, the dependence of the Pc5 occurrence on the angle between the solar wind velocity and the IMF in the ecliptic plane is investigated. It is found that this angle controls the magnetic local time of Pc5 appearance when the solar wind velocity is small. This dependence may be explained by the low threshold of KHI due to an influence of a quasi-parallel bow shock.