A comparative analysis of low-latitude Pi2 pulsations observed by Ørsted and ground stations
A comparative analysis of low-latitude Pi2 pulsations observed by Ørsted and ground stations
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DOI：
10.1029/2004ja010576
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发表时间：
2004-10
影响因子：
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通讯作者：
Desheng Han;T. Iyemori;M. Nosé;H. Mccreadie;Yu-fen Gao;Fuxi Yang;S. Yamashita;P. Stauning
中科院分区：
文献类型：
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作者：
Desheng Han;T. Iyemori;M. Nosé;H. Mccreadie;Yu-fen Gao;Fuxi Yang;S. Yamashita;P. Stauning
[1]Orsted是一颗低空极地轨道卫星，它有利于研究Pi2脉动等低频事件的空间结构。利用1999年4月至2002年5月在Orsted和Kakioka磁台站获得的1-S矢量磁场资料，发现Pi2脉动在卫星高度的场向分量(B∥)与地面的H分量高度相关，而另外两个分量，即向东分量(BE)和径向分量(BR)与地面观测值没有明显的相关性。夜间事件的观测结果提供了低纬地区夜间Pi2s是由空穴共振产生的证据。Orsted观测到的位于天边或天边的两个例子也显示出空腔共振特性。然而，当Orsted在白天时，卫星观测到的振荡与地面观测到的振荡是不同的，这表明白天Pi2s更可能与某些白天电离层电流系统有关，而不是由全球空腔共振模式引起的。Orsted记录的振幅变化显示在赤道区有一个峰值，这第一次为早期的模型计算提供了明显的观测支持。我们还估计了电离层对MHD波的屏蔽作用，并提出当空腔共振模式对低纬Pi2脉动的产生是有效的时，屏蔽作用可以忽略不计，也就是说，压缩波直接被视为地面的Pi2脉动。
[1] Orsted is a low-altitude polar orbiting satellite, which is advantageous for investigating the spatial structure of low-frequency events like Pi2 pulsations. Using 1-s vector magnetic field data from April 1999 to May 2002 obtained from Orsted and Kakioka magnetic observatories, we found that the field aligned component (B∥) of Pi2 pulsations at the satellite height is highly correlated with the H component on the ground, but the other two components, i.e., eastward component (BE) and radial component (BR), do not show a clear correlation with the ground observations. The observed results for nightside events provide evidence that nightside Pi2s at low latitude are generated from cavity resonance. Two cases observed by Orsted when it was located on the dawnside or duskside also show cavity resonance properties. However, when Orsted was on the dayside, the oscillations observed by the satellite are out of phase with that observed on the ground, suggesting that the dayside Pi2s are more likely related to some dayside ionospheric current systems rather than that caused by a global cavity resonance mode. The amplitude variation recorded by Orsted shows a peak in the equatorial region, which, for the first time, gives clear observational support for earlier model calculations. We also estimated the screening effect of the ionosphere on MHD waves and suggest that when the cavity resonance mode is valid for generation of Pi2 pulsations at low latitudes, the screening effect is negligible; that is, the compressional waves are seen directly as Pi2 pulsations at the ground.