Observations and analysis of Alfvén wave phase mixing in the Earth's magnetosphere
Observations and analysis of Alfvén wave phase mixing in the Earth's magnetosphere
复制标题
地球磁层阿尔文波相位混合的观测与分析
DOI：
10.1029/2008ja013606
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发表时间：
2009
影响因子：
--
通讯作者：
Xinlin Li
中科院分区：
文献类型：
--
作者：
T. Sarris;A. Wright;Xinlin Li
(1)提出了地球磁层中Alfven波相位混频的特征，并与理论进行了比较，该特征表现为一个横向的Pc5磁层脉动的偏振旋转。极化旋转发生在1997年11月24日至30日连续5天的罕见日侧窄带极低频磁层脉动期间；Sarris等人（2009）通过地球同步轨道和地面观测报告了这一事件的细节。在本文中，我们通过对其横向分量的详细分析来研究脉冲的偏振特征。洛斯阿拉莫斯国家实验室（Los Alamos National Laboratory， LANL）的L壳最接近GOES-8的航天器之一的密度测量用于计算地球同步轨道上的场线共振频率；这些频率计算与观测到的脉动很好地吻合，但也有局部时间偏移。对于观测到的极化旋转的一个实例，我们通过极向和环向振幅相等的时间来估计观测到的脉动的极向寿命，我们将其与Mann和Wright（1995）在箱型磁层模型中计算的极向寿命的理论近似进行比较。利用地球同步轨道上不同LANL航天器的密度测量值及其由不同的局部时间推导出的不同的L壳来估计局部Alfven速度的局部梯度，然后将其用于预测极向寿命的计算。这是第一次直接观察到这种极化旋转，并与理论预测进行了比较。
(1) Signatures of Alfven wave phase mixing in the Earth's magnetosphere, observed as polarization rotation of a transverse, Pc5 magnetospheric pulsation, are presented and compared to theory. The polarization rotation occurred during a rare event of a dayside narrowband ULF magnetospheric pulsation that lasted for 5 consecutive days, from 24 to 30 November 1997; details of this event were reported by Sarris et al. (2009) through observations at geosynchronous orbit and on the ground. In this paper we investigate the polarization signatures of the pulsation by performing a detailed analysis of its transverse components as observed through hodogram plots. Density measurements from one of the Los Alamos National Laboratory (LANL) spacecraft which had its L shells closest to GOES-8 are used to calculate field line resonance frequencies at geosynchronous orbit; these frequency calculations show good agreement with the observed pulsations but also have a local time offset. For an instance of an observed polarization rotation we estimate the observed poloidal lifetime of the pulsation by the time taken for the poloidal and toroidal amplitudes to become equal, which we compare with the theoretical approximation to the poloidal lifetime, as calculated in a box model magnetosphere by Mann and Wright (1995). Density measurements from different LANL spacecraft at geosynchronous orbit and their varying L shells as derived from their varying local times are used to estimate a local gradient in the local Alfven speed, which is then used in the calculation of the predicted poloidal lifetime. This is the first time that such polarization rotations are directly observed and compared with theoretical predictions.