ULF wave characteristics at geosynchronous orbit during the recovery phase of geomagnetic storms associated with strong electron acceleration
ULF wave characteristics at geosynchronous orbit during the recovery phase of geomagnetic storms associated with strong electron acceleration
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强电子加速地磁暴恢复阶段地球同步轨道超低频波特征
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
H. Singer
中科院分区：
文献类型：
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作者：
L. Clausen;J. Baker;J. Ruohoniemi;H. Singer
在2007年1月到2008年12月之间，我们发现了17次地磁风暴。利用粒子测量，每次风暴被划分为高通量事件或低通量事件。高通量事件是那些与地球同步轨道上相对论性电子通量增强有关的风暴，而低通量事件则没有这种增强。利用磁场资料研究了高通量风暴恢复阶段0 ~ 80mhz的超低频波特征。通过确定波的传播方向和磁扰动方向，我们能够计算出能量在环向、极向和纵波模式之间的分布。我们发现，在夜侧，大多数波能在80兆赫以下的所有频率上都是压缩的。在日侧，20 mHz以下的最低频率以压缩波能为主；环向波在20至50兆赫之间携带大部分能量，而极向波在50至80兆赫之间具有更高的功率水平。这表明，在夜侧，电子主要通过涉及压缩波模式的机制传输和激发；在白天，电子能量是通过涉及环向波和依赖于极向波和纵波的加速机制实现的。
[1] We identified 17 geomagnetic storms between January 2007 and December 2008. Using particle measurements, each storm is classified as a high-flux event or a low-flux event. High-flux events are those storms associated with enhanced flux of relativistic electrons at geosynchronous orbit, and low-flux events show no such enhancement. We study the characteristics of ultralow frequency waves between 0 and 80 mHz during the recovery phase of the high-flux storms using magnetic field data. By determining the wave propagation direction and magnetic perturbation direction, we are able to calculate how the power is distributed between toroidal, poloidal, and compressional wave modes. We find that on the nightside most wave power is compressional at all frequencies below 80 mHz. On the dayside compressional wave power dominates the lowest frequencies below 20 mHz; toroidal waves carry most energy between 20 and 50 mHz, and poloidal waves are associated with higher power levels between 50 and 80 mHz. This suggests that on the nightside electrons are predominantly transported and energized by mechanisms involving the compressional wave mode; on the dayside, electron energization is achieved by acceleration mechanisms involving toroidal waves and mechanisms dependent on poloidal and compressional waves.