Geomagnetic negative sudden impulses: Interplanetary causes and polarization distribution
Geomagnetic negative sudden impulses: Interplanetary causes and polarization distribution
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DOI：
10.1029/2001ja900152
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发表时间：
2002-07
影响因子：
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通讯作者：
T. Takeuchi;T. Araki;A. Viljanen;J. Watermann
中科院分区：
文献类型：
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作者：
T. Takeuchi;T. Araki;A. Viljanen;J. Watermann
[1] 我们利用 Wind 和 ACE 航天器的数据，研究了中纬度地磁 SYM 指数中识别的地磁负突发脉冲 (SI−s) 的特征以及太阳风的致病结构。 1995 年至 1999 年期间，总共发现了 28 个 H 分量 SYM 指数中幅度大于 20 nT 的 SI−，其中 50% 与正突然脉冲 SI+（即 SI 对）一起发生。在 SI 对中，SI− 的幅度几乎总是大于前面的 SI+ 的幅度。我们首次尝试对太阳风中与 SI−s 相关的结构进行分类。研究发现反向冲击并不是造成 SI−s 的原因。相反，SI−s 与各种结构相关，例如高低速流界面处的切向不连续性、行星际磁云的前边界以及日光层等离子体片的后缘。我们的样本中的 SI−s 与任何特定类型的太阳风结构没有优先关联。我们统计研究了高纬度 SI−s 的偏振特性。极光带的偏振方向下午呈顺时针方向，上午呈逆时针方向。极帽中的旋转方向相反。纬度反转发生在65°至80°范围内。因此SI−的极化分布与SI+的极化分布不是相反而是一致的。我们认为，双涡旋电离层流系统的纵向运动对产生 SC 和 SI− 的极化起主导作用。
[1] We made a study of the characteristics of geomagnetic negative sudden impulses (SI−s) identified in the midlatitude geomagnetic SYM indices and the causative structures in the solar wind using data from the Wind and ACE spacecraft. A total of 28 SI−s with an amplitude larger than 20 nT in the H component SYM index were found over the period 1995 through 1999, with 50% of them occurring in conjunction with a positive sudden impulse, SI+ (i.e., SI pair). In the SI pairs the amplitude of SI− was almost always larger than that of the preceding SI+. We attempted for the first time a classification of structures in the solar wind associated with SI−s. It is found that reverse shocks are not responsible for SI−s. Instead, SI−s are associated with varied structures such as tangential discontinuities at high-low speed stream interfaces, front boundaries of interplanetary magnetic clouds, and trailing edges of heliospheric plasma sheets. There is no preferential association of SI−s in our sample with any particular type of solar wind structure. We investigated statistically the polarization characteristics of SI−s at high latitude. The sense of the polarization in the auroral zone tended to be clockwise in the afternoon and counterclockwise in the morning. The rotational sense reversed in the polar cap. The latitudinal reversal occurred in the range from 65° to 80°. Thus the polarization distribution of SI− is not opposite to but is consistent with that of SI+. We suggest that the contribution from the longitudinal movement of a twin vortex ionospheric current system is dominant to produce the polarization of SC and SI−.