Transition of Interhemispheric Asymmetry of Equatorial Ionization Anomaly during Solstices
Transition of Interhemispheric Asymmetry of Equatorial Ionization Anomaly during Solstices
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至日期间赤道电离异常的半球不对称转变
DOI：
10.1029/2018ja026055
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Qiaoling Li
中科院分区：
文献类型：
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作者：
He Huang;Xian Lu;Libo Liu;Wenbin Wang;Qiaoling Li
赤道电离异常（EIA）的两个波峰的强度随当地时间的变化而变化。冬至至日中午/午后前，冬半球的EIA峰值大于夏半球；之后，夏季半球的波峰增强，较强的EIA波峰向夏季半球过渡。利用星座观测系统的气象、电离层和气候电离层射电掩星数据，我们研究了在低/高太阳活动条件下，这种半球间转变在四个纵向扇区和七个高度的纵向和高度变化。结果表明：6月至日期间，在地磁赤道离太阳次点较远、地磁场赤纬较大的区域，冬夏半球强EIA峰值的过渡时间较早，而12月至日期间的纵向变化与6月至日相反。地磁赤道到太阳亚点的距离和地磁场结构控制着夏冬半球等离子体的上下运动，导致不同纵扇区的转变时间不同。两个至点的跃迁时间都随着高度的增加而提前，这主要是由于夏半球的有效尺度高度大于冬半球，导致高海拔电子密度差较小，跃迁速度快。太阳活动改变了320 km以下的过渡时间，而在更高的海拔上没有明显的影响。
The magnitudes of the two crests of equatorial ionization anomaly (EIA) vary with local time. During the solstices, EIA crest in the winter hemisphere is larger than that in the summer hemisphere before noon/early afternoon. Whereafter, the crest in the summer hemisphere becomes intensified, and the stronger EIA crest transits to the summer hemisphere. Using Constellation Observing System for Meteorology, Ionosphere, and Climate ionospheric radio occultation data, we examine the longitudinal and altitudinal variations of this interhemispheric transition in four longitudinal sectors and at seven heights under low/high solar activity conditions. The results show that during the June solstice the transition of the stronger EIA peak from the winter to the summer hemisphere is earlier in the sectors where the geomagnetic equator is further away from the subsolar point and the geomagnetic field declination is larger, while during the December solstice the longitudinal variations generally show the opposite compared with that in the June solstice. The distance between the geomagnetic equator and subsolar point and the geomagnetic field configuration control the upward/downward plasma movements in the summer/winter hemisphere, leading to the different transition times in different longitudinal sectors. For both solstices, transition times emerge earlier as height increases, which is mainly caused by the larger effective scale height in the summer hemisphere than in the winter hemisphere, resulting in a smaller electron density difference at higher altitudes with a fast transition. Solar activity alters the transition time below 320 km, whereas it has no evident effect at higher altitudes.