The magnitude and inter-hemispheric asymmetry of equatorial ionization anomaly-based on CHAMP and GRACE observations
The magnitude and inter-hemispheric asymmetry of equatorial ionization anomaly-based on CHAMP and GRACE observations
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DOI：
10.1016/j.jastp.2013.09.010
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发表时间：
2013-12
影响因子：
1.9
通讯作者：
C. Xiong;H. Lühr;S. Ma
中科院分区：
文献类型：
--
作者：
C. Xiong;H. Lühr;S. Ma
利用CHAMP和GRACE近9年（2001-2009年）的观测资料，对赤道电离异常（EIA）的形态进行了全面的研究，重点分析了EIA的大小、半球间不对称性、不同高度和太阳活动水平下的季节变化和当地时间变化。EIA的电子密度和磁纬度都在1400 LT左右达到峰值，而EIA的波峰波谷比（CTR）在日落后的2000 LT左右达到最高值，几乎是白天水平的两倍。在CHAMP高度（~400 km）的EIA磁纬度在太阳活动高和低的年份都可以在12月至日附近达到13°，而在GRACE高度（~480 km），在太阳活动低的年份可以观察到更接近倾角赤道的波峰。在高太阳活动年，EIA峰的平均顶点高度可达800 km。在夏至季节，可以看到EIA的半球间不对称性。在CHAMP高度，EIA波峰的电子密度在冬季半球的早晨到中午时间较强。在太阳活动高年和低年，它在中午后反转，转换时间分别出现在1400 LT和1200 LT左右。在高海拔地区（GRACE），EIA峰的电子密度在整个白天都是夏半球较强。SAMI 2模式的模拟结果也显示了EIA半球间不对称性在两个高度上的差异。
Based on nearly nine years (2001–2009) of observations from CHAMP and GRACE, a comprehensive study has been made on the morphology of the equatorial ionization anomaly (EIA), focusing on the EIA's magnitude, inter-hemispheric asymmetry by resolving their seasonal and local time variations at different altitudes and solar activity levels. The electron density and the magnetic latitudes of the EIA crests both peak around 1400 LT while the crest-to-trough ratio (CTR) of the EIA reaches its highest value post-sunset around 2000 LT, with a value almost twice the daytime level. The magnetic latitude of the EIA at CHAMP altitude (~400 km) can reach 13° around December solstice during both high and low solar activity years, while at GRACE altitude (~480 km) the crests are observed much closer to the dip equator during low solar activity years. During high solar activity years the averaged apex height of the EIA crests can reach 800 km. During solstice seasons a clear inter-hemispheric asymmetry of the EIA can be seen. At CHAMP altitude the electron density of the EIA crest is stronger in the winter hemisphere during morning to noontime hours. It reverses after the noontime and the transition time appears around 1400 LT and 1200 LT for high and low solar activity years, respectively. At higher altitude (GRACE), the electron density of the EIA crest is always stronger in the summer hemisphere over the whole daytime. Simulation results from the SAMI2 model also show the differences in EIA inter-hemisphere asymmetry at the two altitudes.