基于经验正交分析法的暴时热层大气密度时空分布规律

本文选取2002-2006年期间的36个强磁暴为研究对象,对CHAMP卫星加速度仪反演的实测大气密度进行经验正交分解,研究暴时热层大气密度的纬度分布特征,以及大气密度与ap指数、Dst指数的关系.结果表明,大气密度的纬度分布与季节相关,夏季半球的密度大于冬季半球,春秋季节南北半球的大气密度几乎对称分布;春秋季节白天大气密度在低纬地区呈现出赤道密度异常结构,在中高纬地区密度随纬度增加而减小,夜间则呈现抛物线的形状,赤道附近密度值最小.大气密度的纬度分布特征在若干天内具有良好的稳定性,发生时间相近的磁暴事件,纬度分布曲线非常相似,并且暴前与暴时的纬度分布变化不大.相关性分析表明,大气密度滞后ap指数2~6 h,相对Dst指数平均提前0~1 h,对磁暴的响应速度在日照区比在阴影区快,大气密度与ap指数、Dst指数具有较好的相关性.

Thermospheric density during geomagnetic storm based on EOF analysis

The Empirical Orthogonal Function (EOF) analysis has been applied to study the thermospheric density at 400 km height with accelerometer data from CHAMP satellite during geomagnetic storm from 2002-2006. The global latitudinal distribution of thermospheric density on storm-time is investigated. Additionally, the relations of density and ap index, as well as Dst index are analyzed. The results show that thermospheric density has strong seasonal dependence in latitude variation. Summer hemisphere density is larger than that in winter hemisphere, whereas in spring and autumn density is symmetrical in northern and southern hemisphere. On the dayside of spring and autumn, there exists a structure of double crests at low latitude which is known as Equatorial Mass density Anomaly (EMA). Moreover, at mid- and high-latitude, density decreases as the latitudes change from low to high. On the night side, density distribution has a profile of parabola with the minimum amplitude near equator. The characteristic of density latitudinal distribution is steady in several days, which leads to similar distribution curves of different storms occurring at close times. Furthermore, the variation of density latitudinal distribution from pre-storm to storm time is small. By correlation analysis it is found that the change of density lags behind ap index by 2~6 hours and before Dstindex 0~1 hour. In addition, thermospheric density response to geomagnetic storm on the dayside is faster than on the night side. Density has close correlation with ap index and Dst index.