基于CHAMP卫星观测数据对热层大气密度的经验正交分析

对2003年(太阳活动较高年)至2007年(太阳活动低年)CHAMP卫星的热层大气密度观测数据进行了经验正交函数(EOF)分析,得到了400 km高度上白天平均大气密度ρ的太阳活动周变化与年度变化等不同变化分量.研究结果表明,ρ受太阳活动影响较大,其太阳周变化分量与F_(10.7)指数变化之间的相关系数可高达94.5%;ρ的太阳周变化分量随纬度增加而减小,且在中高纬地区,南半球的值明显大于北半球的值,在低纬地区则出现基本对称的双峰分布,即赤道质量密度异常(EMA)结构.在ρ的年变化中,呈现出明显的季节变化,即夏季低冬季高;同时ρ的年变化幅度随太阳活动增加而增强,随纬度增加而增强.将本文结果与经验模式NRLMSISEOO在观测条件下的输出数据进行对比,发现两者的太阳周变化与年变化分量基本一致,但本文观测数据的太阳周成分随纬度变化略小,年变化幅度略大,且NRLMSISEOO模式不能再现EMA结构.研究结果对揭示热层气候学变化特征具有重要意义.

Empirical Orthogonal Function (EOF) Analysis on the Thermospheric Total Mass Density Retrieved From CHAMP Observation

The Empirical Orthogonal Function (EOF) analysis was applied to study the thermo-spheric total mass density at the altitude of 400 km with the data obtained from German CHAMP satellite during the interval from 2003 to 2007, when the solar activity is in declining period. The solax cycle and yearly variations of the thermospheric total mass density p are obtained. It is found that the total mass density p was obviously affected by the solar activity, the correlation coefficient between solar cycle variation component of p and F10.7 index can reach 94.5%. At the mid-and high-latitudes, the amplitude of solar cycle variation is larger in the south hemisphere than in the north. The amplitude of the solar cycle variation is decreased as the latitudes change from low to high. At low latitudes there exists a structure of double crests which is recently known as the Equatorial Mass density Anomaly (EMA). In the yearly variation of the total mass density, there is a seasonal variation that the density is larger in summer than in winter. The amplitude of the yearly variation of density p increases with solar .F10.7 index as well as the absolute latitude. Comparing the result of CHAMP data with the output of NRLMSISEOO model under the input of the same condition of observation, it is found that both the solar cycle and the yearly variations of thermo-spheric total mass density are in good agreement. Even though, the latitude difference of the solar cycle variation of p is a little bigger from NRLMSISEOO than CHAMP data and there is no EMA structure in NRLMSISEOO model. Furthermore, there is an obvious semiannual variation component while analyzing the NRLMSISEOO data without 130-day-wide sliding window. Thus it is considered that, with the restriction of CHAMP orbit, the 130-day-wide sliding window may smooth out the semiannual component, as well as the higher. It is concluded that the present results are meaningful in the study of the thermospheric climatology.