【作者】 阿尔察； 张东和； 肖佐；

【机构】 北京大学地球与空间科学学院空间物理与应用技术研究所；

【摘要】 本文运用经验正交函数分析法(EOF)对美国喷气动力实验室(JPL)计算的1999～2009年的全球电离层总电子含量TEC进行经验建模。经验正交函数分解所得的基函数和对应的系数可以反映太阳辐射,地磁活动等因素对电离层总电子含量TEC的影响。正交经验函数分解的快速收敛性使得我们只需要前四阶基函数和对应系数就可以表征原始TEC数据98%以上的的变化特征。其中基函数可以反映出TEC的空间上的全球经纬度分布特征和时间上的周日变化、半球不对称和赤道异常等特点;系数可以反映出原始TEC数据随时间的较长周期变化。第一阶EOF系数A1主要反映原始TEC数据中随太阳长周期变化的成分,并同时叠加有较明显的半年变化和较弱的年变化成分;第二阶EOF系数A2主要包含原始TEC数据的年变化成分;第三阶EOF系数A3主要包含原始TEC数据的年变化和半年变化成分;第四阶系数主要反映原始TEC数据中季节变化和更小尺度的变化。我们采用能体现太阳周期变化的F10.7辐射通量,反映半年(季节)变化的Ap指数,反映低纬和高纬地磁活动的Dst和AE指数的线性和三角函数的组合来拟合经验正交函数分解后的系数并最终建立电离层总电子含量TEC的全球经验模型。通过模型与实测数据的比较和检验,我们发现利用经验正交函数建立的TEC的经验模型可靠性高,与实测值符合度较好,能够反映出TEC全球分布的主要变化和时空分布特征。更多还原

【Abstract】 An empirical orthogonal function analysis method is used to construct global empirical model for the ionospheric vertical TEC using the Global Ionospheric Maps (GIMs) provided by the Jet Propulsion laboratory (JPL) during the years 1999~2009. The influence of solar radiation and geomagnetic activity toward ionospheric vertical TEC can be well indicated by the characteristics of the base functions and corresponding coefficients which are acquired from the empirical orthogonal decomposition of the GIMs. The essential feature of the global latitudinal-longitudinal distribution and the nature of diurnal variation, hemispheric asymmetry and equatorial anomaly of the original TEC data can be well reflected from the EOF base functions. While the EOF coefficients can represent the long-term alteration tendency of original TEC data. The quick convergence of EOF decompositions made it possible to use the first 4-order EOF series to represent the 98% of the characteristics of the variation of the original TEC data. The 1st order EOF coefficient A1 can reflect the feature of the components with solar cycle variation. An evident semi-annual variation components as well as relatively weak annual fluctuation components are also included in A1 though they are not as prominent as the solar cycle variation due to the overlapping. The 2nd order coefficient A2 contains mainly annual variation components. The 3rd order coefficient A3 contains both annual and semi-annual variation components. The seasonal variation and the small-scale irregularities are included in the 4th order coefficient A4. The amplitude range and developing tendency of all these coefficients are depending on the level of solar activity and geomagnetic activity. Here we use a combination of linear and trigonometric functions of F10.7, Ap, Dst and AE index to express the solar cycle, semiannual (seasonal), equatorial and polar variations in which the EOF coefficients can be fitted and the global TEC model can be constructed. The reliability and validity of EOF model are verified by comparison with observational data. The agreement between observations and EOF model is quite well, indicating that the EOF model can reflect the major changes and the spatial-temporal distribution characteristics of the global ionospheric TEC.更多还原