北美与东亚中纬地区电离层TEC变化的EOF建模和分析

Comparison of Ionospheric Total Electron Content over North America and East Asia with EOF Analysis

考察了北美(30°N—50°N,140°W—50°W)与东亚(42.5°N—57.5°N,65°E—140°E)中纬地区电离层总电子含量(TEC)的变化.TEC数据来自美国喷气动力实验室(JPL)约15年的全球电离层图(Global Ionospheric Map,GIM)数据.利用经验正交函数(Empirical Orthogonal Functions,EOF)得到上述两地区前三阶本征模及相关时间系数,分别约占TEC总变化的99.57%和99.79%.结果表明,两地区前三阶:EOF分量所表现出的TEC变化基本一致.第一阶EOF分量表现为受太阳活动调制的半年变化;第二阶EOP、分量表现为关于零磁偏线的经向电子浓度东西不对称结构,计算表明该结构与受地磁偏角控制的热层纬向水平风引起的等离子体向上漂移密切相关;第三阶EOF分量表现为磁倾控制的热层子午向风引起的等离子体向上漂移影响.

In the present work,variations of ionospheric Total Electron Content(TEC) are investigated and compared with applying Empirical Orthogonal Functions(EOF) on the dataset from the Global Ionospheric Maps(GIMs) which are produced by Jet Propulsion Laboratory(JPL) over two concerned areas:the North America(30°N-50°N,140°W-50°W) and East Asia(42.5°N-57.5°N,65°E-140°E).The first three EOF components attribute about 99.57%and 99.79%to the total variations separately,and spatial-temporal features manifested by each EOF components are similar for the two areas:the first order EOF component for both areas represents semiannual variation which is strongly modulated by the solar activity;the second order component exhibits pronounced east-west longitude difference to the zero valued geomagnetic declination line,and these east-west longitude differences are coincidently consistent with plasma drift velocity caused by thermospheric zonal wind;the third order component demonstrates latitudinal variations possibly influenced by plasma drift velocity caused by thermospheric meridional wind.Results of the this paper are useful for understanding the physics mechanism of the ionospheric variations.