基于IGS台网观测的2001—2008年赤道电离异常的强度和半球不对称特征

赤道电离异常（Equatorial Ionization Anomaly，EIA）是低纬电离层中的一个重要现象.本文基于IGS台网提供的2001—2008年期间的电离层总电子含量（Total Electron Content，TEC）数据，分析了120°E区的EIA强度和磁南北半球不对称性在磁平静时期的变化特征，包括对地方时、季节和太阳活动的依赖.本文结果表明，（1） EIA强度表现出显著的随地方时和季节的变化特征.EIA强度在0200LT和2000LT附近分别出现一个极值，且2000LT附近的EIA强度更大；EIA强度通常在春/秋季较大，在夏/冬季较小，且冬季要大于夏季.（2） EIA南北半球不对称也表现出随地方时和季节变化特征.EIA半球不对称在0200LT和2000-2200LT附近分别出现一个极值；EIA半球不对称的季节变化特征还依赖于太阳活动，太阳活动高年期间，EIA半球不对称通常在春/秋季更显著；太阳活动低年期间，EIA半球不对称通常在冬季更显著.（3） EIA强度和半球不对称性的逐日变化和月变化表现出对太阳活动存在一定的依赖，但依赖性并不显著.2000LT （0200LT）附近的EIA强度的月变化与太阳活动整体呈正（负）相关，而2200LT （0200LT）附近的EIA半球不对称的月变化与太阳活动整体呈负（负）相关.（4）影响EIA强度变化的主要因素可归于纬圈电场和中性风场；影响EIA半球不对称变化的主要因素可归因为子午中性风场.

Characteristic of the Equatorial Ionization Anomaly strength and hemispheric asymmetry based on IGS network during 2001-2008

Equatorial Ionization Anomaly(EIA) is a significant phenomenon of low-latitude ionosphere. Based on ionospheric Total Electron Content (TEC) data from IGS network during 2001-2008, the characteristics of EIA strength and magnetic north-south asymmetry were studied in 120°E during magnetically quiet days, including the dependence on local time,season and solar activity. In this study, the results can be concluded:(1) EIA strength showed significant variations with local times and seasons. EIA strength reached a maximum value around 0200LT and 2000LT, respectively; and EIA strength around 2000LT was stronger than that around 0200LT. EIA strength was always stronger in spring and autumn equinox than that in summer and winter,and the strength in winter was stronger than that in summer. (2) EIA north-south asymmetry also displayed variations with local times and seasons. EIA north-south asymmetry reached a maximum value near 0200LT and 2000-2200LT, respectively; the seasonal variations of EIA asymmetry also depended on solar activity. During high solar activity, EIA north-south asymmetry was always more significant in spring and autumn; while during low solar activity, EIA north-south asymmetry was more remarkable in winter. (3) The variations of EIA strength and north-south asymmetry also depended on solar activities, though the dependences were not remarkable. There was a positive (negative) correlation between the monthly variations of EIA strength around 2000LT (0200LT) and solar activity overall, while a negative(negative) correlation between the monthly variations of EIA hemispheric asymmetry and solar activity. (4) The major factors leading to the variations of EIA strength can be attributed to neutral wind and zonal electric field; and the key factor affecting the variations of EIA hemispheric asymmetry can be attributed to meridional neutral wind.