The total electron content (TEC) measured by GPS observations from the network of International GNSS Service (IGS) at the altitude of about 450 km in the 110°E longitude sector for more than a solar cycle term from January 2000 to December 2011 are used to study the north-south asymmetry of the equatorial ionization anomaly (EIA).The parameters of the EIA crest obtained from the daytime TEC profiles for conditions of different solar activity have been used to study the solar cycle variations of EIA in the Southeast Asian region.Results show that the latitudinal position,occurrence time and strength of the EIA crest are found to be asymmetric about the magnetic equator and the conditions of solar activity have a remarkable effect on EIA crest and the north-south asymmetry.The strength of EIA crest is obviously higher during periods of high solar activity,and the TEC average value of the EIA crest is obviously higher in the northern hemisphere during the daytime in all seasonal.The strength of the north crest is higher than that of the south crest in summer and autumn during low solar activity period,while smaller in winter.During high solar activity period,the occurrence time of the northern crest appears about 1 h later than that of the southern crest from June to August.And during low solar activity period,the occurrence time of the northern crest appears about 1 h earlier than that of southern crest in winter,while about 2 h later from May to September.With the solar activity increased gradually,the mean value of asymmetry index (Ia) increased obviously during winter solstice.%利用IGS提供的太阳活动第23-24周期间2000年1月1日至2011年12月31日的GPS TEC数据,分析了东南亚地区经度110°E区域在不同的太阳活动情况下白天电离层赤道异常(EIA)各参数的南-北不对称性变化,以及不对称性随太阳活动变化的关系.结果表明:太阳活动的强弱与赤道异常双峰强度和双峰差异大小的关系明显,赤道异常双峰在驼峰强度、纬度位置和出现的时间等都有明显的季节变化特征,且有比较明显的南-北不对称性.在太阳活动高时,EIA双峰强度差异明显比太阳活动低时要大,各季节的峰值强度均值表现为北驼峰比南驼峰强,6-8月份北驼峰峰值出现的时间平均比南驼峰出现时间晚约lh.在太阳活动低时,夏季和秋季节时北驼峰比南驼峰强,秋冬季节南驼峰比北驼峰强,且冬季北驼峰出现的时间要比南驼峰早约lh,在5-9月份期间北驼峰出现的时间要比南驼峰晚约2h.随着太阳活动的逐渐升高,冬至期间不对称性指数Ia均值增大的趋势非常明显.
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