中文摘要：

本文尝试利用COSMIC低轨卫星对GPS信号的顶部TEC观测资料研究等离子体层电子含量（简称PEC）的变化规律.首先介绍从低轨卫星对GPS的顶部TEC观测资料提取等离子体层垂直电子含量的方法,然后利用该方法提取2008年全年的PEC数据,进而研究了2008年这一太阳活动低年PEC随地磁纬度（MLAT）、磁地方时（MLT）以及不同季节的变化规律.此外,还利用提取的120°E和300°E经度链上的数据对比研究了PEC的经度变化情形.研究结果表明：（1）PEC主要集中分布在磁赤道±45°之间的一个绕地球的环带状区域中;（2）PEC表现出以下的昼夜变化规律特征：白天时段之值高于夜间,约在12—16MLT之间达到最高峰值,而最小PEC值出现在日出前大约4—5MLT左右的时段;（3）相比其他季节月份而言,PEC在北半球夏季月份（5—8月）具有最小值;（4）PEC存在明显的经度变化,不同经度链上的PEC存在不同的季节变化特征.

英文摘要：

We tried to study the variations of the plasmaspheric electron content（PEC）using the PEC data derived from the podTEC observation of the COSMIC low Earth orbit（LEO）satellite to the GPS satellite signals.We first give a brief introduce to the method we used to convert the slant podTEC to the vertical PEC.Then we used the converted PEC data of the year 2008 to study the variations of PEC with the geomagnetic latitude（MLAT）,magnetic local time（MLT）and with four different seasons.Besides,we made a study on the longitudinal variation of PEC using the extracted PEC data from two different longitudes（120°E and 300°E）.Our study showed that：（1）The distribution of PEC is mainly confined to a region within ±45°of the magnetic equator of the Earth;（2）PEC shows a well-defined diurnal variation pattern withhigher values during daytime hours than during nighttime hours.PEC reaches its peak value at the hour around 12—16MLT,whereas it reaches its minimum value at around 4—5MLT.（3）PEC has a lowest value in the June solstice season（May-August）compared with other seasons.（4）PEC shows an evident longitudinal variation and it has different seasonal variations for different longitudes.