中文摘要：

本文利用CHAMP卫星以及全球电离层-热层模型（GITM）来研究太阳活动低年（2007—2009年）中纬热层大气质量密度（ρ）的经度结构变化.结果如下：（1）ρ存在明显的经度单波结构（单峰和单谷）,且南北半球反相,波峰和波谷随着地方时增加而向东移动;（2）模拟表明离子拖曳效应在ρ结构差异的形成中起到了重要的作用,欧亚地区电子密度经度差异性较弱,不足以影响ρ经度分布,导致该地区ρ经度差异不明显;（3）在磁中纬地区,太阳天顶角的经度差异可达20°~30°,太阳光加热的经度不均匀性是导致ρ经度差异的另一个主要原因.

英文摘要：

This study investigated the longitudinal difference in the thermospheric neutral mass density（ρ）during the solar minimum period from year of 2007 to 2009at mid-latitudes.Both CHAMP observation and global ionosphere-thermosphere model（GITM）simulation were analyzed.ρexhibited wave-1structure in the longitudinal profile（i.e.one peak and one trough）,which was almost 180°out of phase in the two hemispheres.The phase of the wave changed with the local time,exhibiting a clear diurnal variation.ρhad few longitudinal variation in the north eastern hemisphere,which was the main difference from the electron density.The reason was that the ion density variation was too weak to affectρin the European-Asian sector through ion drag.As confirmed by simulation,the longitudinal difference ofρwas reduced greatly when the ion drag was negligible.Thus,both model and observation confirmed the important role of the ion drag in the longitudinal structuring of the neutral density.This study further indicated the obvious longitudinal difference of the solar heating at magnetic mid-latitudes.The peak to trough difference in the solar zenith angle could reach 20°~30°.The non-uniformity of the solar heating can be another causation for the longitudinal structure of the air mass density.