中文摘要：

比较美国国家环境预报中心（NCEP）和欧洲中期天气预报中心（ECMWF）的再分析资料,分析了二者用低层风场表征南海夏季风上的差异.结果表明,NCEP得到的南海夏季风指数有明显的减小趋势,而ECMWF则没有;二者在年际尺度上都能较好地表征南海夏季风强度,而年代际尺度上有明显的位相差.与西沙站的探空资料比较结果表明,NCEP在经向风上更接近观测资料,而经向风的趋势变化正是西沙站西南风减小趋势的主要贡献项;ECMWF资料在年代际尺度变化上更接近观测资料.与1998年南海夏季风试验SCSMEX的再分析资料比较显示,NCEP资料在空间上与SCSMEX资料更相似.

英文摘要：

Analyzing the differences of South China Sea Summer Monsoon （SCSSM） denoted by lower tropospheric winds from the NCEP and ECMWF reanalysis data, and the results indicate that SCSSM indices by NCEP data trend to decrease and that by ECMWF data have very slight trend. On interannual timescale, they are consistent with each other, while there are phase differences on interdecadal timescale. The results by comparing them with the sounding data from Xisha station show that NCEP meridional winds, which play a main role in the trend of southwesterly over Xisha station, are in better agreement with the observations. On the other hand, ECMWF data are probably nearer reality on the interdecadal timescale. To more degrees, the NCEP data show a better spatial similar to 1998 SCSMEX data than the ECMWF data.