中文摘要：

基于近10年（1999-2008年）地基GPS遥感的大气可降水量（GPS-PW）资料和地面气象资料,分析了拉萨河谷各季GPS-PW日变化特征及其对夏季降水日变化特征的影响。结果表明,在拉萨河谷各季GPS-PW都具有明显的日变化特征。春、夏、秋和冬季GPS-PW平均日变化幅度分别为1.0 mm、1.7 mm、1.0 mm和0.8 mm。GPS-PW日最小值和最大值出现的时间随季节变化不大,分别出现在08：00-10：00UTC和15：00-18：00UTC。各季GPS-PW日变化序列的谐波分析结果表明,日循环（24 h）与半日循环（12 h）是GPS-PW日变化的主要信号。日循环信号夏季最强,冬季最弱;半日循环信号夏季最强,春季最弱。在夏季GPS-PW达到日最大值的时间比平均逐时降水频次和降水量达到日最大值的时间约早2 h。GPS-PW日变化对夏季降水日变化特征具有重要影响。

英文摘要：

A 10-year（1999-2008） half-hour dataset of precipitable water（PW） vapor amount was produced from ground-based global positioning system（GPS） measurements in the Lhasa river valley of the Tibetan Plateau.The diurnal variation of GPS-PW is investigated using the dataset as well as hourly observations from automatic weather stations in the valley.The result reveals a pronounced diurnal variation in GPS-PW,reaching the minimum around 08：00-10：00 UTC and the maximum around 15：00-18：00 UTC during all seasons.The average diurnal variations of GPS-PW are 1.0 mm,1.7 mm,1.0 mm and 0.8 mm in spring,summer,autumn and winter,respectively.The diurnal（24 h） and semidiurnal（12 h） cycles of the GPS-PW were fitted using the harmonic analysis method.The results indicate that diurnal and semidiurnal cycles are the main signal of diurnal variation of GPS-PW during all seasons.The diurnal cycle of GPS-PW is the strongest in summer and the weakest in winter.The semidiurnal cycle of GPS-PW is the strongest in summer and the weakest in spring.The relationship between diurnal variations of GPS-PW and that of rainfall was conducted in summer.It can be seen that the occurrences of the diurnal variations of GPS-PW are nearly 2 h earlier than those of mean hourly precipitation and precipitation frequency in summer.The diurnal variations of GPS-PW have an important impact on the diurnal variations of hourly rainfall in summer.