基于GPS资料分析西藏中东部夏季可降水量日变化特征

Diurnal Variation Characteristics of GPS-Retrieved Precipitable Water Vapor over Mid-East Xizang in Summer

利用中日JICA项目2010-2013年地基GPS探测的逐时大气可降水量PWV资料以及西藏自治区气象局信息中心提供的2011年自动气象站逐时降水资料,分析了西藏中东部地区4个测站（丁青、那曲、隆子和林芝）夏季PWV日变化特征及有、无降水日的差别,并初步讨论了其与累积降水的关系。结果表明：（1）西藏中东部各站PWV存在明显的日变化特征,通常于02：00（世界时,下同）左右达到最低值,此后迅速上升,高值普遍从08：00持续到19：00。各站PWV日变化幅度普遍随测站的海拔升高而减小;（2）各站PWV日平均值随海拔降低而增加,在有降水日PWV要比无降水日高出10.2%~31.3%,且有、无降水日PWV差值随海拔升高而增大;（3）谐波分析表明,各站PWV日变化主要以日循环为主,同时各站PWV日变化也表现出不同程度的半日循环,这种双峰型变化特征在海拔较高的测站较为明显。与有降水日相比,无降水日PWV半日循环信号普遍有所增强;（4）各站累积降水量和累积降水频次的日变化具有较明显的日循环特征,降水主要出现在当地傍晚以后;（5）各站PWV开始上升的时间普遍超前于降水,并在降水结束后出现明显回落,降水量通常在PWV还处于较高值时达到最大。

JICA（Japan International Cooperation Agency）project was carried out from 2005 to 2009 which established 24 ground-based GPS stations over Qinghai-Xizang Plateau and around area. The range of mid-east Xizang includes four GPS stations：Naqu,Dingqing,Linzhi and Longzi. Using GPS-retrieved atmospheric precipitable water vapor（PWV）data of JICA from 2010 to 2013 and the hourly AWS（Automatic Weather Station）precipitation in 2011,on the basic of revealing the diurnal variation,focus on analyzing the diurnal variation characteristics with and without precipitation,as so as the relationship with accumulative precipitation. The results are obtained as follows：（1）The PWV is decreasing while the altitude and latitude increase. And it has obvious diurnal variation over mid-east Xizang. The PWV minimum ordinarily appears at 02：00（UTC,the same as after）and then increases quickly. The high value can usually last from 08：00 to 19：00.（2）The average and anomaly range of PWV at each station is increasing with the altitude decreasing. And the PWV values in different precipitation events are obviously different. PWV with precipitation would surpass the PWV without 10. 2% ~31. 3%. The difference may get more significant with the altitude increasing.（3）The result of harmonic analysis indicates that the diurnal（24 h）cycle is the main signal of PWV diurnal variation at each station. The signal of semi- diurnal cycle is in different extent and it gets stronger during the day without rain except Linzhi station which has a stronger diurnal cycle.（4）The largest accumulative precipitation occurs at Dingqing station in2011,and then follows Naqu. The diurnal variation of precipitation has significant characteristic of diurnal cycle at each station. And precipitations often occur after nightfall. The peak of rainfall frequency is usually later than hourly accumulative precipitation.（5）PWV accumulates gradually and decreases rapidly before and after precipitation. The time when PWV begins to rise is generally earlier than hourly accumulative precipitation and rainfall frequency. The precipitation reaches the peak as PWV is still high.