水汽输送对雅鲁藏布江流域降水中稳定同位素的影响

Influence of Moisture Transport on Stable Isotope in Precipitation in Yarlungzangbo River Basin

利用NCEP/NCAR全球大气再分析格点资料和2005年西藏雅鲁藏布江流域4个站点(拉孜、奴各沙、羊村和奴下)降水中δ18O数据,分析了雅鲁藏布江流域降水中1δ8O变化同水汽输送通量的关系。从空间上来看,雅鲁藏布江流域降水中δ18O同水汽输送通量呈明显的正相关,从下游至上游,随着水汽输送通量的减少,降水中的1δ8O逐渐降低;从时间上来看,春季水汽通量较小,降水中的δ18O较高,而在夏季,水汽通量大,降水中的1δ8O较低。在此基础上,又利用NCEP/NCAR气象数据建立水汽追踪模型,以羊村站为例对雅鲁藏布江流域降水的水汽输送过程进行了追踪模拟,并讨论了降水中1δ8O变化同水汽源地以及输送过程的关系。结果发现,在季风降水之前的春季,降水中较高的δ18O主要受西风带水汽输送以及当地蒸发水汽的影响;在季风期间,降水中较低的δ18O主要受来自印度洋暖湿水汽输送的影响。

Relation between variation of δ^18O in precipitation in Yarlungzangbo River basin and the moisture flux was analyzed with NCEP/NCAR reanalysis grid data and δ^18O in precipitation at four stations （ Lazi, Nugesha, Yangcun and Nuxia ） of the region investigated. For the spatial variations, there is obviously positive correlation between them for the whole basin. With the decrease of moisture flux from the downstream to the upstream, δ^18O in precipitation becomes lower gradually. However, for the temporal variations, higher δ^18O in precipitation of spring is linked to small moisture flux and low δ^18O in precipitation of summer is linked to large moisture flux. And then, a model involving meteorological data from NCEP/NCAR was established and successfully traced the moisture transport trajectories at Yangcun station. Based on the traced results and δ^18O in precipitation at Yangcun station, the relation between δ^18O in precipitation in Yarlungzangbo River basin and the moisture transport history was discussed. We found that humid marine air mass from the Indian Ocean in general had significantly lower δ^18O values than continental air mass from north or local re-evaporation. The fluctuation of δ^18O in precipitation during monsoon season is very pronounced and the lower values are usually related to far distance and muhilayer of moisture transport, as well as moisture crossing the Himalaya Mountain.