柴达木盆地夏季极端强降水特征及大气环流成因

Characteristics of summer extreme heavy precipitation in the Qaidam Basin and causes of atmospheric circulation

利用柴达木盆地气象台站逐日降水资料和国际卫星云气候学计划D2资料分析了柴达木盆地夏季极端强降水、云量及云水资源的时空分布特征,结合NCEP/NCAR再分析资料对夏季极端强降水事件发生时的大气环流进行了分析.结果表明,夏季极端降水阈值和极端降水日数在柴达木盆地东部大于西部,极端降水量也明显增加.柴达木盆地各种云量的空间分布形态不一,云量上升趋势不明显.云水路径、固态云水和液态云水的空间分布形态一致,具有"南低北高"的特征,三者的线性趋势在年和四季尺度均明显上升.环流分析显示,极端强降水事件发生时,对流层上层,西风急流向北移动,柴达木盆地位于急流南侧,有异常反气旋式环流,对应高空辐散区;对流层中层,柴达木盆地位于异常偏强的槽区及槽前;对流层低层,柴达木盆地东部位势高度异常偏低,出现异常气旋式环流,对应低空辐合,这种高层辐散低层辐合的环流配置为极端强降水提供了良好的动力条件.柴达木盆地极端强降水的水汽来源为印度夏季风对热带海洋的水汽经青藏高原东侧输送;西风带对欧亚大陆的水汽输送;西北太平洋异常气旋式环流西北侧的异常偏北风的水汽输送.

Based on the daily precipitation data from the meteorological stations in the Qaidam Basin, the international satellite cloud climatology project D2 data and NCEP/NCAR reanalysis data, the temporal and spatial distribution characteristics of the summer extreme heavy precipitation(SEHP), cloud amount and cloud water resources in the Qaidam Basin were analyzed, as well as the atmospheric circulation associated with the process of SEHP. The results showed that the SEHP threshold and SEHP days in the eastern Qaidam Basin were larger than those in the western, and the amount of extreme precipitation in the Basin obviously increased during 1981-2017. The spatial distribution of cloud amount, including the total, high, middle and low in the Qaidam Basin, were different, and the upward trend of cloud amount was not obvious. The spatial distribution patterns of Cw, Iwand Lwwere consistent, which, characterized as cloud water resources in the southern Basin, was less than those in the northern Basin and significantly increased in linear tendency in the whole year. Circulation analyses showed that when the summer extreme heavy precipitation events occurred in the Basin, the westerly jet moved northward in the upper troposphere, and the Basin was located at the south flank of the jet, where an anomalous anticyclonic circulation existed corresponding to the divergence zone. The Basin was under the control of an abnormally strong trough in the middle troposphere. The geopotential height was of negative anomaly in the eastern Basin in the low troposphere, which was an abnormal cyclonic circulation corresponding to convergence zone. This circulation configuration could provide perfect dynamic conditions for extreme heavy precipitation in Basin. There were three sources of water vapor for the SEHP. The Indian summer monsoon transported water vapor from the tropical ocean to the Qaidam Basin through the eastern side of the Qinghai-Tibet Plateau. The westerly transported vapor water from the Eurasian continent to the Basin. The anomalous northerly wind transported water vapor to the Basin through a circulation on the northwestern side of the anomalous cyclonic circulation around the northwest Pacific.