青藏高原西侧地区冬季降水的年际变率及其影响因子

Interannual Variability of Winter Precipitation over the Western Side of Tibetan Plateau and Its Impact Factors

基于全球降水气候中心(GPCC)和全球降水气候计划(GPCP)的降水数据及ERA-interim再分析资料,分析了1979~2012年冬季青藏高原(简称高原)西侧地区降水的基本特征及影响其年际变率的潜在因子。结果表明高原冬季降水主要发生在其西侧地区且为全区变化一致型,降水所需的水汽主要来自上游地区,从该区域的西边界输入。然而,高原西侧地区冬季降水的年际变率主要由水汽输送的动力过程所决定,表现为高原西侧的西南风异常。此外,高原西侧冬季降水的年际变率与其上游典型的大气内部变率北大西洋涛动和北极涛动相关性不强,而与赤道西印度洋和热带中东太平洋的海温显著相关。热带中东太平洋海温异常通过影响大气环流变化,在印度洋北部激发一个反气旋式的环流异常,使得高原西侧地区出现异常西南风,从而加强了水汽通量输送的动力作用。同时在赤道异常东风的作用下,暖水也向印度洋西部输送堆积。赤道中东太平洋海温的异常可进一步导致西风急流发生南北移动,从而也在一定程度上影响了高原西侧冬季水汽输送以及降水的年际变率。

Based on monthly precipitation datasets of the Global Precipitation Climatology Centre (GPCC) and the Global Precipitation Climatology Project (GPCP) and daily ERA-Interim reanalysis data, characteristics of winter precipitation over the western side of Tibetan Plateau (TP) from 1979 to 2012 and the impact factors of interannual precipitation variability in this region are investigated in the present study. Results indicate that winter precipitation over the TP mainly occurs over the western side and the principal spatial pattern is uniform. The moisture source for precipitation is largely from upstream areas and enters the TP from the western boundary. However, the interannual variability of winter precipitation over the western side of TP is mainly explained by the dynamic component of the moisture transport, which is featured by a southwesterly circulation anomaly over the western side of TP. Besides, the interannual variability of winter precipitation over the western side of TP is more related to SST (sea surface temperature) in the equatorial oceans than to the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) over upstream regions. The anomalous SST over the central and eastern tropical Pacific Ocean can affect the atmospheric circulation, triggering anticyclonic anomaly over the northern Indian Ocean and southwesterly anomaly over the west side of TP, which further enhance the dynamic process of moisture transport. Besides, under the influence of the tropical easterly anomalies, warm ocean water is transported to the western Indian Ocean and accumulates there. The anomaly of the equatorial SST also regulates the meridional location of the westerly jet, which further affects wintertime moisture transport and interannual variability of precipitation over the western side of TP.