南亚高压的东西偏向对亚洲季风区对流层顶附近水汽分布的影响

Impact of the East–West Phase of South Asia High on Water Vapor Distribution near Tropopause over the Asian Monsoon Region

基于1958~2002年欧洲中期数值预报中心(ECMWF)提供的ERA-40再分析资料和美国气象环境预报中心/美国国家大气研究中心提供的NCEP/NCAR再分析资料研究了夏季南亚高压的东西偏向与亚洲季风区对流层顶附近水汽输送之间的关系。结果表明:(1)南亚高压的东西偏向对上对流层200 h Pa水汽高值中心的位置影响较小,主要影响其强度,对100 h Pa水汽高值中心的位置和强度有着较强的影响,而对平流层下部70 h Pa的水汽分布几乎没有影响。(2)南亚高压偏东年,高原上空和高原南部的垂直上升运动较强,在西风急流的共同作用下可将低层丰富的水汽向上输送,使200 h Pa和100 h Pa的水汽高值中心位于高原上空,而100 h Pa南亚高压范围内偏北风和偏东风增强,在水平输送的作用下使高值中心周围水汽的分布形态与高压中心的分布形态一致。(3)南亚高压偏西年,沿着高原西部的地形抬升作用比高原上空的对流上升运动更强,西风急流北移,对流层顶附近在60°E^80°E范围内形成气旋式环流,因此水汽高值中心向西偏移到伊朗高原。(4)南亚高压范围内200 h Pa的温度异常分布与水汽的异常分布一致,暖中心有利于高水汽的生成。而100 h Pa的温度异常分布与水汽异常分布相反,暖中心对应异常偏低的水汽,说明南亚高压范围内下平流层的水汽分布受环流场和温度场共同作用的影响。该研究对理解南亚高压东西偏向机制及提高亚洲气候预测有一定的参考意义。

Based on the ERA-40 reanalysis data provided by the European Center for Medium-Range Weather Forecasts（ECMWF） from 1958 to 2002 and the NCEP/NCAR reanalysis data provided by the National Centers for Environmental Prediction and the National Center for Atmospheric Research, we study the relationship between the east-west phase of the South Asia High（SAH） and water vapor distribution near the tropopause over Asian monsoon region. The results show that the east-west phase of the SAH is correlated with the intensity of high water vapor center at 200 h Pa and has an obvious impact on the intensity and location of high water vapor center at 100 h Pa, but it has almost no effect on the intensity and location of water vapor at 70 h Pa. During the east phase of the SAH, the high value centers of water vapor at 200 h Pa and 100 h Pa both are located over the Tibetan Plateau, which are related to strong ascending motion and the subtropical westerly jet that transport water vapor to near tropopause over the Tibetan Plateau. At 100 h Pa, the strong northerly and easterly winds play an important role for horizontal transport of water vapor, which explains why the spatial distribution of water vapor and its high value center are similar to that of pressure. During the west phase of the SAH, the center of high water vapor shifts westward to Iranian Plateau because of the strong ascending motion resulted from the terrain lifting effect along the western Tibetan Plateau and the northward displacement of the westerly jet. The distribution of temperature anomaly is consistent with that of water vapor, and the warm center is favorable for the generation of high moisture at 200 h Pa in SAH. The distribution of temperature anomaly is contrary to that of water vapor and the warm center corresponds to low water vapor at 100 h Pa, indicating that the distribution of water vapor in the stratosphere in SAH is influenced by the interaction of the circulate and temperature fields. The present study is helpful for understanding the mechanism of the east-west phase of the SAH and improving the quality of climate forecast.