青藏高原北侧地区干湿年夏季垂直环流差异的对比分析及青藏高原的热力影响

THE COMPARATIVE ANALYSES OF DIFFERENCES BETWEEN VERTICAL CIRCULATION ON NORTH SIDE OF TIBETAN PLATEAU IN WET AND DRY SUMMER AND THERMAL EFFECTS OF THE PLATEAU

为了分析西北干旱的形成原因，本文首先利用高原北侧地区５站历年夏季的降水量资料等，制定了该区的干湿标准，划分了历年夏季的干湿等级。接着又利用ＥＣＭＷＦ的格点资料等对比分析了该区干湿年夏季间垂直环流的差异，也探讨了青藏高原地面热状况与高原北侧干湿状况的联系。其主要结论是：１）文中制定的以降水标准差为判据的干湿标准适合西北干旱区；２）高原北侧干湿年夏季间在高原北侧和高原上的垂直环流存在明显差异；３）青藏高原地面热状况与上列差异有关，也即青藏高原的热力作用是西北干旱的重要成因之一。

o analyze the causes of the drought over northwest China, first of all,the wet and dry year criterion and their division on the north side of Tibetan Plateau(NTP)centered the northwest China drought area have been made utilizing the precipitation data of five stations over the area during the period from June to August of 1952-1990 in this paper. Then,the differences between the vertical circulation over NTP in wet and dry summer have been comparatively analyzed using the gridded data of EOMWF from 1979 to 1986.At last,the connection between the surface thermal characteristic of the Plateau and the wet and dry summer over NTP was discussed as well.The main results show that:1)the wet and dry summer criterion with precipitation standard deviation is proper for the drought area of northwest China;2)there are clear differences between the vertical circulations over NTP and the Plateau in wet and dry summer:in wet summer upward motion over NTP dominates and the upward motion over the Plateau is stronger,but vice versa in dry summer;3)the wet and dry summer of NTP is closely related to the surface thermal condition of the Plateau, namely,theheating effect of the Plateall surface is stronger in wet summer than in dry summer.