东北夏季月低温事件的定义及大气环流年代际特征分析

利用1960-2009年东北地区150个地面测站的逐日气温资料，定义了东北三省夏季月低温事件（简称MCSE），并将其分为5类。结果表明：MCSE发生频率在20世纪60-70年代较高，80年代逐渐减少，90年代显著减少； 6月和8月以第Ⅲ类MCSE为主，而7月则是第Ⅱ类；在冷气候背景下，第Ⅱ类MCSE正涡动能量是由高纬向中纬度传播，正常背景下是由中纬度向高纬度传播，第Ⅲ类则与之相反，暖背景下第Ⅱ类MCSE的能量传播方向与冷背景一样，而第Ⅲ类则先是由低纬度向高低纬度传播，然后是由高纬度向低纬度传播；同时还发现，在冷背景下第Ⅱ类和第Ⅲ类MCSE，中国东北地区都是处于大范围强冷空气带的覆盖下，而正常期气候背景下这两类MCSE的东北冷涡和乌拉尔山阻塞高压（西阻）都比较明显，在暖背景下，第Ⅱ类MCSE的阻塞高压（中阻）、鄂霍次克海阻塞高压（东阻）以及东北冷涡系统都很明显，而第Ⅲ类MCSE的阻塞高压（中阻）和东北冷涡明显。

Definition of monthly cool summer events over northeast China and interdecadal characteristics of atmospheric circulation

Based on the daily temperature data from 150 weather stations in the northeast China during 1960-2009, the monthly cool summer event (MCSE) was defined and it was classified into 5 types. The results indicate that the frequency of MCSEs is the highest during 1960s to 1970s, and then reduces gradually afterwards, especially significantly in 1990s. The Ⅲ type MCSE mainly appears in June and August, and the Ⅱ one is in July. The eddy energy of the Ⅱtype MCSE mainly transports from high to middle latitudes under the cold climate background and from middle to high latitudes under the normal climate background respectively, while the reverse is true for the Ⅲ type MCSE. The transfer direction of the eddy energy under the warming background is the same as that under the cold background for the Ⅱtype MCSE, while that is firstly from lower to upper and then from upper to lower for the Ⅲ type MCSE. In addition, the strong and cold air belt covers over the northeast China under the cold background for the Ⅱ and Ⅲ type MCSEs, while it is obvious northeast cold vortex and Ural blocking (west blocking) under the normal climate background. Under the warming climatic background, the Baikal Lake blocking high (middle blocking), the Okhotsk blocking high (eastern blocking) and cold vortex are all significant for theⅡtype MCSE, while the Baikal Lake blocking high (middle blocking) and cold vortex are obvious for the Ⅲ type MCSE.