Abstract:

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.

Key words: Monthly cool summer event, Eddy energy, Blocking high