【摘要】 <正>我国位于季风气候区域区,季风一直为我国气象学者所重视。但过去由于资料短缺,只能通过一些个例或平均资料的分析来研究我国的季风气候,不能了解季风的变化。目前地面和高空资料,都已连续累积了30多年,因此有可能对季风在近三十年的变化进行更多还原

【Abstract】 Considering the fact that in winter the pressure is higher over the land than that over the sea and in summer the pressure gradient is reversed, the intensities of summer monsoon is designated by summing pressure differences between 110°E (land) and 160°E (sea) from 10°N to 50°N at 10 degree latitude interval, in the summing process, only the pressu-re differences ^ -5mb were included. The annual intensities were calculated on the basis of 12 calendar months for each year from 1951 to 1980, and the normal was obtained as a thirty year mean. Finally the intensities for individual year from 1951 to 1980 are divided by the normal values, and the ratio are called as summer monsoon index (SMI). The rela-tionships between the SMI and the circulation in northern hemisphere and precipitation over China are analysed. The variation of the SMI for the 30 years period from 1951 to 1980 is discussed. The main results obtained are:(1) The SMI reflects in some extent the characteristics of atmospheric circulation over East Asia, correlation coefficients between the SMI and sea level pressure over East Asia show that the SMI closely relates to hot low over Asia continent. The large the SMI, the deeper the hot low and the later extends to the north and the east. On the contrary, the hot low is weaken as the SMI belows the normal. At the same time, the SMI is linked ob-viously with the geographical position of West Pacific High and the intensities of anticyclo-ne over Tibet Plateau at 500 mb level. When the SMI is above normal, the West Pacific High usually extends to the north and the east, and Tibet Plateau anticyclone is intensified. When the SMI is weaken the West Pacific High retreats to the South-East, and Tibet Plateau anticyclone weakens. The integrated seasonal mean circulation characteristics at 500 mb level and sea level for typical SMI years show an overall reversed features to that of typi-cal low SMI.(2) The summer rainfall over east China is also correlated closely to the SMI. In the high SMI period, north of the Huai River and south of the Yangtze River the precipitation is abundant, but the Yangtze River valley experienced severe drought. When the SMI is lower, the drought is observed in the north of Yangtze River. In the mid and low reaches of Yangtze River the wet period is appeared, when the SMI is approximated to the normal.(3) The variations of SMI indicate that three separate phase can be identified in the last thirty year period, that is the normal phase from 1951 to 1959, characterized by the less variability of SMI, the strong monsoon phase from 1960 to 1966, there are six years out of seven years the SMI were above normal, and finally the weak monsoon phase from 1967 to 1980, in this period the SMI decreased evidently most years. It is interesting to note that accompanying the abrupt transformation from second phase to the third phase, in the middle of 60’s, the hot low over the Asia continent and West Pacific High both expe-rienced dramatic variations. This fact confirmes the close connection between SMI and the general circulation.更多还原