关键词:

Abstract: A comparative analysis is made of the 500 mb mean monthly circulation patterns over Asia during the wet months from May to August in the Yangtze Valley and North China. It is found that the 500 mb circulation patterns and the monthly height anomaly patterns are fundamentally different between the dry and the wet months. Furthermore, the characteristics of the circulation in the wet months are nearly the same as those of the mean circulation in June based on the average for ten years. The 500 mb circulation over North China Plain at the 10-day period of the wet month from July 21 to August 20 is markedly different between dry and wet periods. The circulation characteristics in the 10-day period of the wet months are nearly the same as those of the first 10-day period of August. Based on the result of the above mentioned analysis, the authors sug- gested that from the climatological view, June is the most rainy month in the Yangtze Valley while the first 10-day period of August is the most rainy period for the North- China Plain. The climatic periods during which the occurrence of rain is most frequent are closely related to certain climatic conditions of the general circulation. Only under such favourable circumstances, is it possible for warm and cold air masses to keep continual contact with the result of frequent rain in the afore-mentioned regions. It is apparent that there are close connections between weather and climate, circulation and precipita- tion. These arc of importance for the explanation of the great precipitation anomalies.