Climatic Characteristics of Rainy Seasons in China
中国雨季的气候学特征

The major rainy seasons in whole China are firstly defined using the climatic pentad rainfall amounts datasets of 740 stations,and then the climatic characteristics of the rainy season,including the major rainy season,the spring and autumn rainy seasons,are discussed.It is found that:(1) The major rainy season bursts out earliest in central South China but latest in West China provinces.The major rainy season can last 4 to 14 pentads with the rainfall amounts accounting for 30%-60% of the annual total amounts.In East China,the major rainy season of monsoonal nature advances from south to north.But in West China,the major rainy season commences slightly earlier in its northern part than that in the southern part due to effects of the westerlies with obvious local features.(2) Rainy seasons in China have distinct regional characters.In most area of China including North and Northeast China,Northwest China and the Tibetan Plateau,rainfalls highly concentrate and show single peak mode,with the major rainy season showing the main characters of rainfalls there.However,rainfalls show double peak mode both in South China and West China and triple peak mode in the middle and lower reaches of the Yangtze River.These modes indicate that the intraseasonal cycle of active-break-reactive lies in the rainy season of China,which shows the modulation of the intraseasonal oscillation to annual cycle of rainfalls.(3) The rainy season in China experiences several obvious stages,including the spring rainy season to the south of the Yangtze River,the pre-flooding season in South China,the Meiyu in the Yangtze River and Huaihe River valleys,the rainy season in North and Northeast China,the latter flooding season in South China and the autumn rainy season in the areas of Sichuan,southern Gansu and Shaanxi.Rainy seasons from the pre-flooding season to the latter flooding season are mainly controlled by the East Asian summer monsoon systems,while the combined effects of the westerlies in mid-high latitudes and the summer monsoon cause the spring and autumn rainy seasons.And rainy seasons in West China are mainly impacted by the westerlies.(4) Seasonal cycle is the most obvious signal in the climatic summer rainfalls in China.But the 10-90-day climatic intraseasonal oscillation has important modulating effect on the advancement and maintenance of main rain belts in East China.Three obvious oscillations and their northward propagation are observed from April through September,with each high value center of oscillations corresponding to a rainy season.And the second one is strongest and propagating farthest northward.The 30-60-day period is an important section of the intraseasonal oscillation and mainly modulates the rainfalls to the south of the Yangtze River.