Advance and Retreat of Baili Necktie

"This trip to Europe is fruitful." Mr. Liu Dejun, general manager of Zhejiang Baili Necktie & Accessory Co., Ltd, said as he come back from the Europe and couldn’t help holding his excitement. "We negotiated with professional

ADVANCE AND RETREAT OF THE SUMMER MONSOON IN CHINA

By using the daily-14 year(1983—1996)NCEP/NCAR 2.5°×2.5° reanalysis data,we carefully study in each pentad the advance and retreat of the summer monsoon in China and given to it a new definition.This definition considered the intensity of southwesterly winds at 850 hPa together with its degree in temperature and moisture.The result revealed that: (1)The advance of the summer monsoon in China shows three abrupt northward shifts and four relatively stationary stays.The four stable stages correspond to the peak of the pro-summer rainy period in South China,the“Meiyu”season in the Changjiang(Yangtze)-Huaihe River Valleys.the rainy season in the downstream of the Huanghe(Yellow)Riyer Valleys and the rainy season in northern China.The retreat of the summer monsoon is so fast that it totally retreats from the mainland at about the mid-August. (2)The northward advance of summer monsoon in China is basically controlled by the seasonal variation latitudinally of the upper level planetary westerlies.It is in roughly accord with the temporal variation in the position of 15 m s^(-1) isotaeh at 200 hPa.The fast retreat of the summer monsoon is mainly due to the blocking effect of the Tibetan Plateau. (3)The advance of 500 hPa subtropical high of the western Pacific is also in aecordanee with the advance of the summer monsoon in China.During the advancement of the summer monsoon, the eastward movement of the subtropical high shows great meaning that it creates the essential condition for the convergence of southward intrusion cold airs with the warm and humid southwesterly winds,which result in precipitation.There are three manifest eastward movements of the subtropical high during its northward advancement.They coincide correspondingly to the beginning of the peak of the pre-summer rainy period in South China,the“Meiyu”season in the Changjiang(Yangtze)-Huaihe River Valleys and finally the rainy season in northern China.The western part of the subtropical high moves eastward to the region of Japan in late July and the beginning of August.It then stays there for quite a long time which results in the straight movement of cold airs intruding from the north to the east of Tibetan Plateau,i.e.the eastern region of China.This provides good condition for the fast southward retreat of the summer monsoon. (4)The intensifieation and development of the Tibetan high at 200 hPa are closely related to the eastward movement of the subtropical high,they often occur simultaneously.