Location Variation of the East Asia Subtropical Westerly Jet and Its Effect on the Summer Precipitation Anomaly over Eastern China

The location change of the East Asia subtropical Westerly Jet (EAWJ) axis and its impacts on the spatial distribution of summer precipitation anomaly in eastern China are investigated by using the NCEP/NCAR reanalysis mean pentad data and observed daily rainfall data from 1951 to 2004. The main results are as follows: (1) The location change of the EAWJ is greatly abrupt in summer (July and August) during 1975－1980, since then the westerly jet core shifted southward and westward remarkably.(2) Both rainfall amount and rainfall intensity in North China have been decreasing in summer since 1980. At the same time, the length of the rain season shortens, because the beginning date of the rainy season is late and the ending date early, respectively. In contrast, the plum rains start date is early and the end date late. The rainfall increases more than before in the middle-lower reaches of the Yangtze River, so the precipitation distribution with flood in the south and drought in the north of China forms.(3) There is more precipitation in North China during 1957－1964, corresponding to the EAWJ longitudinal distribution. There is coupling between the upper-level jet and the low-level jet in North China. Meanwhile, the strong convergence and the sufficient water vapor supply appear in this region, which are related to the more precipitation occurrence. There are two periods of the less precipitation in North China, which are 1980－1987 and 1997－2002, respectively. The EAWJ core is abnormally southward and westward remarkably without coupling of the 200-hPa jet and 850-hPa jet during the periods of 1980－1987 and 1997－2002, respectively. Meanwhile, the stronger convergence and sufficient water vapor supply appear in the Yangtze River, which are related to more precipitation in the south and less precipitation in the north of China. This suggests that the change in the westerly jet location and intensity is associated with the precipitation distribution in eastern China. Therefore, not only the latitudinal location, but also the longitudinal location and intensity of the westerly jet center are important for the relationship between the EAWJ and the abnormal rainfall in eastern China.