Role Of The Low Frequency Oscillations In The Persistent High Temperature Processes In The Middle And Lower Of Yangtze River During Boreal Summer

Using the data of daily highest temperature (DHT) of the Middle and Lower of Yangtze River and the NCEP daily reanalysis data covering the period of 1961-2008, we analyze the climatic characteristics of the high temperature (HT) and persistent high temperature (PHT) in the Middle and Lower of Yangtze River summer. Finally, by using of the relation of PHT events and low-frequency oscillations, we make prediction of the HT and PHT events of 2009. The results are summarized as follows:In the Middle and Lower of Yangtze River region, the DHT has a significant descending trend during1961-2008, which has an oscillation of 5-6 years. According to the EOF and REOF analysis, the Middle and Lower of Yangtze River can be divided into 3 parts. In this paper, we pick up 23 typical PHT from 8 HT years, and based on the analysis of 200hPa and 500hPa circulation, SAH has effects on westward advancement maintenance and strengthening of SAWP. Further analysis of the relationship between PHT events and low-frequency oscillations (30-60) in the Middle and Lower of Yangtze River region, we found a disturbance located in the Northwest Pacific at 500hPa in the 25 days before PHT. and the path of this disturbance to China's eastern coast is semi-circle, meanwhile, the low-frequency negative vorticity area extended to the Middle and Lower of Yangtze River region.15 days before PHT at 850hPa, there was a low-frequency warm advection, the center of that located near (20°N,130°E), which lasted until the beginning of PHT. The summer temperature in the Yangtze River Delta show that the low-frequency of summer temperature cycle is 10-30 days, three key areas are found in well correlation of east of Lake Balkhash, southeast of Lake Balkhash and South of Lake Balkhash by correlation analysis. According to the propagation characteristics of low-frequency perturbations. we found that the variation of 10 days ahead of key areas is very important to the trend of the Yangtze River Delta summer temperature. Finally, based on two previous stable signals of the low-frequency height field at 500hPa and the low-frequency temperature advection at 850hPa, the PHT events in the Middle and Lower of Yangtze River of 2009 are predicted and indicate better results. By using these key areas (east of Lake Balkhash, southeast of Lake Balkhash and South of Lake Balkhash), the summer temperature in the Yangtze River Delta of 2009 is predicted by a forecast model which also indicates better results.