The Spatial-temporal Analysis Of Persistent High-Temperature Events In China And Its Relationship With Low Frequency Oscillation

Based on daily maximum temperature data for522stations in China and NCEP/NCAR reanalysis daily data during1959-2008. the bivariate MJO index of WH04during1979-2008and NCEP/NCAR reanalysis monthly mean SST data during2000-2008and using EOF. EEOF. butterworth band-pass filter, multiple linear regression and correlation analysis methods,the spatial-temporal charact-eristics of persistent high-temperature events in China are analyzed and the evolutions of typical persistent high-temperature events in the south of China are revealed. Then,we analyse the the distribution of low-frequency circulation while the persistent high-temperature events in the south of China happen and predict the low-frequency maximum temperature in the south of China in2008. The main conclusions are as follows:(1) The persistent high-temperature events mainly occur in the south-east of China and Xinjiang province, while rarely occur in Northeast China and North China and almost do not occur in Tibet, Qinghai and the west of Sichuan.The first three EOF patterns in the south of China are respectively characterized by a uniform anomaly over the whole area, a dipole pattern with two centers in southern China and the areas to north and an out of phase pattern between east and west parts of the area. The duration of high-temperature events in the south of China are becoming shorter, while increasing in South and East China.(2) In the south of China, there are four categories of the evolution of typical persistent high-temperature events:(I)It mainly influences Central China,South China, ChongQing and the east of Sichuan and its center is in ChongQing and the west of Hunan. It begins in the southwest of Hunan, and expands eastward and northward to the maximum strength, then withdraws westward and disappears in Guangxi;(II)It almost influences the whole area and its center is in Anhui and Hubei,but it has little impact on South China.It begins in the north of Zhejiang and expands westward to the maximum strength, then shrinks westward and ends in the east of Sichuan;(Ill)It mainly influences the south of Yangtze and its center is in Zhejiang.It begins in Zhejiang, then expands westward to the maximum strength and disappears in the junction of Jiangsu and Zhejing;(IV) It begins in the north of Zhejiang and expands southwestward to Guangdong and Guangxi, ends in Guangxi.(3) In the low-frequency scale,the major systems which influence the high-temperature events are:On500hPa;the positive anomaly of geopotent-ial height fields formed in the northeast of Taiwan constantly evolves and affects China,at the same time,there is a strong negative anomaly center in the north,which causes the positive anomaly of geopotential height fields control the area in the south of China stably. On l00hPa, the positive anomaly of geopotential height fields in the Western Pacific affect the south of China with a northwestward path which causes persis-tent high-temperature events happen.Meanwhile,the location the center of positive anomaly on5O0hPa and l00hPa is basically same.(4) The results from the multiple linear regression model for low-frequency temperature field with the bivariate MJO index of WH04are relati-vely smoother in space and time.And it can clearly reflect the differences between each phase of MJO before and after the high temperature events.10days before the persistent high-temperature events,it is mainly warm(cold) anomaly in phase1、2、7、8(3、4、5、 6) of MJO,then,the warm anomaly evolves from phase1,2^7>8to3、4、5、6.(5) While we use the linear regression equation to forecast the high-temperature events in the south of China in2008,we find that it can effectively forecast the1st and2nd events,but it omitting the3rd event. Overall,the forecasting results for the high-temperature events using the linear regression equation is good.