The Relationship Between The Characteristics Of Precipitation Evolution During The Post-flood Season In South China And The Asia-Pacific Sea And Land Differences

Based on the precipitation data collected from the daily data and NECP/NCAR reanalysis data set of China's national surface meteorological stations from 1961 to 2015,and the statistical methods such as percentile,correlation analysis,wavelet analysis,synthetic analysis and abrupt change analysis are used.this paper first defines the regional rainstorm event process in the post-flood season of South China,and secondly,establishes a method for evaluating the rain intensity.Then the APO index is defined to represent the sea-land thermal contrast in Asia and Pacific,and the correlation analysis is made with the rain intensity in flood season,and the strong and weak years of APO are classified.At the same time,the characteristics of atmospheric circulation in strong and weak years of APO and its relationship with precipitation during the late flood season in South China are analyzed and discussed.The results show:(1)In the last 55 years,the average annual frequency of regional rainstorm events in the late flood season in South China is 7.9.In the interannual change,the fluctuation range is obvious,presents the slight decrease tendency.In terms of periodic variation,the frequency of regional rainstorm events has a relatively short-period of 2.5 a and 4 a and a long-period oscillation of 11 a and 20 a,in which the first principal period is 20 a,the second and the third period are 2.5 a and 4 a respectively.However,the frequency of regional rainstorm events has no obvious mutation in recent 55 years.The average frequency of regional heavy rain events in the late flood season of South China is 2.0,and the interannual fluctuation range is larger,which shows a slight increase trend.(2)In the last 55 years,the maximum daily precipitation of the annual average regional rainstorm event in the late flood season in South China is 360.4mm.The interannual fluctuation is obvious,showing a slight increasing trend,in which the fluctuation period is normal from the early 1960 s to the mid-1970 s,the period from the mid-1970 s to the early 1980 s is relatively multiphase,and the period from the mid-1980 s to the early 1990 s is relatively small.From the mid 1990 s to the present,the relatively small period has been transferred to the normal fluctuation period.The maximum rainfall of the annual mean regional rainstorm event is 544.3mm.Interannual fluctuation is obvious,showing a slight increase trend.From the early 1960 s to At the beginning of 1990's,the period is relatively few,but from the middle period of 1990's to the middle period of 2000 s,the period is relatively many,and from the late period of 2000 s to the present,it is in the period of normal fluctuation.The maximum duration of the annual mean regional rainstorm event is 5.0 days.The range of interannual fluctuation is obvious,showing a slight increase trend.From the early 1960 s to the early 1970 s,there was a obvious transition from the relatively small period to the normal fluctuation period,and from the mid-1970 s to the present,it entered the normal fluctuation period.The annual average number of regional rainstorm events is 97.3.Interannual The fluctuation is obvious,presents the slight increase tendency.From the early 1960 s to the early 1980 s,there was a obvious transition from the relatively small period to the normal fluctuation period,and from the middle period of 1980's to the present,it entered the normal fluctuation period.The maximum comprehensive intensity of the annual average regional rainstorm event is 25.4.The interannual fluctuation is obvious,showing a slight increasing trend,in which the fluctuation period is normal from the early 1960 s to the late 1970 s,the period from the early 1980 s to the early 1990 s is relatively many,and the period from the mid-1990 s to the present is in the normal fluctuation period.(3)In the last 55 years,the average annual rain intensity in the late flood season in South China is 72.8.In the interannual change,the fluctuation range is obvious,showing a slight increase trend.In terms of periodic variation,there is a relatively short-period of 2.5 a,4a and 7a and a long-period oscillation of 11 a and 22 a.The first main period is 7 a,and the second and third period are 4 a and 11 a respectively.At the same time,there is a sudden phenomenon of rain intensity increasing in the early 1990 s in South China,starting from 1990.(4)The interannual variation of APO intensity in July and September has a significant negative correlation with rainfall intensity in South China in the same period,that is,in the strong(weak)years of APO,there is less rain(heavy rain)in South China.In the strong(weak)years of APO,the subtropical high is northeastward(south-west),and the eastward flow of the southern side of the subtropical high weakens(strengthens),(not)conducive to the influence of tropical cyclones westward on southern China.Moreover,the East Asian subtropical summer monsoon is strong(weak),and the cold air is weak(south),which is not conducive to the development of tropical cyclones in South China and offshore waters,resulting in less rain(heavy rain)in South China.The vertical shear of the tropical western Pacific warm pool and the high and low troposphere of the South China Sea increases(decrease),the vertical rising motion weakens(strengthen),(benefit)the formation of tropical cyclones,and the vertical shear of zonal wind over the South China Sea increases(decrease)obviously,(have)not conducive to the development of tropical cyclones,tropical western Pacific water conditions are favorable for tropical cyclone formation(South East North West),influence Chinese offshore area is also easy to the North(South),Southern China(rainy)easy to lead to dry.