The Division And Cause Of Summer Rainfall In The Monsoon Region Of Eastern China

China is located in the East Asian monsoon region and the interannual variability of summer precipitation is relatively large,extreme weather and climate events such as drought and flood occur frequently,its very meaningful to understand the causes of precipitation for production and living and social economic development.As viewed from the national range,the summer rainfall prediction for the East China monsoon regions focuses on the northern or southern locations of the rain belt,in general terms,rain belt movement is characterized by a stepwise northward advance from South China to the Yangtze River valley and to North China.However,owing to the anomaly of the EASM and other factors,the speed of the rain belt can be accelerated or the belt can remain in a certain region for along time,thereby forming different rainfall patterns.In this study,we objectively redivided the summer rainfall patterns in the East China monsoon region of four summer rainfall patterns(FRP)and extended the analysis to 2015 based on the previous studies and similarity measurement method,the climatic characteristics of moisture transport and summer monsoon circulation system over east China monsoon region and their relationships with summer precipitation,as well as the differences of moisture transport among the FRP are investigated.(1)Combining previous research,the summer rainfall patterns in the east China monsoon region during 1951-2015 were objectively classified into four typical categories:the northern China rainfall pattern(NCP),the intermediate rainfall pattern(IRP),the Yangtze River rainfall pattern(YRP),and the South China rainfall pattern(SCP).The periods of the four patterns show significant decadal characteristics.The NCP occurred mainly between the late 1950s and the early 1990s,and the IRP in the late 1950s to the early 1970s and the 2000s.The YRP occurred mainly between the 1980s and the 1990s,and the SCP between the mid-1990s and the early 21st century.(2)The simultaneous atmospheric circulation system configuration characteristics of the four rainfall patterns(FRP)over the East China during the period 1951-2015 are analyzed in order to investigate their formation mechanisms.The results confirm that the FRP possess obvious differences in the upper-level,middle-level,and lower-level troposphere.In northern China rainfall pattern(NCP)years,the East Asian subtropical westerly jet stream(EAJS)shows a northward trend,with a higher intensity than normal;the blocking high(BH)in the mid-high latitudes is inactive;and the western Pacific subtropical high(WPSH)tends to be stronger,with a location to the north of its normal position.The East Asian summer monsoon(EASM)is stronger,which promotes vapor transport to northern China,and this leads to increased rainfall.In intermediate rainfall pattern(IRP)years,the EAJS position is close to that in normal years;the BH is inactive;the WPSH tends to be weaker,with a location to the east of its normal position;and the EASM is stronger,which is conducive to increased rainfall over the Huaihe River Basin.In Yangtze River rainfall pattern(YRP)years,the circulations are found to be almost opposite in their features to those in NCP years.In South China rainfall pattern(SCP)years,the circulations are found to be almost opposite in their features to those in IRP years.This leads to increased rainfall over South China.Therefore,the different circulation system configuration characteristics lead to the different rainfall patterns.(3)The climatological characteristics and differences of moisture transport over eastern China monsoon region and their relationships with summer precipitation of the FRP are investigated.The results are as follows.There exist six MTC(Moisture Transport Channel)that affect the summer rainfall over eastern China.The first one is IOMTC(the Indian Ocean Moisture Transport Channel).The second one is TPMTC(the Tibetan Plateau Southern Side Moisture Transport Channel).The third one is POMTC(the Pacific Ocean Moisture Transport Channel).The fourth one is WMTC(the Westerly Moisture Transport Channel).The fifth one is BBMTC(the Bay of Bengal Moisture Transport Channel).The last one is SCSMTC(the South China Sea Moisture Transport Channel).The moisture transport paths associated with precipitation anomalies over different areas in eastern China are obviously different.Furthermore,the relationship between the same moisture transport path and precipitation in different summer stages is not entirely the same.