Asymmetric Effect Of Pacific-Japan Pattern On Summer Precipitation In Middle And Lower Area Of The Yangtze River

The characteristics of the anomalous distribution of summer rainfall over middle and lower area of the Yangtze River during different phases of PJ teleconnection patterns are analyzed based on various oceanographic and atmospheric data from 1979 to 2015,and the possible causes for asymmetric precipitation changes are discussed.The result show that in the negative phase of PJ(E1 Nino decaying year),precipitation in the middle and lower reaches of the Yangtze River increased significantly,with the two maximum precipitation zones located in the Yangtze River and the southern Japan.In the positive phase of PJ(La Nina decaying year),the precipitation in the middle and lower reaches of the Yangtze River did not decrease obviously.It is found that during the negative PJ phase,the SST anomalies in the eastern and central Pacific,Indian Ocean and South China Sea are stronger than those in the PJ positive phase.In the PJ positive phase,the warm SST over the Indian Ocean excite an abnormal anticyclone in the Philippine sea,and an abnormal cyclones in the middle and lower reaches of the Yangtze river.It is vice verse in the PJ negative phase.However,the intensity of the anomalous anticyclone over the Philippine Sea and the anomalous cyclones in the middle and lower reaches of the Yangtze River were significantly stronger in the negative years of PJ,which led to an asymmetric response to the anomaly of precipitation and intensity in the middle and lower reaches of the Yangtze River.Numerical simulations using the atmospheric circulation model ECHAM4.8 show that even though the Indian Ocean's SST anomalies are relatively warm and cold,the anti-cyclone intensity of the Philippine Sea triggered by the warm Indian Ocean SST anomaly is obviously stronger.It has caused more precipitation in the middle and lower reaches of the Yangtze River than in the lesser extent.This can confirm the following fact:El Nino's next year(PJ negative phase)predicts that the rainfall in the middle and lower reaches of the Yangtze River is higher than that predicted by La Nina's less precipitation in the next year.At the end of the 1970s,there was an interdecadal mutation in the PJ type.Before and after the year 1979,the asymmetry of summer precipitation in the middle and lower reaches of the Yangtze River showed an increase in precipitation,and the annual precipitation increase before the negative phase in 1979 was even more pronounced.The tropical-eastern-eastern Pacific SST maintained the ENSO-type SST around 1979,but its intensity was less than 1979.This shows that after 1979,the PJ type became closely related to the SST in the tropical middle east.The characteristics of the SST variation in the Indian Ocean north of the equator did not change before and after 1979,but the SST anomaly intensity was stronger before 1979 than after 1979.In the summer of the same period,around 1979,the impact of SST in the tropical and middle east and the Pacific Oceans on the PJ type was greatly degraded,and during the negative years,the SST A in the Middle East and Pacific Ocean even reversed from decadal,from a weak El Nino SST distribution to a La Nina type.SSTs are distributed,while SSTs in the East Indian Ocean,South China Sea,and the Philippines are more closely related to the PJ type.The analysis of the 850 hPa wind field shows that before and after the PJ interdecadal catastrophic changes,the negative anomalous year in the low latitude is stronger than the positive anomaly year,and the PJ positive phase in the mid latitude of Japan and the high latitudes is stronger than the negative phase year.The cyclone circulation was controlled both before and after the decadal mutation in the middle and lower reaches of the Yangtze River.