Study On Teleconnection Of Summer Precipitation In East Asia

East Asia(EA)is located in the monsoon region,which is not only regulated by thermal and dynamic factors,but also affected by tropical and subtropical factors.Under the influence of many factors,the summer precipitation in EA is significantly different in time and space,accompanied by the decrease of precipitation in one region and the increase of precipitation in another region.This phenomenon is close to the teleconnection concept of atmospheric circulation.Focusing on the theme of the teleconnection of summer precipitation in EA,this paper reveals the improvement effect of the two teleconnections of summer precipitation in North China(NC)-lower reaches of the Yangtze River Basin(YRB)and Southwest China-Central Northeast China on the prediction skills of the models.And we study the reasons for the interdecadal variation of the teleconnection of summer precipitation in the YRBNorthwest Pacific(NWP).The main conclusions of this paper are as follows:(1)Teleconnection of Summer Precipitation in China and Its Improvement on Model Forecasting SkillsBased on the summer precipitation data of China in 1961-2017,it is found that there are four significant spatial teleconnections of summer precipitation in China:(1)NC-lower reaches of the YRB,(2)East China-Central and Northern China,(3)South China-YRB,and(4)Southwest China-Central Northeast China.The climate models can only predict the large-scale and climatology precipitation distributions,but the precipitation teleconnection between different regions cannot be well predicted,and there are many false teleconnections.To improve the precipitation prediction ability of the models,a correction scheme is constructed by taking the precipitation teleconnection pattern in the actual situation as the constraint condition to correct the precipitation teleconnection's distribution in the model.Results show that the correction can effectively improve the model's ability for predicting the precipitation in Central Northeast China and the lower reaches of the YRB.Four-year return test results show that the average anomaly consistency rate of the models' prediction increases from 47%to 58%,the root mean square error decreases from 1.7mm/d to 1.3mm/d,and the average Prediction Score(PS)score increases from 64 to 73.(2)Interdecadal Variation Mechanisms of YRB-NWP Summer Precipitation teleconnectionThe summer precipitation anomalies over EA-NWP during in 1979–1998(1999–2012)present a more(less)significant dipole pattern between YRB and tropical NWP.Research finds that the anomalous dipoles of low-level winds,geopotential height,convection,and associated wave activity fluxes over NWP significantly shift westward(eastward)and enhance(weaken)in 1979–1998(1999–2012),which are regarded as the direct causes of the adjustment of dipole pattern between YRB and tropical NWP.Further analysis reveals that the significant(insignificant)positive sea surface temperature(SST)anomalies in the Center East Pacific in winter can cause the significant(insignificant)positive SST anomalies in the Indian Ocean and negative SST anomalies in the tropical NWP in summer,resulting in the stronger(weaker)Pacific–Japan Teleconnection(PJ)over Japan and tropical NWP during the period 1979–1998(1999–2012),and ultimately lead to the interdecadal change of summer precipitation teleconnection.