Impacts Of North Eurasian Spring Soil Moisture On Summer Rainfall In Northern East Asia: Mechanism And Prediction Experiment

The prediction for summer rainfall in northern East Asia has been maintaining on a low level for several years.From the perspective of climatic effects of soil moisture,this research explored the physical mechanism through which late-spring North Eurasian soil moisture influences summer rainfall anomalies in northern East Asia.By prediction experiment,we provided new initialization scheme of soil moisture to improve the prediction level of summer rainfall in northern East Asia.Via statistical prediction model,the potential contribution of precedent soil moisture to the predictability of summer rainfall in northern East Asia was clarified.The main conclusions are summarized as follows:The late-spring North Eurasian soil moisture is found to be significantly connected with the summer rainfall of northern East Asia.The soil in North Eurasia in spring is obviously wetter and more variable than the one in other seasons.The anomalous soil moisture in autumn and winter is significantly positively correlated with the one in spring and summer.Therefore,late-spring is supposed to be the critical season that the signal of soil moisture could release and have impact on climate.Typical issues show that the late-spring North Eurasian soil moisture is significantly negatively correlated with the summer rainfall of northern East Asia and closely related to the circulation that affects rainfall.The late-spring North Eurasian soil moisture can significantly affect the summer circulation related to rainfall.The lower soil moisture in spring over North Eurasia may persist into the following summer,then heat the lower-level atmosphere at higher latitudes by affecting the heat fluxes,and effectively reduce the meridional temperature gradient north of East Asia.The weakened temperature gradient could induce the decreased vertical shear of zonal wind and generate an anomalously cyclonic center over northern East Asia.The anomalous circulation over northern East Asia is favorable for the strengthened storm track and the activity of synoptic eddies,providing beneficial conditions for rainfall.The persistence of soil moisture and the affected heat fluxes are the key links in the process of influencing rainfall.The late-spring North Eurasian soil moisture has obvious impacts on the prediction of summer rainfall.More accurate prediction by operational model will be generated under the circumstance of persistence of soil moisture in model or amendment using realistic soil moisture data.The regression statistical model based on soil moisture is able to predict summer rainfall in northern East Asia well.