Large-scale Drivers of Sustained North China Drought Persisting from Spring to Summer and Its Potential Predictability

The large-scale circulation drivers of North China drought persisting from boreal spring to summer and its potential predictability in ENSEMBLES multi-model seasonal retrospective forecast are investigated in this study. It is shown that drought over North China both in spring and summer is directly related to lower-tropospheric anomalous cyclone over Northwestern Pacific and weaker upper level westerly north to the jet core due to tropospheric temperature cooling along the westerly jet core. The consecutive spring-summer North China drought tends to occur in the year when La Niña in the previous winter develops to El Niño in the subsequent winter, when the two key circulation anomalies are both observed. In the spring following La Niña (summer preceding El Niño peak phase), the anomalous lower-tropospheric cyclone in the western North Pacific is forced by cool (warm) SST anomalies over central Pacific through Pacific-East Asian teleconnection (Matsuno-Gill response to anomalous heating equatorial central-eastern Pacific), and cooling along the upper-level westerly jet is resulted from wave train triggered by heating anomalies of excessive precipitation in the maritime continent (upper-level circumglobal teleconnection by less rainfall over Indian monsoon). The hindcasts of the ENSEMBLES started from 1^st May reasonably predicted the dry condition over North China in the observed summer drought years but with weaker magnitude. The reasonable prediction is because that warm SST anomalies over equatorial Pacific Ocean and associated atmospheric teleconnection are well predicted.