The mechanism of EAP-EU combined impact on summer rainfall over North Asia

This article uses wave activity flux and sea surface temperature (SST) to explore the mechanism of EAP-EU combined impact on summer rainfall in North Asia (NA). EAP and EU teleconnections can be divided into four categories of configuration according to their anomaly phase features. The category I (II) configurations cause rainfall in the Urals and the Okhotsk Sea and the region from Northeast China to Japan being less (more), the Lake Baikal to the Okhotsk Sea being more (less), which leads to the summer rainfall in NA mainly presenting the "- + -" ("+ - +") a tripole wavelike structure. Category I (II) configurations also show the West-East reverse anomalies of summer rainfall in northern NA and the North-South opposite anomalies in eastern NA. The EAP and EU teleconnections have an obvious correlation with the ENSO-like pattern of SST anomalies over the tropical Pacific. When warm ENSO is in the development phase, it is conducive to stimulate Rossby waves propagating eastward from the North Atlantic Ocean via the PNA teleconnection, forming the EU teleconnection across the Eurasia continent. Meanwhile, the warm summer SSTA anomalies over tropical east Pacific and IMC are conducive to the local thermal convective over Indo-Pacific warm pool and motivate the EAP teleconnection, propagating northward to mid-high latitude region. EAP and the EU teleconnections overlapped with each other, form the tripole atmospheric structure in NA, and produce relevant rainfall anomaly patterns. For the category IV of EAP-EU configuration, the warm SST anomalies in the equatorial region gradually weaken from previous winter to summer. Weak tropical east Pacific SST anomalies are conducive to excite the EU teleconnection with different wave train features against the category II, presenting a strong positive anomaly center over the Ural mountain and Baikal lake. This positive center connected with the EAP caused positive anomalies over FER resulting in the dipole pattern of atmospheric and rainfall anomalies in the summer season. The condition is opposite for the category III (I) configuration against that of category IV (II). It is also found that the influence on EAP-EU configuration caused by ENSO-like pattern of SST anomalies over the tropical Pacific has an obvious asymmetric feature that category II (I) configuration relevant SST forcing is much significant than that of category IV(III) configuration.