Influences of tropical circulation and sea surface temperature anomalies on extreme heat over Northeast Asia in the midsummer of 2018

A destructive extreme heat attacked Northeast Asia (NEA) in the midsummer of 2018, characterized by the average midsummer T-max (daily maximum air temperature at 2 m) ranking first during the study period. The current study indicates that the cyclonic anomaly over the western North Pacific (WNP) was an important cause, which presents an anomaly of two standard deviations. The cyclonic anomaly over the WNP was accompanied by anomalous convection, which favored descending and anticyclonic anomalies over NEA through a local meridional cell. The anticyclonic anomaly over NEA corresponds to the northwestward extension of the WNP subtropical high and facilitated the occurrence of extreme heat. The tropical sea surface temperature anomaly (SSTA) presents a La Nina decaying episode, but the SSTA over the tropical Pacific and North Indian Ocean was weak in the summer. In contrast, the southeastern tropical Indian Ocean (SETIO) was obviously cool, which was the coolest after detrending. The SETIO cooling triggered a low-level southeasterly anomaly, which turned into a southwesterly after crossing the equator, due to the Coriolis force. The southwesterly anomaly extended eastwards and favored the cyclonic anomaly over the WNP. Meanwhile, the circulation anomalies over the SETIO and WNP were connected via a local meridional cell, with the ascending branch over the WNP. Moreover, the above mechanism also operates for the climate statistics, verifying the robust influence of the SETIO SSTA. Considering the consistency of the SETIO SSTA, it could be a potential predictor for the climate over the WNP and NEA.