Unconventional cold vortex as precursor to historic early summer heatwaves in North China 2023

In mid-June to July 2023, North China experienced historic heatwaves with intense near-surface warming and an advanced seasonal cycle of local air temperature. An unconventional upper-tropospheric cold vortex in early June, departing from conventional heat-dome patterns, preceded the extreme heat. A strong zonal SSTA gradient across the Indo-Pacific warm pool initially suppressed Indian summer monsoon (ISM) convection, exciting a tropical–extratropical teleconnection that generated a cold vortex over and to the east of North China. This anomaly intensified the air–land thermal contrast, increased sensible heating, and reduced soil moisture in situ. The drier soils then sustained and amplified sensible heating and surface air temperature, culminating in extraordinary heatwaves; subsequent lower-tropospheric warming destabilized the column and mitigated the upper-level cold vortex. Historical data corroborate the extremity of 2023 air–sea interactions. ECMWF real-time subseasonal-to-seasonal (S2S) forecasts captured the cold-vortex precursor and air–land feedbacks but underestimated heatwave intensity due to soil moisture biases. Thus, the initial cold-vortex condition and coupled air–land–sea interactions provided S2S predictability of the historic 2023 North China heatwaves.

Boqi Liu, Yanan Duan, Shuangmei Ma, Yuhan Yan, Congwen Zhu