In mid-June to July 2023, North China witnessed extreme heatwaves, marked by intense near-surface warming with an advanced seasonal cycle of local air temperature. An unconventional upper-tropospheric cold vortex in early June, deviating from conventional “heat dome” patterns, preceded the heatwave extremes. The zonal SSTA gradient in Indo-Pacific warm pool initially suppressed Indian summer monsoon convection, which stimulated the cold vortex around North China via a tropical-extratropical teleconnection. This anomaly intensified the air-land thermal contrast, leading to increased sensible heating and reduced soil moisture in situ. The drier soil conditions maintained and further augmented sensible heating, escalating surface air temperature, and culminating in extraordinary heatwaves. The air column was then destabilized to mitigate the upper-level cold vortex. Historical records corroborate the extremity of the air-sea interactions in 2023. The ECMWF real-time subseasonal-to-seasonal (S2S) forecasts successfully capture the air-land feedback in both cold vortex and heatwave stages, albeit with an underestimation of heatwave intensity due to biases in soil moisture anomalies. Consequently, the initial cold vortex condition and air-land-sea interactions yield S2S predictability to the historic 2023 heatwaves in North China.

2023年6月中旬至7月，华北地区出现极端热浪，近地表升温强烈，当地气温季节性周期提前。六月初，在极端热浪出现之前，出现了一次非常规的对流层上层冷涡，这与传统的“热穹”模式不同。印太暖池纬向海温梯度最初抑制了印度夏季风对流，印度夏季风对流通过热带-温带遥相关激发了华北周围的冷涡。这种异常现象加剧了空地热反差，导致显热增加和原位土壤湿度减少。干燥的土壤条件维持并进一步增强了显热，使地表气温不断上升，并最终导致异常热浪。然后空气柱变得不稳定，以减轻上层冷涡的影响。历史记录证实了2023年海气相互作用的极端情况。ECMWF实时次季节到季节（S2S）预报成功捕捉到了冷涡和热浪阶段的海陆反馈，尽管低估了热浪强度由于土壤湿度异常的偏差。因此，最初的冷涡条件和海陆相互作用为华北地区 2023 年历史性热浪提供了 S2S 可预测性。