Sub-seasonal variability of extreme heatwaves in eastern China and its structural linkage to the Tibetan Plateau atmospheric heat source

Recent extreme heatwaves in eastern China have caused escalating socio-economic and environmental vulnerabilities. This study identifies distinct sub-seasonal variability in summer heatwaves, with the North China Plain (NCP) prominently affected in June and the Yangtze River Valley (YRV) during July–August (JA). The Tibetan Plateau atmospheric heat source (TP AHS) exhibits corresponding spatial differences, displaying significant interannual co-variability with regional heatwave features. During June, an intensified TP AHS is accompanied by a southward displacement of the upper-level westerly jet stream, driving differential thermal advection and deep subsidence over the NCP. Spatially overlapping with this aloft downwelling, the westward expansion of the western Pacific subtropical high (WPSH) aligns with a positive horizontal temperature advection center over the NCP, closely tied to an anomalous mid-to-lower tropospheric cyclonic circulation along the northern flank of the WPSH. During JA, the enhanced TP AHS corresponds to a northward jet stream shift and a northwestward relocation of the South Asian High (SAH), establishing anomalous upper-level convergence over the YRV. These multi-scale circulation configurations, together with a V-shaped isentropic downglide structure radiating from the TP, form a coherent dynamic framework driving persistent subsidence over the YRV. Additionally, these dynamically aligned subsidence zones feature prominent cloud reduction that enhances surface downward solar radiation and sensible heat flux. Through a land–atmosphere coupling loop, these localized diabatic feedbacks structurally match the enhanced intensity and persistence of regional extreme heatwaves. These findings demonstrate that the TP AHS exhibits a month-dependent configuration structurally coupled with sub-seasonal heatwaves across eastern China, co-varying with 35–51% of the extreme heatwave days. This provides process-level insights into the physical linkages between upstream TP thermal anomalies and downstream thermodynamic extremes.