This study employs station observation and Meiyu monitoring data in the middle-lower Yangtze River (MLYR) basin to investigate a distinctive heatwave phenomenon, characterized by an accelerated onset following the Meiyu termination in 2001–2022. In the basin, the proportion of rapid heatwaves (transition duration less than two days) is 30 % in the period 1981–2000, while it increased markedly to 77 % in the period 2001–2022. Furthermore, the accelerating onset of heatwaves in the basin is not limited to the surface. The results of the statistical analysis demonstrate the significant influence of circulations in the middle-low troposphere. In comparison to the circulations observed during the period between 1981 and 2000, the geopotential height (GPH) over the basin displays a considerable increase between 300 and 700 hPa following the termination of Meiyu in the later period. Additionally, there is a notable acceleration in the warming of the lower troposphere. The abrupt evolution of the circulation patterns resulted in the formation of a rapid heat-dome effect over the entire basin. This effect persists even when the warming trend of air temperatures and the enhancing trend of GPHs are removed. The heat-dome effect is closely associated with the rapid shift of the western Pacific subtropical high (WPSH), particularly its western boundary. The rapid westward extension of the WPSH after the Meiyu event and its subsequent control of the MYLR basin form an “Ω”-shape circulation structure, which block the cold air invasion from high latitudes and enhance the geopotential heights by downward shortwave radiation, to induce the heat dome over the basin. This, in turn, will accelerate the onset and persistence of heatwaves.

中文翻译：

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梅雨雨终止后长江中下游流域热浪加速爆发


本研究利用长江中下游流域 （MLYR） 的站点观测和梅雨监测数据，研究了一种独特的热浪现象，其特征是 2001-2022 年梅雨终止后加速发作。在该流域中，1981-2000 年期间快速热浪（过渡持续时间少于两天）的比例为 30%，而在 2001-2022 年期间显著增加到 77%。此外，盆地中热浪的加速发作不仅限于地表。统计分析结果表明，环流对对流层中低层具有显著影响。与 1981 年至 2000 年期间观测到的环流相比，在梅雨后期终止后，该流域的位势高度 （GPH） 在 300 至 700 hPa 之间显示出相当大的增加。此外，对流层低层的变暖明显加速。环流模式的突然演变导致整个盆地形成快速的热穹顶效应。即使去除了气温的变暖趋势和 GPHs 的增强趋势，这种影响仍然存在。热穹顶效应与西太平洋副热带高压 （WPSH） 的快速移动密切相关，尤其是其西部边界。美雨事件后 WPSH 的快速西伸及其对 MYLR 盆地的控制形成了“Ω”形环流结构，阻断了来自高纬度地区的冷空气入侵，并通过向下的短波辐射提高了位势高度，从而在盆地上空诱发了热穹顶。反过来，这将加速热浪的发生和持续。