Using observation data and numerical simulations, we have demonstrated that the stratospheric Quasi-Biennial Oscillation (QBO) can predict extreme high temperatures (EHTs) in South Asia in June. The vertical structure of the QBO plays a crucial role in this prediction. When the QBO in June shows easterlies (westerlies) at 50 hPa and westerlies (easterlies) at 70 hPa, more (fewer) EHT events occur. This likely results from the QBO’s vertical structure causing positive (negative) temperature anomalies in the lower stratosphere and negative (positive) static stability anomalies near the tropical tropopause. These anomalies enhance (weaken) convective activity over the equatorial Indian Ocean, leading to anomalous circulation with ascending (descending) air over the equatorial Indian Ocean and descending (ascending) air over northern and central South Asia. This suppresses (promotes) convection over northern and central South Asia, affecting cloud formation and precipitation. Consequently, more (less) solar radiation reaches the region, along with weaker (stronger) evaporative cooling effects, warming (cooling) the surface and creating a background state conducive to (against) EHT events. Additionally, the opposite zonal winds at 30 hPa and 50 hPa in April may serve as a reference factor for predicting the probability of EHT events in northern and central South Asia. This study provides a potential approach for forecasting tropospheric extreme weather events based on stratospheric signals.

利用观测数据和数值模拟，我们证明平流层准两年期振荡（QBO）可以预测南亚六月的极端高温（EHT）。 QBO 的垂直结构在这一预测中起着至关重要的作用。当 6 月 QBO 显示 50 hPa 的东风（西风带）和 70 hPa 的西风带（东风）时，会发生更多（更少）的 EHT 事件。这可能是由于 QBO 的垂直结构导致平流层下部出现正（负）温度异常，以及热带对流层顶附近出现负（正）静态稳定性异常。这些异常增强（减弱）赤道印度洋上空的对流活动，导致赤道印度洋上空出现上升（下降）空气以及南亚北部和中部上空下降（上升）空气的异常环流。这抑制（促进）南亚北部和中部的对流，影响云的形成和降水。因此，更多（更少）的太阳辐射到达该区域，伴随着更弱（更强）的蒸发冷却效应，使地表变暖（冷却），并创造出有利于（对抗）EHT事件的背景状态。此外，4月份30 hPa和50 hPa的相反纬向风可以作为预测南亚北部和中部EHT事件概率的参考因素。这项研究为基于平流层信号预测对流层极端天气事件提供了一种潜在的方法。