Concurrent extremes in mid-latitude Asia triggered by resonance of multi-scale zonal wind

Abstract

Climatic changes worsen concurrent extreme climate events. In July and August of 2022 and 2020, respectively, unexpected concurrent extreme events occurred in mid-latitude Asia. The sudden and severe consequences highlight the importance of a thorough understanding of the drivers of such extreme events, which is crucial for improving predictions and implementing preventive measures to mitigate future risks. By applying multi-scale window transform methodology, a unique mechanism of multi-scale zonal wind resonance is identified, which manifests as a quasi-stationary co-coupling with low-frequency zonal winds. This resonance leads to barotropic instability, triggering abnormal low-frequency Rossby wave behavior in the entrance and exit regions of the quasi-stationary jet stream. Simultaneously, the intensified meridional wind, coupled with adiabatic atmospheric warming, amplifies baroclinic instability, resulting in an enhanced wave pattern and the high concurrence events of 2022. Under long term future global warming levels of 4 °C, the concurrence, strengthened by multi-scale zonal wind resonance, is expected to persist. The mechanism evident in 2022 plays a broader and more significant role in concurrent events compared to the mechanism in 2020. Under the process of warming, resonance phenomena, as observed in 2022, are projected to become more frequent.