The dominant role of upper tropospheric-lower stratospheric process in increasing summer heatwave intensity over East Asia and Northwestern Pacific

Abstract The unprecedented strong heatwave event in East Asia and the Northwestern Pacific during the summer of 2022 has been attributed to global oceans under global warming¹–⁵. However, their contributions are limited and do not exert a dominant effect on the increase of heatwave intensity, especially in East Asia⁶,⁷. Clearly, the reasons for the increasing strong heatwave events remain mysterious. Here we report that the intensified upper troposphere-lower stratosphere (UT-LS) temperature dipole structure plays the dominant role in the escalating trend of heatwave intensity in East Asia and the Northwestern Pacific during the recent decades, while oceans play a minor role. Through observational diagnosis and numerical simulation, we establish that the depleting trend of the lower-stratospheric ozone, along with a thinner ozone layer in the lower-stratosphere, is the primary driver behind the intensified UT-LS dipole structure and the tropospheric warming over extratropical Asia. The warming troposphere increases heatwave intensity in East Asia and the Northwestern Pacific through cloud, radiation, and temperature advection. With further ozone depletion under the Shared Socioeconomic Pathway 2-4.5 scenario, the projected heatwave events in these areas will likely become stronger. Consequently, the coastal areas of East Asia and Northeast Asia will encounter an increasing risk of strong heatwave events.