Two major sudden warming events in the unprecedentedly active stratosphere during the boreal winter of 2023/2024 and their distinct surface impacts over China

Abstract

In the boreal winter of 2023/2024, the 10-hPa stratosphere experienced unprecedented planetary wave activity. This led to two major sudden stratospheric warming (SSW) events occurring on January 16 and March 4. The onset processes of both SSWs demonstrated clear stratosphere-troposphere coupling. On one hand, notable precursor signals were detected in the troposphere before each SSW. Approximately 15 days prior to the first SSW, a markedly intensified 500-hPa high pressure emerged over the high-latitude Atlantic, resulting in the strongest wave 3 in the troposphere since 1979. Additionally, an anomalous high over eastern Europe served as a precursor signal for the second SSW, contributing to a rapid increase in waves 1 and 2 approximately 20 days before its occurrence. On the other hand, these two SSWs exhibited distinct impacts on subsequent surface air temperature (SAT) over China. Specifically, the first SSW was characterized as a reflecting event. Following its onset, strong planetary wave reflections were observed in the troposphere over the Siberian and North Pacific regions, leading to local high-pressure ridge development. The two ridges, along with troughs between them, created an “inverted Ω-shaped” circulation pattern and caused a cold wave across China during January 18–22. In contrast, the second SSW was identified as an absorbing event; its impact aligned with typical effects of SSWs on SAT over Eurasia. After its onset, a negative phase of Northern Annular Mode emerged in the stratosphere and propagated downward into the troposphere over time, resulting in warming conditions over China during the following month.