Stronger Warming Effect of Sudden Stratospheric Warmings on the Late Winter Climate in China during El Niño than during La Niña

Abstract This study examines the combined effects of sudden stratospheric warming (SSW) events and El Niño–Southern Oscillation (ENSO) on late winter (January–March) climate in China. It is found that SSWs significantly modulate El Niño’s impact over China. During El Niño winters with SSWs, southern China tends to experience notable warming; conversely, without SSWs, the surface air temperatures there are generally colder. However, SSWs do not effectively alter La Niña’s impact; southern China remains anomalously colder during La Niña winters even when SSWs occur. The net warming effect of SSWs over much of China during La Niña, defined as the difference between scenarios with and without SSWs, is found considerably weaker than during El Niño. These discrepancies arise from the contrasting tropospheric pathway of ENSO teleconnection over the East Asia–Pacific region. Specifically, El Niño influences the occurrence of SSWs primarily by enhancing the tropospheric planetary wave 1. This enhancement corresponds to an emergence of a dipole pattern of geopotential height anomalies, characterized by an anomalous low over northeastern Eurasia and an anomalous high over China. In contrast, La Niña contributes to SSW occurrences via an increase in the tropospheric wave 2, which corresponds to only an anomalous low over northeastern Eurasia. The consistently significant high over China both before and after SSWs during El Niño, but much weakened or even absent during La Niña, is mainly responsible for the stronger net warming in late winter over China in El Niño years.