Asymmetric Relationship Between the East China September Precipitation and El Niño‐Southern Oscillation in the Decaying Phases Over the Past Three Decades

ABSTRACT Early autumn precipitation over East China is crucial for local agriculture and economy. Based on observational and reanalysis data, this study explores the asymmetric effects of El Niño‐Southern Oscillation (ENSO) on the East China September precipitation (ECSP) during the decaying stages in 1991–2022. The results indicate an evident positive relationship between the ECSP and the ENSO‐related sea surface temperature (SST) anomalies in the preceding winter, while the situation is asymmetric for El Niño and La Niña events. In the El Niño cases, East China shows a weak positive precipitation anomaly in the decaying September. In contrast, a strong precipitation deficit occurs over East China in September during the decaying stage of La Niña. Further analyses show that the meridional path of ENSO affecting the ECSP plays a key role in such asymmetric precipitation anomalies. In particular, El Niño and La Niña SST anomalies trigger the anomalous low‐level cyclone and anticyclone over the North Pacific, causing local cold and warm SST anomalies, respectively. The ENSO‐induced North Pacific SST anomalies could stimulate anomalous atmospheric circulation anomalies over the Northwestern Pacific through local atmosphere–ocean feedback during decaying ENSO stages. Due to the asymmetric duration of ENSO events, the warm El Niño SST anomalies rapidly turn to cold during the following summer, and the anomalous cyclone and cold SST anomalies over the North Pacific could not sustain. Thus, the water vapour flux over East China is barely affected in September. On the other hand, the cold La Niña SST anomalies show strong duration and persist into the following early autumn, maintaining the warm North Pacific SST anomalies through continuously stimulating local anomalous anticyclone. This results in an abnormal northerly wind over East China and below‐normal water vapour transport, which results in local precipitation deficit.