Impacts of the SSTs over Equatorial Central–Eastern Pacific and Southeastern Indian Ocean on the Cold and Rainy/Snowy/Icy Weather in Southern China

Low temperature together with snow/freezing rain is disastrous in winter over southern China. Previous studies suggest that this is related to the sea surface temperature (SST) anomalies, especially La Niña conditions, over the equatorial central–eastern Pacific Ocean (EP). In reality, however, La Niña episodes are not always accompanied by rainy/snowy/icy (CRSI) days in southern China, such as the case in winter 2020/2021. Is there any other factor that works jointly with the EP SST to affect the winter CRSI weather in southern China? To address this question, CRSI days are defined and calculated based on station observation data, and the related SST anomalies and atmospheric circulations are examined based on the Hadley Centre SST data and the NCEP/NCAR reanalysis data for winters of 1978/1979–2017/2018. The results indicate that the CRSI weather with more CRSI days is featured with both decreased temperature and increased winter precipitation over southern China. The SSTs over both the EP and the southeastern Indian Ocean (SIO) are closely related to the CRSI days in southern China with correlation coefficients of −0.29 and 0.39, significant at the 90% and 95% confidence levels, respectively. The SST over EP affects significantly air temperature, as revealed by previous studies, with cooler EP closely related to the deepened East Asian trough, which benefits stronger East Asian winter monsoon (EAWM) and lower air temperature in southern China. Nevertheless, this paper discovers that the SST over SIO affects precipitation of southern China, with a correlation coefficient of 0.42, significant at the 99% confidence level, with warmer SIO correlated with deepened southern branch trough (SBT) and strengthened western North Pacific anomalous anticyclone (WNPAC), favoring more water vapor convergence and enhanced precipitation in southern China. Given presence of La Niña in both winters, compared to the winter of 2020/2021, the winter of 2021/2022 witnessed more CRSI days, perhaps due to the warmer SIO.