Prolonged Effects of the Madden–Julian Oscillation on Persistent Rainfall over Eastern China during Summer 2020

Using precipitation derived from CPC MORPHing technique (CMORPH) of the US National Oceanic and Atmospheric Administration, the US National Centers for Environmental Prediction Climate Forecast System version 2 reanalysis (CFSv2), ERA-5 reanalysis obtained from the European Centre for Medium-Range Weather Forecasts, and the Madden–Julian Oscillation (MJO) index of Wheeler and Hendon, the effects of MJO on rainfall persistence over eastern China in the summer of 2020 were analyzed. Three major conclusions were made based on the analyses of correlation, regression, and wave source. 1) Summer precipitation over eastern China in 2020 was extremely strong compared with rainfall in the previous 21 years. This is because the summer monsoon rain belt has been maintained for a very long time over southern China and the middle and lower reaches of the Yangtze River during 2020. 2) A negative geopotential height anomaly in the middle and upper atmosphere, with water vapor convergence between 1000 and 300 hPa and instability at the lower levels, has been maintained over eastern China. Thus, atmospheric circulation favored prolonged rainfall in the 2020 summer. 3) During this period, MJO was abnormally active in phases 1 and 2 with significant periods of 10–30 days, indicating that MJO convective centers were sustained over eastern Africa and the western Indian Ocean. Therefore, significant Rossby wave sources have been found over eastern Africa and the western Indian Ocean, which is consistent with the Gill mode. Finally, a Rossby wave train was excited at the sources and transported by a jet stream, which induced the negative geopotential height anomaly over eastern China. Negative geopotential height anomaly over the eastern region maintained and prolonged the rainfall during 2020 because the MJO was sustained in phases 1 and 2. Sensitivity experiments further prove that the 10–30-day signal favors the formation of the negative anomaly of the 500 hPa geopotential height and the positive anomaly of precipitation over eastern China.