Influence of MJO active days over the Indian Ocean on precipitation days in the reaches of the Yangtze River

The influences of active days of the Madden-Julian oscillation (MJO) over the Indian Ocean on summer precipitation days over the middle and lower reaches of the Yangtze River were investigated. Daily precipitation data collected at 753 stations, monthly sea surface temperature (SST) data from the Hadley Centre, daily mean reanalysis data from the National Centers for the Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), and all-season real-time multivariate Madden-Julian Oscillation (RMM) index during 1980—2020 were used. The results show that the active days of MJO over the Indian Ocean have a statistically significant relationship with precipitation days over the middle and lower reaches of the Yangtze River, especially with the heavy precipitation days, since the MJO related circulation anomalies can continuously transport water vapor to eastern China. Further research indicates that the relationship between active days of MJO over the Indian Ocean and the precipitation days over the middle and lower reaches of the Yangtze River has experienced a decadal change with their relationship being significant since the 2000s. The decadal change of this relationship might be attributed to decreased variability in SST in the Indian Ocean. This decreased interannual variability of SST suggests weakened modulation effects on precipitation over the middle and lower reaches of the Yangtze River by the tropical Indian Ocean. In contrast, the MJO effects on the precipitation days over the middle and lower reaches of the Yangtze River turn to be significant after the 2000s due to less disturbances from the Indian Ocean SST.