Influence of Madden–Julian Oscillation on Wintertime Rainfall Extremes in Southern China and Its Predictability

The influence of Madden-Julian oscillation (MJO) on rainfall distribution of southern China is studied by using daily rainfall datasets from 2400 stations in China. It is shown that the probability density function of November-March rainfall in southern China is skewed towards large (small) values in phases 2-4 (6-7) of MJO, during which the probability of extreme rainfall events increases (reduces) by 30-50% (20-40%) relative to the PDF of all days. Moisture budget analysis indicates that the favorable environment for rainfall extremes is associated with northward moisture transport to mainland China coming from the Bay of the Bengal and the South China Sea and enhanced vertical moisture advection over southern China during the phases 2-3 of MJO, while the horizontal moisture advection contributes insignificant. Based on the above results, the predictability for extreme rainfall is examined by using hindcasts from NOAA Climate Forecast System version 2 (CFSv2). It is shown that CFSv2 forecasts the modulations of MJO on rainfall extremes well albeit a slight bias in the magnitude. This study suggests the feasibility of deriving a monitoring and probabilistic forecasts of extreme rainfall in southern China.