Impact Of ENSO On The Low-frequency Precipitation Over Southern China

Features of intra-seasonal (10-30d) variability of precipitation over southern China during autumn, winter and the following spring of different types of ENSO,The characteristics of MJO impact on precipitation in China are analyzed based on the Hadley Centre sea surface temperature (SST), the National Centers for Environmental Prediction (NCEP)/the National Center for Atmospheric Research(NCAR) atmospheric circulation data, Real-time multivariate MJO index, and China daily rainfall station data,and a statistical model of extended-range forecast are established based on RMM index.The main conclusions can be summarized as follows:(1) Impacts of different ENSO types on the intra-seasonal (10-30d) precipitation variability over southern China vary with different seasons. During the winter and following spring of EP El Nino events, the 10-30d precipitation variability over southern China is significantly enhanced. Intra-seasonal precipitation variance is weakened during the CP El Nino autumn while strengthened during the CP El Nino winter, showing inverse features. The impacts of La Nina events on the 10-30d precipitation variability are relatively small and unstable. Compared with the normal years, a strong anticyclonic circulation anomaly occurs over the Philippines during the EP El Nino years. The anomalous southerly winds in the west side of the anticyclone transport much more water vapor northward to southern China, which favors strengthened 10-30d rainfall variability. n anomalous cyclonic circulation occurs in the western North Pacific during CP El Nino autumn, which suppressed the tropical water vapor transporting northward to the East Asian continent. During CP El Nino winters, an anomalous anticyclone appears over the western North Pacific although its intensity is weak, which accounts for the inverse low frequency rainfall responses in autumn and winter. La Nina is relatively weaker responses of the 10-30d precipitation variability over southern China.(2)In EP El Nino events, the intensity of MJO is weaker than mean state.In CP El Nino events, the intensity of MJO is stronger than mean state. The possible reason is that EP El Nino changes the baroclinic structure of MJO, and weaken the intensity of MJO. While the CP El Nino increase the intensity of the MJO, so the amplitude of low-frequency rainfall in China is increased.(3)Based on the RMM index and SVD, a statistical extended-range forecast model are established to forecast the low-frequency rainfall in China. The model can reflect the characteristics of low frequency precipitation in the south of China during the MJO propagation, which has a certain effect on the prediction of the extension of the winter low frequency precipitation in China. The forecast skill in La Nina year is better than El Nino year.