Extended Range Forecast Experiment Based on Intraseasonal Oscillation

2－4 weeks extended range forecast (ERF) has become an important research area for operational developments of both weather forecast and climate prediction in the last decades. In order to provide scientific clues to establish ERF, by taking Meiyu over the Yangtze－Huaihe basin as an example, based on intraseasonal oscillation (ISO) signals of rainfall, key influential systems and strong signals of tropical MJO extracted by Ensemble Empirical Mode Decomposition (EEMD) and multi-variable EOF, optimal subset regression (OSR) statistical method, empirical wave propagation (EWP) dynamical method, and global ocean－atmosphere coupled model output are respectively employed to explore ERF of rainfall variation over the Meiyu region. Experimental results suggest that (1) the ISO may be an important system contacting weather processes and weather anomaly, which can be potential signals of the extended range forecast for pentad rainfall over the Meiyu region.(2) LFO (Low Frequency Oscillation) predictors extracted from rainfall in the Meiyu region during earlier period by EEMD can be used to forecast pentad rainfall amount in the Meiyu region about 30 days in advance by the OSR statistical method. (3) For the EWP method in dynamical sense, it can well forecast the eastward propagation of the tropical ITCZ 40 days in advance. At the same time, the EWP method has potential ability of forecasting wind anomaly over the Meiyu region. (4) The global ocean－atmosphere coupled model output is a worthwhile reference for the ERF of atmospheric circulation and MJO index 20 days in advance.