Impacts of Sea Surface Temperature in the Tropical Pacific on Interannual Variability of Madden-Julian Oscillation in Precipitation

The Madden-Julian Oscillation (M JO) is investigated in two sets of 11-year records of observed precipitation, the daily mean Microwave Sounding Units (MSU) oceanic rainfall (Spencer, 1993) data and the pentad Climate Prediction Center Merged Analysis of Precipitation (CMAP) data (Xie and Arkin, 1997).Obvious interannual variability is found in the M JO in the tropical Pacific. M JO is limited to the west of dateline in normal years while extends more east during the year of warm sea surface temperature (SST) appeared in the eastern Pacific (i.e., El Nino years of 1982-1983, 1986-1988, 1991-1992) and manifested in the central-eastern Pacific for several months. The most significant correlation between interannual variability of M JO in the central-eastern Pacific and SST was found in the vicinity of the Nino3 region. Forced by observed SST, CCM3 presents a realistic trend of interannual variability to M JO in the 11 years, with a smaller magnitude than that from the observation. Comparison between the two realizations of the CCM3 simulation, which are forced by weekly and monthly mean SST respectively, showed that the M JO activities resemble each other in central-eastern Pacific while there is discrepancy in the western Pacific. It is suggested that the interannual variability of M JO is controlled, to certain extent by the powerful interannual variability of SST in the central-eastern Pacific. In the western Pacific, however, there were remarkable impacts of the intraseasonal oscillation of SST on the M JO, where there was active M JO around the year. The notable disagreement between simulated and observed M JO in the western Pacific may come from the lack of high frequency variation of SST force, or from the shortage of air-sea interaction for the intraseasonal time scale. It might be of importance to the M JO which is unable to be represented in the atmospheric model.