A NUMERICAL STUDY OF SHORT-RANGE CLIMATIC OSCILLATION WITH VARIOUS TIME SCALES FORCED BY EL NINO DURING THE NORTHERN SUMMER

The normal mode method is adopted to decompose the differences between simulations with SST (sea surface temperature) anomahes over centra-eastern Pacific and normal SST by use of a nine-layer global spectral model in order to investigate short-range climatic oscillation with various time scales forced by El Nino during the northern summer.Investigation shows that El Nino may have the following influence on atmosphere on various space-time scales.Extra-long wave components of Rossby mode forced by conve ctiveanomaly over equatorial western Pacific resulting from El Nino produce climatic oscillation on monthly (seasonal) time scale in middle-high latitudes of Southern and Northern Hemispheres;extra-long wave components of Kelvin mode forced by SST anomalies propagate along the equator,resulting in 30-60 day oscillation of tropical and subtropical atmosphere;and its long waves move eastward with westerly,resulting in quasi-biweek oscillation.