CEOF ANALYSIS OF ATMOSPHERIC LOW FREQUENCY OSCILLATION IN LOWER LATITUDE REGION AND FREQUENCY MODULATION PHENOMENA OF LOW FREQUENCY SIGNALS

The low frequency oscillation of the low level atmospheric circulation in lower latitudes region is studied by usingthe CEOF method and other normal spectral analysis methods.It is found that in the atmospheric motion frequencyspectrum,there exist certain frequency bands with relatively-concentrated energy among low frequency bands,andthere is nonlinear interaction of frequency modulation among peak signals.It is this modulating action that leads to thechange of the temporal-spatial features of frequency and phase of these low frequency signals.In the paper,the propa-gation picture of low frequency waves modulated and its influence on midium-range variation of summer monsoon arealso discussed.