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 using the CEOF method and other normal spectral analysis methods.It is found that in the atmospheric motion frequency spectrum,there exist certain frequency bands with relatively-concentrated energy among low frequency bands,and there is nonlinear interaction of frequency modulation among peak signals.It is this modulating action that leads to the change of the temporal-spatial features of frequency and phase of these low frequency signals.In the paper,the propagation picture of low frequency waves modulated and its influence on midium-range variation of summer monsoon are also discussed.