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 motio...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 propa- gation picture of low frequency waves modulated and its influence on midium-range variation of summer monsoon are also discussed.展开更多
Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSO year,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters and their influences upon 30—60 day oscilla...Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSO year,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters and their influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta- tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that in the winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone are mainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982— 1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonal changes of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinal progression or regression of about 40 day period.There are marked differences between propagat- ing passages of low frequency modes responsible for changes of subtropical jet stream in the normal year(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude show obvious phases.In general,the one in late winter is stronger than that in early winter,strongest one occurs in February.展开更多
文摘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 propa- gation picture of low frequency waves modulated and its influence on midium-range variation of summer monsoon are also discussed.
基金This work was supported by the National Natural Science Foundation of China.
文摘Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSO year,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters and their influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta- tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that in the winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone are mainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982— 1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonal changes of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinal progression or regression of about 40 day period.There are marked differences between propagat- ing passages of low frequency modes responsible for changes of subtropical jet stream in the normal year(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude show obvious phases.In general,the one in late winter is stronger than that in early winter,strongest one occurs in February.
