Harmonic Analysis On Tropically Anomalous Wind Field

This paper presents a Harmonic analysis scheme on a sequence of monthly anomalous wind {V'(t)} in the tropical field (30°S～30°N) on basis of the decomposition of Lorenz.The analysis of tropically monthly {V'(t)} with the pressure on levels 850 and 200 from 1948 to 2006 shows that: 1) Module square of steady wave abnormalities S'^* is much larger than that of the zonal uniform abnormalities [S']. It is significantly different from the spectral structure of module square (?) of climatological wind, which is mainly about the trade wind. Strong module square of steady wave abnormalities and it's fitting rate of abnormally steady wave varies with latitudes (?) and seasons,whose spectral structure is relatively more simple of level 200 than that of 850. Module square of zonal wind anomalies has obviously side-interannual changes, but its great value less corresponds to ENSO events. 2){V'(t)} is characterized by low dimension and low order.Apart from a few months, the module square of all-terrain abnormally unsteady wave S'_|m|^* reduces with the increase of |m|.The components of |m| =1,2 are significantly higher than that of other components. Strong module square of steady wave abnormalities and it's fitting rate of abnormally steady wave varies with latitudes (?) and seasons of |m| =(?), which is complxed on level 200 than 850. 3) The steady-wave abnormalities of important components |m|=1,2,all have significant interannual variability ,and the phase and amplitude are related to ENSO events closely.The amplitude in the most years of El Nino is less in January than that in July,which is large in La Nina years. The phase of -1 wave is in the west (negative anomalies) in most years of El Nino,whose amplitude is small. The phase of +1 wave is in the east (anomalies) in most years of El Nino, whose amplitude is large except July of level 200,and the phase is the opposite in July. It is anti-related of the phase of La Nina, and it isn't obvious of El Nino in Junuary. It is in contrary of July. A majority of anti-La Nina phase exsit in January and July of level 200 of +2 wave. At the same time, it becomes the anti-phase between levels 200 and 850 in July. 4) Circulation varies significantly, and it is conducive to strengthening and weakening circulation, which meets the kinetic theory.Steady wave abnormalities is associated with index ONI highly.The circulation significance of V'_|1|^*,V'_|2|^* is clear in the strong El Nino events of 1983. Therefore, Harmonic analysis is very effective to study the tropical structure of the space-time of anomalous wind.