Harmonic Analysis On Low Latitudinal Climatological Wind Field

A scheme of complex Fourier analysis on monthly wind field is put forward.850hPa, 200hPa climatological wind fields((?)) in low-latitude zone from 30°S to30°N and Asia are investigated, moreover the harmonic analysis on outgoinglong-wave radiation field (OLR) is combined. The results show that it has providesda series of valuable information. 1) Climatological wind fields ((?)) is characterizedby low dimension and low order, whose module square is centered upon the first few(3～5) wave components. 2) The most important wave component (?)₀ (m=0)characterizes the configuration of mean zonal trade winds. On 850hPa, trade windsare more extensive then the edge of westerlies all the year around; the highest tradewinds in the Northern and Southern Hemispheres and the thermal equator, matchingalong with hemispherical Hedley cell centers and the common ascending leg, movenorthwardly and southwardly approximately together with the seasons. 200hPaeasterlies and westerlies are also important in the whole year, but the former isweaker than the latter obviously. The seasonal movement of the tropical easterlies,towards north and south, shows clear hemispherical variations. 3) More than 80percents of the steady wave ((?)^*) module square are centered upon the first fewcouples of wave components (|m|=(?) on 850hPa and |m|=(?) on 200hPa),which show the main circulation system of (?)^*. The first couple ((?)_|1|^*), whosemodule square fitting rate ((?)_|1|^*) is much larger than others, displays the equatorialWalker cell and the seasonal movement of the intertropical convergence zone (ITCZ).The third and the second couples (|m|=3 and |m|=2) are the second mostsignificant in January and July respectively. Climatological OLR field has the same spectral structure, and analysis on it checks the veracity of the harmonic analysis onwind field. 4) Two couples of the most important wave components (|m|=1,3 inJanuary and |m|=1,2 in July) are able to show the main circulation structure of thesteady wave in Asia monsoon region. In winter, freezing air goes down along the eastof Qinghai-Tibet Plateau. There is great Hedley cell in East Asia, with northerly onlow altitude and southwester on the high. South Asia summer monsoon is controlledby westerly, while East Asia summer monsoon by southeaster. The analysis on therelevant wave components of OLR field supports the results above.