RETRIEVAL OF THE TROPICAL DIVERGENT WIND FROM OLR AND ITS APPLICATION IN ENSO DIAGNOSIS

In this paper,two schemes proposed by Julian(1984)and Krishnamauti(1986)are used toretrieve the tropical divergent wind at 200 hPa and 850 hPa from the satellite observational Outgoing Long-wave Radiation(OLR).The comparison study has been conducted among the OLR-derived divergent wind field and those directly from wind fields of ECMWF and CAC tropical analysis,and NCEP/NCAR reanalysis for examining their reliability.Then,the divergent windretrieved from OLR by using Julian's scheme is used to composite the diagrams of the Walker circulation and the local Hadley circulation during 1982-1983 ENSO event.The possible linkagebetween the anomalies of summer rainfall in East China during this period and the anomalous Walker and local Hadley circulations is discussed.It is shown that it is practically feasible to use the satellite observed OLR data in theestimation of the tropical divergent wind.It is aiso indicated that NCEP/NCAR reanalysis hasmade a progress for improving the reliability of the tropical divergent wind,though some biasesstill exist in the description of the intensity and position of the divergence (convergence) maximumcenters over Asian monsoon region.The application of Julian's method to a diagnosis on the evolutions of the anomalous Walker and Hadley circulations during 1982-1983 ENSO event showsthat the development of this ENSO event is not companied with the sudden reversal of the Walker circulation,but the propagation of the ascending branch over the western Pacific to the central-eastern Pacific and crossing through the date line,which results in a significant displacement of thevertical circulation over the West Pacific(WP)and the central-east Pacific(CEP).It is alsoindicated that there exists a close linkage between the change of local Hadley circulation in the WPand the Walker circulation in the CEP,implying that the Walker circulation possibly severs as abridge between the anomalies of the SST in the CEP and the change of local Hadley circulation inNorthwest Pacific.The latter is responsible for the climate anomaly over eastern China during thisperiod.