Tropical 200 mb Divergent Circulations and Their Relation to Outgoing Longwave Radiation
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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Annual and interannual variability of the 200 mb level mean meridional circulations Hadley and Ferrel cells and 200 mb tropical east-west circulations Walker circulations are presented as inferred from the velocity potential field. Also, a relationship is presented between divergence at 200 mb and outgoing longwave radiation OLR. A major feature of the 200 mb tropical divergent velocity field is the dominance of the western Pacific monsoon region as the source for meridional and zonal overturning motions. Smaller, but significantly similar source regions are found over South and Central America as well as central Africa. Intra-annual variations of the equatorial Hadley cell are dominated by the variations of Asian Monsoon circulations. The seasonal fluctuations in the divergent velocity field in the western Pacific contribute to a strong annual cycle in the inter-annual pattern in the tropics. The results on east-west over-turning motions show that there are three cells associated with the three ascending branches over the Asian monsoon, South and Central America, and Central Africa. The most dominant cell is the Walker cell with its ascending branch over the western Pacific Asian monsoon and descending branch in the eastern equatorial Pacific. The intensity and location varies within the year. The inter-annual variability appears to be associated with the El Nino event. The relationship between divergence and the equivalent blackbody temperature index, is significant in the tropical convective region. Theses.