SEASONAL AND INTERANNUAL VARIABILITY OF ATMOSPHERIC HEAT-SOURCES AND MOISTURE SINKS AS DETERMINED FROM NCEP-NCAR REANALYSIS

Using the National Centers for Environmental Predictions (NCEP)-Nation al Center for Atmospheric Research (NCAR) reanalysis, distributions of the heat source Q(1) and moisture sink Q(2) between 50 degrees N and 50 degrees S are determined for a 15-yr period from 1980 to 1994. Heat ing mechanisms operating in various parts of the world are examined by comparing the horizontal distributions of the vertically integrated h eat source [Q(1)] with those of the vertically integrated moisture sin k [Q(2)] and outgoing longwave radiation (OLR) flux and by comparing t he vertical distributions of Q(1) with those of Q(2). In northern wint er, the major heat sources are located (i) in a broad zone connecting the tropical Indian Ocean, Indonesia, and the South Pacific convergenc e zone (SPCZ); (ii) over the Congo and Amazon Basins; and (iii) off th e east coasts of Asia and North America. In northern summer, the major heat sources are over (i) the Bay of Bengal coast, (ii) the western t ropical Pacific, and (iii) Central America. Throughout the year, the S outh Indian Ocean, eastern parts of the North and South Pacific Oceans , and eastern parts of the North and South Atlantic Oceans remain to b e heat sinks. The desert regions such as the Sahara are characterized by large sensible heating near the surface and intense radiative cooli ng aloft: Over the tropical oceans, heat released by condensation with deep cumulus convection provides the major heat source. The radiative cooling and moistening due to evaporation are dominant features over the subtropical oceans where subsidence prevails. Over the Tibetan Pla teau, the profiles of Q(1) and Q(2) show the importance of sensible he ating in spring and contributions from the release of latent heat of c ondensation in summer. Off the east coast of Japan, intense sensible a nd latent heat fluxes heat and moisten the lower troposphere during wi nter. Heat sources in various regions exhibit strong interannual varia bility. A long (4-5 yr) periodicity corresponding to the variations in OLR and sea surface temperature (SST) is dominant in the equatorial e astern and central Pacific Ocean, while a shorter-period oscillation i s superimposed upon the long-period variation over the equatorial Indi an Ocean. The interannual variations of [Q(1)] OLR, and SST are strong ly coupled in the eastern and central equatorial Pacific. However, the coupling between the interannual variations of [Q(1)] and OLR with th ose of SST is weak in the equatorial western Pacific and Indian Ocean, suggesting that factors other than the local SST are also at work in controlling the Variations of atmospheric convection in these regions.