The thermally coupled response of the planetary scale circulation to the global distribution of heat sources and sinks

The time-averaged structure of global monsoonal circulations and planetary scale transport processes are determined from the FGGE Level IIIa operational data set generated by the US National Meteorological Center. Through isentropic diagnostics, rotational and irrotational components of the horizontal mass transport and the distribution of heating for the planetary scale are analyzed for the months of January. April, July and October of 1979. The global monsoonal circulations coupled with the planetary scale of differential heating occur in the form of large scale Hadley-type and Walker-type circulations. Net heating within a given region and net cooling in another region in association with latent heat release and differences in boundary flux of energy through the earth’s surface and the top of the atmosphere result in forcing of isentropic mass circulations that link energy source with energy sink regions, a result basic to thermally forced circulations. The primary planetary source of energy in the region of Indonesia-Philippines-Southeast Asia is linked through isentropic mass transport with sinks of energy in the regions of the two circumpolar vortices, the Sahara and subtropical anticyclonic circulations. This primary center of the source of energy in the Indonesia-Southeast Asia area moves seasonally from one hemisphere to the other. Other source regions of energy occur over Brazil in January and Central America and Africa in July.

Through horizontal transport of mass and energy, the winter Asiatic monsoonal circulation links radiative cooling over Asia to sensible and latent heat release within mid-latitude baroclinic waves and also to latent heat release in the Indonesia, Philippine and New Guinea regions. The rôle of mid-latitude baroclinic waves in providing for mass and energy exchange between polar and subtropical regions within the time-averaged isentropic structure is briefly discussed.