Abstract
The mass circulation of the zonally averaged global circulation is investigated in isobaric and isentropic coordinates through the use of a FGGE Level IIIa data set. The isobaric mass circulation during the First GARP Global Experiment is consistent with previous results, i.e., direct Hadley cells in low latitudes and indirect Ferrel cells in midlatitudes of both hemispheres.
Within the isentropic framework, the combination of a geostrophic mean mode of mass transport within the baroclinic wave structure of extratropical latitudes, and an ageostrophic mean mode in tropical latitudes, yields an isentropic mass circulation spanning the hemisphere. The asymmetric structure of midlatitude baroclinic waves provides the degree of freedom for a geostrophic mode of mass transport that is fundamental to the direct Hadley-type circulation in isentropic coordinates. This direct Hadley-type circulation is explicitly linked to heat sources and sinks on a planetary scale. The diabatic heating estimated from the mean meridional mass transport through the isentropic continuity equation reveals a realistic distribution for the zonally averaged atmosphere. Within the isentropic perspective, the scale of thermodynamic forcing by diabatic beating explicitly determines the hemispheric scale of atmospheric response for the mean meridional circulation.
