Global vorticity budget over the tropics and subtropics at 200-mb during northern hemisphere summer

The large-scale terms in the vorticity equation are evaluated usingKrishnamurti's (1971a, b) summer mean winds at 200 mb for a global belt from 25°S to 45°N. The production of vorticity by the divergent wind field is found to be imbalanced over all of the tropical and subtropical belt. As a result there is a requirement for a sub-grid scale (space or time) mechanism which removes negative vorticity from the regions of strong divergence (Tibetan and Mexican highlands) and removes positive vorticity from the regions of strong convergence (mid-oceanic troughs) at 200 mb during northern summer at a rate of approximately 4×10^–10 sec^–2. As suggested byHolton andColton (1972), in regions of strong and persistent convection, such as the Tibetan Plateau, deep cumulus clouds can account for this transport. However, the mechanism for removing positive vorticity in the vicinity of the upper tropospheric mid-oceanic troughs is still an intriguing and open question.On leave-of-absence at the National Science Foundation, Climate Dynamics Research Section.