An Estimate of the Summertime Tropospheric Vorticity Budget over South America

Abstract

Objectively analyzed wind fields from summertime (January and February) cloud wind data are used to estimate the average values of the large-scale upper tropospheric vorticity budget components over tropical and subtropical South America. Limited vertical resolution of cloud wind data limit their use in evaluating the components involving vertical motion and vertical derivatives. The predominant component in the vorticity budget, the horizontal divergence of vorticity, is not balanced by the other large-scale components in the budget. Thus, large imbalances in the budget, interpreted as representing the effects of subgrid-scale processes, are found over the Amazon River basin. The results indicate good spatial correlation between patterns of the imbalances and intense cumulus convective activity. Based upon these results and similar studies of convectively active tropical oceanic regions elsewhere, it is suggested that the vertical advection of vorticity by subgrid-scale intense cumulus convection contributes significantly to maintain the vorticity budget over this continental region.