A contribution to the upper‐air climatology of tropical south america

An upper‐air climatology of tropical South America is presented using objectively analysed geopotential height, temperature and wind data from various radiosonde stations for the common period 1970‐1974. In the lower troposphere the South Atlantic high dominates the geopotential height patterns extending deeply into interior Brazil in Southern winter. In the upper troposphere, contour gradients are concentrated around the subtropical region in winter. Temperature analysis shows the steep meridional gradient in winter. In summer, the Peruvian‐Bolivian Altiplano heating effect is manifested in the mid‐tropospheric temperature fields and also in the thickness field. Lower‐tropospheric flow throughout the year is marked by an anticyclonic turning of easterlies over much of eastern Brazil. Easterlies originating from the South Atlantic high penetrate further inland in Southern winter. Upper‐tropospheric flow changes dramatically from mainly westerly in winter to a well‐defined anticyclone over the Altiplano and a trough downstream over northeast Brazil in summer. Thickness and temperature patterns indicate that the upper anticyclone is maintained by a warm‐core system whereas the trough is marked by a relatively cold temperature. Upper tropospheric flows are equivalent barotropic in nature over tropical South America. The map discussion of summer and winter circulation is complemented by cross‐sections of meridional wind component along approximately 60°W.