Climatic Control FeaturesSouth AmericaTropical Upper Tropospheric Trough
This is an upper-level trough extending from the central South Atlantic into northern Brazil (see Figure 2-15a). From November to March it splits the Subtropical Ridge into two parts--one over South America, the other over Africa. Flow between the trough and the Bolivian High contributes to precipitation in the tropics by bringing surface and upper-level disturbances into the area. The trough itself acts as an area of upper-level cyclogenesis in the tropics (see Low-Latitude Upper-Level Cyclonic Vortices). Upper-level cyclones typically weaken the trough, disrupting normal flow patterns.