Simulations of the Summer Circulation over the South American Region with an Eta Coordinate Model

Abstract

A multilevel limited-area primitive equations model in eta coordinate is used to simulate the effects of the Amazonian latent heat source and the Andean topography on the summer (December, January, February) circulation over the South American region. The observed circulation features, such as the Bolivian high and the trough near the coast of Northeast Brazil in the upper troposphere, the elongated South Atlantic convergence zone (SACZ) oriented northwest to southeast from the southern Amazon region into the Atlantic Ocean, and the subtropical anticyclones in the South Pacific and South Atlantic Oceans in the lower levels are well simulated. Although heating alone produces the SACZ, the mountain and the basic flow put it in the observed position. It is found that regular daily pulses of heating are necessary for the maintenance of the SACZ. The position and intensity of the SACZ change rather substantially from the no-mountain case to the mountain case, thus showing the importance of the effect of the Andes on determining the convergence zone.