The response of a stably stratified atmospheric flow to large-scale elevated and low-level thermal forcing on a β plane at several latitudes are investigated using a simple nonlinear numerical model. The formation of a westerly jet at the equator, a pair of low-pressure and cyclonic circulation regions, and the decoupling of the westerly jet and the heating center are explained by the β effect. It is found that the vertical motion in the case with heating centered at the equator is much larger than that with heating centered at higher latitudes. This is explained by the trapping of more wave energy in equatorial regions when the heating is centered at the equator. On the other hand, the pressure perturbation is much stronger for cases with heating located at a higher latitude due to vortex stretching. It is found that there exists a vertical phase tilt which is explained by the upward propagating Kelvin waves near the equator and mixed Rossby gravity waves at higher latitudes. The vertical wavelength of the disturbance increases as the heating center is located at a higher latitude. In addition, we find that this type of flow is not sensitive to the existence of the stratosphere. One interesting feature is that the maximum vertical velocity for the case with heating centered at the equator is significantly larger than that with heating centered at 30¿N. Comparing both linear and nonlinear cases with surface heating or cooling, we find (1) the nonlinearity suppresses (enhances) the disturbance induced by cooling (heating), (2) the differences between the nonlinear and linear responses are larger when the forcing is located at lower latitudes, and (3) the disturbed areas are much wider in the zonal direction for cooling cases than for cases with heating. The nonlinear effects are studied by inspecting individual terms. To explore the relationships between Atlantic sea surface temperature anomaly (SSTA) and rainfall anomalies in the Sahel and northeastern Brazil, the SSTA is represented by low-level diabatic forcing in the numerical model. With a coupled warm SSTA in the South Atlantic and cold SSTA in the North Atlantic, model results indicate a combination of offshore flow and downward motion in the Sahel, while there exists an upward motion and an offshore flow in northeastern Brazil. When the SSTA pattern is reversed, then there exists an onshore flow and an upward motion in the western Sahel, while there exists a strong onshore flow and a downward motion in northeastern Brazil. ¿ American Geophysical Union 1996