Southern African orography impacts on low clouds and the Atlantic ITCZ in a coupled model

Abstract

We examine the influence of southern African orography on the Namibian stratocumulus deck, the South Atlantic ocean-to-atmosphere energy transport, and the Intertropical Convergence Zone (ITCZ), using an atmosphere-only model and a coupled atmosphere-ocean model. For both models, a control simulation with realistic orography is compared to a simulation where the orography in southern Africa was removed. As in the previous studies, the removal of orography results in thinning of the Namibian stratocumulus deck. In the coupled model, the increased sea surface temperature in the southern Atlantic due to the reduction of low clouds forces the Atlantic ITCZ to shift southward toward the warmer hemisphere. However, changes in the ocean circulation cool the South Atlantic atmosphere, lessening the ITCZ shift and changing the structure of precipitation. These results show the importance of orography on shaping Atlantic rainfall and highlight the role of dynamical ocean processes in atmospheric dynamics.