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

• Published in: Geophysical research letters 2017-04, Vol.44 (7), p.3283-3289
• Main Authors: Potter, S. F., Dawson, E. J., Frierson, D. M. W.
• Format: Article
• Language: English
• Subjects: Atmosphere; Atmospherics; Clouds; Decks; energy flux; equatorial Atlantic; Geophysics; interhemispheric energy balance; Intertropical Convergence Zone; Marine; Ocean circulation; Ocean currents; Ocean models; Ocean-atmosphere interaction; Orography; Reduction; Sea surface temperature; Water circulation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL073098

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. Key Points Namibian stratocumulus deck thins significantly due to the removal of southern African orography Atlantic ITCZ shifts south due to the increase in temperature resulting from the reduction of Namibian low clouds Use of a coupled model allows ocean circulation to cool the South Atlantic, which lessens and changes the structure of the ITCZ shift