Simulating midsummer climate over southern Africa using a nested regional climate model

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) Division of Atmospheric Research limited area model (DARLAM) is used to simulate midsummer (January) climate over southern Africa. Using a one-way nesting procedure, lateral boundary and initial conditions are supplied by the CSIRO nine-level Mark 2 general circulation model (GCM), CSIRO9. In general, the DARLAM results are improved in comparison with those from CSIRO9, although certain deficiencies in the GCM climatology over southern Africa are also present in the nested model results. DARLAM captures the spatial pattern of observed rainfall and interannual rainfall variability over the region as a whole more accurately than CSIRO9. Over most parts of the subcontinent, interannual rainfall variability simulated by DARLAM is not significantly different from observations. Over the steep escarpment region of south-east South Africa, DARLAM simulates more rainfall than CSIRO9 and significantly more rainfall than observed. Over Madagascar, DARLAM simulates more rainfall than CSIRO9, but less than observed, and interannual variability is also significantly less than the observed variability.