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Radiative forcing of Southern African climate variability and change
Expanded Title:This report is concerned with exploring the effects of various forms of tropospheric and stratospheric radiative forcing (e.g. Antarctic stratospheric ozone, increasing CO2 concentrations and time-varying aerosol forcings) on southern African climate variability and change. A large set of sensitivity tests, following the experimental design of the Atmospheric Model Intercomparison Project (AMIP) was performed for this purpose. An ensemble of projections of future climate change has also been analysed, to investigate the relative importance of enhanced CO2 concentrations and recovering stratospheric ozone in forcing southern African climate during the 21st century. The simulations of seasonal circulation anomalies are in general most skilful for the austral summer. This result provides some insight in the relatively high levels of skill reported in general for the prediction of summer rainfall totals over southern Africa at the seasonal time-scale – this skill stems from the underlying circulation fields being forecasted skilfully for summer. The drastic reduction in skill that occurs in the autumn, winter and spring seasons over Southern Africa (as demonstrated in this report) may be attributed at least partially to the seasonal northward-displaced westerlies, with its associated transient weather systems of which the variability is simulated less skilfully. Another important contributing factor may be that ENSO related SST anomalies are generally the largest during the early summer, with important regional SST anomalies such as those associated with the South Indian Ocean subtropical dipole being the largest in the late summer. That is, the abilities of the tropical Pacific Ocean and regional oceans to force climate variability over southern Africa are reduced outside the austral summer. These arguments suggest that improvements in forecast skill may be extremely difficult to attain for the seasons of autumn, winter and spring.
Date Published:01/09/2015
Document Type:Research Report
Document Subjects:Ecosystem - Climate Change
Document Keywords:Climate, Environment
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:2163/1/15
ISBN No:978-1-4312-0704-6
Authors:Engelbrecht F; Ndarana T; Landman W; Van der Merwe J; Ngwana I; Muthige M
Document Size:5 300 KB
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