General circulation model simulations of Southern African regional climate.

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dc.contributor.authorJoubert, Alec Michael.
dc.date.accessioned2018-10-22T12:40:12Z
dc.date.available2018-10-22T12:40:12Z
dc.date.issued1994
dc.descriptionDissertation submitted to the Faculty of Science, University of the Witwatersraild, Johannesburg for the Degree of Master of Science.en_ZA
dc.description.abstractSix general circulation model simulations of present-day southern African climate are assessed, Each of these models are early-generation equilibrium climate models linked to simple mixed-slab oceans. Simulations of surface air temperature over the subcontinent are sensitive to the grid-scale parameterisation of convection in summer. At high latitudes, large simulation errors are caused by errors in the specification of sea-ice albedo feedbacks. Increased spatial resolution and the inclusion of a gravity wave drag term in the momentum equations results in a markedly-improved simulated mean sea level pressure distribution. Tho models successfully simulate the pattern of rainfall seasonality over the Subcontinent, although grid-point simulation of precipitation is unreliable. Treatment of convection, cloud radiative feedbacks and the oceans by this generation of models is simplistic, and consequently there is a large degree of uncertainty associated with predictions of future climate under doubled-carbon dioxide conditions. For this reason, more reliable estimates of future conditions will be achieved using only those models which reproduce present climate most accurately. Early-generation general circulation models suggest a warming of 4°C to 5°C for the southern African region as a whole throughout the year. Over the subcontinent, warming is expected to be least in the tropics, and greatest in the dry subtropical regions in winter. Estimated changes in mean sea level pressure indicate a southward shlft of all pressure systems, with a weakening of the subtropical high pressure belt and mid-latitude westerlies. Little agreement exists between the models concerning predictions of regional precipitation change. However, broad scale changes in precipitation patterns are in accordance with predicted circulation changes over the subcontinent. Generally wetter conditions may be expected in the tropics throughout the year and over the summer rainfall region during summer. Decreased winter rainfall may be expected over the winter rainfall region of the south-western Cape. However, estimated precipitation changes are grid-point specific and therefore must riot be over-interpreted. The present climate validation has resulted in more reliable estimates of future conditions for the southern African region. This approach should be extended to recent slrnulations which include more comprehensive treatment of important physical processes.en_ZA
dc.description.librarianAndrew Chakane 2018en_ZA
dc.identifier.urihttps://hdl.handle.net/10539/25869
dc.language.isoenen_ZA
dc.subjectClimatology -- Mathematical models.en_ZA
dc.subjectAtmospheric circulation -- South Africa.en_ZA
dc.subjectAfrica, Southern -- Climate.en_ZA
dc.titleGeneral circulation model simulations of Southern African regional climate.en_ZA
dc.typeThesisen_ZA
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