Dissertation submitted to the Faculty of Science,
University of the Witwatersraild, Johannesburg
for the Degree of Master of Science. / Six 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. / Andrew Chakane 2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/25869 |
| Date | January 1994 |
| Creators | Joubert, Alec Michael. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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