Ocean model diagnosis of variability in the South Indian Ocean

Evidence exists that sea surface temperature (SST) variability in the South Indian Ocean may significantly influence weather and climate patterns in the southern African region. SST, in tum, can be influenced by variability in ocean fluxes, observations of which are limited in the South Indian Ocean and it is necessary to augment them with estimates derived from models. Two sets of variability in this region are examined in this thesis. The first concerns the large-scale interannual variability of the oceans neighbouring South Africa and the second, inter-ocean fluxes south of Africa on meso-through to interannual timescales. In terms of the former, a global ocean model forced with 50 years of NCEP (National Centre for Environmental Prediction) re-analyses winds and heat fluxes, has been used to investigate the evolution and forcing of interannual SST variability in the South Indian Ocean and co-variability patterns in the South Atlantic. Secondly, an eddy- permitting model is used to investigate volume, heat and salt fluxes in the oceanic region south of Africa and the effect of variations in the strength of wind forcing. Interannual dipole-like SST variability in the South Indian and South Atlantic Oceans were realistically simulated using the global ocean model, ORCA2. The model results imply that there are connections between large-scale modulations of the midlatitude atmospheric circulation of the Southern Hemisphere and co-evolving SST variability in the South Atlantic and South Indian Oceans. The atmospheric variability results in an increase (decrease) in strength of the anticyclonic wind fields over each ocean during positive (negative) dipole events. The resulting wind anomalies lead to changes in surface heat fluxes, short wave radiation, meridional Ekman heat transport and upwelling, all of which contribute to the evolution of these SST dipole patterns. Evidence is found of links between these dipole patterns and the Antarctic Oscillation and ENSO (El Niño Southern Oscillation).

Grantor dc:publisher.institution

Department of Oceanography

Year dc:date.issued

2005

Author dc:creator

• Hermes, Juliet C

Advisors dc:contributor.advisor

• Reason, Chris
• Lutjeharms, Johann R E

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/8649

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/8649