Simulation of variability in the tropical Western Indian Ocean

Includes bibliographical references.The oceanic circulation and properties in the Tanzanian shelf region in the tropical western Indian Ocean have been studied in this thesis using a regional ocean model. The study investigated the influences of the Northeast Madagascar Current (NEMC) in the Tanzanian shelf waters at the annual cycle. Furthermore, the thesis examined the interannual variability of the sea surface temperature (SST) in the Tanzanian shelf region, and compares it with that offshore or with subsurface temperature. At the annual cycle, the westward-flowing NEMC advects relatively warm and fresh waters from the north of Madagascar towards the Tanzanian shelf region by interrupting the upwelled water from the Seychelles-Chagos ridge. At interannual timescales, the weakest interannual SST variations, which lie over the weak subsurface waters variations, occur in the coastal waters off Tanzania, where its variance is shared with waters to the north of Madagascar. Such SST variations are dominated by variability at about five year periods. The strongest interannual SST variations, which lie over the strongest subsurface temperature variations, occur offshore, being dominated by two periods, one at about 2.7 and the other near five years. The interannual variability of the region seems to be linked to El Niño- Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) events, which induce changes in the thermocline and surface forcing in the region. Local surface heat flux exchanges driven by the anomalous shortwave radiation dominate the weakest interannual SST variability in the Tanzanian shelf region, with some contribution by the advection of heat anomalies from the NEMC. Further offshore, the strongest interannual variability of the SST is dominated by the thermocline variations induced by local Ekman pumping from local wind stress curl and by remote forcing from large-scale climate modes.