Intrusions of warm equatorial water in the South East Atlantic Ocean off Angola and Namibia may be linked with above average rainfall along the coast of those countries but sometimes also with inland areas of southern Africa e.g. Zambia. During the 1984, 1986, 1995 and 2001 warm events, above average rainfall occurred near the sea surface temperature (SST) anomalies and extended inland from the coast to an extent that appeared to depend on the intensity of the regional moisture convergence and atmospheric circulation anomalies. Rainfall over western Angola/Namibia is greatest for those events for which the local circulation anomalies act to strengthen the climatological westwards flux of Indian Ocean sourced moisture across low latitude southern Africa and which flow anticyclonically over the warmest SST off the coast thereby weakening the mean southeasterly moisture flux away from Africa over the SE Atlantic. The significance of the warm events occurring during the February to April period is that this is the time when SST reaches its maximum in the annual cycle (up to 28°C off northern Angola) and this favours more intense local evaporation and convection and a greater impact on late austral summer rainfall. Better understanding of these warm events is necessary for assessing impacts on regional rainfall, agriculture and fisheries and for improving seasonal forecasting in this region.

Extreme warm episodes in the southeast Atlantic Ocean, known as Benguela Niños, have devastating environmental impacts and have been shown to be remotely forced. To place these extreme events into perspective, the investigation is here extended to minor warm events as well as to cold episodes. To this end, different sets of observations have been combined with outputs from a numerical simulation of the tropical Atlantic for the period 1982-99. It is shown that both warm and cold surface events develop regularly in the same specific region along the coast of Angola and Namibia. Some cold events compete in magnitude with major warm episodes. Local sea-air heat flux exchanges do not seem to precondition the sea surface in the Angola-Benguela region prior to the arrival of an event. Most warm and cold episodes are large-scale events despite their limited surface signature. They appear to be generated by wind anomalies in the western and central equatorial Atlantic in the same way as Benguela Niños. Seasonal fluctuations of the depth and shape of the tropical thermocline seem partly to control the way subsurface anomalies eventually impact the surface. During austral summer, surface anomalies create an identifiable pool centered near 15ЊS, whereas in winter they show an elongated pattern along the coast stretching toward the equator. Local upwelling or downwelling favorable wind regimes, as well as local net heat fluxes, may modulate the surface expression of events.

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The intermittent occurrence of anomalous warm events in the upwelling regions of the Pacific – El Niños – has been intensively studied. Pacific Niños have striking effects on the local ecosystem, hence on the fisheries, and on rainfall. Similar dramatic events have been observed in the South Atlantic off the coasts of Angola and Namibia and named Benguela Niños. They tend not to occur in unison with their Pacific counterpart and may thus have unrelated forcing mechanisms. Using an ocean general circulation model, forced by real winds and verified with satellite data, it is shown that Benguela Niños are generated by specific wind stress events in the west‐central equatorial Atlantic, and progress from there as subsurface temperature anomalies that eventually outcropped only at the south‐west African coast. These results suggest that it now may be possible to predict the occurrence of these disruptive events with a lead‐time of 2 months.

Western boundary currents are driven by zonally integrated wind‐stress curl over the width of subtropical basins. This cross‐basin integration is interrupted in the South Indian Ocean where Madagascar presents a formidable barrier. Nevertheless, a western boundary current has been thought to exist in the Mozambique Channel, the Mozambique Current. Recent observations have however shown that no such current exists and that the flow in the channel instead consists of a train of eddies. Is this western boundary anomaly due to the presence of Madagascar? We have used a primitive equations model to investigate the flow in the South West Indian Ocean as if there were no Madagascar. We show that a normal, continuous western boundary current is then formed that constitutes a continuum with the Agulhas Current. The presence of Madagascar is shown to affect the frequency of inter‐ocean exchange events south of Africa.