Ocean climate of the South East Atlantic observed from satellite data and wind models

The near-coastal South East Atlantic Ocean off Africa is a unique and highly dynamic environment, comprising the cool Benguela Current, warm Angola Current and warm Agulhas Current. Strong coastal upwelling and the Congo River strongly influence primary production. Much of the present knowledge of the South East Atlantic has been derived from ship-borne measurements and in situ sensors, which cannot generally provide extensive spatial and temporal coverage. Similarly, previous satellite studies of the region have often focused on small spatial areas and limited time periods. This paper provides an improved understanding of seasonal and interannual variability in ocean dynamics along the South East Atlantic coast of Africa using time series of satellite and model derived data products. Eighteen years of satellite sea surface temperature data are complimented by 7 years of sea level data. Three years of chlorophyll a data illustrate the seasonal biological response, but the time series is not of sufficient length for investigating interannual variability in chlorophyll biomass. Modelled wind fields are used to describe atmospheric forcing of the surface ocean. This is the first synoptic-scale description of the South East Atlantic from a suite of large spatial coverage, long time series products. Previous studies of seasonal and interannual variability in the region are reviewed and used to interpret key oceanographic features and processes identified in the satellite data. Key findings of this study are: 1. Descriptions of seasonal and interannual variability from these data show climate forcing of the South East Atlantic coast of Africa from both the northern and southern boundaries. Bimodal seasonal signals of equatorial origin propagate poleward along the Angolan coast, while the trade winds and events in the Agulhas region dominate the Agulhas Bank and Southern Benguela. The Northern Benguela is a mixed regime, under the influence of forcing from both directions. 2. The Benguela Nino years of 1984 and 1995 are clearly observed in sea surface temperature and sea level anomalies and correspond to anomalously weak southerly winds at the equator. These conditions were also observed in 1999, suggesting this too may have been a Benguela Nino year. 3. Consideration of putative Nino-type events in the equatorial Atlantic from this and other studies suggests that the frequency of these events is much higher than previously estimated and may be similar to the frequency of El Nino-Southern Oscillation (ENSO) events in the Pacific Ocean. Furthermore, years of anomalously strong southerly winds at the equator occur during Pacific ENSO years. (C) 2003 Elsevier Ltd. All rights reserved.