Understanding Decadal Variations in the Southeastern Atlantic Climate

Analysis of high resolution observations and reanalysis data for the past 32 years (1982 – 2013) reveals a warming trend of the Angola current, a northerly ocean current along the Angola/Namibian coast that forms the eastern section of a large cyclonic gyre in the Gulf of Guinea. Sea surface temperatures (SSTs) are estimated to have warmed by over 2 K over the 32 year period, with 30 – 50% of the SST variance accounted for by this trend. The warming trend has distinct seasonality, with the largest warming occurring during November – January and a secondary maximum during August. The austral summer warming trend is associated with a southwestward shift of the South Atlantic sub-tropical anticyclone as well as changes in heating over continental Africa that affect the Angola continental thermal low's position and influence the low-level circulation along the coast. Together these atmospheric circulation changes are found to be associated with a weakening of the coastal and equatorial South Atlantic wind stress, a decrease in the coastal and equatorial upwelling, an increase in coastal sea surface temperatures, and a deepening of the mixed layer depth along the Angola coast. These results are relevant for improving our understanding regional climate variability associated with global warming over this area, as the land is likely to warm faster than the ocean in the future.