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Atmospheric Sources of Oceanic Bias in the Southeastern Tropical Atlantic

  • 112 O&M Building, Texas A&M University (map)

Abstract

Coupled atmosphere-ocean general circulation models (AOGCMs) have long been plagued by persistent warm sea surface temperature (SST) biases in the eastern equatorial and southeastern tropical Atlantic, where biases can reach 6°C off the coast of Namibia and Angola. These SST biases can be attributed to errors in representation of both oceanic and atmospheric processes. We investigate atmospheric sources of oceanic bias using suites of uncoupled atmosphere and ocean regional climate model simulations and identify processes that require improved representation in order to achieve SST bias reduction. One substantial source of coastal SST bias is representation of the Benguela low-level coastal jet (BLLCJ), an atmospheric southerly jet oriented parallel to the Angola coast. We examine the characteristics and dynamics of the BLLCJ, factors that support the jet's formation and variability, and impacts of coastal geometry and model resolution on the jet’s representation in models. This work highlights the need for a sufficiently resolved BLLCJ in coupled AOGCMs in order to reduce SST bias. The warm SST biases in the equatorial and southern tropical Atlantic, together with common cool SST biases in the northern tropical Atlantic, hinder our ability to represent the West African monsoon and Atlantic tropical cyclones in climate models.