Response of the Southern Benguela Upwelling System to Fine-scale Modifications of the Coastal Wind

Fabien Desbiolles1,2, Bruno Blanke3, Abderruhim Bentamy2 and Claude Roy1, (1)Laboratoire de Physique des Océans, Brest, France, (2)IFREMER, Plouzané, France, (3)Laboratoire d'Océanographie Physique et Spatiale (LOPS), Brest, France
Abstract:
Considering the amount of daily wind stress products available with increasingly finer horizontal scales, this study aims at highlighting the short-term response of the ocean to a simple change of momentum fluxes in a hydrodynamic model. Specifically, we use the last QuikSCAT-derived wind products processed at Ifremer (Institut Français de Recherche pour l’Exploitation de la Mer) to document and quantify the effect of small-scale wind stress structures on the Southern Benguela dynamics. We analyze the results of a regional model forced by wind stress fields derived from QuikSCAT observations. Two different horizontal resolutions are considered for the wind stress: QS25 and QS50, corresponding to native 25- and 50-km grids, respectively. The differences between both products highlight the primary importance of fine-scale momentum fluxes for both the structure and intensity of the wind- and wind curl-driven upwelling. Using QS25, we show that the coastal Ekman transport is reduced, leading to a warmer SST and a reduced oceanic coastal jet. QS25 finer wind stress curl patterns also favor the development of a stronger and shallower poleward undercurrent. The addition of a coastal wind correction to QS25 lets us investigate the possible implications of an imbalance between Ekman transport and Ekman pumping: a wind reduction in the coastal band often reduces the SST cooling, but the two mechanisms compensate each other when the characteristic length scales of the coastal upwelling and the orography-induced wind drop-off are similar.