Eastern Boundary Upwelling Systems response to different atmospheric forcing in a global eddy-permitting ocean model

Abstract Three-dimensional ocean dynamics (e.g. coastal upwelling, Ekman Pumping, meridional currents) in the Eastern Boundary Upwelling Systems (EBUS) is largely dictated by the strength of equatorward wind and its cross-shore gradients. Ocean dynamics, in turn, affects the coastal sea surface temperature (SST). Mis-representing the wind fields may therefore lead to inaccurate current structures and, thus, to significant SST biases. Analysis of two atmospheric reanalysis products, ERAInterim (ERAINT) and JRA55-do version 1.1 (JRA55), shows differences in the structure of the wind stress and wind stress curl (WSC) over the EBUS regions, when compared to the satellite records from QuikSCAT. Our study shows that ERAINT product is affected by too strong and wide wind-drop off in the cross-shore direction, whereas the wind field is more accurate in the JRA55 product, characterized by weak and narrow wind drop-off and strong coastal winds. To better understand the impact of different fine structures of the near-coast wind on upwelling dynamics, we performed long-term ocean hindcast simulations over the period 1985–2015 with a global eddy-permitting configuration of the NEMO ocean general circulation model. We find that (1) weak ERAINT coastal wind stress and strong WSC promote offshore Ekman pumping, weak coastal vertical velocity and meridional currents and transport dominated by upwind flows; (2) stronger JRA55 coastal wind stress associated with weak WSC generates weaker Ekman Pumping, localized intense coastal upwelling and strong downwind currents and transport; (3) SST discrepancies between experiments are mostly related to the different near-shore wind stress rather than incoming heat fluxes.