Impact of currents on surface fluxes computation and their feedback on coastal dynamics

A twin numerical experiment was conducted in the seas of Sardinia (Western Mediterranean) to assess the impact, at coastal scales, of the use of relative winds (i.e. taking into account ocean surface currents) in the computation of heat and momentum fluxes through bulk formulas. The model, the Regional Ocean Modeling System (ROMS), was implemented at 2 km of resolution in order to well resolve (sub-)mesoscale dynamics. Small changes (1–2%) in terms of spatially-averaged fluxes correspond to quite large spatial differences of such quantities (up to 15–20%) and to comparably significant differences in terms of mean velocities of the surface currents. Wind power input of the wind stress to the ocean surface P results also reduced by a 15%, especially where surface currents are stronger. Quantitative validation with satellite SST suggests that such a modification on the fluxes improves the model solution especially in areas of cyclonic circulation, where the heat fluxes correction is predominant in respect to the dynamical correction. Surface currents changes above all in their fluctuating part, while the stable part of the flow show changes mainly in magnitude and less in its path. Both total and eddy kinetic energies of the surface current field results reduced in the experiment where fluxes took into account for surface currents. Dynamically, the largest correction is observed in the SW area where anticyclonic eddies approach the continental slope. This reduction also impacts the vertical dynamics and specifically the local upwelling that results diminished both in spatial extension as well in magnitude. Simulations suggest that, even at local scales and in temperate regions, it is preferable to take into account for such a component in fluxes computation. Results also confirm the tight relationship between local coastal upwelling and eddy-slope interactions in the area.