Wind mediated vorticity-generation and eddy-confinement, leeward of the Madeira Island: 2008 numerical case study

This study assesses the influence of the atmospheric wind-wake of the Madeira Island on oceanic-eddy generation. Ocean surface wind fields derived from the QuikSCAT scatterometer were compared to the Weather Research and Forecast (WRF) modeled winds at 6 km resolution. The main difference between the two wind products is found southwest of Madeira where QuikSCAT's spatial resolution [0.5°] does not resolve the near-field atmospheric wake dynamics. Nevertheless, high resolution wind extracted from ENVISAT Advanced Synthetic Aperture Radar (ASAR) confirms that WRF is able to realistically reproduce the island-induced wind-wake. The Regional Oceanic Modeling System (ROMS) was used to simulate the oceanic effects of the wind-wake. A “no-wind-wake” case was simulated with ROMS using the QuikSCAT wind, whereas the WRF wind was used for an island-induced wind-wake simulation. Oceanic surface kinetic energy and vorticity are found to increase during the summer months concurrently with strong wind-wake episodes resolved by WRF. The downstream propagation of this oceanic vorticity, as a result of the shedding of the leeward eddies, was captured with an eddy tracking algorithm. In the initial stage, the oceanic leeward eddy corridor was delimited by the zonal wind-shear. This study suggests that the wind-wake is the main contributor to the generation and containment of the oceanic eddies in the lee of the Madeira Island.

► We investigate the oceanic response of the wind wake of Madeira Island. ► QuikSCAT forcing does not resolve the near field atmospheric wake dynamics; whereas WRF is able to realistically reproduce it. ► Wind curl generated by the island induces an increase in oceanic vorticity. ► Increase in vorticity is the results of eddy formation and propagation. ► Eddies appear to be contained by the zonal wind-shear produced by the island.