Numerical study of a coastal current on a steep slope in presence of a cape: The case of the Promontorio di Portofino

Abstract

[1] A process study aimed at investigating the winter circulation in the area of the Promontorio of Portofino (northwestern Mediterranean) is presented, motivated by historical current measurements suggesting the presence of an attached recirculating eddy in the lee of the Promontorio (cape). A sensitivity study is first performed in an idealized setting, considering the interaction of a steady incoming current with the cape. Numerical experiments are performed using both two-dimensional (2-D) (vertically integrated) and 3-D versions of the POM model. From the 2-D results, the main controlling parameter appears to be the equivalent Reynolds number Re f , in agreement with previous historical results. In the 3-D case, the dependence on the vertical Ekman number Ek v is investigated at fixed Re f , and a significant intensification of the attached eddy with respect to the 2-D solutions is obtained. The main difference between the 2-D and 3-D dynamics is the presence of a resolved bottom Ekman layer in 3-D, introducing a vertical shear in the incoming current, particularly noticeable in the region of the shelf break. This shear is likely to be responsible for a ''secondary circulation'' (dominated by Coriolis effect), inducing an inshore surface current and associated upwelling in the lee of the cape, and causing the observed eddy intensification. Experiments with realistic bathymetry are performed, and the 3-D results are found to be in good qualitative agreement with the measurements. The results are expected to be relevant for biological transport, pointing out to a mechanism for eddy intensification connected with surface inshore transport and upwelling.

Diurnal variability of inner-shelf circulation in the lee of a cape under upwelling conditions

“…The upwelling jet deflection and corresponding cyclonic circulation due to the presence of a cape and the intensified upwelling in the leeside of the cape is consistent with several studies (Barth et al, 2000;Gan and Allen, 2002;Doglioli et al, 2004;Kuebel Cervantes and Allen, 2006;Meunier et al, 2010;Perlin et al, 2011;Liu and Gan, 2014). However, most of these studies deal with steady upwelling regimes or with relaxation periods of more than one day, and do not describe the diurnal variability caused by a daily oscillating upwelling regime.…”

“…Ganju et al (2011) pointed out the importance of topographic features in the circulation over the inner-shelf by showing that the dynamical balance was dominated by pressure gradient and horizontal advection terms, which varied with subtle bathymetric changes. Finally, several studies found that non-linear advection is particularly important in the vicinity of topographic features (Doglioli et al, 2004;Meunier et al, 2010;Liu and Gan, 2014). It is expected that Cape Sines will have a similar effect on the circulation, which will promote the generation of localized wind-forced pressure gradients and enhance the cross-shelf exchange in the leeside of the cape.…”

“…These pressure gradients are accompanied by geostrophically balanced cross-shelf flows over the innershelf, resulting in the intensification of the upwelling in the lee of the cape. A cyclonic recirculation that may form in the presence of a cape, can also be relevant since it enhances the onshore transport in the leeside of the cape (Barth et al, 2000;Doglioli et al, 2004;Meunier et al, 2010;Liu and Gan, 2014).…”

Historical Drifter Data and Statistical Prediction of Particle Motion: A Case Study in the Central Adriatic Sea

“…Downstream of the cape, the current widens, following the shelf. A small recirculation region can be seen in the lee of the cape, with reduced sampling suggestive of a "shadow zone" resulting from the classical detachment of a boundary current in the presence of an obstacle (Doglioli et al 2004). The WAC appears connected with the interior flow through two branches of the cross-basin recirculations, along the slopes of the MAP and SAP, respectively.…”

On the use of optical remote sensing to assess phytoplankton biomass dynamics in the Pelagos Sanctuary (Ligurian-Provençal Sea)

“…The general circulation within the Ligurian-Provençal basin follows a cyclonic gyre, being a part of the general cyclonic circulation of the Western Mediterranean Sea, due to the presence of baric depressions which produce an intensification of the coastal currents towards the west. The gyre shows a seasonal cycle; its extension and intensity are related to the seasonal variations of the atmospheric forcing (Esposito and Manzella, 1982;Dagnino, 1978;Doglioli et al, 2004;Manzella, 1983). This hydrodynamic feature involves the two main Mediterranean water masses, i.e.…”