Numerical simulation and decomposition of kinetic energy in the Central Mediterranean: insight on mesoscale circulation and energy conversion

Abstract

Abstract. The spatial and temporal variability of eddy and mean kinetic energy of the Central Mediterranean region has been investigated, from January 2008 to December 2010, by mean of a numerical simulation mainly to quantify the mesoscale dynamics and their relationships with physical forcing. In order to understand the energy redistribution processes, the baroclinic energy conversion has been analysed, suggesting hypotheses about the drivers of the mesoscale activity in this area. The ocean model used is based on the Princeton Ocean Model implemented at 1/32 • horizontal resolution. Surface momentum and buoyancy fluxes are interactively computed by mean of standard bulk formulae using predicted model Sea Surface Temperature and atmospheric variables provided by the European Centre for Medium Range Weather Forecast operational analyses. At its lateral boundaries the model is one-way nested within the Mediterranean Forecasting System operational products.The model domain has been subdivided in four subregions: Sardinia channel and southern Tyrrhenian Sea, Sicily channel, eastern Tunisian shelf and Libyan Sea. Temporal evolution of eddy and mean kinetic energy has been analysed, on each of the four sub-regions, showing different behaviours. On annual scales and within the first 5 m depth, the eddy kinetic energy represents approximately the 60 % of the total kinetic energy over the whole domain, confirming the strong mesoscale nature of the surface current flows in this area. The analyses show that the model well reproduces the path and the temporal behaviour of the main known subbasin circulation features. New mesoscale structures have been also identified, from numerical results and direct observations, for the first time as the Pantelleria Vortex and the Medina Gyre.Correspondence to: R. Sorgente (roberto.sorgente@cnr.it)The classical kinetic energy decomposition (eddy and mean) allowed to depict and to quantify the permanent and fluctuating parts of the circulation in the region, and to differentiate the four sub-regions as function of relative and absolute strength of the mesoscale activity. Furthermore the Baroclinic Energy Conversion term shows that in the Sardinia Channel the mesoscale activity, due to baroclinic instabilities, is significantly larger than in the other sub-regions, while a negative sign of the energy conversion, meaning a transfer of energy from the Eddy Kinetic Energy to the Eddy Available Potential Energy, has been recorded only for the surface layers of the Sicily Channel during summer.

Impact of SLA assimilation in the Sicily Channel Regional Model: model skills and mesoscale features

“…This is also in agreement with literature (e.g. Robinson et al, 1999;Sorgente et al, 2011) that describes this branch, in which transport is associated with the Atlantic Ionian Stream (AIS), as a typical summer feature that reduces its intensity during late autumn, winter and early spring in favour of an increase of the AW flow along the African coast spreading over the Tunisian shelf. Figure 5 shows surface elevation model and analyse fields for 18 October 2008 compared to satellite SST signature.…”

“…The Sicily Channel (sub-)Regional Model (SCRM Sorgente et al, 2003;Gaberšek et al, 2007;Olita et al, 2007;Sorgente et al, 2011) has produced, since 2003, forecasts and simulations of the central Mediterranean Sea including the southern Tyrrhenian Sea, the Sardinia Channel, the Sicily Channel, the western part of the Ionian Sea and a wide area over the Tunisian and Libyan continental shelves. SCRM is part of the national and Mediterranean networks of operational oceanography, namely GNOO (Italian National Group of Operational Oceanography) and MOON (Mediterranean Operational Oceanography Network).…”

Design and validation of MEDRYS, a Mediterranean Sea reanalysis over the period 1992–2013

“…The Mediterranean eddy field also shows semipermanent structures (Rhodes and South Adriatic gyres for example) that define the general circulation in the basin. Modeling the different timescales and spatial scales of this circulation is still challenging because, for example, of approximations and uncertainties on nonlinear dynamical balance, atmospheric forcing or the bathymetry (Sorgente et al, 2011;Pinardi et al, 2013).…”

Variability of water mass properties in the Strait of Sicily in summer period of 1998–2013

“…From a dynamic point of view, three main spatial and temporal scales characterize the CMED (Sorgente et al, 2011): (i) the mesoscale (characterized by horizontal scale less than a few tens of kilometres and periods in the range from a few days to a few tens of days), (ii) the large Mediterranean Basin scale including the thermohaline circulation, and (iii) the sub-basin scale (oceanographic phenomena characterized by diameters ranging between 200 and 300 km). The mesoscale structures, (i), under the influence of wind stress, topography and internal dynamical processes generate boundary currents and jets, which can bifurcate, meander and grow, then forming ring vortices and filament patterns interacting with the large-scale flow fields (Lermusiaux, 1999;Lermusiaux and Robinson, 2001).…”