Modeling the baroclinic circulation in the area of the Sicily channel: The role of stratification and energy diagnostics

Abstract

[1] Aspects of the circulation of the Sicily channel region are studied with a highresolution, primitive equation, sigma coordinate model. This work is an attempt to study the process governing the purely baroclinic dynamics and its sensitivity to seasonal stratification, thus no atmospheric forcing is used. Two numerical experiments are analyzed using, as initial conditions, diagnostic velocity fields derived from the winter and summer climatological hydrologies. The quasi-steady state is characterized by circulation patterns, in the depth range of the Modified Atlantic Water (MAW) and the Levantine Intermediate Water (LIW), strongly controlled by mesoscale eddies and topography. Seasonal difference is found in the surface current which exhibits the major variability on the African side, downstream of Adventure Bank and the Ionian Slope where the absolute maximum occurs. The intermediate circulation instead does not show relevant seasonal differences. LIW enters through the two passages south of Malta Plateau and preferentially flows along the Sicilian shelf edge exiting over the northern sill. Its pathway is strongly controlled by subsurface cyclonic and anticyclonic cells. The results are in good agreement with observations. An energy diagnostics is applied to model results and sheds important light on dynamical characteristics of the mesoscale eddy field and indicates seasonal differences in the energetic exchange with the mean flow. The analysis of the mean (MKE) and eddy (EKE) kinetic energy, the transfer terms between energy compartments and the eddy momentum flux divergence indicates how eddies are strongly energetic in summer and exchange energy more efficiently with the mean flow. In the quasi-steady state MAW volume transport and MKE and EKE fluctuations are strongly correlated. This result suggests that mesoscale motions can control up to 40% of volume transport variability.INDEX TERMS: 4255 Oceanography: General: Numerical modeling; 4512 Oceanography: Physical: Currents; 4520 Oceanography: Physical: Eddies and mesoscale processes; KEYWORDS: Mediterranean, Sicily Strait, mesoscale, modeling Citation: Napolitano, E., G. Sannino, V. Artale, and S. Marullo, Modeling the baroclinic circulation in the area of the Sicily channel: The role of stratification and energy diagnostics,

Pathways of the Modified Atlantic Water across the Strait of Sicily

“…Indeed, the ATC becomes weak in summer and may even disappear during some other years. This could explain the contradiction between those who assert that the ATC does not exist in summer [Béranger et al, 2004] and those who assert its existence during the same season [Napolitano et al, 2003]. The dynamics of the area is also characterized by a permanent anticyclonic gyre located in the Gulf of Hammamet and by a pair of small-scale anticyclonic gyres during spring/summer (see Fig.…”

“…Monthly mean vertical sections of salinity and potential temperature in Аugust and January along latitude 36,4°N (Sicily strait, SS section), and along latitude 34,1°N (Gulf of Gabes, GG section). Zambianchi, 2007;Napolitano et al, 2003]. The ATC is characterized by an important seasonal variability.…”

Record of Ellisella paraplexauroides (Anthozoa: Alcyonacea: Ellisellidae) in Italian waters (Mediterranean Sea)

“…In the Sicily Strait, representing the connection between the eastern and western basins of the Mediterranean Sea, two water layers have been observed. The most superficial is composed of the surface Atlantic Waters (AW), running eastward, while the deepest one by the Levantine Intermediate Waters (LIW) flowing in the opposite direction, down to about 500 m (Napolitano et al, 2003). The particular hydrographic conditions of this area probably favour the presence of rich benthic communities of filter-feeding organisms .…”

X-band COSMO-SkyMed wind field retrieval, with application to coastal circulation modeling

“…The basin-scale circulation yields an important interannual variability shaped by a strong seasonal cycle and energetic mesoscale features (e.g., see Artale et al, 1994;Pierini and Simioli, 1998;Schroeder et al, 2008;Vetrano et al, 2010). Local driving mechanisms are the heat, evaporative and momentum fluxes at the air-sea interface, while an important Sardinia and Sicily straits (e.g., Pierini and Rubino, 2001;Molcard et al, 2002;Napolitano et al, 2003;Béranger et al, 2004;Gaberšek et al, 2007). In the south-eastern Tyrrhenian Sea a small semi-enclosed basin, the Gulf of Naples, is present: this is a very interesting zone, not only because it is ideal in terms of physical processes occurring in such a regular geometry, but also from environmental, social and economic viewpoints.…”

“…The sigma-coordinate vertical discretization of the governing equations allows one to have a sufficiently high number of vertical levels both in shallow and deep water, a particularly advantageous feature in coastal area such as the one under investigation. Our coastal model has been one-way nested with a POM Tyrrhenian Sea model (TSM, Napolitano et al, 2013), which is, in turn, nested with the NEMO-OPA (Nucleus for European Modelling of the Ocean-Ocean PArallelise) implemented in the Mediterranean at 1/16 • × 1/16 • horizontal resolution and 72 unevenly spaced vertical levels (Oddo et al, 2009). The nesting (which follows the approach of Zavatarelli and Pinardi, 2003) has required the initialization of the hydrological and dynamical structure of the coastal model with data obtained from the TSM, and the prescription, along the open lateral boundaries, of dynamical boundary conditions derived, again, from the TSM.…”