Simulation and characterization of the Adriatic Sea mesoscale variability

Abstract

[1] This paper presents simulations of the Adriatic Sea using the DieCAST model applied on a 1.2-min grid (about 2-km resolution). The simulations resolve the mesoscale variability because the grid size falls below the first baroclinic deformation radius (about 5-10 km) and DieCAST has very low horizontal dissipation. The model is initialized with seasonally averaged temperature and salinity data and forced with climatological winds and surface buoyancy fluxes (both heat flux and evaporation minus precipitation). River discharges are varied daily according to a perpetual year for every river, and the open-boundary conditions at Otranto Strait are obtained by nesting in two larger-scale models. The present simulations demonstrate that the DieCAST model allows mesoscale instabilities to develop at length scales of 5-20 km and over time scales of a few days. The simulated variability exhibits pronounced similarities with the actual mesoscale variability, in terms of location, nature and temporal evolution of the features. Meanders, swirls and eddies are noted along the relatively smooth Italian coast while offshore jets and filaments better describe the mesoscale activity along the more rugged coast of Croatia. In sum, DieCAST is highly suitable for the study of mesoscale variability in the Adriatic Sea. The present simulations also show that the seasonal hydrography of the Adriatic Sea is intrinsically unstable to mesoscale perturbations, and that the mesoscale variability along the Italian coast is the result of baroclinic instability of the Western Adriatic Current. It is shown how the properties of this instability are related to the local bottom topography.

Relative dispersion from a high-resolution coastal model of the Adriatic Sea

“…Like Richardson's original time-distance graphs (Richardson, 1926), the FSLE provides a measure of dispersion as a function of the spatial scale and serves to isolate the different dispersion regimes corresponding to the different scales of the oceanic flows. Spatial distributions of the FSLE and related measures such as finite-time Lyapunov exponents have recently been used to define so-called Lagrangian coherent structures (Shadden ct al., 2005) and to map transport barriers and mixing regimes in a number of oceanic applications (Abraham and Bowen, 2002;d'Ovidio et al, 2004;Waugh et al, 2006;Olascoaga et al, 2006).…”

Effects of bottom topography on dynamics of river discharges in tidal regions: case study of twin plumes in Taiwan Strait

“…As was shown by Chuang (1985Chuang ( , 1986 and Jan et al (2002), semidiurnal tidal oscillations play a crucial role in the circulation of TS. Tides penetrate into TS through the northern and the southern openings, then converging in the central part of the strait.…”

“…Due to continuity requirements imposed by the coast, the offshore-directed surface currents and onshore-directed bottom currents lead to coastal upwelling tending to displace the plume offshore (de Boer et al, 2009). This effect on river plumes has been investigated in a number of field and model studies (Simpson and Souza, 1995a, b;Souza and James, 1996;de Boer et al, 2006de Boer et al, , 2009Burchard and Schuttelaars, 2012). However, energetic tidal currents impinging on the CYR produce strong bottom-generated turbulence penetrating upward which will tend to destroy the classical patterns of tidal straining system existing for a flat or gently sloping bottom.…”

“…The major topographic features are the shallow, sandy Chang-Yuen Ridge north of the Peng-Hu Channel (PHC), the Taiwan Bank (TB) in the southwestern TS, and the deepening topography in the northeastern TS. Most of the strait is shallower than 80 m. The PHC is located between the PengHu Archipelago and Taiwan Island, descending southward sharply from 70 m to deeper than 1000 m. It is generally believed that the PHC is important in conducting the water from the southern opening of TS into the rest of the strait (Chuang, 1985(Chuang, , 1986Wang and Chern, 1992;Jan et al, 1994).…”

“…Boicourt, 1981;Münchow and Garvine, 1993;Simpson and Souza, 1995a, b;Zavialov et al, 2003;Guo and Valle-Levinson, 2007;O'Donnell et al, 1998;MacCready et al, 2009;Jay et al, 2009;Warrick and Stevens, 2011;Kilcher et al, 2012), theoretical and numerical approaches (e.g. Chao, 1988;Oey and Mellor, 1993;Garvine, 1995Garvine, , 2001Ruddick et al, 1995;Kourafalou et al, 1996;Yankovsky and Chapman, 1997;Kasai et al, 2000;Korotenko, 2000;Valle-Levinson et al, 2003;Cushman-Roisin et al, 2007;Schiller and Kourafalou, 2010;Hwang et al, 2011), as well as laboratory experiments (Whitehead and Chapman, 1986;Avicola and Huq, 2002;Lentz and Helfrich, 2002;Horner-Devine et al, 2006;Yeping and Horner-Devine, 2013). …”