Numerical investigation of the Sicily Channel dynamics: density currents and water mass advection

Abstract

The Sicily Channel connects the western and eastern Mediterranean sub-basins, playing a fundamental role in the dynamics of the Mediterranean circulation. The flow in the Channel is driven by direct forcing such as wind and by thermohaline processes leading to density difference between the two sub-basins. Assessing the relative role of these two types of forcing mechanisms is still an open question in the literature, despite its importance for a correct understanding and prediction of the Channel circulation. In this paper, we isolate the remotely forced, density-driven component of the circulation, considering a simplified setting, where the forcing is schematized as an imposed density difference along the channel, Δ ρ. The study is carried out considering results from a high resolution numerical model of the circulation in the Channel area. A range of values for Δ ρ is considered, and the effects of changing Δ ρ on the circulation patterns, transport values and water mass advection are studied. The patterns of the average circulation and water mass advection remain qualitatively similar at varying Δ ρ. The simulations reproduce a number of realistic circulation features for both the surface Modified Atlantic Water (MAW) and the Levantine Intermediate Water (LIW). These include the complex branching patterns of the MAW at the entrance of the Channel, and the appearance of the characteristic structure of the Atlantic Ionian Stream (AIS) inside the Channel. At a more detailed level, the nonlinearity at increasing Δ ρ appears to influence some aspects of the circulation, such as the relative strength of the Tyrrhenian and Sicilian MAW branches. The transport across the Channel is found to increase approximately linearly with Δ ρ in the considered range, with values ranging from ≈0.3 to ≈0.8 Sv. The lowest value corresponds to Δ ρ based on climatological density value in the neighbouring regions (Sardinia Channel and Ionian Sea), while the highest values correspond to more remote density values, i.e. to differences between the far-field western and eastern Mediterranean sub-basins.