Barotropic M2 Tides and Tidal Currents in Long Island Sound: A Numerical Model

Abstract

 

The tides and tidal currents of Long Island Sound, dominated by the lunar semidiurnal M² tide are characteristic of a quarter wave oscillator in a narrow semi-enclosed basin. Although complicated by irregular coastline geometry and basin bathymetry, the Sound exhibits a pattern typical of a near resonant system. The open eastern end experiences strong tidal currents (over 1.0 m s-1) at full flood or ebb) and a relatively small tide range (0.8meters). Although technically connected to the Atlantic Ocean through the East River, the western end behaves as a solid boundary, characterized by weak, currents (0.1 to 0.3 m s -1) and a large tide range (2.2 meters). In spite of numerous observational and theoretical studies of the Sound's circulation, no numerical model appears to have been previously published. As a preliminary step, this study presents the formulation and results of a numerical computation for the barotropic M² tide and tidal current. The finite-difference model solves the vertically integrated equations of motion for a homogeneous fluid. Except for bottom friction, all non-linear terms are neglected. Realistic coastline and bathymetry, bottom friction, and Coriolis effects are incorporated. The results of the model correlate well with the observed tide heights and current velocities obtained at stations throughout the Sound. The overall tide and current structure is also consistent with empirical and theoretical results.