Current structure on the Long Island inner shelf

Abstract

Current velocity records from a deployment of 17 current meters across a ridge and swale topography with a 5 m amplitude, 6.5 km off the coast of Long Island, were analyzed to determine the interaction between the flow field and the topography which might maintain these special bottom features. No first‐order interactions were found; the flow field was generally parallel everywhere. Correlation, coherence, and empirical orthogonal modal (EOM) analysis showed no significant differences between meters as a function of alongshore or cross‐shore separation. EOM analysis showed that 79% of the variance was in the first barotropic mode with a strong vertical shear that was probably related to friction. Tide and wind response models can replicate about 64% of the variance in the alongshore velocity, of which about 30–40% is tidal. The residual record, uncorrelated to wind or tide, shows the effect of alongshore variations in the pressure field following a storm event by reversing the flow opposite to the diminishing wind stress. By regression of the averaged alongshore bottom velocities to wind stress, a linear bottom friction coefficient of 0.14 cm s−1 is found, which is in agreement with previous estimates, and a time average alongshore pressure gradient of 0.3 × 10−7 is found which is an order of magnitude smaller than previous estimates. By scaling the results of the wind response model, the linear bottom friction coefficient is also found to be 0.14 cm s−1.