Comparison of Observed (HF Radar and ADCP Measurements) and Computed Tides in the North Channel of the Irish Sea

Abstract

A three-dimensional high-resolution (grid of order 1 km) model of the North Channel of the Irish Sea, incorporating a one equation turbulence energy submodel to parameterize vertical mixing, is used to compute the M2, S2, N2, K1, and O1 tides. Elevations and currents are compared with observations, with particular emphasis on a detailed comparison with current profiles recorded by two acoustic Doppler current profilers (ADCPs) and HF radar measurements of the surface current. The comparison with the HF radar shows small-scale spatial variations in both modeled and observed currents superimposed upon the larger scale tidal currents. These small-scale changes appear to be associated with variations in bottom topography and can only be resolved by using fine-grid models or detailed measurements. Computed M2 current profiles derived from a multiconstituent calculation are in excellent agreement with profiles measured by the ADCPs. However, in a single constituent M2 calculation, the magnitude of the current is overpredicted. Increasing the bottom friction coefficient to compensate for the absence of other constituents improves the accuracy of the bottom current, although the thickness of the turbulent boundary layer is underpredicted with a resulting overprediction of the surface current that cannot be corrected for by changing the bottom friction coefficient.