Comparison of observed (HF radar and ADCP measurements) and computed tidesin the North Channel of the Irish Sea

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 s ubmodel to parameterize vertical mixing, is used to compute the M-2, S-2, N -2, K-1, and O-1 tides. Elevations and currents are compared with observati ons, with particular emphasis on a detailed comparison with current profile s recorded by two acoustic Doppler current profilers (ADCPs) and HF radar m easurements of the surface current. The comparison with the HF radar shows small-scale spatial variations in bo th modeled and observed currents superimposed upon the larger scale tidal c urrents. 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 M-2 current profiles derived from a multiconstituent calculation a re in excellent agreement with profiles measured by the ADCPs. However, in a single constituent M-2 calculation, the magnitude of the current is overp redicted. 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 wi th a resulting overprediction of the surface current that cannot be correct ed for by changing the bottom friction coefficient.