The subtidal behaviour of the Celtic Sea-II. Currents

Abstract

Subtidal currents observed in the Celtic Sea during spring 1978 are described in terms of empirical orthogonal functions and rotary spectra. Less than half the current variance can be related to local wind forcing. It is suggested that the remaining variance is partly due to the influence of winds acting over the adjacent Irish Sea and North Sea. There is no evidence in this limited data set of a strong coupling between the Celtic Sea and adjacent North Atlantic at subtidal frequencies. Examination of the terms in the subtidal momentum equation shows that the interior of the Celtic Sea is essentially in geotrophic balance. Close to the tidally energetic St George's Channel, both bottom friction and mean tidal advection become important. A diagnostic model for estimating circulation patterns from bottom pressure and wind data is developed and successfully applied to the Celtic Sea. An attempt to use the model with both bottom pressures and coastal sea levels was less successful than with bottom pressures alone. We attribute this to the nearshore distortion of the coastal sea levels.