On the St Kilda shelf tidal regime

New records of tidal elevation from St Kilda and the west coast of North Uist make it possible to estimate pressure gradients across the shelf, to supplement existing records parallel to the shelf edge. Results confirm the existence of relatively large diurnal currents, which are clearly barotropic. Diurnal elevations are markedly smaller at the coast, and this is explained by the superposition of a Kelvin wave and a shelf wave of similar amplitude but in anti-phase. The currents corresponding to this model agree fairly well with those measured directly by Cartwright (Nature, London, 223, 5209, 928–932, 1969), and confirm less exact calculations made by Huthnance (University of Cambridge, 1973).