A description of the tides in the Eastern North Atlantic

A description of the Eastern North Atlantic tidal dynamics tin a region spanning from 20 degrees N to 48 degrees N in latitude and from 34 degrees W to 0 degrees in longitude) is obtained by means of new in situ measurements and numerical modelling based on TOPEX/POSEIDON-derived data sets. The main source of measurements is the tide gauge network REDMAR (RED de MAReografos de Puertos del Estado), operative since July 1992 and managed by Clima Maritime (Puertos del Estado). Results derived from the harmonic analysis of the first years of measurements are presented and compared with model results. In order to obtain a global picture of the tides in the region, a large compilation of harmonic constants obtained from other institutes is included. The availability of new TOPEX/POSEIDON-derived harmonic constants data sets provides a chance to include the benefits derived from satellite altimetry in high resolution regional applications of numerical models. Richard Ray's tidal model (RAY et al., 1994), based on a response type tidal analysis of TOPEX/POSEIDON data, was employed within a model of the studied area The numerical model employed is HAMSOM, a 3-D finite difference code developed both by the Institut fur Meereskunde (Hamburg University) and Clima Maritime. Results from simulations of seven major harmonics are presented, providing a comprehensive view of tidal dynamics, including current information. The results of tidal simulations show good agreement between semidiurnal harmonic components and the values measured by both coastal and pelagic tidal gauges and by current meters. The modelled diurnal constituents show larger relative differences with measurements than semidiurnal harmonics, especially concerning the phase lags. The non-linear transfer of energy from semidiurnal to higher order harmonics, such as M-4 and M-6, was mapped. Those transfers were found to be important only in two areas: the French continental shelf in the Bay of Biscay and the widest part of the African shelf, south of Cabo Bojador. (C) 1998 Elsevier Science Ltd All rights reserved.