THE NORTH-SEA POLE TIDE DESCRIBED THROUGH A TIDE-SURGE NUMERICAL-MODEL

Monthly mean sea level values from tide gauges at the coasts of the North Sea are compared with the monthly means from an operational tide-surge numerical model for the time period 1955-1984. The model describes most of the variability at all frequencies except the annual. Most of the energy around the pole tide frequency is also reproduced by the model and since its tidal forcing does not include the equilibrium pole tide frequencies it is concluded that the deviations from the equilibrium pole tide are of meteorological origin. The east-west wind stress component is found to be energetic at this frequency thus providing the meteorological forcing. The annual cycle due to steric effects is also estimated. The meteorological correction modifies the determined sea-level secular trends by up to 0.8mm/yr for this 30 year period for stations in the eastern North Sea.