The M4 Shallow Water Tidal Constituent From Altimetry and Tide Gauges

Present global ocean tide models based on the TOPEX/POSEIDON satellite data are still not accurate enough on the continental shelves for detailed oceanographic studies. The need for increasing accuracy in shelf regions calls for inclusion of more than just semidiurnal and diurnal constituents in future global ocean tide models. This study is an extension to previous investigations on the Northwest European Shelf by (Andersen, 1999) which demonstrated that the major non-linear shallow water tidal constituent could be mapped from T/P altimetry. The purpose of this work is to locate in which regions of the world the M4 shallow water constituent is of importance to tidal modelling and to advise where it should be included in future tidal models. Maximum amplitude of more than 10 centimetres are found at the Newlyn tide-gauge in the English Channel. Significant amplitudes are not just concentrated to the Northwest European shelf but is also found at several other shelves like the Patagonian Shelf and several coastal shelves around the Atlantic Ocean..