| Accurate sea level measurements from the TOPEX/POSEIDON satellite have
vastly improved our knowledge about global ocean tide since its launch
in 1992. Similarly hydrodynamic models have advanced in both resolution
and ability include more and more diurnal and semi-diurnal constituent,
and even higher harmonic shallow water constituents like M4.
In this presentation 16 years of TOPEX+JASON1 altimetry have been used
to investigate the stability of the ocean tide estimates. On the northwest European shelf the major semidiurnal tide has different
amplitude in summer and winter ranging up to nearly 8% of the tidal
amplitude and a slight phase change. This seasonal modification of the
semi diurnal tide has also been seen from local gauges around the North
Sea, but has not been registered elsewhere.
In addition some minor year to year fluctuations in the amplitude of the
largest tidal constituents are seen from local tide gauges and these
very local phenomena are also investigated from altimetry. |