APPLICATION OF A BAROTROPIC MODEL TO NORTH-ATLANTIC SYNOPTIC SEA-LEVEL VARIABILITY

A barotropic, shallow-water model of the North Atlantic is used to inv estigate variability in adjusted sea level on time scales of a few day s to a few months (by ''adjusted,'' we mean that the inverse barometer is removed from both the model-computed sea level and the observation s). The model has 1/3 degrees x 0.4 degrees resolution in latitude and longitude, respectively, and is forced using atmospheric pressure and wind stress data derived from European Centre for Medium Range Weathe r Forecasts (ECMWF, 1994) analyses. The model results are compared wit h coastal tide gauge data. Along the western boundary, from St. John's , Newfoundland, to Fernandina Beach, Florida, coherence squared betwee n model and data is greater than 0.5 in the period range 3 to 10 days. South of Cape Hatteras, the model underestimates the amplitude seen i n the data, with much better agreement north of the Cape. Model perfor mance on the eastern boundary is generally poor. We suggest this is be cause on the eastern boundary, the shelf width is much narrower, compa red to the internal radius of deformation, than on the western boundar y. In addition, the model resolution is insufficient to adequately rep resent the shelf on the eastern boundary. The poorer agreement south o f Cape Hatteras may be due Gulf Stream effects not accounted for by th e model dynamics. Finally, we discuss the model-computed variability i n the ocean interior.