The effects of stratification and alongshore currents on the propagation of coastal-trapped waves

A hierarchy of models has been developed to describe coastal-trapped wave (CTW) propagation along continental shelves. In this paper, the results of four models are compared with respect to predictions of phase speeds for low-frequency non-dispersive CTWs propagating through the ACE (Australian Coastal Experiment) study area along the southeast Australian coast. The ACE experiment demonstrated that the stratification there significantly increased theoretical CTW phase speeds. At times substantial mean alongshore currents, apparently associated with meanders of the East Australian Current, were observed to intrude onto the continental shelf. Such currents can alter CTW propagation speeds by advection and by altering background vorticity if the current has shear. Accordingly, the models chosen here for intercomparison incorporate first, no stratification and no current [Buchwald and Adams, (1968) Proceedings of the Royal Society Series A, 305, 235-250]; secondly, barotropic currents and no stratification [Niiler and Mysak (1971), Geophysical Fluid Dynamics, 2, 273-288]; thirdly, vertical stratification but no currents (Huthnance (1978), Journal of Physical Oceanography, 8, 74-92]; and fourthly, full stratification and baroclinic currents [Luther and Bane (1985) Journal of Physical Oceanography, 15, 3-23]. The stratification and currents used in these models were determined from CTD casts and ship drift data obtained during six ACE cruises. Between the six cruises the oceanographic conditions on the shelf and offshore were observed to undergo considerable variation. Hence, it has been possible to compare the models over a wide range of parametric variations. The results show that there is considerable variation in the predicted phase speeds between models.