Sketch of the situation that can give rise to coastal trapped waves. The key ingredients are
The wind stress drives water in the surface mixed layer (the Ekman layer) away from the coast and back, producing periodic upwelling and downwelling near the coast. This produces alternating onshore and offshore directed flow below the mixed layer.
- the earth's rotation, indicated in the upper left of the diagram,
- a sloping continental shelf, and
- variable external forcing such as a periodic wind stress τw.
If the shelf region is in the southern hemisphere and north is up, the northward acting wind stress produces downwelling and the southward acting wind stress produces upwelling.
© 2000 CSIRO Marine Research, reproduced by permission.