Coastal-Trapped Waves on the East Australian Continental Shelf Part I: Propagation of Modes

Abstract

The currents observed over the shelf and slope during the Australian Coastal Experiment (ACE) are used to determine the amplitudes (as functions of time) of the first three coastal-trapped wave (CTW) modes at three locations along the southeast coast of Australia. A statistical ?eddy? mode is included to minimize contamination of the coastal-trapped wave currents from East Australian Current eddies. The first three CTW modes account for about 65% of the observed variance in the alongshelf currents on the shelf and slope at Cape Howe, about 40% at Stanwell Park, but only about 24% at Newcastle. Currents associated with the East Australian Current dominate the observations offshore from Newcastle. CTWs account for all but 10%, 37% and 27% of the currents observed at the most nearshore locations on the shelf at Cape Howe, Stanwell Park and Newcastle. The first two coastal-trapped wave modes propagate at close to the appropriate theoretical phse speeds, but the third coastal-trapped wave mode and the eddy mode are not coherent between the three current meter sections along the coast. Surprisingly, mode 2 carries a greater fraction of the coastal-trapped wave energy than does mode 1 at two of the sections. Modes 1 and 2 are coherent with each other at the 95% significance level. The major energy source for the CTWs is upstream (in the CTW sense) of the first line of current meters.