THE DIFFRACTION OF COASTALLY TRAPPED WAVES INTO AND FROM A STRAIT

For the idealised geometry in Figure 2, the results of Buchwald and Kachoyan (1987) for a barotropic ocean are extended to include the diffraction of shelf waves by a strait. Assuming a known flux through the strait together with an independent incident shelf wave, the amplitudes of the scattered shelf wave modes are calculated by the adoption of a modal expansion in the strait. The boundary condition at the strait mouth is then satisfied by the use of a Galerkin technique. The results show that higher mode amplitudes are underestimated by Buchwald and Kachoyan (1987). These results are extended to the case of a strait of finite length joining two semi-infinite oceans. An incident shelf wave in one ocean gives rise to a pressure gradient along the strait, and strait oscillations ensue. For a range of geometries and frequencies, calculations show that up to half the incident energy is diffracted through the strait, with some transfer into higher modes. The generation of oscillations in the strait by a periodic wind-stress along the strait is also considered. For parameters relevant to the Bass Strait and the ACE observations the results indicate that incident shelf waves on the south coast are the more likely source of the waves observed on the east coast of Australia.