COASTAL-TRAPPED WAVE MODE FITTING - REANALYSIS OF THE AUSTRALIAN COASTAL EXPERIMENT

The original time domain analysis of data from the Australian Coastal Experiment involved fitting coastal-trapped wave modes to an array of velocity time series using a truncated singular value decomposition. W hile the truncation was necessary for noise reduction, it is shown tha t important information concerning the separation of mode 1 and mode 2 was discarded. A weighted least-squares mode-fitting technique is int roduced that uses the data to estimate both the signal-to-noise ratio and the relative weighting of the fitted modes. In addition, the veloc ity data are augmented by sea-level data. Findings from the present an alysis differ in several important respects from the original results. It is found that mode 1 has approximately twice the energy flux of mo de 2 and that mode 3 is statistically insignificant at the southern en d of the East Australian waveguide. In addition, mode 1 is not highly correlated with mode 2. These differences are primarily due to changes in mode 1; mode 2 remains essentially unchanged from the original ana lysis. These revised modes, when used as boundary conditions to a wind -forced coastal-trapped wave model that predicts velocity and sea leve l along the coast, lead to a small but significant increase in predict ion skill over the original modes. The reanalysis raises questions reg arding the energy source for the coastal-trapped wave modes. The diffe rence between the original and present analyses is reduced by the incl usion of sea-level data. The ability of the instrument array to resolv e coastal-trapped wave modes is discussed, and the problems associated with nonorthogonality of the theoretical modal structures as sampled by the array are highlighted. It is noted that the small number of deg rees of freedom in the data leads to 95% confidence limits on modal en ergy fluxes that are as large as 69% of the estimated values.