Abstract
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. While the truncation was necessary for noise reduction, it is shown that important information concerning the separation of mode 1 and mode 2 was discarded. A weighted least-squares mode-fitting technique is introduced that uses the data to estimate both the signal-to-noise ratio and the relative weighting of the fitted modes. In addition, the velocity data are augmented by sea-level data.
Findings from the present analysis differ in several important respects from the original results. It is found that mode 1 has approximately twice the energy flux of mode 2 and that mode 3 is statistically insignificant at the southern end 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 analysis. These revised modes, when used as boundary conditions to a wind-forced coastal-trapped wave model that predicts velocity and sea level along the coast, lead to a small but significant increase in prediction skill over the original modes. The reanalysis raises questions regarding the energy source for the coastal-trapped wave modes.
The difference between the original and present analyses is reduced by the inclusion of sea-level data. The ability of the instrument array to resolve 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 degrees of freedom in the data leads to 95% confidence limits on modal energy fluxes that are as large as 69% of the estimated values.
