Relation between mean sea level, current and wind stress on the east coast of Australia

Abstract

Five-day mean sea level differences between Evans Head (29º 07'S.) and Coffs Harbour 30º 19'S.), and between Coffs Harbour and Crowdy Head (31º 50'S.) were regressed on estimates of longshore current acceleration, mean longshore current and longshore wind stress, with the following results: (i) A relation was found between sea level difference from Coffs Harbour to Crowdy Head, and current acceleration. There was no similar relation for the section Evans Head to Coffs Harbour, and no reason could be found for the difference in behaviour between the two sections. (ii) A weakly defined relation was found, in both sections of the coast, between sea level difference and the square of the mean longshore current (a friction effect). (iii) An apparent relation was found, again in both sections of the coast, between sea level difference and longshore wind stress. This relation was more marked than expected from theory.

The longshore currents were obtained from ships' drift, and covered a period of 2 years. The current data show a southward drift of current pattern, at an average rate of 9 km day^-1. They also show a clear correlation between currents at the shelf edge (approximately 19 km offshore) and currents nearer shore (approximately 6.5 km offshore). It was found that the nearer-shore currents lagged the shelf-edge currents by between 7 and 10 days. Time and space correlations of the shelf-edge currents confirm earlier estimates from similar data. A frequency spectrum of the shelf-edge currents showed a broad maximum in the period range 50-170 days.