Local and Remote Wind Forcing of New South Wales Inner Shelf Currents and Sea Level

Abstract

Linear multiple regression analysis is used to identify the locally and remotely wind-driven components of the nearshore current and adjusted sea level (ASL) variability at Sydney, New South Wales. The data analyzed comprise a one year time series of current meter records acquired 3 km offshore in 60?80 m of water together with coastal sea level and wind date from one local and 12 remote stations in NSW, Bass Strait and the Great Australian Bight Approximately 60% to 70% of the ?weather band? (40 h to 20 d period) current and ASL variance at Sydney appears to be wind-driven, with the major contributors to the variance being the southern New South Wales and Bass Strait winds, both lagged by intervals corresponding to the propagation speed of the first coastal trapped wave (CTW) mode. The ?multipath? nature of wind energy transmission by at least two CTW modes is evident but the energy flux at Sydney of the freely propagating second mode from Bass Strait appears to be only one-fifth to one-third of the first of the flux mode, instead of exceeding it as was the conclusion of the Australian Coastal Experiment. The importance of Bass Strait forcing (via two CTW modes) appears to be greatest in the summer, when it is nearly as important as NSW forcing for the nearshore current and slightly more so for the ASL. Winter analyses are less conclusive for the current but ASL analyses show that NSW winds contribute 50% more variances than do Bass Strait winds. The influence of winds farther west than Bass Strait is not easily identifiable in the current and ASL variance at Sydney, even during winter when winds in the Great Australian Bight are strongest. This suggests that CTW energy incident from the west on Bass Strait is usually of secondary importance to local wind forcing there, at least in terms of its ability to generate CTWs at the eastern end of Bass Strait.