FEATURES OF MARINE WIND FIELDS OVER NEW-ZEALAND WATERS FROM ERS-1 SCATTEROMETER DATA

Wind data from the ERS-1 scatterometer have been processed for New Zealand waters. These show spatial features of marine wind fields which have previously been difficult to resolve using conventional surface-based measurements. Winds across the western access to Cook Strait, delineated by a corridor between Farewell Spit and western Taranaki, were analysed and profiles of wind stress extracted. These show characteristic structures for south-easterly events in which the stress steadily increases from Farewell Spit towards the Taranaki Coast. In westerly or north-westerly events the structure is more uniform. The mean stress across this corridor has been compared to that calculated from surface-based measurements at Farewell Spit and the Maui-A oil and gas production platform off Cape Egmont. The Farewell spit data lead to underestimates of the stress, which partially reconciles previous attempts to model wind-driven currents off the west coast of the South Island from these data. In these the currents were underestimated. The Maui-A data are unbiased in westerly events but give overestimates in southeasterly winds. An improved estimate of the mean stress can be derived from using a combination of wind data from these two stations.