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Modulation of wind drag by tidal currents in an embayment
Journal article   Open access

Modulation of wind drag by tidal currents in an embayment

Stephen Thurgate and Michael V. W. Cuttler
Quarterly Journal of the Royal Meteorological Society, Early View
2026
DOI: https://doi.org/10.1002/qj.70194
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Open Access CC BY-NC V4.0

Abstract

air-sea momentum exchange tidal modulation wave-current interaction wind-wave coupling young wind seas
Shark Bay is a semi-enclosed embayment on Australia's west coast that experiences persistent southerly winds, limited offshore swell, and moderate tidal currents. The alignment of the bay's primary axis with the prevailing wind direction, combined with a fixed fetch, provided a natural setting in which to examine interactions between winds, tides, and locally generated wind waves. This study examines how wind–wave interactions modulate sea-surface roughness and atmospheric drag through their impact on the distribution and energetics of the wave field. Wave spectra measured by an in-situ buoy were analysed together with wind observations and hindcast wind modelling. The spectral results showed that the energy extracted from the wind was not solely associated with changes in bulk wave height or roughness proxies. Instead, a significant fraction of the wind work was transferred into the wave field through the creation and amplification of short wind waves, with strong sensitivity to background water-velocity modulation through its effect on intrinsic wave phase speed. As a result, modest changes in current led to large variations in wind–wave energy exchange and effective atmospheric drag. These findings indicated that, under conditions characterised by young waves, unsteady winds, and current-modified phase speeds, roughness-based drag formulations alone may be incomplete, and additional wind–wave coupling pathways can play an important role in mediating energy transfer between the atmosphere and ocean.

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