Directional wave climate and power variability along the Southeast Australian shelf

• Published in: Continental Shelf Research
• Main Authors: Mortlock, Thomas R., Goodwin, Ian D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: Southern Ocean; Tropical Ridge
• Online Access: https://researchers.mq.edu.au/en/publications/80c60eff-1ee0-42c7-a2ec-760fe0d29a49; https://doi.org/10.1016/j.csr.2015.02.007; http://www.scopus.com/inward/record.url?scp=84924932063&partnerID=8YFLogxK

Variability in the modal wave climate is a key process driving large-scale coastal behaviour on moderate- to high-energy sandy coastlines, and is strongly related to variability in synoptic climate drivers. On sub-tropical coasts, shifts in the sub-tropical ridge (STR) modulate the seasonal occurrence of different wave types. However, in semi-enclosed seas, isolating directional wave climates and synoptic drivers is hindered by a complex mixed sea-swell environment. Here we present a directional wave climate typology for the Tasman Sea based on a combined statistical-synoptic approach using mid-shelf wave buoy observations along the Southeast Australian Shelf (SEAS). Five synoptic-scale wave climates exist during winter, and six during summer. These can be clustered into easterly (Tradewind), south-easterly (Tasman Sea) and southerly (Southern Ocean) wave types, each with distinct wave power signatures. We show that a southerly shift in the STR and trade-wind zone, consistent with an observed poleward expansion of the tropics, forces a n increase in the total wave energy flux in winter for the central New South Wales shelf of 1.9GJm -1 wave-crest-length for 1° southerly shift in the STR, and a reduction of similar magnitude (approximately 1.8GJm -1 ) during summer. In both seasons there is an anti-clockwise rotation of wave power towards the east and south-east at the expense of southerly waves. Reduced obliquity of constructive wave power would promote a general disruption to northward alongshore sediment transport, with the cross-shore component becoming increasingly prevalent. Results are of global relevance to sub-tropical east coasts where the modal wave climate is influenced by the position of the zonal STR.