The Effect of the Leeuwin Current on Offshore Surface Gravity Waves in Southwest Western Australia. Issue 11 (22nd November 2017)

• Record Type: Journal Article
• Authors: Wandres, Moritz; Wijeratne, E. M. S.; Cosoli, Simone; Pattiaratchi, Charitha
• Is Part Of: Journal of geophysical research. Volume 122:Issue 11(2017)
• Page Start: 9047
• Page End: 9067
• Publication Date: 2017-11-22
• Subjects: wave‐current interaction -- surface gravity wave -- Leeuwin Current -- ocean modeling -- COAWST -- wave regime; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2017JC013006
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The knowledge of regional wave regimes is critical for coastal zone planning, protection, and management. In this study, the influence of the offshore current regime on surface gravity waves on the southwest Western Australian (SWWA) continental shelf was examined. This was achieved by coupling the three dimensional, free surface, terrain‐following hydrodynamic Regional Ocean Modelling System (ROMS) and the third generation wave model Simulating WAves Nearshore (SWAN) using the Coupled Ocean‐Atmosphere‐WaveSediment Transport (COAWST) model. Different representative states of the Leeuwin Current (LC), a strong pole‐ward flowing boundary current with a persistent eddy field along the SWWA shelf edge were simulated and used to investigate their influence on different large wave events. The coupled wave‐current simulations were compared to wave only simulations, which represented scenarios in the absence of a background current field. Results showed that the LC and the eddy field significantly impact SWWA waves. Significant wave heights increased (decreased) when currents were opposing (aligning with) the incoming wave directions. During a fully developed LC system significant wave heights were altered by up to ± 25% and wave directions by up to ± 20°. The change in wave direction indicates that the LC may modify nearshore wave dynamics and consequently alter sediment patterns. Operational regional wave forecasts and hindcasts may give flawed predictions if wave‐current interaction is not properly accounted for. Plain language Summary: The knowledge of regional wave climates is critical for coastal zone planning, protection, and management. Large‐scale currents are known to alter wave conditions, however, minimal consideration has been given to the effect of offshore currents on the southwest Western Australian wave regime. The Western Australian offshore circulation is dominated by the Leeuwin Current (LC). The LC is a strong eastern boundary current that carries warm, low salinity water and features a large mesoscale eddy field. The LC is unique as it is the only pole‐ward flowing eastern boundary current in the world. Using state‐of‐the‐art numerical models, for the first time, the influence of the LC on Western Australian waves was studied and quantified. Wave heights increased (decreased) by ±25% when currents were opposing (aligning with) incoming waves and wave directions changed by up to ±20°. Changes in offshore wave height and direction may modify nearshore dynamics and consequently alter sediment patterns along the Western Australian coast. Operational wave simulations may give flawed predictions if wave‐current interaction is not properly accounted for. Key Points: The Leeuwin Current, a pole‐ward flowing eastern boundary current in the Indian Ocean, modulates the southwestern Australian wave regime In areas of strong currents such as meanders and eddies significant wave heights are altered by up to ± 25% Wave directions are modified by up to ± 20° which may result in changes in nearshore dynamics