The Effect of the Leeuwin Current on Offshore Surface Gravity Waves in Southwest Western Australia

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.

Interoperability of Direction-Finding and Beam-Forming High-Frequency Radar Systems: An Example from the Australian High-Frequency Ocean Radar Network

“…R U values typically exceeded 0.95 within the radar footprint (Figure 5a), while R V values also exceeded 0.9 (Figure 5b), suggesting good agreement between datasets. Good agreement was confirmed in the general circulation pattern: the offshore southward current and the weaker northward current mapped by the WERA HFR radar (black arrows), associated, respectively, with the Leeuwin Current (LC) and the Capes Current (CC) [40,42], they are also well reconstructed in the merged WERA-SeaSonde data (red arrows). Typical bias for the zonal component (Figure 6a) was below 0.15 m/s across the radar domain, and increases for the meridional component, particularly in areas of weak currents (Figure 6b).…”

“…When comparing the time-averaged current pattern, results show good agreement between the two data sets and further support the hypothesis of interoperability of the different HFR systems. There is good agreement between the main offshore meandering structure as well as the current reversal in the coastal shelf area (Figure 5d), that are associated respectively with the Leeuwin Current (LC) and Capes Current (CC) system [40,42].…”

“…The primary product of the HFR network is ocean current maps; waves and winds can also be obtained where the phased-arrays systems are installed. Radar data, freely available from the IMOS portal (https://portal.aodn.org.au/), are used for scientific research, operational modeling, coastal monitoring, fisheries, and other applications [36][37][38][39][40][41][42].…”

Improving Data Quality for the Australian High Frequency Ocean Radar Network through Real-Time and Delayed-Mode Quality-Control Procedures

“…Quality-controlled subsurface mooring data for the Rottnest Shelf region (Figure 1) are used for validation and fine-tuning purposes, primarily for the large number of sustained moorings and the wide range of oceanographic processes in the area [5][6][7]. The data set used here spans a time period between 01 February 2015, 00:00 UTC, and 30 June 2015, 23:59 UTC.…”

“…Each HFR node is configured primarily to sample ocean currents with a maximum range of over 200 km; however, at selected locations where the phased-arrays systems are installed, waves and winds can also be obtained. Radar data, freely available from the IMOS portal (https://portal.aodn.org.au/), are used for scientific research, operational modeling, coastal monitoring, fisheries, and other applications [1][2][3][4][5][6][7]. This paper focuses on the quality-control (QC) procedures that have been implemented for the phased array systems in Australia and are applied operationally on both the near real-time (NRT) and delayed-mode (DM) products.…”