Abstract
Abstract. The dynamical interaction between currents, bathymetry, waves, and estuarine outflow has significant impacts on the surf zone. We investigate the impacts of two strategies to include the effect of surface gravity waves on an ocean circulation model of the south shore of O'ahu, Hawaii. This area provides an ideal laboratory for the development of nearshore circulation modeling systems for reef-protected coastlines. We use two numerical models for circulation and waves: Regional Ocean Modeling System (ROMS) and Simulating Waves Nearshore (SWAN) model, respectively. The circulation model is nested within larger-scale models that capture the tidal, regional, and wind-forced circulation of the Hawaiian archipelago. Two strategies are explored for circulation modeling: forcing by the output of the wave model and online, two-way coupling of the circulation and wave models. In addition, the circulation model alone provides the reference for the circulation without the effect of the waves. These strategies are applied to two experiments: (1) typical trade-wind conditions that are frequent during summer months, and (2) the arrival of a large winter swell that wraps around the island. The results show the importance of considering the effect of the waves on the circulation and, particularly, the circulation–wave coupled processes. Both approaches show a similar nearshore circulation pattern, with the presence of an offshore current in the middle beaches of Waikiki. Although the pattern of the offshore circulation remains the same, the coupled waves and circulation produce larger significant wave heights ( ≈ 10 %) and the formation of strong alongshore and cross-shore currents ( ≈ 1 m s−1).
Highlights
Our objective is to describe how ocean waves and currents interact in the south shore of the island of O’ahu, Hawaii, with a goal towards the development of an operational ocean forecast system
We implemented the coupled Regional Ocean Modeling System (ROMS)–Simulating Waves Nearshore (SWAN) simulations for the south shore of Honolulu, Hawaii, using a vortex force formalism to account for the wave–current interaction described by Uchiyama et al (2010) and Kumar et al (2012), which gives better performance than the traditional (Mellor, 2005, 2008) radiation stress approach (Lane et al, 2007)
Since no observations are available inside the nearshore domain, we proceed with a comparison of the National Database Buoy Center (NDBC) buoys with the outer SWAN grid (SWAN only) that provide the boundary conditions to the inner domain
Summary
Our objective is to describe how ocean waves and currents interact in the south shore of the island of O’ahu, Hawaii, with a goal towards the development of an operational ocean forecast system. We investigate the impacts of surface gravity waves on the nearshore circulation in a highresolution regional ocean model for the coast of Honolulu, Hawaii (Fig. 1). This work was developed under the umbrella of the Pacific Islands Ocean Observing System (PacIOOS) project (http://oos.soest.hawaii.edu/pacioos/), aiming to improve an operational coastal ocean forecast system for the island of O’ahu. The south shore of O’ahu is mostly contained within Mamala Bay including Waikiki beach. The challenge is to provide useful forecasts of the nearshore circulation in this region that includes the primary dynamical processes while remaining feasible in computational cost. Alternatives are sought and tested for the development of such a system
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