Internal wave shoaling in Mamala Bay, Oahu, Hawaii

Internal waves shoaling in nearshore systems are an important factor in the internal wave energy budget. The Hawaiian Island Ridge is known as a site of strong internal tide generation, but the propagation of the internal tide energy into the island nearshore regions is less well studied. An array of three moorings with vertical thermistor chains was deployed in Mamala Bay, off the south shore of Oahu. The deepest mooring at 500 m, which also was equipped with a downward-looking ADCP, observed large breaking semidiurnal internal tides along the boundary. While these did not occur consistently, they were associated with significant mixing. The shallowest mooring, at 90 m, observed small but frequent internal bores along the bottom not linked with tidal phase. The middle mooring, at 300 m, displayed elevated energy in a high frequency band (6–40 cpd) close to the slope. This may be explained as the concentration of high frequency energy due to nonlinear interactions along the near-critical slope. While some of the nearshore internal wave observations can be attributed to internal waves from remote sources propagating in the onshore direction, a significant portion is due to locally generated internal waves propagating in the alongshore direction, leading to complex interactions on the south Oahu slope.