Structure, propagation, and mixing of energetic baroclinic tides in Mamala Bay, Oahu, Hawaii

Large semidiurnal vertical displacements (approximate to 100 m) and strong baroclinic currents (approximate to 0.5 m s(-1); several times as large as barotropic currents) dominate motions in Mamala Bay, outside the mouth of Pearl Harbor, Hawaii. During September 2002, the authors sought to characterize them with a 2-month McLane moored profiler deployment and a 4-day intensive survey with a towed CTD/ADCP and the Research Vessel (R/V) Revelle hydrographic sonar. Spatial maps and time series of turbulent dissipation rate epsilon, diapycnal diffusivity K-rho, isopycnal displacement eta, velocity u, energy E, and energy flux F are presented. Dissipation rate peaks in the lower 150 m during rising isopycnals and high strain and shows a factor-of-50 spring-neap modulation. The largest K-rho values, in the western bay near a submarine ridge, exceed 10(-3) m(2) s(-1). The M-2 phases of eta and u increase toward the west, implying a westward phase velocity c(p) approximate to 1 m s(-1) and horizontal wavelength approximate to 60 km, consistent with theoretical mode-1 values. These phases vary strongly (approximate to +/- 45 degrees) in time relative to astronomical forcing, implying remotely generated signals. Energy and energy flux peak 1-3 days after spring tide, supporting this interpretation. The group velocity, computed as the ratio F/E, is near approximate to 1 m s(-1), also in agreement with theoretical mode-1 values. Spatial maps of energy flux agree well with results from the Princeton Ocean Model, indicating converging fluxes in the western bay from waves generated to the east and west. The observations indicate a time-varying interference pattern between these waves that is modulated by background stratification between their sources and Mamala Bay.