High frequency radio observations of tides and currents south of O'ahu

Abstract

A year of radial current data from a high frequency radio current meter (HFR) on Oahu's south shore is analyzed from long to short time scales. Monthly and seasonal currents reveal a large scale inversion in the winter months of the typically westward propagating flow. A region of significant cyclonic flow west of Penguin Bank is identified as an eddy generation zone likely driven by cyclonic wind stress curl. Island trapped waves are investigated while complications from local vorticity and the close proximity of the inertial period are considered. Observed tidal characteristics are compared with three existing models. Incoherent tidal features, presumably attributed to energetic internal tides in the area, are presented. Deep-ocean Assessment and Reporting of Tsunamis (DART) buoy data is used to determine the open ocean characteristics of waves generated by the Samoan and Chilean tsunamis and predict the surfaces currents excited as they approached Oahu. An complex-demodulation based on the tsunami's dominant period is conducted to amplify any evidence for the tsunamis in the record because the predicted currents were below the detection threshold of the HFR.