Energy Levels, Phase, and Amplitude Modulation of the Baroclinic Tide off Hawaii

Abstract

Inverted echo sounder data from Station Aloha north of Oahu, Hawaii, are used to determine the absolute energy levels and time-varying nature of the first-mode baroclinic tide north of Hawaii. The semidiurnal tide amplitude and phase are modulated with 60?120 day periodicity, which indicates interaction between the baroclinic tide and intra-annual mesoscale variability seen off Hawaii. Close to the presumed generation site, there is less phase modulation, and amplitude modulation is uncorrelated with the far-field variability. These results are consistent with a model of phase-locked generation, together with phase and amplitude distortion during propagation. The sense of the amplitude modulation is opposite to that previously observed at decadal timescales. Semidiurnal energy flux at Station Aloha ranges from 2.2 to 8.0 kW m?1, with a mean value of 4.4 kW m?1.