The HOME Farfield Experiment

Ocean acoustic tomography and TOPEX/POSEIDON (T/P) altimetry have brought a new dimension to the subject of the tides. We are presently working toward an energy budget for the barotropic and low-mode baroclinic tides in the farfield of the Hawaiian Ridge. The basic energy equation is:

(Energy Lost from the Barotropic Tide) =
      (Baroclinic Tide Radiative Energy) + (Local Dissipation)

The goals of the HOME Farfield Experiment are to better quantify the first two terms of this equation. The data are vital in establishing the barotropic to baroclinic mode conversion which is believed to play an important role in maintaining pelagic turbulence and, more important, the abyssal stratification. The tidal energy budget will determine limits on the energy dissipated in the nearfield of the Hawaiian Ridge. The results of these process-oriented studies at Hawaii will be used to better model tidal dissipation and internal-tide radiation in the global ocean.

The two acoustic tomography arrays shown here obtained data for 150-200 days between 2001 and 2002. The acoustic data determine the current along the acoustic paths for measuring tidal currents and the sound speed fluctuations caused by internal-tide displacements of isotherms. Thermistors were mounted at various depths on the tomography moorings. The purple stars indicate the locations of pressure and electrometer instruments. Pressure is a measure of tidal elevation, of course, while the electrometers may provide an alternate measurement of tidal current.

The HOME Farfield Experiment is supported by the National Science Foundation. The original proposal to NSF for the HOME Farfield Experiment can be downloaded from HERE. (700 KB)

Field work was conducted between 2001 and 2002 to measure tidal pressure and currents with sufficient precision to better quantify the tidal power dissipated in the nearfield of the Ridge. Data to determine the radiation of internal tides into the farfield of Hawaii was also obtained using acoustic transmissions for tomography, hydrography, and thermistors. The analysis of these data are presently underway.

For one month during the deployment of the southern array, the R/V FLIP (Floating Instrument Platform) was moored near the tomography mooring closest to the Hawaiian Ridge. The data collected during this expedition consisted of rapid hydrographic casts to 800 m to measure the internal wave field. These measurements give a better picture of the internal-tide "soup" that is emanating from the Hawaiian Ridge, e.g., the high-vertical-mode variability and incoherent components of tidal radiation.

Click on an appropriate link to left for more information about the analysis for barotropic and baroclinic tides.