Japan Geoscience Union Meeting 2016

Presentation information

International Session (Oral)

Symbol A (Atmospheric and Hydrospheric Sciences) » A-OS Ocean Sciences & Ocean Environment

[A-OS04] Ocean Mixing Frontiers

Sun. May 22, 2016 1:45 PM - 3:15 PM 102 (1F)

Convener:*Toshiyuki Hibiya(Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo), Louis St Laurent(Woods Hole Oceanographic Institution), Ren-Chieh Lien(Applied Physics Laboratory, University of Washington), Chair:RenChieh Lien(University of Washington, Seattle)

3:00 PM - 3:15 PM

[AOS04-06] Numerical Study of the Impacts of Ocean Bottom Roughness and Tidal Flow Amplitude on Abyssal Mixing

*Toshiyuki Hibiya1, Takashi Ijichi1, Robin Robertson2 (1.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo, Japan, 2.School of Physical, Environmental and Mathematical Sciences, The University of New South Wales, Canberra, Australia)

Keywords:Abyssal Mixing , Parameterization, Global Overturning Circulation, Ocean Bottom Roughness, Tidal Flow

Although an accurate representation of ocean mixing processes in global circulation models is essential for accurate climate predictions, parameterization of mixing over rough bathymetry remains uncertain. We perform here a series of eikonal calculations for a wide range of physical parameters to investigate the transfer of energy from upward propagating internal waves generated by tide-topography interactions to dissipation through nonlinear interaction with background three-dimensional Garrett-Munk-like internal waves.

Following the previous study (Mohri et al., 2010) and using a fixed N value, we assume that internal waves generated by tide-topography interactions can be classified into linear internal tides when kU0/ω<1 and quasi-steady lee waves when kU0/ω>1, where U0 is the tidal flow amplitude, k the benthic bathymetric wavenumber, N the buoyancy frequency and ω the semidiurnal tidal frequency. Of special note is that the vertical group velocity Cgz is inversely proportional to k for linear internal tides and proportional to kU02 for quasi-steady lee waves, although the resonant interaction time is roughly inversely proportional to k for both cases. As a result, the resulting mixing hotspot becomes more restricted to the ocean bottom as bottom roughness increases for kU0/ω<1, independent of the tidal flow amplitude, but it extends upward as the tidal flow amplitude increases for kU0/ω>1, independent of the bottom roughness. In both cases, we can find a trade-off relationship between the energy dissipation rate at the ocean bottom and its vertical extent.

The accuracy of global circulation models will be improved by reflecting these results in the parameterization of mixing over rough bathymetry.