variety of [tidally] non-critical slopes for sub-inertial motions (e.g., [23, 33]).
Near-inertial shear, the largest internal wave shear outside internal tidal generation
areas, is important for (high-frequency) internal wave breaking away from the
bottom, in case shear-induced mixing is the dominant turbulence generation process. Thus, most internal wave—turbulence transitions seem associated with nonlinear deformation of internal wave motions near local buoyancy frequencies.
The ocean interior is a much smoother linear-wave-like environment, but it too is
in permanent motion rather than quiescent. This ocean in permanent motion is
driven by surprisingly weak kinetic energy forcing of about 20% of the total energy
presently used by mankind, about 500 times less than the heat flux transported in
the ocean [3] and 25,000 times less than the solar energy received by the ocean.
Man can maximally retrieve about 3% van the kinetic tidal energy or maximum
0.6% of his present-day demand with the notion that the present-day technology is
not economically viable. In the hypothetical case that man were able to efficiently
extract more tidal energy he would destroy the ocean stratification and with it ocean
life, not only in the deep ocean but especially also in tidal inlets of nursery areas
where currents are largest.
Of all the power of 100-m breaking waves above deep-ocean topography, while
highly important for redistribution of sediment and for life e.g. by replenishing
nutrients to cold-water coral mounds (e.g., [71]), which are found at depths where
mineralization is relatively large as inferred from the seasonal oxygen minimum
layer coinciding with nutrient maxima (e.g., [72]), very little is sensed at the surface. Therefore, in order to learn more about internal wave-turbulence processes it
is mandatory to continue studying their characteristics in the deep sea and ocean,
above sloping topography but especially also their extend into the interiors. Future
instrumentation development should be directed to a truly four-dimensional, 3-D
spatial plus temporal, resolution of the internal wave-turbulence motions to
understand their intrinsic properties. Typical turn-over scales generated by KHI and
frontal bores are between 1 and 100 m, whereas typical internal wave lengths are
100–1000 m. A small array with T-sensors a few meters apart would be useful to
study internal wave—turbulence resolving the short spatial scales. A larger cubic
hectometer array with T-sensors O(10 m) apart would be useful to study the statistical properties and internal wave propagation and will yield new insight in
internal wave development. After all, deep-ocean sloping topography generates
great surf!
Acknowledgements I greatly thank M. Laan, L. Gostiaux, A. Cimatoribus and F. Cyr for their
discussions, collaboration in design and construction of NIOZ temperature sensors. NIOZ temperature sensors has been financed in part by NWO, the Netherlands Organization for Scientific
Research.
142
H. van Haren
Near-inertial shear, the largest internal wave shear outside internal tidal generation
areas, is important for (high-frequency) internal wave breaking away from the
bottom, in case shear-induced mixing is the dominant turbulence generation process. Thus, most internal wave—turbulence transitions seem associated with nonlinear deformation of internal wave motions near local buoyancy frequencies.
The ocean interior is a much smoother linear-wave-like environment, but it too is
in permanent motion rather than quiescent. This ocean in permanent motion is
driven by surprisingly weak kinetic energy forcing of about 20% of the total energy
presently used by mankind, about 500 times less than the heat flux transported in
the ocean [3] and 25,000 times less than the solar energy received by the ocean.
Man can maximally retrieve about 3% van the kinetic tidal energy or maximum
0.6% of his present-day demand with the notion that the present-day technology is
not economically viable. In the hypothetical case that man were able to efficiently
extract more tidal energy he would destroy the ocean stratification and with it ocean
life, not only in the deep ocean but especially also in tidal inlets of nursery areas
where currents are largest.
Of all the power of 100-m breaking waves above deep-ocean topography, while
highly important for redistribution of sediment and for life e.g. by replenishing
nutrients to cold-water coral mounds (e.g., [71]), which are found at depths where
mineralization is relatively large as inferred from the seasonal oxygen minimum
layer coinciding with nutrient maxima (e.g., [72]), very little is sensed at the surface. Therefore, in order to learn more about internal wave-turbulence processes it
is mandatory to continue studying their characteristics in the deep sea and ocean,
above sloping topography but especially also their extend into the interiors. Future
instrumentation development should be directed to a truly four-dimensional, 3-D
spatial plus temporal, resolution of the internal wave-turbulence motions to
understand their intrinsic properties. Typical turn-over scales generated by KHI and
frontal bores are between 1 and 100 m, whereas typical internal wave lengths are
100–1000 m. A small array with T-sensors a few meters apart would be useful to
study internal wave—turbulence resolving the short spatial scales. A larger cubic
hectometer array with T-sensors O(10 m) apart would be useful to study the statistical properties and internal wave propagation and will yield new insight in
internal wave development. After all, deep-ocean sloping topography generates
great surf!
Acknowledgements I greatly thank M. Laan, L. Gostiaux, A. Cimatoribus and F. Cyr for their
discussions, collaboration in design and construction of NIOZ temperature sensors. NIOZ temperature sensors has been financed in part by NWO, the Netherlands Organization for Scientific
Research.
142
H. van Haren