High-Resolution Observations of Internal
Wave Turbulence in the Deep Ocean
Hans van Haren
Introduction
The dynamics of the ocean resembles that of the atmosphere in many respects. Both
are basically driven by the heating of the sun and adjusted by the rotation of the
Earth [1]. One crucial difference is that the atmosphere is cooled at a higher
geopotential level than where it is heated, while the ocean is heated at its top. As
warm air/water is generally less dense than cold air/water, the heating generates
natural vertical turbulent convective motions in the atmosphere, as an effective heat
engine [2], while the ocean is merely a heat transporter as its heat engine is very
ineffective [3]. Thus, a large amount of potential energy is stored in the ocean, but it
requires a mechanical energy source to transport the heat downward against the
stable stratification. Although the stable stratification in the ocean interior is 1000
times less than the density difference between air and water across the ocean
surface, vertical diapycnal exchange is considered weak. The weak exchange may
seriously affect life in the ocean and the replenishment of nutrients to the photic
zone, for example.
However, the turbulent exchange is not blocked but hampered. This is because
the density stratification may support destabilizing shear to the point of marginal
stability (e.g., [4]) and mechanical energy in the form of waves, just like at the
ocean surface. With the 1000 times weaker stratification in the interior, ‘internal
waves’ may grow to attain 100 m large amplitudes that go barely unnoticed at the
surface. Although linear, sinusoidal waves transport momentum but not matter,
nonlinear waves can break and generate irreversible turbulent diapycnal mixing. It
is the paradox of Munk and Wunsch [3] that demonstrates the importance of the
relatively small amount of kinetic energy put into internal waves that is crucial to
H. van Haren ( ✉ )
Royal Netherlands Institute for Sea Research (NIOZ), Utrecht University,
Den Burg, The Netherlands
e-mail: hans.van.haren@nioz.nl
© Springer International Publishing AG, part of Springer Nature 2018
M. G. Velarde et al. (eds.), The Ocean in Motion, Springer Oceanography,
https://doi.org/10.1007/978-3-319-71934-4_11
127
Wave Turbulence in the Deep Ocean
Hans van Haren
Introduction
The dynamics of the ocean resembles that of the atmosphere in many respects. Both
are basically driven by the heating of the sun and adjusted by the rotation of the
Earth [1]. One crucial difference is that the atmosphere is cooled at a higher
geopotential level than where it is heated, while the ocean is heated at its top. As
warm air/water is generally less dense than cold air/water, the heating generates
natural vertical turbulent convective motions in the atmosphere, as an effective heat
engine [2], while the ocean is merely a heat transporter as its heat engine is very
ineffective [3]. Thus, a large amount of potential energy is stored in the ocean, but it
requires a mechanical energy source to transport the heat downward against the
stable stratification. Although the stable stratification in the ocean interior is 1000
times less than the density difference between air and water across the ocean
surface, vertical diapycnal exchange is considered weak. The weak exchange may
seriously affect life in the ocean and the replenishment of nutrients to the photic
zone, for example.
However, the turbulent exchange is not blocked but hampered. This is because
the density stratification may support destabilizing shear to the point of marginal
stability (e.g., [4]) and mechanical energy in the form of waves, just like at the
ocean surface. With the 1000 times weaker stratification in the interior, ‘internal
waves’ may grow to attain 100 m large amplitudes that go barely unnoticed at the
surface. Although linear, sinusoidal waves transport momentum but not matter,
nonlinear waves can break and generate irreversible turbulent diapycnal mixing. It
is the paradox of Munk and Wunsch [3] that demonstrates the importance of the
relatively small amount of kinetic energy put into internal waves that is crucial to
H. van Haren ( ✉ )
Royal Netherlands Institute for Sea Research (NIOZ), Utrecht University,
Den Burg, The Netherlands
e-mail: hans.van.haren@nioz.nl
© Springer International Publishing AG, part of Springer Nature 2018
M. G. Velarde et al. (eds.), The Ocean in Motion, Springer Oceanography,
https://doi.org/10.1007/978-3-319-71934-4_11
127