Chapter 5. SPATIALLY-COHERENT STRUCTURES
remarkable influences over the vertical distribution and transport of
momentum and TKE. Wind-wave boundary conditions, resulting from a
balance between diffusion and dissipation of TKE are capable of
reproducing the realistic scales of phenomena in this model. It is remarkable
that vertical profiles of the turbulent kinetic energy in the presence of
Langmuir circulations demonstrate a reduction of TKE rather than its
increase as in LES. This appears to be consistent with the data from
laboratory experiment (Figure 5-57). The explanation is that the organized
motion increases the vertical transport of properties, while reducing
dissipation in the system. This is consistent with the concept of selforganization introduced in the beginning of this chapter.
5.8 Convection
Free convection is fluid motion due to unbalanced buoyancy forces.
Free convection, also referred to as simply convection, is driven by the static
instability that results when relatively dense fluid lies above relatively light
fluid. In the ocean, greater density is associated with colder and/or saltier
water, and it is possible to have thermal convection due to the vertical
temperature gradient, haline convection due to the vertical salinity gradient,
or thermohaline convection due to the combination.
Since convection has a preferred direction (determined by the gravity
force), it is a two-dimensional hydrodynamic process, which, therefore, has
tendency to self-organization. Soloviev and Klinger (2001) provided a
comprehensive review of convection in the upper layer of the ocean. Here
we focus on the coherent properties of convection.
Since seawater is about 1000 times denser than air, the air-sea interface
from the waterside can be considered a free surface. So-called thermocapillary convection can develop near this surface due to the dependence of
the surface tension coefficient on temperature. There are experimental
indications that in the upper ocean layer more than 2 cm deep, buoyant
convection dominates. Surfactants, however, may substantially affect the
surface renewal process (see Section 2.2). Here, we consider convection
without these capillary effects.
Convection is one of the key processes driving mixed layer turbulence,
though mechanical stirring driven by wind-stress and other processes is also
important. Therefore understanding convection is crucial to understanding
the mixed layer as well as property fluxes between the ocean and the
atmosphere.
Thermal convection is associated with the cooling of the ocean surface
due to sensible (Q T ), latent (Q E ), and net long-wave radiation (Q L ) heat
fluxes. Q T may have either sign; its magnitude is, however, much less than
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remarkable influences over the vertical distribution and transport of
momentum and TKE. Wind-wave boundary conditions, resulting from a
balance between diffusion and dissipation of TKE are capable of
reproducing the realistic scales of phenomena in this model. It is remarkable
that vertical profiles of the turbulent kinetic energy in the presence of
Langmuir circulations demonstrate a reduction of TKE rather than its
increase as in LES. This appears to be consistent with the data from
laboratory experiment (Figure 5-57). The explanation is that the organized
motion increases the vertical transport of properties, while reducing
dissipation in the system. This is consistent with the concept of selforganization introduced in the beginning of this chapter.
5.8 Convection
Free convection is fluid motion due to unbalanced buoyancy forces.
Free convection, also referred to as simply convection, is driven by the static
instability that results when relatively dense fluid lies above relatively light
fluid. In the ocean, greater density is associated with colder and/or saltier
water, and it is possible to have thermal convection due to the vertical
temperature gradient, haline convection due to the vertical salinity gradient,
or thermohaline convection due to the combination.
Since convection has a preferred direction (determined by the gravity
force), it is a two-dimensional hydrodynamic process, which, therefore, has
tendency to self-organization. Soloviev and Klinger (2001) provided a
comprehensive review of convection in the upper layer of the ocean. Here
we focus on the coherent properties of convection.
Since seawater is about 1000 times denser than air, the air-sea interface
from the waterside can be considered a free surface. So-called thermocapillary convection can develop near this surface due to the dependence of
the surface tension coefficient on temperature. There are experimental
indications that in the upper ocean layer more than 2 cm deep, buoyant
convection dominates. Surfactants, however, may substantially affect the
surface renewal process (see Section 2.2). Here, we consider convection
without these capillary effects.
Convection is one of the key processes driving mixed layer turbulence,
though mechanical stirring driven by wind-stress and other processes is also
important. Therefore understanding convection is crucial to understanding
the mixed layer as well as property fluxes between the ocean and the
atmosphere.
Thermal convection is associated with the cooling of the ocean surface
due to sensible (Q T ), latent (Q E ), and net long-wave radiation (Q L ) heat
fluxes. Q T may have either sign; its magnitude is, however, much less than
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