THE NEAR-SURFACE LAYER OF THE OCEAN
creating sublayers where the energy takes different forms. Accordingly,
Benilov and Ly (2002) suggested that the upper ocean turbulent boundary
layer where stratification and rotation effects are negligible could be
conveniently divided into three sublayers. These are
1)
The wave-stirred layer: The turbulent kinetic energy (TKE)
production by wave breaking significantly exceeds the mean
shear effect, and the turbulent diffusion of the wave kinetic
energy dominates in the range of depths where the wave motion
continues to be vigorous;
2)
The turbulent diffusion layer: Here the turbulent diffusion of
TKE exceeds the wave (as well as the mean shear) effect in the
TKE budget; and
3)
The wall layer: The mean shear production of turbulent energy
dominates. In terms of the classic horizontally homogeneous
and steady turbulent boundary layer problem, this layer, in
steady or quasi-steady cases, obeys wall-layer laws. As
discussed in Section 3.1.2, a classic wall layer consists of an
inner and outer part. In the inner part, a logarithmic velocity
profile can develop; stratification and rotation effects are
important in the outer part.
Figure 3-1 illustrates the concept described above. In order to complete
the Benilov and Ly (2002) dynamical scheme we have included an
additional characteristic feature of the upper ocean turbulent boundary layer:
4)
The aqueous viscous sublayer. Viscous sublayers develop at
both the water- and air-side of the air-sea interface due to the
suppression of the normal component of turbulent velocity
fluctuations near the density interface. This sublayer is
controlled by the tangential wind stress t
W and is an important
component of the sea surface microlayer (Section 2.2). Under
low wind speed conditions, the aqueous viscous sublayer is also
controlled by the buoyancy flux. Under high wind speed
conditions, t
W represents only a small fraction of the total
momentum flux, 0
W , from the atmosphere to the ocean.
Breakers disrupt the viscous sublayer; however it recovers
rapidly and is believed to exist between the wave breaking
events even in high seas. The viscous sublayer is found within
the upper few millimeters of the ocean; its thickness is
proportional to the Kolmogorov internal scale of turbulence,
Q
K , defined in (2.1). Note that the viscous sublayer should be
considered in the wave following coordinate system (3.1)-(3.2),
because the sublayer thickness is much less than the wave
height.
150
creating sublayers where the energy takes different forms. Accordingly,
Benilov and Ly (2002) suggested that the upper ocean turbulent boundary
layer where stratification and rotation effects are negligible could be
conveniently divided into three sublayers. These are
1)
The wave-stirred layer: The turbulent kinetic energy (TKE)
production by wave breaking significantly exceeds the mean
shear effect, and the turbulent diffusion of the wave kinetic
energy dominates in the range of depths where the wave motion
continues to be vigorous;
2)
The turbulent diffusion layer: Here the turbulent diffusion of
TKE exceeds the wave (as well as the mean shear) effect in the
TKE budget; and
3)
The wall layer: The mean shear production of turbulent energy
dominates. In terms of the classic horizontally homogeneous
and steady turbulent boundary layer problem, this layer, in
steady or quasi-steady cases, obeys wall-layer laws. As
discussed in Section 3.1.2, a classic wall layer consists of an
inner and outer part. In the inner part, a logarithmic velocity
profile can develop; stratification and rotation effects are
important in the outer part.
Figure 3-1 illustrates the concept described above. In order to complete
the Benilov and Ly (2002) dynamical scheme we have included an
additional characteristic feature of the upper ocean turbulent boundary layer:
4)
The aqueous viscous sublayer. Viscous sublayers develop at
both the water- and air-side of the air-sea interface due to the
suppression of the normal component of turbulent velocity
fluctuations near the density interface. This sublayer is
controlled by the tangential wind stress t
W and is an important
component of the sea surface microlayer (Section 2.2). Under
low wind speed conditions, the aqueous viscous sublayer is also
controlled by the buoyancy flux. Under high wind speed
conditions, t
W represents only a small fraction of the total
momentum flux, 0
W , from the atmosphere to the ocean.
Breakers disrupt the viscous sublayer; however it recovers
rapidly and is believed to exist between the wave breaking
events even in high seas. The viscous sublayer is found within
the upper few millimeters of the ocean; its thickness is
proportional to the Kolmogorov internal scale of turbulence,
Q
K , defined in (2.1). Note that the viscous sublayer should be
considered in the wave following coordinate system (3.1)-(3.2),
because the sublayer thickness is much less than the wave
height.
150