THE NEAR-SURFACE LAYER OF THE OCEAN
synchronization,
3
1
2
k
k
k
Z
Z
Z
at 3 1 2
k k k
are never fulfilled.
At the same time for three-dimensional waves, the synchronism conditions
can be satisfied for certain oblique perturbations (Voronovich et al., 1998b).
Plane (three-dimensional) solitary waves in infinitely deep water appear to
be unstable with respect to transverse perturbations (Pelinovsky and Shrira,
1995).
The properties of the intermediate asymptotic solution of equation
(5.54) are consistent with the qualitative scheme of Townsend (1961)
discussed in the previous section (Section 5.6.5). Perturbations that develop
across the spine of a low-speed streak (Figure 5-50) are apparently long
enough to satisfy the left side of inequality (5.55). The fact that the threedimensional solution of (5.53) is unstable with respect to transverse
perturbations is also qualitatively consistent with the McNaughton and
Brunet (2002) phenomenology stating (see Figure 5-50) that the flow
instability is initiated by transverse roll vortices
The active motions are dissipative; the viscosity effects can therefore no
longer be ignored. This imposes an upper bound on the horizontal length
scale, which is determined by the right side of inequality (5.55).
The interpretation of the ramp-like coherent structures as non-linear
wave-like perturbations in shear flow due to the inhomogeneous mean
vorticity field is consistent with observational data. The theory of vorticity
waves can therefore serve as the basis for the interpretation of the ramp-like
coherent structures. This theory, however, describes evolution of weakly
nonlinear waves only and cannot handle the dynamics of the horseshoe
vortex.
5.7 Langmuir Circulations
5.7.1 Phenomenology
Long before oceanography developed as a distinct branch of science,
sailors and seafarers noted long narrow “bands,” “streaks,” or “lanes” on the
sea surface, which were often nearly aligned with wind. This phenomenon
appears in the notes of Charles Darwin from his voyages on the Beagle
(Leibovich, 1983). In 1938, Langmuir came to the conclusion that the
streaks or “windrows” are the visible manifestations of a parallel series of
counter-rotating vortices in the surface layers of the water with axes nearly
parallel to the wind. At present, while the existence and many features of
Langmuir circulations are generally accepted, their role in the mixed layer
dynamics is still ambiguous.
Different floating substances ranging from seaweed and marine
organisms to organic films and foam from breaking waves tend to
370
synchronization,
3
1
2
k
k
k
Z
Z
Z
at 3 1 2
k k k
are never fulfilled.
At the same time for three-dimensional waves, the synchronism conditions
can be satisfied for certain oblique perturbations (Voronovich et al., 1998b).
Plane (three-dimensional) solitary waves in infinitely deep water appear to
be unstable with respect to transverse perturbations (Pelinovsky and Shrira,
1995).
The properties of the intermediate asymptotic solution of equation
(5.54) are consistent with the qualitative scheme of Townsend (1961)
discussed in the previous section (Section 5.6.5). Perturbations that develop
across the spine of a low-speed streak (Figure 5-50) are apparently long
enough to satisfy the left side of inequality (5.55). The fact that the threedimensional solution of (5.53) is unstable with respect to transverse
perturbations is also qualitatively consistent with the McNaughton and
Brunet (2002) phenomenology stating (see Figure 5-50) that the flow
instability is initiated by transverse roll vortices
The active motions are dissipative; the viscosity effects can therefore no
longer be ignored. This imposes an upper bound on the horizontal length
scale, which is determined by the right side of inequality (5.55).
The interpretation of the ramp-like coherent structures as non-linear
wave-like perturbations in shear flow due to the inhomogeneous mean
vorticity field is consistent with observational data. The theory of vorticity
waves can therefore serve as the basis for the interpretation of the ramp-like
coherent structures. This theory, however, describes evolution of weakly
nonlinear waves only and cannot handle the dynamics of the horseshoe
vortex.
5.7 Langmuir Circulations
5.7.1 Phenomenology
Long before oceanography developed as a distinct branch of science,
sailors and seafarers noted long narrow “bands,” “streaks,” or “lanes” on the
sea surface, which were often nearly aligned with wind. This phenomenon
appears in the notes of Charles Darwin from his voyages on the Beagle
(Leibovich, 1983). In 1938, Langmuir came to the conclusion that the
streaks or “windrows” are the visible manifestations of a parallel series of
counter-rotating vortices in the surface layers of the water with axes nearly
parallel to the wind. At present, while the existence and many features of
Langmuir circulations are generally accepted, their role in the mixed layer
dynamics is still ambiguous.
Different floating substances ranging from seaweed and marine
organisms to organic films and foam from breaking waves tend to
370