THE NEAR-SURFACE LAYER OF THE OCEAN
temperature change as the profiles discussed above, may be interpreted as
the result of intersection of a region where cold water was moving along the
frontal interface toward the ocean surface. This corresponds to profiler
trajectory B in Figure 5-48
The profiles obtained at 01:06 GMT have no substantial changes either
in temperature or in vertical component of velocity. These profiles might be
located in the space between the large-scale eddies (trajectory C in Figure
5-48. The other four pairs of profiles shown in Figure 5-47 are supposedly
related to the cases when the profiler passes through less pronounced regions
of the vortex structure.
The vertical profiles shown in Figure 5-47 are thus consistent with the
presence of ramp-like coherent structures in the near-surface layer of the
ocean. This is, however, fragmentary information; alternate interpretations
are not excluded.
Before moving on to theoretical aspects of the problem of ramp-like
coherent structures we would like to point the reader to one unresolved
question relating to the problem of organized motions in the upper ocean.
The field study performed by Thorpe et al. (2003) using an autonomous
underwater vehicle suggests that both types of coherent structures do
coexist. How can ramp-like structures coexist with Langmuir circulations?
Vortices associated with ramp-like structures have transverse axes, while
Langmuir circulations have a longitudinal axis, relative to the wind.
Moreover both phenomena have similar space and time scales. Each of these
motions in isolation is two-dimensional. However, two uncorrelated twodimensional motions with mutually perpendicular axes represent a threedimensional motion, which, according to principles of self-organization
should have a tendency to randomization rather than organization. At first
glance, the ramp-like structure and Langmuir circulations should not coexist
at all. This appears possible only if they are synchronized in some way in
space and time.
Microstructure measurements in the near-surface layer of the ocean are
still very rare. Further studies will have to address the question posed above,
as well as some other important questions relating to the problem of coherent
structures in the upper ocean. Though previous studies in the atmospheric
boundary layer can provide guidance to ocean boundary layer studies, the
analogy between the atmospheric and oceanic boundary layers, however, is
not exact. The oceanic turbulent boundary layer differs from its atmospheric
analog due to the presence of a free surface. The importance of free-surface
effects (including breaking waves) increases towards the surface. Processes
in the near-surface layer are therefore crucial to understanding the coherent
structures in the upper ocean turbulent boundary layer and must be sampled
adequately.
364
temperature change as the profiles discussed above, may be interpreted as
the result of intersection of a region where cold water was moving along the
frontal interface toward the ocean surface. This corresponds to profiler
trajectory B in Figure 5-48
The profiles obtained at 01:06 GMT have no substantial changes either
in temperature or in vertical component of velocity. These profiles might be
located in the space between the large-scale eddies (trajectory C in Figure
5-48. The other four pairs of profiles shown in Figure 5-47 are supposedly
related to the cases when the profiler passes through less pronounced regions
of the vortex structure.
The vertical profiles shown in Figure 5-47 are thus consistent with the
presence of ramp-like coherent structures in the near-surface layer of the
ocean. This is, however, fragmentary information; alternate interpretations
are not excluded.
Before moving on to theoretical aspects of the problem of ramp-like
coherent structures we would like to point the reader to one unresolved
question relating to the problem of organized motions in the upper ocean.
The field study performed by Thorpe et al. (2003) using an autonomous
underwater vehicle suggests that both types of coherent structures do
coexist. How can ramp-like structures coexist with Langmuir circulations?
Vortices associated with ramp-like structures have transverse axes, while
Langmuir circulations have a longitudinal axis, relative to the wind.
Moreover both phenomena have similar space and time scales. Each of these
motions in isolation is two-dimensional. However, two uncorrelated twodimensional motions with mutually perpendicular axes represent a threedimensional motion, which, according to principles of self-organization
should have a tendency to randomization rather than organization. At first
glance, the ramp-like structure and Langmuir circulations should not coexist
at all. This appears possible only if they are synchronized in some way in
space and time.
Microstructure measurements in the near-surface layer of the ocean are
still very rare. Further studies will have to address the question posed above,
as well as some other important questions relating to the problem of coherent
structures in the upper ocean. Though previous studies in the atmospheric
boundary layer can provide guidance to ocean boundary layer studies, the
analogy between the atmospheric and oceanic boundary layers, however, is
not exact. The oceanic turbulent boundary layer differs from its atmospheric
analog due to the presence of a free surface. The importance of free-surface
effects (including breaking waves) increases towards the surface. Processes
in the near-surface layer are therefore crucial to understanding the coherent
structures in the upper ocean turbulent boundary layer and must be sampled
adequately.
364