PREFACE
xiii
based on some analogy between the atmospheric and oceanic turbulent
boundary layers. This analogy has been employed in the studies of Steve
Thorpe and Michael Gregg. It may only be observed starting from the depth
where wave-breaking turbulence is not important. A discussion of the
surface mixed layer versus the Ekman layer concept will illustrate the depth
to which momentum supplied by the wind penetrates relative to where the
base of the mixed layer is found.
Chapter 4 is devoted to the fine thermohaline structure of the nearsurface layer. We consider the penetrative solar radiation and the impacts of
the distribution of radiant heating on the mixed layer dynamics. Stable
stratification in the near-surface ocean due to diurnal warming or rainfall can
reduce the turbulence friction, which results in intensification of near-surface
currents. Unstable stratification leads to convective overturning, which
increases turbulent friction locally. In addition, discrete convective
elements—analogs of thermals in the atmosphere—penetrate into the stably
stratified layer below and produce non-local transport. Experimental studies
at the equator have produced striking examples of local and non-local effects
on the dynamics of the diurnal mixed layer and thermocline. The last section
of this chapter demonstrates how the local (diffusive) and non-local
(convective) transport can be parameterized and incorporated into one- or
three-dimensional models. This chapter contains a few effective examples of
spatial near-surface structures. These examples should motivate the reader to
study in detail the relatively lengthy Chapter 5.
Chapter 5 is devoted to the coherent structures within the near-surface
layer of the ocean. Spatially-coherent organized motions have been
recognized as an important part of turbulent boundary layer processes. In the
presence of surface gravity waves, the Ekman boundary layer becomes
unstable to helical motions (Langmuir cells). “Wind-rows” can often be seen
from space due to spray patches and have already been used in advanced
remote sensing algorithms to determine the direction of near-surface winds.
Ramp-like structures are a common feature of boundary layer flows; they
are, however, oriented perpendicular to the wind direction, while Langmuir
cells are roughly aligned with wind. The Langmuir cells and ramp-like
types of quasi-periodical structures in the near-surface ocean, such as
freshwater lenses produced by rainfalls and near-inertial oscillations induced
by moving storms may have distinct signatures in the sea surface
temperature field. Sharp frontal interfaces are an intriguing example of selforganization. These interfaces are supposedly related to the subduction
process and are of different nature in mid- and low-latitudes. Internal waves,
resonant interactions between surface and internal modes, and billows in the
diurnal thermocline also produce signatures on the ocean surface under
certain conditions.
structures entrain bubbles and can be traced with side-scan sonars. Other
xiii
based on some analogy between the atmospheric and oceanic turbulent
boundary layers. This analogy has been employed in the studies of Steve
Thorpe and Michael Gregg. It may only be observed starting from the depth
where wave-breaking turbulence is not important. A discussion of the
surface mixed layer versus the Ekman layer concept will illustrate the depth
to which momentum supplied by the wind penetrates relative to where the
base of the mixed layer is found.
Chapter 4 is devoted to the fine thermohaline structure of the nearsurface layer. We consider the penetrative solar radiation and the impacts of
the distribution of radiant heating on the mixed layer dynamics. Stable
stratification in the near-surface ocean due to diurnal warming or rainfall can
reduce the turbulence friction, which results in intensification of near-surface
currents. Unstable stratification leads to convective overturning, which
increases turbulent friction locally. In addition, discrete convective
elements—analogs of thermals in the atmosphere—penetrate into the stably
stratified layer below and produce non-local transport. Experimental studies
at the equator have produced striking examples of local and non-local effects
on the dynamics of the diurnal mixed layer and thermocline. The last section
of this chapter demonstrates how the local (diffusive) and non-local
(convective) transport can be parameterized and incorporated into one- or
three-dimensional models. This chapter contains a few effective examples of
spatial near-surface structures. These examples should motivate the reader to
study in detail the relatively lengthy Chapter 5.
Chapter 5 is devoted to the coherent structures within the near-surface
layer of the ocean. Spatially-coherent organized motions have been
recognized as an important part of turbulent boundary layer processes. In the
presence of surface gravity waves, the Ekman boundary layer becomes
unstable to helical motions (Langmuir cells). “Wind-rows” can often be seen
from space due to spray patches and have already been used in advanced
remote sensing algorithms to determine the direction of near-surface winds.
Ramp-like structures are a common feature of boundary layer flows; they
are, however, oriented perpendicular to the wind direction, while Langmuir
cells are roughly aligned with wind. The Langmuir cells and ramp-like
types of quasi-periodical structures in the near-surface ocean, such as
freshwater lenses produced by rainfalls and near-inertial oscillations induced
by moving storms may have distinct signatures in the sea surface
temperature field. Sharp frontal interfaces are an intriguing example of selforganization. These interfaces are supposedly related to the subduction
process and are of different nature in mid- and low-latitudes. Internal waves,
resonant interactions between surface and internal modes, and billows in the
diurnal thermocline also produce signatures on the ocean surface under
certain conditions.
structures entrain bubbles and can be traced with side-scan sonars. Other