THE NEAR-SURFACE LAYER OF THE OCEAN
microscale wave breaking. Note the bore-like structure at the crest
accompanied by parasitic capillary waves distributed along the forward face.
Microscale wave breaking is far more widespread than whitecapping.
Absence of air entrainment makes the microscale breaking difficult to
identify visually. The microscale wave breaking, however, produces the
convergence of flow that leads to intense renewal of surface water. The
process of surface renewal substantially determines properties of the aqueous
molecular sublayers under moderate wind speed conditions (Csanady, 1990).
The widespread occurrence of microscale wave breaking suggests that its
cumulative effect on the fluxes of heat and gas across the air-sea interface is
significant (Csanady, 1990; Banner and Peregrine, 1993; Soloviev and
, 1994; Donelan, 1995; Melville, 1996).
2.2.3 Wave breaking and whitecapping
The aqueous molecular sublayers at the air-sea interface are associated
with the action of the tangential wind stress on the sea surface. The
tangential component represents only a part of the total wind stress that is
transferred from the atmosphere to the ocean. Under high wind speeds, a
significant portion of the momentum is transferred to surface waves. Surface
waves periodically break destroying the aqueous viscous sublayer as well as
the thermal and diffusion sublayers. The molecular sublayers regenerate
between wave breaking events.
The ratio of the tangential wind stress W t controlling the aqueous viscous
sublayer to the total air-sea momentum flux 0
W is as follows (Soloviev and
1996):
1
0 1
/
t
c r
Ke Ke
W W
,
(2.8)
where
3 /
Ke u gQ
.
(2.9)
is the Keulegan number, which is a fundamental parameter in the dynamics
of free interfaces (Csanady, 1990). At low Keulegan numbers,
cr
Ke
Ke
interfacial instabilities are suppressed by molecular viscosity.
Formula (2.8) reflects the transformation of a substantial part of the
surface wind stress to form drag and whitecapping at high wind speeds
(valid for stationary conditions only). Figure 2-9 illustrates this dependence
for
cr
Ke = 0.18 in comparison with the data from the Banner and Peirson
(1998) laboratory experiment. The theoretical curve is in reasonably good
agreement with the experimental data taking into account that the estimate,
82
Schl ssel
ü
Schl ssel
ü
microscale wave breaking. Note the bore-like structure at the crest
accompanied by parasitic capillary waves distributed along the forward face.
Microscale wave breaking is far more widespread than whitecapping.
Absence of air entrainment makes the microscale breaking difficult to
identify visually. The microscale wave breaking, however, produces the
convergence of flow that leads to intense renewal of surface water. The
process of surface renewal substantially determines properties of the aqueous
molecular sublayers under moderate wind speed conditions (Csanady, 1990).
The widespread occurrence of microscale wave breaking suggests that its
cumulative effect on the fluxes of heat and gas across the air-sea interface is
significant (Csanady, 1990; Banner and Peregrine, 1993; Soloviev and
, 1994; Donelan, 1995; Melville, 1996).
2.2.3 Wave breaking and whitecapping
The aqueous molecular sublayers at the air-sea interface are associated
with the action of the tangential wind stress on the sea surface. The
tangential component represents only a part of the total wind stress that is
transferred from the atmosphere to the ocean. Under high wind speeds, a
significant portion of the momentum is transferred to surface waves. Surface
waves periodically break destroying the aqueous viscous sublayer as well as
the thermal and diffusion sublayers. The molecular sublayers regenerate
between wave breaking events.
The ratio of the tangential wind stress W t controlling the aqueous viscous
sublayer to the total air-sea momentum flux 0
W is as follows (Soloviev and
1996):
1
0 1
/
t
c r
Ke Ke
W W
,
(2.8)
where
3 /
Ke u gQ
.
(2.9)
is the Keulegan number, which is a fundamental parameter in the dynamics
of free interfaces (Csanady, 1990). At low Keulegan numbers,
cr
Ke
Ke
interfacial instabilities are suppressed by molecular viscosity.
Formula (2.8) reflects the transformation of a substantial part of the
surface wind stress to form drag and whitecapping at high wind speeds
(valid for stationary conditions only). Figure 2-9 illustrates this dependence
for
cr
Ke = 0.18 in comparison with the data from the Banner and Peirson
(1998) laboratory experiment. The theoretical curve is in reasonably good
agreement with the experimental data taking into account that the estimate,
82
Schl ssel
ü
Schl ssel
ü