THE NEAR-SURFACE LAYER OF THE OCEAN
Wu (1975) concluded that
/
17.0
wd
u u |
and has no obvious systematic
dependence upon friction velocity. Phillips and Banner (1974) laboratory
experiment indicated that
/
16.1
wd
u u |
.
Values of
/
wd
u u derived from particle image velocimetry and from
infrared imaging also demonstrate no obvious dependence on the friction
velocity but consistently indicate smaller surface drift currents than those
derived from drifter measurements (Zhang and Harrison, 2004). The windinduced velocities derived from the infrared images are shown in Figure
2-12. Averaging over all friction velocities results in
/
7.4
wd
u u |
. Based
on these laboratory results we accept an estimate 0
/ §7.4. This is in fact an
upper estimate, because it does not take into account the existence of
relatively small current velocity difference across the turbulent layer (i.e.,
below the viscous sublayer).
A fit of parameterization (2.57) to the results of the Zhang and Harrison
(2004) is shown in Figure 2-12. In (2.57), the term
1/ 4
3 4
0
0
0
1 a
Rf
/
relating to buoyancy effects is of importance under low wind speed
conditions. Figure 2-12 therefore shows parameterization (2.39) for two
values of the net surface heat flux 0
Q .
A tentative estimate of
cr
Ke § 0.18 was derived by Soloviev and
(1994) from indirect data–the critical wind speed, 10
U § 10 m s
-1 ,
at which, according to the visual Beaufort scale, long-wave breaking sets in.
Later, Zhao and Toba (2001) proposed a parameter
2 /
B
a
a
p
R u
Q Z
with a
critical value of B
R =10
3 for the onset of wind-wave breaking. Parameter B
R
can be rewritten as
3 /
B
w
a
a
R
A u
gQ
(2.63)
where w
A is the wave age defined as
/
w
p a
A g
u
Z .
3/ 2
3/ 2
3
3
1
1
a
a
a
a
a
B
a
w
w
u
u
Ke
R
g
g
A
A
E Q U
Q U
Q
Q Q U
Q U
§ ·
§ ·
¨ ¸
¨ ¸
© ¹
© ¹
(2.64)
From (2.64), it follows that critical value B
R =10
3 corresponds to
0.18
cr
Ke
at wave age w
A =3.25.
102
Schl ssel
ü
Wu (1975) concluded that
/
17.0
wd
u u |
and has no obvious systematic
dependence upon friction velocity. Phillips and Banner (1974) laboratory
experiment indicated that
/
16.1
wd
u u |
.
Values of
/
wd
u u derived from particle image velocimetry and from
infrared imaging also demonstrate no obvious dependence on the friction
velocity but consistently indicate smaller surface drift currents than those
derived from drifter measurements (Zhang and Harrison, 2004). The windinduced velocities derived from the infrared images are shown in Figure
2-12. Averaging over all friction velocities results in
/
7.4
wd
u u |
. Based
on these laboratory results we accept an estimate 0
/ §7.4. This is in fact an
upper estimate, because it does not take into account the existence of
relatively small current velocity difference across the turbulent layer (i.e.,
below the viscous sublayer).
A fit of parameterization (2.57) to the results of the Zhang and Harrison
(2004) is shown in Figure 2-12. In (2.57), the term
1/ 4
3 4
0
0
0
1 a
Rf
/
relating to buoyancy effects is of importance under low wind speed
conditions. Figure 2-12 therefore shows parameterization (2.39) for two
values of the net surface heat flux 0
Q .
A tentative estimate of
cr
Ke § 0.18 was derived by Soloviev and
(1994) from indirect data–the critical wind speed, 10
U § 10 m s
-1 ,
at which, according to the visual Beaufort scale, long-wave breaking sets in.
Later, Zhao and Toba (2001) proposed a parameter
2 /
B
a
a
p
R u
Q Z
with a
critical value of B
R =10
3 for the onset of wind-wave breaking. Parameter B
R
can be rewritten as
3 /
B
w
a
a
R
A u
gQ
(2.63)
where w
A is the wave age defined as
/
w
p a
A g
u
Z .
3/ 2
3/ 2
3
3
1
1
a
a
a
a
a
B
a
w
w
u
u
Ke
R
g
g
A
A
E Q U
Q U
Q
Q Q U
Q U
§ ·
§ ·
¨ ¸
¨ ¸
© ¹
© ¹
(2.64)
From (2.64), it follows that critical value B
R =10
3 corresponds to
0.18
cr
Ke
at wave age w
A =3.25.
102
Schl ssel
ü