THE NEAR-SURFACE LAYER OF THE OCEAN
where t is the elapsed time from the beginning of the diurnal warming.
From X (4.7)X , X (4.9)X , X (4.24)X and an obvious inequality
0.5
0.5
D
D
D
h
H
H
!
, it
follows that
2
1
2
/
cr
T
D
p
u
Ri
g
c
D
U
'
. Hence, the upper limit of the
diurnal jet velocity is
1/ 2
1
max
2
/
cr
T
D
p
u
R i
g
c
D
U
ª
º
'
b
¬
¼ .
(4.25)
The heat accumulated in the upper ocean due to diurnal warming is
mainly determined by solar radiation. The maximum quantity of the solar
radiation absorbed by the ocean during daytime is roughly equal to 2 x 10P
7
P
J
mP
-2
P.
Substituting this value into X (4.25)X gives an estimate
max
u
'
|0.3 m sP
-1
P,
which represents the upper velocity limit for the diurnal jet.
4.2.4 Upper velocity limit for the rain-formed jet
Slippery layers can also develop due to freshwater input from rain. An
equation similar to X (4.25)X can be derived for estimating the upper velocity
limit in the case of rain-formed jet:
1/ 2
1
max
0
2 cr S
r
u
Ri
gS M
E
ª
º
'
¬
¼ ,
(4.26)
where r
M is the cumulative precipitation, defined from equation
0
t
r
M
Pdtc
³ ,
(4.27)
where P is the precipitation rate and t is the elapsed time from the beginning
of the rain event. For a strong tropical rainfall with
100
r
M
mm, the upper
estimate of the velocity following from X (4.26)X is
-1
max
0.5 m s
u
'
|
.
4.3 Evolution of the Diurnal Mixed Layer and Diurnal
Thermocline Under Low Wind Speed Conditions
X Figure 4-16X offers the following classification of the diurnal mixed layer
and diurnal thermocline evolution under low wind speed conditions. During
layer. After sunrise, increasing solar radiation gradually suppresses
convective mixing forming a diurnal mixed layer, which rapidly thins (Phase
246
b
Phase I, nighttime convection typically penetrates to the bottom of the mixed