EI>I>Y IXFF1JSION COEFFICIENTS
41 5
Of coiirse, the profiles KJZ) are no longer universal now. Since thc
friction velocity varies with time. the riondimensionalisation would also vary
with time. The values are therefore comparable only if they are all nondimensionalized with the same value: for that purpose the scale height H ,
for p = 0 in the stationary case has been used.
Figure 7 shows the ratio kJk, for four diflerent times of day. For the
computation of the temperature profiles O(Z) and of the kh profiles, reference is made to the paper by Wippermann et al. (1973). Since in a PBL
(without radiative effects) the turbulent heat flux qo is constant with height
(but dO/?Z 4 0 for Z + a), kh + 00 for 2 4 oc. The large increase of kJk,
with height is seen in Fig. 7.
1D
7
3
3
1
1 " d
7
5
1
I
1 X d
7
I
I
I
I ,Id
I
s
1
1
1.16'
12;
,
I
,
FIG. 7. The vertical profiles of kJk, for various times of the day. obtained with a
time-dependent boundary layer model. (After Wipprmann er a/., 1973.)