14
F. Berger and W. Schmitz
and BRA is calculated according to Angstroem as
BRA = σ . (TA + 273)
4 . (0.806 - 0.236 . 10
- 0 . 0 6 9 EA ).
TA is temperature of the air (Fig.3) and EA is the water vapour pressure of the air
(Fig.4).
a = 0.826. 10"
10 cal. cm'
2 . min
-1 . Grad K"
4
.
0.95 σ ~ 0.7847
b is a factor, depending on the degree and character of cloudiness, of the size between
1 (no clouds) and 0.5 (deep rain clouds).
35
25
20
15r-YYX
K
Y 1 „ . .
tej_^^
Γ
JAM
"7/ " "
yoKM
γ
SPM\
APM
\
A \
Y Y
V^
\N
0 Κ Μ Ί
0
6
12
18
24
HOUR
Fig.3. Daily Fluctuation of Air Temperature
6) EV = f . (EW - EA) . VcT(in cal. cm"
2 . h'
1 ), whereas EW and EA are mean water
vapour pressure of the water and the air (in mm Hg), and C the velocity of wind
relative to the surface of the flowing water. EA is taken from meteorological humidity
observations (hour step averages from Fig.4) and EA is calculated from
EA = 760 . 10(-2300.2/(TW + 273) + 6.207).
f equals 10.2 to 9.8 for water temperatures between 0 and 35°C depending on the
evaporation heat of water.
7) HCA = 0.50 . (TA - TW) . v/c"(in cal.cm"
2 .h'
1 ). Hour step averages of TA are taken
from graphs (Fig.3), based on actual observations.
The numerical calculation of ATW is inaccurate in the first approximation because
BRW, EV and HCA depend on the value of TW, which is not equal over the flow time At.
Therefore the calculations of ATW were repeated, replacing TWA by TWA + ^3p^, until
in the course of iteration the results of subsequent calculations were equal within the