
ZENO
®
-3200 USER MANUAL
Coastal Environmental Systems (206) 682-6048 Page D-23
The canopy resistance is set to 70 sm
-1
. During the night, the canopy resistance is increased by a factor of
10 to allow for stomatal closing.
Water Vapor Pressure e
This is equal to the product of the saturation vapor pressure e
s
(T) and the relative humidity h
r
.
Saturation Vapor Pressure e
s
(T)
This is related to the saturation vapor pressure e
s
(T*) at temperature T*=273.15K through the expression:
eT eT
aTT aTT
T
eT
a
a
ss
s
*exp
**
;
*Pa;
.
.K;
12
2
1
2
1
611
19 82;
0 00814
(10)
where all temperatures are given in Kelvin.
Air Pressure p
This is related to the site altitude A and the pressure p
0
at sea level through:
pA p
A
a
p
a
0
3
0
5
3
1012 10
8500
exp ;
.Pa;
m.
(11)
The altitude A is given in meters.
Rate of Change of Saturation Vapor Pressure
This is given by the derivative of equation (10):
eT
aT a T T
T
s
12
22
2
**
,
(12)
where the constants a
1
and a
2
take the same values as in equation (10).
Latent Heat of Vaporization of Water
This is fit to a linear form:
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