Vaisala AWS330 - Manual (Page 288)

User's Guide ______________________________________________________________________
286 _________________________________________________________________ M211296EN-B
Soil Heat Flux (G)






Δ
−
= −
t
T T
d c G n n
s s
1
where
T
n
= Temperature on day n [ ° C]
T
n-1
= Temperature on preceding day n-1 [ ° C]
Δ t = Time period [days]
c
s
= Volumetric heat capacity [MJ m -3 ° C -1 ] (2.1 for average
moist soil is used)
d
s
= Estimated effective soil depth [m] (0.2 m is used)
Psychometric Constant ( γ )
λ ελ
γ
P P C
p 00163 . 0 10 3 = ⋅ = −
where
γ = Psychometric constant [kPa ° C -1 ]
C
p
= Specific heat of moist air = 1.013 kJ kg -1 ° C -1
P = Atmospheric pressure [kPa]
ε = Ratio molecular weight water vapor/dry air = 0.622
λ = Latent heat of vaporization [ML kg -1 ]
λ is given by the following formula:
T ) 10 361 . 2 ( 501 . 2 3 − ⋅ − = λ
Average Air Temperature (T)
Where hourly data is available:

=
= 24
0 24 i
i
T
T