
Appendix B _______________________________________________________ Calculation Formulas
VAISALA_______________________________________________________________________ 141
∑
−=
Θ+Θ=
3
1
4
lnln
i
i
iws
bbP
(6)
where:
b
i
= coefficients
b
-1
= -0.58002206 × 10
4
b
0
= 0.13914993 × 10
1
b
1
= -0.48640239 × 10
-1
b
2
= 0.41764768 × 10
-4
b
3
= -0.14452093 × 10
-7
b
4
= 6.5459673
The water vapor pressure is calculated using:
100
ws
w
P
RHP ⋅=
(7)
Parts per million by volume is calculated using:
()
w
w
v
Pp
P
ppm
−
⋅=
6
10
(8)
Symbols:
T
d
= dewpoint temperature (°C)
P
w
= water vapour pressure (hPa)
P
ws
= water vapour saturation pressure (hPa)
RH = relative humidity (%)
x = mixing ratio (g/kg)
= atmospheric pressure (hPa)
a = absolute humidity (g/m
3
)
T = temperature (K)
h = enthalpy (kJ/kg)
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