Dynamax Inc
34
4.3 ET Variables and complete algorithm
Constants or site-specific variables:
Notation Description
Units
zom
Height of measurement
M
Zot
Roughness parameter for heat and vapor profile M
Lev
Latent Heat of vaporization
J/Kg
has
Specific heat air capacity
J/Kg.degC at 30C
Input variables:
Notation Description
Units
hgr
Hourly average solar radiation
W/m2
hta
Hourly average of air temperature
degC
hrh
Hourly average or relative humidity %
hpr
Average Barometric Pressure
MBar
hws
Hourly average of wind speed
M/s
Calculated variables:
Notation Description
Units
had
Air Density
Kg/m3
hum
Ambient Humidity
Kg/m3
has
Aerodynamic resistance
S/m
skl
Sky long-wave radiation
W/m2
htc
Surface temperature
DegC
rnt
Net radiation balance
W/m2
sht
Sensible heat flux
W/m2
hums
Humidity at the surface
Kg/m3
evt
Evapotranspiration
Kg/m2.s
EVT
Evapotranspiration in standard units mm/hour