Roman Alphabet
Symbol 
Unit 
Definition 
b' 

Calibration factor for square root minimum temperature prediction 
C 

Certainty that an event will occur (i.e. C = 1  R) 
C_{V} 
J m^{3} °C^{1} 
Volumetric heat capacity of soil 
E 
kPa 
Water vapour pressure or actual water vapour pressure 
E 
kg m^{2} s^{1} 
Water vapour mass flux density 
E 
W m^{2} 
Energy from radiation 
e_{a} 
kPa 
Saturation vapour pressure at temperature T_{a} 
e_{d} 
kPa 
Saturation vapour pressure at the dewpoint temperature T_{d} (note that e_{d} = e) 
e_{f} 
kPa 
Saturation vapour pressure at the frostbulb temperature T_{w} 
e_{i} 
kPa 
Saturation vapour pressure at the ice point temperature T_{i} (note that e_{i} = e) 
E_{L} 
m 
Elevation relative to mean sea level 
E_{o} 
MJ l^{1}, MJ kg^{1} 
Energy output 
E_{R} 
W m^{2} 
Energy requirement 
e_{s} 
kPa 
Saturation vapour pressure over a flat surface of liquid water or ice at temperature T 
e_{w} 
kPa 
Saturation vapour pressure at wet bulb temperature T_{w} 
F 
— 
Function to account for cloudiness effect on longwave downward radiation 
F_{C} 
l h^{1}, kg h^{1} 
Fuel consumption rate 
G 
W m^{2} 
Soil heat flux density 
G_{1} 
W m^{2} 
Soil heat flux density at the soil surface (i.e. G_{1} = G) 
G_{2} 
W m^{2} 
Soil heat flux density measured with a flux plate at some depth in the soil 
G_{sc} 
W m^{2} 
Solar constant. G_{sc} = 1367 W m^{2} 
H 
— 
Number of hours from two hours past sunset until sunrise 
H 
W m^{2} 
Sensible heat flux density 
H_{H} 
— 
Heaters per hectare 
K_{h} 
W m^{1} °C^{1} 
Thermal conductivity 
K_{s} 
W m^{1} °C^{1} 
Thermal conductivity of the soil 
L 

Latent heat of vaporization 
LE 
W m^{2} 
Latent heat flux density 
p 
— 
p = 86 400 s per day 
P 
— 
Probability that an event will occur in any given year 
P_{b} 
kPa 
Barometric pressure 
R 
— 
Risk or probability that an event will occur during a known number of years 
R_{1} 
°C 
Residual R_{1} = T_{n}  T_{p} 
R_{1}' 
°C 
Residual R_{1} prediction using T_{d} at time t_{0} 
R_{A} 
mm h^{1} 
Sprinkler application rate 
R_{Ld} 
W m^{2} 
Downward positive longwave (terrestrial) radiation 
R_{Ln} 
W m^{2} 
Net longwave radiation (R_{Ln} = R_{Ld} + R_{Lu}) 
R_{Lu} 
W m^{2} 
Upward negative longwave (terrestrial) radiation 
RMSE 

RMSE = [S(YX)^{2}/n]^{0.5} where n is the number of pairs of random variables Y and X 
R_{n} 
W m^{2} 
Net radiation 
R_{o} 
°C 
Range of soil surface temperature 
R_{Sd} 
W m^{2} 
Downward positive shortwave (solar) radiation 
R_{Sn} 
W m^{2} 
Net shortwave (solar) irradiance (R_{Sn} = R_{Sd} + R_{Su}) 
R_{So} 
W m^{2} 
Downward shortwave (solar) radiation from a clear sky 
R_{Su} 
W m^{2} 
Upward negative shortwave (solar) radiation 
R_{z} 
°C 
Range of soil temperature at depth z in the soil 
T 
°C 
Temperature 
t 
— 
Time 
T_{10} 

The critical temperature at which 10 percent damage is expected 
T_{90} 

The critical temperature at which 90 percent damage is expected 
T_{a} 
°C 
Air temperature 
T_{C} 
— 
Critical temperature or critical damage temperature  the temperature at which a particular damage level is expected 
T_{cf} 
°C 
Citrus fruit peel temperature 
T_{d} 
°C 
Dewpoint temperature 
T_{e} 
°C 
Equivalent temperature (the temperature achieved if all latent heat in a parcel of air is adiabatically converted to sensible heat) 
T_{f} 
°C 
Frostbulb temperature 
t_{f} 
— 
Time at the end of a sample interval 
T_{i} 
°C 
Ice point temperature 
t_{i} 
— 
Time at the beginning of a sample interval 
T_{i} 
°C 
Temperature at the i^{th} hour following t_{0} 
T_{K} 
K 
Absolute temperature in kelvins (273.15 K = 0°C) 
T_{n} 
°C 
Observed minimum temperature at sunrise 
t_{0} 
— 
Starting time for FFST.xls application (i.e. two hours past sunset) 
T_{0} 
°C 
Temperature at time t_{0} 
T_{p} 
°C 
Minimum temperature predicted from air and dewpoint temperature at t_{0} 
t_{p} 
— 
Time of sunrise for predicted minimum temperature (T_{p}) 
T_{p}' 
°C 
Minimum temperature predicted using T_{0} at time t_{0} 
T_{sf} 
°C 
Soil temperature at the end of a sample interval 
T_{si} 
°C 
Soil temperature at the beginning of a sample interval 
T_{w} 
°C 
Wetbulb temperature 
V_{m} 
— 
Volume fraction of minerals in the soil 
V_{o} 
— 
Volume fraction of organic matter in the soil 
z 
m 
Depth below or height above the surface (e.g. in metres) 
Greek Alphabet
Symbol 
Unit 
Definition 
D 
kPa °C^{1} 
Slope of saturation vapour pressure curve at temperature T 
a 
— 
Albedo (i.e. reflection of shortwave radiation) 
e 
— 
Emissivity 
e_{0} 
— 
Apparent emissivity downward from clear sky 
g 
kPa °C^{1} 
Psychrometric constant 
k_{T} 
m^{2} s^{1} 
Thermal diffusivity in the soil 
l 
MJ kg^{1} 
Latent heat of vaporization 
l_{max} 
m 
Wavelength of maximum energy emission 
m_{d} 
— 
Mean value for a date 
q 
— 
Volume fraction of water in the soil 
s 
W m^{2} K^{4} 
StefanBoltzmann constant s = 5.67 × 10^{8} W m^{2}K^{4} 
s 
mol m^{3} 
Density of air 
s_{d} 
Mg m^{3} 
Density of water 
s_{d} 
— 
Standard deviation of a date 
Note that sprinkler irrigation rate conversions are:
1 mm h^{1} = 1 litre m^{2} h^{1} = 10^{4} litre ha^{1} h^{1} = 10 m^{3} ha^{1} h^{1}.