Opening /docrep/X0490E/x0490e03.htm
List of principal symbols and acronyms

Previous Page Table of Contents Next Page


List of principal symbols and acronyms

apsy

coefficient of psychrometer [°C-1]

as

fraction of extraterrestrial radiation reaching the earth on an overcast day [-]

as+bs

fraction of extraterrestrial radiation reaching the earth on a clear day [-]

cp

specific heat [MJ kg-1 °C-1]

cs

soil heat capacity [MJ m-3 °C-1]

CR

capillary rise [mm day-1]

De

cumulative depth of evaporation (depletion) from the soil surface layer [mm]

Dr

cumulative depth of evapotranspiration (depletion) from the root zone [mm]

d

zero plane displacement height [m]

dr

inverse relative distance Earth-Sun [-]

DP

deep percolation [mm]

Dpe

deep percolation from the evaporation layer [mm]

E

evaporation [mm day-1]

Epan

pan evaporation [mm day-1]

e°(T)

saturation vapour pressure at air temperature T [kPa]

es

saturation vapour pressure for a given time period [kPa]

ea

actual vapour pressure [kPa]

es - ea

saturation vapour pressure deficit

ECe

electrical conductivity of the saturation extract of the soil [dS m-1]

ECe, threshold

electrical conductivity of the saturation extract of the soil above which yield begins to decrease [dS m-1]

ET

evapotranspiration [mm day-1]

ETo

reference crop evapotranspiration [mm day-1]

ETc

crop evapotranspiration under standard conditions [mm day-1]

ETc adj

crop evapotranspiration under non-standard conditions [mm day-1]

exp[x]

2.7183 (base of natural logarithm) raised to the power x

Fr

resistance correction factor [-]

fc

fraction of soil surface covered by vegetation (as observed from overhead) [-]

fc eff

effective fraction of soil surface covered by vegetation [-]

1 - fc

exposed soil fraction [-]

fw

fraction of soil surface wetted by rain or irrigation [-]

few

fraction of soil that is both exposed and wetted (from which most evaporation occurs) [-]

G

soil heat flux [MJ m-2 day-1]

Gday

soil heat flux for day and ten-day periods [MJ m-2 day-1]

Ghr

soil heat flux for hourly or shorter periods [MJ m-2 hour-1]

Gmonth

soil heat flux for monthly periods [MJ m-2 day-1]

Gsc

solar constant [0.0820 MJ m-2 min-1]

H

sensible heat [MJ m-2 day-1]

HWR

height to width ratio

h

crop height [m]

I

irrigation depth [mm]

IW

irrigation depth for that part of the surface wetted [mm]

J

number of day in the year [-]

Kc

crop coefficient [-]

Kc ini

crop coefficient during the initial growth stage [-]

Kc mid

crop coefficient during the mid-season growth stage [-]

Kc end

crop coefficient at end of the late season growth stage [-]

Kc max

maximum value of crop coefficient (following rain or irrigation) [-]

Kc min

minimum value of crop coefficient (dry soil with no ground cover) [-]

Kcb

basal crop coefficient [-]

Kcb full

basal crop coefficient during mid-season (at peak plant size or height) for vegetation with full ground cover of LAI > 3 [-]

Kcb ini

basal crop coefficient during the initial growth stage [-]

Kcb mid

basal crop coefficient during the mid-season growth stage [-]

Kcb end

basal crop coefficient at end of the late season growth stage [-]

Ke

soil evaporation coefficient [-]

Kp

pan coefficient [-]

Kr

soil evaporation reduction coefficient [-]

Ks

water stress coefficient [-]

Ky

yield response factor [-]

k

von Karman's constant [0.41] [-]

kRs

adjustment coefficient for the Hargreaves' radiation formula [°C-0.5]

Lini

length of initial growth stage [day]

Ldev

length of crop development growth stage [day]

Lmid

length of mid-season growth stage [day]

Llate

length of late season growth stage [day]

LZ

longitude of centre of local time zone [degrees west of Greenwich]

Lm

longitude [degrees west of Greenwich]

LAI

leaf area index [m2 (leaf area) m-2 (soil surface)]

LAIactive

active (sunlit) leaf area index.[-]

N

maximum possible sunshine duration in a day, daylight hours [hour]

n

actual duration of sunshine in a day [hour]

n/N

relative sunshine duration [-]

P

rainfall [mm], atmospheric pressure [kPa]

p

evapotranspiration depletion factor [-]

R

specific gas constant [0.287 kJ kg-1 K-1]

Ra

extraterrestrial radiation [MJ m-2 day-1]

Rl

longwave radiation [MJ m-2 day-1]

Rn

net radiation [MJ m-2 day-1]

Rnl

net longwave radiation [MJ m-2 day-1]

Rns

net solar or shortwave radiation [MJ m-2 day-1]

Rs

solar or shortwave radiation [MJ m-2 day-1]

Rso

clear-sky solar or clear-sky shortwave radiation [MJ m-2 day-1]

ra

aerodynamic resistance [s m-1]

rl

bulk stomatal resistance of well-illuminated leaf [s m-1]

rs

(bulk) surface or canopy resistance [s m-1]

Rs/Rso

relative solar or relative shortwave radiation [-]

RAW

readily available soil water of the root zone [mm]

REW

readily evaporable water (i.e., maximum depth of water that can be evaporated from the soil surface layer without restriction during stage 1) [mm]

RH

relative humidity [%]

RHhr

average hourly relative humidity

RHmax

daily maximum relative humidity [%]

RHmean

daily mean relative humidity [%]

RHmin

daily minimum relative humidity [%]

RO

surface runoff [mm]

Sc

seasonal correction factor for solar time [hour]

SF

subsurface flow [mm]

T

air temperature [°C]

TK

air temperature [K]

TKv

virtual air temperature [K]

Tdew

dewpoint temperature [°C]

Tdry

temperature of dry bulb [°C]

Tmax

daily maximum air temperature [°C]

Tmax, K

daily maximum air temperature [K]

Tmean

daily mean air temperature [°C]

Tmin

daily minimum air temperature [°C]

Tmin, K

daily minimum air temperature [K]

Twet

temperature of wet bulb [°C]

TAW

total available soil water of the root zone [mm]

TEW

total evaporable water (i.e., maximum depth of water that can be evaporated from the soil surface layer) [mm]

t

time [hour]

u2

wind speed at 2 m above ground surface [m s-1]

uz

wind speed at z m above ground surface [m s-1]

W

soil water content [mm]

Ya

actual yield of the crop [kg ha-1]

Ym

maximum (expected) yield of the crop in absence of environment or water stresses [kg ha-1]

Ze

depth of surface soil layer subjected to drying by evaporation [m]

Zr

rooting depth [m]

z

elevation, height above sea level [m]

zh

height of humidity measurements [m]

zm

height of wind measurements [m]

zom

roughness length governing momentum transfer [m]

zoh

roughness length governing heat and vapour transfer [m]

a

albedo [-]

g

psychrometric constant [kPa °C-1]

g psy

psychrometric constant of instrument [kPa °C-1]

D

slope of saturation vapour pressure curve [kPa °C-1]

D SW

variation in soil water content [mm]

D t

length of time interval [day]

D z

effective soil depth [m]

d

solar declination [rad]

e

ratio molecular weight of water vapour/dry air (= 0.622)

h

mean angle of the sun above the horizon

q

soil water content [m3 (water) m-3 (soil)]

q FC

soil water content at field capacity [m3 (water) m-3 (soil)]

q t

threshold soil water content below which transpiration is reduced due to water stress [m3 (water) m-3 (soil)]

q WP

soil water content at wilting point [m3 (water) m-3 (soil)]

l

latent heat of vaporization [MJ kg-1]

l ET

latent heat flux [MJ m-2 day-1]

r a

mean air density [kg m-3]

r w

density of water [kg m-3]

s

Stefan-Boltzmann constant [4.903 10-9 MJ K-4 m-2 day-1]

j

latitude [rad]

w

solar time angle at midpoint of hourly or shorter period [rad]

w 1

solar time angle at beginning of hourly or shorter period [rad]

w 2

solar time angle at end of hourly or shorter period [rad]

w S

sunset hour angle [rad]


Previous Page Top of Page Next Page