Description Usage Format Source See Also

This data set contains the universal constants, and examples of other variable constants required for calculating evapotranspiration in function `ET`

, based on the climatic condition at Kent Town station in Adelaide, Australia.

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A list containing 46 constant values including:

- 20 universal constants, which should be kept unchanged for most conditions:

*lambda* latent heat of evaporisationin = 2.45 MJ.kg^-1 at 20 degree Celcius,

*sigma* Stefan-Boltzmann constant = 4.903*10^-9 MJ.K^-4.m^-2.day^-1,

*Gsc* solar constant = 0.0820 MJ.m^-2.min^-1

*Roua* mean density of air = 1.2 kg.m^-3 at 20 degree Celcius

*Ca* specific heat of air = 0.001013 MJ.kg^-1.K^-1

*G* soil heat flux negligible for daily time-step = 0 (Allen et al., 1998, page 68)

*alphaA* Albedo for Class-A pan = 0.14

*alphaPT* Priestley-Taylor coefficient:

= 1.26 for Priestley-Taylor formula (Priestley and Taylor, 1972, Sect. 6;
Eichinger et al., 1996, p.163);

= 1.31 for Szilagyi-Jozsa formula (Szilagyi and Jozsa, 2008);

= 1.28 for Brutsaert-Strickler formula (Brutsaert and Strickler, 1979),

*ap* constant in Penpan formula = 2.4,

*b0* constant in Morton's procedure = 1 (Chiew and McMahon, 1991, Table A1),

*b1* constant in Morton's procedure = 14 W.m^-2 (Chiew and McMahon, 1991, Table A1),

*b2* constant in Morton's procedure = 1.2 (Chiew and McMahon, 1991, Table A1),

*e0* constant for Blaney-Criddle formula = 0.81917 (Frevert et al., 1983, Table 1),

*e1* constant for Blaney-Criddle formula = -0.0040922 (Frevert et al., 1983, Table 1),

*e2* constant for Blaney-Criddle formula = 1.0705 (Frevert et al., 1983, Table 1),

*e3* constant for Blaney-Criddle formula = 0.065649 (Frevert et al., 1983, Table 1),

*e4* constant for Blaney-Criddle formula = -0.0059864 (Frevert et al., 1983, Table 1),

*e5* constant for Blaney-Criddle formula = -0.0005967 (Frevert et al., 1983, Table 1),

*epsilonMo* Land surface emissivity in Morton's procedure = 0.92,

*sigmaMo* Stefan-Boltzmann constant in Morton's procedure = 5.67e-08 W.m^-2.K^-4.

- 16 variable constants, which are specific for the climatic condition at Kent Town station in Adelaide, Australia:

*lat* latitude = -34.9211 degrees for Kent Town station,

*lat_rad* latitude in radians = -0.6095 radians for Kent Town station,

*as* fraction of extraterrestrial radiation reaching earth on sunless days = 0.23 for Australia (Roderick, 1999, page 181),

*bs* difference between fracion of extraterrestrial radiation reaching full-sun days and that on sunless days = 0.5 for Australia (Roderick, 1999, page 181),

*Elev* ground elevation above mean sea level = 48m for Kent Town station,

*z* height of wind instrument = 10m for Kent Town station,

*fz* constant in Morton's procedure:

= 28.0 W.m^-2.mbar^-1 for CRAE model for T >= 0 degree Celcius;

= 28.0*1.15 W.m^-2.mbar^-1 for CRAE model for T < 0 degree Celcius;

= 25.0 W.m^-2.mbar^-1 for CRWE model for T >= 0 degree Celcius;

= 28.75 W.m^-2.mbar^-1 for CRWE model for T < 0 degree Celcius (Morton, 1983a, page65).

*a_0* constant for estimating sunshine hours from cloud cover data = 11.9 for Adelaide (Chiew and McMahon, 1991, Table A1),

*b_0* constant for estimating sunshine hours from cloud cover data = -0.15 for Adelaide,

*c_0* constant for estimating sunshine hours from cloud cover data = -0.25 for Adelaide,

*d_0* constant for estimating sunshine hours from cloud cover data = -0.0107 for Adelaide,
*gammaps* product of Psychrometric constant and atmospheric pressure as sea level:

= 0.66 mbar. degree Celcius^-1 for CRAE model for T >= 0 degree Celcius;

= 0.66/1.15 mbar. degree Celcius^-1 for CRAE model for T < 0 degree Celcius.

*PA* annual precipitation = 285.8mm for Kent Town station,

*alphaMo* constant in Morton's procedure:

= 17.27 when T >= 0 degree Celcius;

= 21.88 when T < 0 degree Celcius.

*betaMo* constant in Morton's procedure:

= 237.3 degree Celcius when T >= 0 degree Celcius;

= 265.5 degree Celcius when T < 0 degree Celcius.

*lambdaMo* latent heat of vaporisation in Morton's procedure:

= 28.5W.day.kg^-1 when T >= 0 degree Celcius;

= 28.5*1.15W.day.kg^-1 when T < 0 degree Celcius.

various references

Evapotranspiration documentation built on Nov. 17, 2017, 7:01 a.m.

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