♦ DESCRIPTION ♦
The program ONLINE_PENMAN_MONTEITH_GENERAL
calculates potential evapotranspiration (PET) for selected ecosystems by the PenmanMonteith method.

The input is:
(1) the chosen month,
(2) air temperature T_{a} (^{o}C),
(3) net radiation Q_{n} (cal cm^{2} d^{1}),
(4) relative humidity RH (%),
(5) atmospheric pressure p (mb),
(6) stomatal resistance (s/cm), and
(7) aerodynamic resistance (s/cm).
 The output is: (a) daily potential evapotranspiration (cm d^{1}), and (b) monthly potential evapotranspiration (cm).
 Potential evapotranspiration is a function of:
(a) net radiation in evaporation units E_{n},
(b) netradiation weighting factor Δ,
(c) masstransfer evaporation rate E_{a}, and
(d) modified psychrometric constant γ∗.
 The modified psychrometric constant γ∗ is a function of: (a) the psychrometric constant γ, (b) the stomatal (internal)
resistance r_{s}, and (c) the aerodynamic (external) resistance r_{a}.
 The psychrometric constant γ is a function of: (a) specific heat of moist air c_{p},
(b) atmospheric pressure p, and (c) heat of vaporization λ.
 The stomatal resistance is either chosen for one of several vegetation types (input 6A) or specified as a value (input 6B).
For input 6A, in s/cm: tropical rain forests, 0.8; deciduous, 0.85; general conifers, 0.85;
savannah, 1.; citrus 2.; upland vegetation, 1.2; bare soil, 1.; water, 0.; short crop (daily) [ASCE], 0.7; tall crop (daily) [ASCE], 0.45.
 The aerodynamic resistance is either chosen for one of several vegetation types (input 7A) or specified as a value (input 7B).
For input 7A, in s/cm: Indonesia forest, 0.5; wheat, 0.5; eucalyptus, 0.2.
 The netradiation weighting factor Δ is a function of air temperature T_{a}.
 The net radiation in evaporation units E_{n} is a function of: (a) net radiation Q_{n}, (b) mass density of water ρ, and (c)
heat of vaporization λ.
 The masstransfer evaporation rate E_{n} is a function of: (a) vaporpressure difference (e_{s}  e_{a}),
(b) stotamal resistance r_{s}, (c) aerodynamic resistance r_{a}, and (d) a factor K dependent on physical properties [of air and water].
 The vaporpressure difference (e_{s}  e_{a}) is approximated as: (e_{s}  e_{a}) ≅
e_{o}[1  (RH)/100].
 The factor K is a function of: (a) mass density of the air ρ_{a}, (b) specific heat of moist air c_{p},
(c) mass density of water ρ, (d) latent heat of vaporization λ, and (e) psychrometric constant γ.
 The units of E_{n} and E_{a} are cm/d.
 The units of Δ and γ∗ are mb (^{o}C)^{1}.
 The units of r_{s} and r_{a} are s cm^{1} [the reciprocal of units of conductance, or cm s^{1}].
 The units of K are (mb)^{1}.
 Input allowable ranges: (1) air temperature, 040 ^{o}C; (2) net radiation, 1001000 cal cm^{2} d^{1};
(3) relative humidity 1100%; (4) atmospheric pressure 5001013.25 mb. Input data
outside of these ranges
will trigger error messages and stop execution.
DISCLAIMER
