Difference between revisions of "Module PorousMediaProperties"
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<math>J=-K\left ( \theta \right )\left ( \frac{\partial h}{\partial \theta } + 1 \right )</math> | <math>J=-K\left ( \theta \right )\left ( \frac{\partial h}{\partial \theta } + 1 \right )</math> | ||
===Evapotranspiration=== | ===Evapotranspiration=== | ||
| − | + | :<math> \overset{\text{Energy flux rate}}{\lambda_v E=\frac{\Delta R_n + \rho_a c_p \left( \delta q \right) g_a } | |
{\Delta + \gamma \left ( 1 + g_a / g_s \right)}} | {\Delta + \gamma \left ( 1 + g_a / g_s \right)}} | ||
~ \iff ~ | ~ \iff ~ | ||
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</math> | </math> | ||
| − | + | :''λ''<sub>v</sub> = [[Latent heat of vaporization]]. Energy required per unit mass of water vaporized. (J/g) | |
| − | + | :''L''<sub>v</sub> = Volumetric latent heat of vaporization. Energy required per water volume vaporized. (''L''<sub>v</sub> = 2453 MJ m<sup>-3</sup>) | |
| − | + | :''E'' = Mass water evapotranspiration rate (g s<sup>-1</sup> m<sup>-2</sup>) | |
| − | + | :''ET''<sub>o</sub> = Water volume evapotranspired (m<sup>3</sup> s<sup>-1</sup> m<sup>-2</sup>) | |
| − | + | :Δ = Rate of change of saturation specific humidity with air temperature. (Pa K<sup>-1</sup>) | |
| − | + | :''R''<sub>n</sub> = Net [[irradiance]] (W m<sup>-2</sup>), the external source of energy flux | |
| − | + | :''c''<sub>p</sub> = [[Specific heat]] capacity of air (J kg<sup>-1</sup> K<sup>-1</sup>) | |
| − | + | :''ρ''<sub>a</sub> = dry air [[density]] (kg m<sup>-3</sup>) | |
| − | + | :δ''e'' = [[vapor pressure]] deficit, or [[specific humidity]] (Pa) | |
| − | + | :''g''<sub>a</sub> = [[Hydraulic conductivity|Conductivity]] of air, atmospheric conductance (m s<sup>-1</sup>) | |
| − | + | :''g''<sub>s</sub> = Conductivity of stoma, [[surface conductance]] (m s<sup>-1</sup>) | |
| − | + | :''γ'' = [[Psychrometric constant]] (''γ'' ≈ 66 Pa K<sup>-1</sup>) | |
In Figure below it can be seen that the actual transpiration and evaporation are calculated in Porous Media module of MohidLand. The actual evaporation, which happens only at the soil surface, is calculated based on a pressure head limit imposed by the user. It allows the model to not evaporate any surface water, even if it is available, when the soil is very far way from the saturation point. | In Figure below it can be seen that the actual transpiration and evaporation are calculated in Porous Media module of MohidLand. The actual evaporation, which happens only at the soil surface, is calculated based on a pressure head limit imposed by the user. It allows the model to not evaporate any surface water, even if it is available, when the soil is very far way from the saturation point. | ||
Revision as of 17:10, 7 February 2011
Contents
Overview
Main Processes
Water flow
The water movement in soil will be dependent on the pressure gradients existing in the soil profile and also according to gravity. The equation that describes this motion is the Buckingham Darcy equation (Jury et al,1991) where J is the water velocity, h is the pressure head, θ is the water content and K is the hydraulic conductivity.
Evapotranspiration
- Failed to parse (unknown error): \overset{\text{Energy flux rate}}{\lambda_v E=\frac{\Delta R_n + \rho_a c_p \left( \delta q \right) g_a } {\Delta + \gamma \left ( 1 + g_a / g_s \right)}} ~ \iff ~ \overset{\text{Volume flux rate}}{ET_o=\frac{\Delta R_n + \rho_a c_p \left( \delta q \right) g_a } { \left( \Delta + \gamma \left ( 1 + g_a / g_s \right) \right) \lambda_v }}
- λv = Latent heat of vaporization. Energy required per unit mass of water vaporized. (J/g)
- Lv = Volumetric latent heat of vaporization. Energy required per water volume vaporized. (Lv = 2453 MJ m-3)
- E = Mass water evapotranspiration rate (g s-1 m-2)
- ETo = Water volume evapotranspired (m3 s-1 m-2)
- Δ = Rate of change of saturation specific humidity with air temperature. (Pa K-1)
- Rn = Net irradiance (W m-2), the external source of energy flux
- cp = Specific heat capacity of air (J kg-1 K-1)
- ρa = dry air density (kg m-3)
- δe = vapor pressure deficit, or specific humidity (Pa)
- ga = Conductivity of air, atmospheric conductance (m s-1)
- gs = Conductivity of stoma, surface conductance (m s-1)
- γ = Psychrometric constant (γ ≈ 66 Pa K-1)
In Figure below it can be seen that the actual transpiration and evaporation are calculated in Porous Media module of MohidLand. The actual evaporation, which happens only at the soil surface, is calculated based on a pressure head limit imposed by the user. It allows the model to not evaporate any surface water, even if it is available, when the soil is very far way from the saturation point.
