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Numerical Analysis of Coupled Water, Vapor, and Heat Transport in the Vadose Zone

Hirotaka Saito^a,*, Jiri imnek^a and Binayak P. Mohanty^b

^a Dep. of Environmental Sciences, Univ. of California, Riverside, CA 92521
^b Biological and Agricultural Engineering, Texas A&M Univ., College Station, TX 77843-2117

View larger version (50K): [in a new window]   Fig. 1. Soil temperatures and water contents measured at three depths (2, 7, and 12 cm) from 24 November (Day of the Year [DOY] 328) to 5 December (DOY 339) at the experimental site in Riverside, CA.

View larger version (17K): [in a new window]   Fig. 2. Water retention curve measured on a soil core sample collected at the experimental site in Riverside, CA. Both drainage and imbibition curves are plotted (open symbols: drainage, closed symbols: imbibition). The van Genuchten (1980) model (VG) is fit to the measured data.

View larger version (31K): [in a new window]   Fig. 3. Diurnal changes of three meteorological variables—air temperature, relative humidity, and wind speed—generated from daily information during the simulation period along with hourly values measured at the weather station near the study site from 23 November (Day of the Year [DOY] 327) to 6 December (DOY 340).

View larger version (19K): [in a new window]   Fig. 4. Vapor densities calculated from generated air temperatures (Eq. [44]) and relative humidities (Eq. [45]) along with vapor pressures calculated hourly at the weather station from 23 November (Day of the Year [DOY] 327) to 6 December (DOY 340).

View larger version (33K): [in a new window]   Fig. 5. Net radiation calculated from 6 Nov. 1995 (Day of the Year [DOY] 310) to 16 Nov. 1995 (DOY 320) using the standard daily meteorological data obtained from the weather station at the UC-Riverside Agricultural Operations Department Area in Riverside, CA. Measured hourly net radiation values were obtained at the experimental site near the University of California Agricultural Experimental Station in Riverside. Net radiation was calculated as the sum of the net incoming shortwave solar radiation and net outgoing longwave radiation.

View larger version (25K): [in a new window]   Fig. 6. Simulated and measured volumetric water contents during the simulation time period (Day of the Year [DOY] 328–DOY 339) at three depths (2, 7, and 12 cm) at the experimental site.

View larger version (28K): [in a new window]   Fig. 7. Simulated and measured soil temperatures during the simulation time period (Day of the Year [DOY] 328–DOY 339) at three depths (2, 7, and 12 cm) at the experimental site.

View larger version (23K): [in a new window]   Fig. 8. Simulated surface energy balance components at the experimental site: net radiation, sensible heat flux, latent heat flux, and surface heat flux from 24 November (Day of the Year [DOY] 328) to 5 December (DOY 339). All fluxes are positive upward, except for the net radiation where positive value indicates incoming radiation to the soil surface (downward) and negative value outgoing radiation from the soil surface (upward).

View larger version (22K): [in a new window]   Fig. 9. Temporal changes of the pressure head and relative humidity at the soil surface during the simulation period from 24 November (Day of the Year [DOY] 328) to 5 December (DOY 339). The corresponding surface relative humidity was calculated from the surface pressure head using Philip and de Vries' equilibrium model (Eq. [18]).

View larger version (16K): [in a new window]   Fig. 10. Temporal changes of transmission coefficient, surface albedo, surface emissivity, and atmosphere emissivity required for calculations of the net radiation at a given time of day for the simulation time period (Day of the Year [DOY] 328–DOY 339). These variables are calculated directly by the program.

View larger version (16K): [in a new window]   Fig. 11. Calculated vertical distributions of the thermal and isothermal fluxes of liquid water and water vapor at 1200 and 0000 h of a typical dry 24-h period during Days of the year [DOY] 329 and 330. Positive values indicate upward and negative values downward fluxes.

View larger version (17K): [in a new window]   Fig. 12. Vertical profiles of thermal and isothermal fluxes of liquid water and water vapor at 0000 h of Day of the Year (DOY) 335. Light irrigation was applied at 1200 h of DOY 334. Positive values indicate upward fluxes, while negative values indicate downward fluxes.

View larger version (25K): [in a new window]   Fig. 13. Simulated profiles of water contents (left) and soil temperatures (right) at 1200 h of Day of the Year (DOY) 329 (top row) and DOY 334 (bottom row), and 6, 12, 18, 24 h after. Light irrigation was applied at 1200 h of DOY 334.