Soil Heat Flow Research Articles

A RESISTANCE PARAMETER FOR BARE-SOIL EVAPORATION MODELS

A bare-soil surface resistance parameter significantly improved the fit of a numerical model of heat and moisture flow in soils to 3 days of field measurements. The resistance removed a positive bias from the model estimates of daily cumulative evaporation on days with minimum surface soil moisture (0 to 0.5 cm) less than about 10% by volume. The model calibration was also made more stable. Saturated hydraulic conductivity and surface roughness were estimated by fitting the model to daily maximum surface temperature and minimum soil moisture. Without the surface resistance parameter, their values had to be changed from day to day to fit the surface measurements, though their day-today changes were minimal when surface resistance was included. A procedure is outlined to estimate the resistance as a function of soil moisture when independent measurements of the latent heat flux are available.

Modelling soil temperature in forest clearcuts using climate station data

A physically based numerical model was developed to estimate the time courses of soil temperature in forest clearcuts from measured solar irradiance, air temperature and wind speed. The model is based upon a finite difference solution of the one-dimensional soil heat flow equation with a surface boundary condition determined from aerodynamic heat transfer and energy balance theory. Modelled soil temperatures were compared with data from two other studies reported in the literature and with temperatures measured in a forest clearcut during 6 and 16 day periods in the summer. The model calculated surface and subsurface soil temperatures accurately over these long intervals. Modelled soil temperatures were relatively insensitive to air temperature, soil thermal properties and the lower boundary soil temperature but quite sensitive to solar irradiance, wind speed and surface roughness.

Two-Dimensional Model of Coupled Heat and Moisture Transport in Frost-Heaving Soils

A two-dimensional model of coupled heat and moisture flow in frost-heaving soils is developed based upon well known equations of heat and moisture flow in soils. Numerical solution is by the nodal domain integration method which includes the integrated finite difference and the Galerkin finite element methods. Solution of the phase change process is approximated by an isothermal approach and phenomenological equations are assumed for processes occurring in freezing or thawing zones. The model has been verified against experimental one-dimensional freezing soil column data and experimental two-dimensional soil thawing tank data as well as two-dimensional soil seepage data. The model has been applied to several simple but useful field problems such as roadway embankment freezing and frost heaving.

The Cross‐Coupling Transport Coefficient for the Steady Flow of Heat in Soil Under a Gradient of Water Content

AbstractA theoretical discussion based on the thermodynamics of irreversible processes (TIP) is given concerning the flux equations for the coupled, steady flows of water and heat in a soil as formulated by Jury and Miller. It is shown that a unique definition of the heat flux vector in a coupled flow process is not possible within the context of TIP alone, although differences between heat flux vectors can be defined uniquely. It is shown also that any set of coupled expressions for simultaneous, steady water and heat flow in soil that is compatible with TIP can be used to derive the Jury‐Miller formulation of the flux equations by means of linear transformations. Moreover, the cross‐coupling coefficient that links the heat flux to the gradient of water content vanishes identically in this formulation. However, a particular definition of the heat flux is implied by the Jury‐Miller equations and its relationship to the measured heat flux cannot be established solely by the methods of TIP. An examination of the data on heat and water flow reported by Jury and Miller indicated that the experimental sensitivity was not sufficient to discriminate among several alternative definitions of the heat flux that can be developed within TIP. This result serves to emphasize the point that the identification of the heat flux actually measured in a coupled flow experiment must be on the basis of either a theoretical model of the coupled flow processes or an application of the general equation of total energy balance.

A Model to Predict Tillage Effects on Soil Temperature

AbstractA simulation model was developed to predict tillage effects on average daily soil temperature at the 5‐cm depth. A two‐step procedure was utilized: (i) an average daily soil temperature was predicted on a flat, bare, undisturbed soil; and (ii) the temperature from step 1 was modified due to tillage‐induced changes in solar radiation absorption and soil thermal inertia. Soil and residue properties required for the model were: soil water content at the wilting point, soil bulk density, soil random roughness, initial residue dry weight, residue reflection coefficient at model initiation, soil reflection coefficient, and percentage of quartz, clay, and organic matter. Daily soil and climatic inputs required were: maximum and minimum air temperature, incoming solar radiation, wind travel, soil water content at the 5‐cm depth, and stage of evaporation. Results indicated this approach may have significant potential when soil heat flow is predominantly by conduction.

Soil Heat Flow under an Orchard Heater

Soil Heat Flow under an Orchard Heater

Stubble height effects on seasonal microclimate, water balance, and plant development of no-till winter wheat

To investigate some of the effects of standing stubble on microclimate and on the energy and water balance in relation to plant development, winter wheat ( Triticum aestivum L.) was seeded directly into spring wheat stubble of three heights: 0 (bare), 15–19, and 30–35 cm. The soil near Sidney, Montana was Williams loam (fine-loamy mixed, frigid family of Typic Argiborolls) a bench mark soil for dryland cropping in the northern Great Plains of the U.S.A. Total wind passage at 9 cm above ground level was 1.5 and 5 times greater over bare as compared with that over short and tall stubble, respectively. Snow accumulation after a late winter storm was 2 and 4 times greater on short and tall stubble treatments, respectively, than on the bare plots. The first overwinter soil recharge was 3 cm more on both stubble treatments, a difference that persisted throughout the growing season. The second overwinter recharge was ca. 1.5 and 4 cm more on short and tall treatments, respectively. Midday net radiation was as much as 15% higher over the bare treatment in the fall and varied from 5 to 11% lower over the bare treatment in the spring, as compared with that over stubble. Stubble albedo was as much as 1.5 times greater than bare albedo in the fall; differences in the spring were small. On heating days, maximum soil surface temperatures were as much as 10°C higher on bare as compared with stubble treatments and soil heat flow as much as 30% greater on bare as compared with stubble treatments; on freezing days, heat flow differences were small.

An Approach toward Energy Balance Simulation over Rugged Terrain

We develop a digital computer model, based upon equilibrium temperature theory, of the magnitudes of the components of the energy balance for a mountainous topographic surface. The model includes an algorithm for calculating slope, exposure, and horizon information for every point on a digitized grid. Incoming solar and thermal radiation are then simulated for every point. At present the model is designed for clear‐sky conditions, but it could be modified for cloudy skies. Air temperature and humidity variations are specified by externally defined relations, and values for albedo and soil thermal properties are specified for every point on the grid. Wind speed variation over the grid is not modeled, but is specified by an empirical function. The model simulates net radiation, soil heat flow, sensible and latent heat flow, and surface temperature at specified time intervals. Output is in the form of contour maps.

Modeling heat and moisture flow in soils

This paper describes a new model of the simultaneous flow of heat and moisture in soils. The model is a user-oriented experimental tool specifically designed for use in research. Computer optimization techni ques, numerical methods, and soil physics were used in developing the model. The model has been used in simulating the two-dimensional transfer of heat and moisture. It includes the effects of the environment and of subsurface sources and sinks.

Heat and Water Movement Under Surface Rocks in a Field Soil: I. Thermal Effects

AbstractResults of a field experiment designed to evaluate the effect of surface rocks on soil heat flow are presented. Temperature observations were made by thermocouples at 12 locations under and adjacent to rocks placed over bare soil. Continuous readings were taken for 24‐ and 48‐hour intervals using seven different kinds of rock cover, ranging from large granite slabs to gravel piles, during the time between December 1974 and August 1975.Experimental results consistently showed a nonnegligible 24‐hour net horizontal heat flow toward the rock at both the 2.5 and 5.0 cm depth. Net vertical heat flow was always downward in the soil under the bare surface, but was observed to be either upward or downward in the soil under the rock cover depending on prior conditions. Because water vapor movement in moist soil is generally in the same direction as heat flow it was suggested that surface rock cover may be a mechanism for water collection in arid climates.A simulation model was constructed to describe two‐dimensional heat flow in a uniform soil with a rectangular rock on the surface. Using the measured surface temperature as boundary values and a soil thermal conductivity corresponding to the mean daily soil surface temperature, the simulation model adequately reproduced the observed temperatures under and adjacent to the rock.

An estimate of the heat balance in an alpine valley in the New Zealand southern Alps

Daily, monthly and annual values of net radiation, soil heat flow, sensible heat flow and evaporative heat loss were measured, or estimated, for the period 15 August, 1969 to 14 August, 1970 at the Chilton valley in the New Zealand southern Alps (altitude 780 m a.s.l.). In the estimation of these values use was made of a regression equation between net radiation and incoming shortwave radiation, drainage lysimeter measurements, and a modified form of the Penman formula for estimating daily values of evapotranspiration. The average values of the energy flows during the study year were: net radiation, 136 ly day−1, soil heat flow, 2 ly day−1, sensible heat flow, −58 ly day−1, and evaporative heat loss, −82 ly day−1. In comparison with the heat balances of other mid-latitude stations, near the west coasts of land masses, the heat balance of the Chilton valley during the study year was noteworthy for (a) a positive mean monthly value of net radiation in winter (b) a net mean monthly flow of sensible heat away from the surface in winter, and (c) the possibility of high monthly and daily mean values of Bowen ratio, owing to soil moisture deficits in months of consistently high net radiation.

A Simple Model for Determining Evaporation from High-Latitude Upland Sites

Energy-budget calculations and equilibrium, model estimates of evaporation from a lichen-dominated upland site in the Hudson Bay lowlands are presented. The energy-budget calculations reveal that the lichen surface is relatively resistant to evaporation with an average of only 54% of the daily net radiation being utilized in the evaporative process. Equilibrium model estimates of evaporation consistently over-estimate actual evaporation by 5 and 8% for hourly values and daily totals, respectively. A simple model, a function of the equilibrium model, is derived from a comparison of actual and equilibrium evaporation. The only inputs required for the model are net radiation, soil heat flow and screen temperatures. Tests of the model indicate that it will predict actual evaporation within 5% and that it can probably be applied to any high-latitude surface which exhibits a relatively large diffusive resistance to evaporation.

Comparison of the Calorimetric and Flux Meter Measurements of Soil Heat Flow

AbstractComparisons of soil heat flow as estimated by the calorimetric, flux meter, and a combination of the two methods were made during the summer of 1969 in an oat field (Avena sativa L.). Error analysis indicated the calorimetric method had a smaller relative error than the combination method for daily soil heat flow measurements. The relative error for hourly and part‐day measurements was about the same. Daily or part‐day integrated heat flow averaged over 30 days was 24% higher for the flux meter alone than the calorimetric measurement. The combination method yielded average daily estimates that were about 65% higher than the calorimetric method. Calorimetric measurements to 16 cm and 32 cm yielded daily average values that were slightly lower than calorimetric measurements made to 64 cm. Hourly comparisons showed the correlation coefficient of the calorimetric and combination methods to be 0.97, and of the calorimetric and heat flux meter methods to be 0.93.

A test of the potential accuracy of the water-budget approach to estimating evapotranspiration

The water-budget approach to estimating evapotranspiration was tested against energy-budget calculations to determine its potential accuracy. Measurements of soil moisture change were made using both neutron attenuation and gravimetric techniques for one-day and four-day periods. Hydraulic head gradients were measured routinely in the field and moisture characteristics and capillary conductivities were calculated from both field and laboratory data. The energy-budget calculation of evapotranspiration was derived from measurements of net radiation, soil heat flow and Bowen ratios. The measurements were made in a corn field and the experimental period spanned 25 days in July, 1969. An error analysis of the water-budget approach and the experimental results lead to the same conclusion. The water-budget cannot accurately estimate evapotranspiration on a daily basis due to unavoidable large potential errors. Accuracy arises with an increasing time span between soil moisture measurements. If actual evapotranspiration is high, there is no precipitation and six sites are averaged a reasonable accuracy can be achieved for four-day periods. If only one measurement site is used or if evapotranspiration is low or if precipitation occurs, the necessary time lapse between measurements increases substantially. Moisture characteristics and capillary conductivities varied greatly from site to site and from soil horizon to soil horizon. For the entire measurement period the water lost by deep seepage was less than 10% of that lost by evapotranspiration.

Observations on the Growth of Needle Ice

Observations of needle ice were made in the field and in the laboratory. In both situations multitiered needles formed during a single freeze‐thaw cycle. Four freeze‐thaw cycles were induced in the laboratory. Ice needles grew during each cycle but became less abundant as the soil surface dried out. During the first cycle two‐tiered needles grew; in later cycles a layer of frozen soil developed under a single layer of needles. Measurements of soil heat flow, changes of soil moisture, and loss of moisture by evaporation allowed calculations of the heat balance of the surface to be made. These measurements demonstrate the importance of heat released in the conversion of water into ice. Comparison of field and laboratory results shows a contrast in the mechanism of heat loss in the two situations (radiative as opposed to evaporative), but this contrast is unimportant in the formation of ice needles. Water availability appears to be a more important control of ice needle growth. Development of multitiered ice needles is not dependent on the number of freeze‐thaw cycles but may result from a critical balance between the soil cooling rate, the amount of available moisture, and the release of heat by conversion of water into ice.

Soil heat flow investigation at Cass, South Island high country

Abstract Soil heat flow was measured in a high country valley for periods at different seasons of the year when rain followed a dry spell. The thermal conductivity and the heat capacity of the soil are computed. Heating is then compared with periodic models. Periodic heating at the surface is demonstrated, but a model describing heating through all depths is not found satisfactory. Finally, the heat flow for the periods investigated is related to the other components of the heat balance at the surface.

Digital Simulation of Heat Flow in Soils

During the winter of 1964-1965 daily temperature measurements were made of in-place soil and a simultaneous, finite-difference digital simulation of underground heat flow was carried out. The one-dimensional simulation have reasonable predictions of the measured soil temperatures at depths of 6 in. to 4 ft below the surface. In the course of making this simulation the thermal-reservoir effect of deep soil and the influence of the surface convective coefficient on near-surface temperature-predictions were investigated.

Influence of Fertilization and Altitude on Energy Budgets for Native Meadows1

AbstractExperiments were conducted for 2 years near Gunnison, Colorado, to evaluate the influence of N fertilizer and altitude on energy budgets of native wet meadows. Measurements included evapotranspiration from lysimeters (Et), evaporation from Weather Bureau pans (E), net radiation (Rn), total short‐wave radiation (R2), soil heat flow (S), air and soil temperatures, wind velocity, precipitation, and forage yields.During two periods of 1963, Rn, advected heat (A), and Et were slightly but not significantly altered at one location by application of N fertilizer. S was 2% or less of Rn, and A to lysimeters ranged from 6 to 11% of Et when data from all plots were averaged.Studies during the entire growing season of 1964 at altitudes of 2240, 2350, 2670, and 3080 m indicated that Rn, Rs, and E cannot be used to accurately predict Et for high‐altitude wet meadows. Although changes in Rn or Rs were generally accompanied by changes in E or Et, the ratios of the values changed sharply during the season because of advected energy and crop harvest. During at least 1 or 2 weeks just before midseason harvest, S was negligible and sensible heat flux to the lysimeters (−A) was as much as 26% of Et; after harvest, however, S was about 20% of Et and sensible heat flux from the lysimeters (+A) was as much as 97% of Et. Et, E, and A (to lysimeters) during comparable periods generally decreased as altitude increased. The greatest photosynthetic efficiency obtained was about 2% of Rn; usually it was much less.

Frost Heave in Soils

The Jackson-Chalmers model of frost heave is extended with a more detailed treatment of the heat flow and water transport problems in soils. Concepts derived from a study of the interaction between particles and a solid-liquid interface are combined with the previous model and applied to the formation and growth of ice lenses. Quantitative predictions relating heave rate with various soil parameters are found to agree well with available experimental data.

Portable Integrator for Net Radiation, Total Radiation, and Soil Heat Flow

Portable Integrator for Net Radiation, Total Radiation, and Soil Heat Flow