Samuel I. Outcalt

Non-conductive heat transfer associated with frozen soils

Abstract The assertion that pure conductive heat transfer always dominates in cold climates is at odds with decades of research in soil physics which clearly demonstrate that non-conductive heat transfer by water and water vapor are significant, and frequently are for specific periods the dominant modes of heat transfer near the ground surface. The thermal regime at the surface represents the effective boundary condition for deeper thermal regimes. Also, surface soils are going to respond more quickly to any climatic fluctuations; this is important to us because most facets of our lives are tied to earths surface. To accurately determine the surface thermal regime (for example, the detection of climate change), it is important to consider all potential forms of heat transfer. Gradients that have the potential to alter the thermal regime besides temperature include pore water pressure, gravitational, density, vapor pressure and chemical. The importance of several non-conductive heat transport mechanisms near the ground surface is examined. Infiltration into seasonally frozen soils and freezing (release of latent heat) of water is one mechanism for the acceleration of warming in surficial soils in the spring. Free convection due to buoyancy-induced motion of fluids does not appear to be an important heat-transfer mechanism; estimates of the Rayleigh number (the ratio of buoyancy to viscous forces) are generally around 2, which is too low for effective heat transfer. The Peclet number (ratio of convective to conductive heat transfer) is on the order of 0.25 for snowmelt infiltration and up to 2.5 for rainfall infiltration for porous organic soils. In mineral soils, both vertical and horizontal advection of heat can be neglected (Peclet number is approximately 0.001) except for snowmelt infiltration into open thermal contraction cracks. The migration of water in response to temperature or chemical gradients from unfrozen soil depths to the freezing front, and the redistribution of moisture within the frozen soil from warmer depths to colder depths, can also result in heat transfer although this effect has not been quantified here. Many of these processes are seasonal and effective only during periods of phase change when the driving gradient near the ground surface is relatively large.

The Development and Application of a Simple Digital Surface–Climate Simulator

Abstract A digital equilibrium temperature model for the simulation of the diurnal surface thermal and energy transfer regimes is presented together with a discussion of the modifications, necessary to achieve realistic simulations and numerical stability. In addition, application examples and the details of the convergence tests at point and areal scales are presented.

Detection of nonconductive heat transport in soils using spectral analysis

Variance spectra were generated for three high-frequency near-surface soil temperature time series representative of soil conditions typically encountered in temperate regions: saturation, strong evaporation, and soil frost penetration. For the latter two conditions, a surrogate measure of the soil water ionic concentration was also obtained and variance spectra were calculated. In a purely conductive system of multiday duration, maximum thermal variance should occur at a wavelength of 1 day and should decrease with depth. During ground saturation, when the pores are occupied by water, this pattern is observed. However, a spectral power density peak is observed in the subditirnal and subhourly range coincident with surface evaporation or freezing. In addition, the ionic concentration of soil water at depth is strongly coupled to temperature variations at the surface. These patterns are atypical of conductive systems and suggest the operation of nonconductive heat transfer processes, particularly water advection, phase transformations of water, and high-velocity internal distillation.

ANTHROPOGENIC GEOMORPHOLOGY IN NORTHERN ALASKA

Two classes of anthropogenic landforms can be recognized in the permafrost environment of northern Alaska. Primary anthropogenic landforms result from the operation of natural geomorphic processes on man-made features such as roads or gravel berms. Secondary anthropogenic forms are identical to natural geomorphic features, but evolve as indirect consequences of human actions. The first group is illustrated by a badly thermokarsted road, which has caused serious drainage disruptions likely to persist over a long time period. Secondary forms are exemplified by fields of palsa-like features, which are common where pipeline-related construction activities or structures cause shallow ponding. Because they evolve rapidly, anthropogenic permafrost landforms can provide great insight into the development of natural periglacial features.

NIGHT-FROST MODULATION OF NEAR-SURFACE SOIL-WATER ION CONCENTRATION AND THERMAL FIELDS

The modulation of the soil-water ion concentration and thermal fields resulting from night frost is illustrated with data from temperature-electric potential probes in the upper 15 cm of a sandy loam soil. The relative soil-water ion concentration, calculated from soil electric potential observations, aids in the detection of these modulation effects produced by non-conductive heat-mass transfer processes. The apparent thermal diffusivity, calculated from soil-temperature data, further facilitates the detection and analysis of these non-conductive processes. This new technology demonstrates the distorting effects of soil-water advection to the freezing zone, “ice purification” of soil water in the freezing zone and other coupled mass-heat transport effects produced by night frost. The conversion of electric potential observations to a relative index of soil-water ion concentration and the calculation of the apparent thermal diffusivity from the temperature data matrix are demonstrated as effective methods...

The soil electric potential signature of summer drought

SummaryDuring the period from late April to early August, a timeseries of soil electric potential measurements in the upper 15 cm of mineral soil were collected daily at the University of Michigan Botanical Gardens using an automatic data collection system. These data, after conversion to a surrogate measure of electrolyte concentration, provide a unique record of the 1988 summer drought in a continental location. The effects of rainfall-dewfall electrolyte dilution, evaporation-induced electrolyte concentration and upward-downward soil water advection are well-illustrated in the data. These observations demonstrate that soil electric potential is an easily measured variable of high information content, especially when collected with other system-linked environmental data.

Soil temperature and electric potential during diurnal and seasonal freeze-thaw

Abstract Combined measurements of soil temperature and electric potential in the upper 15 cm of a glacial sandy-loam soil were made during the winters of 1986–1987 and 19871988 at the University of Michigan Botanical Gardens using an electronic data acquisition system at frequencies varying from 10 min to daily (midnight). Most of the data was collected at hourly intervals. Analysis of temperature-potential time series at two locations with probes at (0, 3, 6, 9) and (0, 5, 10, 15) cm depths indicated that the variation of electric potential relative to the potential of a 1.5 m ground spike could be interpreted as the response of an electrolytic concentration cell without transference formed by a probe and the ground spike. As the electrolyte concentration is much greater at the ground spike, and electric potential varies inversely with concentration, the potentials at the soil probes varied over the range of approximately 300–700 mV in a manner consistent with the behavior of a concentration cell. The rapid and systematic pattern of potential variation during freeze-thaw events demonstrates that the effects of electrolyte concentration and dilution are products of evaporation-distillation, the melting of frost-purified ice, soil water advection to the freezing-evaporating region, concentrated electrolyte expulsion from the freezing region and the infiltration of rain and snow melt waters.

A Reconnaissance Experiment in Mapping and Modeling the Effect of Land Use on Urban Thermal Regimes

Abstract A simple digital climate simulator was modified for the simulation of land-use-de-pendent surface thermal contrast in urban terrain. The simulations were tested using thermal maps acquired at 1144 and 0252 EST over Ann Arbor, Mich. These maps were sampled to assign mean temperatures to four terrain blocks (i.e., farmland, city center, new subdivisions,, and old residential). It was discovered that the relative thermal rank (hot to cold) was correctly evaluated by the simulator at the test periods and the largest relative simulation error was only 13% of the diurnal thermal range at these times.

A study of time dependence during serial needle ice events

SummarySoil surface temperature, net radiation and soil heave data during a series of eleven consecutive needle ice growth-melt cycles at Vancouver, Canada, were studied using computer-graphic techniques. A method of analyzing the morphologic evolution of a needle growth using surface temperature and soil heave data is presented. Lastly, an atmospheric-geomorphic correlation matrix derived partially from the analysis of surface temperature-heave data is used to highlight the importance of afternoon evaporation in determining the course of an individual needle ice event within an event series.ZusammenfassungBodentemperatur, Strahlungsbilanz und Bodenbewegungsdaten aus Vancouver, Kanada, werden für eine Serie von elf aufeinanderfolgenden Wachstums- und Schmelzzyklen von Eisnadeln graphisch wiedergegeben. Eine Methode zur Analyse der morphologischen Entwicklung des Nadelwachstums mit Hilfe von Bodentemperaturen und Bodenbewegungsdaten wird beschrieben. Schießlich wird eine Korrelationsmatrize zwischen atmosphärischen und geomorphologischen Daten teilweise aus den Daten der Bodentemperatur und Bodenbewegung abgeleitet und dazu benützt, die Bedeutung der Verdunstung am Nachmittag für den Verlauf der Nadelbildung innerhalb der beschriebenen Serie zu demonstrieren.

A simulation model of river ice cover thermodynamics

Abstract A model of ice cover thermodynamics was used to simulate ice growth and decay along the international section of the St. Lawrence River for winter 1980–1981. This winter was chosen because of the exceptionally cold weather in December and January, and because of the abnormally warm air temperatures during the second half of February. At the air-ice interface, the model computes the surface energy transfer components and a resulting equilibrium surface temperature. At the lower boundary, an empirical algorith simulates the turbulent transfer of heat from the water. Within the ice, and implicit numerical solution to the general heat diffusion equation is used, permitting stable solutions for a variety of time intervals and node distances within the model. The model was used to simulate ice growth and decay at five sites characterized by their flow velocity, the date of ice-cover formation, and the water temperature regime. The model adequately represented growth rates at all five sites, but produced decay rates slower than those observed. Simulated breakup was 1–7 days later than observed, presumably because mechanical weakening of the ice was not taken into consideration. During the growth period, the model is far more sensitive to the values assigned to ice properties than it is to the error range in the meteorological variables. During the breakup period, the most sensitive boundary variable is water temperature.