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The frost table depth is a critical state variable for hydrological modelling in cold regions as frozen ground controls runoff generation, subsurface water storage and the permafrost regime. Calculation of the frost table depth is typically performed using a modified version of the Stefan equation, which is driven with the ground surface temperature. Ground surface temperatures have usually been estimated as linear functions of air temperature, referred to as ‘n-factors’ in permafrost studies. However, these linear functions perform poorly early in the thaw season and vary widely with slope, aspect and vegetation cover, requiring site-specific calibration. In order to improve estimation of the ground surface temperature and avoid site-specific calibration, an empirical radiative–conductive–convective (RCC) approach is proposed that uses air temperature, net radiation and antecedent frost table position as driving variables. The RCC algorithm was developed from forested and open sites on the eastern slope of the Coastal Mountains in southern Yukon, Canada, and tested at a high-altitude site in the Canadian Rockies, and a peatland in the southern Northwest Territories. The RCC approach performed well in a variety of land types without any local calibration and particularly improved estimation of ground temperature compared with linear functions during the first month of the thaw season, with mean absolute errors

Automated monitoring that combines time-lapse photography and sensor-based data logging can elucidate the environmental conditions, processes and rates of soil movement on remote periglacial hillslopes. This study presents the results from 5 years of time-lapse photography of soil movements, supported by time series data on frost heave, soil temperature, soil moisture and surface weather, on an alpine stone-banked lobe subject to frequent diurnal freeze-thaw cycles and deep seasonal frost on Mt Ainodake in the Japanese Alps. The lobe is dominated by biannual shallow soil movements, mostly originating from diurnal frost heave by needle ice or shallow ice lens formation and approximated by potential frost creep. The surface velocity shows a small interannual variation mainly reflecting snow conditions that control the spatio-temporal variability of freeze-thaw action, while it is independent of mean annual air temperature that influences the intensity of seasonal freezing. Occasional rill erosion occurs when the topmost frozen soil is rapidly thawed and super-saturated by intensive rainfall during seasonal thawing periods. Copyright © 2014 John Wiley & Sons, Ltd.

The dynamics of stone-banked lobes were investigated by monitoring soil movements and environmental parameters over 14 years on a limestone slope subject to deep seasonal frost. The monitored parameters included downslope soil movement, frost heave, soil temperature, moisture and snow depth. Despite being composed of the same soil, lobes on the upper slope (∼20°) display pressure ridges on the tread and terminate in a high riser (∼1 m), whereas lobes on the lower slope (∼10°) have a flat tread and a low riser (∼0.5 m). The long-term monitoring demonstrates that gelifluction, resulting from seasonal frost heave of approximately 5 cm and thaw settlement, occurs annually in the lower lobes at a mean surface rate of 4 cm a−1 and with a movement base at approximately 40-cm depth. The rate of gelifluction shows some interannual fluctuation depending primarily on the annual frost heave amount, but overall regularity of the rate and depth of movement regardless of seasonal frost depth results in lobes having similar morphologies. On the upper, steeper lobes located just below late-lying snow patches, rapid, shallow mudflows (∼20 cm thick) are often superimposed on gelifluction. The rate of surface movement varies spatially, in places exceeding 2 m per event. The prolonged water supply and low consistency limits of the limestone soil favour mudflows on seasonal thawing. The transported sediments pile up near the lobe front, resulting in a high riser. Such modification of solifluction lobes by mudflows can occur in other slopes with similar gradients, soils, frost and snow conditions. Copyright © 2010 John Wiley & Sons, Ltd.

The depth of soil frost is decreasing in cold regions around the world as a result of climate warming. To evaluate the potential impacts of the reduction in frost depth on the hydrologic cycle, it is necessary to understand snowmelt infiltration processes in frozen soils. A field study was conducted at an agricultural site characterized by volcanic ash soil in Tokachi, Hokkaido, Japan, where frost depths have decreased significantly in the last 20 yr. Soil temperature, water content, matric potential, snow cover, and meteorological parameters were monitored to quantify snowmelt infiltration flux for four winters that had different snow and soil conditions. When snowmelt began, the soil frost was 0.1 to 0.2 m thick in two winters and was absent in two other winters, providing a unique opportunity to compare snowmelt infiltration under frozen and unfrozen conditions. Most of the snowmelt water infiltrated into the soil under both frozen and unfrozen conditions, indicating that the frozen soil layer did not impede infiltration. The lack of flow impedance in the frozen soil was partly due to relatively high air temperature and an absence of freeze-back events during the snowmelt period. Furthermore, the temperature of the frozen soil layer was close to 0°C when the melt started, meaning that very little meltwater refroze in the soil before the temperature reached 0°C. The thick (>1 m) snow cover insulated the soil surface, allowing the frozen soil layer to warm up with the upward conduction of heat from the unfrozen layer below. These results indicate the importance of the interaction between snow cover and soil, which can be significantly affected by climate change.

This paper reviews frost-weathering studies in the last five years and proposes key questions to be answered. New techniques have enabled us to monitor moisture contents and crack movements in near-surface hard jointed bedrock and to evaluate seasonal rockfall activity in high mountains. Field monitoring has highlighted the roles of diurnal and annual frost cycles in controlling the timing and magnitude of frost weathering. In the laboratory, bidirectional freezing in soft, porous rocks has produced fractures containing segregated ice layers near the permafrost table, which imply the development of ice-filled fractures in permafrost bedrock over long time-scales. This finding, combined with numerical modelling of the thermal regime in permafrost rock slopes, contributes to the prediction of large-scale rockfalls and rock avalanches triggered by permafrost degradation. Future studies should also focus on explosive shattering, frost weathering of hard-intact rocks, field monitoring of ice segregation and bedrock heave, and the role of frost weathering in landscape evolution.

Hillslope runoff in permafrost regions covered by organic soil is strongly influenced by subsurface flow in the active layer, as well as surface flow where the active layer is very shallow. Flow rates in the organic-rich active layer are strongly dependent on the depth to the thawing front (i.e. frost table) and the corresponding soil hydraulic conductivity at that depth. Therefore, hydrological models for permafrost terrains need to simulate the thawing of the active layer accurately. In order to simulate the downward movement of the frost table, a simple heat-conduction model was proposed and compared to field data from a wet, organic-covered watershed in a discontinuous permafrost region of Canada. Ground heat flux was measured simultaneously using the calorimetric, gradient, and flux-plate methods to increase the confidence in data sets. The majority (>86%) of ground heat flux was used to melt the ice in frozen soil, and the soil temperature had a linear profile from the ground surface to the frost table when averaged over several days. Assuming a linear temperature profile, the proposed method calculates the daily rate of thawing from ground surface temperature and bulk thermal conductivity, where the latter is essentially determined by soil water content. Simulated depths to the frost table during three thaw seasons (2003-2005) matched closely with the observed data for two contrasting ground-cover types with distinctly different thaw rates. The method can be easily implemented in hydrological models, and will provide a useful tool for simulating hillslope drainage in organic-covered permafrost terrains, and for evaluating the effects of topography and land cover on the temporal and seasonal variability of the frost table.

Our aim is to measure and explain the seasonal changes in soil ice content in the frost boils of Galbraith Lake, Alaska. Instruments were installed in a frost boil to monitor the ground surface position and soil state over a period of 4 years. By comparing the subsidence and thaw rates, we calculate the soil ice content as a function of depth. Measured soil temperatures, liquid water contents and bulk apparent thermal conductivities are used to estimate latent heat production and release in the soil. The frost boil heaves during freezing and settles during thaw while the surrounding tundra heaves negligibly, but subsides measurably. Despite large changes in freezing rates from year to year, total heave and its distribution across the frost boil are similar between years. Winter air temperature and snow depth influence the freezing rate and ice distribution as a function of depth, but not the overall heave. This suggests that heave is controlled by water availability rather than the rate of heat removal from the soil. Areal ground subsidence rates between 2 and 5 cm/yr are due to the disappearance of ice at the base of the active layer, raising the possibility of ongoing thermokarst expansion around Galbraith Lake.

It is argued that the assumption of negligible temperature gradients across the thickness in blown film extrusion is not valid in the vicinity of the die exit. Numerical simulation of heat transfer involving convection and radiation shows significant temperature differences between the inside and outside film surfaces, which gradually decrease and eventually become negligible near the frost line. The differences are influenced by the magnitude of local heat transfer coefficients. In blown film lines having internal bubble cooling (IBC), temperature gradients in the thickness direction may be reduced, but still they cannot be considered negligible for typical production rates. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24:83–90, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20039

Frost boils in northern Alaska vary from large, 2–3-m diameter, barren non-sorted circles to completely vegetated hummocks. Summer warmth increases southwards from the coast. Average thaw-layer thickness shows the opposite trend. Frost heave shows no trend along the climate gradient but is affected by soil texture. Heave is greatest on frost boils with fine-grained sediments. Biomass increases from 183 g m � 2 at the coast to 813 g m � 2 in the Arctic Foothills. An aggrading permafrost table is evident in most of the frost-boil soil profiles, indicating that, over time, accumulation of plant biomass leads to reduced thaw-layer thickness. A conceptual model suggests how vegetation affects the morphology of patterned ground forms. In the coldest parts of the High Arctic well-developed frost boils do not form and there is little vegetation on frost boils or the inter-boil areas. In the warmest parts of the Low Arctic, vegetation is usually sufficient to stabilize the frost boil soils. Frost boils play an important role in Arctic ecosystems functions, including the flux of trace gases to the atmosphere, flux of water and nutrients to streams, and the recycling of important nutrients to wildlife populations. Copyright # 2004 John Wiley & Sons, Ltd.

In this paper, the performance of a new in-line scanning camera system for the study of various bubble instabilities in film blowing extrusion is critically evaluated. Three commercial film-grade polyethylenes. LmPE, LLDPE and LDPE, were used to generate the bubble instabilities. Reliable and objective criteria for differentiating various bubble instabilities such as draw resonance, helicoidal instability, and frost line height instability are proposed by using the new device. Detailed dynamics of each bubble instability was carefully investigated as a function of time in a broad range of the take-up ratio (TUR), blow-up ratio (BUR) and frost line height (FLH). In addition, effects of melt temperature and mass flow rates on dynamics of the bubble instabilities are discussed. It was found that the new system could capture the main characteristics of ail bubble instabilities quantitatively. It was also found that magnitude and periodicity of radius variation during draw resonance of LmPE decreased as TUR increased at constant FLH and BUR. This implies that the origin of draw resonance in film blowing seems to be different from that observed in fiber spinning. In the case of helicoidal instability, eccentricity, which defmes the deviation of the bubble center from the die center, decreased as TUR increased. However, the bubble could not be stabilized as expected. A graphical quantification approach to determine the stable zone in the bubble stability map is also discussed.

Radiation frosts during clear and calm weather can damage crops in the growing season. In complex topography, large spatial variations in near surface temperatures occur, which makes it more difficult to predict frost events and plan preventive actions. One approach followed in this study is to embark on detailed measurements of temperatures at high spatial and temporal resolution. Data were collected in a small vineyard (0.5 km2) in north-eastern Tasmania, Australia. Mobile measurements were used to register temperatures five times each night at two levels. A digital elevation model and a GIS (geographical information system) were used to create descriptive landscape parameters. Multiple linear regression was used to model temperatures and cooling rates as a function of topography. Between 50% and 60% of the variation in temperature was explained by the model. Variability in cooling rates was more difficult to describe. The efficiency of using wind machines for frost prevention was studied during one night. Due to topography, they were only efficient in parts of the property that were higher than the fans. At lower elevations, ground frost was not prevented. Proper location of wind machines is therefore important.

The effect of soil frost on runoff was investigated using a comprehensive data set collected at the Svartberget Experimental Forest, near Vindeln, Vasterbotten in northern Sweden. Measurements of snow depth, soil temperature, frost depth and other climate parameters have been made at three sites since 1981, as part of a long-term climate monitoring programme. Simulation residuals from the HBV rainfall-runoff model, in which no effect of soil frost is assumed, were compared with 16 years of measured soil frost conditions. A simple model for simulation of soil frost depth was developed and incorporated into the HBV model. The model parameters were calibrated to observations of snow depth, soil frost depth, groundwater levels and runoff, by use of a simple weighted optimization criterion. No clear effect of soil frost could be seen on the timing and magnitude of runoff in this analysis, or when analysing data on the conservative oxygen isotope O-18. The soil at the forested site froze in only slightly more than half the years, despite the high latitude and low winter temperatures. Furthermore, the soil had often thawed before the start of the spring flood. Almost all spring floods, therefore, occurred when the soil was unfrozen. Snow depth and soil frost depths were inversely related, with the deepest soil frost during winters with little snow. Soil frost therefore is unlikely to aggravate the very high floods in forested basins of this type, except perhaps under exceptional circumstances such as large rain events on frozen ground. Copyright (C) 2002 John Wiley Sons, Ltd.

Ground water and surface water interaction in the prairie pothole region of the United States and Canada is seasonally dominated by the presence of thick, frozen soil layers that affect infiltration. During a spring thaw, the subsoil may remain frozen, preventing infiltration. The impact of the frozen soil layer on the timing of infiltration of depressional-focused recharge to the ground water is not clearly understood. The objective of this paper is to relate changes in the water table during spring to changes in frost depth and soil water content. A depression and adjacent upland study site were instrumented with CRREL-type frost tubes, neutron probe access tubes, and ground water monitoring wells. Increases in water table levels in a depression occurred before the frost layer decomposed and infiltrating water quickly formed a recharge mound. Water table responses at the upland site took place as two events. The first event was a gradual rise, probably caused by the lateral dissemination of the recharge mound. The second rise was a rapid rise coinciding with the decomposition of the soil frost layer. Because of the accumulation of surface water in depressions, agricultural practices that remove water from a field can affect water resources management by limiting the addition of water recharge to unconfmed ground water.

Bubble instabilities observed in film blowing using four different polyolefins are discussed: high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and polypropylene (PP). Special attention is given to the effect of the frost line height on the bubble stability, an effect mostly ignored in the literature. A video-camera system was used to record the bubble shape and oscillations. In general, three forms of instabilities and combinations were observed: (1) axisymmetric periodic variations in the bubble diameter; (2) helical motions of the bubble; and (3) variations in the position of the solidification line. The four resins show different stability behaviors. The LDPE has the most stable operating space and the PP is the most unstable one. No correlation was observed between bubble stability and oscillatory shear rheological properties of the resins. Instability is enhanced by increasing take-up ratio, increasing blow-up ratio, and decreasing frost line height. Furthermore, for the LDPE, some operating points were not attainable and multiple steady states were observed. Our results are in a poor agreement with the predictions Cain and Denn's 1988 analysis.

Rock temperatures were monitored for a year at two alpine rockwalls in the Akaishi Range, Japan, where permafrost is absent. Diurnal frost and thaw penetration depths were evaluated from subsurface isotherms drawn on the basis of the temperature records at 0, 10 and 40 cm depths. The surface of the rockwalls experienced more than 100 diurnal freeze-thaw cycles, most of which accompanied a frost or thaw penetration shallower than 50 cm, and several long duration cycles with deeper frost or thaw penetration. Theoretical frost and thaw depths were also calculated by incorporating the surface freezing indices into the modified Berggren equation, the results from which were then compared with the actual values. The modified Berggren equation provided values that showed a strong correlation with observed depths, despite somewhat underestimating the actual values. Using the modified Berggren equation, the seasonal frost depth in the observed winter was estimated to be about 4·5 m. The frost and thaw depths are considered to give the maximum estimation of the depth to which frost-induced cracking can propagate in the bedrock.

Long-term data from the Hubbard Brook Experimental Forest in New Hampshire show that air temperature has increased by about 1 °C over the last half century. The warmer climate has caused significant declines in snow depth, snow water equivalent and snow cover duration. Paradoxically, it has been suggested that warmer air temperatures may result in colder soils and more soil frost, as warming leads to a reduction in snow cover insulating soils during winter. Hubbard Brook has one of the longest records of direct field measurements of soil frost in the United States. Historical records show no long-term trends in maximum annual frost depth, which is possibly confounded by high interannual variability and infrequency of major soil frost events. As a complement to field measurements, soil frost can be modelled reliably using knowledge of the physics of energy and water transfer. We simulated soil freezing and thawing to the year 2100 using a soil energy and water balance model driven by statistically downscaled climate change projections from three atmosphere-ocean general circulation models under two emission scenarios. Results indicated no major changes in maximum annual frost depth and only a slight increase in number of freeze-thaw events. The most important change suggested by the model is a decline in the number of days with soil frost, stemming from a concurrent decline in the number of snow-covered days. This shortening of the frost-covered period has important implications for forest ecosystem processes such as tree phenology and growth, hydrological flowpaths during winter, and biogeochemical processes in soil.

The melt strength method is analyzed in terms of its ability to predict the axial stress levels found in tubular film extrusion of low density polyethylene. For certain values of the capillary L/D, the level of axial stresses and average Newtonian viscosity found in the filament stretching and film blowing are comparable at the same draw ratio. The elongation to break of the finished film was found to be primarily determined by the axial stress during the film blowing, at constant frost line height.

An extensive experimental study of the effect of processing and resin variables on the light transmission of polypropylene tubular blown film is reported. The resin variables investigated include melt flow rate (average molecular weight), molecular weight distribution, and the addition of a nucleating agent. Processing variables studied include blow-up and draw down ratios, and frost line height (cooling rate). Increasing the draw down and blowup ratios and decreasing the frost line height generally lead to increased light transmission. Decreasing the resin melt flow rate, narrowing the molecular weight distribution, and the addition of a nucleating agent also improve light transmission. The overall light transmission properties of the films are dominated by their surface roughness characteristics, while the internal morphology of the films plays a secondary role. The changes in light transmission of the films in response to changes in processing or resin variables were traced to their effect on the surface texture and internal morphology.

A video camera tracer technique (T. A. Huang and G. A. Campbell, paper to be presented at ANTEC '85, Washington, D. C.) was used to obtain MD velocity profile and bubble shape above the air ring under industrial film blowing conditions. Subsequently, the velocity profile and bubble shape were utilized to calculate strain and strain rate histories for a fluid element before it solidified. The deformational history of a fluid element was compared between LDPE and LLDPE of similar melt index and density. Also, the study was extended to two groups of LLDPE/LDPE blends: blends rich in LLDPE and blends rich in LDPE. We used a 100-mil die gap for extruding resins rich in LLDPE to avoid melt fracture. A 30-mil die gap was used to process blends that were rich in LDPE. Under the same film blowing conditions and frost line height, LDPE exhibits higher peak strain rates than LLDPE and the peak strain rates for LDPE occur closer to the air ring. Moreover, the MD strain of LLDPE continues to increase above the frost line. Conversely, the MD strain profile of LDPE levels off quickly before the frost line. The observed differences in fluid element deformation between LLDPE and LDPE on the blown film line are attributed to the higher melt tension of LDPE. For LLDPE, a 10 wt % LDPE addition causes a significant increase in strain and strain rate at lower positions. Interestingly, a further addition up to 25 wt % LDPE causes little or no further change in deformational history. The increased strain rates associated with an increased strain results in a stabilized LLDPE bubble. For LDPE, only slight differences in strain and strain histories were observed with the addition of LLDPE up to 25%.

DETAILED account of the lowering of cast-iron pipes under pressure will first be given as an outline of the operation as a whole, and then the author will cover several additional points which he has found important. In this outline an effort has been made to cover all situations which may arise in such operations. As the reader may have guessed, the operation is a rare one, for there are only a few reasons why, or occasions when, it would be necessary to resort to it. If it is at all convenient, the pressure should be turned off when the pipe is being lowered, but often or, in fact, usually, the pipe with which one must work supplies a town. Shutting it off, therefore, would entail considerable inconvenience; and fire hazards might even make it impracticable. The situations that would force one to lower the pipe are also few in number, the most common being where a pipe is exposed or left with so little cover, e.g. from the regrading of a road, as to be unsafe, and must be lowered enough to make it safe from mechanical shocks. Such a grading may be only a slight one, but one which is necessary to get it below the frost line. A second situation is that when a new sewer line or culvert crosses the water pipes. As the sewer line must be laid to an established grade, it is usually given the right of way so the water pipe must be lowered. Let us assume that such a situation has arisen. In starting the job, the lowest point on which the pipe will finally rest must be determined. It is obvious that this depth is merely the depth of the grading or the necessary amount to allow the sewer's clearance, as the case may be.

It is shown that freezing of columns of moist soil that lack an external source of water may or may not produce frost heaving. In either case, the frozen soil imbibes liquid water from the unfrozen soil and induces hydraulic flow of water toward the sites of ice formation. Thermal water transport is inconsequential. Heaving occurs whenever and wherever the frozen soil becomes virtually saturated with ice and may be accompanied by the formation of air-filled voids. /S.S.S. AM.PROC./