55933954
A theory for the scalar roughness and the scalar transfer coefficients over snow and sea ice
Although the bulk aerodynamic transfer coefficients for sensible (CH) and latent (CE) heat over snow and sea ice surfaces are necessary for accurately modeling the surface energy budget, they have been measured rarely. This paper, therefore, presents a theoretical model that predicts neutral-stability values of CH and CE as functions of the wind speed and a surface roughness parameter. The crux of the model is establishing the interfacial sublayer profiles of the scalars, temperature and water vapor, over aerodynamically smooth and rough surfaces on the basis of a surface-renewal model in which turbulent eddies continually scour the surface, transferring scalar contaminants across the interface by molecular diffusion. Matching these interfacial sublayer profiles with the semi-logarithmic inertial sublayer profiles yields the roughness lengths for temperature and water vapor. When coupled with a model for the drag coefficient over snow and sea ice based on actual measurements, these roughness lengths lead to the transfer coefficients. CE is always a few percent larger than CH. Both decrease monotonically with increasing wind speed for speeds above 1 m s−1, and both increase at all wind speeds as the surface gets rougher. Both, nevertheless, are almost always between 1.0 × 10−3 and 1.5 × 10−3.
131236488
Sensible and Latent Heat Flux Measurements over the Ocean
Abstract This papar presents an extensive act of sensible heat (Reynolds flux and dissipation methods) and latent heat (dissipation method) flux measurements from a stable deep water tower and from ships on the deep sea. Operational difficulties associated with ship spray and flow distortion and with sensor calibration, response and contamination are discussed. The influence of atmospheric stability on the dissipation measurements and the bulk transfer coefficients is considered and a parameterization of Z/ L in terms of wind speed and the sea-air potential temperature difference is found to be adequate. Temperature variances, Stanton numbers and w–t cospectra from the Roynolds flux measurements are compared to previous results. The dissipation method is shown to be a viable means of measuring the heal fluxes over the deep sea by comparison with simultaneous Reynolds flux measurements, using our data for the sensible heat and the data of others for the latent heat. The neutral drag coefficient at 10 m hei...
130362232
Bulk Transfer Coefficients for Heat and Momentum over Leads and Polynyas
Abstract Leads and polynyas are areas of open water surrounded by pack ice. In winter, when the polar oceans have extensive ice covers and the water-air temperature difference is typically 20°–40°C, they allow enormous amounts of sensible and latent heat to escaoe from the ocean to the atmosphere. Parameterizing these fluxes accurately is thus an important part of modeling the growth and decay of sea ice. To develop a unified method for parameterizing the turbulent transfer from open water surrounded by pack ice, we have reanalyzed data reported in the literature on momentum and heat transfer over Arctic leads and polynyas. The neutral stability value of the 10-m drag coefficient, CDN10 = 1.49×10−1, is independent of wind speed and open-water fetch for winds from 1 to 10 m s−1 and fetches from 7 to 500 m. That value is slightly higher than values typical of the open ocean at these wind speed probably because of the form drag over the upwind ice or at the ice edges and because the wave field is still activ...
120795804
Flux-Profile Relationships in the Atmospheric Surface Layer
Abstract Wind and temperature profiles for a wide range of stability conditions have been analyzed in the context of Monin-Obukhov similarity theory. Direct measurements of heat and momentum fluxes enabled determination of the Obukhov length L, a key independent variable in the steady-state, horizontally homogeneous, atmospheric surface layer. The free constants in several interpolation formulas can be adjusted to give excellent fits to the wind and temperature gradient data. The behavior of the gradients under neutral conditions is unusual, however, and indicates that von Karman's constant is ∼0.35, rather than 0.40 as usually assumed, and that the ratio of eddy diffusivities for heat and momentum at neutrality is ∼1.35, compared to the often-suggested value of 1.0. The gradient Richardson number, computed from the profiles, and the Obukhov stability parameter z/L, computed from the measured fluxes, are found to be related approximately linearly under unstable conditions. For stable conditions the Richar...
120235134
Bulk transfer coefficient over a snow surface
The drag coefficient CDand the bulk transfer coefficient for sensible heat CHover a flat snow surface were determined experimentally. Theoretical considerations reveal that CDdepends on the friction velocity u* as well as on the geometrical roughness h of the snow surface. It is found that CDincreases with increasing u* and/or h. The dependency of CHon u* and h is so small that it is possible to consider CHas a constant for practical purposes: CH, 1= 2.0 × 10−3 for a reference height of 1 m. The bulk transfer coefficient for water vapor is estimated at CE, 1= 2.1 × 10−3 for a reference height of 1 m.
129186254
Contribution of form drag on pressure ridges to the air stress on Arctic ice
Various methods of measuring air stress on the arctic ice surface are discussed; however, none of them could possibly take into account the form drag due to pressure ridges. An expression is derived for the form drag per unit area in terms of certain key parameters of ridge statistics and a suitable drag coefficient. By using the available field and laboratory measurements of these parameters an estimate is made of the ratio of the form drag to the frictional stress. It depends on the geographical location in the Arctic, the season of the year, and the meteorological conditions in the atmospheric surface layer. It is found, contrary to the common assumption, that the form drag on pressure ridges may be much larger than the frictional stress on the ice surface, especially under stably stratified conditions.
130203617
A drag partition theory for determining the large-scale roughness parameter and wind stress on the Arctic pack ice
A simple drag partition theory is developed for the classical problem of boundary layer flows over regular arrays of two- or three-dimensional roughness elements. The theoretical expression for the ratio of the form drag on these elements to the total drag is shown to be in good agreement with wind tunnel observations. It is used for determining the contribution of form drag on pressure ridges to the total wind stress on the arctic pack ice. The theory also leads to an expression for the large-scale roughness parameter as a function of mean ridge height, ridging intensity, small-scale or local roughness parameter, and an average form drag coefficient. It is required for determining the average wind stress over large areas of the Arctic on a routine basis, using the so-called geostrophic drag method, as envisaged in the Aidjex program.
120915665
Atmospheric turbulent fluxes over snow
On March 26, 1971, eddy fluxes of momentum, sensible heat and water vapour were measured over Lake Mendota, Wisconsin, U.S.A., which was covered by an extensive snowfall. An evaporation rate of about 0.7mm day−1 (2.2 mW cm−2) was detected. Wind speeds were light and the atmosphere near the surface was highly stable. In these conditions, the average sensible heat transfer and Reynolds stress were -0.9 mW cm−2 and 0.10 dyn cm−2, respectively. Comparison with measured gradients of wind speed, temperature and humidity yield a drag coefficient of about 0.54 × 10−3, and bulk transfer coefficients for sensible and latent heat of 0.41 × 10−3 and 0.78 × 10−3, respectively, applied to 10-m data. When corrected for the effect of atmospheric stability, these three coefficients become (in the same order) 1.2 × 10−3, 0.9 × 10−3 and 2.5 × 10−3. The errors in these estimates are such that the drag coefficient is not significantly different from that corresponding to an aerodynamically smooth surface, while the heat coefficients are similar to those normally applied over liquid water surfaces.
129581534
Eddy correlation measurements of evaporation and sensible heat flux over Arctic Sea ice
A sonic anemometer, lyman alpha humidiometer, and thermistor thermometer were operated on ice at 75°N, 15°W in March-April 1972 as part of the Aidjex pilot study. Spectra of temperature and humidity fluctuations and cospectra for the sensible and latent heat fluxes were similar to those published for neutral conditions over sea and land. Bulk transfer coefficients were CT = 1.2 × 10−3 and CQ = 0.55 × 10−3, respectively. The Bowen ratio of sensible to latent heat fluxes ranged from 1 to 15 and can be obtained from values of the temperature and humidity spectra at low frequencies except when the latent heat flux is very small. These data were recorded at the spring equinox, and the dominant feature of the heat fluxes is their diurnal variation. Evaporation continued for several hours after the sensible heat flux changed to the downward direction. Over Robeson Channel in July 1972 the heat transfer coefficient was CT = 1.0 × 10−3 for stable conditions.
130681268
A large-scale numerical model of sea ice
Work at the National Center for Atmospheric Research has resulted in the construction of a large-scale sea ice model capable of coupling with atmospheric and oceanic models of comparable resolution. The sea ice model itself simulates the yearly cycle of ice in both the northern and the southern hemispheres. Horizontally, the resolution is approximately 200 km, while vertically the model includes four layers, ice, snow, ocean, and atmosphere. Both thermodynamic and dynamic processes are incorporated, the thermodynamics being based on energy balances at the various interfaces and the dynamics being based on the following five stresses: wind stress, water stress, Coriolis force, internal ice resistance, and the stress from the tilt of the sea surface. Although the ice within a given grid square is of uniform thickness, each square also has a variable percentage of its area assumed ice free. The model results produce a reasonable yearly cycle of sea ice thickness and extent in both the Arctic and the Antarctic. The arctic ice grows from a minimum in September, when the edge has retreated from most coastlines, to a maximum in March, when the ice has reached well into the Bering Sea, has blocked the north coast of Iceland, and has moved southward of the southernmost tip of Greenland. Maximum arctic thicknesses are close to 4 m. In the Antarctic the ice expands from a minimum in March to a maximum in late August, remaining close to the continent in the former month and extending northward of 60°S in the latter month. Maximum thicknesses are about 1.4 m. The distribution of modeled ice concentrations correctly reveals a more compact ice cover in the northern hemisphere than in the southern hemisphere. Modeled ice velocities obtain both the Beaufort Sea gyre and the Transpolar Drift Stream in the arctic summer as well as the Transpolar and East Greenland Drift streams in the winter. In the Antarctic, simulated velocities reveal predominantly westerly motion north of 58°S, with smaller-scale cyclonic motions closer to the continent.
140617156
Energy exchange over young sea ice in the central Arctic
A simple model of heat transport through young sea ice is combined with climatological data on air temperatures and incoming radiation in the central Arctic to predict how each component of the surface heat balance is affected by changes in ice thickness. Results indicate that during the cold months the net heat input to the atmosphere from ice in the 0- to 0.4-m range is between 1 and 2 orders of magnitude larger than that from perennial ice. Once the ice exceeds a meter in thickness, there is little change in any of the heat fluxes as the ice thickens. Although both the amount of absorbed shortwave radiation and the emitted longwave radiation depend on ice thickness, it is the turbulent fluxes which undergo the largest changes. The rate of heat exchange over thin ice is shown to be extremely sensitive to snow depth and assumed boundary layer temperatures. It is concluded that with the present ice thickness distribution in the central Arctic, total heat input to the atmospheric boundary layer from regions of young ice is equal to or greater than that from regions of open water or thick ice.
129785910
A theory for local evaporation (or heat transfer) from rough and smooth surfaces at ground level
A model proposed earlier (Brutsaert, 1965) for evaporation as a molecular diffusion process into a turbulent atmosphere is extended by joining it with the similarity models for turbulent transfer in the surface sublayer. The assumed mechanisms were suggested by available flow visualization studies near smooth and rough walls; the theoretical result is in good agreement with available experimental evidence. The important dimensionless parameters governing the phenomenon near the surface are the Dalton (or Stanton) number (i.e., mass transfer coefficient), the drag coefficient (u*2/U2), the roughness Reynolds number (u*z0/v) (except for smooth surfaces), and the Schmidt (or Prandtl) number (v/k). The proposed formulation allows the evaluation of the effects of some parameters, such as surface roughness or molecular diffusivity, that were hitherto not well understood. An important practical result is that in contrast to the drag coefficient, the Dalton number is relatively insensitive to changes in roughness length Z0.
124420731
Bulk Parameterization of Air-Sea Exchanges of Heat and Water Vapor Including the Molecular Constraints at the Interface
Abstract A model is developed for the marine atmospheric surface layer including the interfacial sublayers on both sides of the air-sea interface where molecular constraints on transports are important. Flux-profile relations which are based on the postulation of intermittent renewal of the surface fluid aye matched to the logarithmic profiles and compared with both field and laboratory measurements. These relations enable numerical determination of air-sea exchanges of momentum, heat and water vapor (or bulk transfer coefficients) employing the bulk parameters of mean wind speed, temperature and humidity at a certain height in the atmospheric surface layer, and the water temperature. With increasing wind speed, the flow goes from smooth to rough and the bulk transfer coefficient for momentum also increases. The increase in roughness is associated with increasing wave height which in the present model results in sheltering at the wave troughs. Due to the decrease in turbulent transports, the transfer coef...
120228434
Structural features of turbulent flow over smooth and rough boundaries
An experimental study of boundary-layer turbulence in a free surface channel flow is described. Attention is concentrated on the effects of different surface roughness conditions on the turbulence structure in the boundary region. Hydrogen bubble flow tracers and medium high-speed motion photography were used to obtain an instantaneous visual and quantitative description of the flow field. In particular it proved possible to record instantaneous longitudinal and vertical velocity profiles from which distributions of the instantaneous Reynolds stress contribution were computed. Two well-defined intermittent features of the flow structure were visually identified close to the boundary. These consisted of fluid ejection phases, previously reported by Kline et al. (1967) for smooth boundary flow, and fluid inrush phases. Conditional averaging of the instantaneous velocity data yielded quantitative confirmation that ejection phases corresponded with ejection of low momentum fluid outwards from the boundary whilst inrush phases were associated with the transport of high momentum fluid inwards towards the boundary. Inrush and ejection events were present irrespective of the surface roughness condition. Conditional averaging also indicated that both inrush and ejection sequences correlate with an extremely high contribution to Reynolds stress and hence turbulence production close to the boundary. Indeed the present results, taken with those from previous studies, suggest that turbulence production is dominated by the joint contribution from the inrush and ejection events. It is emphasized that these structural features are intermittent, forming important linked elements of a randomly repeating cycle of wall-region turbulence production which is apparently driven by some violent three-dimensional instability mechanism. Whilst the most coherent effects of the observed inrush phases appear to be mainly confined to a region close to the boundary, the influence of the ejection phases is far more extensive. The ejected low momentum fluid elements, drawn from the viscous sublayer and from between the interstices of the roughness elements, travel outwards from the boundary into the body of the flow and give rise to very large positive contributions to Reynolds stress at points remote from the boundary. This effect is sufficiently strong to prompt the suggestion that the ejection process could represent a universal and dominant mode of momentum transport outside the immediate wall region and possibly extending across the entire thickness of the boundary layer. A structural model based on the present observations is seen to exhibit consistency with many commonly visualized features and recorded average properties of turbulent boundary-layer flows in general.
121173097
Spectra of fluctuations in refractivity, temperature, humidity, and the temperature‐humidity cospectrum in the inertial and dissipation ranges
Recent theoretical and experimental advances have produced a model of the power spectrum of quantities mixed by turbulence. This model is applicable for arbitrary diffusivity and is thereby capable of predicting the high wavenumber shape of the spectra of refractivity, temperature, humidity, and the temperature-humidity cospectrum. Equations for the mean refractivity and the refractivity variance are formed from temperature, pressure, and humidity fluctuations; the accuracy of neglecting the higher-order terms in the fluctuations is determined. In order to apply the model power spectrum for temperature and humidity fluctuations in the atmosphere, it is first determined under what conditions temperature and humidity satisfy a simple continuity equation that balances temporal changes, advection, and diffusion. Experiments have shown that the temperature spectrum in air has a “bump” at high wave numbers. This feature is understood in terms of the theoretical model, and the bump is predicted to appear in the refractivity and humidity spectra and in the temperature-humidity cospectrum as well as in the temperature spectrum. The bump in the humidity spectrum is smaller than that in the temperature-humidity cospectrum, which is in turn smaller than the bump in the temperature spectrum; this effect is caused by the fact that the diffusivity of water vapor in air is slightly greater than that of heat in air. The shape of the refractivity spectrum depends on the relative contributions of the temperature spectrum, humidity spectrum, and temperature-humidity cospectrum. The refractivity spectrum can have an enhanced bump if the contribution of the temperature-humidity cospectrum is negative and nearly cancels the contributions of the temperature and humidity spectra. The impact of these developments on radio wave propagation is discussed.
128884795
Laboratory Studies of Evaporation and Energy Transfer Through a Wavy Air-Water Interface
Abstract Interfacial evaporation and energy flux are presented for a series of experiments in a laboratory wind wave flume (neutral stratification) with varying free stream velocity and with and without mechanically generated waves. Integral conservation or budget techniques are the means of flux determination. Fluxes normalized to a 6-cm height are independent of fetch, increase with wind speed, and decrease if mechanically generated waves are introduced. Excellent correspondence between normalized energy and mass transfer exists except for the case involving spray which causes a reduction in the thermal field.
122706446
Heat transfer across rough surfaces
It is argued that the heat transfer between a roughened surface and a stream of incompressible fluid flowing over it is dependent on both the viscosity and thermal conductivity of the fluid even when the roughness is large enough for viscosity to have ceased to affect the skin friction. Concentrating on closely spaced roughness, sufficiently large for the skin friction to be independent of Reynolds number, a simple model is constructed of the flow near the surface. It consists of horseshoe eddies which wrap themselves round the individual excrescences and trail unsteadily downstream; the eddies are imagined to scour the surface and thereby to transport heat between the surface and the more vigorous flow in the neighbourhood of the roughness crests. Taken in conjunction with Reynolds analogy between temperature and velocity distributions in the fluid away from the surface, the model leads to an expression for the rate of heat transfer which contains a function of the roughness Reynolds number and the Prandtl number of the fluid whose detailed form is found by appeal to the limited experimental data available. An order-of-magnitude argument suggests that the functional form established empirically is consistent with the assumed model of the flow close to the surface. The object of the work is to establish a basis for the analysis of experimental data and for their extrapolation with respect to Reynolds number and Prandtl number.
97905262
Transport of gases to and from grass and grass-like surfaces
A radioactive vapour of thorium-B (lead-212) has been used to measure the vertical flux of a gas to grass and similar surfaces in a wind tunnel, as a function of the difference in vapour concentration between the air and the surface. Experiments were done over a range of values of the parameters friction velocity (u) and roughness length (zo). The results have been analysed in term s of the reciprocal sublayer Stanton number B-1of Owen & Thomson (1963), which is a measure of the degree to which Reynolds’s analogy between transport of momentum and matter (or heat) breaks down at the surface. B-1 is equal to the difference between the dimensionless resistances of the boundary layer for momentum and for mass. Experiments with grass and other surfaces having roughness elements of a fibrous character gave values of B-1 in the range 6 to 12. Some variation of B-1 with u* was found, but less than expected from Owen & Thomson’s work. Little effect of variation in z0 was found. For values of u* and z0 applicable in normal conditions to vapour transport to or from short grass in the field, B-1 was found to equal 8 ± 1. Experiments with a surface of rough glass, having roughnesses of a pyramidal nature, confirmed Owen & Thomson’s results, and gave values of B-1 in the range 20 to 40. The dependence of B-1 on the shape of the roughness elements, suggested by Owen & Thomson, was strongly exhibited in the present work, and R~x cannot be considered to be a single function of the roughness Reynolds number u*z0/v. Comparative experiments were done on the rate of evaporation of water from two of the surfaces (artificial grass and towelling) used in the experiments with thorium-B, in order to obtain an estimate of the dependence of B-1 on the molecular properties of the vapour. The ratio of the molecular diffusivity of water vapour to that of thorium-B vapour is 4.4:1. The ratio of values of B-1 was found to be 1:1.6, with some variation according to the surface and the wind speed. Under average conditions of evaporation in the field, a value about 5 is suggested for B-1, but this may not apply for values of z0 outside the range of the experiments. The dimensionless resistance for momentum, between a height z1 and the surface, is and if z1 is of order 1 m, this term is several times larger than B-1. Since it is the sum of u1/u* and B-1 which enters into the formula for the rate of evaporation, it is sufficient to obtain B-1 to a moderate accuracy. The wetted artificial grass, subjected to forced evaporation in the wind tunnel, could be considered as a wet-bulb thermometer, and the surface temperature was found to approximate very closely to the wet-bulb temperature of the air, especially a t high wind speeds, when the transport of heat to the surface by radiation from above or conduction from below was relatively small. I t follows from this that the eddy diffusivities of heat and vapour in the boundary layer are equal, at least to within 10 %. Moreover the molecular diffusivity of water vapour is not very different from the thermometric conductivity of air at room temperature, and therefore nearly the same values of B-1 should apply to the transport of heat and water vapour. Temperature profiles obtained by Pasquill and Rider over short grassland at Cambridge are shown to give values of B-1 of 5.7 and 3.9, in good agreement with the results from the wind tunnel.
123541198
Vertical profiles of wind speed, snow concentration, and humidity in blowing snow
To estimate the sublimation rate of snow during relocation by wind, sizes and concentration of ice crystal fragments were measured at 6 levels in the lowest 1 m, during ten 10-min runs, in a nocturnal blizzard. Power-law functions of height described the decrease in mean particle diameter and concentration. The vertical gradient of water vapor, measured with a thermocouple psychrometer, was approximately linear from 0.2 to 1.0m above the surface. Evaporation of blowing snow over 3 km of transport distance was estimated to be 39% of transport rate, under conditions of the experiment.
122305794
The transfer of heat across a turbulent boundary layer at very high prandtl numbers
Abstract The paper considers a problem which was first treated mathematically by Lighthill in a different physical context. Solutions are provided for the limiting case of forced convection across a turbulent boundary layer when Pr →∞, i.e. when the thermal boundary layer is wholly confined within the laminar sublayer whose velocity profile is linear. The case of a flat plate with a uniform temperature or with one step in temperature is treated in great detail, and a convenient tabulation of formulae for a number of cases is provided. The case of a variable wall temperature is solved in two ways. First, the temperature distribution is replaced by a sequence of steps and superposition is used. Secondly, an exact analytic solution is given for the case when the temperature function consists of a step followed by a distribution given analytically. In the latter ease, closed-form equations are given for a polynomial temperature variation of which a linear temperature variation is a special case.
121872322
The Roughness Length for Water Vapor Sensible Heat, and Other Scalars.
Abstract An expression is presented for the roughness length of water vapor (or sensible heat, etc.) that is the surface value intercept of the straight line resulting from a semi-logarithmic plot of the mean specific humidity (or potential temperature, etc.) profile in the dynamic sublayer. The derivation is based on the standard assumption of continuity in the mean profile at the interface between the interfacial transfer sublayer and the fully turbulent surface sublayer. It is found that the resulting formulation yields similar results for a number of empirical and theoretical equations for the interfacial transfer that are available in the literature. The roughness length of any scalar admixture depends not only on the nature of the surface but also on the intensity of the surface shear stress and on the molecular diffusivity and the viscosity. In meteorological applications under rough flow conditions this roughness length may be considerably smaller than the aerodynamic roughness length Z0, whereas ...
109137280
A critical examination of the requirements for model simulation of wind-induced erosion/deposition phenomena such as snow drifting
Abstract This paper examines the requirements for correct model simulation, in wind tunnels, of wind-induced erosion and deposition phenomena such as snow drifting. The similarity analysis draws heavily on physical analysis of the saltation process and on experimental evidence. The important similarity criteria are identified and the limit above which the process is insensitive to Reynolds number is tentatively established. Modelling procedures, including a procedure for selecting model particles, are outlined. It will often be impracticable to simultaneously satisfy all the simulation requirements and the compromises involved in such cases are discussed. Simulation of these phenomena in water is shown to be inadvisable.
120125340
Air-sea bulk transfer coefficients in diabatic conditions
On the basis of recent data for the roughness Reynolds number of the sea surface, and using the Owen-Thomson theory on the transfers of heat and mass between a rough surface and the flow above it, the bulk transfer coefficients of the sea surface have been estimated. For a reference height of 10 m, the neutral-lapse transfer coefficient for water vapor is larger by only a few percent than that for sensible heat. When the wind speed at the 10-m height is u10>3 m s−1, the coefficient for sensible heat CH is larger by about 10% than that for momentum CD. For u10<5 m s−1, however, the value of CD exceeds the value of CH, and for u10=15 m s−1 it is shown that CH≈0.8CD. It may be also proposed that 103CD=1.11 to 1.70, 103CE=1.18 to 1.30, and 103CH=1.15 to 1.26 for a range of u10=4 to 20 m s−1. A plot of diabatic transfer coefficients versus wind speed is obtained by using a parameter of the sea-air temperature difference. For practical purposes, the coefficients are approximated by empirical formulae.
128572042
A new method of measuring the snow-surface temperature
Abstract Because a snow cover is so tenuous, measuring its surface temperature is not easy. The surface is illdefined and easily disturbed; invasive transducers commonly used for other surfaces are, thus, generally inappropriate for snow. We therefore describe a hygrometric method of measuring the snow-surface temperature. The advantages are that the method is non-invasive, that its accuracy depends only weakly on the surface structure, and that it is reliable even in bright sunlight. The key assumption is that the air at a snow surface is in saturation with the snow; the dew-point temperature of air right at the snow surface is thus the surface temperature. Consequently, under a fairly wide range of conditions we can, in effect, measure the surface temperature by measuring the dew-point temperature 10 cm above the surface. We develop a theoretical justification for the hygrometric measurement, discuss the meteorological parameters that affect the accuracy of the method, and compare hygrometer data with more traditional measurements.
128802491
The permeability of a melting snow cover
Data from snow lysimeters in California and Vermont are used to find the saturated permeability of a melting snow cover in the range of 10–40 × 10−10 m2 depending on snow density. The unsaturated permeability increases as about the third power of liquid saturation. The gravity flow theory is shown to be an accurate representation of meltwater drainage from snow covers in two diverse areas even though the snow covers are treated as homogeneous units. The variation of saturated permeability with snow density occurs about as predicted by Shimizu's formula for dry snow, although ice layers decrease the permeability somewhat.