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  • 1
    Call number: ZSP-202-74
    In: Research report / Cold Regions Research and Engineering Laboratory, 74
    Description / Table of Contents: Summary: The heat exchange of a snow cover was studied with respect to the effects of heat transfer processes on metamorphic action within the snow cover and the prediction of heat fluxes and the resulting changes in snow cover characteristics from standard meteorological information. Data collected at the USA SIPRE Keweenaw Field Station, Houghton, Michigan, were used to determine heat transfer by thermal radiation, convection, and conduction. The percent of daily incident solar radiation at the outer limits of the earth's atmosphere which reaches the snow surface ranged from 94 with clear skies to less than 20 with an overcast less than 1000 ft high and precipitation. Average diurnal patterns of total solar radiation may be estimated for various cloudiness. Total solar radiation with overcast clouds less than 5000 ft high averaged about 70% of the clear-sky radiation. Atmospheric radiation related to temperatures during clear nights gave a curve paralleling the black body radiation curve, although about 7 ly/hr lower in absolute values. Atmospheric radiation during clear skies was about 9 ly/hr less than that with low overcast conditions with no snow falling. In the presence of falling snow, total hemispherical radiation was about 5 ly/hr greater than with no snow falling but with' similar low overcast cloudiness. With low overcast cloudiness, the net long-wave exchange averaged about -17 ly/day in January and -8 ly/day in February. With clear skies the net long-wave exchange averaged about -128 ly/day in January and -120 ly/day in February. The net radiation exchange with clear skies during midday remained slightly negative in January and became increasingly positive through February. The highest positive values of net radiation occurred during the day with low overcast or broken cloudiness and precipitation. The largest net radiational loss of 9 ly/hr occurred at night with clear skies and nearly calm winds. The average magnitude of surface temperature inversions over snow was related to observations of cloudiness and wind speeds for both day and night. With winds of 12 knots or greater, the temperature difference in the first 10m was usually near adiabatic even with clear skies at night. During the day inversions seldom exceeded 1-2°C, and a slight lapse commonly occurred during low overcast conditions and moderate winds. The Liljequist method for computing turbulent heat transfer and conductive heat transfer in snow was used. Average air temperature is shown to exert a pronounced effect upon snow heat conduction, cold content and temperature profile. Average temperature differences through the snow, responsible for metamorphic action leading to the formation of depth hoar, can be estimated by a knowledge of the previous 20-hr average temperature. Snow hardness distributions, indicators of supporting capacity of snow, can be estimated graphically from snow density and depth observations.
    Type of Medium: Series available for loan
    Pages: v, 73 Seiten , Illustrationen
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory 74
    Language: English
    Note: CONTENTS Preface Summary Part 1. Data analysis Introduction Estimating snow temperature distributions from meteorological information Radiative heat transfer Short-wave radiation Long-wave radiation Net radiation exchange Convective heat transfer Liljequist method Monin-Obukhov method Conductive heat transfer Heat transfer in soil Heat transfer in snow Direct relationships Measurement of snow properties Cold content of snow Vertical temperature gradient in snow and its effects Snow hardness Summary of the analysis Thermal radiative heat transfer Convective heat transfer Heat transfer processes in soil and snow Part II. Tabulated data for Keweenaw Field Station Description of data Location and periods of measurement Instrumentation Data processing Explanation of tables Thermal radiation data, Keweenaw Field Station References
    Location: AWI Archive
    Branch Library: AWI Library
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  • 2
    Call number: ZSP-202-111,1
    In: Research report / Cold Regions Research and Engineering Laboratory, 111,1
    Description / Table of Contents: Summary: Optical scintillation, visual resolution, and wind and temperature profiles were measured over snow, ice and frozen ground. The data were analyzed to determine relationships between (1) scintillation and visual resolution and (2) scintillation and meteorological and surface conditions. The experimental results included (1) estimates of the limit of visual resolution, (2) telephotometer measurements of the apparent fluctuations in brightness (scintillation) of an artificial light source, and (3) measurements of wind direction and of the vertical distributions of wind speed and temperature. The optical path was 543 m long and 1.5 m above uniform horizontal surfaces. All scintillation and meteorological data are given in an appendix. The principal results of the analysis showed that for turbulent flow in stable stratification over snow (1) visual resolution deteriorated systematically as scintillation increased in intensity and (2) scintilliation intensity increased with increase in vertical temperature gradient. Scintilliation was at a minimum in the absence of thermal stratification and at a maximum (in very stable thermal stratification) during the sudden transition from laminar to turbulent flow. For a given temperature gradient, scintilliation increased with increase in wind speed. When wind and temperature gradients were combined in terms of the Richardson number and related to scintilliation, the data obtained over snow indicated a critical Richardson number of about 0.35. Scintilliation power spectra for eight periods revealed characteristics that could be related to visual resolution, the Richardson number and the mean wind speed component normal to the optical path. NOTE: This file is large. Allow your browser several minutes to download the file.
    Type of Medium: Series available for loan
    Pages: iii, 32, A17, B44 Seiten , Illustrationen
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory 111,1
    Language: English
    Note: CONTENTS Preface Page Summary Introduction The problem Previous work Plan of the investigation Conclusions Visual resolution and scintillation Visual resolution and wind, temperature, and surface conditions Visual resolution and height and length of optical path Results Measurements Analysis and discussion Visual resolution and scintillation relationships Scintillation and micrometeorological parameters Index of refraction fluctuations Scintillation and the temperature profile Scintillation and average wind speed Combined effects of wind speed and temperature gradient Scintillation and surface roughness Scintillation power spectra Scintillation and path length References Appendix A: Equipment and procedures Appendix B: Micrometeorological and scintillation data
    Location: AWI Archive
    Branch Library: AWI Library
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  • 3
    Call number: ZSP-202-111,2
    In: Research report / Cold Regions Research and Engineering Laboratory, 111,2
    Type of Medium: Series available for loan
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory 111,2
    Language: English
    Location: AWI Archive
    Branch Library: AWI Library
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