Call number:
ZSP-202-242
In:
Research report, 242
Description / Table of Contents:
The attenuation of visible light by falling snow was studied by making simultaneous attenuation measurements and snow concentration measurements. The attenuation coefficient was calculated from photometric measurements and from visual observations. Snow concentration in the air was evaluated by two methods: from Formvar replicas collected during the snowfall, and by mass accumulation of snow in collecting pans. The snowflakes were arbitrarily classified by crystal types according to their estimated fall velocity. It was found that the correlation between extinction coefficient (attenuation) and snow concentration was generally much higher by types than when all snowflakes were considered together regardless of crystal components and degree of riming. Two types, apparently improperly classified, displayed lower correlations than the overall group. When no fog is present during the snowfall, the experimental results coincide well with attenuation theory if a reasonable correction is applied to the values obtained in the measurement of snowflake diameters. Measurements of mass flux indicate that for a given intensity the attenuation caused by snow is an order of magnitude greater than that caused by the same mass flux of rain.
Type of Medium:
Series available for loan
Pages:
iv, 27 Seiten
,
Illustrationen
Series Statement:
Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 242
URL:
https://hdl.handle.net/11681/5949
Language:
English
Note:
CONTENTS: Preface. - Abstract. - Introduction. - Initial theoretical considerations. - Light attenuation by particles. - Basis of attenuation meter measurements. - Contrast reduction and visual range. - Transmissometer theory, Pritchard photometric method. - Terminal velocity of snowflakes. - Methods of measurement: Light attenuation. - Duntley (Scripps Institution) attenuation meter. - "Meteorological range" observations. - Pritchard photometric method. - Methods of measurement: Atmospheric concentration of snowflakes. - Replication method. - Mass accumulation method. - Analysis of snow samples. - Terminal velocity of snowflakes. - Flux density and atmospheric concentration. - Mass accumulation rate. - Concurrent attenuation due to fog. - Discussion of results. - Computational methods. - Correlations: Attenuation coefficient vs area concentration. - Correlations: Attenuation coefficient vs are a flux. - Correlations: Attenuation coefficient vs mass concentration and mass flux. - Comparison of sampling methods for mass flux. - Attenuation of visible light by snow compared to rain. - Literature cited. - Appendix A.
Location:
AWI Archive
Branch Library:
AWI Library
