Fig. 9. Calculated (this work) and measured (29, 47) extinction and absorption coefficients for snow. If the liquid-drop particle distribution given in Eq. 10 is modified by Eq. 13, we have an approximate relation giving the actual snowflake particle size distribution. We expect that the equivalent liquid-drop model will underestimate and /3a because the particle diameters are too small, whereas the aggregate snowflake model will overestimate these coefficients because the actual snowflake distribution is approximated by spherical particles composed of liquid density water. The results of calculations, shown in Fig. 9 for a wavelength of 11 jam, bound the experimental measurement of Chu and Hogg (29) and Sokolov (47) as would be intuitively expected. At low snowfall rates, the aggregate snowflake model more closely estimates the measured extinction coefficients of Sokolov, whereas at higher snowfall rates, the aggregate snowflake model clearly overpredicts observed behavior and the equivalent liquid-drop model establishes a lower bound for the estimates. In general, the attenuation and forward scattering properties of snow appear to be between those of rain and dense fog.
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