Terminal velocities of ice crystals

Abstract

A theoretical consideration of the terminal velocities of several ice crystal types is presented. The Best number-Reynolds number relationship for objects whose shapes simulate ice crystals is employed in the computations. The computed terminal velocities as a function of crystal size are shown. A parallel field study has been performed. Photographs of crystals falling in natural snowfall were made using a strobe light for illumination. From the photographs, a determination of crystal type, size, and falling attitude and the distance the crystal fell between successive strobe flashes was made. Terminal velocities were then calculated and the data was plotted as a function of crystal type and size. Curves were fitted to the data using the least squares method. These results are shown with the computed values. Also shown are Nakaya's findings for comparison. Experimental results of the study show that all of the crystal types observed exhibit a functional relationship between terminal velocity and crystal size. This is consistent with theoretical predictions developed in the study. Reasons for some disagreement between observational and theoretical results are discussed.