Empirical Formula for the Melting Rate of Snowflakes

[摘要] The melting experiment has been carried out on freshly fallen snowflakes supported on a nylon net in a vertical wind tunnel at an airstream of 100cm sec-1 in wind velocity and of 5.5°C in temperature. The morphological variations of snowflakes by melting were shown in a series of photographs taken every ten seconds. Examinations of the melting process with eyes and through a camera revealed that most of water produced at snowflake surface by melting was not accumulated on the surface but penetrated into the inside, and this is markedly different from the melting processes of ice spheres and crystals. A simple microphysical model was proposed for the melting process of snowflakes. Using the model, it was shown that the rate of decrease in snowflake radius R by melting, assuming spherical symmetry, could be expressed as -dR/dt=εa(KΔT+LvDΔσ)/L_??_σiR in connection with the problem of heat transfer. a is a kind of adjustable parameter to bridge the gap between the experiment and the theory, and was evaluated experimentally as 1.75. a is a ventilation coefficient of spheres determined by Yuge (1960) which is given by a=1+0.275 P1/3r R1/2e.

[学科分类] 大气科学