The density and structure of ice formed by accretion

Studies have been made of ice formed by accretion over a wide range of controlled conditions to ascertain the influence of the wind speed, ambient temperature, droplet diameter and liquid‐water concentration in the supercooled cloud, and the size of the accreting object. The density of the deposits ranged from 0·1 to 0·9 g cm −3 , the density increasing with increases in the first four of the above parameters but decreasing with increasing object size. It was found that the density could be expressed as a function of − rv 0 / T s , r being the median volume radius of the droplets comprising the cloud, v 0 the speed with which the droplets struck the object and T s the mean temperature of the accreting surface (in °C). The quantity rv 0 is interpreted as being a measure of the force with which the droplets were packed together and T s the temperature which governed their freezing rate. A microscopic examination of the deposits showed that at low values of − rv 0 / T s (corresponding to low densities) the droplets tended to freeze together as spheres while at higher values they were distorted and spread considerably before freezing.