On the Freezing of Liquid Water in a Cloud

Abstract

A technique due to Saunders is used to give quantitative information on the amount of heating to be realized from the freezing of liquid water in a cloud. The commonly accepted value of ?C per gram of water frozen per kilogram of air plus an additional amount due to saturation adjustment from water to ice is shown to be imprecise. The total heating is realized only after ice pseudo- or saturated-adiabatic ascent to higher levels in the atmosphere; less than one-half of the maximum temperature difference between liquid water and ice processes is realized at the time of freezing, if freezing of cloud contents of 7 gm kg?1 or less is done at ?5C. The delay in the freezing of rainwater in operational, one-dimensional numerical models biases the results against natural clouds, leading to overestimates of ?seedability.? Also the neglect of the temperature dependence of the latent heat of condensation (increasing with lower temperatures) in those models causes the same kind of bias.