Abstract
The growth equation of ice crystals was solved under assumption that the latent heat of sublimation is dispersed by conduction through the air and radiative cooling. Such condition can be expected for ice cystal growth in the polar atmosphere during the polar night or in cirrus clouds at night. The growth rate of ice crystals was computed under the condition of no temperature difference between ice crystal and the ambient air. The critical relative humidity was computed for dry air which is in vapor equilibrium with ice crystal cooled by radiation. It can be concluded that the radiative cooling of ice crystals results in an increase of thickness and area of air layer suitable for their growth.
