Sublimation in Outdoor Air and Seeded Sublimation

Abstract

AT intervals over the past twelve months, expansion chamber tests of the threshold temperature for the formation of ice crystals in supersaturated air have been carried out at this College. Of the various weather conditions experienced, it was found that with strong sea winds (N. and S., 5 or more on the Beaufort scale), the threshold value remains constant at - 41.2° C., which is the value found previously for nuclei-free air¹. In other weather conditions the threshold is variable between - 41·2° C. and - 32·2° C. The latter is the value already found for the ground layer of air in England. Diurnal variations are sometimes as large as 4° C. It appears that there is a whole 'spectrum' of sublimation nuclei in polluted air.