The forms of ice‐clouds

The observation of the forms of high clouds suggests that ice clouds usually arise at humidities representing saturation with respect to water and therefore at a considerable supersaturation with respect to ice, which in combination with a sparsity of effective nuclei leads to the rapid growth and high falling‐speed of the few ice particles. Recent theoretical and experimental investigations, principally by German meteorologists, fully support this view, and a brief account of their work is given in Part I of the present paper. In Part II it is shown how the new views provide an explanation of the distinctive fibrous structures of ice‐clouds, and give additional insight into the nature of cirrus uncinus and zig‐zags, of mixed clouds and of virga or fallstreifen, and also into the processes which bring about the decay of cumulonimbus and the formation of mammato‐clouds. Possible practical applications include that of dispersing natural clouds and the production of rain by the use of artificial ice nuclei.