The growth of snow crystals at low supersaturations

Abstract The result of experiments in which ice crystals are grown from the vapour at supersaturations of only a few per cent show that the c/a ratio tends towards limiting value of 1·4 for priams and 0·8 for plates. Thus the habit of snow crystals is now clearly delineated with respect to both temperature and supersaturation or flux of vapour. The basic habit, as determined by the relative growth rates along the c and a axes, is controlled by the temperature bat the secondary features of growth are governed by supersaturation as follows; in the plate regime, increasing supersaturation causes transitions from very thick plate → thick plate → sector plate → dendrite and, in the prism regime, the development is from short solid priam. → longer hollow priam → needle. There now appears to be no basis for believing that the basic crystal habit is modified by changing the diffusivity of water vapour into the inert carrier gas.