Freezing and Shattering of Water Droplets in Free Fall

THE shattering of freezing water droplets has been suggested as a source of the large concentrations of ice crystals found in relatively warm supercooled clouds by a number of workers (ref. 1, for example). But recent work by Dye and Hobbs 2,3 and Johnson and Hallett 4 , using droplets approximately 1 mm in diameter suspended on thin insulating fibres, has shown that nearly all the shattering observed in earlier experiments can be attributed to contamination with carbon dioxide or to the droplets not being in thermal and solution equilibrium with the surrounding air. Johnson 5 found that suspended droplets ventilated at their terminal velocity shattered very frequently if they were rotated during freezing but not at all if they were not rotated. Because it is difficult to decide if freezing water droplets do rotate as they fall, the experiments reported here were undertaken as a direct test of the shattering of water droplets freezing in free fall.