Production of secondary ice particles during the growth of graupel by riming

Experiments indicate that secondary ice crystals are produced when rime grows in a supercooled cloud containing drops ≥ 24μm in diameter. This occurs between temperatures of −3 and −8°C, the production rate being greatest at −5°C. These temperatures are constant to about ±0.5 deg C for velocities of the riming body ranging from 1.4 to 3.0m s −1 . On average, one ice splinter is thrown off for every 250 drops of diameter ≥ 24μm accreted, at cloud temperature −5°C, and this value does not change much with target velocity. Various possible splintering mechanisms are discussed.