Temperature dependence of secondary ice crystal production during soft hail growth by riming

Simple experiments confirm that the production of secondary ice particles during the growth of rime depends upon the surface temperature of the riming particle rather than upon the cloud temperature. The required surface temperature of −2.5 to −7.5 °C may be produced over a wide range of cloud temperatures depending on the liquid water content of the cloud and the nature of the riming particle. A particle of high fall velocity in a cloud of high liquid water content may produce secondary ice particles at cloud temperatures considerably below −8 °C.