Freezing modes of riming droplets with application to ice splinter production

Abstract

AbstractLaboratory studies of riming have shown that, provided the heat loss is fairly symmetrical, the internal freezing pattern of an accreted drop shows two distinct modes in the temperature range −3°C to −9°C and a transition to a third below this temperature. (1) At high temperatures the freezing is dominated by an ice front growing outwards from the rimer with a somewhat enhanced growth rate around the drop edge. (2) At temperatures below about −5°C two ice fronts are evident, one from the substrate, one from the remote edge of the drop. (3) At temperatures of −9°C and below the freezing is essentially symmetrically inwards. Freezing modes (1) and (2) sometimes give rise to protuberances which may be associated with the Hallett‐Mossop ice splinter production. These are suppressed by the addition of ammonia to the drop. The three modes of freezing are accounted for in terms of the pattern of dendritic growth during the first stage of freezing, and it is suggested that this explains the low temperature cut‐off in secondary ice particle production.