The production of high ice‐crystal concentrations in stratiform clouds

The appearance of ice crystals in high concentrations, of ∼ 500 1 −1 in the −3 to −8°C zone of stratiform clouds, recently reported by Bower et al. , is explained by the shedding of splinters by riming ice crystals at rates observed in the laboratory earlier by Hallett and Mossop. The appearance of a second maximum at −15°C, with small crystals of diameter less than 125 μm in concentrations of ∼ 1000 1 −1 , is attributed to the transport of small ice splinters produced in the Hallet‐Mossop zone that grow at small ice supersaturations in weak updraughts between the −8°C and −12°C levels, and thereafter at water saturation in convective cells containing liquid water and updraughts of 1 m s −1 between the −12°C and −15°C levels.