THE PRODUCTION OF HIGH ICE-CRYSTAL CONCENTRATIONS IN STRATIFORM CLOUDS

The appearance of ice crystals in high concentrations, of similar to 5 00 l(-1) in the -3 to -8 degrees C zone of stratiform clouds, recently reported by Bower et al., is explained by the shedding of splinters b y riming ice crystals at rates observed in the laboratory earlier by H allett and Mossop. The appearance of a second maximum at -15 degrees C , with small crystals of diameter less than 125 mu m in concentrations of similar to 1000 l(-1), is attributed to the transport of small ice splinters produced in the Hallet-Mossop zone that grow at small ice s upersaturations in weak updraughts between the -8 degrees C and -12 de grees C levels, and thereafter at water saturation in convective cells containing liquid water and updraughts of 1 m s(-1) between the -12 d egrees C and -15 degrees C levels.