Mystery of ice multiplication in warm-based precipitating shallow cumulus clouds

High concentrations of ice crystals exceeding those of background ice nuclei have often been observed in warm-based precipitating shallow cumulus clouds. Laboratory experiments reveal that such ice multiplication can occur when large ice particles collide with cloud droplets (Hallett-Mossop mechanism). Further studies suggested that this mechanism is unable to account for the exceedingly high ice concentrations in those kinds of clouds. However, the results of our numerical simulations show that the ice multiplication phenomena can be explained by the Hallett-Mossop mechanism with the freezing of a narrow band of supercooled raindrops which act as rimers playing a crucial role