The fall speeds of sub-100μm ice crystals

Estimates for the sedimentation rate of realistic ice crystals at sizes smaller than 100 μm are presented. These calculations, which exploit new results for the capacitance of ice crystals, are compared with laboratory studies and found to be in good agreement. The results highlight a weakness in contemporary ice particle fall speed parameterisations for very small crystals, which can lead to sedimentation rates being overestimated by a factor of two. The theoretical approach applied here may also be useful for calculating the sedimentation rate and mobility of non-spherical aerosol particles. Copyright c © 2007 Royal Meteorological Society