The fall speeds of sub-100 micron ice crystals
  Estimates for the sedimentation rate of realistic ice crystals at sizes smaller than 100 $\mu$m 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. 
C. D. Westbrook