Parameterizing the Fall Speeds of Freezing and Frozen Raindrops

This study investigates the fall speeds of freezing and frozen raindrops. Field observations have shown that fall speed distributions of freezing and frozen raindrops (i.e. fall speed versus hydrometeor diameter) are different than the typical distribution for warm raindrops (i.e. raindrops that are in liquid state during fall and after impact on a surface). As such, widely used fall speed parameterizations for warm raindrops are not well suited for predicting the fall speeds of freezing and frozen raindrops. Predictions for freezing and frozen raindrop fall speeds have important meteorological applications: for example, radar retrieval of precipitation rates during such events. Our investigation utilized warm, freezing, and frozen raindrop fall speed data that we collected using the High-speed Optical Disdrometer (HOD). The HOD is an optical-type disdrometer that we recently developed and have tested for accuracy. This field data provided us valuable insights and a basis for parameterization developments for the fall speeds of freezing and frozen raindrops, which will be discussed in our presentation. This material is based upon work supported by the National Science Foundation under Grants No. AGS-1144846 and AGS-1612681.