Fall and Shape Characteristics of Freezing and Frozen Raindrops

This study investigates the fall speed and vertical to horizontal axis ratio characteristics of freezing and frozen raindrops. The information on these characteristics has important applications, including radar precipitation retrievals. Despite various studies on the characteristics of warm raindrops (raindrops that are in liquid state during fall and after impact on a surface), the available information on such characteristics of freezing and frozen raindrops is limited. As observed in our field experiments using a new optical-type disdrometer that we developed (HOD – High-speed Optical Disdrometer), each of the hydrometeor types (warm, freezing, and frozen raindrops) has distinct fall speed and axis ratio characteristics, necessitating different representations for each of these hydrometeor types in relevant applications. We will present our field measurements for the axis ratios and fall speeds of warm, freezing, and frozen raindrops along with the predictions of the available parameterizations for the axis ratio and terminal speeds of warm equilibrium-shaped raindrops. In this presentation, we will also discuss our relevant parameterization efforts and relate the observed fall speed behaviors to the observed hydrometeor axis ratios. This material is based upon work supported by the National Science Foundation under Grants No. AGS-1144846 and AGS-1612681.