Estimations of Cirrus Particle Fall Velocity-Size Relations from Radar Measurements

The representation of high-altitude ice clouds such as cirrus in general circulation models (GCMs) remains to be one of the uncertainties of these models. In addition to a better description of cloud microphysical parameters, another process that needs an improved parameterization in GCMs is the fallout of cirrus particles. This parameterization is based on the cloud particle fall velocity (vt)-size (D) relations that are usually expressed by a power-law function. These relations have been studied both experimentally and theoretically based on calculations using drag-law equations for different flow regimes and particle habit (shape) information together with size-dependent estimates of such properties as the crystal mass and normal to the flow cross sectional area (e.g., Mitchell 1996). Experimental studies of the terminal fall velocity-size relations, however, are mostly limited to the ground observations of larger precipitating particles, although crystal properties in high-altitude ice clouds and those properties at the ground may differ significantly.