Diagnostic of Supercooled Clouds from Single-Doppler Observations in Regions of Radar-Detectable Snow

Abstract

Liquid water is produced in the updraft regions of subfreezing clouds when the generation of vapor excess over the water saturation value exceeds the vapor depletion through the depositional growth of the solid particles. A diagnostic technique for the presence of supercooled cloud in the presence of snow is presented here. The data required are single-Doppler observations of reflectivity and radial velocity as well as a nearby sounding of temperature. From these data, the 3D wind field is retrieved by a variational method. From the retrieved vertical motion, the supercooled water is derived from the steady-state balance relation between snow content and cloud liquid water. The method is tested with a kinematic model that includes the main microphysical processes expected to occur in stratiform subfreezing conditions. A comparison between aircraft in situ measurements of supercooled water content and the diagnosed as well as model-generated values shows good agreement.