Cloud Layers, Particle Identification, and Rain-Rate Profiles from ZRVf Measurements by Clear-Air Doppler Radars

Abstract

Networks of radars that point almost vertically and continuously measure the vertical profile of the horizontal wind will, in the future, be operated at many locations around the world. Although such radars are designed to measure the Doppler-sensed movement of clear-air refractive-index inhomogeneities, they are an exceptional tool for sensing precipitating ice and water particles in clouds. Because of the low detection threshold and long averaging time of these radars water-particle-size distributions can be measured down to 100-µm diameter and mean vertical fall velocities Vf as small as 0.2 m s?1 can be accurately measured. In this paper, data are presented from two events in which clouds form, intensify, and finally produce precipitation. Height profiles are analyzed in terms of ZRVf plots versus height, where Z is the radar reflectivity factor and R is liquid flux (rainfall rate). The observations provide new insight into drop-growth and breakup processes. Special attention is given to the transition zone through the melting level. It is shown how these radars can provide 1) cloud-layer structure above lower overcast, 2) height profiles of liquid mean drop size, 3) the ice-water transition level compared with the 0° isotherm, 4) height profiles of rain rate, and 5) inferences about the identity of hydrometeors versus height.