Radar Observations of Transport and Diffusion in Clouds and Precipitation Using TRACIR

Abstract

A remote-sensing technique called TRACIR (tracking air with circular-polarization radar) was developed recently for studying air-parcel trajectories in clouds. The technique uses a dual-circular-polarization radar to detect microwave chaff fibers that serve as tracers of the air motion. The radar is able to detect the chaff inside clouds and precipitation by measuring the circular-depolarization ratio, which is much higher for chaff than for hydrometeors. Chaff concentrations are also estimated by the technique, thus permitting turbulent diffusion in clouds to be examined. Demonstrations of TRACIR's capabilities are presented for three cases in which chaff was used to simulate the movement of cloud-seeding nuclei in clouds and precipitation. In two cases involving airborne chaff releases, the gradual drift and diffusion of chaff in a stratiform cloud are contrasted with its abrupt transport and dispersion in a convective cloud. In the third case study, the technique successfully detected a plume of chaff released from the ground in a snowstorm. In each case the radar data provided three-dimensional visualizations of the extent of the chaff region and maps of the chaff concentration with excellent spatial and temporal resolution.