Evaluation of a 35 GHz Radar for Cloud Physics Research

Abstract

A 1960 35 GHz radar has been modernized through the use of solid state electronics, Dopplerization and improved data-display capabilities. Radars of this frequency are particularly useful for observing the internal structures of clouds and for detecting low concentrations of ice particles in the atmosphere. The minimum effective radar reflectivity factor of a cloud of water drops that is measurable by this radar at a range of 1 km was estimated to be ?36 ± 4 dBZ. Simultaneous airborne and radar measurements showed that the radar reflectivity factors for various water clouds determined from radar measurements were generally in good agreement with those derived from in situ measurements of the drop size spectra. These measurements also showed that the radar can detect clouds in which the diameters of the droplets do not exceed ?27 ?m provided there are sufficient concentrations of 10?15 ?m diameter droplets. Clouds containing only 1 L?1 of 100 ?m diameter ice crystals (corresponding to a mass concentration of ?10?3 g m?3) are detectable by the radar. Due to its narrow beamwidth (0.26°), reflectivity measurements with the 35 GHz radar can reveal more detailed structural information on clouds and precipitation than more powerful 5.5 GHz radars. The 35 GHz radar has been Dopplerized using a new magnetron phase correlation technique that allows detailed measurements to be obtained of the velocities of particles down to ?25 cm s?1. Some examples are presented of measurements of the spectra of the vertical velocities of cloud particles using this technique.