Richard R. Weiss

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 μm provided there are sufficient concentrations of 10–15 μm diameter droplets. Clouds containing only 1 L−1 of 100 μm diameter ice crystals (corresponding to a mass conce...

Radar Detection of Cloud-Seeding Effects

The effects on precipitation of artificially seeding clouds with Dry Ice have been monitored from cloud to ground with a radar that has a wavelength of 8.6 millimeters.

Deduction of Ice Particle Types in the Vicinity of the Melting Layer from Doppler Radar Measurements

Abstract A technique is described for deducing, from vertically pointing Doppler radar measurements, whether the predominant ice particles just above the melting layer are graupel or aggregates of ice crystals. Under certain conditions, the type of graupel and the type of ice crystals which comprise the aggregates can be deduced.

Simultaneous Observations of Cloud and Precipitation Particles with Vertically Pointing X-Band and Ka-Band Radars

The backscattered energy received at a radar from a cloud is proportional to several parameters which include peak power, antenna constants, and ¿-4, where ¿ is the radar wavelength. The wavelengths of weather radars vary from centimeters to millimeters. In theory, all such radars should be able to detect both cloud and precipitation particles but, because of practical limitation on antenna size and power output, only the shortest wavelength weather radars are sensitive to the full range of sizes covered by these particles (0.01 mm to over 5 mm in dimensions) which can produce echoes ranging over 160 dB. Simultaneous observations of cloud and precipitation systems with X-band (3-cm wavelength) and Ka-band (0.86-cm wavelength) radars provide the needed realizable dynamic range. Simultaneous measurements of this type are described and are shown to reveal the locations within clouds where precipitation is developing and the growth of precipitation with fall distance, as well as providing continuous measurements of cloud top heights. The inadequacy of X-band radars to measure cloud top heights is demonstrated.

The Use of a Vertically Pointing Pulsed Doppler Radar in Cloud Physics and Weather Modification Studies

Abstract It is shown that Doppler radar measurements of the changes with height of the average fallspeeds of solid precipitation particles can be used together with radiosonde data to distinguish between growth of ice particles by riming and growth by deposition from the vapor phase. Under some conditions this information can be deduced from real-time observations, but generally spectral broadening by turbulence requires that the velocity measurements be time-averaged. Examples of the use of this technique to deduce information on the modes of growth of ice particles in natural and in artificially seeded clouds are given.

Spectral Errors from Single-Mode Analog Filters in Processing Geoscientific Data

The use of a single-mode filter for obtaining spectral estimates with an analog computer is discussed. The equivalent bandpass filter that results may have some undesirable selectivity characteristics. Examples are given and suggestions made on ways of avoiding these errors. Some applications of this type of data analysis are given by Jones and Pasquill [1] and Businger et al. [2].