Triple-wavelength Doppler Spectra Radar Analysis of Ice Particles

To determine ice microphysical properties and processes we use three, co-located, vertically pointing Doppler radars at 3.2mm, 8.6mm and 97.5mm. Use of the Doppler spectra from the three radars allows us to determine ice particle sizes, concentration and fall velocity. This analysis can simultaneously reveal the size distribution and fall velocity of ice particles and therefore allows us to analyze the evolution of the particle size distribution and investigate processes such as aggregation.

Results are presented from a new field experiment at the Chilbolton Observatory in the UK in which high-resolution measurements were collected simultaneously from the three co-located radars in deep ice clouds. The sensitivity of all three radars is high (approx -40dBZ at 1km). Full pulse-to-pulse power and phase data were recorded at 3 wavelengths, allowing complete flexibility in construction and averaging of the Doppler spectra. Attenuation at the shorter wavelengths can be overcome by matching the reflectivity from the Rayleigh-scattering particles to the data collected at the longest wavelength, which is absolutely (and independently) calibrated to within 0.5dB.

We have analyzed several different cases covering different meteorological conditions. The velocity-size relationship for ice particles was revealed from our analysis over several cases. Furthermore, we have identified regions of rapid aggregation within clouds, apparently associated with the growth of dendritic crystals. The triple-wavelength Doppler spectra technique is able to provide a wealth of information; this presentation will summarize the technique and microphsyical insights from the data collected so far.