The Retrieval of Ice Particle Size Information from VHF Wind Profiler Doppler Spectra

Abstract

Recently, the authors observed significant echoes from precipitating ice particles above the freezing level in the stratiform region of tropical squall lines with a 50-MHz wind-profiling radar. A technique is described that allows ice particle size distributions to be obtained from the 50-MHz wind-profiling radar spectra. A model ice echo is developed in which it is assumed the number density of ice particles is exponentially distributed. A composite spectrum of dendrites, plates, columns, and bullets is assumed, and good fits to the observed spectra are obtained. To test the reliability and stability of the retrieval technique, simulated data with realistic statistical properties were generated and the shape of the model size distribution varied. Only two types of ice particles are considered. It is shown that the population spectra are recovered well for a wide range of exponential slopes. Relative precision of about 10% is obtained when the clear-air spectral width is 0.1 m s?1, and is about 30% when the spectral width is 0.3 m s?1. However, when the spectral width is large, such as 0.5 m s?1, the relative error can exceed 100%. Spectral widths of about 0.3 m s?1 are typically observed in the trailing stratiform region of tropical squall lines.