Procedural Guide for the Retrieval of Dropsize Distributions in Water Clouds from Ground-Based Clear-Air-Sensing Doppler Radar Observations

摘要

The advent of Doppler clear-air radars for wind-height profiling opens the way for their use in a variety of other applications. The paper uses knowledge of the clear-air Doppler spectrum from a zenith-pointing radar together with the measured water droplet Doppler vertical velocity spectrum to calculate spectra of drop number density through clouds of droplets having substantial fall velocity. The report extends the method and describes procedures that allow spectral lines and details to be extracted from the radar data. Spectra measured with a 915 MHz, wind-profiling radar are used as examples and compared with the spectra that would have been obtained if the clear-air information were ignored. From the number density vs. dropsize distribution, the corresponding liquid water distribution can be calculated. Failure to take into account turbulence in the medium can result in large errors in number density and liquid water especially in the neighborhood of spectral lines and large gradients. The advantages and limitations of a radar remote sensing drop spectrometer are described.