Speaker: Christopher Williams (Univ Colorado)
Topic: Drizzle Droplet Distributions Retrieved from Vertically Pointing Doppler Lidar and Ka-Band Radar Observations

This study uses vertically pointing Doppler lidar and Ka-band Doppler radar to estimate drizzle droplet distributions falling below cloud base in maritime warm boundary-layer (WBL) clouds. The aerosol-rich environment enabled the Doppler lidar to measure the vertical air motion, even in the presence of falling drizzle droplets. The Ka-band Doppler velocity power spectra observed the falling drizzle droplets, which are shifted upwards or downwards by the vertical air motion and broadened by turbulent broadening effects. The retrieval algorithm consists of four steps: (1) deconvolve the observed Ka-band Doppler velocity spectra to remove turbulent broadening, (2) shift the spectra by the observed Doppler lidar air motion, (3) convert reflectivity spectral density in each velocity bin to number concentration, and (4) convert each velocity bin to drizzle diameter so that the discrete drizzle droplet distribution is in units of number concentration per drizzle drop diameter. This study uses observations collected on the Scripps Pier in San Diego, California, during the year-long US Department of Energy (DOE) EPCAPE field campaign. The key instruments used in this study include a ceilometer to determine cloud base, a vertically pointing Doppler lidar to measure vertical air motion from aerosol scattering, and a Ka-band zenith pointing radar (KAZR) to measure Doppler velocity power spectra of drizzle sized hydrometeors below the ceilometer cloud base.