FEASIBILITY OF RETRIEVING CLOUD CONDENSATION NUCLEUS PROPERTIES FROM DOPPLER CLOUD RADAR, MICROWAVE RADIOMETER, AND LIDAR

This paper explores the possibilities of using K-a-band Doppler radar, microwave radiometer, and lidar as a means of retrieving cloud conden sation nucleus (CCN) properties in the stratocumulus-capped marine bou ndary layer. The retrieval is based on the intimate relationship betwe en the cloud drop number concentration, the vertical air motion at clo ud base, and the CCN activation spectrum parameters. The CCN propertie s that are sought are the C and k parameters in the N = CSk relationsh ip, although activation spectra based on the lognormal distribution of particles is also straightforward. Cloud droplet concentration at clo ud base is retrieved from a Doppler cloud radar combined with a microw ave radiometer following a previously published technique. Cloud base is determined from a Lidar or ceilometer. Vertical velocity just above cloud base is determined from the vertically pointing Doppler cloud r adar. By combining the simultaneous retrievals of drop number and vert ical velocity, and assuming theoretical relationships between these pa rameters and the subcloud aerosol parameters, the C parameter can be d erived, under the assumption of a fixed k. If a calibrated backscatter lidar measurement is available, retrieval of both C and k parameters is possible. The retrieval is demonstrated for a dataset acquired duri ng the Atlantic Stratocumulus Transition Experiment using a least squa res minimization technique. Sensitivity to assumptions used in the ret rieval is investigated. It is suggested that this technique may afford the acquisition of long-term datasets for climate monitoring purposes . Further investigation with focused experiments designed to address t he issue more rigorously is required.