Doppler Radar and Microwave Radiometer Derived Stratus Cloud Particle Size Distributions

Some earlier studies demonstrate that the size distribution of stratus cloud particles can be retrieved using radar reflectivity factor from millimeter-wave cloud radar and liquid water path estimated from microwave radiometer radiance measurements (White et al. 1991; Frisch et al. 1995, 1998). One source of error in these retrievals is the use of a climatological value for the geometric standard deviation (Miles et al. 1999). In this paper, we discuss an alternative retrieval method that incorporates the median radius of the cloud particle number concentration (count median radius, Hinds 1982), as opposed to the geometric standard deviation. The algorithm retrieves vertical profiles of liquid water content, number concentration, and effective radius using vertical profiles of radar reflectivity factor, Doppler velocity, and estimated particle median radius, together with integrated liquid water path. The advantage of this approach is that it does not rely on climatological values and that the extinction coefficients computed from retrieved size distribution are less sensitive to errors in median radii as opposed to geometric standard deviations. The retrieved values are also less sensitive to instrumental errors compared with the algorithm given by Frisch et al. (1995, 1998).