Retrieval of LWC in stratocumulus clouds using two mode representation of drop size distributions

Drop size distributions in a stratocumulus clouds are approximated by two narrow (actually delta functions) modes representing cloud droplets and drizzle, respectively. Detailed comparison with in-situ measurements as well as with the results obtained using an microphysical cloud topped model of the boundary layer indicates that such representation allows one to accurately describe the main microphysical cloud properties, such as the mean and effective radii, LWC, radar reflectivity, Z-LWC relationships, etc. The two mode DSD are described by four parameters: mean radii and drop concentration of each mode. Remote measurements of any four parameters, e.g., effective radius, extinction coefficient, radar reflectivity and Doppler velocity (mean sedimentation velocity of drizzle) allow one to calculate parameters of two mode DSD and, therefore, to calculate liquid water content, drizzle flux, etc. It is shown that the two-mode representation of DSD is much more efficient in different retrievals than the traditional gamma- or exponential size distributions.