Influence of drizzle on Z– M relationships in warm clouds

• Published in: Atmospheric research 2007-12, Vol.86 (3), p.297-314
• Main Authors: Pujol, Olivier, Georgis, Jean-Francois, Sauvageot, Henri
• Format: Article
• Language: English
• Subjects: Atmospheric and Oceanic Physics; Cloud physics; Cumulus liquid water content; Cumulus radar reflectivity; Drizzle; Earth, ocean, space; Exact sciences and technology; External geophysics; Geophysics. Techniques, methods, instrumentation and models; Meteorology; Physics; Radar observation simulations
• ISSN: 0169-8095; 1873-2895
• DOI: 10.1016/j.atmosres.2007.06.005

This paper addresses the sensitivity of the relationships between radar reflectivity ( Z) and liquid water content ( M) for liquid water clouds to microphysical drizzle parameters by means of simulated radar observation at a frequency of 3 GHz of modeled cumulus clouds. A power law relationship for non drizzling clouds with water content as high as 3 gm − 3 : Z c = 0.026  M c 1.61 is numerically derived and agreed with previous empirical relationships relative to cumulus and stratocumulus. This relationship is then used to explore the influence of drizzle on the correlation between radar reflectively and water content. Due to their large diameters with respect to cloud droplets, drizzle sized drops dominate radar reflectivity but do not carry the cloud water content so that reflectivity and liquid water content are expected to be not correlated in clouds containing drizzle. It is shown that for congestus or extreme congestus cumuli, microphysical conditions for which the Z c – M c relationship can be used with a tolerance of 5 and 10% are provided whereas for humilis or mediocris cumuli, the presence of drizzle breaks down the Z c – M c relationship whatever the situations.