Using MIE Raman S ratio lidar measurements to explore cloud droplet properties and the aerosol indirect effect

Abstract

In this paper, the properties of Low-level clouds are explored with a Raman-elastic lidar. In particular, we examine two complementary methods to measure thin cloud optical depth (COD). The first is direct integration of Raman Derived extinction while the second method utilizes a regression technique. We show that if we correct for aerosol influences the regression method for low cloud optical depth can be dramatically improved. Furthermore, estimates of extinction to backscatter ratio can be made within the cloud. We find that when the lidar ratio in cloud is averaged over the vertical extent, an S ratio on the order of 20 sr is found which is consistent with conventional water phase cloud droplet models. Key words: Low cloud, optical depth, Raman lidar. Finally, correlations between aerosol loading below clouds and small droplets in cloud interior are studied illustrating possible connections between aerosols and small droplet seeding.