Obtaining number of activated CCN from satellite-retrieved vertical profiles of cloud drop size in convective clouds

Description

Here we present our first preliminary results from the first year of the funded proposal titled "Vertical microphysical profiles of convective clouds as a tool for obtaining aerosol cloud-mediated climate forcing.” A major challenge towards this goal is retrieving CCN from space in the cloudy boundary layer. CCN can be obtained if we can retrieve the number of activated CCN, Na, and the maximum super saturation near cloud base, S. We have already shown that vertical profiles of aircraft-measured cloud drop effective radius, Re, in convective clouds can be used for calculating Na (Freud et al., 2011). In principle, the same can be achieved with satellite-retrieved vertical profiles of Re in convective clouds. When combining Na with estimated cloud base updrafts, S can be calculated and respectively the CCN concentration at that S can be obtained. We used such satellite retrievals for calculating Na in convective clouds over the SGP site and compared Na to the CCN measured at the ground. Lidar measurements are used for validating that the cases are in well mixed boundary layer, so that the surface-measured CCN are applicable to the cloud base. The S for which CCN and Na are the same is found, and the required updraft for sustaining this S is calculated using the model developed in the companion research of Dr. Khain. The validation of this method will pave the way for retrieving Na in convective clouds from MODIS and AVHRR, as a major milestone towards quantifying the climate impacts of cloud-aerosol interactions.

Reference: Freud E, D Rosenfeld, and JR Kulkarni. 2011. “Resolving both entrainment-mixing and number of activated CCN in deep convective clouds.” Atmospheric Chemistry and Physics 11: 12887–12900, doi:10.5194/acp-11-12887-2011.