Improving Observations of Aerosol Modifications in the presence of clouds

Aerosols are expected to have significant effects on cloud properties by providing CCN nuclei which can modify the water droplet spectrum of liquid phase clouds. It is well known that these effects are significantly enhanced for hygroscopic aerosols which can be activated at all radii and thus the testing of aerosol hygroscopic properties is important in interpreting the modification of clouds in the presence of aerosols. In this paper, we describe the experimental procedures being developed at City College of New York to measure simultaneous aerosol and cloud properties. This includes the use of a Multifilter Shadowband Radiometer (MFRSR) for cloud optical depth as well as a Microwave Radiometer for total liquid water path which combine to give cloud droplet diameters. For aerosols, a CIMEL sky radiometer together with a Multiwavelength Elastic-Raman lidar are used to estimate both the vertical structure and aerosol column loading. This configuration allows us to estimate the aerosol extinction below cloud base. Furthermore, using the fine mode fraction from CIMEL allows us to isolate the fine mode extinction which should be a better indicator of hygrosopic aerosols. In particular, we use the combined MWR and raman Lidar to explore the increase in scattering due to RH effects. For hygroscopic conditions, we are able to observe dramatic increase in the extinction to backscatter (S) ratio as we move closer to cloud base and these enhances S ratios are observed even within the cloud illustrating a smooth transition from dyry-state aerosol to saturated aerosol to mature droplet. This signature is particularly relevant in identifying the extent of the aerosol seeding within the cloud. Finally, the retrieved optical S ratio profiles are tested against Air-Quality Transport Models such as CMAQ to assess CMAQ outputs and parameterization schemes