The effect of aerosols on the cloud droplet size profile, thermodynamics, and precipitation

Understanding the interaction between cloud and aerosol particles is a key element in determining future fresh water availability and its global distribution. The abundance and nature of the aerosol particles acting as CCN can directly influence cloud structure, the glaciation temperature, the height the cloud needs to reach before droplets can grow by coalescence, time of onset of precipitation, and the intensity of convection. In order to understand these processes and the actual role of the aerosol particles, we must be able to resolve the vertical distribution of the droplet size distribution and determine the level of freezing in the cloud. The vertical information is absolutely essential to furthering our understanding of cloud and precipitation development that will lead to better applications of interest to hydrologists and society. The measurement of vertically resolved cloud microphysical parameters in combination with state of the art aerosol measurements and the vertical profile of the cloud temperature provides a fundamental set of parameters to understand the effect of aerosol on clouds. The realization of these measurements using our current in situ capabilities can be very cumbersome, time consuming, and even dangerous. During the time required for a full set of vertically resolved in situ measurements the cloud dynamic properties can change significantly and seriously affect our final conclusions. Obviously fundamental knowledge is missing and a new type of observation is necessary. This work describes new measurements based on radiances coming from the side of the cloud, which provide key information to unlocking the secrets of aerosol-cloud interaction and the role of aerosol in precipitation processes. These new measurements are designed to advance our understanding of cloud and precipitation development by measuring vertically resolved cloud microphysical parameters in combination with state of the art aerosol measurements. Aircraft measurement and cloud 3D radiative transfer results will be presented and discussed as proof of concept.