Towards Satellite Retrievals of Cloud Base CCN and Updrafts—The Greatest Observational Needs in Aerosol-Cloud Interactions (Invited Presentation)

Cloud mediated aerosol radiative forcing is a major component of the uncertainty in anthropogenic impact on Earth's energy budget and climate prediction. Its reduction requires global satellite observations of cloud condensation nuclei (CCN) and cloud base updraft speeds (W_b), which in combination determines cloud microstructure and cloud radiative effects (CRE). Only crude approximation of CCN exists based on retrieved aerosol optical properties, and none for W_b. This prevented reducing the uncertainty through the IPCC assessments. This stagnation can be ended by introducing break-through capabilities of measuring W_b for both convective and stratiform boundary layer clouds. They are based on our new method of measuring cloud base height, along with retrieving the energy fluxes that drive the vertical air motions. This capability, when combined with our new methods for retrieving cloud base drop concentrations (N_d), allows retrieving cloud base vapor supersaturation (S). Retrieving both N_d and S amounts to retrieving CCN(S) by using clouds as CCN chambers. Having the satellite retrieved cloud properties (liquid water path, cover, and CRE) along with CCN(S) and W_b wil allow to separate the contributions of updrafts and CCN to CRE. When attributing the CCN to anthropogenic emissions, the change in CRE is considered as the much sought anthropogenic effect on cloud radiative forcing. The remaining observational frontier that is still not yet addressed in satellite capabilities is measuring updrafts above cloud bases.