Evaluation of a new Cloud Droplet Activation Parameterization with In Situ Data from CRYSTAL-FACE and CSTRIPE

The accuracy of the prognostic, physically-based aerosol activation parameterization of Nenes and Seinfeld [2003] (NS) with modifications introduced by Fountoukis and Nenes [2004] (modified NS) is evaluated against extensive microphysical data sets collected on board the CIRPAS Twin Otter aircraft for cumuliform and stratiform clouds of marine and continental origin. The cumuliform cloud data were collected during NASA’s CRYSTAL-FACE (Key West, FL; July, 2002), while the stratiform cloud data were gathered during CSTRIPE (Monterey, CA; July 2003). In situ data sets of aerosol size distribution, chemical composition, and updraft velocities are used as input for the NS parameterization, and the evaluation is carried out by comparing predicted cloud droplet number concentrations (CDNC) with observations. This is the first known study in which a prognostic cloud droplet activation parameterization has been evaluated against a wide range of observations. On average, predicted droplet concentration in adiabatic regions is within ~20% of observations at the base of cumuliform clouds and ~30% of observations at different altitudes throughout the * Corresponding author