Cloud Parameterization in Global Climate Models: Evaluation with Atmospheric Radiation Measurement Data

The goal of our work is to develop and evaluate a prognostic The aqueous reaction to convert SO to in clouds is aerosol model and to parameterize the effects of aerosols, actassumed to have an average e-folding lifetime of 30 hours at ing as cloud condensation nuclei (CCN), on initial cloud drop40° N at the surface in summer. This e-folding lifetime is let concentrations. This, together with global climate models scaled to be proportional to the square of the locally specified which are able to treat the microphysics of clouds, should concentration of OH at other locations. This formulation is a allow us to improve the climate models’ representation of simplified attempt to account for the observed seasonal clouds to enable them to more accurately predict future variations in sulfate concentrations and wet deposition in climate change. Development of models capable of treating North America by assuming that the rate at which forms the microphysics of clouds after the initial size distribution is in clouds depends on how frequently the cloud is intercepted determined is proceeding under separate investigators within by an air parcel (average cloud-free periods vary from 10 to the ARM program. 80 hours [Lelieveld and Crutzen, 1990]) and on the local