Evaluating cloud tuning in a climate model with satellite observations

This study examines the validity of a tunable cloud parameter, the threshold particle radius triggering the warm rain formation, in a climate model. Alternate values of the model’s particular parameter within uncertainty have been shown to produce severely different historical temperature trends due to differing magnitude of aerosol indirect forcing. Three different threshold radii are evaluated against satellite observations in terms of the statistics depicting microphysical process signatures of the warm rain formation. The results show that the simulated temperature trend best matches to observed trend when the model adopts the threshold radius that worst reproduces satellite-observed microphysical statistics and vice versa. This inconsistency between the “bottom-up” process-based constraint and the “top-down” temperature trend constraint implies the presence of compensating errors in the model.