A new empirical relationship between aerosol and cloud droplet number concentrations (Naer and Nd, respectively) was established based on observed data from different regions around the world to implement in the Hadley Centre Global Environmental Model version 2-Atmosphere-Ocean (HadGEM2-AO). Compared to the original relationship used in HadGEM2-AO, which utilized observed data from only limited regions, this new relationship provides a lower Nd than the original relationship for Naer < 680 cm-3, and the opposite for Naer > 680 cm-3. The complete historical run with the new relationship (newHIST) shows a number of significant differences from the original historical run (HIST). Nd increased in industrialized regions while it generally decreased over the oceanic regions in newHIST compared to HIST. Interestingly, in newHIST a significant change in total cloud amount occurred mainly in the intertropical convergence zone (ITCZ) due to a change in the wind circulation pattern over the North Pacific. Notably, the surface temperature in newHIST was closer to the observational data than that in HIST - especially over the Northern Hemisphere. Despite the small change in Nd in the new relationship, not only the variables directly associated with cloud microphysics but also the variables representing atmospheric circulation patterns changed significantly. This implies that accurate parameterization of Nd is critical for better climate model prediction.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry
- Environmental Science(all)
- Atmospheric Science