Specifying Aerosol Concentration Improves Usefulness of Single-Column Version of the ACME and CAM5 Climate Models

Summary

Many global climate models (GCMs) can run in a mode where a single column (representing a particular latitude and longitude) from the full three-dimensional model is run independently, forced by initial and boundary conditions from observations or from GCM output. The single-column model (SCM) is important for climate model parameterization development because it is simple (allowing users to dig deeply into the processes governing model behavior) and computationally efficient (permitting users to quickly try many code permutations).

Version 5 of the Community Atmosphere Model (CAM5), which serves as the basis for the Department of Energy’s Accelerated Climate Model for Energy (ACME) initiative, includes prognostic aerosol equations but does not specify initial or boundary conditions for aerosols in SCM mode. A recent study notes this lack, documents its effect, and tests several solutions. The findings show that lack of aerosol information causes major problems for SCM studies involving non-convective clouds, but has little impact on convective cloud regimes because convection schemes currently do not use aerosol information. Fixing this problem is important because SCM functionality is often used for non-convective cloud regimes and because future model versions will include aerosol effects on convection. All three fixes for aerosols in the SCM were effective; the best solution depends on the case study being run and the modeler’s goals.

References

Reference: Lebassi-Habtezion, B., and P. M. Caldwell. 2015. “Aerosol Specification in Single-Column Community Atmosphere Model Version 5,” Geoscientific Model Development 8, 817-28. DOI: 10.5194/gmd-8-817-2015, 2015. (Reference link)