Assessing the Role and Impacts of Cloud, Aerosol, Radiation Processes in the Community Earth System Model (CESM)

Abstract:

Representing the interaction of clouds, aerosols, precipitation and radiation in climate models has seen significant advances in recent years. In particular, the use of aerosol emissions rather than burdens has enabled a more explicit representation of droplet activation, ice nucleation and associated microphysical processes. This overview will summarize our experiences building and using the Community Earth System Model (CESM) as we transition to more advanced, and complex process interactions. Chief among these interactions is the relationship between aerosols, activation and cloud drop size distributions and radiation. New processes add extra constraints on what constitues an acceptable climate in a GCM and the difficulty this entails for maintaining a credible simulation covering all existing aspects of the climate system. For the evolution of 20th century and ultimately future climate changes the regions and regimes that manifest the models' climate sensitivity are often co-located with the regions of greatest aerosol indirect effect sensitivity and we will show our efforts to disentangle these processes and gain a greater insight into their relative roles.