24 November 2015

Global Radiative-Convective Equilibrium in the Community Atmosphere Model 5


To advance climate models and further understanding of atmospheric processes, it is important to develop a hierarch of model configurations to focus attention and reduce complexity. This holds true even as climate models move toward high horizontal resolutions (i.e., grid spacing less than 50 km) as such simulations need to be evaluated carefully in light of the fact that most of the parameterizations are not developed to be accurate at small grid spacing. In this work, an idealized  global radiative–convective equilibrium (RCE) configuration is proposed to explore the implication of horizontal resolution on equilibrium climate. RCE is the statistical equilibrium in which the radiative cooling of the atmosphere is balanced by heating due to convection. Simulations with the Community Atmosphere Model, version 5 (CAM5), configured in RCE are presented at the standard resolution near 1-degree and also at the next-generation resolution near 0.25-degrees. The RCE setup consists of an ocean-covered Earth with diurnally varying, spatially uniform insolation and no rotation effects. Surface temperature effects are considered by comparing simulations using fixed, uniform sea surface temperature with simulations using an interactive slab-ocean model. The various CAM5 configurations provide useful insights into the simulation of tropical climate as well as the model’s ability to simulate extreme precipitation events. In particular, the manner in which convection organizes is shown to be dependent on model resolution and the surface configuration (including surface temperature), as evident by differences in cloud structure, circulation, and precipitation intensity.