Observational Constraints on Scale-Awareness; Illumination of Scale-Incognizance in CAM

We use observations of robust scaling behavior in clouds and precipitation to derive constraints on how partitioning of precipitation should change with model resolution. Our analysis indicates that 90--99% of stratiform precipitation should occur in clouds that are resolvable by contemporary climate models (e.g. 200~km or lower horizontal resolution). Furthermore, this resolved fraction of stratiform precipitation should increase sharply with resolution, such that effectively all stratiform precipitation should be resolvable above scales of ~50km. We show that the Community Atmosphere Model (CAM4) also exhibits the robust cloud and precipitation scaling behavior that is present in observations (impressively so), yet the resolved fraction of stratiform precipitation actually decreases with increasing model resolution. A suite of experiments with multiple dynamical cores provides strong evidence that this `scale-incognizant' behavior originates in one of the model's parameterizations. An additional set of sensitivity experiments rules out both convection parameterizations and the sub-grid stratiform scheme, which implicates the microphysics parameterization. Tests with the CAM5 physics package show improvements in the resolution-dependence of resolved cloud fraction and resolved stratiform precipitation fraction.