An idealized test of the response of the Community Atmosphere Model to near-grid-scale forcing across hydrostatic resolutions

The test consists of a set of rising bubble experiments, in which the horizontal radius of the bubble and the model grid spacing are simultaneously reduced. The test is performed with moisture, through incorporating moist physics routines of varying complexity, although convection schemes are not considered.

Results confirm that the vertical velocity in CAM is to first-order, proportional to the inverse of the horizontal forcing scale, which is consistent with a scale analysis of the dry equations of motion. In contrast, experiments in which the coupling time step between the moist physics routines and the dynamical core (i.e., the "physics'' time step) are relaxed back to more conventional values results in severely damped vertical motion at high resolution, degrading the scaling.