Differences in tropical rainfall in aquaplanet simulations with resolved or parameterized deep convection

A series of aquaplanet simulations are analyzed using the Model for Prediction Across Scales-Atmosphere with horizontal cell spacings from 120 to 3 km. The 3-km experiment uses a novel configuration with 3-km cell spacing between 20 degrees S and 20 degrees N and 15-km cell spacing poleward of 30 degrees N/S. A comparison of those experiments shows that resolved deep convection yields a narrower, stronger, and more equatorward intertropical convergence zone, which is supported by stronger nonlinear horizontal momentum advection in the boundary layer.

There is also twice as much tropical rainfall variance in the experiment with resolved deep convection than in the experiments with parameterized convection. All experiments show comparable precipitation variance associated with Kelvin waves; however, the experiment with resolved deep convection shows higher precipitation variance associated with westward propagating systems. Resolved deep convection also yields at least two orders of magnitude more frequent heavy rainfall rates (>2 mm hr(-1)) than the experiments with parameterized convection.