A new three-dimensional nonhydrostatic model has been developed for ensemble simulation of tropical convection. The model conserves energy, enstrophy and entropy. As a result, the model has low computational noise and doesn't need artificial smoothing techniques even in long numerical integrations. The model was checked by comparison to experimental observations and analytical solutions.
The model is applied to simulate the tropical atmosphere with a constant radiative cooling rate. The model's results support the conclusion of Tompkins and Craig (1998) that there are two timescales in the approach of the atmosphere to radiative-convective equilibrium. Once the atmosphere deviates from equilibrium, it first reaches quasi-equilibrium between moisture flux and precipitation on the time scale of 1 or 2 days. Then the equivalent potential temperature adjusts on a time scale of 10 days to a steady radiative-convective equilibrium.
At the steady state, convective heating is controlled by the radiative cooling rate, rather than surface wind or sea surface temperature. However, the vertical temperature profile in the steady state is sensitive to surface wind and sea surface temperature. The model behaves similarly to Raymond's scheme of cumulus parameterization (1994).