GridAlt, an `alternate grid' technique for GCMs, allows different GCM components to be computed on different grids. Results are presented from simulations with an implementation of GridAlt in which all the physics increments are computed on a higher resolution vertical grid than the dynamics in the near surface regime where the turbulent length scales are smaller than typical GCM vertical grid spacing.

A suite of aquaplanet simulations, for which GridAlt and fully resolved experiments can be compared directly, show that the GridAlt experiments successfully capture the structure of the latent heating, the turbulent kinetic energy, relative humidity and mass streamfunction fields. The structure of the zonal wind field is less well simulated in the GridAlt experiments. A suite of realistic simulations with GridAlt shows an increased low level cloud cover, and an increased atmospheric response to the variations of the underlying surface temperature.