Abstract
We examine the results of the Aqua-Planet Experiment Project (APE), focusing mainly on the structure of equatorial precipitation in the subset of participating models for which the details of model variables are available. Despite the unified setup of the APE, the Hovmöllor plots of precipitation in the models exhibit a considerable degree of diversity, presumably as a result of the diversity among the implementation of the various physical processes. Nevertheless, the wavenumber-frequency spectra of precipitation show certain similarities, and the power spectra can be divided into Kelvin, westward inertio-gravity, and “advective” components. The intensity of each of these three components varies significantly among different models. The composite spatial structures corresponding to these three components are produced by performing regression analysis with space-time filtered data. The composite horizontal structures of the Kelvin and westward inertio-gravity components are similar among the models, and resemble those expected from the corresponding equatorial shallow-water wave modes. These resemblances degrade at the altitude levels where the value of phase velocity approaches the zonal mean zonal wind speed. The horizontal structure of the advective component diverges significantly among the models. The composite vertical structures are strongly model dependent for all three components. The comparison of the vertical and horizontal structures associated with convective and stratiform heating of the composite disturbances indicates that the diversity of the vertical structures originates from differences in the implementation of the physical processes, especially the implementation of cumulus parameterization.
