Sensitivity of Dynamical Quantities to Horizontal Resolution for a Climate Simulation Using the ECMWF (Cycle 33) Model

Abstract

The European Centre for Medium-Range Weather Forecasts (ECMWF) model (cycle 33) was integrated for a full seasonal cycle at four horizontal resolutions, T21, T42, T63, and T106. Within the limits imposed by the varying horizontal resolution all other aspects of the model were identical for each integration. In this paper a comparison is made of the dynamical aspects of the simulations. Fields of zonally averaged zonal wind, eddy heat and momentum fluxes, global divergent wind and vorticity, and stationary wave patterns are presented and compared for each resolution. The conclusions reached by this study are (i) T21 is qualitatively different from the higher resolutions; (ii) the highest resolution does not provide a simulation that is egregiously superior to T42. There are aspects of the T21 simulation, especially in tropical convection, that are clearly better than the higher resolutions; (iii) aside from differences in smaller-scale boundary forcing at the higher resolutions, the T42. T63, T106 simulations are nearly identical in the dynamical aspects of the circulation considered here, and (iv) increasing horizontal resolution alone will not result in an overall superior simulation, unless other aspects of the model are modified at an equal pace.