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ABSTRACT The U.K. Meteorological Office now uses a single model for atmospheric simulation and forecasting from all scales from mesoscale to climate. The constraints which numerical methods for such a model have to satisfy are described. A new version of the model is being developed with the aims of improving its accuracy by better treatment of the ‘balanced’ part of the flow, and increasing its applicability by including non-hydrostatic effects. Unusual features of this version are the use of the Charney-Phillips grid in the vertical, to improve the geostrophic adjustment properties, and the method of constructing the semi-implicit algorithm for solving the fully compressible equations. Idealized tests of these two aspects of the scheme are presented, showing that the Charney-Phillips grid reduces spurious gravity wave generation without compromising the treatment of the atmospheric boundary layer, and that the semi-implicit integration scheme can give stable solutions without the need for added temporal diffusion.
Cullen et al. (Wed,) studied this question.