The non-hydrostatic global IFS/ARPEGE model: model formulation and testing

TitleThe non-hydrostatic global IFS/ARPEGE model: model formulation and testing
Publication TypeMiscellaneous
Year of Publication2009
AuthorsWedi, NP, Yessad, K, Untch, A
Secondary TitleTechnical Memorandum

In preparation for global applications at horizontal scales finer than about 10 km, where nonhydrostatic dynamics becomes important, the efficacy and stability of the nonhydrostatic model developed by the ALADIN group and made available byM´et´eo-France in the global IFS/ARPEGE model are assessed. The main attraction of this nonhydrostatic dynamical core is its algorithmic similarity to the existing hydrostatic IFS (H-IFS). The performance of the nonhydrostatic model (NH-IFS) is assessed for a wide range of scales and for a set of canonical test cases relevant to atmospheric flows. The results obtained for a range of idealized nonhydrostatic flow problems compare satisfactorily to Cartesian-domain analytic solutions, where available, and to the nonhydrostatic research code EULAG. At hydrostatic scales (for grid-sizes upto 10 km) the NH-IFS gives very similar forecasts to the operational hydrostatic IFS, and can be run stably with the rather long timesteps used with the latter model. However, the computational cost of the NH-IFS per timestep is substantially larger than with the H-IFS (double at 10 km resolution). It is concluded that the NH-IFS dynamical core is a possible choice for future, globally-uniform high resolution applications at ECMWF, provided its cost can be reduced.