Introduction of a local mapping factor in the spectral part of the Meteo-France global variable mesh numerical weather forecast model

Année de publication

1996

For variable horizontal resolution simulations, a new formulation of spectral computations has been implemented in the ARPEGE/IFS spectral global numerical weather forecast model. The formulation makes use of a property of the conformal transformation which defines the stretched geometry: the local mapping factor is a combination of zero and first-order Legendre polynomials only. Consequently, the mapping factor dependency in the spectral part of the computations can be introduced by simple extra multi-diagonal operator multiplication. This idea is applied to both the semi-implicit and the horizontal diffusion schemes to eliminate problems occurring when variable resolution is used together with either long time-steps or steep orographies. The positive impact of these modifications is presented for semi-Lagrangian and high-resolution integrations. The relatively small extra computation and memory cost of the modified schemes is well suited to operational applications.</div>

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