Effective spectral resolution of ECMWF atmospheric forecast models
Abdalla, Saleh ; Isaksen, Lars ; Janssen, Peter A. E. M. ; Wedi, Nils
Very sharp atmospheric phenomena (e.g. frontal zones or tropical cyclones) with scales of 50–80 km or the equivalent of 3–5 model grid spacings are frequently seen in the forecasts from the ECMWF Integrated Forecasting System (IFS). Since 26 January 2010, the highresolution forecasts (HRES) use a model with a spectral truncation of T1279 which corresponds to a horizontal grid resolution of 16 km (see Table 1 for a list of some of the common horizontal resolutions of ECMWF atmospheric forecast models). However, due to the nature of numerical solutions and parametrizations, the model effective resolution degrades to several grid spacings. It is of interest to estimate this effective resolution. In this article we will estimate the effective model resolution at the ocean surface by comparing the spectrum of some model fields against a corresponding spectrum from the independent radar altimeter measurements. The restriction to the ocean surface is due to the fact that altimeter wind speed measurements are only possible over the water surface. It is found that the effective useful resolution of the current HRES is 3–5 grid spacings supporting the possibility of observing sharp phenomena at this scale.
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