Naslov
Extended-range predictions with ECMWF models. II. Influence of horizontal resolution on systematic error and forecast skill.

Autori
Tibaldi, S. ; Palmer, T.N. ; Branković, Č. ; Cubasch, U.

Izvornik
ECMWF Technical Memorandum 152

Vrsta, podvrsta
Ostale vrste radova, izvještaj

Godina
1989

Ključne riječi
extended-range; horizontal resolution; systematic errors; forecast skill

Sažetak
The influence of horizontal resolution on model systematic error and skill scores are examined for both winter and summer seasons from a set of extended-range integrations of the ECMWF numerical weather prediction model. The forecast data are composed of 24 30-day integrations, two per month from successive 12 GMT operational analyses, from April 1985 to March 1986 at four (triangular truncation) horizontal spectral resolutions of T21, T42, T63 and T106. Systematic errors in wind, temperature, heat and momentum fluxes are discussed, both in the tropics and extratropics. Dynamical reasons for differences between various model resolutions and between simulations and observations are proposed. Diagnosis of model systematic error is aided by comparing zonal-mean diagnostics of the observed flow in the northern hemisphere winter and southern hemisphere winter. The impact of resolution on regional simulations of rainfall during the Indian and African monsoons is also discussed. In the extratropical troposphere, the behaviour of the T21 model is quite distinct from the higher-resolution models. The southern hemisphere flow is weak, and in both hemispheres horizontal momentum fluxes are severely underestimated. The systematic errors of the T42, T63 and T106 models are quite similar to each other in the extratropical troposphere. Errors at these higher resolutions resemble the observed difference (in zonal-mean wind, temperature and eddy fluxes) between diagnostics in the northern hemisphere winter and southern hemisphere winter, suggesting that orographic forcing in this version of the ECMWF model is inadequate, despite the inclusion of envelope orography.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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