The representation of the analysis in three error simulation techniques
La représentation de l'analyse dans trois techniques de simulation d'erreur
Berre L. ; S. E. Stefanescu ; M. Belo Pereira
Three error simulation techniques are compared formally, in particular regarding their representation of the analysis
step. The associated results are moreover examined for the Aladin-France limited-area model, which is coupled with<br>the Arp`ege global model.<br>It is first shown that the analysis error equation involves the same operators as the analysis equation. This implies<br>that the analysis ensemble approach is appropriate, as the analysis equation is used to transform the background and<br>observation dispersions into the analysis dispersion.<br>By contrast, the standard NMC method relies essentially on the analysis increment equation, which contributes to a<br>large extent to the excessive emphasis on the large-scale structures. The so-called lagged NMC method is shown to be<br>closely related to the Arp`ege/Aladin model differences.<br>The analysis ensemble approach gives error spectra that are intermediate between those of the two other methods.<br>This is in agreement with the representation of the initial and lateral boundary uncertainties, in a way that is consistent<br>with the influence of the analysis equation and with the short forecast ranges.<br>
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