Juist de vraag of de control elke keer bovenin of onderin zit is de essentie. Als dat steeds wisselt weet de meteoroloog dat numeriek gezien de oplossingen uit het computermodel niet stabiel zijn.
Naast het inschatten van de impact van modelresolutie op de voorspelbaarheid, is dat ook zeker een belangrijk nut. Het wordt verduidelijkt in de User Guide van het ECMWF (alleen Engels):
,,If forecasts starting from the perturbed analyses agree more or less with the forecast from the non-perturbed analysis (the EPS Control forecast), then the atmosphere can be considered to be in a predictable state and any unknown analysis errors would not have a significant impact. In such a case, it would be possible to issue a categorical forecast with great certainty.
If, on the other hand, the perturbed forecasts deviate significantly from the Control forecast and from each other, it can be concluded that the atmosphere is in a rather unpredictable state. In this case, it would not be possible to issue a categorical forecast with great certainty. However, the way in which the perturbed forecasts differ from each other may provide valuable indications of which weather patterns are likely to develop or, often equally importantly, not develop.''
Gr. Ben
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