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1 Météo-France Paris

Abstract : The performance of single models and ensemble prediction systems has been investigated with respect to quantitative precipitation forecasts. Evaluation is based on the potential economic value of + 72 h- + 96 h forecasts. The verification procedure consists of taking into account all precipitation amounts that are predicted in the vicinity of an observation in order to compute spatial, multi-event contingency tables. A probabilistic forecast from an ensemble can thus be compared to a probabilistic forecast from a single model run. The main results are the following: 1 The performance of the forecasts increases with the precipitation threshold. High levels of potential value reflect high hit rates that are obtained at the expense of a high frequency of false alarms. 2 The ECMWF ensemble performs better than a single forecast based on the same model, even when the resolution of the ensemble is lower. This is true for the NCEP ensemble as well, but only for morning precipitations. 3 The ECMWF ensemble performs better than the 5-member NCEP ensemble running at 12:00 UTC, even when the population of the former is reduced to 5 members. 4 The impact of reducing the population of the ECMWF ensemble is rather small. Differences between 51 members and 21 members are hardly significant. 5 A 2-member poorman ensemble consisting of the control forecasts of the ECMWF and the NCEP ensembles performs as well as the ECMWF ensemble for afternoon precipitations.





Autor: F. Atger -

Fuente: https://hal.archives-ouvertes.fr/



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