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A spatial view of ensemble spread in convection permitting ensembles

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Dey, S. R. A., Leoncini, G., Roberts, N. M., Plant, R. S. and Migliorini, S. (2014) A spatial view of ensemble spread in convection permitting ensembles. Monthly Weather Review, 142 (11). pp. 4091-4107. ISSN 0027-0644

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To link to this article DOI: 10.1175/MWR-D-14-00172.1

Abstract/Summary

With movement toward kilometer-scale ensembles, new techniques are needed for their characterization. A new methodology is presented for detailed spatial ensemble characterization using the fractions skill score (FSS). To evaluate spatial forecast differences, the average and standard deviation are taken of the FSS calculated over all ensemble member–member pairs at different scales and lead times. These methods were found to give important information about the ensemble behavior allowing the identification of useful spatial scales, spinup times for the model, and upscale growth of errors and forecast differences. The ensemble spread was found to be highly dependent on the spatial scales considered and the threshold applied to the field. High thresholds picked out localized and intense values that gave large temporal variability in ensemble spread: local processes and undersampling dominate for these thresholds. For lower thresholds the ensemble spread increases with time as differences between the ensemble members upscale. Two convective cases were investigated based on the Met Office United Model run at 2.2-km resolution. Different ensemble types were considered: ensembles produced using the Met Office Global and Regional Ensemble Prediction System (MOGREPS) and an ensemble produced using different model physics configurations. Comparison of the MOGREPS and multiphysics ensembles demonstrated the utility of spatial ensemble evaluation techniques for assessing the impact of different perturbation strategies and the need for assessing spread at different, believable, spatial scales.

Item Type:Article
Refereed:Yes
Divisions:Faculty of Science > School of Mathematical and Physical Sciences > National Centre for Earth Observation (NCEO)
Faculty of Science > School of Mathematical and Physical Sciences > Department of Meteorology
ID Code:38944
Uncontrolled Keywords: Ensembles, Mesoscale forecasting, Mesoscale models, Model evaluation/performance
Publisher:American Meteorological Society

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