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Evaluation of probabilistic quality and value of the ENSEMBLES multimodel seasonal forecasts: Comparison with DEMETER

TitoloEvaluation of probabilistic quality and value of the ENSEMBLES multimodel seasonal forecasts: Comparison with DEMETER
Tipo di pubblicazioneArticolo su Rivista peer-reviewed
Anno di Pubblicazione2011
AutoriAlessandri, Andrea, Borrelli A., Navarra A., Arribas A., Déqué M., Rogel P., and Weisheimer A.
RivistaMonthly Weather Review
Volume139
Paginazione581-607
ISSN00270644
Parole chiaveAtmospheric temperature, Boundary forcing, Calibration, Climate change, climate effect, climate prediction, Climatology, data assimilation, Demeter, Economical value, ensemble forecasting, Ensembles, European Commission, Forecasting, Global warming, greenhouse gas, Greenhouse gases, Inter-annual predictions, Midlatitudes, Model comparison, Multi-model, Multi-model ensemble, Multimodel systems, Physical process, Potential users, probability, Sea ice, Seasonal forecasting, Seasonal forecasts, Seasonal prediction, Seasonality, Sub-grids, Surface properties, surface temperature, Surface temperatures, temporal variation, Time variations, Tropics, Weather forecasting
Abstract

The performance of the new multimodel seasonal prediction system developed in the framework of the European Commission FP7 project called ENSEMBLE-based predictions of climate changes and their impacts (ENSEMBLES) is compared with the results from the previous project [i.e., Development of a European Multimodel Ensemble System for Seasonal-to-Interannual Prediction (DEMETER)]. The comparison is carried out over the five seasonal prediction systems (SPSs) that participated in both projects. Since DEMETER, the contributing SPSs have improved in all aspects with the main advancements including the increase in resolution, the better representation of subgrid physical processes, land, sea ice, and greenhouse gas boundary forcing, and the more widespread use of assimilation for ocean initialization. The ENSEMBLES results show an overall enhancement for the prediction of anomalous surface temperature conditions. However, the improvement is quite small and with considerable space-time variations. In the tropics, ENSEMBLES systematically improves the sharpness and the discrimination attributes of the forecasts. Enhancements of the ENSEMBLES resolution attribute are also reported in the tropics for the forecasts started 1 February, 1 May, and 1 November. Our results indicate that, in ENSEMBLES, an increased portion of prediction signal from the single-models effectively contributes to amplify the multimodel forecasts skill. On the other hand, a worsening is shown for the multimodel calibration over the tropics compared to DEMETER. Significant changes are also shown in northern midlatitudes, where the ENSEMBLES multimodel discrimination, resolution, and reliability improve for February, May, and November starting dates. However, the ENSEMBLES multimodel decreases the capability to amplify the performance with respect to the contributing single models for the forecasts started in February, May, and August. This is at least partly due to the reduced overconfidence of the ENSEMBLES single models with respect to the DEMETER counterparts. Provided that they are suitably calibrated beforehand, it is shown that the ENSEMBLES multimodel forecasts represent a step forward for the potential economical value they can supply. A warning for all potential users concerns the need for calibration due to the degraded tropical reliability compared to DEMETER. In addition, the superiority of recalibrating the ENSEMBLES predictions through the discrimination information is shown. Concerning the forecasts started inAugust, ENSEMBLES exhibitsmixed results over both tropics and northernmidlatitudes. In this case, the increased potential predictability compared to DEMETER appears to be balanced by the reduction in the independence of the SPSs contributing to ENSEMBLES. Consequently, for the August start dates no clear advantage of using one multimodel system instead of the other can be evidenced. © 2011 American Meteorological Society.

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URLhttps://www.scopus.com/inward/record.uri?eid=2-s2.0-79953224507&doi=10.1175%2f2010MWR3417.1&partnerID=40&md5=b3f4c45ce4a0d6f90350df94c963c8cb
DOI10.1175/2010MWR3417.1
Citation KeyAlessandri2011581