Reanalysis and reforecast of three major European storms of the twentieth century using the ECMWF forecasting system. Part II: Ensemble forecasts

Jung, Thomas; Klinker, E.; Uppala, S.

doi:10.1017/s1350482705001623

Cited by 18 publications

(15 citation statements)

References 28 publications

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“…Previously studies of the prediction of storms by EPS had focused on individual case studies of particular storms (Buizza and Chessa 2002;Buizza and Hollingsworth 2002;Jung et al 2005). This paper therefore presents the first statistical analysis of the regional differences in the prediction of storms by EPS.…”

Section: Introductionmentioning

confidence: 97%

Regional Differences in the Prediction of Extratropical Cyclones by the ECMWF Ensemble Prediction System

Froude

2009

Monthly Weather Review

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A regional study of the prediction of extratropical cyclones by the European Centre for Medium-Range Weather Forecasts (ECMWF) Ensemble Prediction System (EPS) has been performed. An objective featuretracking method has been used to identify and track the cyclones along the forecast trajectories. Forecast error statistics have then been produced for the position, intensity, and propagation speed of the storms. In previous work, data limitations meant it was only possible to present the diagnostics for the entire Northern Hemisphere (NH) or Southern Hemisphere. A larger data sample has allowed the diagnostics to be computed separately for smaller regions around the globe and has made it possible to explore the regional differences in the prediction of storms by the EPS. Results show that in the NH there is a larger ensemble mean error in the position of storms over the Atlantic Ocean. Further analysis revealed that this is mainly due to errors in the prediction of storm propagation speed rather than in direction. Forecast storms propagate too slowly in all regions, but the bias is about 2 times as large in the NH Atlantic region. The results show that storm intensity is generally overpredicted over the ocean and underpredicted over the land and that the absolute error in intensity is larger over the ocean than over the land. In the NH, large errors occur in the prediction of the intensity of storms that originate as tropical cyclones but then move into the extratropics. The ensemble is underdispersive for the intensity of cyclones (i.e., the spread is smaller than the mean error) in all regions. The spatial patterns of the ensemble mean error and ensemble spread are very different for the intensity of cyclones. Spatial distributions of the ensemble mean error suggest that large errors occur during the growth phase of storm development, but this is not indicated by the spatial distributions of the ensemble spread. In the NH there are further differences. First, the large errors in the prediction of the intensity of cyclones that originate in the tropics are not indicated by the spread. Second, the ensemble mean error is larger over the Pacific Ocean than over the Atlantic, whereas the opposite is true for the spread. The use of a storm-tracking approach, to both weather forecasters and developers of forecast systems, is also discussed.

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Section: Introductionmentioning

confidence: 97%

Regional Differences in the Prediction of Extratropical Cyclones by the ECMWF Ensemble Prediction System

Froude

2009

Monthly Weather Review

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“…The procedure relies on the definition of a scalar index (an Extreme Wind Index, EWI) that characterizes storminess in a two-dimensional wind field, and the subsequent analysis of the resulting index time series with methods of extreme value statistics. We apply this procedure to derive RPs for a set of prominent high-impact storm events of the recent decades, building on a coarse resolution reanalysis (the reanalysis ERA-40 of the European Centre for Medium Range Weather Forecasting, Uppala et al, 2005). In our study, we address the following specific questions:…”

Section: Introductionmentioning

confidence: 99%

The return period of wind storms over Europe

Della-Marta

Mathis

Frei

et al. 2008

Intl Journal of Climatology

137

116

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Accurate assessment of the magnitude and frequency of extreme wind speed is of fundamental importance for many safety, engineering and reinsurance applications. We utilize the spatial and temporal consistency of the European Centre for Medium Range Forecasts ERA-40 reanalysis data to determine the frequency of extreme winds associated with wind storms over the eastern North Atlantic and Europe. Two parameters are investigated: 10-m wind gust and 10-m wind speed. The analysis follows two different view-points: In a spatially distributed view, wind-storm statistics are determined individually at each grid-point. In an integral, more generalized view, the wind-storm statistics are determined from extreme wind indices (EWI) that summarize storm magnitude and spatial extent. We apply classical peak over threshold (POT) extreme value analysis techniques (EVA) to the EWI and grid-point wind data. As a reference, a catalogue of the 200 most prominent European storms has been compiled based on available literature. The EWI-based return periods (RP) estimates of catalogue wind storms range from approximately 0.1 to 300 years, whereas grid-point-based RP estimates range from 0.1 to 500+ years. EWIs sensitive to the absolute magnitude of wind speed rank the RP of wind storms in the 1989/1990 and 1999/2000 extended winter season similarly to the RP derived from the distributed approach. The RP estimates derived from EWIs are generally higher when calculated using only land grid-points compared to RPs derived using whole domain. Both the uncertainties in EWIs and grid-point-based RPs show a greater dependence on the wind parameter used than on the uncertainty associated with the EVA for RPs less than 10 years, whereas for RPs greater than 10 years the effect of the different datasets is lower. The EWIs share up to approximately 50% of the variability of the local grid-point RPs.

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“…This is done by perturbing the numerical analysis within the range of uncertainty of the initial state due to sparsity of observations, as in the ensemble prediction system (EPS), e.g. Jung et al (2005). These perturbations, introduced in regions indicated as sensitive by SV analysis, are expressed mathematically by the SVs which form basis vectors in phase space.…”

Section: Introductionmentioning

confidence: 99%

Improving simulations of severe winter storms by initial modification of potential vorticity in sensitive regions

Røsting¹,

Kristjánsson²

2006

Quart J Royal Meteoro Soc

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SUMMARYIn this paper simulations of three selected severe winter storms over the North Atlantic are presented. Modifications of potential vorticity (PV) fields according to features in water vapour (WV) images are combined with information from singular vectors (SVs) in an attempt to improve the initial state over data-sparse regions. The apparent mismatch between features in the WV images and the upper-level PV anomalies in the numerical analyses is corrected, mainly at levels indicated as sensitive by the fastest-growing SVs. The procedure is based on the fact that modification of the analysis in regions where SVs show a pronounced signal may have a large impact on the simulation. Model reruns, based on the inverted corrected PV fields, were then performed. Three cases are presented: the two French Christmas storms of 1999, and the storm affecting UK, the North Sea and southern Norway on 30 October 2000. In these cases a substantial improvement of the simulations of the storms was achieved.The PV modifications were carried out by a digital analysis system, implemented at the Norwegian Meteorological Institute. This system allows the PV modifications to be done interactively within an operational time limit.

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Reanalysis and reforecast of three major European storms of the twentieth century using the ECMWF forecasting system. Part II: Ensemble forecasts

Abstract: In Part II of this study the ECMWF Ensemble Prediction System (EPS) is used to study the

Cited by 18 publications

References 28 publications

Regional Differences in the Prediction of Extratropical Cyclones by the ECMWF Ensemble Prediction System

Regional Differences in the Prediction of Extratropical Cyclones by the ECMWF Ensemble Prediction System

The return period of wind storms over Europe

Improving simulations of severe winter storms by initial modification of potential vorticity in sensitive regions

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