Page History

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• ECMWF strategy 2015-2025 is centred on ENS development
• The horizontal and vertical resolutions of the medium range control member ensemble (CTRLENS) became almost identical to HRES upon the introduction of Cy48r1 in June 2023the same as for the HRES after the upgrade to IFS (Cy48r1) introduced in June 2023.  The HRES forecast and the unperturbed ENS control forecast are meteorologically equivalent and equally skilful on average.  They have the same physical and dynamical representation of the atmosphere and use the same parameterisation of sub-gridscale effects.  However, they can diverge on a day-to-day basis due to small technical differences and the chaotic nature of the atmosphere.  The HRES will continue for the time being for ease of use by customers and users.

Use of the ensemble control member (CTRL)

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The main strategy to adopt is to avoid over-interpreting non-predictable features.  Therefore the detail of the most recent ensemble members should not be used in isolation.   Run-to-run jumpiness can on the one hand be tackled as something negative that has to be dampened, but on the other hand as something positive which can enrich the forecast information by giving alternative scenarios.  Ensemble members can give an indication of the probability and the consistency of features of the forecast.

Ensemble control member and HRES

Since introduction of Cy48r1 in June 2023, HRES and the ensemble control member have the same horizontal and vertical resolution.  However, there are some minor differences in the model structure.

HRES should be considered as just another (unperturbed) member of the ensemble.  Sometimes quite large differences from other ensemble members occur.  But analysis of HRES and ensemble forecasts give some evidence that HRES and Control forecast are meteorologically equivalent.  See further comments on the similarity and differences between HRES and ENS control.  

Use of the ensemble mean (EM)

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