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Description of the upgrade
A new set of cluster products for the ENS has been introduced. The new system includes two applications of clustering methodology:
A daily clustering of the forecast fields from the EPS, similar in principle to the old EPS clustering but using a different algorithm. The daily clustering determines weather scenarios, defined as the ensemble members closest to the centroid of each cluster.
A set of fixed climatological regimes for each season, computed using 29 years of reanalysis data (ERA-Interim and ERA-40).
This combined approach provides the user with:
a set of weather scenarios that appropriately represent the ensemble distribution
an additional objective measure of the differences between scenarios in terms of large scale flow (by using the attribution of each weather scenario to the climatological regimes)
easy computations of flow-dependent skill measures (under development)
The new products are computed on a new European domain (domain=H). For type cluster means they will replace the old products and a new type cluster representative (type=CR) will be added. Type cluster standard deviations will not be produced.
The new cluster products have been added to the Catalogue of ECMWF Real-Time Products Set III- Atmospheric Model low resolution 15-day forecast (ENS) on 8 Mar 2011.
The old cluster products have been discontinued on 6 Feb 2013.
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Implemented: 08 March 2011 |
Old cluster products
The old operational clustering algorithm is based on the RMS differences between the 500 hPa geopotential height ensemble forecasts, averaged from +120h to +168h taking the synoptic continuity into account.
The graphical products for the old clustering algorithm have been discontinued.
Products in GRIB code using local definition 2 are available from MARS and dissemination as follows:
The old cluster products have been discontinued on 6 Feb 2013.
The ENS cluster products replace the old Cluster means and introduce the new type Cluster representatives.
New cluster products
The new clustering method combines a daily clustering of ENS forecasts, similar in principle to the old ENS clustering, with a set of fixed climatological regimes for each season, computed from 29 years of reanalysis data (ERA-Interim and ERA-40). Weather scenarios derived from the daily clustering and defined as the ensemble members closest to the centroid of each cluster are called cluster representative members in MARS language (type=CR).
The new graphical cluster products are available for the time windows 72-96, 120-168, 192-240 and 264-360 hours.
Products in GRIB code using local definition 32 are available from MARS and dissemination as follows:
Note that the new products, based on 500 hPa geopotential, are computed in a new domain H (30°-75°N, 20°W-40°E).
Technical characteristics of the new cluster products
As the new products have been coded using local definition 32, they have to be handled with the following software versions:
libemos 372 onwards
grib_api 1.9.0 onwards
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Implemented: 08 March 2011 |
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