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 old cluster products have been discontinued on 6 Feb 2013.
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).
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:
Implemented: 08 March 2011 |
Resolution
Unchanged