COSMO Limited-Area Ensemble Prediction System

August 2008

COSMO-LEPS is the Limited Area Ensemble Prediciton System developed within COSMO consortium in order to improve the short-to-medium range forecast of extreme and localised weather events.
It is made up of 16 integrations of COSMO model, which is nested on selected members of ECMWF EPS.

1. Basic model set-up
2. Recent Changes
3. Operational schedule

1. Basic model set-up

COSMO- LEPS started to run on an experimental-operatonal basis on November 2002 and, in November 2005, it became an ECMWF member-state time-critical application, managed by ARPA-SIM.
COSMO-LEPS runs on a daily basis using a 10 km grid spacing and 40 vertical layers, starting at 12UTC and with a forecast range of 132 hours. The computer time to run the system at ECMWF is provided by a joint account, with the contributions of the COSMO countries which are also ECMWF member state (namely, Greece, Germany, Italy and Switzerland).

The rotated lat-lon coordinates of the lower left and upper right corner of the integration domain are lon=-12.5^o, lat=-16.0^o and lon=14.95^o, lat=7.13^o, respectively. The following figure shows the orography (height in m) of the COSMO-LEPS integration domain used.

Fig. 1: The Cosmo domain used for the COSMO LEPS (enlarge)

2. Changes

Since 1 December 2007

Since 1 December 2007, the following changes were implemented in the operational suite:

• use of COSMO-model version 4.0
• use of Runge-Kutta numerical scheme
• use of multi-layer soil scheme in int2lm and in cosmo-model
• introduction of new random perturbations in each COSMO-LEPS integration:
  pat_len can take the following values: either 500 or 10000,
  tur_len can take the following values: either 500 or 1000, (in addition to the random choice between Kain-Fritsch and Tiedte as convection scheme).

Since September 2003

Since September 2003, a 10-member suite is being experimented. In addition to the 5 Cosmo integrations with the operational convection scheme ("Tiedtke runs"), 5 more runs are performed using the recently-implemented Kain-Fritsch convection scheme ("KF runs"). In order to minimize modifications to the operational suite and to test properly the impact of the new scheme, the 5 KF integrations use the same boundary and initial conditions as the Tiedtke runs. Rainfall probability maps using the 10-member suite are being produced and disseminated in addition to the operational ones. The skill of the KF runs as well as the usefulness of a 10-member suite will be evaluated during 2004.

Two test suites started on 1/10/2003 to assess the impact of the clustering-selection technique when either the most recent EPS or the two most recent EPSs are used to select the representative members (when compared to the operational suite when 3 successive EPS sets are employed). The verification will be performed only on EPS runs by assessing the performance of the "reduced" EPS, that is the 5-member EPS obtained after the clustering-selection technique.

3. Operational schedule

COSMO-LEPS application starts at about 20.50 UTC, once the ECMWF EPS starting at 12UTC has passed fc+144h forecast range. Products are disseminated to Met Ops rooms of COSMO weather offices starting from 23.00UTC.