- Created by Helen Setchell on Dec 11, 2022
Description of the upgrade
ECMWF upgraded its operational seasonal forecasts from System 2 to System 3. The change to operational status took place in March 2007, when System 2 ceased to be operational, and System 3 became the new operational forecast system.
Description of System 3
The resolution of the atmosphere model is increased from TL95 with 40 vertical levels to TL159 with 62 vertical levels.
The resolution of the ocean model is unchanged. The horizontal zonal resolution is 1.4 degrees and the horizontal meridional resolution smoothly varies from 0.3 degrees in the equatorial region (within 10 degrees of the equator), to 1.4 degrees polewards of 30 degrees. There are 29 vertical levels.
The ensemble s are changed. The real-time forecasts will now have 41 members (previously 40). The re-forecasts will have 11 members uniformly for all start months (previously 5 members, with 40 members for May and November starts only).
The period of the re-forecasts have been extended, and covers the 25 years from 1981 to 2005. This is significantly longer than the 1987-2001 15 year period of the previous system, and should allow better calibration of the forecasts and better assessment of their skill.
The standard forecast length (for both forecasts and back integrations) is increased from 6 to 7 months. This gives a forecast range of 6.5 months from the release date of the forecasts.
Four times a year, from the Feb, May, Aug and Nov starts, 11 members (out of 41) of the forecast ensemble will run to 13 months. This will allow an "ENSO outlook" to be given. The re-forecasts for these start months have 5 ensemble members (out of 11) that extend to 13 months. (The November starts are actually 14 months long in all cases, so they extend to the end of the following calendar year.) Note that, at least initially, these extended runs will be classed as experimental rather than operational, and data from them will not be available via dissemination.
Scientifically, there have been many enhancements to the ocean analysis system used to prepare ocean initial conditions. The atmosphere model has been upgraded to IFS cycle 31r1, which is the latest version for medium-range forecasting at ECMWF (introduced on 12 September 2006). There have also been significant revisions to the perturbation methods used to generate the forecast ensemble.
Tests show that the prediction skill for Pacific equatorial SSTs (i.e. El Niño variability) is measurably improved in the new system. Changes in skill for atmospheric variables are less clear cut with the limited test sample presently available. Overall, improvements in predictive skill are expected to be more evident during the Northern Hemisphere summer season, and in tropical regions throughout the year.
Further reading
- Development of the ECMWF Seasonal Forecast System 3 - ECMWF Technical Memorandum No. 503 (April 2007)
- The ECMWF System 3 ocean analysis system. - ECMWF Technical Memorandum No. 508 (Februaryl 2007)
- Seasonal Forecast System 3 - ECMWF Newsletter No. 110 (pp19-25) - Winter 2006/07
- New web products for the ECMWF Seasonal Forecast System 3 - ECMWF Newsletter No. 111 (pp28-33) - Spring 2007
- Seasonal Forecast User Guide (System 3) - http://www.ecmwf.int/products/forecasts/seasonal/documentation/
- Full information on the forecast skill, including the WMO SVS scores is available at http://www.ecmwf.int/products/forecasts/d/charts/seasonal/verification/
Content as it was published on 07.08.2009
Implemented: 01 March 2007
Resources
ECMWF Newsletter: See Newsletter 111
Contents of this page
All IFS cycles
- Terminology for IFS testing
- Implementation of IFS Cycle 48r1
- Implementation of IFS Cycle 47r3
- Implementation of IFS Cycle 47r2
- Implementation of IFS Cycle 47r1
- Implementation of IFS cycle 46r1
- Implementation of IFS cycle 45r1
- Implementation of Seasonal Forecast SEAS5
- Implementation of IFS cycle 43r3
- Implementation of IFS Cycle 43r1
- Implementation of IFS cycle 41r2
- Introducing the octahedral reduced Gaussian grid
- Horizontal resolution increase
- Boundary-Condition Programme ENS at 06 and 18 UTC
- Implementation of IFS Cycle 41r1
- IFS cycle upgrades pre 2015