The Boundary Conditions Suite was set up in June 2000. It is set up as a separate operational suite to limit the impact on the core ECMWF activities. A data cut-off time of 4 hours is used. 3D-Var analysis and forecasts to 90 hours, with 3-hourly post-processing, are run at 00, 06, 12 and 18 UTC. The 18 UTC 3D-Var analysis uses preliminary fields from the 12 UTC operational 4D-Var assimilation. Experimentation has shown that there is no benefit to be gained in resetting the BC suite to the state of the operational 4D-Var assimilation more than once a day. This scheme works equally well with the newest 12 hour 4D-Var assimilation as it was with the previous 6 hour 4D-Var assimilation. In the event of interruption, the BC suite can be restarted from any of the operational 4D-Var analysis.

To minimise the risk of disruption to users, the initial system was set up to run in parallel with the 00 UTC project. The final system introduces an additional and very specific product generation and dissemination for full field forecast products from the 00 UTC cycle only. As previously, these fields are sent as soon as they are ready, not to a schedule as for the frame products (see below). This specific product generation of full field forecast products for 00 UTC will be terminated by 31 December 2001 at the latest.

Only the analysis data are archived in MARS. No access to any of the forecast fields is allowed.

Dissemination is to a schedule, with analysis products available for transmission five hours and 50 minutes after analysis base time and forecasts available some 30 minutes later. If there are problems for cycles 06 and 18 UTC based and dissemination data are not available six and a half hours after analysis base time, that cycle will be abondoned.

Since the 14. March 2006 Boundary Condition project has been merged with the main deterministic operational forecast suite. In the new configuration, only the 06 and 18 UTC runs are part of the BC suite. For the 00 and 12 UTC runs data are provided from the main deterministic forecast suite. This new configuration has incorporated the following changes:

- All four data assimilation cycles are based on 4D-Var, combining the boundary value forecasts with ECMWF core forecast runs for 00 and 12 UTC, and replacing the 3D-Var (FGAT) analysis cycles for 06 and 18 UTC;

- The data for 00 and 12 UTC are sent with STREAM DA instead of SCDA in the GRIB description; 06 and 18 UTC data have continued to be sent with stream SCDA in the GRIB description.

Even though the input data comes from different data streams, DA and SCDA, ECMWF has continued to provide users of BC data with separate dissemination files for all four cycles 00, 06 12 and 18 UTC. Data from the 00 and 12 UTC runs requested for the BC project (specifying USE=BC in the requirements, see bellow) have continued to be delivered in dissemination files with the data stream id 'S'.

07-11-2011