TIGGE, the THORPEX Interactive Grand Global Ensemble, is a key component of THORPEX: a World Weather Research Programme to accelerate the improvements in the accuracy of 1-day to 2 week high-impact weather forecasts for the benefit of humanity. Centralized archives of ensemble model forecast data, from many international centers, will be used to enable extensive data sharing and research. The designated TIGGE archive centers include the Chinese Meteorological Administration (CMA), The European Center for Medium-Range Weather Forecasts (ECMWF), and The National Center for Atmospheric Research. Scientific data requirements and archive planning solidified in late 2005, and archive colletion began in October 2006.

The Unidata Internet Data Distribution (IDD) system is used to transport the ensemble model data from the providers to the archive centers. Currently, the output from the ECMWF, UK Met Office (UKMO), Japan Meteorological Agency (JMA), National Centers for Environmental Prediction (NCEP-USA), Meteorological Service of Canada (CMC), Bureau of Meteorology Australia (BOM), Centro de Previsao Tempo e Estudos Climaticos Brazil (CPTEC), Korea Meteorological Administration (KMA), and MeteoFrance (MF) global models, totaling 240 GB/day, is moved at up to 20 GB/hour to NCAR (Realtime Statistics). By requirement the parameter fields, atmospheric levels, and physical units are consistent across all data from the providers and encoded in WMO GRIB-2 format. In contrast, each provider may submit their model output in a resolution they choose.

TIGGE data will be available to the public for non-commercial research, with a 48-hour delay after forecast initialization time. At NCAR, users can discover data through the TIGGE portal and directly download complete forecast files for the most current two-week period. Long term TIGGE data archives are available through RDA datasets for 2006, and 2007. Forecast files are organized by level type (single level, pressure level, potential vorticity level, and potential temperature level), and forecast time-step for a specified model. All ensemble members are included in each forecast file. At ECMWF, users can discover and download data through a web interface linked to the Meteorological Archival and Retrieval System (MARS). Each center will offer fast access to terabytes of data kept online and delayed access to the long term archives preserved in their archive systems. Planned future additions to the NCAR TIGGE portal include user specified sub-setting and uniform interpolation across multiple center output, and web services that will give users a common interface to request data at all archive centers.

The Key Objectives of TIGGE

• An enhanced collaboration on development of ensemble prediction, internationally and between operational centers and universities.

• New Methods of combining ensembles from different sources and of correcting for systematic errors (biases, spread over-/under-estimation).

• A deeper understanding of the contirbution of observation, initial and model uncertainties to forecast error.
• A deeper understanding of the feasibility of interactive ensemble systems responding dynamically to changing uncertainty (including use for adaptive observing, variable ensemble size, on-demand regional ensembles) and exploiting new technology for grid computing and high-speed data transfer.

• Test concepts of a TIGGE Prediction Center to produce ensemble-based predictions of high-impact weather, wherever it occurs, on all predictable time ranges.

• The development of a prototype future Global Interactive Forecasting System.