A new version of the ECMWF forecasting and analysis system, Cycle 37r2, was implemented on 18 May 2011. The new cycle includes both meteorological and technical changes.
The main meteorological changes included in this cycle are the use of flow-dependent background errors in the data assimilation, reduced AMSU-A observation errors and improvements to the cloud scheme. The changes show clear benefits in terms of objective upper-air scores in the medium range. Temperature and winds are improved throughout the troposphere in the extra-tropics. The improvements to the cloud scheme increase the humidity in the upper troposphere, providing a better fit to observations and improving humidity scores in the extra-tropics in the early forecast range.
The impact of Cycle 37r2 is shown in the figure below.
Impact of Cycle 37r2. The figure shows the normalised difference in anomaly correlation of 500 hPa geopotential height (bold blue lines) between Cycle 37r2 and the previous operational cycle (36r4) together with the 95% confidence interval (light blue bars) for the Northern and Southern hemispheres and Europe. The plot for the tropics shows normalized difference in root-mean-square error of 850 hPa vector wind. The positive impact of Cycle 37r2 is important in all areas and at almost all forecast ranges.
The new cycle also includes a significant technical change: WMO FM-92 GRIB edition 2 (GRIB-2) is used for the encoding of model-level data; GRIB-1 model-level data are no longer produced or disseminated. In the course of the cycle implementation several major codes have been migrated to using the grib_api software for the handling of GRIB data, for instance the Integrated Forecasting System (IFS), the product generation and the Meteorological Archival and Retrieval System (MARS). The grib_api is the application program interface developed at ECMWF to provide an easy and reliable way for encoding and decoding GRIB-1 and GRIB-2messages. For further information please see http://www.ecmwf.int/products/data/software/grib_api.html
ECMWF has achieved this technical milestone in close collaboration with its Member States, Co-operating States and other users of the model-level data, and ECMWF is very grateful for their support.