Operational analysis are affected by major changes in models, analysis technique, assimilation and observation usage, which are an essential product of research and progress.
The ECMWF (European Centre for Medium-Range Weather Forecasts) performed a consistent re-analysis of atmospheric data using a "frozen" production system. The ECMWF Re-Analysis (ERA) Project produced a new, validated 15 year dataset of assimilated data for the period 12/1978-02/1994.
The assimilation scheme consisted mainly of the Integrated Forecast System (IFS) version of the ECMWF forecast model with T106 resolution on 31 vertical hybrid levels. An intermitted statistical (optimum interpolation) analysis with 6 hour cycling was performed. It includes a diabatic, non-linear normal mode initialisation (5 vertical modes).
This data set consists of a multilevel, multicode initialized model level field which is stored in spherical harmonics in 6h-intervals (0,6,12,18).
The data are given in the spectral domain of the spectral T106 forecast model. The T106 representation corresponds in the spatial domain to Gaussian N80 representation (approximately equivalent to latitude/longitude 1.125 degrees).
In order to perform the transformation from the spectral to the spatial domain please refer to the postprocessing of the T106 forecast model (DKRZ afterburner).