Orography files for the European Centre for Medium-Range Weather Forecasts's (ECMWF) operational forecast model. Archived data are on the 1.125 and 2.5 degree regular longitude-latitude grids, N80 (full) Gaussian grid and Spectral (T106) grid. These files are updated each time the model orography is changed. For the Operational data (March 1994-present day) there are orography files for the following dates: 1 March 1994, 4 April 1995, 8 September 1996, 10 December 1996, 1 April 1998 and 12 October 1999. The orography for the ERA-15 project was constant so only the start date orography is stored here: i.e. for 1 Jan 1979. The spectral orography file only contains the orography data (surface geopotential). Depending on the age and grid type, the remaining files contain some of the constant fields: Geopotential (at the surface, orography), Standard deviation of orography, Anisotropy of subgrid scale orography, Angle of subgrid scale orography, Slope of subgrid scale orography, Land/Sea mask, EW component of sub-grid scale orographic variance, NScomponent of sub-grid scale orographic variance, NWSE component of sub-grid scale orographic variance, NESW component of sub-grid scale orographic variance.