UKCP09: Format of 25 km grid files

The 25 x 25 km grid files contain 1961-1990 baseline averages for the grid boxes of the HadRM3 regional climate model. This model uses a rotated-pole grid to define the grid boxes, i.e. a latitude-longitude grid in which the North Pole has been rotated away from its real-world position. A description of the HadRM3 rotated-pole grid is available online.

To find the row and column numbers of a grid box in a specific part of the UK, please use this map or refer to Q19 in the list of FAQs. A map showing the outlines of all the 25 km grid boxes is available online.

The 25 km grid files are available in two formats.

Text files

These are similar in format to the 5 km grid text files. A matrix of values covering the whole of the UK is provided in one file for each month, season, or the year as a whole. Each value represents an estimate of the average for a HadRM3 model grid box.

The data are preceded by six header rows constructed as follows.

The number of columns (39)
The number of rows (52)
A dummy value for the longitude of the south-west corner of the most south-westerly grid cell (-0.50)
A dummy value for the latitude of the south-west corner of the most south-westerly grid cell (-0.50)
A dummy value for the grid cell size (1.00)
The value which indicates no data (9999.00, this indicates that the grid square is outside the scope of the climate data, which is UK land areas)

The matrix of values follows, arranged according to the natural geography of the UK when presented on screen or paper, i.e. the values in each row run from west to east (reading from left to right) and the rows are ordered from north to south (reading from top to bottom). The data are presented as space-delimited values.

Note: The format of the grid text files is the same as that used by ESRI GIS software (e.g. ArcView) to import/export gridded data as plain text. However, due to the use of a rotated-pole grid, dummy values have been used for the location of the south-west corner and the grid cell size. Users of ESRI software can import the files without modification, but it may not be possible to combine the data with other information that uses a different grid system.

netCDF files

The 25 km grids are also available in CF-netCDF format. This is a commonly used binary format for climate and forecast data sets. Further information can found via the following links.