Important Note, 23 July 2012: On July 12, 2012, BADC added the following note to its CRU TS3.1 documentation page: "A systematic error was discovered in the CRUTS v3.01 process generating the precipitation, wet days and frost frequency data files. New precipitation data files (version 3.01.01) have been generated and are now available in the archive. Wet days and frost frequency files will be made available at a later time." The revised precipitation file and both precipitation station count files were added to the IRI Data Library holdings on July 23, 2012, replacing the previous version of these files.
Additionally, also in July 2012, BADC added the file "READ_ME_CRUTS_PRE_v3.01.01.txt" to its documentation, which states the following:
READ ME file for CRUTS v3.01.01 (PRE only) In July 2012, a systematic error was discovered in the CRUTS v3.01 process. The effect was, in some cases, to reduce the gridded values. The files were immediately removed from BADC and from the Climate Explorer at KNMI. This corrected run, based on the v3.01 precipitation station data, should be used as a direct replacement. The version number 3.01.01 reflects this status.
CRU TS 3.1 data are produced used the same methodology as for the 3.0 dataset. The main differences is that the 3.1 dataset extends from 1901-2009, and all of the data in this period can now be used. Slight differences may be noticed between the results for a given time/location between the 3.0 and 3.1 versions, due to additional data now being available. CRU have examined the 3.1 dataset in detail and are confident that such differences are not significant.
The station count files are all integer, because they are counts.
'stn' is all stations reporting within the CDD of the variable in question.
'st0' is all stations reporting within the cell itself.
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NOTE: (added 20/5/11)
Due to an encoding error, the station count files ('st0' and 'stn') will need to be multiplied by a scale factor to obtain their true integer values, as follows:
* For 'wet', multiply by 100.
* For all other station count files, multiply by 10.
The station counts are scaled by the parameter scale factor:
tmp 0.100
dtr 0.100 \
tmn 0.100 > ('tmpdtr' st0 & stn counts)
tmx 0.100 /
pre 0.100
vap 0.100
wet 0.010
cld 0.100 (only 'stn' files)
frs 0.010 (no station counts)
pet 0.100 (no station counts)
Calculation of Potential Evapotraspiration (PET)
The method used is the FAO (Food and Agricultural Organization) grass reference evapotranspiration equation (Ekstrom et al., 2007, which is based on Allen et al., 1994). It is a variant of the Penman Monteith method using the gridded TMP, TMN, TMX, VAP and CLD. Note that PET values are mean mm/day for each month (with a scaling factor of 10 applied to the netcdf files). The pet values in the datafiles therefore need to be muliplied by the number of days for each month to get the mean pet for that month
* note that a scaling factor of 10 has been applied to the PET ascii data but NOT the PET netcdf data. *
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It is planned that the dataset will be updated every 6 months, with the first 3.1 update scheduled for July 2011.
Note: The files themseleves are >2GB when unzipped, which may cause problems on the computer systems of some users.
A reference paper is available for CRU TS3.10:
Harris, I., Jones, P.D., Osborn, T.J., and Lister, D.H., 2014: Updated high-resolution grids of monthly climatic observations - the CRU TS3.10 Dataset. Int. J. Climatol., 34: 623-642. Doi: 10.1002/joc.3711
Background
At present, the BADC holds the preliminary CRU TS3.0 datasets for the period 1901-2006 as well as the final CRU TS3.1 datasets for the period 1901-2009 (which entirely supersede CRU TS3.0). TS (time-series) datasets are month-by-month variation in climate over the last century or so. These are on high-resolution grids. They allow the comparison of variations in climate with variations in other phenomena. Variables include cloud cover, diurnal temperature range, frost day frequency, precipitation, daily mean temperature, monthly average daily maximum temperature, vapour pressure and wet day frequency. The CRU TS3.0 data are monthly gridded fields based on monthly station values -hence the ASCII and netcdf files both contain monthly mean values for the various parameters.
CRU TS3.0 data were orginally produced and held by the CRU, however in 2007 it was decided that the BADC could provide dedicated long term support for these data and work began to port the software to the BADC systems where they could run on an operational basis. The system has now been ported to the BADC, and BADC are responsible for updating these (3.1) data on a regular basis.
BADC Team 11/4/11