|Met Office Hadley Centre observations datasets|
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CRUTEM is a gridded dataset of observed near-surface air temperature anomalies over land. It is a collaborative product of the Climatic Research Unit at the University of East Anglia, the Met Office Hadley Centre and the National Centre for Atmospheric Science. CRUTEM5 is the fifth major version of the dataset, covering the time period from 1850, with a spatial resolution of 5° latitude by 5° longitude and a monthly-mean time resolution. Hemispheric and global mean time series of land air temperature anomalies are also provided.
The CRUTEM5 grids and derived time series currently include data for the years 1850 to present. The current version of CRUTEM5 is CRUTEM.126.96.36.199, available from the download page.
CRUTEM5 substantially increases the number of meteorological stations included in CRUTEM. New quality control proceedures are applied to screen for outliers in station data. CRUTEM5 also introduces an alternative version of the CRUTEM5 grids, provided alongside the standard grids. Gridded temperature anomaly fields are based on a compilation of monthly-mean temperature records from 10639 weather stations, of which 7983 records are used to produce the gridded dataset.
Each station temperature is converted to an anomaly (difference from the 1961-90 average temperature) for that station before gridding. In the standard version of the CRUTEM5 grids each grid-box value is the mean of all the station anomalies within that grid box. In the alternative version each station can contribute to multiple grid cells at the latitude of the station. This compensates for the reduced longitudinal extent of a grid cells at high latitudes.
The assessed uncertainties include those arising from thermometer accuracy, homogenisation, sampling of grid boxes with a finite number of measurements, large-scale biases such as urbanisation and estimation of regional averages with non-complete global measurement coverage.
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