Article,
Identifying homogenous sub-periods in HadISD
Climate of the Past Discussions, 10 (2): 1567--1607 (Apr 11, 2014)
DOI: 10.5194/cpd-10-1567-2014
Abstract
We report on preliminary steps in the homogenisation of HadISD, a sub-daily, station-based dataset covering 1973–2013. Using temperature, dewpoint temperature, sea-level pressure and wind speeds, change points are detected using the Pairwise Homogenisation Algorithm from Menne and Williams Jr. (2009). Monthly mean values and monthly mean diurnal ranges (temperature and dewpoint temperature) or monthly maximum values (wind speeds) are processed using the full network of 6103 stations in HadISD. Where multiple change points are detected within one year, they are combined and the average date used. Under the assumption that the underlying true population of inhomogeneity magnitudes is Gaussian, adjustments as small as around 0.5 °C, 0.5 hPa or 0.5 m s<sup>−1</sup> have been successfully detected. No strong biases are present in the distributions of the adjustment values. The change point dates and adjustment values for each of the calculation methods will be provided alongside the dataset to allow users to select stations which have different levels of homogeneity. We give an example application of this change point information in calculating global temperature values from HadISD and comparing these to CRUTEM4. Removing the most inhomogeneous stations results in a better match between HadISD and CRUTEM4 when matched to the same coverage. However, further removals of stations with smaller and fewer inhomogeneities worsens the match.
