01 November 2013

How Well Does ERA-Interim Reanalysis Replicate Trends in Extremes of Surface Temperature Across Europe

Summary

Trends in extremes of daily maximum and minimum temperature across Europe during the period 1980-2011 as shown in the ERA-interim reanalysis data are analysed  to determine the likely success of the forthcoming ERA-20C data in replicating such trends. Both station series and the gridded E-OBS data are used to determine the success of the ERA-interim reanalysis in this respect, with indices of the numbers of days above or below the 90th and 10th percentiles of daily temperature used as metrics. It is shown in this paper that the reanalysis data are generally very good at replicating both the seasonally and spatially varying trends in the indices observed across Europe. At the station-level the reanalysis data are also able to depict the observed trends well. However, the success of the reanalysis data depends on the season and the extremes index considered. The reanalysis is least successful in depicting trends in the number of days exceeding the 90th percentile of maximum temperature, particularly during the summer season. There are also differences apparent in the time-step of the reanalysis used. Daily maximum and minimum temperature calculated from the 3-hourly time-step reanalysis data tend to be more reliable than those derived from the 12-hourly data. It is also shown that the reanalysis data tend to accentuate the annual cycle of the 90th percentiles of maximum daily temperature compared to values observed at station sites.

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