By using surface data from 57 UK meteorological stations, a national [British Atmospheric Data Centre (BADC)-57] and regional wind index for the UK has been calculated for the period 1983–2011. For a subset of seven stations, an additional national index (BADC-7) has been calculated for the period 1957–2011. The indices show an annual variability of 4% over their respective periods, corresponding to a variation in typical wind turbine capacity factor of 7%. These indices are compared with indices calculated from other sources, namely an index generated using a gridded dataset of observed values interpolated across the UK, an index calculated from an area bounding the UK using the ERA-40 re-analysis dataset, indices calculated from bilinear interpolation of the ERA-40 re-analysis dataset to the 57 and 7 stations and another independent UK wind index. The indices show variation in trends, with all showing some level of decline with the exception of that generated using the ERA-40 re-analysis dataset averaged over the UK, which shows a significant increase. The various indices show varying degrees of agreement with correlation coefficients, after trends are removed, ranging between 0.611 and 0.979. The effect of changes in site exposure, instrument bias and measuring height was considered for the BADC-7 and BADC-57 indices. The change in instrument measurement height appears to have a significant biasing effect, and it is likely that this along with changes in exposure at urban sites has caused the decline in annual wind speeds observed for some of the indices. There does not appear to be evidence for significant changes in large-area (mesoscale) surface roughness. The correlation between annual mean wind speeds at the seven surface station sites used to calculate the BADC-7 index is seen to be quite weak, indicating very localized variations in inter-annual variability. When regional differences in the index are investigated, it is seen that wind speeds show a very slight decline across the UK in all regions except the south-east, which shows a slight increase. The greatest decrease is seen in the north-west. These changes are in the same direction as the tentative predictions given by climate models for future changes in wind speed across the UK, although the uncertainty is large given the large degree of inter-annual variation. Copyright © 2013 John Wiley & Sons, Ltd.
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