Interannual and Multidecadal Changes of Wind Speed and Directions over the North Sea from Climate Model Results

The temporal changes of 10 m wind speed and direction over the North Sea were examined using an ensemble of Regional Climate Model (RCM) runs. The presented results for the time period 1961–2099 are based on different RCM runs forced with 20th century and A1B scenario greenhouse gas concentrations, as well as various driving Global Climate Models. Time series of the 50th and 99th percentiles of yearly wind speed frequency distributions were constructed and their long-term trends and significance were examined for the whole period. Wind direction was sampled in eight classes and yearly frequencies were either calculated independent of the wind speed or only for directions of wind with higher speed. Yearly frequencies of the wind direction classes were merged into time series and analysed accordingly to the time series of the wind speed percentiles.All time series of percentiles and wind direction frequencies and also of all the RCM results, show strong year-to-year as well as long-period fluctuations. The majorities of both the 50th and 99th percentile time series of the wind speed have negative trends in the northern part and positive trends in the southern part of the North Sea. Even though in some RCM results these trends occur over an extended area, they are often statistically insignificant in many regions.Positive wind direction frequency trends have been calculated for the westerly wind directions South-West, West, and North-West, negative trends for North, North-East, East, and South-East in all sub-areas. If frequencies of directions of wind with higher speed are analysed, then positive trends are detected for wind directions West and South-West. No temporal change has been found for the frequencies of the other wind directions. The number of significant trends is higher if the wind direction has been analysed for all wind speed; but the majority of wind direction trends of all RCM results and in all areas are not statistically significant.