The wind climate of northwestern Europe in SWECLIM regional climate scenarios

Abstract: The effects of a global climatic change on the wind climate of northwestern Europe are investigated with the aid of a regional climate model. There have up to date been few studies of how the wind climate will react to a greenhouse gas warming. Those that have been done are mostly global scale studies and centered on changes in storm activity during the winter season. I’m using data from a regional scale model developed by the Swedish Regional Climate Modelling Programme, or SWECLIM. The regional model uses two different global circulation models for boundary conditions (the HadCM2 model and the ECHAM4 model). The data consists of 4-times daily sea level pressure and geostrophic wind speed from a 10- year control and scenario run time slice. The scenario time slice has a 2.5 times higher concentration of CO2 then the control. I also calculated the wind direction using the modelled geostrophic wind. I have investigated both the yearly, monthly and seasonal changes and well as changes of the extremes of the wind climate in the form of 95 and 99 percentiles and percentages of windspeed over 20 and 25 m/s. The model predicts an increased meridional pressure gradient as a result of the greenhouse warming. Regarding the wind climate the model predicts a higher frequency of westerly winds. In the North Sea and the Norwegian Sea there is a small increase of the yearly mean geostrophic wind speed. Sweden and northern Germany also experiences an increase of the yearly mean geostrophic wind speed when running the model with the HadCM2 boundary data, but a decrease when using the other model as boundary conditions. The storm climate shows no major increases in the number of storms per year due to the global warming. What I did find is an increase during autumn in the intensity of storms over the North Sea and the Norwegian Sea. During winter I found a decrease in storm intensity over the same area when using the ECHAM4 model as boundary data. An increase in the intensity of gale winds during autumn was found over Sweden and northern Germany when using HadCM2 boundary data. The ECHAM4 driven model showed a decrease during winter in the intensity of storm and gale winds in this area.