Wind Trends in the Highlands and Islands of Scotland and Their Relation to the North Atlantic Oscillation

Several studies based on observational data as well as with global climate models (GCMs) suggest that the wind regime is impacted by climate change. Changes in circulation patterns and shifts in the storm tracks have been predicted (e.g. Andersen et al., 2001, Bengtsson et al., 2006). Besides, there is an indication of enhanced westerly winds and an increase in extreme events and/or storminess (Schmith et al., 1998, Ekström, 2002, Bromirski et al., 2003). The North Atlantic Oscillation (NAO) is a complex mode of variability in the atmosphere and is normally represented by an index that describes the change in strength of the pressure gradient between the ‘Greenland low’ and the ‘Azores high’. Most climate models suggest that the winter NAO index is likely to increase in response to increasing concentrations of greenhouse gases. Since positive NAO is associated with stronger than average westerlies (Hurrell and Van Loon, 1997), any increase or change in the index would be relevant for a regional wind climate variability. Located on the north-western fringe of Europe, Scotland has a wind climate largely dominated by the Atlantic depressions. Average wind speeds and frequency of strong winds and gales are higher than in other parts of the United Kingdom. In addition, the flow of the wind over the region can be significantly influenced by the complex topography (figure 1). As a result, variations of the wind regime and its extremes may be important in considering the regional impact of climate variability for the Scottish Highlands and Islands and may have an important impact on a wide range of