Interannual wind variation from observations and numerical weather analyses.
EWEA Annual Event 2012, EWEA, (April 2012)Abstract
Variations of the annual average wind speed are important to the wind energy sector for long-term planning purposes. A claimed ” rule-of-thumb” interannual variability of the wind speed as a percentage of the mean is 6\%. We investigate this by using observations and numerical weather model data.
Wind data at 22 meteorological stations throughout the UK, and 28 stations in the rest of Europe are extracted from the Met Office Unified Model (UM) using the Met Office Virtual Met MastTM , for 2001-2010, and compared with observations. Wind speeds are obtained for 15 European regions from the 12km UM and compared with the ERA Interim re-analysis. The 20th Century Re-analysis (20CR) is used for long-term context.
The site-specific analysis shows that the variability is often higher than 6\% in highly complex terrain, and lower than 6\% in less complex terrain. The percentage variability has little height dependence. A higher resolution model produces a larger spread of variabilities at the sites, as reflected by the observations. The regional results demonstrate an interannual variability lower than 6\%, particularly in Southern Europe, with a 3-4\% regional variability generally. The higher resolution UM data, however, shows high variability in complex terrain such as the Alps.
The 20CR data implies that a short time period of ten years is useful for estimating the long-term wind distribution. The period from 2001-2010, however, is both less variable and less windy than the 1990s or the 1980s. The 2001-2010 period coincides more closely with the long-term distribution than either of the two previous decades.