The SNaefellsnes EXperment (SNEX) - observations of local winds in a mesoscale mountain ridge

From 1999, winds and other meteorological parameters have been observed by a number of automatic weather stations in the Snaefellsnes peninsula in Western Iceland. A short distance upstream of the peninsula there are regular upper air measurements providing a good description of the airmass impinging the mountains. The collection of data already available provides insight into the links between the upstream conditions and the local response of the atmosphere to the topography. There is strong correlation between the surface wind speed on both the upstream side and the downwind side with the upstream wind speed observed at 850 hPa. On the upstream side, the surface mean wind speed is 54% of the mean wind speed at 850 hPa and the mean gust factor is 1.4. The winds and the gusts increase close to linearly with the wind speed at 850 hPa. On the downstream side, the mean wind speed is 78% of the 850 hPa upstream winds and the mean gust factor exceeds 1.7. The mean downstream winds and the windgusts increase rapidly with upstream winds at 850 hPa between 5 and 20 m/s. The maximum mean winds downstream are found for statically stable conditions in this range of upstream winds. For stronger upstream winds, the mean surface wind speed and the wind gusts on the downstream side increase more slowly with the 850 hPa wind speed.