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Long-term changes in frequencies of wind directions on the western coast of Estonia

Long-term changes in frequencies of wind directions on the western coast of Estonia Jaak Jaagus Institute of Geography, University of Tartu Second International ASTRA Conference Gdansk, 27 October 2006 Objective

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Long-term changes in frequencies of wind directions on the western coast of Estonia

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  1. Long-term changes in frequencies of wind directions on the western coast of Estonia Jaak Jaagus Institute of Geography, University of Tartu Second International ASTRA Conference Gdansk, 27 October 2006

  2. Objective • Analyse long-term variability and trends in frequency of wind directions at Vilsandi meteorological station during different months and seasons

  3. Hypotheses • Climate warming should be related to changes in frequencies of wind directions • Increasing trend in NAO index in winter should increase a percentage of westerly and southwesterly winds • Increase in frequency of wind directions bringing milder weather in winter (W, SW, NW), decrease in frequency of wind from the “cold” directions (N, NE, E, SE)

  4. Vilsandi 58°23’N, 21°49’E

  5. Data • Ordinary observations 8 times per day • Period 1966-2005 • Monthly, seasonal and annual frequencies of N, NE, E, SE, S, SW, W and NW winds • Seasons: spring (MAM), summer (JJA), autumn (SON), winter (DJF) • Weathercock (1966-1976 Oct) • Anemorhumbometer (1976 Nov – 2003 Aug) • Automatic weather station (since September 2003)

  6. Method • Linear regression analysis • Significance level P<0.05

  7. Annual windrose over Vilsandi

  8. Seasonal windroses

  9. Changes in annual windrose

  10. Changes in annual windrose

  11. Changes in spring windrose

  12. Changes in summer windrose

  13. Changes in autumn windrose

  14. Changes in winter windrose

  15. Percentage of SE and SW winds in winter

  16. Changes in frequency of monthly wind direction • N winds: increase in March • NE winds: decrease in May and June • E winds: decrease in January • SE winds: decrease in January and February, increase in August • SW winds: increase in January and February • W winds: increase in January and May • NW winds: increase in January, decrease in September

  17. Conclusions • During 1966-2005, a significant increase in annual percentage of SW winds have occurred • Frequencies of NE, E and SE winds have slightly decreased • Changes in windrose in spring, summer and autumn are mostly insignificant, however a shift to W in spring, to S in summer and to SE in autumn is evident • Windroses in winter are changed dramatically, turning mostly from SE and E to SW and W

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