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Gustiness parameterization in the atmospheric boundary layer

Gustiness parameterization in the atmospheric boundary layer. Irene Suomi Timo Vihma Sven-Erik Gryning. Definition. Peak gust ( or here gust ) is the maximum wind speed of short duration (t = 1…3 s) during a sampling period of length T=10min…1h.

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Gustiness parameterization in the atmospheric boundary layer

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  1. Gustiness parameterization in the atmospheric boundary layer Irene Suomi Timo Vihma Sven-Erik Gryning

  2. Definition Peak gust (orheregust) is the maximumwindspeed of shortduration (t = 1…3 s) during a samplingperiod of length T=10min…1h. Gustfactoris the ratio of peakgust and meanwindspeed:

  3. Motivation • largeimpacts: in Finland typicallycuttrees/forests, powercuts, brokenstructures, etc • relevant for the windenergy (siting and turbinecontrol) at differentheights (~100m) • gustsarenot (yet) directlyavailablefromnumericalweatherpredictionmodels: parameterizationsareneeded

  4. Researchquestions • Aregustparameterizationsapplicableabove 10 m height? • Whatkind of a gustparameterizationmethod is optimal (based on observations)?

  5. Overview Observations Gustparameterizationmethods A new method Results Conclusions and ongoing/futurework

  6. Observations • Twoweathermasts: Isosaari (83m) and Loviisa (143m) • One year of data: 4/2009-3/2010, excludingfrom Isosaari monthswhensea ice

  7. Observations Loviisa 143m 103m Isosaari 83m 62m 42m 30m

  8. Gustparameterizationmethods Type A Type B • Wieringa (1973, W73) G = f ( U, t, T, z, z0 ) • Woetman-Nielsen and Petersen (2001, WNP01) G = f ( U, u*0, w* ) • WichersSchreur and Geertsema (2008, WSG08) G = f ( U, t, T, z, E ) U = meanwindspeed t = gustduration T = samplingperiod z = heighta.g.l. u*0 = surfacefirctionvelocity w*0 = convectivevelocityscale E = turbulentkineticenergy  = potentialtemperature • Brasseur (2001, B01) G = f ( U, z, , v, E )

  9. A new method (”type A”) From the definition of gustfactor: where is the normalizedgust. For unstableconditions: and stableconditions: (Gryninget al, 1987)

  10. Results: Isosaari East/South (marinesector) OBS W73

  11. Results: Isosaari East/South (marinesector) OBS WNP01

  12. Results: Isosaari East/South (marinesector) OBS New method

  13. Results: Isosaari West (”rough” sector) OBS W73

  14. Results: Isosaari West (”rough” sector) OBS WNP01

  15. Results: Isosaari West (”rough” sector) OBS New method

  16. Results: Loviisa North (landsector) OBS W73

  17. Results: Loviisa North (landsector) OBS WNP01

  18. Results: Loviisa North (landsector) OBS New method

  19. Conclusions • In marinesectorstabilitydidnothavesignificantrole • Overroughsurface, stabilityhadeffect, but the methodby WNP01 overestimatedit, especially in Loviisa with unstableconditions • The new methodperformedbest in allcases. But: tuningof normalizedgustis needed • Ongoing / futurework: • Normalizedgust: gx= f ( t, T, z0, z, ? ) • Testallmethodswithin NWP modelframework

  20. ThankYou!

  21. Acknowledgements The researchleading to theseresultshasreceivedfundingfrom the EuropeanResearchCouncilunder the EuropeanCommunity's 7 th Framework Programme (FP7/2007-2013) / ERC grantagreementnumber 227915, project PBL-PMES.

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