On the determination of stability conditions over forested areas from velocity measurements

D. Medici, A. Segalini, Ebba Dellwik

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Abstract

Two proxies able to determine the sign of the atmospheric stability in the absence of temperature measurements were investigated using data from four forested sites in Sweden. The results indicate that the simple proxy based on the time of the day when the measurement was taken was sufficient to identify approximately 75% of the stable occurrences. However, also during daytime, stable stratification was not infrequent. A criterion based on a combination of the local turbulence intensity and shear exponent was therefore also investigated, and the combination of the two criteria was able to estimate approximately 90% of the overall stable data. When selecting data with mean wind speeds over 5 m/s at 80 m height, the presented data sets include mostly data where temperature effects are small (near-neutral), followed by stable data. Only few occurrences of unstable conditions were anyway observed. The investigated data sets show large variation of shear and turbulence intensity with increasing stability, indicating the need for proxies that also can be used to characterize the degree of atmospheric stability.
Original languageEnglish
Title of host publicationProceedings of EWEA 2014
Number of pages9
PublisherEuropean Wind Energy Association (EWEA)
Publication date2014
Publication statusPublished - 2014
EventEuropean Wind Energy Conference & Exhibition 2014 - Fira de Barcelona Gran Via, Barcelona, Spain
Duration: 10 Mar 201413 Mar 2014
http://www.ewea.org/annual2014/

Conference

ConferenceEuropean Wind Energy Conference & Exhibition 2014
LocationFira de Barcelona Gran Via
CountrySpain
CityBarcelona
Period10/03/201413/03/2014
Internet address

Keywords

  • Atmospheric stability
  • Obukhov length
  • Richardson number

Cite this

Medici, D., Segalini, A., & Dellwik, E. (2014). On the determination of stability conditions over forested areas from velocity measurements. In Proceedings of EWEA 2014 European Wind Energy Association (EWEA).