Submitted to: Journal of Environmental Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2006
Publication Date: 3/1/2007
Citation: Ro, K.S., Hunt, P.G. 2007. Characteristic wind speed distributions and reliability of the logarithmic wind profile. Journal of Environmental Engineering. 133(3):313-318.
Interpretive Summary: Wind is important in studying the fate of environmentally significant gases such as greenhouse gases. Wind speeds vary continuously, but there is a lack of standardized procedures for its monitoring and characterization. We first characterized the wind speed patterns for the Year 2005 at Florence, SC. As expected, the daytime winds were stronger than nighttime. We also tested the impacts of using different averaging times (1, 5, 10, 15, 20, 30, and 60 minutes). Averaging time had little effect on seasonal wind speed patterns; however, it affected daily patterns. Averaging times more than 15 minutes should not be used. We also tested the validity of using a logarithmic method to estimate wind speed at 10 m (or 10-m wind speed). Although the 10-m wind speed is an important reference speed, it is both difficult and costly to measure. With the logarithmic method, one can estimate the 10-m wind speed from more convenient lower-height wind speed. Although the logarithmic method is theoretically valid only for certain limited atmospheric conditions, we showed that the logarithmic profile yielded good estimates of the 10-m wind speed at all atmospheric conditions.
Technical Abstract: Wind produces turbulence facilitating the exchange of pollutants and other environmentally important trace gases such as oxygen and greenhouse gases between stationary water bodies and the atmosphere. Because wind speeds vary constantly, standardized wind speed monitoring and characterization procedures are needed for the gas exchange studies. The Weibull probability density function was used to model the wind speed variation, characteristic wind speed distributions for the year 2005. Different averaging times of 1, 5, 10, 15, 20, 30, and 60 min did not affect the fitting of the yearly and seasonal wind speed data to the Weibull distribution. However, for shorter-period wind speed data, conformity to the Weibull density function decreased as averaging time increased. The logarithmic profile effectively described vertical wind speed variations irrespective of atmospheric stability conditions. With the wind speed data sets during neutrally stratified atmospheric conditions, the logarithmic profiles yielded similar values of the surface roughness length even when the wind speeds were averaged over different time scales. Use of the logarithmic profile predicted the actual U10 with a reasonable accuracy even if a wide range of surface roughness values were used under all stability conditions.