Wind and Temperature Profile Characteristics from Observations on a 1400 ft Tower

Abstract

Profiles of mean wind speed obtained from a 1420-ft tower are analyzed on the basis of similarity theory to determine the relationship of profile shape to lapse rate structure. A total of 274 profiles representing four observation times (0600, 1000, 1400, and 1800 CST) are used in the analysis. Thirty minute averages of the wind speed are taken at eleven levels on the tower at these observation times. The wind speed values are normalized by means of the friction velocity as well as a reference height velocity computed at the lowest observation level, and profiles for these wind speeds are grouped according to profile shape characteristics. For each group, an average profile is computed and the vertical variation of mean wind speed is compared to a logarithmic or power law profile form. Results of the study indicate that the mean wind profiles are dependent on the lapse rate structure and can be divided into “non-inversion” (lapse rates greater than isothermal) and “inversion” (lapse rates less than isothermal) profiles. For near adiabatic or slightly unstable lapse rates (mid-day non-inversion profiles), the logarithmic wind law represents the data well to a height of 300 to 400 ft. Above this height the wind speed is nearly constant. The more stable non-inversion wind profiles (lapse rates varying from about 2F to 5F per 1000 ft) generally show greater wind shears. These profiles are represented with a power law. The wind profiles associated with lapse rates containing inversions are highly variable and depend on the nature of the inversion present. There appears to be an inter-dependence of vertical shear and inversion lapse rates for these profiles.