Analysis of the power law exponent applied to Lake Erie wind shear

Abstract

An investigation of power law exponents (wind shear coefficients) was conducted using LiDAR data collected offshore in Lake Erie. The purpose was to investigate discrepancies found by previous studies between calculated power law exponents from measurements and recommended values from international standards. In this study, power law exponents were evaluated using the LiDAR measurements at heights of 80–200 m. The average power law exponent during the study period was found to be 0.09, which was lower than the 0.14 standard assumed by international standards. A detailed investigation of the distribution of power law exponents revealed a bi-modal distribution comprising the two most frequent exponent ranges between 0.01–0.02 and 0.19–0.20. The gap between these peaks was found to be dependent on the atmospheric stability of the boundary layer. Average power law exponents of 0.02 and 0.14 were found for atmospheric conditions indicating unstable regimes and neutral/stable regimes, respectively. Regime stability also showed directional dependence where winds from the 180° ± 45° directions were prevailing during neutral/stable conditions and winds from the 326° ± 67° directions were prevailing during unstable conditions.