A tall tower study of the impact of the Low-level jet on wind speed and shear at turbine heights

Beginning in 2006, ten tall communication towers have been outfitted with anemometers and wind vanes at heights up to 150 m across the State of Missouri. The primary goal of this network was to improve the wind climatology at heights corresponding to those at which modern utility scale wind turbines operate. In this work two years of observations are used to further investigate the wind resource in Missouri. Initially it was seen that a strong diurnal variation in wind speed occurs at all towers with the maximum mean wind observed at night. This was seen as preliminary evidence of the importance of the low-level jet.

A comparison was made between the wind conditions during periods when the low-level jet is active compared to times when it is not at heights relevant to wind power applications. In particular, it is found that wind speed and shear at these heights are greater when the jet is present. The magnitude of these increases is important when assessing the likely wind power potential in an area, but also has application to wind farm operations when energy output is being forecast. Most notably, wind farm operators are concerned about rapid changes in wind speed that increase or decrease power generation over a short period. Such changes are frequently the result of low-level jet formation in the Midwest.