The effect of four example wind shears (surface textures) based on a common 15 mph wind speed at 160 feet and ground clutter averaging about 20 feet tall. Below this height, the speeds measured are erratic due to the interaction between the turbulent winds and the ground clutter. As a result, the unreliable data for this wind is not plotted on the graph. The lower end of any given wind profile will vary with average height of the ground clutter. Taller ground clutter will result in the wind shear curves starting at a higher point on the graph.
Note, for example, how at 80 feet, the alpha of 0.20 has about 25% greater wind speed than the alpha of 0.50—that’s almost double the power. Also notice that for an alpha of 0.50, the wind speed at 160 feet is about 45% more than the alpha of 0.50 at 80 feet—more than three times the power. (The alphas used here were developed for Wisconsin’s Focus on Energy program and are not the “textbook” alphas sometimes used.)