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Because the purpose of wind machines is to take energy out of the wind, it is counterintuitive to find the wind’s average velocity increases inside the wind farm. This is not what I learned in Aerodynamics I. Some clarification, please.

John Toomay
Carlsbad, Calif.

Remember boundary layers. The wind speed at windmill level is higher than it is at ground level. The turbine is extracting energy from that high-altitude wind, and its rotating blades are sending some of that faster airflow down to ground level, where it increases the average wind speed .—S. Perkins The title, headline, and photo caption of your article create the false impression of large-scale weather effects from wind turbines unsubstantiated in the article. For instance, the text explains a daily average increase in ground wind speed of 1.3 miles per hour.

Chris Carter
Graham, N.C.

The weather effects were averages estimated over the entire wind farm. The slight increase in wind speed may be a smaller concern than the boost in the evaporation of ground moisture .—S. Perkins