Wind turbines at farm in Texas. Courtesy/Wikimedia Commons

AGU News:

Single wind turbines and large wind farms modify local scales of atmospheric boundary layer (ABL) turbulence through different mechanisms dependent on location within the wind farm.

These changes in turbulence scales would most likely have notable influence on surface fluxes and microclimate during the afternoon and early evening stability transition. Profiles of Richardson number, shear and buoyancy from 1‐Hz tall‐tower measurements in and near a wind farm in an agricultural landscape were used to quantify departures in stability characteristics during the fallow seasons.

A single turbine wake decoupled turbulent connection between the surface and above the wind turbine, changed the onset of near‐surface stabilization (earlier by a few hours), and lengthened the transition period (by up to an hour) within the rotor wake. Deep within a large wind farm, turbulence recovered to near‐ambient conditions and departures of the transition onset and duration were within 30 min of the natural ABL.

Plain Language Summary

Wind farms and single wind turbines change low‐level atmospheric transport of momentum, heat, and water vapor, increase surface nighttime temperature, and decrease surface humidity. We infer that wind farms and single turbines also modify transitions in warming and cooling of the air during the daytime to nighttime hours. Measurements are used from a twin 120‐m tall tower network in Iowa to detect differences in the evening transition between a location outside of a wind farm and near a single turbine or inside the wind farm. Behind a single turbine, the surface air cools two hours earlier while the air within the blade swept area cools one hour later when compared to outside the wind farm. Wind farm flow causes a small difference (±30 minutes) to the transition. The results provide additional evidence that wind turbines may influence biological regulation of soil microorganisms, plants, or animals in the proximity of wind energy production facilities.

Key Points

• Wind turbines and wind farms generate turbulence at scales different from the natural atmosphere and modify the evening transition
• Wind turbine wakes shift the onset of near‐surface stability ahead a few hours and shift the completion within the wake behind by one hour
• Differences in the transition are about one‐half hour within an aggregate of wakes from multiple wind turbines in a large wind farm