Observations Show That Wind Farms Substantially Modify the Atmospheric Boundary Layer Thermal Stratification Transition in the Early Evening

Abstract

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 and 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.