A First Look into Boundary Layer-Wind Farm Interactions from the American Wake Experiment

Variations in the atmospheric boundary layer (ABL) due to onshore wind farms have been analyzed in the past. Previous work has discovered enhanced vertical mixing, an increase in land-surface temperature at night, and dependence on ABL stability. Still, many questions remain unanswered since measuring wake properties and how they influence the ABL is a challenge, and the interactions may be dependent on terrain, local climatology, and other regional factors. The American Wake ExperimeNt (AWAKEN) field campaign has now collected several months of data in the U.S. Southern Great Plains and provides an opportunity to better understand the effects of wind farm wakes on the ABL. Here, data from two sites are analyzed: one close enough to wind farms to be influenced by their collective wakes and a second in an undisturbed location far upwind of any wind farms during fall 2022 and summer 2023. Available at both sites was the Collaborative Lower Atmospheric Mobile Profiling System (CLAMPS), which houses a scanning Doppler Lidar (HALO Photonics lidar), microwave radiometer, and other valuable observation tools. During the fall 2022 campaign, a profiling lidar (ZephIR300) was codeployed with CLAMPS at these sites. The CLAMPS Doppler lidars continuously measured wind speed and direction from 10-4000 m every 10-15 minutes while the profiling lidars measured the same quantities from 10-200 m (1-second and 10-minute-averaged outputs available) for a thorough analysis of wind farm impacts.

Preliminary findings indicate enhancements in vertical velocity measurements at the site near wind farms. This result is noticeable during the day when both upward and downward mixing is deeper than the site far from the turbines and at night during notable features such as nocturnal low-level jets and gravity waves. It is suggested that turbines mechanically increase localized mixing throughout the day and night as seen in previous literature, which can be aided by typical ABL features in the Southern Great Plains, such as the daytime heating and the NLLJ. This information is valuable as wind farms gradually increase throughout the United States and beyond. These analyses may also provide insights into how the relatively recent development of wind farms in this area may affect the long-term DOE climatological data collection at the Atmospheric Radiation Measurement Southern Great Plains site.