Impact of wind farms on the occurrence and characteristics of low-level jets

Abstract. The low-level jet (LLJ) is an occurrence of super-geostrophic wind speeds in the lower regions of the atmosphere, typically below 1 km. LLJs are highly relevant for wind energy as they can substantially modulate power production, wake recovery, and loads of wind turbines and wind farms. However, it is not clear how the presence of wind farms affects the occurrence rate and characteristics of LLJs, with some simulations suggesting that the presence of farms leads to fewer LLJs and to LLJs occurring at higher elevations. In this work, we develop methods to take advantage of unique long-term wind profile measurements to experimentally assess the impact of wind farms on the occurrence rates and morphologies of LLJs. We use more than 27 years of profiling radar wind measurements collected for the period August 1998–April 2026 at the Atmospheric Radiation Measurement Southern Great Plains site in Lamont, Oklahoma, with over ten large wind farms (each comprising up to 100 turbines) installed near the measurement site at ranges from 17 km to 67 km, with the closest (and largest) installations just to the east, west, and south. We apply both traditional LLJ detection methods (i.e., drop-off and shear) and a data-driven agglomerative-clustering method to hourly-averaged wind speed profiles. The aggregate LLJ occurrence rates are essentially indistinguishable pre- and post-construction (approximately 40 % by the shear method and 36 % by the drop-off method), with a transient reduction of approximately 3 % (shear method) and 4.5 % (drop-off method) during the construction era (2012–2020). Data-driven analysis further resolves sector- and time-of-day-specific shifts: in all wind sectors examined, including a sector with no upstream farms, clusters with strong near-ground shear seem to be replaced by clusters with reduced near-ground shear. However, LLJ rates are not significantly affected, although the results suggest a stronger modification at night (local time 0–6, reductions of around 50 % for specific clusters). Given concerns about long-term background climatological variability, it is very difficult to ensure that these results are statistically significant. In contrast to previous simulations, we find no statistically significant evidence of wind farm modifications of LLJ rates.