Diurnal surface heat-flux forcing controls wind-farm performance, blockage, and gravity-wave formation

We use large-eddy simulations coupled with a soil-conduction scheme to quantify how diurnally varying surface heat fluxes affect wind-farm performance, blockage, and gravity-wave formation across the four seasons. Seasonal forcing strongly modifies wind speed, turbulence intensity, and thermal stability. In all cases, low-level jets in the night and morning increase wind-farm production, which declines later in the day as the jets weaken. In summer, stronger daytime turbulence accelerates wake recovery by enhancing momentum replenishment within the wind farm. This partially mitigates the power decline and leads to the highest wind-farm performance due to stronger surface forcing. In autumn and winter, weaker surface forcing reduces turbulence and boundary-layer depth, producing smaller diurnal variations in power production. During winter, gravity-wave footprints are observed and are attributed to the higher wind-farm blockage and stronger atmospheric stability. These results show that seasonal and diurnal boundary-layer variability is essential for accurately predicting wind-farm performance.