Atmospheric stability has a significant influence on the wind profile, or the degree of increase of wind velocity with height. For tall wind turbines atmospheric stability is not a ‘small perturbation’ but a major factor determining the energy yield as well as the noise impact in the environment. Noise complaints and recent research show that noise from modern, tall, variable speed wind turbines is not a relatively featureless sound increasing steadily with near-ground wind speed, but – in a stable atmosphere – a thumping sound relatively independent of near-ground wind speed.