The impact of snow on sound propagating from a wind farm in northern Sweden has been investigated. Simultaneous acoustic and meteorological measurements, combined with daily snow observations, have been analysed for the snow season in 2013 to 2014. Such measurements are crucial since significant knowledge gaps exist, especially for conditions in cold climates, in the implementation of atmospheric boundary layer complexity in sound propagation models. The effect of snow on sound propagation is shown to be dependent on the snow quality. Moreover, snow on trees (upplega) also has an influence on sound propagation. Compared with conditions without snow on trees, the average sound level is approximately 2 dBA lower. The effect is more distinct for higher frequencies compared with lower frequencies.

Amplitude modulation is assumed to be a major annoyance factor of wind turbine sound. However, studies on the generation of amplitude modulation and the impact of atmospheric conditions on amplitude modulation are limited, especially in cold climates. Long-term acoustic and meteorological measurements in the vicinity of a wind farm in northern Sweden show a dependence of the occurrence of amplitude modulation on wind direction and atmospheric stability. The occurrence of amplitude modulation is highest for crosswinds from southwest, compared with the other wind directions. Moreover, the occurrence of amplitude modulation is clearly linked to atmospheric stability and highest for very stable conditions. The impact of atmospheric stability is supported by analyses of wind shear, the wind speed gradient close to the surface and the bulk Richardson number. Amplitude modulation is more likely during winter than during summer and more likely during night and early morning than during noon and early afternoon. (C) 2019 Elsevier Ltd. All rights reserved.