A study of air and road‐surface temperature variations during clear windy nights

Abstract In this paper, temperature recordings from mobile measurement and field stations in the Swedish Road Weather Information System were analysed to determine the variation in temperatures during clear nights with varying mean night‐time wind speeds. It was found that the differences in air temperatures could amount to as much as 10°C owing to local variations in wind shelter. The largest variations occur during nights with a mean wind speed of 1 to 1·5 m s −1 , as this wind is strong enough to prevent stabilization of the surface‐cooled air at wind‐exposed locations, whereas such a stabilization can occur at wind‐sheltered locations. There is normally a close relation between areas with low air and road‐surface temperatures. However, the effect of the air temperature variations on the road surface temperature is found to be reduced as a result of the obstruction of the longwave cooling caused by the wind shelters. The cooling rate especially has been found to differ between stations with varying sky view factors. The paper further includes a discussion of the factors that must be taken into account for the calculation and forecasting of air and road‐surface temperatures in areas where wind shelters have a pronounced effect on temperature variations.