Climatology of Diurnal Variation of Surface Wind Speed in Japan

Using data at 724 stations for 12 years (2010-2021) in Japan, the climatological characteristics of diurnal variation in surface wind speed were examined. It was found that wind speed reached a maximum in early afternoon at most sites in all seasons. Even the 99.9th percentile winds have a weak peak in early afternoon as an average over all stations. In the spatial distribution, the amplitude and phase of the first harmonics of wind speed are positively correlated with those of temperature, but have larger variabilities among stations than those of temperature. The features of the diurnal variation are dependent on geographical factors such as the percentage of water surface, topographic convexity, and population density, with smaller amplitudes and earlier phases at coastal sites and later phases at urban sites. Some inland stations have an exceptionally high nighttime wind speed that is comparable to the daytime wind speed, apparently because of dominant mountain breezes.