Climatology of diurnal variations of wind speed in the atmospheric boundary layer in Japan

抄録

The diurnal variation of boundary layer wind speed in Japan was statistically investigated using wind profiler data for 2002-2013. The analysis was made for 17 stations where the diurnal variation in surface air temperature had an amplitude of 2°C or more. It was found that the wind speed in the upper boundary layer (985 m above the surface) had a minimum in early afternoon in all seasons, in agreement with the general understanding that winds in the daytime boundary layer are reduced due to enhanced frictional force. However, the wind speed in the lower boundary layer (394 m) had a maximum in the afternoon at some stations in contrast to the general feature mentioned above. This afternoon maximum is more conspicuous in summer than in winter and in southern Japan than in northern Japan, and appears to be due to thermally driven local circulations. Nevertheless, the ratio of wind speeds at 394 m with respect to surface had a minimum during the daytime in all stations and seasons, indicating the daytime reduction of surface-relative boundary layer wind speed as a common feature over land.