This study investigates diurnal variations in lower-tropospheric wind over Japan during 2002-2008 using data from 31 stations of the Wind profiler Network and Data Acquisition System (WINDAS) and the Automated Meteorological Data Acquisition System (AMeDAS). The diurnal and semidiurnal components are extracted and analyzed to identify the dominant processes for each height range and for each season. Near the surface, the diurnal component is controlled by local wind systems (e.g., land-sea breezes) throughout the year. At 1-3 km, the diurnal component is primarily controlled by the return currents of local wind systems, with additional influence by other disturbances; the superposition of these two wind systems generates amplitude maxima in spring (∼0.5 m s^-1) and autumn (∼0.6 m s^-1). At 3-5 km, the diurnal wind in DJF-MAM is controlled by medium-scale eastward traveling waves, which generate the amplitude maximum (∼0.8 ms^-1) in winter-spring. In JJA-SON, the diurnal component is controlled by a large-scale wind system with an amplitude of ∼0.3 m s^-1, probably related to the diurnal tide. At stations located on small islands located south of the Japanese mainland, the diurnal wind within the lower troposphere has different characteristics from those described above throughout the year. Throughout Japan, the semidiurnal wind component is controlled by the semidiurnal migrating tide above ∼1 km, and is influenced by local wind systems below ∼1 km. The amplitude of the semidiurnal tide below 5 km is largest in DJF (∼0.4 ms^-1) and smallest in JJA (∼0.2 ms^-1).