Abstract
The regional variations of the spectra of the surface winds in Japan are investigated from the viewpoint of spectrum climatology. For the 206 stations in Japan, the spectra of the surface winds over the period from 2 hours to a few years are analyzed using 5 years of 10min averaged, hourly data.
The diurnal variation and synoptic fluctuations depend on the local topography. Their geographical distributions show a regional contrast. The diurnal variation is dominant at the inland stations. On the other hand, the synoptic fluctuations are dominant at the coastal stations. The 10-20 day fluctuations are systematically dominant on the Nansei Islands (24-31°N, 123-130°E). The geographical distribution of the 10-20 day fluctuations coincides with that of the 40-60 day fluctuations and that of the zonal components of the surface winds. This feature is related to the climate on the Nansei Islands, which is subtropical and maritime. The geographical distribution of the annual variation does not show a clear pattern, except for the Nansei Islands where the annual variation is small. This is because the annual variation depends both on the local topography and latitude.
Models of the spectrum of the surface winds accounting for the relationship between the mean wind speed and the latitudinal distribution are derived from the results. The models show that the short-term fluctuations (less than 10 days) depend on the mean wind speed, that is, the local topography and that the long-term fluctuations (more than 10 days) are affected by the latitude. Characteristics of the spectrum can be used as a climatic indicator. The models may have application to the same climatic regions as Japan.
