Abstract
　Method of estimating a representative wind speed over land surface was developed for l55 meteorological stations of the Japan Meteorological Agency. Two types of wind speed, UA and UB, were considered here.
　UA is defined as the wind speed at 50m above ground for each meteorological station. Statistical analysis for 5 years showed that the observed wind speeds at the inland stations are 0.4 to 0.9 times of the theoretical values over flat surface, which are derived from Rossby number similarity theory. When averaged for the 106 stations (excluding the stations locat-ed in cape, mountain and small island), the observed wind speed is 0.67 times of the theoretical value. The factor 0.67 (≡αmean) implies the topographical reducing factor averaged over Japan.
　The representative wind specd UB is defined as αmean U50, where U50 is the theoretical 50m-height wind speed over flat surface (assuming the aerodynamic roughness Z0=1m). UB does not include both the two effects of local topography and local ground condition, and is suitable for analysis of synoptic-scale wind field.

【キーワード】：地上風速，地域代表風速，空気力学的粗度，ロスビー数相似則
Key words: surface wind speed, representative wind speed, aerodynamic roughness, Rossby number similarity theory

*東北大学理学部地球物理学教室
Geophysical Institute, Faculty of Science, Tohoku University