Investigation of spatial variability in power law index of wind profiles above the urban area around Tokyo Bay based on local objective analysis data

By utilizing meteorological local objective analysis (LA) data on a local scale, this study investigated the spatial distribution of the power law index (PLI) of the mean wind speed profile in an urban area around Tokyo Bay in Japan. First, the reliability of the LA data was verified by comparison with observational data. The PLIs of the area for the 16 wind directions at a spatial resolution of 5 km were then estimated using LA data. Under neutral atmospheric conditions, the effects of the roughness length and terrain elevation on the PLI were investigated, and the spatial distribution characteristics of the PLI were analyzed. The results showed that the LA data were consistent with the observational data, indicating that high-precision LA data produced by data assimilation can be a practical supplement to observational data over urban areas. The influence of wind direction on the PLI was evident in the urban area. Furthermore, the metropolis appeared to affect the wind profile significantly when it was within the fetch of other cities, resulting in a larger PLI in the surrounding area. Because the PLI has complex spatial heterogeneity, in addition to urban substrate roughness, changes in terrain elevation and wind direction are thought to affect the PLI significantly. Therefore, generalizing the wind profile characteristics of large-area urban regions using local on-site observational data is not recommended.