Effects of Topography and Urbanization on Local Winds and Thermal Environment in the Nohbi Plain, Coastal Region of Central Japan: A Numerical Analysis by Mesoscale Meteorological Model with a k−ε Turbulence Model

Abstract

Influence of both urbanization in modified land use in a plain area, the Nohbi Plain of central Japan, and surrounding large-scale topography, such as the Japanese Alps, on the temperature and local wind over the plain has been investigated utilizing numerical simulations with a mesoscale meteorological model that uses the k?ε model for turbulence. Obtained results are as follows. 1) Relative importance of natural topography and human-modified land use in various spatial scales has been clarified in the formation of characteristic diurnal patterns of sea breeze and temperature in the plain area. The Japanese Alps, which are the largest topographic feature in central Japan and are located far from the Nohbi Plain, around 100?200 km away, gave the most important influence on the wind over the plain area. The effect of the high mountains on the wind was caused by heating of the air mass over the plain due to weak subsidence associated with the return flow of the plain?plateau circulation. The urbanization in the Nohbi Plain showed little significant effect on the diurnal flow pattern. 2) The mechanism of the formation of an inland high-temperature zone associated with coastal urbanization under sea-breeze situations has been explained: an urban area, as a local heat source, placed in the topographically induced sea-breeze/valley wind, forms a weak wind zone at the downwind side of the urban area due to the pressure gradient adverse to the sea breeze. In the weak wind convergence zone, the mixed layer rapidly develops and the air mass is strongly heated there from the surface before the arrival of the sea breeze. This high-temperature zone moves inland with an advancing sea-breeze front.