The Thermally Induced Local Wind and Surface Inversion over the Kanto Plain on Calm Winter Nights

Abstract

The nighttime local wind and accumulation of cold air over the Kanto Plain in Japan were investigated with a three-dimensional hydrostatic numerical model under the condition of no synoptic pressure gradient. Numerical results strongly support the hypothesis that cold air accumulated in the western portion of the plain owing to the convergence of drainage flow from the mountain slopes in the northern and western parts of the plain. The accumulated cold air generated a deep surface inversion layer over the region, as suggested by observations. The cold air drained along three large rivers located in the plain after 1900 LST, when the daytime valley winds ceased. The heat flux between the surface and the atmosphere was exchanged mainly over the relatively steep slopes of forest-covered mountains, although the drainage flow there was not very strong. The low-temperature area generated in the center of the Kanto Plain could be distinguished even after noon the following day.