A numerical experiment of the “extended sea breeze” over the Kanto Plain

Abstract

Numerical experiments have been employed to simulate the “extended sea breeze (ESB)” over the Kanto Plain in a three-dimensional mesoscale model. Through some observations in the field, it has been found that there are two characteristics of ESB which distinguish ESB from a typical sea breeze. (1) The thickness of the ESB is 1–1.5 km, which is almost two times the thickness of a typical sea breeze. (2) The wind direction throughout the Kanto Plain shifts northward in the early afternoon. The numerical experiments reproduced these two characteristics rather well in both cases with no general wind and with a SW general wind (5 m/s). Some additional experiments with artificial topography indicated that when there was no general wind an ESB-like wind was generated from the combination of the sea breeze and the thermally and orographically induced flow over the mountainous area of the central part of Japan. However, when there was a SW general wind, another type of ESB-like wind was formed in combination with the general wind and the thermally and orographically induced flow. It was very difficult to distinguish the two types of ESB by observation, because there were southerly winds in the south of the Kanto Plain in both cases.