Numerical Study on the Effects of Mountains on the Land and Sea Breeze Circulation in the Kanto District

Abstract

A three-dimensional numerical model of the land and sea breezes allowing mountain effect was developed. The system of governing equations is so-callde Boussinesq hydrostatic one, using z*-coordinate system as a vertical coordinate which refers the lower and upper boundaries to the ground surface and the upper surface of the model, respectively.
The model atmosphere with a vertical scale of 2800m and a horizontal scale of 217.5km is divided vertically into 12 layers and horizontally into 30×30 grids with 7.5km mesh.
It is assumed that the surface temperature on sea is constant but that on land changes sinusoidally with a constant diurnal range around the mean temperature at each level. Temperature contrast induced by the above mechanism causes the land and sea breezes and the mountain and valley winds.
By using this model, some experiments were carried out for studying the influence of mountains on the land and sea breezes in the case of the Kanto district.
In mountain-free model, the most prominent sea breeze circulation was restricted within about 40km from sea shore. The local circulations simulated by the model including mountain effects are in good agreement with observation in the Kanto district. The experimental results show that the mountain and valley winds appear earlier than the appearance of the land and sea breeze circulation. But this phenomenon is not yet confirmed by observation.