A Numerical Study on the Effects of a Mountain on the Land and Sea Breezes

Abstract

Thermal and dynamical effects of mountain on the land and sea breezes are studied numerically, by paying special attention to the growth and decay of the circulations and the extent of them. A two dimensional model in a vertical plane perpendicular to a seacoast line and a mountain chain is used. The horizontal extent and the depth of the computational region are assumed to be 130km and 3km, respectively. The mountain is assumed to have a simple trapezoidal form with 8km in width and 450m in height, and is located at 18km from the coastal line. In order to estimate the thermal and dynamical effects of the mountain, numerical experiments are conducted for the following three cases: case (a) no mountain case (b) mountain with thermally insulated boundary condition (insulated mountain) case (c) mountain with the diurnal change of its surface potential temperature (heating mountain) Main conclusions are summarized as follows: (1) The sea breeze can not invade inland beyond the heating mountain, while the breeze invades inland beyond the insulated mountain faster and deeper than expected in case of no mountain. (2) The land breeze develops strong in case of the heating mountain. This is due to the down-slope winds. In case of the insulated mountain, this down-slope winds do not develop and the land breeze remains weaker than that of no mountain case. (3) The phase difference between the time of the maximum land-and-sea surface temperature contrast and that of the strongest induced circulation is much reduced, compared to the case of no mountain, regardless of the thermal boundary condition of the mountain surface.