No 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 mo untain 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.

The sea and land breezes in the northern region of Kyushu Island in Japan under the condition of no synoptic wind in typical summer season are simulated by a three dimensional numerical model.This study provides an evaluation of the diversification of the local circulation owing to the topography, e. g. irregular seashore lines and mountainous topographies.In order to investigate the influence of mountainous topography on the local circulation in Kyushu, we compared the case of the realistic ground elevation with that of the flat in the northwestern region of Kyushu which is characterized by the irregular coastal lines, the comparative flat topography and dispersive mountains.Further we also compared them with the case of the realistic topography in the north-eastern region of Kyushu which has the monotonus seashores and the spread mountain areas.In the northern region of Kyushu, the irregular coastal lines (esp. topography of peninsula) produce characteristic local circulations and variation of winds in connection with mountainous topographies.The mountainous topographical effects are summarized; (1) the upward vertical winds concentrate above the mountain area in the day time (down slope wind in the night), (2) the horizontal winds are oriented by the valley (e. g. in the sea area surrounded by a mountainous topography) and (3) the winds are enforced in the area of converged mountainous topography.The sea breezes in the small islands near the Kyushu are strongly affected by that in Kyushu.Further the penetration of sea breeze to inland or other area is effective factor on the diurnal wind variation at any place (esp, in the western region).

No abstract

Parameter dependence of the sea breeze is discussed by using four types of simplified two-dimensional numerical models; (A) linear and hydrostatic, (B) linear and non-hydrostatic, (C) non-linear and hydrostatic, (D) non-linear and non-hydrostatic models. Various combinations of parameters with regard to the basic situation in the sea breeze are considered. The parameters are the amplitude *T, the frequency *, of the diurnal change of land-surface temperature, the eddy diffusion coefficient t, and the lapse rate of basic potential temperature * (or Brunt Vaisala frequency N). Two non-dimensional parameters are a non-linear parameter r (=* T/[*(*/*)1/2]) and a hydrostatic parameter * (=*/N), which appear in the governing equations through a scaling (Niino, 1987).The main conclusions are as follows, (1) The behavior of flows is quite different, depending on whether the set of equations is linear or non-linear. However, there is no serious difference between the cases with and without the hydrostatic assumption under the common sea-breeze parameters. (2) The size of the computation domain plays an important role in determining the scale of the sea breeze. (3) In the non-linear model, the maximum wind velocity of the sea breeze varies in proportion to *2. When * is greater than about 3, the maximum wind velocity in the non-linear model becomes much greater than that in the linear model. (4) The maximum wind velocity varies in proportion to *-1 in both linear and non-linear cases. The dependency on 6 slightly differs with s in the non-linear cases.(5) The maximum Rayleigh number over land during the daytime is estimated to be Ra=0.1*4*-2 The computational results suggest that the maximum wind velocity is proportional to Ra1/2 in the non-linear case.Further, the dependence of the maximum wind velocity on the mesh size in the numerical computation is discussed.

No abstract

No abstract

Roll type Rayleigh convection with a linear temperature distribution along the bottom is experimentally investigated with silicone oil. Results are: a) Convection due to the horizontal temperature gradient is an asymmetric single circulation. b) Rayleigh convection is deformed by the differential heating so that large direct convection cells (whose sense of rotation is same with that driven by the differential heating) and small indirect convection cells stand alternately. c) When stable and unstable regions exist side by side, a single convection due to the horizontal temperature gradient develops in the stable region, while deformed Rayleigh convections develop in the unstable region. d) As the horizontal gradient increases, the wave length of the Rayleigh convection tends to increase to converge to a certain value.