On the Parameter Dependence of Two-Dimensional Sea-Breeze Models

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.

Maximum Velocity of the Sea Breeze in a Two-Dimensional Model

“…Values of UMAX and WMAX are found at about t ti 7r/12 in the calculated domain, and depend on the nondimensional parameters and S, as reported in Ookouchi (1992). Here, the values of and S are assumed as 3.37 and 6.36x10-3, respectively.…”

“…In the study by Ookouchi (1992) the maximum velocities, UMAX/Us and WMAX/Ws, approach constant values as the ratio of computational width of land and sea area Lw/Ls increased. In the present simulation, the size of the computational region is partitioned as 50 km for sea and 78 km for land areas.…”

“…This reflects the difference in the nondimensional width of the sea area, Lw/Ls, which is about 0.86 for Case (i) and 0.43 for Case (ii). According to Ookouchi (1992), UMAX/Us and WMAX/Ws gradually increase as the sea width increases Lw/Ls. The SB front can not move inland at the same speed as the sea breeze, since the leading part of the SB undergoes a strong airmass transformation due to the diabatic heating from the ground surface.…”

“…The background potential temperature is assumed to be linear with height, T=To+I'z where To=298K and F=0.004K m-1. The simplified model described in Ookouchi (1992) is adopted for this study. The basic scaling employed in the model is after Niino (1987) as fol-…”