Numercal Experiments of Humidity Change of Air Mass Moving from Seashore into Inland

Abstract

In this paper are presented results of numerical study of the humidity change of air-mass, which moves from the sea into inland. Simultaneous differential equations (see Eqs. 1-3) as nonstationary two-dimensional diffusion of heat and water vapor in the lower atmosphere and of heat in the soil layer were numerically integrated by the difference method on an electronic computer. Profiles of turbulent diffusivity were estimated on the basis of KEYPS equation, in which is considered the effect of stability of lower air layer on the turbulent diffusivity of earch physical quantity. In numerical experiments soil moisture condition is parameterized by μ(=es/e(To)). The sets of physical parameters used in the experiments are presented in Table 1.The results obtained can be summarized as follows:1) Numerical experiments indicate that a mean K-profile calculated at the fetch of 7km can be used in investigating the air-mass transformation as representative one with acceptable error, although the turbulent diffusivity changes initialy some what rapid in both the profile and abosolute values, as air-mass moves over land (see Fig. 3).2) The height at which the difference of humidity (Δq=q(x, z)-q(o, z)) becomes 0, 1g/kg is adopted for characterizing (ZH) the thickness of internal boundary layer developing over the surface Fig. 7 shows the fetch dependence of boundary layer thickness. These relationships can be approximated by (ZH/L)=2.86×[(Kx/L2U)1/2]1.27, μ=0.4strong wind (ZH/L)=1.06×[(Kx/L2U)1/2]2.0, μ=0.25weak wind (ZH/L)=20.1×[(Kx/L2U)1/2]1.17, μ=0.6(ZH/L)=0.9×[(Kx/L2U)1/2]1.42, μ=0.4The thickness of internal boundry layer is thicker for weak wind conditions than for strong wind conditions. With increasing surface wetness, the humidity boundary layer becomes thicker due to intensive supply of water vapor from the ground surface.3) The part of diurnal changes of specific humidity, of temperature and of turbulent diffusivity are sensitive to the variation in thermal stability near the ground as shown in Fig. 10.Mean values of turbulent diffusivity (case-1) are greater for dry surface than for wet surface (case-5) from 1.1 to 1.5 times, indicating that increased thermal instability under dry surface conditions causes more strong turbulent mixing.4) Fig. 11 shows the variation in heat balance structure with the fetch. In the case of dry surface, total heat amount stored into layer during the daylight period was found to incease proportionally with the fetch.On the other hand, total heat amount transferred from the ground surface into air layer as sensible heat flux during the daylight period decreased somewhat, mainly because of decrease of temperature difference between air layer and the ground surface. It appeared that the heat balance structure at the wet ground surface did not very change with the fetch.