Starting from simple fundamental equations, a differential equation is obtained which prescribes the velocity distribution in plant canopies. When the density of the plant is constant with height, the differential equation gives exponential wind profile as a solution. It is assumed that logarithmic wind profile prevailes both above the plant canopies and in the lowest air layer near the canopy floor. Effect of variation of the plant density, being assumed constant with height, is investigated, and it is found that when the density is large the surface at the height of the plant canopies acts as a smooth surface for the wind profile, whereas when the density is small the earth surface becomes a smooth one. The roughness parameter, which has been introduced only as an integration constant, is expressed in terms of roughness height and density, and it is found that it has a maximum at a certain value of the density when the height is constant.

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In this paper the method of measurement of transmissivity of atmospheric (long wave) radiation through plant layer and of calculation of net long wave radiation within plant communities are described.
(1) There are two methods for determining the transmissivity. The first method is used under isothermal conditions at night. The method is described in the followings. The net radiation at the top surface of plant communities, R_n0, is expressed by
R_n0=L₀^↓-σT⁴ (1)
where L₀^↓ is the atmospheric radiation and T is the plant temperature. If the transmissivity of atmospheric radiation through the plant layer between z=0 and z=z is t_z, the emissivity of the layer (1-t_z). Then the downward long wave radiation from the plant layer above z is (1-t_z)·σT⁴. Net long wave radiation at z, R_nz, is written as
R_nz=t_z·L₀^↓+(1-t_z)·σT⁴-σT⁴ (2)
The first term in the right-hand side of eq. (2) represents the contribution of atmospheric radiation, and the third term the up-ward radiation from the plant layers below z and the soil surface. From eqs. (1) and (2)
t_z=R_n0/R_nz (3)
Thus, t_z is obtained from observed values of net radiation at z=0 and z=z.
The second method can be used under the condition of arbitrary vertical distribution of plant temperature. The transmissivity can be determined more directly than in the first method. Let L₀^↑ be the up-ward radiation at z=0, L_pz^↓ downwrd radiation from the plant layers above z, L_z^↑ up-ward radiation from the plant layers below z and the soil surface, R_n0 and R_nz are expressed by
R_n0=L₀^↓-L₀^↑ (4)
R_nz=t_z·L₀^↓+L_pz^↓-L_z^↑ (5)
Sudden change in incoming long wave radiation at the top is applied-in practice, plants were covered with a large sheet of linen. Under this condition, L₀^↑, L_pz^↓ and L_z^↑ remain practically unchanged. Hence net radiation at z=0 and at z=z, R′_n0 and R′_nz, are expressed by
R′_n0=L′₀^↓-L₀^↑ (6)
R′_nz=t_z·L′₀^↓+L_pz^↓-L_z^↑ (7)
wher L′₀^↓ is downward long wave radiation emitted from the sheet. From eqs. (4)-(7)
t_z=(R_nz-R′_nz)/(R_n0-R′_n0) (8)
Then the transmissivity is calculated from eq. (8) with four observed values of net radiation. This experiment was conducted at night. Fig. 1 shows variation of the transmissivity with height within a paddy field by the second method. The transmissivity may be expressed by
t_z=exp(-∫A(z)dz)
where A(z) is a function of plant densities.
(2) Provided that the transmissivity of atmospheric radiation in the plant layer is given, net long wave radiation within plant layers can be calculated. The transmissivity at a, b, z, c and d are expressed as t_a, t_b, t_z, t_c and t_d respectively (Fig. 3). The transmissivity of long wave radiation thro

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In recent years, increasing interest has been taken in reducing evaporation from water and land surfaces, and a number of studies have been published of the effect of fatty alcohols as the evaporation suppressor. But little attention has been paid to the relationships among suppression rate, subsequent increase in temperature and diffusion resistance of monolayer film to evaporation.
In this paper, th rate of evaporation was investigated by employing monolayer films of fatty alcohol's members as shwn in Table 1. Using the instrumentation presented in Figure 1 the diffusian resistance to evaporation was mersured for each substance and was shown in Figure 2 as a function of the number of carbon atoms in fatty alcohols.
The relationship between the number of carbon atoms and the diffusion resistance was found to be approximately
r_f=0.172·N-2.0, N≥11
where, r_f is the diffusion resistance (sec/cm), and N the number of carbon atoms. From the above result, it can be seen that fatty alcohols with carbon atoms less than N=11 are ineffective for reducing the rate of evaporation of water.
On the basis of diffusion theory, the suppression rate of evaporation by monolayer films was expressed by
(1-β)=[D_t/D_f+D_t]
where, (1-β) is the suppression arte (defined as a rate of evaporation from water surface covered by films to that from free water surface under the same weather conditions), D_t and D_f are the integral exchange coefficient (cm/sec.) in the air layer above films and in films (D_f is the reciprocal of r_f), respectively. The dependence of the suppression rate on both D_f and D_t calculated from the above relation is presented in Figure 3. As can be seen in this figure, the rate increases with increasing the integral exchange coefficient in the air layer. This fact seems to indicate that the suppression rate is not a physical quantity for monolayer films.
Temperature increase in shallow water which results from reducing evaporation was found to be approximated by Eq. (11). As has been reported by several authors, monolayer film spread on water surface is swept and is piled upon the leeshore by the action of the wind. Temperature increase expected from Eq. (11) may not be achieved in practice and may be the potential increase in water tempereture. But it provides an interesting upper limit to the increase in water temperature which can be produced by spreading monolayer film on water surface. The results calculated from Eq. (11) are presented as a function of the suppression rate in Figure 4. It is seen in this figure that there is clear dependence of the temperature increase on the suppression rate. When evaporation is completely suppressed, the temperature increase reaches 13.1°C(θ_w′=29.9°C) under assumed weather conditions (S_w=0.5ly/min., θ_a=15°C, e_a=7.7mmHg, D_t=2.0cm/sec.). Bowen's ratio characterizing the heat balance condition at water surface shows considerably increase from about 0.18 at (1-β)=0 to 1.5 at 0.8, indicating that more heat is transferred as sensible heat into air. Figure 4 also shows the decrease in the relative humidity at the upper surface of monolayer films with increasing the suppression rate.

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The following is the summary of the result of the observation on the down slope wind at Hakatajima of the Inland Sea of Seto (at 39°4′ Lat.; 133°05′ E, Long.) from October to November in 1961.
(1) The down slope wind on clear and calm nights arises immediately after sunset and lasts till the sun rises next morning, so long as there is no special change. The wind velocity, in many cases, is one meter per second and the wind goes on blowing at an almost constant speed with little change all night long.
(2) The down slope wind in a small valley is 25-30 meters thick, and the air temperature falls till about 4°C and the maximum wind velocity is generally found in the five meters' layer.
(3) The down solpe wind both on the ridge of the side of the valley and in the upper part of the valley is weaker in the strength and more irregular than that in a valley, but it has the characteristics of the down slope wind and blows down along the slope, Its thickness is not fixed.
(4) The observed down slope wind coincides with PRANDTL's theory either for the vertical distribution or maximum wind velocity, but the observed air temperature distribution does not coincide with it. The discrepancy may be explained by the fact that, though the theroy treats the two-dimensional phenomenon, it is three-dimensional in the actual cases.

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