Characteristics of year to year change in mean air temperature with different averaging period were analysed, and the confidence limits of return periods determined by an empirical method were discussed in relation to the averaging period, season and the place. Results are summarized as follows:
(1) Both annual and monthly mean air temperatures for the warm season with the return period of 50 years are found to be nearly equal to the temperature (M-2σ), where M and σ are the mean and standard deviation of the yearly change in annual and monthly mean temperatures. Monthly mean temperatures for the return period of 10 years are lower by about 0.4°C than the temperature (M-σ) in average.
(2) Air temperatures for the same return period are decreased with the decrease of the averaging period, and the difference between monthly and half-decade mean air temperatures for the return period of 10 years are in the range of 1 to 2°C.
(3) Empirical relations were obtained to explain the change in relative standard deviation of yearly fluctuation of period-mean temperature (Eq. 4). These values of the relative standard deviation are somewhat smaller than those predicted by the -1/2 power law of averaging days.
(4) Significant values of return periods (T_j) estimated by the empirical method (Eq. 1) vary with season, place, and the averaging period. T_j for half-decade and decade mean temperatures in the case of statistical period of 78 years, are considered to be about 15 and 20 years, respectively.

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In order to investigate the micrometeorological modification of cool weather damage by use of 2-m high cheese cloth and PE russell windbreak nets in paddy rice fields, the author carried out the meteorological observation and growth measurement during periods from June to August in 1979 in Naganuma, Hokkaido.
The weaker region of relative wind speed was from 1 to 5H (distance expressed in net height) leeward and the relative wind speed for cheese cloth net was generally 10% smaller than that of russell net. The maxima of surface water and leaf-stem temperatures were in 2 to 5H and the effective range in -5 to 20H. The cheese cloth net was more efficient than russell net in the highly affected range at 2, 3.5 and 5H. Because of the convergence and divergence winds through an opening at the bottom of the nets, the temperatures at 1H were generally lower than those at -2.5 and 2H. The warming effect on clear or fine days was larger than that on cloudy or rainy days. It was also recognized even in the night of cloudy or rainy days. Surface leaf-stem temperature increased faster and higher than surface water temperature in the early morning on clear day because of specific heat and heat capacity differences of water and leaf-stem.
The effective range on rice plant length was from -5 to 35H for cheese cloth net and -5 to 20H for russell net. The plant length was fairly high in 1 to 5H for both the nets. It is effective to grow grasses in the 25-cm open space under nets in order to protect paddy rice plants near nets.

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The present paper deals with the relationships between 1) dew formation and meteorological elements, 2) dew amount on leaves and acrylic plate, and the observed dew amounts were compared with the calculated values from the Yamamoto's dew estimation equation based on heat balance. The results obtained were summarized as follows:
(1) Dew formation is related to cloud amount (i.e., net radiation) and wind speed. When the sky was clear (cloud amount less than 3), the dew amount increased from 2.0 to 2.8mgcm^-2hr^-1 accompanied with wind speed increased from 10 to 120cm sec^-1, and in another case, when the sky was cloudy (cloud amount more than 4), the dew amount increased from 0.6 to 1.4mgcm^-2hr^-1 accompanied with wind speed increased from 50 to 190cm sec^-1.
(2) The relationship between the ratio (Y, %) of dew amount on leaves to that on acrylic plate and the difference of the surface temperature (X, °C) between leaves and acrylic plate could be expressed as following equation,
Y=ae^-bX,
where a and b are the empirical constants.
(3) The net radiation on the surface of a body that factorized in the Yamamoto's dew estimation equation was revised. As a result, the calculated values of dew amount were close to the observed values and showed a similar variation tendency and fairly good agreement.

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Greenhouses should be designed to meet requirements of construction costs, durability against loads and the possibility of providing suitable environment to plant growth. To get guides to design an optimal greenhouse from the above-mentioned three viewpoints, one of the optimization techniques, which is called the steepest descent method, is applied in this study. The direct light transmission into the greenhouse in winter is regarded as one of the most important environmental factors.
The steepest descent method gives the combination of the design variables which constitute the optimal (minimum or maximum) value in the objective function under some constraints. In this study the design variables were, for example, the shape of the house, the moment of inertia and crosssection features of each member and the ratch measure. The allowable stress or deflection of each member played a role of constraints in the course of the optimization. The objective function was the construction cost or the direct light transmission. In the steepest descent method, however, only one objective function is allowed. For this reason the following two steps were used. First the construction cost (J_s) is chosen as the objective function and is minimized. Then the inequality (1) is added to the constraints and the light transmission is maximized, where k is the coefficient of construction cost allowance and larger than 1.0, and J_sopt is the minimum construction cost.
Because in the steepest descent method all variables should be continuous and differentiable, some discontinuous variables, e.g. the number of purlins, were approximated with appropriate continuous functions. For the same reason any size and shape of steel member were assumed to exist. The crosssection features of the member are expressed with three independent variables on the basis of the empirical relations.
The optimizations were carried out under the conditions of a snow load of 30cm and a wind speed of 50m/s. The span was fixed at 9m. The latitude and the coefficient of construction cost allowance in the optimization of the light transmission were 34°N and 1.10, respectively. The following points became clear by the optimizations.
1) The steepest descent method can be applied to greenhouse design and the results show appreciable improvement both in the construction cost and in the light transmission in comparison with an example of commercial greenhouses.
2) The results of the optimization of the construction cost (cost optimization, hereafter) and the light transmission of the N-S oriented greenhouse (N-S optimization, hereafter) show a symmetric shape, whereas the optimal E-W oriented greenhouse has a ridge nearer to the south wall, so that the south roof slope becomes steeper.
3) Every optimization results in a ratch measuer of about 4m, which is wider than that of commercial greenhouses.
4) The moment of inertia of the rafters and the posts ranges from 150 to 290cm⁴. In the cases of the cost and N-S optimizations, the rafters have a larger moment of inertia than the posts. In the E-W optimization, the north rafter has an appreciably larger moment of inertia than the three others.
5) The cost optimization shows that members of the crosssection with larger depth and width are more suitable for the rafters and the posts, if the moment of inertia is the same. This holds true for the north members in the E-W optimization and for the posts in the N-S optimization. In the E-W oriented greenhouse, a member with shorter depth and larger section area and a member with shorter width are more suitable for the south rafter and for the south post, respectively.
6) In this study the strength of the glass was not taken into consideration. This resulted in very wide purlin intervals, which seem to be unrealistic, but this still proves that larger purlins with wider intervals are more suitable

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Effect of rainfall (mist) on dry matter production in the leaves of kidney bean (Phaseolus vulgaris L.), sweet potato (Ipomoea batatas Lam.) and maize (Zea mays L.) was investigated. The rate of dry matter accumulation was measured by using the improved half-leaf method. The results were as follows.
1) On rainy days, dry matter accumulation rates of these crops exposed to rainfall showed 30-50% lower values as compared with those of crops protected from rain by a plastic roof, though the light intensity in the former was greater 10% than that in the latter.
2) The mist treatment in growth chamber also decreased the rates of dry matter accumulation of crop leaves. The effect of mist treatment was rather smaller on maize than on kidney bean or sweet potato. From the response curves of accumulation rates to various intensities of light, it was noticed that light compensation point of these crops was about 1000-1500lux, but it became higher up to 2000-2500lux with mist treatment.
3) The effects of mist treatment on environmental factors such as air- and leaf-temperature and light intensity in the growth chamber were markedly small. Therefore, it can be considered that the effect on dry matter production rate is apparently an effect of rainfall (mist) itself rather than an effect of environmental conditions produced by mist treatment.
Two reasons may be suggested to explain these phenomena. First, the layer of rain water on the leaf surface prevents the exchange of gases, and the photosynthetic activity of the leaf is suppressed. Second, carbohydrates may be leached from leaves by rainfall.

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[in Japanese]

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