When net radiation flux on the ground turns the direction from incoming to outgoing about half an hour before the sun down, temperature within unheated shelters accelerates lowering and in a few hours approaches the air temperature outside shelters. It is not uncommon that the air temperature in row coverings and unheated small glasshouse gets below the outside air temperature on calm and clear nights in cold seasons.
Interrelations between inside and outside air temperatures and shelter wall temperatures under the process mentioned above were formulated on the basis of heat balance and with several assumptions.
The temperature of the shelter roof wall (T_w) goes down faster than the inside air temperature (T_i) in the evening, and becomes equal to the outside air temperature (T₀) when T_i is still higher than T₀ or T_w by εR(T₀)/h_i where εR(T₀) is the net heat loss through radiation from the roof wall of which temperature is equal to T₀, and hi is inside heat transfer (latent and sensible) coefficient This is the moment that convection heat transfer on the outer surface vanishes, and that heat loss consists of radiation only.
When T_i is equal to T₀, the wall temperature T_w will be lower than them by εR(T₀)/(h_i+h₀+h_r), where h_o is outside heat transfer coefficient and h_r is radiative heat transfer coefficient for the wall.
T_w of the roof wall can generally be written as equation (4). Examples of the relationship between three temperatures T_i, T₀ and T_w, are illustrated in figure 1.
On the assumption that T0, R and soil heat flux B are steady, the critical condition under which T_i in the shelter goes below T₀ is expressed as follows.
B/R(T₀)<F/γ(1-h_r+ε·h₀/h_i+h₀+h_r)
or
B/RT_i=T₀<F/γ(1-ε·h₀/h_i+h₀)
where R(T₀) is net radiation flux measured over the roof wall of which temperature is T₀, RT_i=T₀ is similar value measured when T_i=T₀, F is mean coefficient in radiation for all surface of the shelter, γ is rate of floor area to wall area, and ε is emissivity of the wall
Figure 3 shows the critical values of inversion calculated for a semicircle row cover under the various values of h_o and h_i.
The terminal difference in air temperatures of inside and outside the shelter will be obtained from following equation,
T_i-T₀=γB-(1-εC)FR(T₀)/h_i·C+h_ad, C=h₀+h_r/h_i+h₀+h_r, where h_ad is ventilating heat transfer coefficient.
The heat capacity within a shelter such as the raw covering and the small plastic or glass greenhouse is about tens times as large as the coefficient of heat loss from the surface of the shelter. Let us suppose that the outside temperature suddenly falls one unit degree from the steady condition, it will take only a few minutes to reach new equilibrium between outside and inside temperatures. Then, the above mentioned equaions obtained under steady conditions are thought to hold under the natural condition that the outside air temperature falls gradually.

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The temperature condition in a snow-covered, unheated greenhouse shown in Fig. 1 is investigated.
The measurements of solar radiation, air temperature and glass surface temperature were made from the end of December to the beginning of March. 1968.
An average inside air temperature was determined from the data at nine positions distributed uniformly in the space of the greenhouse.
The typical results of this experiment are indicated in Figs. 2, 3, 4, 5 and 6. Overall transmission coefficient of the greenhouse (Rall) was calculated from the solar radiation data, which was 0.62. Temperature measurements inside and outside show that the amplitude of daily temperature variation on cold and clear days is greater than that of snowy days. It also indicates that the wall surface temperature is lower than that of the roof (fig. 6).
Therefore, it seems that the roof temperature is greatly affected by the accumulation of snow.

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In order to check TAKEDA's theory (equation (2)), observations of wind velocity profiles were made over the sorgo canopy in August 1967. Furthermore, to test the theory another set of observations were made over the corn canopy in Tanashi, Tokyo, in July and August 1968. The author wants to know if the theory can be applied to all wind velocity profiles over different kinds of plant canopies at different stages of growth and development.
The wind velocity profiles were measured with five small cup-anemometers. The plant height (h), the leaf area index (L.A.I.) the mean leaf area density (M.L.A.D.=L.A.I./h) and the rate of heading were measured, too.
Five results were obtained from these observations as follows:
I. An opposite relationship between the zero-plane displacement (d) and the roughness length (z₀) was found, in which a decrease in d and an increase in z₀ with wind velocity were shown (see Fig. 3).
II. A good correspondence was found between d versus u_* (friction velocity) and M.L.A.D. with growth and development of the corn canopy (see Fig. 3).
III. A good correspondence was found between z₀ vs. u_* and the heading of corn plants with growth and development of the corn canopy (see Fig. 3).
IV. It was found that the values d and z₀ moved with the particular characteristic on the rough surface diagram introduced by TAKEDA (see Fig. 4).
V. It was found that the variation of H (effective plant height), obtained from equation (2), in which α is taken to be 0.087, vs, u_* decreased slightly with the increase of friction velocity on 24.25 July, that H was constant, even if u_* increase, on 1-3 August and that the variation of H vs. u_* increased slightly with the increase of u_*, furthermore the plotting points scattered under the condition of u_*>80cm/sec on 5-9 August (see Fig. 5).
Finally it was concluded that the theory was applicable even to the corn canopy taking structures of canopy on 24.25 July and on 1-3 August into account, and that, on the contrary, observed results on 5-9 August disagreed with the theory probably due to the oscillatory movements of plants with long periods.

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Remarkable damage was caused by a thunderstorm with hail in a south part of Fukuoka prefecture on 28th May 1967. The damage was observed over a zonal district extending from Tosu (Saga prefecture) to
Kuroki, through Kurume, Jyoyo. Especially, the damage to agricultural products was heavy. The author has investigated this hail damage form the following points:
1. Hail damages in the past.
The largest hailstorms recorded in the Fukuoka prefecture was seen on Feb. 19, 1684, in Kurume. The maximum size of the stones was about 7cm in diameter, weighing aobut 82 grams. The author made use of a 285-year period (1682-1967), for a total 31 haildamage days, to investigate the relation between hail storms and the months. Haildamage occurred preimarily in May (31%), and secondarily in April (21%).
2. Synoptic weather condition of hailfall.
Various ways have been employed for collecting data from radar observations, aerial observation by pilots through flights over the area of the hail path, Weather Bureau's upper soundings, surface observations by the persons in the storm area and the author took photographs of hail damage area. Also the data for crop loss of hail storm were supplied by the public offices.
A 5.7cm radar set operated at the Seburi radar site can depict thunderstorm cells in the storm by PPI photographs, . This photograph as indicated in Fig 4, helps delineate the hail path, its movement, development, and orientation. It also delieates the hail boundary within a 100km radar range. The echo areas shown reveal that the thunderstorm under study developed as a clam shell shape, the first hail falling from the south western edge of east-southeastward moving thunder storm cell (see echo area Fig. 6).
From analysis of upper (850-, 700-, 500-, and 300mb levels) and surface synoptic maps of May 28, 1967, it is evident that the thunderstorm and hailstorm developed along a meso low pressure, pushing forward across south central mountains of Fukuoka (Minou mountains). The 500-mb level jet stream appeared to be about 27m/s, probably responsible for the development of the storm through its vertical shear effects on the vertical movements of the individual storm cells along the meso low.
3. Distribution of hail damage.
The topographic effect on hail distribution is of importance, because it determines the speed and direction of local winds and, in turn, affects the distribution of hailstorms.
The author has made investigation on the duration and the begining and ending hours of storms, as well as the degrees of the haildamage. Data included the time of hailing (begining), size distribution of hailstones from photograph, stone density on the ground, lightning, direction of destructive wind, and estimates of crop and property damage damage types. The analysed haildamage lines are showr in Fig-6.
4. Condition of hail damage.
Damage caused by the hailstorm is vast. For small animals, the damage is serious when the hailstones range from 3 to 6cm in diameter. Stones of about 3cm diameter are considered disastrous to crops in general.
Theoretically, the degree of damage inflicted upon plants by hailstorms depends upon the stone size, areal density, depth of coverage, duration of the storm, falling velocity, area coverage, and age of the plants. Heavy rainfall and severe wind accompanying the hail cause considerable addintional damage.
It has been found that the area of crop damage coincides fairly closely with the density of stones; in general, the damged crop area coincides with the areas of stone density of 100 or more per square meter. Factors other than stone density influencing crop damage were a maximum stone size above 3cm diameter a longer point duration than 10 minutes, and a surface wind exceeding 20m/s. Finally, in the isohyetal analysis, it was revealed that the rain core was generally associated with the hailstorm and with 10mm rainfall during the 3-hour period

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カンキツの樹冠内にみられる凍害の方位性の原因を明らかにするために, 樹冠内における葉温, 気温, 夜間における気流の強さとその方向, 可照時数ならびに葉の浸透濃度の方位性をしらべた。
1. 凍害は夜間における気流の下流測の南から北東側にかけての方位の樹冠外周部にいちじるしく, 気流の上流側の南西から北西側にかけての方位と樹頂部附近では, 被害が全くないかあるいは軽微であつた。
2. 冬季の夜間における葉温は, 南から北東側にかけての方位が低温になり, 南西から北西側にかけての方位が高温になつて, 凍害の方位性とよく一致した分布を示した。被害のいちじるしい気流の下流側の葉温は, 気流の上流側に対して1.5～2℃低温になつた。さらに樹冠中心部附近が最も高温で, 樹冠外周部に行くにしたがつて低温になる。
3. 冷却のはげしい夜間の気流の方向は, 南西から北西にかけての範囲にあつた。さらに樹冠外周部附近の気流の強さの分布は, 気流の下流側の南東から北東側にかけての方位が弱く, 気流の上流側のとくに樹頂部附近が強い。このような気流の強さと方向の方位性は, 葉温分布や被害分布とよく一致し, 気流を強くうける方位の葉は冷却度が少なく, 葉温は気流の強さに支配されている。
4. 樹冠の方位による葉の浸透濃度には方位による差がなく, したがつて樹冠内の方位による葉の耐凍性には差がないものと判断された。
5. 本供試樹の樹冠内にみられた凍害の方位性の主因は, 被害のいちじるしい南から北東側の方位の葉温が低くなること. さらにその結果, 凍結時間も長くなつて, この方位の被害が助長されたものと考えられる。

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