1. The abundant summer rainfall in the eastern part of Asia including Japan has been commonly explained by the southwesterly monsoon winds carrying with much moisture from the Pacific Ocean. However, this problem is not so simple because the rainy season in summer has a threefold structure instead of a single continuous period. Except the northern region, there exists in Japan the double or triple maxima of monthly amount of precipitation. Fig. 1. shows the three regimes of precipitation, A, B and C, classified as follows
A: Pacific type with double maxima in summer.
A₁ Primary maximum in. September and the secondary one in June.
A₂ Inverted type of A₁, primary maximum in June and the secondary one in September.
B: Japan Sea type with triple maxima.
Of them, the primary maximum appears in winter and the other two in summer (June and September).
C: Northern type with single maximum in September.
In both regions of type A and B, two maxima of summer appear in September and June separated by the July-August minimum forming a short dry period which is very important not only from the geographical but also from the economic points of view.
2. The dry period above-mentioned is considered to be a result of the special type of pressure pattern developing in the special type of pressure patterns developing in the mid-summer over the north Pacific Ocean. After the Bai-u front along which the cloudy and rainy weather persists for a long spell parse: away to the north, the north Pacific anticyclone extends westward to the Japanese Islands and its western part is called the Ogasawara High. Even in a normal year, the main part of Japan, especially its western half, is located underneath a huge anticyclone (Fig, 2.) and fine weather lasts for many days with scarce rainfall, bright sunshine and strong evaporation. Because of the prevalence and westward expansion of the Ogasawara High, northward movement of cyclones and typhoons from the southwestern seas are checked to turn their paths to the westward direction along the outer periphery of the high pressure area and sc the frequencies of cyclones become very scarce (Fig. 3.). This strengthens further the occurrence of clear sky and scanty rain during this period.
In connection with this subject, summer rain in the Far East is very important for the theory of non -soon, and it has been commonly explained by the monsoon winds from the Pacific Ocean laden with abundant moisture. However, this is inconsistent with the threefold structure of summer rainy season in Japan. Recent upper air observations afford another interpretation for this subject. That is, water vapor for summer precipitation in the Far East is originally transfered by the subtropical airmass from the equatorial region inflowing as southwesterly winds along the southern coast of Asiatic continent. This airmass is very moist with high equivalent potential temperature and connective instability. With the westward expansion of the Ogasawara High, tropical easterly with less moisture becomes strong and interrupts northward invasions of the southwesterly winds. As a result, fine weather persists for a long period. In such a way, the monsoon does really exist if it means only the seasonal alternation of winds with opposite directions. Hence; summer monsoon in East Asia is not exactly the same as that with abundant rainfall in India and other regions of southeastern Asia.
3. Furthermore, in summer season, the temperature becomes much higher with less rainfall because of intense solar heating unhindered and unweakened by the thick layer of clouds. A striking negative correlation is found between the amount of monthly rainfall and average monthly temperature in summer. Numerical figures for Fig. 4. give an amount of August rainfall in 1939 expressed as a percentage of normal year and those for Fig. 5, the August temperature deviation in 1939 from the normal.

View full abstract

As to the lower stream (0-17km) of the Abe-kawa in Shizuoka Prefecture, the author estimated the amount of the degradation of river bed in recent years by considering (a) fluctuations in the mean heights of river bed and (b) quantities of deposition or scouring in the river bed. Regarding the causes of the degradation, he considered (a) the decrease of tractional loads to the construction of sand catch dams and (b) the effect of gravel mining in the river bed. Conclusions are summarized as follows:
1) The degradation of river bed in the lower stream of the Abekawa has been increasingly remarkable since about 1954, and the quantity of degradation during the past 10 years (1954-1964) is larger in the lower reaches below the 9km. point from the river mouth, the maximum being about 2 meters at the 6km. point.
2) The yearly records of total deposition or scouring in the river bed show a huge amount of scouring for every year since 1954 excepting 1957, and that of the last year (March 1963—March 1964) amounted to about 2×10⁶m³ of scouring.
3) In the upper stream (above the 34km. point) of the Abe-kawa, four large sand catch dams were constructed between 1951 and 1958. From the quantity of gravels deposited in those dams, mean annual volume of the tractional loads at the 34km. point (Ôgôchi Dam) is calculated to be 2.5×10⁵m³, corresponding to about 20% of the total sediment transportation. The effect of those dams to the river bed in the lower stream, however, is indirect and has a minor importance as compared with that of the gravel mining.
4) The relation between the degradation of river bed and the gravel mining is direct and decisive. Based on the analysis of data from 1952 to 1959, the author pointed out that there is a close correlation between quantities of scouring in the river bed and quantities of mined gravels, in the reaches of 1-6km. Moreover, there is a considerable correlation too in the reaches of 2-6km. between the lowering of river bed calculated from the quantity of mined gravels and the degradation -based on the actual measurement.
Therefore, it is to be said that gravel mining has been definitely too excessively undertaken in recent years and the scale of operation is still expanding. If this trend is not reversed in the immediate future, serious social problems will be caused by the degradation of river bed.

View full abstract

In the previous paper, the author analyzed the detailed distribution of temperature in and around Kumagaya City, situated in the central part of Kantô Plain, concerning various weather conditions (Geographical Review of Japan, Vol. 37, No. 5, pp. 243-254). Relationship between city temperature and meteorological factors suggests that the cause of city temperature of a local city in Japan is seen in the difference of radiation balance between urban areas and surroundings and especially construction materials of a city plays an important role in deciding city temperature.
Further considerations on the cause of city temperature were attempted in this paper. The comprehensive book about city climate by A. Kratzer shows that the following three factors are important as the causes of city temperature: artificial heat produced in urban areas, pollution of city air and effect of construction materials of a city.
In the case of this paper, however, it seems that the amount of artificial heat is relatively small and pollution of city air is unimportant, because the city size is small and there are very few factories in the city which consume a large amount of coal. Especially in summer season, these two factors are negligible.
Difference of radiation balanced between the urban area and the surroundings affects on the city temperature in two ways. Those are the physical properties of constrution materials of the city concerning heat balance and the unevennss of the surface coverage of the city influencing heat transfer. Physical nature of construction materials of the city decides surface temperature of the earth. Nocturnal cooling of surface temperature of the earth is represented by Brunt's formula in accuracy of first approximation. The surface of the earth (T) is given by
_??_
wher T₀; surface temperature of the earth at the time of sunset, R; nocturnal radiation from the surface of the earth, ρ; density of ground, c; specific heat of ground, κ; specific conductivity of heat of ground. Assuming that the nocturnal radiation from the ground to the air (R) does not vary with time, T is decided by 1/cρ√_κ.
This formula was applied to the surface temperature of various construction materials of the city and then evaluation of nocturnal cooling was attempted as follows. Firstly, areas of roads, houses, grounds and so on in each 50m-meshed square were measured by using the map of 1/3000 scale and the relative portion of their respective areas for each section was calculated. Secondly, 1/cρ√_κ in each section was computd. Values of 1/cρ√_κ of each material are given in Table 1. (Concrete, asphalt, roofing the and soil are listed from above to below.) Then, this value in each section was converted into value of 1/cρ√_κ, in 200 mmeshed setion. The result is shown in Figure 2.
The close relationship between temperature in the urban area and the value of 1/cρ√_κ is shown in Figure 3. This figure shows that both physical properties of construction materials and unevenness of the city play important roles in deciding city temperature.
Unevenness of surface coverage in an urban area results in the decrease of nocturnal radiation and wind velocity. Consequently, decrease of noctvrnal radiation accelerates decreasing of nocturnal cooling in an urban area and drop of wind speed in an urban area promotes decreasing of heat tranfer from below to above in city air. As a result, temperature in an urban area becomes higher than in the surroundings.

View full abstract