In summer 1939, Southern part of Tyosen and Western and Central parts of Japan experienced a great drought which is one of the heaviest ever recorded since the routine of meteorological services was established in this country. The present note explains the main results of the investigation on this drought. carried out by the staff of Central Meteorological Observatory of Japan. The details will appear in the Report of the Observatory. It is shown that the direct cause of this drought was the persistence of high pressure belt over Japan and her neighbourhood, which hindered the visit of depressions to the drought regions. Here is also shown the effect of relatively low surface temperature and small temperature gradient over Western North Pacific on the persistence of the pressure anomaly. Some considerations on sunspots relation were also alluded.
The problem whether cyclones are waves or vortices is one of the fundamental problems in meteorology. The wave theroy of cyclones is the leading idea of Norwegian school. But inspite of her brilliant success in finding unstable cyclone waves, much difficulties lie on her way from both physical and mathematical points of view. It is obvious that cyclones are vortices or of vortical nature in hydrodynamical sense. Further, it is a possible solution of cyclone formation that extratropical cyclones bear itself on the surface of polar front and grow there. But at the present state of development of Norwegian wave-theory, the connexion between wave and vortex is impossible and there is no hope of giving connexion between them in the near future(1). In our present investigation, the author starts from another point of view, introducing an idea of vortical waves, and intends to treat the whole evolution of cyclones mathematically. The vortical wave is defined by where vxvy; u, v are velocities of propagation of the vortical wave and those of the air respectively. In Chapter I, the author derives the fundamental equation of the problem. Namely, from the equations of motion on the rotating earth, the following equation is obtained: where x, y, z are cartesian coordinates taken southwards, eastwards and upwards respectively, u, v, w, the velocity components, (horizontal divergence), (vertical components of vorticity), θ, latitude, a, radius of the earth, k, kinematic coefficieut of viscosity, p, pressure, p, density, ω, angular velocity of rotation of the earth, and In Chapter II are discussed the vortical waves in a uniform and nonvariable fundamental flow for following special cases: In the first case, following results are obtained: When there is no viscosity and the solenoidal field vanishes, there exist free waves which propagate with the velocity of the fundamental flow. The effect of coriolis' force on the velocity is very small, when the wave-length of the vortical wave is of the same order with cyclones. From the above solution of sinnusoidal type can be easily constructed a vortex of solitary type which represents a cyclone by Fourier double integral theorem, provided that the term due to the latitudinal variation of coriolis' force is neglected. When the viscosity is taken into consideration, vortical waves of dissipating nature are obtained, as it may be expected. The time requisite for that the amplitude becomes 1/e of its initial value is given for various values of viscosity-coefficient and wave-length. Finally, the baroclinic term is discussed and the general solution is obtained for the case: From the general solution, it follows that the vortical wave is constant as for time when j(t) is constant, i. e. the bounded vortical wave is constant when the baroclinic field is constant. The above result is interpreted as follows: If there is an invariable baroclinic field in the fundamental flow, there are vortical waves with constant amplitude associated with the field, so that the baroclinic field does not contribute to the development of cyclones. Next the author gets the solution for the case where the baroclinic field mores with a certain velocity. When the velocity is different from that of the fundamental flow, the bounded vortical wave moves only with the velocity of the baroclinic field, but when the velocity of the solenoidal field is the same as that of the fundamental flow, the vortical wave develops with the time linearly.
Various natures of summer weather in Far East Asia were investigated for the purpose of short and long range weather forecasting, and the results are summarized as follows. 1) The alternation of weather is slow and the diurnal variation of various meteorological elements is quite distinct. Hence, daily weather is predicted by air-mass analysis of morning observation. 2) One of the most important factor which controles the weather is Ogasawara high. Most depressions in summer, say, typhoon, one of the most distructive storm of the world, travel clockwise around Ogasawara high. If there is no depression about Ogasawara high, tropical maritime air-mass is brought from Ogasawara and usually continues fair weather. 3) On an average, six depressions lie around the Ogasawara high, and 5 days periodicity of pressure is explained by the drift of the depression due to the upper wind. 4) The velocity distribution at the surface in Ogasawara high is given by provided that circular symmetry of Ogasawara high is assumed, where V is velocity, r distance from the center, Vo, ro are constants. Such a distribution agrees with the distribution of pressure as it should be and the descending current in Ogasawara high is estimated to be about 2.5mm/sec. 5) Thermodynamical nature of Ogasawara air-mass is calculated from the condition of the equilibrium of energy transfer of various kinds and the lapse rate of temperature is calculated to be about 0.5°C/100m. 6) When the cold air of high latitude invades in low latitude, say, about N 40°, rainy weather is expected at northern part of the main island of Japan. 7) Water vapor which evaporates from sea in the domain of Ogasawara high can be considered to diffuse in all directions and the coefficient of diffusivity is calculated to be about 3×1009cm2/sec 8) Thunder storms in the season are classified into two kinds; one is the outbreak of instability due to invasion of cold air, the other due to ascending current caused by insulation, and they have different structure. It is shown further that every strong heat thunder storm has warm sector like a polar front depression which is important for the practice of the prediction of heat thunder storm.
Over the past twenty and more years, the temperature of well water has been continuously observed in a well at the Mito Meteorological Station which is 10.50 m deep and has a diameter of 0.98m. These observed data are studied and the following results are obtained. (1) The annual variation of temperature of well water is nearly parallel to that of the air temperature and presents a single maximum in August, a single minimum in February, au l its amplitude is 0.44°C, which does not come to 4% of the amplitude of air temperature. (2) A secular variation is noticed for the temperature of well water. The difference between the temperature of well water and the soil temperature at the same depth correlates considerably with the Wolf's relative sun-spot number. (3) Sudden changes of temperature of well water are chiefly due to rainfalls. When the diurnal precipitation exceeds 50mm, the effect of rainfall appears suddenly after a rainy day and approaches its maximum two or three days later, and its mean value becomes 0.5_??_0.7°C. Thus, the effect of rainfall acts upon the temperature of well water so as to make it low in winter and high in summer. (1) and (2) are explained by the effect of air column with which the well is filled, and the (3) is determined by the difference between the temperature of raindrops and the temperature of well water and by the circumstances of permeation of raindrops into the soil.
The present note points out that the warm front, which is the cause of the birth of depression in the East China Sea in winter, seems to be formed by the heating of lower air from the Kurosio. And the author describes the alternation of weather in the Ryukyu Islands which is experienced at the time of birth of the depression.