A convective shower-cloud is numerically simulated, entrainment and the drag force of raindrops being taken into account, and the initiation of a downdraft in the cloud is studied. Rainfall is considered in the model in accordance with a relation of itss intensity with the water content of raindrops. The relation is in satisfactory agreement with observations and has some evidences on the theoretical basis. It is concluded that the downdraft is initiated in a cloud by the drag force of raindrops, when the air-temperature in the cloud is still higher than that of the surrounding atmosphere. Further, it is found that in a cloud with larger horizontal size, the updraft and the downdraft are more vigorous, and the downdraft is more rapidly initiated by the accumulation of larger amount of liquid water.
The recently developed sonic anemometer-thermometer has many excellent characteristics which cannot be attained by traditional anemometers, and we can measure air temperature as well as wind velocity with the same sensor at the same time. But most of the examples developed in the past were aimed for the application to the study of micrometeorology in light winds. The present author has aimed to develop the sonic anemometer-thermometer for general purposes including storm observations. The system adopted is of the pulse-time difference method. It is decided to adopt this method because the instrument in this method is less affected by noises and has wide observational ranges. But the past instruments in this method had the fault that the timing of the receiving pulse becomes erroneous in case of decreasing of receiving power of the signal. This fault is covered in this case by adopting high efficient barium titaniate sound transducers and high gain amplifiers to get sharp rising of the receiving pulse wave forms. A new votlage analogue output circuit was developed for this instrument that enables to use various kinds of recorders. The shape of the sound head has great importance to attain good signal to noise ratio when wind direction coincides with sound path orientation in high winds. The shape of the head has been developed through wind tunnel experiments and the present one is not the final one but a temporary choise. It is found by the wind tunnel experiment that it does not work well if wind is stronger than 30m/sec along the sound path. But except such case the instrument has proved to work satisfactory well and to be easy to handle with. The sound frequency of the pulse is 100kc and pulse frequency is about 300 pulses per second. The attenuation of short period changes on the records caused by the line averaged character of the sensor is also discussed in this paper.
Quasi-horizontal wave motions in the equatorial area are discussed. A single layer of homogeneous incompressible fluid with free surface is treated. The Coriolis parameter is assumed to be proportional to the latitude. In general, waves of two different types are obtained as solutions, one being the inertio-gravity wave and the other Rossby wave. They are distinguished from each other by the difference of frequencies and by the relationships between pressure and velocity fields. For the solutions of the lowest mode (waves confined near the equator), however, the distinction between the Rossby and the inertio-gravity waves is not clear. The wave moves westward and the frequency of this wave is compared to that of the gravity wave, if wave length is large. With the increase of the wave number the frequency decreases and approaches to that of the Rossby type wave. The pressure and wind fields of this wave show somewhat mixed character of the two types, and change continuously with the wave number. In this connection it seems impossible to "filter out" gravity waves from large scale motions. Another interesting feature of the equatorial disturbances is that the low frequency waves are trapped near the equator. It is shown that the both waves of inertio-gravity type and of the Rossby type have appreciable amplitude only near the equator. The characteristic north-south extent of the waves is (c/β)1/2, where c is the velocity of long gravity waves and β is the Rossby parameter. This expression is identical with that derived by Bretherton (1964) for inertio-gravity oscillations in a meridional plane. In the later half, "forced stationary motion" in the equatorial region is treated. Based on the same model, mass sources and sinks are introduced periodically in the east-west direction. Then the motions and surface topography caused by them are calculated. As expected, high and low pressures appear where mass source and sink are given respectively. But these high and low cells are splitted into two parts separated by troughs or ridges located along the equator. Strong east-west current was formed along the equator. The flow directs from source to sink and it is intensified by the turning of the circular flow in the higher latitudes.
The summer monsoon of southern and eastern Asia was analyzed, and particularly the emphasis was put on the time variations of the space distributions of water vapour and wind system. The determination of the areas of the monsoon and trades was based upon the wind constancy and the vertical shear of wind. A distinct moist tongue appeared along the southern coast of the China continent early in June and advanced northward. The tongue was usually found to the north of the SW or SE monsoon rather than in the monsoon itself. Associating with the northward advances of the tongue and of the monsoon, a northward moving anticyclonic cell was well defined at 300mb over southern China. The regiaonl water vapour balances on the continent and Japan and surrounding sea were analyzed. The results show that the supply of considerable amount of vapour is necessary on the continent.
A high altitude aerial photographic cloud observation was made over the Japan Sea on January 20, 1965 when a comparatively weak monsoon covered the Japan Sea and her neigh-bourhood. Remarkable facts are that the cloud amount was closely related to the sea surface temperature, that the cloud height was almost uniformly about 2km which coincides with the height of inversion observed downstream and that the size of convection system was also uniform. Some quantitative discussions are tried on vapor, condensed water and heat budget under steady state assumption.
A finite difference scheme for solving marching problems is designed. It is a two step iteration to simulate the backward difference method, i.e., first the tentative values at the later time stage are calculated by using the foreward difference and then the correction is made using these quantities. Applying this scheme to oscillatory equations, the high frequency oscillation is shown to be damped under certain conditions. Numerical integrations of the primitive equations for the so-called divergent barotrophic model were carried out by making use of this scheme. The result show that, because of an unbalanced initial state, gravity waves of fairly large amplitudes are initially generated. However, they are damped out with the lapse of time, while the quasi-geostrophic part of motions is kept less disturbed. For comparison, calculations were made for the same model and for the same initial conditions, by applying both the present method and the centered difference method commonly used. The two patterns thus calculated coincide in main features but differences are found in the distribution of divergence, especially near the boundary of the integration domain.