Characteristic features of cloud and echo distribution and their temporal variation over the east coast of the Asian Continent are studied for the one month period of February 1968 by analyzing the ES SA cloud brightness maps and PPI pictures over the Japan Islands. The study lays special emphasis on the relation among the air-mass transformation, generation of convective clouds and the development of the wave disturbances over the Kuroshio region. The results of the analysis reveal the existence of a pers i s tent zone of convective cloud along the Kuroshio current. Two kinds of quasi-periodic variation in the cloud/echo amount with a time scale of about 4 and 2 days, respectively, predominate along the cloud zone. These variations are known to be associated with the wave cyclones. The echo system associated with the disturbance which developed under the influence of the long wave trough grows quite rapidly into a huge vortex-shaped echo system. The very intense or penetrative convections within the echo system are confined within a mesoscale area. The echo system associated with an undeveloped disturbance, on the one hand, does not grow remarkably.
The heavy rainfall over Japan in the Baiu season is usually associated with a well-developed low-level jet stream. The relation between the heavy rainfall and the low-level jet is here examined over southwest Japan throughout the Baiu season of 1968. As for the spatial relation, it is concluded that the occurrence of heavy rainfall is mostly confined within the zone of about 200 km wide along the north side of the low-level jet axis. The wind speed in the heavy rainfall zone is almost vertically uniform in the thick convective layer while the geostrophic wind speed increases with height. This characteristic wind profile suggests that the intensification of the super geostrophic low-level jet is to be attributed to convective momentum mixing. These observational facts about the relation between the heavy rainfall and the low-level jet is explained well from the dynamic model of the low-level jet circulation proposed by MATSUMOTO and NINOMIYA (1971).
According to some observati o nal analyses, it is reasonable to give the order of ten days in size as a representative time scale for the zonal motion of ultra-long wave disturbances with a long scale in meridional direction in the troposphere and the lower stratosphere. In this paper, we examine sets of equations applicable to this kind of disturbances by minimizing fundamental scales to be provided, that is, by providing each magnitude for space and time scales first. As a result, it is derived that the magnitude of meridional motion must be one order of magnitude less than that of zonal motion in the disturbances examined here. The first-approximate set of equations becomes a type of the quasi-geostrophic system in the troposphere and the barotropic equation in the stratosphere, and a type of linearized balance system is derived as the second-approximate one in the troposphere and the stratosphere.
The observation of the microphysical structure of shallow orographic cumuli was carried out from its initial stage to the precipitation stage. Cloud droplets larger than 100 pm in diameter were observed in a relatively short time, whenever the cloudy thermal was developed pulsationally in proto-cloud. The proto-cloud is a kind of cloud that has already appeared before a new cloudy thermal begins to develop. It has a relatively broad spectrum of low concentration. The analysis of the microstructure of cloud suggests that the cloudy thermal gradually reaches higher levels and carries up the larger droplets as well as numerous smaller droplets which were formed in the new rising thermal. The formation of the proto-cloud and the interaction between the proto-cloud and the new cloudy thermal seems an important mechanism for the formation of precipitation from a shallow orographic cumulus.
The dispersion data from an elevated source in a stable layer were obtained. Analyzing the vertical concentration profiles, the following results were obtained. When the air tracer was released in the stable layer over a flat terrain, the vertical spread of concentration cr, was almost constant without the variation of the height of the stable layer with the downwind distance. Though the horizontal spread of concentration σy increased slightly with the distance, the plume became the so-called "fanning" type. Whereas in the case of a rising stable layer by which the air Mass changed gradually from the lower layer with the downwind distance, the plume axis varied accompanying the rise of the stable layer base, and σz, increased in a normal way. Over the complex terrain with some undulations, the plume centerline height z followed topographical elevations. Especially, in the case of extremely stable conditions, z, was constant while z was affected by topographical undulations.