Time variations of the hydrodynamical system were followed by numerical process using the non-divergent barotropic vorticity equation. It was found that, in a fluid system, the kinetic energy initially tends to flow into the component of larger scale, and the mean flow kinetic energy oscillates with respect to time with a definite period. The period of the oscillation of energy thus computed was compared with the analytic solution of a simple non-linear hydrodynamical system. The solution seems to explain some features of the fluid qualitatively. A numerical example of the system which has a close resemblance to the situation observed in the middle layer of the atmosphere was followed for 20-day period. It was found that the kinetic energy of the mean flow was supplied by the existing disturbance through the barotropic process.
Some problems relating to the extended-period forecasting of 500 mb heights by the correlational analysis are studied. In order to examine how the 10-day lag correlation field varies according to the various choices of data periods, an equation which governs the correlation field is derived from the vorticity equation. It is next shown that the simple linear regression method cannot seize the dynamical non-linear effect. And cor-relation coefficients between the terms of barotropic vorticity equation which was divided into the linear and non-linear parts, are examined.
The formation of typhoon Doris 1958 which appeared in the Marshall Islands area is described from the stage of an easterly wave under a large high-level anticyclonic cell to the stage of an incipient vortex. It is revealed that the initial easterly wave possessed a fairly large horizontal extension of strong wind region, together with a systematic vertical motion. The formation of a thick moist layer and the variation of thermal structure of the disturbance from of a cold- to of a warm-core type are clearly shown by the analysis. Quantitative discussions of the three-dimensional distributions of vorticity, horizontal divergence and vertical velocity are made. The mechanisms of increase of vorticity at low levels, and of maintenance of negative vorticity at high levels are also discussed. The analysis reveals that the warming of ascending air was the result of liberation of latent heat of condensation. This, coupled with the cooling of surrounding air due to evaporation, created a horizontal temperature gradient of the warm-core type. The importance of the baroclinity thus formed for typhoon development may be supported by th observed fact that rapid fall of the sea-level pressure took place after the completion of the warm-core structure. Based on the results of analysis, a model of typhoon formation is described, in which the whole process of the formation is divided into three stages. Some preliminary remarks on dynamical processes in these stages are also mentioned.
The Rayleigh approximation of small particles for microwave region cannot be satisfied to all raindrops. The approximated value of radar reflectivity factor Z (when πD/λ«1) was compared with the theoretical value (calculated from the Lowan's table and dropsize distributions). The attenuation constants for various kinds of rain are also listed from the same table. The antenna effective area for meteorological target is somewhat less than the effective area for point target. The effective antenna receiving area for the usual meteorological radar is about 0.4 times the actual aperture. Areal rainfall measured by radar rainfall contours is compared to raingauge observations, about 23 gauges in a section of 638 km2. The accuracy of the radar rainfall thus obtained is about ±5.7% when integrated for a period of more than an hour and it corresponds to the raingauge network of about one gauge per 80km2.
n order to represent the forest cover effect on the snow-melt quantitatively and to make it a basis of snow-melt estimation for the whole basin, two experiments were tried in the forest in Okutone region (the headwaters of the Tone River), one to determine the beech-forest cover density by balloon measurements from the sky and the other to compare the amounts of snow-melt and several meteorological factors between inside and outside the forest. The result suggests that our theoretical estimation of the amount of snowmelt in the forest is successful.