The large-scale aspects of the Baiu Front, heavy rainfall and associated phenomena are analyzed over the Far East during the 40day period from June 16 to July 25,1968, mainly by using 5-day mean fields of various meteorological elements. The Baiu Front over the Far East forms a belt-shaped zone of maximum cloudiness, which lies east and west along the northern boundary of the monsoon or tropical airmass. This cloud zone coincides well with the zone of maximum rainfall amount. Heavy rainfalls there indicate successive convective activities. Owing to the convective transport of moisture, sensible heat and release of latent heat, a midtropospheric warm belt and a deep moist layer are formed within the Baiu Front. The most notable feature of the mean Baiu Front is the appearance of the core of the super-geostrophic strong wind in the lower troposphere during the heavy rainfall periods. It is suggested that the low-level jet is intensified by the vertical mixing of horizontal momentum due to active convections there. Medium-scale disturbances develo p successively in the Baiu frontal zone which provides favorable conditions for their generation as inferred from the small Richardson Number. The results of water-vapor budget in the vicinity of the Baiu Front reveal that a large amount of water-vapor convergence within the frontal zone is mainly by northeastward flow along the northwestern rim of the Northern Pacific Subtropical anticyclone. It is also concluded that the evaporation from the western Pacific is one of the important vapor sources which maintain intense rainfall within the Baiu Front.
In order to investigate the characteristics of rainwater in the forest district regarded as a cause of landslides, the author made experimental observation of rainfall in the valley Habiro-sawa, which is located in Yamanashi Prefecture. This valley, with an area of about 1.2 km2, is formed by the upper waters of the river Tama-gawa (Fig.1), and covered with various wooded regions. The species and the age of the trees are uniform in those regions. Eight regions are selected, where an experimental field is established. The characteristics of the wooded regions within which the experimental field is set are shown in Table.1. The raingauges for the measurement of rainfall under the plant cover are put on the surface in the field. Equipments are set for the measurement of the stem flow, which is estimated by means of a large vessel (Fig.2). A special distance recorder for measurement of the stem flow is used in order to record its time variation. The precipitation network, which consists of self-recording raingauges, is established in the open field, where the raindrops from the canopy of trees do not interfere with the raingauge receiver. The position of the instruments for observation of rainwater in Habiro-sawa is shown in Fig.3.
A model has been developed for the prediction of ocean wind waves. The method is based on the energy balance equation, and contains five energy transfer processes. These are the linear and exponential wave growths with time, wave breaking, frictional dissipation and the effect of opposing winds. Computational devices designed for wave propagation give reasonable values for dispersion and angular spreading of the waves. Two hindcasts were perform e d on the Atlantic Ocean and the Japan Sea. The estimated significant wave height and one-dimensional wave spectrum are in reasonable agreement with the observations.
We designed a polar nephelometer with a Xe lamp (500 watts)as light source, and performed the measurements of the scattering functions for the atmospheric aerosol particles near the ground. The scattering functions for the particles under various meteorological conditions were obtained during the period from October 1970 to March 1971. The shapes of the scattering functions obtained were classified into three groups and were compared with the theoretical curves calculated for the size distributions of particles represented by the modified gamma function. The shape of the scattering function measured largely depends on the wind velocity. Hourly measurements were performed on December 4 to 5,1970and March 8 to 9,1971 and the data obtained show that the shapes of the scattering functions and the scattering coefficients are both dependent on the wind velocity at the time of measurement.
The effects of the environmental wind and temperature fields on the measurement of net flux of radiation by conventional net radiometers are examined. The variation in output of the net radiometer due to the wind field exceeds ten percent for both FUNK'S net radiometer ("wind shield-type" net radiometer) and GIER and DUNKLE'S net radiometer ("ventilation-type" net radiometer) in the ranges of wind speeds, vertical temperature gradients and incident radiation fluxes concerned. And as for FUNK'S net radiometer the more accurate value of net flux of radiation is expected to be obtained in the windy condition rather than in the calm condition. The devices hitherto available f or calibrating net radiometers for longwave radiation are discussed in brief and our new device is presented.
The ocean is divided into three layers, i. e., surface (0-100 in), middle (100-1,100 m) and deep (1,100-4,000 m). The concentration of inorganic carbon and the specific activity of radio-carbon relative to that in the air are assumed to be as follows. Surface Middle Deep Concentration; 24 mg C/l 27 mg C/l 29.4 mg C/l Specific activity; 0.950.90 or 0.89 0.85 Taking into consideration the biological effect, the exc h ange of radio-carbon between air and sea, and isotopic fractionation of radiocarbon among different phases, the calculation was done with respect to the residence time of water in each layer and so forth. The results of calculation show that the specific activity of radio-carbon is determined by various transfer processes in the ocean, which gives the apparent age to deep water as high as 1,300 years, while the mean residence time of water in the layer below the surface is from about 200 to 350 years.
During 21th to 30th June 1971, a study on the characteristics of cloud condensation nuclei was carried out, by the continuous sampling of cloud water, and by measuring the water content and size distribution of the droplets in Cu type cloud at the summit of Mt. Ibuki. During the period, the summit was twice completely cov e red with cloud for several hours. In both cases, cloud droplets were small and numerous. As the result of the chemical analysis of cloud water and by considering the size distribution of cloud droplets and the prevailing southerly wind during the sampling, it is inferred that the airpolluting substances from the industrialized area of Nagoya and Yokkaichi are greatly responsible for the formation of those clouds. On the other hand, we analyzed the summer precipitation data for the pasth 40 years at Hikone Weather Station located at the foot of Mt. Ibuki. The data were classified into the prewar and the postwar daysthe prewar precipitation when the industries were not yet fully developed and the postwar period when industrialization was greatly promoted. As a result, it was found the precipitation after the war is 20-30 percent over that of the prewar period. It is considered that such a large in c rease of precipitation in the postwar period is due to the low clouds composed of dense small cloud droplets created by polluted nuclei.