A zonal index on the 1Omb level is defined to describe the time change of the lowlatitude easterly jet stream in the mid-stratosphere. The index shows a remarkable sudden increase on some day in June. This increase of the zonal index occurs simultaneously in the stratosphere. Further, by examining a relationship between this singular phenomenon and the seasonal transition of the Ogasawara anticyclone in the troposphere, it is found that the increase of the 1Omb zonal index occurs about a month prior to the rapid progress of the northern boundary of the Ogasawara anticyclone to 35°N. Then the perfect summer type circulation pattern prevails over Japan.
The authors after a brief review of the winds in tropics, discussed the general circulation over the Asian monsoon region in northern summer. Attention is particularly drawn to the fact that most of the monsoon air comes from the southern hemisphere. This air after ascending into the upper troposphere in the northern tropics, forms the easterly winds and swings back across the equator finally to subside in the southern subtropical ridge. It is specially stressed that if any air subsides north of the equator itself as proposed by Koteswaram, its amount would be very small compared to the total monsoon air. A schematic diagram of the three dimensional flow system in the monsoon area is presented. The period of circulation in the proposed closed cell is evaluated which is found to be approximately equal to the period of the monsoon over India.
The concentrations of chloride in rain water were compared with the height of radar echo top, the height of cloud base and the thickness of the cloud. The characteristics of the relation between them fell into three different groups. It seems likely that this difference was originated from the difference in the rate of entrainment of the air containing giant sea salt nuclei into the cloud.
On the basis of the isotopic analysis of deuterium content in snow crystals and graupel pellets which fell on the coast of Japan facing the Japan Sea, following results were obtained. (a) The D/H ratios of snow were large (mean value 150±2ppm) when the snow flakes consisted of non-rimed crystals having the same shape of crystal habit. (b) The D/H ratios were small (mean value 146±3ppm) when the precipitation consisted of graupel pellets, rimed crystals or a mixture of two different shapes of snow crystals. (c) It is likely that the difference between (a) and (b) was due to the difference in the vertical development of the precipitating clouds. (d) Temperatures of the sea surface from which water of snowfall had evaporated were estimated from the D/H ratio of snow samples. As the horizontal water temperature gradient in the Japan Sea was very steep, the geographic location of thisvapour source could be specified.
At air temperatures around -40°C in the Fairbanks, Alaska, area, dense ice fog is formed by freezing of water droplets condensed from water vapor in flue gases derived from the chimneys of power and heating plants, and the exhausts of automobiles. Ice fog crystals, ice crystals and supercooled fog droplets which formed at temperatures around -40°C, -25°C and -10°C respectively were collected in this area on electron microscope grids covered with collodion film. After sublimation or evaporation, the residues of these specimens were examined with an electron microscope. A solid particle of 0.1μ to 3μ t diameter was observed in the center of the residue of each ice-fog crystal, ice crystal and supercooled droplet. By comparing them under the electron microscope with combustion products from coal, fuel oil and gasoline, the main nucleus substances were identified as organic and inorganic particles, and hygroscopic particles formed by combustion of coal, fuel oil and gasoline. As there is no difference in composition between ice fog nuclei and supercooled fog nuclei in the Fairbanks area, it is concluded that the substances work first as condensation nuclei, then as freezing nuclei when cooled to about -25°C or below. All stages in the process from water droplet formation to ice fog formation with falling temperatures were observed directly during the collection of these specimens. Ice fog crystals formed at around -40°C were mainly spherical ice crystals of 2μ to 15μ diameter, the remainder being hexagonal and columnar crystals of 10μ to 30μ diameter. Ice sintering caused by collision of ice-fog crystals was found even at a temperature of -40°C.