The influence of the time lag in the activation of ice nuclei on the number of ice crystals in cloud was numerically studied. Following conclusions were obtained from computation ; (1) the increase in the number of activated atmospheric ice nuclei with cooling-time is remarkable, particularly under the cooling at lower temperature than -25°C. The total number of atmospheric ice nuclei activated for a few hours under the cooling at -30°C to -40°C becomes 10 times as large as that for 1 minutes, while the number of activated atmospheric ice nuclei in the case of the cooling at the temperature warmer than -20°C is at most 3 times as large even after 10 hours as that for 1 minute, (2) The number of atmospheric ice nuclei activated in the upward air-current with vertical velocity of the order of 10cm/s is 5 to 10 times as large as that in the air-current of the order of 10m/s, if the numbers in both cases are compared at the same level.
The rainfall subdivisions in India have been grouped into homogeneous areas depending on the rainfall inter-correlations among the subdivisions. Noteworthy complementary variation of monsoon rainfall between West Central India and Northeast India has been observed. The role of the upper tropospheric Tibetan anticyclone in the monsoon rainfall variations has been stressed and explained.
The transformation process of a wave disturbance in the Caribbean Sea region into Hurricane Alma (1962) is studied in detail based on conventional surface and upper-air data, TIROS V pictures and some research flight observations. The disturbance was cold-cored in the lower troposphere at the beginning. The vertical motion was thus negatively correlated with virtual temperature in the lower troposphere. Through an interaction between the disturbance and a pronounced upper-level shear line situated to the west, a secondary warm low was initiated at lower levels near the surface. The initial phase of upper-tropospheric warming over the low was related to the downward motion east of the upper shear line. When the secondary low developed, the cold-core wave disturbance disappeared. The precipitation area which was initially located to the east of the disturbance approached the center of the secondary low-level cyclone. The development of the low-level cyclone with a gradual warming in the upper troposphere over the rain area led to the formation of a warm-core storm with a pronounced outflow in upper levels, The change of cloud features with the development is also described.
n cloud physics, it is very important to study the phase change in clouds from supercooled droplets to ice crystals and to observe whether or not the snow crystals coexist with supercooled droplets. The author made the observation of ice crystals in a supercooled fog at Asahigawa from January through March 1967. When ice crystals coexisted with supercooled fog, ice crystals of dendritic type, side plane type and irregular type were observed, the mean size of which was about 100μ. When the supercooled fog disappeared, small ice crystals such as prism and plate were observed. They were of about 20μ and many of them were twinlike crystals. From the results of the present observations, it was found that the snow crystals of spatial dendrite type, side plane and irregular types were formed by the adhesion of supercooled droplets to a snow crystal and that ice crystals of twin shape were formed not by the collision of two ice particles but by the sublimation on one embryo.
Measurements were made of sulfate and other inorganic materials in fog and cloud water in 1963. It was found that in cumulus clouds above Mt. Norikura, sulfate was in the form of ammonium sulfate and sulfuric acid. In upslope fog at Shiobara, and in stratus cloud which covered Mt. Tsukuba, sulfate was supposed to be combined with some metals in addition to ammonium ions, During the periods of September 1962 to February 1963, and of July to December 1966, separate samplings of large and giant particles were made in Tokyo by means of a high volume cascade impactor. It was found that the weight ratio of SO4--/SO2 was above 0.12 at relative humidity above 55%, wind velocity below 4m/sec and visibility below 5km, It seems that atmospheric humidity is an important factor for the atmospheric oxidation of SO2. The relationship of the amounts of sulfate and ammonium was also studied. Thesestudies indicate that various weather and environmental conditions affect the atmospheric oxidation of SO2. The atmospheric concentration of hydrogen ion contained in aerosol was usually below 3×10-2μg/m3 except on October 26, 1966, when the atmospheric concentration of hydrogen in large particles was 1.7 to 7.5μg/m3 in heavy smog.
The basic properties of snow crystals of the single bullet type and a combination of bullets were studied. The length of c-axis, the axial ratio and number of bullets which form a combination of bullets, using approximately one thousand and four hundred snow crystals of bullet type observed in the Ishikari Plain in Hokkaido were studied. The results were as follows ; the mean length of c-axis of the single bullets 0.59mm, the standard deviation 0.16, the skewness 0.05 and the kurtosis 1.67, and the mean axial ratio (c/a) of the single bullets is 3.2. Each value of two, three and four-combined bullets were nearly the same as the single bullets. It was assumed that the single bullets were produced by the disintegration of the combination of the bullets during their descent. In relation to the origin of the combination of bullets, it was surmised that the combination of bullets grew from either dust particles with many corners which were introduced by Stiive, of from frozen droplets with many spicules which produced when supercooled droplets froze suddenly.
Radar data collected by a network of ships, shore stations and aircraft over the Eastern Pacific from mid-February to the end of June 1965, have been studied. Analyses of these radar data and concurrent TIROS IX photographs were made. The data sample included deep cyclones with extensive radar detected precipitation, weaker cyclones with localized rainfall, cold anticyclones with extensive air mass showers, and blocking anticyclones with no precipitation. In the latter case it has been found that the appearance of the cloud cover is a good indicator of areas of anomalous radio propagation. Models have been prepared that illustrate the varying patterned association of cloud and rainfall characteristic of such synoptic situations. Such associations range from comparable cloud-precipitation areas through scattered showers where only a portion of the clouds contain precipitation, to complete absence of precipitation within large areas of low stratiform clouds or fog as in a blocking anticyclone.