Subhumid climates form the intermediate category between the dry and wet types on either side in the so-called “specturum of world climates”. Water balances in these zones fluctuate so markedly from year to year that even in normally moderate climates, extreme conditions of aridity on account of severe water shortages and humidity due to enormous water surpluses are not at all uncommon in them. The average annual rainfall in these regions is just below or above their water need with the result that even a slight departure of the yearly rainfall from normal is very significant in affecting the agricultural production of the region considerably. Hence, an intensive study of droughts and aridity in the subhumid climates, particularly of the dry subhumid category, is very essential. Frequency and intensity of droughts of various categories in the dry subhumid zones of South India are critically examined in this paper. The region is initially delineated employing the Thornthwaite scheme of climatic classification (1948) and the modified water balance procedure (1955). Four representative stations from the different sectors are selected, after studying the water balances of a number of stations in the entire region. “Aridity Index”, (the ratio of annual water deficiency to annual water need, expressed as a percentage) is taken as the basic parameter for the present study. Departures of aridity index from the median are calculated and using the scheme proposed by Subrahmanyam and Subramaniam (1964) droughts are categorised. At each of the four stations, the occurrence of drought is studied, both from the point of view of frequency as well as its intensity. The decennial frequency of droughts, climatic shifts and water balances of some stations for a few extreme years are also examined.
By spectral analyses of upper winds and temperature at Canton Island (S 02°46', W 171°43') from July 1957 to June 1960, two types of disturbances were shown to occur remarkably in the equatorial lower stratosphere: One is considered to be Kelvin waves and the other is to be mixed Rossby-gravity waves. Occurrence of the two types of disturbances have close relations with the quasi-biennial oscillation. Kelvin waves appear predominantly when the basic westerly momentum is rapidly increasing, while mixed Rossby-gravity waves appear when the absolute value of the basic wind speed is decreasing. Both types of disturbances were shown to carry westerly momentum upward. The upward flux of westerly momentum due to mixed Rossby-gravity waves is of the same amount as that due to Kelvin waves.
Remarkable mesoscale disturbances are observed in association with the heavy rainfalls which took place along the western part of the Japan Islands on July 9, 1967. The wave length of 100-200km, the amount of divergence of the order of 10-4 sec-1 and other features are very much similar to those which characterize disturbances in case of heavy snowfall. The large amount of precipitation seems to be fed from immediate neighbourhood of predominant divergence. The rainfall area and intensity of individual cells show a phenomenon of pulsation with a period of about 3 hours, which is reflected upon the short period fluctuation of large scale precipitation. Quantitative discussion is made on the surface wind divergence and vorticity field.
Detailed analyses are made on rain-gauge observations over the western Japan for July 9, 1967 when severe rainfall damages were recorded. It is found that there are two categories of mesoscale rainfall cells, one of which is moving system and the other stationary system. Both systems show a pulsation phenomenon, and as a result the total amount of rainfall over a synoptic scale area fluctuates with rather short period of about 3-4hrs. Basing on 7 moving systems and 18 stationary systems, some statistical properties of mesoscale rainfall cells are investigated as to the life time, areal precipitation, rainfall intensity and so on.
The turbulent effect upon the mechanism of large cloud droplet formation in a warm cloud is discussed. Firstly, the basic data in field works, simultaneous observations of cloud physical elements in a stratiform cloud at a mountainside and observations of the spatial concentration fluctuation of cloud droplets were analysed as regards simulation study and thereby it was suggested that the turbulence arising from the instability of atmospheric layer would exert the influence to the large droplet formation. Secondly, basing upon the above data, the Monte Carlo method was applied to the simulation study for the cases in which cloud droplets distributed spatially at random and in which they distributed spatially in heterogeneous concentration as caused by turbulence, in aiming to obtain the information about the difference in growth of large droplets between the two cases. In the latter case, it was noticed that a few large droplets grew more rapidly than in the former case.
The equation of wind shear proposed by Yamamoto and Shimanuki which is a modified form of so-called KEYPS equation is solved approximately. The approximate formulae of wind shear are rational expressions of|ζ| 1/2 and |ζ|1/3, whereζis defined by the ratio of height and stability length. Relative errors involved in the approximate formulae of wind shear, wind velocity and eddy diffusivity do not exceed 0.4 percent under unstable conditions and 0.6 percent under stable conditions. Function subprograms used for computing velocity and diffusivity by electronic computer are written by FORTRAN language.
A case study of the rainfall associated with Typhoon Vera (the Ise Bay Typhoon) in 1959 is made. From an inspection of hourly precipitation charts, one gets an imprestion that the rainfall amount with the typhoon is solely dependent upon the orographic elect. However, the analysis of time changes of rainfall intensity reveals the existence of well-organized zones of alternating heavy and weak rainfall intensity surrounding the storm center. The surface pressure field also contains similar banded structure. A comparison with the radar pictures shows the correspondence of these zones to groups of radar rain bands.
The horizontal distribution of sea surface temperature was surveyed with a radiation thermometer on the survey ship “Ryofu Maru” in the sea area covering 31°N-31°40'N and 126°40'E-130°E to the west of Kyushu. The surface temperature gradients in the east-west direction at the fronts of the Tsushima Warm Current and scales of water masses as revealed by the continuous records are discussed. A comparison between the skin temperature at the sea surface measured by the radiation thermometer and the temperature of the upper mixed layer of the sea measured by a resistance thermometer indicates that there is no significant difference between them. A preliminary surface temperature measurement with an airborne radiation thermometer was made before the cruise of the “Ryofu Maru.” The decrease of the indicated surface temperature with altitude due to the imperfect transparency of the atmosphere was found to be 2.0° C/km. As to the data obtained at the lower flight level (600m), agreement with the sea surface temperature measured on ships is found to be satisfactory.
This paper describes a direct solution of Poisson's equation where boundary values are prescribed on the perimeter of the rectangular domain. When the number of mesh points along a side of the rectangular domain is a power of 2, the Fast Fourier Transform Method proposed by Cooley and Tukey (1965) is applicable. The number of arithmetic operations required on a N × N mesh is 10 N2 log2 N. This is comparable with that required by Cooley's method (1966) with the Complex Fourier Series, and compares favorably with the best iterative method which would require 40 N2 (log N)2 operations.