Papers in Meteorology and Geophysics
Online ISSN : 1880-6643
Print ISSN : 0031-126X
ISSN-L : 0031-126X
Volume 34 , Issue 3
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  • Masaaki Seino
    1983 Volume 34 Issue 3 Pages 105-141
    Published: 1983
    Released: March 09, 2007
    JOURNALS FREE ACCESS
       For the purpose of investigating the mechanism of the 1977-1978 eruption of Usu volcano, Hokkaido, the observational results of the earthquakes, deformations and eruptions are analyzed and discussed in connection with energetics and statistics.
       The seismic energy and some kinds of the eruption energies discharged during the eruption are approximately estimated. The total seismic energy, 9.6×1020 erg, is comparable to the kinetic energy of ejecta by major pumice eruptions. Daily discharge rates of seismic energy are found to decay exponentially with time separately for the two periods. The data on earthquakes and deformations indicate a proportional relation between seismic energy and upheavals at the summit crater, throughout the period of activity. This relation suggests that the earthquakes and upheavals result from the same source.
       In the eruption period of the latter stage of activity, the seismic activity is complementary to the eruptivity. This means that not only the earthquakes and deformations but also eruptions originate in the same energy source. On the assumption that the sum of the seismic and the deformation energy is quantitatively complementary to the mechanical energy of eruptions, the deformation energy is estimated at about nine times as much as the seismic energy. Moreover, on the basis of the relations among these energies, the exponential decay processes of discharge rates of seismic energy suggest that the magma does work on its surroundings through its volume increase without material and energy supplies from the depths, and the work is converted into the forms of seismic energy and deformation energy in periods without eruptions.
       As for the relations between earthquake magnitude and frequency, the magnitude (or log-amplitude) vs log-cumulative frequency curves show the upward convex type throughout the activity, and this indicates that the earthquake swarm has the upper bound of M4.3, which is far smaller than is expected from the general relation between magnitude and cumulative frequency of tectonic earthquakes. In the seismic activity since 1979 the magnitude vs log-frequency curves show the peculiar type with a peak of frequency, which is explained by the superposition of two different types of distribution belonging to the exponential type and peak type.
       Time intervals between successive earthquakes are analyzed, and it is found that earthquake occurrence is not random in time and even large earthquakes have a tendency to cluster within two days. In the period regarded as stationary in seismic activity, the events of earthquakes clustering within two days are defined, and time intervals between the two successive events are analyzed. The results suggest that the occurrence of the events with a seismic energy sum of 1.4×1018 erg or more has a periodicity with intervals of 9-12 days.
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  • Takashi Aoki
    1983 Volume 34 Issue 3 Pages 143-150
    Published: 1983
    Released: March 09, 2007
    JOURNALS FREE ACCESS
       In order to examine geographical and long-term variations in the frequency of typhoons, empirical orthogonal functions are calculated from a matrix of five-year running means of the annual frequency for 14 squares of 10° latitude-longitude covering the western North Pacific during the years from 1951 to 1980. The first three eigenvectors account for about 82% of the total variance, and this degree of accuracy is sufficient for the purpose of representing frequency patterns.
       The first eigenvector, explaining 45% of the total variance, indicates that frequencies in the South China Sea and those in regions to the southeast of Okinawa and around the Carolines are inversely proportional to each other. The second eigenvector shows the variations of frequencies in regions to the southeast of Japan and to the south of Okinawa. The third eigenvector depicts the variances in regions around the west of Carolines and the southern Philippines.
       To clarify the distinctive periods in the long-term variation of the geographical frequency of typhoons, a cluster analysis was made by using the Euclidean distance as a measure between two sets of the amplitude coefficients. According to the cluster analysis of the amplitude coefficients of the first three eigenvectors, there are three periods with the characteristic frequency pattern of typhoons. These are 1953-1959, 1963-1968, and 1970-1973.
       The frequency of typhoons in the South China Sea and in regions to the southeast of Japan were lowest in 1953-1959. The middle of the 1960s (1963-1968) has higher frequencies except in lower latitudes. The frequency in the South China Sea was highest and those in regions to the southeast of Okinawa and around the Carolines were lowest in 1970-1973.
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  • Tomoyuki Ito
    1983 Volume 34 Issue 3 Pages 151-219
    Published: 1983
    Released: March 09, 2007
    JOURNALS FREE ACCESS
       The global background air pollution has been suspected to play a part in climatic change. In order to obtain a better understanding of global air pollution, especially for aerosol pollution, extensive year-round observation of atmospheric aerosols was carried out in 1978 at Syowa Station (69°00'S, 39°35'E), Antarctica.
       Among aerosol particles of wide size range, submicron particles are of most importance in meteorology because of the essential role they play in cloud formation and radiation processes in the atmosphere. The items of the observation were selected so as to obtain many-sided information about submicron aerosols.
       Main items selected were the concentration and size distribution of Aitken particles (0.002≤radius≤0.1 μm) and Mie particles (0.18≤radius≤1 μm), the volatility of Aitken particles, and the morphology of particles (0.02≤radius≤1 μm) observed by electron microscope.
       For the measurement of Aitken particles was used the Pollak counter which had been improved so as to make possible the year-round measurement of concentration lower than a few hundred cm-3 within the probable error of ±3%.
       From the results of these observations, in conjunction with the results which had been obtained at South Pole Station and Syowa Station by other researchers, the properties of Antarctic submicron aerosols were examined systematically, on which only a few crumbs of information had been obtained so far.
       Main results of analysis are as follows:
       (1) The seasonal and latitudinal variation of concentration of Aitken particles are closely correlated to variation in the influx of solar photons.
       (2) Aitken particles which disappear under furnace condition up to 500°C exist in large fractions in summer but small in winter. Sulfate or organic aerosols as commonly seen in the atmosphere have such volatile properties.
       (3) From April to October, the seasonal variation of Mie particle concentrations closely correlated to the seasonal variation of the influx of the northern maritime air mass, and the seasonal variation of the size distribution of Mie particles is closely correlated to the seasonal variation of the distance which the maritime air mass traverses over sea ice regions from the open sea. From November through December and February through March, when there is a plentiful supply of solar photons, the seasonal variations of the concentration and size distribution give the evidence of photochemical supplement of Mie particles in the Antarctic atmosphere.
       (4) Particles which can be identified as sulfuric acid droplets by their morphology observed under the electron microscope appear in summer through autumn, but disappear from winter through spring.
       (5) The size distribution of submicron aerosols show a bimodal shape which has a trough at 10-6 cm in radius throughout the observation period from August to December. On the basis of this fact, it can be inferred that new particles are produced at an average rate of 10-4 cm-3s-1 at least in the sunlit period in the Antarctic troposphere.
       The present knowledge of Antarctic aerosols thus obtained can be summarized as follows:
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