Papers in Meteorology and Geophysics
Online ISSN : 1880-6643
Print ISSN : 0031-126X
ISSN-L : 0031-126X
Volume 34 , Issue 4
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  • Masanori Yamasaki
    1983 Volume 34 Issue 4 Pages 221-260
    Published: 1983
    Released: March 09, 2007
       As a continuation of previous studies (Yamasaki, 1977a, b) numerical experiments of axially symmetric tropical cyclones are performed. As in the previous studies, a fine resolution model is used in which convective clouds are not parameterized but explicitly resolved. A recent advance in the computer has enabled us to deal with the tropical cyclone with realistic horizontal scale even when a sufficiently small grid size is used. Although assumption of axial symmetry restricts very realistic simulation of real tropical cyclones, it seems that the numerical experiments have revealed many important aspects of the formation and intensification processes and the structures of the tropical cyclone and their mechanisms.
       At the early stage before the tangential velocity attains about 10 ms-1, the area of convective activity and the vortex size expand with time because convection at the outermost part of the convective area propagates outward. Individual convective clouds are usually organized as a convective system with a time scale of about 3 hours, which is referred to as ‘mesoscale convection’ in this paper. As one mesoscale convection weakens, another forms at some distance. As a result of successive formation, convective activity and rainfall propagate outward or inward and persist for a long period of time. A large-scale (cyclone-scale) meridional circulation is intensified by an ensemble of several mesoscale convections, whereas the continuous formation of mesoscale convection is maintained by the large-scale circulation. The mechanism of such cooperative interaction between moist convection and large-scale motion at this stage, however, is different from that of the original CISK found by Ooyama (1964) and Charney and Eliassen (1964). That is, surface friction does not play any significant role, but instead, the downdraft and cooling due to evaporation of rainwater play an essential role. Such a new type of CISK was also discussed in Yamasaki (1975, 1979).
       When the rotational winds are intensified, surface friction becomes important. That is, the radial positions of the outermost convection and of maximum tangential velocity begin to shift inward by frictional inflow. Such an inward shift occurs when the tangential velocity attains 10-15 ms-1. Even at this stage it appears that cooling due to evaporation of rainwater and downdraft have significant effects on the large-scale dynamics.
       When the tangential velocity near the vortex center exceeds about 20 ms-1, an eye and eyewall are formed. Then rapid fall of the central surface pressure as well as rapid intensification of the tangential winds takes place. Surface friction plays an essential role in the formation and maintenance of the eye and eyewall. Several small-scale features, which have not been studied with coarse grid models with parameterized convection, are found in the eye and eyewall, including time variation with a period of about 10 minutes.
       It is suggested that the long-lasting convections obtained in this study may correspond to observed spiral rainbands, which have been interpreted by many authors as internal gravity waves modified by convective heating. The structure and the phase velocity of the long-lasting convections are different from those of internal gravity waves.
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  • Yako Suzuki, Nobuhiko Murayama, Tokiyoshi Toya
    1983 Volume 34 Issue 4 Pages 261-265
    Published: 1983
    Released: March 09, 2007
       The sensible and latent heat fluxes are estimated with the data of the aboard-ship observation on the Inland Sea in summer by the graphical technique of the bulk aerodynamic method based on Kondo's (1975) proposals except for the adoption of Charnock's law on the sea surface roughness. The estimated sensible and latent heat fluxes are large in the early morning and very small in the afternoon. The flux values derived here are checked with the foregoing studies.
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  • Yukio Sugimura, Yoshimi Suzuki
    1983 Volume 34 Issue 4 Pages 267-289
    Published: 1983
    Released: March 09, 2007
       Amino acids dissolved in sea water either in free or combined forms were determined in the wide area of the western North Pacific by means of a fluorometric method of o-phthalaldehyde-amino acids adduct. The concentration of the total amino acids ranged from 44 to 213 μg l-1 and it is found that the concentration in water to the north of the Kuroshio front shows a slightly lower value than that of the south side. The ratio of free to the total amino acids is less than 0.2. In general, the concentration of amino acids was high in the surface and decreased to a nearly constant value in the intermediate and deep water. The molecular size distribution of amino acids revealed that about 60% of amino acids is involved in organic matters with molecular weight ranging from 1.5×103 to 5×104. About 10% of amino acids is involved in organic matters with molecular weight of 15×104. The composition of amino acids indicates that a major group of amino acids is involved in neutral aliphatic amino acids. Among the total amino acids, 40 to 80% is adsorbed on XAD-2 resin and a major fraction is involved in organic matters with molecular weight ranging from 5×103 to 2×104, in which most of the metal organic compounds are included. The composition of individual amino acids adsorbed on the XAD-2 resin is a little different from that of original sea water.
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  • Katsumi Hirose, Yukio Sugimura
    1983 Volume 34 Issue 4 Pages 291-306
    Published: 1983
    Released: March 09, 2007
       The relationship between metallic elements and organic matter in marine environments is examined. Under the thermodynamical equilibrium model, it was assumed that the average values of the activity for some metallic elements in marine organisms were equal to those in sea water. It was also assumed that the chemical equilibria were established in each phase of sea water and marine organisms. According to this model, the concentration of metal organic compounds in sea water is linearly related to the total concentration of metals in marine organisms: it can be expressed by the equation CbM=(CbL/CL)Corg.M. It is obtained from this relationship that the logarithmic concentration factor for some metallic elements in phytoplankton was linearly related to the logarithmic ratio of the concentration of the metal organic compounds to the total concentration of the metallic elements dissolved in sea water. The maximum values of the concentration factor of metals in phytoplankton of about 105 could be anticipated from the present theoretical treatment.
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  • Yosihiro Sawada
    1983 Volume 34 Issue 4 Pages 307-324
    Published: 1983
    Released: March 09, 2007
       Geostationary Meteorological Satellite (GMS)-1 routinely returns 14 images a day at intervals of 30 minutes-4 hours with ground resolution of 1.25 km by visible sensor and of 5.0 km by infrared detector sub satellite point (Table 1 and Fig. 1). Images of eruption clouds from Alaid Volcano, the Kurile Islands (Fig. 2), and from Pagan Volcano, the Mariana Islands (Fig. 5), both of which erupted in April—May, 1981, are well detected by GMS observations (Plates 1-1, 2 and 2). Eruption clouds from Alaid continued for more than 4 days changing the moving directions by prevailing winds in the upper atmosphere in the latter part of April and intermittently continued through the end of May. Its eruption cloud is detected at a distance of more than 3,000 km SE of this volcano (Figs. 3 and 4). In case of Pagan, we can see an almost circular eruption cloud just after an occurrence of eruption and through the decay of the eruptive activity (Fig. 6), and active eruption clouds are detected for more than 10 hours.
       By assuming that the surface temperature of eruption cloud that reached a very high altitude is cooled to the surrounding air temperature, the maximum altitudes of eruption clouds are estimated by isotherms in eruption clouds derived from GMS TBB values (Figs. 7 and 10) and also by using materials of radio sounding observations near these volcanoes (Figs. 8 and 11). The estimated maximum altitudes of eruption clouds at Alaid and Pagan are 11.7 km at 06 Z on April 30 and 16.5 km at 03 Z on May 15, respectively. According to radio sounding observations, it is considered that some of the eruption clouds from Alaid slightly penetrated the tropopause during the activity of April 27-30, but not in case of Pagan. Judging from scanning time around Pagan Volcano in the first image of the eruption cloud (Fig. 12), the eruption at Pagan is considered to have commenced its activity at around 2309 Z on May 14.
       With time variations of the maximum altitudes and the maximum horizontal distances of eruption clouds from volcanoes, it is possible to see the time sequences of intensities of eruptive activities (Figs. 9 and 13). Estimated moving velocities of eruption clouds are 19-32 m/s at Alaid and 14-15 m/s at Pagan and both values are faster by 4-6 m/s than the surrounding wind speed at respective altitudes. Horizontal eddy diffusivity of eruption clouds by the method of Gifford (1959) shows large values of 109-1010 cm2/s for both volcanoes.
       The method of Briggs (1969) is applied to estimating the thermal energy release of eruption cloud and the estimated values during the most active stages at both volcanoes are 1017 erg/s for Alaid and 1018 erg/s for Pagan. By using duration times of eruptive activities, the estimated total thermal energy releases by eruption clouds are 7×1022 erg at Alaid Volcano and 4×1022 erg at Pagan Volcano.
       The eruption clouds spread over lower atmospheric clouds are clearly detected at Alaid, because the Alaid eruption clouds showed very low ALBEDO values, possibly owing to high concentration of ejected materials in clouds. However, there is no clear differences between eruption and atmospheric clouds in case of Pagan (Fig. 14).
       It is considered that the detectability of eruption clouds by GMS images is severely hampered by existence of atmospheric clouds around erupting volcanoes. However, it will be possible to detect eruption clouds higher than several km and larger than about 20 km across under good conditions.
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