Papers in Meteorology and Geophysics
Online ISSN : 1880-6643
Print ISSN : 0031-126X
ISSN-L : 0031-126X
Volume 33 , Issue 4
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  • Jiro Aoyagi
    1983 Volume 33 Issue 4 Pages 187-243
    Published: 1983
    Released: March 09, 2007
    JOURNALS FREE ACCESS
       This paper describes a noncoherent MTI weather radar which makes it possible to reject ground clutter signals but to extract precipitation echo signals. Though the amplitudes of the ground clutter signal fluctuate somewhat due to radar system instabilities, antenna scanning and radar wave propagation effects, the frequency spectra are confined to a relatively narrow low region. Therefore, MTI signal processing is based on the fact that most of the energy of the clutter signal can be rejected by an MTI canceler which corresponds to a high pass filter. In this study, it was found that a no-feedback triple delay-line canceler is the most suitable for the standard weather radar of the Japan Meteorological Agency and that the attainable cancellation ratio is 35 dB, because the uniform noise cannot be rejected by the MTI canceler. Then the MTI residues which cannot be rejected by the canceler will be completely removed by introducing two additional techniques. The first one is an areal integration which makes it possible to decrease some of the MTI signal intensity levels below the threshold level, and if this is not enough, the second one will be used to reject compulsorily the residues of the clutter beyond the specified value of cancellation ratios.
       Meanwhile, since the frequency spectra of the precipitation echo signal are rather uniformly distributed in half of the pulse recurrence frequency which corresponds to the signal processing frequency band, part of the energy of the signal can be extracted through the canceler. Therefore, by considering the deviation from Rayleigh distribution of the signal in amplitude and the randomness of the amplitude fluctuation, it was found that the MTI signal processing can be used quantitatively for radar rainfall measurements referring to the normal signal processing in the noncoherent radar.
       This paper further discusses the rejection of sea clutter. It is found that the proposed MTI signal processing system will make it possible to rapidly obtain objective radar data, as compared with the manual data handling of ground clutter rejection which has been conventional so far. And it will contribute to the development of a system of short-period rainfall prediction based on the radar data transmitted from each radar site in the country to the large-sized computer in JMA.
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  • Michio Takahashi, Ichiro Isozaki, Hiroshi Ishizaki
    1983 Volume 33 Issue 4 Pages 245-255
    Published: 1983
    Released: March 09, 2007
    JOURNALS FREE ACCESS
       Thermal response of the telemetry bottom pressure sensor 100 km off the south coast of the Tokai District, central Honshu, is analyzed. It is shown, through the analysis, that there appear comparatively large (approximately 0.1°C) short-period bottom temperature changes at the rate of once per several months even just above the seabed 2200 m deep. At these times, the tidal residuals of bottom pressure have a tendency to show characteristic short-term changes of durations of ten days or more and amplitude less than 10 cmH2O. It is possibly due to mesoscale ocean eddies. The bottom variations of this temperature and pressure are compared with the oceanographic conditions, especially with the route of the Kuroshio, and some qualitative correlation is observed among them. Thus, it could be concluded that the bottom pressure records are applicable as an indicator for oceanographic variations off the Tokai District.
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  • Hiroshi Ishizaki, Osamu Asaoka, Shunji Konaga, Michio Takahashi
    1983 Volume 33 Issue 4 Pages 257-268
    Published: 1983
    Released: March 09, 2007
    JOURNALS FREE ACCESS
       A direct measurement of the near-bottom current was made by a mooring system at (33°46.0'N, 137°37.3'E) off Omaezaki on the continental slope from December 21, 1980 to May 2, 1981. The observation level was 2200 m in depth and the bottom depth was 2300 m. The location is about 3 km east of the place where a deep sea pressure gage was installed by the Meteorological Research Institute (M. R. I.). The data obtained by the pressure gage are also analyzed.
       The current observed was generally west-southwestward along the isobaths of the continental slope in an opposite direction to the surface Kuroshio flow. For three times during the observed period, it turned its direction to the east-southeast with a down-slope component, lasting for 10 to 15 days. Temperature and pressure also varied, although not always, seemingly with the velocity changes. The time series of half-monthly averaged horizontal temperature distribution at 200 m depth (published by the Hydrographic Office, the Maritime Safety Agency of Japan) shows that the surface Kuroshio was generally flowing south of the observational point and also suggests that its axis possibly approached to or crossed the observation point northward with occurrences of small-scale meander of the axis which happened in the above three periods. It is suggested that there might be a dynamical link between the surface Kuroshio and the near-bottom flow far beneath the thermocline depth.
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  • Yukio Sugimura, Yoshimi Suzuki
    1983 Volume 33 Issue 4 Pages 269-275
    Published: 1983
    Released: March 09, 2007
    JOURNALS FREE ACCESS
       A new method of fluorometric microdetermination of free and total amino acids in sea water is presented by using o-phthalaldehyde (OPTA)-amino acids fluorogenic adduct adsorbed on XAD-2 resin. Free amino acids react to OPTA without any treatment prior to the analysis, and the total amino acids react to the reagent after the acid hydrolysis. Subsequently the reaction adduct was separated from the solution by the adsorption on XAD-2 resin. The fluorogenic product was eluted from the resin with methyl alcohol followed by fluorometric determination of λex=360 nm and λfl=455 nm. The recovery by this method is 93.3% for free amino acids and 90.4% for total amino acids with a standard deviation of less than 2%. The method has advantages over the ninhydrin and fluorescamine method because of high sensitivity and room-temperature reaction.
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  • Yukio Katsuragi
    1983 Volume 33 Issue 4 Pages 277-305
    Published: 1983
    Released: March 09, 2007
    JOURNALS FREE ACCESS
       The monthly fallout of 90Sr at 12 stations from 24°N to 45°N in Japan is given for the period from January 1973 to April, 1981. The cumulative amount of 90Sr fallout is highest in Akita and lowest in Osaka. The cumulative amount of 90Sr in Tokyo from the beginning of nuclear testing to April, 1981 is estimated to be about 78 mCi/km2. After the cessation of the atmospheric tests by US and USSR in 1963, the 90Sr fallout in Japan decreased steadily, but because of the new addition of radioactive debris from the Chinese nuclear tests, the trend of decrease is considerably disturbed in recent years. The isotopic ratio of 89Sr to 90Sr in radioactive debris from each of the Chinese tests varied with time in a similar manner. The ratio increased abruptly several months after of each test and decreased after the inclination of e-(λ8990)t in the case of thermonuclear explosions. On the basis of change of 89Sr/90Sr ratio in the monthly fallout, the residence time of nuclear debris in the atmosphere is estimated to be 30 to 50 days in the troposphere and 1.0 to 1.2 years in the stratosphere. The general trend of 90Sr fallout in Japan essentially depends on the altitude and the time of year of the injection of radioactive debris into the atmosphere.
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  • Hiroshi Ishizaki, Masahiro Endoh, Toshiyoshi Tada
    1983 Volume 33 Issue 4 Pages 307-314
    Published: 1983
    Released: March 09, 2007
    JOURNALS FREE ACCESS
       SEASAT-1 altimeter data (from July 28 to August 8, 1978) are used to obtain the sea surface height distribution over the Kuroshio Extension, east of Japan. Data along 17 orbits are processed to minimize the root mean square (RMS) of the difference between the two surface height values at each intersecting point (47 points in all). Both the biases and linear trends of surface height along the orbits are taken into consideration.
       The resulting RMS of the height differences is about 11 cm, which is the same order in magnitude as the accuracy of the altimeter itself (±10 cm).
       The surface height maps are drawn, first, with a subjective method using only mean values at the intersecting points, and secondly with an objective method by the two-dimensional cubic spline interpolation using all the height data. The two maps are qualitatively the same. Major patterns are considered to be a part of the Kuroshio Extension, although noisy highs remain, which are possibly effects of sea mounts unresolved in the applied geoid.
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