Papers in Meteorology and Geophysics
Online ISSN : 1880-6643
Print ISSN : 0031-126X
ISSN-L : 0031-126X
Volume 48 , Issue 4
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  • Osamu Kamigaichi
    1998 Volume 48 Issue 4 Pages 89-100
    Published: 1998
    Released: October 20, 2006
    JOURNALS FREE ACCESS
       Green functions of the earth at borehole sensor installation depths (0 to 962.5m, at each 68.75m) for the surface vertical point load were calculated using spherical earth model 1066A. Correct calculation requires both eigen functions and Legendre functions whose order n exceeds 1 million. Green function behavior at depth=0 and depth≠0 are significantly different, especially at a short distance from the loading point. In the θ (angular distance) <0.01 degree range, spherical green functions and their Boussinesq approximations coincide well except for those including radial displacement, both at depth=0 and ≠0, but diverge at large θ due to the earth's nonuniformity and surface curvature. Atmospheric coefficients for areal and volume strain show scale dependence reflecting the earth's inner structure and the relative magnitude of installation and skin depths.
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  • Toshimitsu Tsukakoshi, Toshikazu Odaka
    1998 Volume 48 Issue 4 Pages 101-113
    Published: 1998
    Released: October 20, 2006
    JOURNALS FREE ACCESS
       Since the mid-1970's marked crustal upheavals have been observed continuously in the Izu Peninsula. several models constructed on the basis of tectonic, volcanological, and other geophysical consideration have been proposed to explain these movements. However, since small eruptions took place off the east coast of the Izu Peninsula in 1989, most people may have accepted the idea that there exists volcanic background behind, these unusual events.
       When we see the annual variations in contours of these vertical ground movements, we notice some characteristic features: (1) The center of upheavals moves annually and (2) an area of small-amplitude depressions exists adjacent to this large-displacement upheaval area.
       In this paper, we introduce a pressure source with directivity and investigate whether the above characteristic features of crustal movement can be explained qualitatively using this source model. Our computation is based on the three-dimensional finite element method.
       We find that our pressure source with directivity can explain changes in the contour patterns of observed crustal movements if we assume that the direction of the pressure axis changes annually. Our source is preferable to a familiar equi-pressure source because in the latter case we must assume at least two sources with different intensity distributed just under the peak positions of upheaval and depression and their locations have to move annually but, in our case, one source at a fixed position is required.
       Our other conclusion is that a pressure source with directivity gives rise to the depression area adjacent to the upheaval area more efficiently than the inclined tensile fault even though both sources cause similar contour patterns of crustal movements.
       The Appendix discusses elastic deformation of a semi-infinite medium and a layered medium (a half-space with one superficial layer) caused by a buried spherical equi-pressure source. The former example examines the validity of our computational method by comparing numerical results with analytical solutions. From the computation for the latter case, we show that the existence of a low-velocity superficial layer increases horizontal surface displacements as much as 30% compared to that without it.
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  • Kazuhiko Masuda
    1998 Volume 48 Issue 4 Pages 115-122
    Published: 1998
    Released: October 20, 2006
    JOURNALS FREE ACCESS
       The effect of surface wind direction on sea surface emissivity was studied for wavelengths of 3.7, 8.8, 11, and 12μm. Wind direction is considered for 0°, 45°, 90°, 135°, and 180° from the direction of emitted radiation, while wind speed is changed from 1 to 15m/s. Computation showed that wind direction has little effect on sea surface emissivity (<0.002) when the emergent angle (θ) measured from the zenith direction is <60° even at a high wind speed. Wind direction is not essential for practical sea surface temperature retrieval as long as θ<60°. The wind direction effect appears for θ>60° where the wavelength dependence of the emissivity difference caused by wind direction change is low (<0.003).
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