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Volume 39, Issue 12
Displaying 1-6 of 6 articles from this issue
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Tadahiko OGAWA, Kiyoshi IGARASHI, Kazuhiro AIKYO, Hideo MAENO1987 Volume 39 Issue 12 Pages 709-721
Published: 1987
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSFrom March 1985 to January 1986, 428 medium-scale traveling Ionospheric disturbances (TID's) incident to the high-latitudes between 50° and 85°S were detected at Syowa Station, Antarctica, by means of differential-Doppler measurements of the 150 and 400 MHz beacon waves from six NNSS satellites. It is found from statistical analysis that (1) the medium-scale TID's at high-latitudes appear quite often during geomagnetically quiet and moderately disturbed conditions, and their occurrence seems not to increase with increasing geomagnetic activity, (2) they attain the maximum activity in winter and the minimum in summer, (3) diurnal variation shows the maximum occurrence around 1400-1600 LT with a second maximum around midnight, and (4) most of the medium-scale TID's propagate from south toward the equator. These findings are compared with TID observations using NNSS made at mid-latitudes (30°-55°N) to find a fairly good consistency between both results.View full abstractDownload PDF (1503K) -
Leroy R. ALLDREDGE1987 Volume 39 Issue 12 Pages 723-738
Published: 1987
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSWhen regional geomagnetic charts for areas roughly the size of the United States were compiled by hand, some large local anomalies were displayed in the isomagnetic lines. Since the late nineteen sixties, when the compilation of charts using computers and mathematical models was started, most of the details available in the hand drawn regional charts have been lost. One exception to this is the Canadian magnetic declination chart for 1980. This chart was constructed using a 180 degree spherical harmonic model. It managed to show considerable detail, but even more detail might be useful. Suggestions are made about how more detail might be displayed in regional charts when adequate data are available.View full abstractDownload PDF (4593K) -
Xi-shuo WANG, D. I. GOUGH1987 Volume 39 Issue 12 Pages 739-749
Published: 1987
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSNormal parts of magnetovariation fields observed by magnetometer arrays in middle latitudes are represented by plane-wave terms. The divergence-free condition of the normal fields leads to estimates of the complex vertical wave numbers. The sign of the imaginary part of the vertical wave-number identifies the normal field as either internal- or external-dominant. The wave numbers of the horizontal components reveal the characteristic dimensions of the normal fields. 114 frequency components are analyzed from fields recorded with an array in Southern Alberta and British Columbia, Canada. The first plane-wave terms have horizontal wavelengths of about 104km, representing very slowly varying normal fields on the length scale of the array. The horizontal wave vectors of the first terms of internal-dominant fields lie in the NW-SE quadrant and are probably related to the orientation of the internal induced currents. The second plane-wave terms have horizontal wavelengths near 102km, and are regarded as internal anomalous fields.View full abstractDownload PDF (1131K) -
Yoshimori HONKURA1987 Volume 39 Issue 12 Pages 751-767
Published: 1987
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSObservations of electric and magnetic field variations were carried out in the Noboribetsu geothermal area, southwestern Hokkaido, in order to study a local three-dimensional behavior of electric and magnetic fields. Estimates of apparent resistivity and transfer functions are first examined for frequencies of 8-20Hz. The apparent resistivity distribution for this period range clearly shows a local zone of resistivity lower than 10ohm·m. Directions of induction vectors are generally perpendicular to the local gradient of apparent resistivity and hence no anomalous behavior is found. An attempt was made to pursue downward extension of this low resistivity zone by further analyzing the data at lower frequencies. Induction vectors at 0.03Hz all point toward the southeast and this trend is considered to be due to the regional coast effect. The result of two-dimensional model calculations of coast effect accounts for the overall distribution of induction vectors. The computed coast effect was subtracted to yield a local induction anomaly. Comparison of this local anomaly with the result of calculations for a model in which a three-dimensional block of low resistivity is embedded in a uniform half-space discloses the northward extension of the low resistivity zone. This feature is not clearly seen in the apparent resistivity distribution. It is thus concluded that induction vectors, if properly interpreted, provide important information on a local three-dimensional resistivity structure and hence they should be extensively used for geothermal exploration in addition to the conventional magnetotelluric method.View full abstractDownload PDF (1300K) -
M. E. EVANS1987 Volume 39 Issue 12 Pages 769-772
Published: 1987
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSDownload PDF (372K) -
IAGA DIVISION I WORKING GROUP1987 Volume 39 Issue 12 Pages 773-779
Published: 1987
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSDownload PDF (442K)
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