Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
Volume 36, Issue 4
Displaying 1-4 of 4 articles from this issue
  • Manabu KUNITAKE, Takasi OGUTI
    1984 Volume 36 Issue 4 Pages 121-138
    Published: 1984
    Released on J-STAGE: September 14, 2010
    JOURNAL FREE ACCESS
    Using video data obtained by a low-light-level TV camera, spatial-temporal characteristics of flickering spots in flickering auroras are studied. The results show that flickering spots often move in periodic fashion synchronized with their luminosity oscillations. For the examples studied here, the frequency ranges from 3 to 8Hz; the velocity of the motion of spots perpendicular to the magnetic field is in a range from 90 to 240km/s and the horizontal distance of the motion is in a range 10 to 20km, being almost equal to the size of a spot. It is shown that a lot of spots often form a cluster and that a lot of clusters are distributed along an auroral arc. It is also shown that the lifetime of a certain flickering spot is 1 to 2 seconds and that the lifetime of the cluster is tens of seconds to hundreds of seconds. On the basis of these results, a mechanism of flickering auroras is briefly discussed.
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  • Ramesh P. SINGH, B. U. S. KUMAR, Tarkeshwar LAL
    1984 Volume 36 Issue 4 Pages 139-147
    Published: 1984
    Released on J-STAGE: September 14, 2010
    JOURNAL FREE ACCESS
    Wave-tilt amplitudes and phase angle variation in the extended frequency range of 104-107Hz have been presented for a two layer earth surface model. The effect of conductivity and dielectric constant variation of two layers on wave-tilt amplitude and phase angle have been computed. It is shown to vary with changing thickness of the upper layer. The potentiality of such curves in wave-tilt measurement of the subsurface layer has been discussed.
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  • Masaru KONO, Masahiko KOYANAGI, Susumu KOKUBUN
    1984 Volume 36 Issue 4 Pages 149-160
    Published: 1984
    Released on J-STAGE: September 14, 2010
    JOURNAL FREE ACCESS
    A ring-core fluxgate magnetometer was developed and tuned so as to have ideal characteristics for use as a sensor to a spinner magnetometer for rock magnetism and paleomagnetism. The most important points in this tuning is to obtain high sensitivity as well as flat responses in both amplitude and phase, and to make such characteristics little affected by temperature fluctuations, which is the largest error source in ordinary environment. The present design satisfies all of these requirements. A high sensitivity of 10mV/nT is achieved. The system transfer function is very close to Butterworth low-pass filter, with a cut-off frequency of 450Hz. Moreover, because a very linear phase response was obtained, sampling of magnetic signals at a constant time delay of about 500 microseconds will reproduce signals of 200Hz or less without any distortion. This is ideal for use in the recently developed, advanced spinner magnetometer, as multiple frequency components and/or variable rotational speeds are utilized in such systems.
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  • F. E. M. LILLEY, M. N. SLOANE, I. J. FERCUSON
    1984 Volume 36 Issue 4 Pages 161-172
    Published: 1984
    Released on J-STAGE: September 14, 2010
    JOURNAL FREE ACCESS
    The possibility is explored of using total-field fluctuation records to give information on local geomagnetic induction. Total-field fluctuation records will not usually be accompanied by local horizontal fluctuation records, and as a replacement for the latter the use of distant observatory records may be possible. Several examples are given, based on records of instruments which have operated to monitor magnetic activity for the benefit of aeromagnetic survey parties. Transfer functions are computed which appear useful as a guide in a reconnaissance study of geomagnetic induction.
    The use of total-field fluctuation recordings made remote from an observatory may have several applications, such as to studies of geomagnetic induction at sea. The operation of total-field recording instruments in arrays which contain a small number of stations recording three components of magnetic fluctuations may have application to studies of continental induction.
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