Journal of geomagnetism and geoelectricity
Online ISSN : 2185-5765
Print ISSN : 0022-1392
ISSN-L : 0022-1392
Volume 41, Issue 10
Displaying 1-4 of 4 articles from this issue
  • Hing-Lan LAM
    1989 Volume 41 Issue 10 Pages 813-834
    Published: 1989
    Released on J-STAGE: September 14, 2010
    JOURNAL FREE ACCESS
    Ground magnetic data recorded in the auroral zone station at Fort Churchill, Canada (FCC) during 1985 were used to study the spectral content of Pc5 magnetic pulsations. It was found that spectral peaks tend to group into two separate bands of 1-3mHz and 3-6mHz. The power in both bands appears to be linearly related to global planetary geomagnetic activity as represented by the Ap index. While pulsations in both bands show a 27-day recurrence tendency, only intense pulsations in the low frequency band (1-3mHz) seem to recur in the morning a few days after an initial enhancement. On the other hand, pulsations in the high frequency band (3-6mHz) always have low amplitudes in the afternoon. In general, the low frequency band activity is more intense than the high frequency band activity. It is suggested that Pc5 pulsations can be classified into two sub-groups, with pulsations in the low frequency band of 1-3mHz classified as Pc5A and those in the high frequency band of 3-6mHz classified as Pc5B. Probably, Pc5A is associated with the “ringing” of the large-scale three-dimensional magnetospheric and ionospheric current systems and Pc5B is due to field line resonance. This classification scheme would provide a convenient mean of expressing and recognizing the frequency content of Pc5 events.
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  • Tadahiko OGAWA, Akio NOMURA, Takashi TANAKA, Kiyoshi IGARASHI
    1989 Volume 41 Issue 10 Pages 835-849
    Published: 1989
    Released on J-STAGE: September 14, 2010
    JOURNAL FREE ACCESS
    Simultaneous measurements of high-latitude upper mesospheric gravity waves by a 50MHz meteor radar and a dye lidar were made at Syowa Station, Antarctica, in 1985. The radar measured nearly north-south components of neutral wind velocities at altitudes of 80-100km and at slant ranges of 110-600km from Syowa Station, while the lidar measured the sodium density profile and sodium abundance at the same altitudes at the zenith of Syowa Station. From measurements on six nights, it is found that short-period (1-2 hours) and long-period (≥2 hours) perturbations of the wind velocity due to gravity waves are well manifested in the sodium abundance and sodium density perturbations, thus suggesting that the response of the neutral winds to gravity waves is fundamentally consistent with the sodium layer response. From a case study, it is demonstrated that during a mediumscale auroral substorm, a strong equatorward wind attaining a maximum of 60m/s appeared in accord with a gradual decrease in sodium abundance. A mechanism explaining this causal relation is unknown.
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  • Y. IWASAKA, C. X. ZHANG, K. YOSHIMI
    1989 Volume 41 Issue 10 Pages 851-870
    Published: 1989
    Released on J-STAGE: September 14, 2010
    JOURNAL FREE ACCESS
    Aerosol parameters (size distribution, refractive index, and vertical concentration) were estimated from upwelling radiance measurements (over Ise Bay, Nagoya Japan on December 5, 1986) from an airborne platform. The modified adding method and multi-dimension regression method used for data reduction are useful techniques for remote sensing of atmospheric aerosols. The parameters estimated showed good agreement with typical urban atmospheric aerosols: a size distribution of 3.7×105×r-5.1 (particles/μm/m3) and a refractive index of 1.42+0.0069i.
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  • K. YUMOTO, K. TAKAHASHI, T. OGAWA, T. WATANABE
    1989 Volume 41 Issue 10 Pages 871-878
    Published: 1989
    Released on J-STAGE: September 14, 2010
    JOURNAL FREE ACCESS
    Sc- and si-associated ionospheric Doppler velocity oscillations and geomagnetic pulsations observed during the great geomagnetic storm of February 1986 can be explained by the “dynamo-motor” mechanism of ionospheric electric fields and by global compressional oscillations in the magnetosphere and ionosphere, respectively.
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