巻号一覧
31 巻, 5 号
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B. N. RAINA, B. A. MAKHDOMI1979 年 31 巻 5 号 p. 485-494
発行日: 1979年
公開日: 2010/03/12
ジャーナル フリーThe data obtained by simultaneous operation of passive antenna system (during charge dissipation period) and Gerdien's conductivity meter at the height of 1m above the ground are analysed for the estimation of atmospheric electric conductivity by each method. The conductivity obtained by using passive antenna, in its transient state, gives consistently higher values than that by Gerdien's conductivity meter. A way to explain this difference lies in the suggestion that the rate at which the transition from one equilibrium state to another takes place, once an electric disturbance is introduced in the atmosphere may be partly governed by the turbulent mixing of atmospheric air layers close to the surface.抄録全体を表示PDF形式でダウンロード (664K) -
Leroy R. ALLDREDGE, Charles O. STEARNS, Masahisa SUGIURA1979 年 31 巻 5 号 p. 495-508
発行日: 1979年
公開日: 2010/03/12
ジャーナル フリーThe first degree external spherical harmonic coefficients are obtained for each year of a 12-year period centered at 1958.5, using annual mean values of X, Y, and Z components from 54 magnetic observatories. Values of the coefficient g01e of the zonal first degree harmonic clearly show a solar cycle variation. The peak-to-peak amplitude of the variation is approximately 29 nT, which is consistent with values obtained earlier by first filtering data to retain only those variations having periods near the solar cycle and then subjecting the filtered data to a spherical harmonic analysis. The variation in g01e is found to correlate extremely well with the annual mean Dst, index and with the annual number of days having Ap≥60. Based on statistics of the mean square successive difference, an explanation is presented why the obtained solar cycle variation in g01e, which is very much smaller in magnitude than the standard deviations calculated by the conventional method, is statistically meaningful. The determined absolute (not relative) values of g01e are in agreement, within several nanotesla, with the expectation from a theoretical model of solar wind compression of the magnetosphere and an analysis of the Dst index.抄録全体を表示PDF形式でダウンロード (1316K) -
Takesi YUKUTAKE, Joseph C. CAIN1979 年 31 巻 5 号 p. 509-544
発行日: 1979年
公開日: 2010/03/12
ジャーナル フリーSpherical harmonic analyses were made of the annual mean values of the geomagnetic components at 34 observatories for the period from 1940 to 1973. Annual values of the Gauss coefficients were separated into parts of external and internal origin. The external part of the first-degree component is parallel to the internal dipole and changes with solar activity. The maximum change from peak to trough amounts to 47 nanoteslas during this period. During one solar cycle, two peaks appear in the variation of this component. The first peak corresponds to the period of the maximum solar activity, the second at the declining stage of the cycle.
Examination of the time variations of the first-degree components was extended to an analysis for 1900 to 1973 based on annual means from 21 observatories. Although its amplitude is small, the internal part changes with a three-year time lag behind the external field change. After Fourier analyses of the time series of both the internal and external components, their ratio was computed for the 10-year-period band. The modulus of the internal/external ratio (i/e) was obtained to be 0.32 and the phase angle (internal-external) to be 105°.抄録全体を表示PDF形式でダウンロード (3198K) -
R. L. COLES, G. V. HAINES1979 年 31 巻 5 号 p. 545-566
発行日: 1979年
公開日: 2010/03/12
ジャーナル フリーLong-wavelength anomalies in the vertical component of the geomagnetic field over Canada and nearby regions have been examined using data obtained from airborne vector magnetometer surveys. The waveband ranges from a few hundred kilometres to about five thousand kilometres. Spectral analyses have elsewhere suggested that the magnetic anomaly field originating from the lithosphere becomes dominant only above degree 13 (wavelength about 3, 000km). Comparisons among two reference fields (the IGRF of maximum degree 8 and POGO 6/71 of maximum degree 13) and the airborne magnetic data support this interpretation. Two techniques have been used to isolate the long-wavelength anomalies: fitting of polynomial expansions to the data and upward continuation to 100km and 300km altitude. The long-wavelength anomalies relative to the POGO reference field, derived by these two methods, show good correlations with known lithospheric features such as the Alpha Ridge and distinct portions of the Canadian craton. There is often a close connection between regions of intense short-wavelength anomalies and the broader anomalies, but at least one such broad anomaly appears to be caused by a similarly large source region of high magnetization. Viscous enhancement of magnetization at elevated temperatures in the crust, combined with broad scale lateral temperature variations, provides a possible cause of the long-wavelength anomalies. The upward continuation to 300km of the airborne magnetic data gives an estimate of the anomaly field to be expected by planned satellite magnetic surveys.抄録全体を表示PDF形式でダウンロード (4408K)
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