Journal of geomagnetism and geoelectricity

Electromagnetic Induction in Three Dimensional Structures for Various Source Fields

R. D. HIBBS, F. W. JONES

1978 Volume 30 Issue 1 Pages 1-18
Published: 1978
Released on J-STAGE: March 12, 2010

DOIhttps://doi.org/10.5636/jgg.30.1

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A numerical method is used to calculate the electromagnetic fields associated with three-dimensional conductivity anomalies. Three source field-conductivity structure combinations are considered. A uniform source above an island structure as well as a two-dimensional non-uniform source above an L-shaped embedded structure and a horizontal dipole above an embedded square anomaly are studied. Profiles of selected electromagnetic field quantities and ratios are presented along with the appropriate phases for various positions relative to the anomalous structure. Three dimensional figures of the amplitude of the electric and magnetic field components are given for each source field-conductivity structure combination. The source field effect is clearly evident in all profiles.

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On Some Features of Pc5 Pulsations at Choutuppal (Hyderabad), India

D. R. K. RAO

1978 Volume 30 Issue 1 Pages 19-25
Published: 1978
Released on J-STAGE: March 12, 2010

DOIhttps://doi.org/10.5636/jgg.30.19

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Morphological features of Pc5 pulsations observed in the earth currents at an equatorial station over nearly 6 years show a dominant maximum in the morning in occurrence hours of the pulsation, like at high and middle latitudes, and a much subdued maximum in the evening; a peak near midnight is also seen as reported from auroral zone stations. A semidiurnal variation in the period of the pulsations with a distinct maximum at the hour close to dawn and a minor maximum around dusk is noticed in all the seasons and the year. Similarity of the semidiurnal variation in the periods between the equatorial station and a high latitude station is in conformity with the theoretical models wherein it was suggested that ULF waves can also be observed away from the resonance region as the compressional evanescent mode. Time series analysis of the parameter, occurrence hours per day, indicates significant signal corresponding to solar synodic rotation period for the years 1970-72. Some significant quasi-stationary periodicities in occurrence hours per day are noticed.

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Particle Trajectories at a Magnetic Neutral Point

Kaname AMANO, Takao TSUDA

1978 Volume 30 Issue 1 Pages 27-38
Published: 1978
Released on J-STAGE: March 12, 2010

DOIhttps://doi.org/10.5636/jgg.30.27

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The motion of charged particles is studied numerically by a test-particle approach. A Petschek-type electromagnetic field is given for a plasma in which a finite electric conductivity, necessary at a magnetic neutral point, results from the inertia of the particles. The plasma is assumed to be cold in the external flow region. It is found that two gyration frequencies characterize the motions parallel and perpendicular to the external magnetic field. The meandering electrons are concentrated near the neutral point and have a mean velocity, though with a considerable dispersion, big enough to cause some current-induced instabilities.

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Comparison of the Two-Snake Model with the Observed Polarization of the Substorm-Associated Magnetic Pulsation Ps6

Takao SAITO, Kiyohumi YUMOTO

1978 Volume 30 Issue 1 Pages 39-54
Published: 1978
Released on J-STAGE: March 12, 2010

DOIhttps://doi.org/10.5636/jgg.30.39

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The damped-type long-period (T=10-20min) magnetic variation associating with a substorm is called the Ps6-type Pi3 pulsation, or briefly Ps6. The two-snake model including meandering ionospheric currents during a substorm which has been proposed in previous papers to explain the morphological characteristics of Ps6 is examined in the present paper to interpret the observed polarization of the ground-based Ps6. A model calculation suggests that from the viewpoint of the polarization the area near a snake-type model electrojet is expected to be divided into five domains: pole-side pre-midnight domain (right-handed), pole-side post-midnight domain (L), central domain (R & L), equator-side pre-midnight domain (L), and equator-side post-midnight domain (R). This theoretically expected polarization rule is examined by two ways: statistical study and case study of the observed Ps6.
The polarization of 214 Ps6 events observed at Point Barrow and College is statistically found to be governed by the theoretical polarization rule. A case study on Ps6 waves sorted out through a digital filter from five substorm events corresponding to the five domains indicates that the polarization rule obtained observationally in this way also agrees with the theoretical polarization rule.

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Electric-Field Measurements With Double Probes in a Space-Simulation Plasma-Chamber

M. MORITA, T. OGAWA, K. TSURUDA, T. OBAYASHI

1978 Volume 30 Issue 1 Pages 55-64
Published: 1978
Released on J-STAGE: March 12, 2010

DOIhttps://doi.org/10.5636/jgg.30.55

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