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- Issue 12 Pages 721-
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Volume 21 (1969)
- Issue 4 Pages 705-
- Issue 3 Pages 573-
- Issue 2 Pages 471-
- Issue 1 Pages 385-
Volume 21, Issue 4
Displaying 1-9 of 9 articles from this issue
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Tadahiko OGAWA, Kunitomo SAKURAI1969 Volume 21 Issue 4 Pages 705-722
Published: 1969
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThe influence of a cold and collisionless magnetoplasma on the gyro-synchrotron radiation from an accelerated electron is considered in detail by solving Maxwell's equations with the aid of a Green tensor and a Fourier transformation. Electromagnetic fields at great distance from a point source are discussed. The frequency spectra of the radiation power of both ordinary and extraordinary waves are numerically calculated for various values of ambient plasma parameters and energy of a radiating electron. It is pointed out that the waves radiated at low harmonic numbers of the gyro-frequency of a radiating electron cannot propagate in a plasma, and that the influence of a magnetolasm on the spectra is important under the condition of fp≥fH. These are due to dispersion and anisotropy of the medium. Applications of the results to solar radio type IV bursts are briefly discussed.View full abstractDownload PDF (1160K) -
J. R. CATCHPOOLE1969 Volume 21 Issue 4 Pages 723-729
Published: 1969
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSA change in the spiralling-mirroring domain of trapped electrons and a consequent change in the precipitation to ionospheric heights result from the superposition of a longitudinal electric field along the direction of the lines of force of the Earth's magnetic field. A previous assessment of the extent of this effect is here extended to consider precipitation from a model for the distorted magnetosphere. A comparison is made between the relative precipitation increases from the dayside field, the nightside field and the symmetrical (or dipole) field.View full abstractDownload PDF (713K) -
G. M. THOMAS1969 Volume 21 Issue 4 Pages 731-749
Published: 1969
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThis paper describes a search for superposed effects in Sq as revealed by data taken from the publications of Lerwick and Eskdalemuir observatories. The method uses histograms representing the frequency with which different values of H are recorded, after first removing the secular change. The histograms are used to form their associated characteristic functions (Fourier transforms) which are then factorized by locating their zeroes. When the zeroes are all plotted in a suitable representation, the presence of superposed effects should be manifested by the zeroes forming families of radial lines.
The samples of data taken from Lerwick were found to be too small to yield satisfactory results; those from Eskdalemuir were more successful, although only the data relating to the epoch of maximum solar activity provided quantitative results. On the basis of this analysis it seems that the quiet daily variations in the horizontal component at Eakdalemuir in winter consist of two components. The first is dominant only during sunlight and its amplitude depends on the solar zenith angle; the other component is definitely non-cyclic in character.
The investigation also provides a value for the ‘zero level’ of Sq, the value the field would have if the Sq current system, including its purely zonal part, was arrested. Depending on certain assumptions this zero level appears to lie about 12 or 17nT above the daily mean value of field on International Quiet Days.View full abstractDownload PDF (2036K) -
Maurice Aubert1969 Volume 21 Issue 4 Pages 751-756
Published: 1969
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSTo study the regional effects of the secular variation of the Earth's magnetic field, it is shown that the normal field in a region may be expressed as a limited development in spherical functions. The formulae obtained would be directly comparable from one region to another as well as for the geomagnetic field. As an example, the field has been calculated in France since 1948. Emphasis has been particularly put on the calculation of the precision obtained on the Gauss coefficients.View full abstractDownload PDF (529K) -
M. E. EVANS, M. W. MCELHINNY1969 Volume 21 Issue 4 Pages 757-773
Published: 1969
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSExperiments designed to elucidate the nature and source of high-stability remanence in igneous rocks have been carried out. Many of the pyroxene grains of the samples used (from the Modipe gabbro of southern Africa) contain small (from a few microns down to the optical limit) magnetite inclusions, some of which are very probably single-domained by virtue of their size and shape. It is shown that these inclusions contribute significantly to the TRM, and may, in fact, account for virtually all of the remanence. Measured coercivities as high as 1800 œ are attributed to the observed shape anisotropy of some of the magnetite inclusions. A discussion of the various theories of coercive force indicates that this is the only mechanism which enables magnetite to possess coercivities in excess of 1000 oersteds.
The conclusions reached can be strictly applied only to this particular rock; however, it is felt that the natural occurrence of single-domained magnetite is more common than previously supposed. The reason for the comparative rarity of similar observations may well be the minute size and very small total quantity of magnetite necessary to account for typical TRM's in igneous rocks.View full abstractDownload PDF (1884K) -
Kazuo KOBAYASHI1969 Volume 21 Issue 4 Pages 775-780
Published: 1969
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSAvailable data of the ancient geomagnetic field intensity determined by the archeomagnetic measurement are compared with theoretically calculated curves of secular variation in the geomagnetic total force at three mutually remote sites. It is particularly remarkable that the anomalous archeomagnetic results from equatorial America (Peru, Bolivia and Mexico) can be accounted for by the model including the westerly drifting components of non-dipole field superposed on the standing non-dipole and the oscillating dipole fields. The good agreement of the archeomagnetic date and the calculated curves may imply that the drifting non-dipole field given in Yukutake's model has been persistent over the past 4, 000 years.View full abstractDownload PDF (540K) -
Peter N. SHIVE, Robert F. BUTLER1969 Volume 21 Issue 4 Pages 781-796
Published: 1969
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSDifferences in the lattice parameters of hematite, ilmenite and magnetite are responsible for lattice mismatch across the boundaries of magnetite-ilmenite and hematite-ilmenite lamellae. Most of this mismatch is relieved by periodic edge dislocations, the remainder by constant strain of the lattice. The periodic stress field produced by the dislocations and the constant stress due to crystal strain are calculated for both types of lamellae. A model based on magnetostrictive control of magnetization can account for the coercivities of hematite lamellae in ilmenite. The model predicts that the coercive force of such a lamella should be inversely proportional to the square root of the lamella thickness, and calculated coercivities agree well with observed values. High coercivities associated with magnetite-ilmenite lamellae are probably due to single domain effects, since they cannot be accounted for by magnetostrictive control of any type.View full abstractDownload PDF (1547K) -
D. J. DUNLOP1969 Volume 21 Issue 4 Pages 797-799
Published: 1969
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSDownload PDF (339K) -
R. L. WILSON, P. J. SMITH1969 Volume 21 Issue 4 Pages 800-801
Published: 1969
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSDownload PDF (152K)
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