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Volume 20 (1968)
- Issue 4 Pages 289-
- Issue 3 Pages 115-
- Issue 2 Pages 57-
- Issue 1 Pages 1-
Volume 20, Issue 4
Displaying 1-16 of 16 articles from this issue
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Takesi Nagata1968 Volume 20 Issue 4 Pages 289-290
Published: December 20, 1968
Released on J-STAGE: August 11, 2011
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Tatsuzo OBAYASHI1968 Volume 20 Issue 4 Pages 291-297
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSA review is given on the present status of the planetary atmospheric electricity. The ionization and the equilibrium of space charges in the earth's atmosphere are discussed with newly acquired information. Large-scale electric fields existing in the atmosphere are divided into three major sources; they are originated in the lower atmosphere, the ionosphere and the magnetosphere. The lower atmospheric electric field system is generated primarily by thunderstorm electricities, while the ionospheric and magnetospheric ones are attributed to the motion of plasma in the geomagnetic field. It is revealed that the atmospheric electricity in other planets is of considerable interest because of its variety in their environmental conditions. A brief description is also given on the recent experimental techniques for space electricity measurements.View full abstractDownload PDF (689K) -
R. C. WENTWORTH1968 Volume 20 Issue 4 Pages 299-304
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
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Tsutomu TAMAO1968 Volume 20 Issue 4 Pages 305-313
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSBy using the drift kinetic approximation, effects of the electron motion along the magnetic field lines on axisymmetric torsional hydromagnetic oscillations in an inhomogeneous, low-β plasma are considered. The result indicates that eigen oscillations are only possible when there is an energy trapping region between the turning points. If we assume the simple spatial distribution of the Alfvén speed, VA, which has a trough corresponding with the sudden density decrease near the plasmapause, no effective trapping of oscillations appears near the trough for the case of the cold plasma limit, VA>>Ve. The existence of the trapping region of oscillation is strongly dependent on the relative magnitude of VA to the electron thermal velocity, ve. For the case of ve>>VA, the resonance oscillation is possible within the trough. However, the deviation of the resulting eigen-frequency from that corresponding to the field line at the bottom of the trough is small. In general, the condition for the resonance trapping of oscillations near the trough is ve>>Vo (the minimum value of VA) beyond the density knee.View full abstractDownload PDF (832K) -
T. NAGATA, T. TOHMATSU, T. OGAWA1968 Volume 20 Issue 4 Pages 315-321
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSRocket results are presented on visible and ultraviolet dayglow observed in the altitude range of 80-350km, for different values of solar zenith distance. Theoretical interpretotions are given on the basis of calculations made for emission rates for various excitation mechanisms, also using results of simultaneous measurements of electron density and electron temperature.View full abstractDownload PDF (520K) -
T. SHIMAZAKI, A. R. LAIRD1968 Volume 20 Issue 4 Pages 323-335
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThe temporal variation of the electron density distribution observed by radio soundings at Rio Grande, Brazil during the eclipse of November 1966 has been analyzed. Using five models of chemical reaction coefficients and the lower boundary values of neutral constituents, the variation of an ‘equivalent’ temperature has been calculated. The equivalent temperature is that resulting from a minimization (over a range of heights and times) of the mean-square residual differences between the observed ∂N/∂t and the values calculated from the continuity equation. The equivalent temperature variations thus calculated may involve implicitly the effects of diurnal variations in the lower boundary values of neutral constituents and vertical drift velocities as well as the actual temperature variations. Assuming that the difference of the variation of the equivalent temperature between the eclipse and control day is mainly due to the difference of the vertical drift velocity, the additional vertical drift velocity on the eclipse day has been calculated; it is largely upward and starts to rise about 30min. before the ground eclipse for all five models. A simple model calculation indicates that this additional upward velocity could be caused by the effect of the reduced conductivity in the lower dynamo region during the eclipse.View full abstractDownload PDF (1385K) -
Mituko OZIMA, E. E. LARSON1968 Volume 20 Issue 4 Pages 337-351
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThree of eight submarine basalts from various localities of the Pacific show self-reversal of TRM when they are heated in air at about 300°C and cooled to room temperature in the geomagnetic field. As the sample is heated to 300°C, the original ferrimagnetic component with a Curie temperature of 250°C is gradually transformed to another component with a Curie temperature of 300°C and there exist momentarily two magnetic components. Magnetic interaction between these two components seems to be responsible for selfreversal. The fact that TRM produced in an external field of 2600 Oe reverses at low temperatures indicates that the self-reversal phenomenon is caused by an exchange interaction.View full abstractDownload PDF (1452K) -
Masaru KONO1968 Volume 20 Issue 4 Pages 353-366
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThe natural remanent magnetization of Pleistocene andesite and scoria samples collected from Usami Volcano Izu Penninsula was examined by paleomagnetic methods and found to be stable. The directions of the stable magnetization of these rocks show significant departure from that of the present geomagnetic field in Japan A hypothesis based on geological field evidence that the strata in the sampled area have been tilted sometime after the formation of the rocks, can account for this fairly well. Using these samples with stable remanences, the intensity of the Pleistocene geomagnetic field (normal and reversed) in Japan has been determined by means of Thellier's metood. Many samples show some irreversible changes in magnetic properties when they are heated above certain critical temperatures. The intensity estimates were obtained from the linear relation of Jn-Jt in the temperature range where irreversible changes did not occur. The intensity of the Pleistocene geomagnetic field determined in the present study is very similar to the present field intensity in Japan (0.46oe), the mean values being 0.61±0.61oe for reversed samples and 0.55±0.16oe for normal ones.View full abstractDownload PDF (1362K) -
R. L. WILSON, Peter J. SMITH1968 Volume 20 Issue 4 Pages 367-380
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSSecondary natural magnetizations have been examined by thermally demagnetizing a variety of rock types of mainly Tertiary age from Britain, India and Iceland. The conclusion is that the secondary magnetizations are most likely to be viscous magnetizations slowly acquired isothermally in the earth's magnetic field. A theory is developed which predicts an upper limit of temperature needed to erase thermally in the laboratory any viscous magnetization acquired by a rock at or near room temperature. This upper limit is near to 300°C, and is observed to be correct for all except four of the 123 specimens investigated.
It also appears that if, during laboratory heating, the Curie point of a specimen rises due to oxidation before complete demagnetization of the NRM, then the NRM direction may be retained by the specimen unchanged, and only disappears at the new, higher, Curie point.View full abstractDownload PDF (1413K) -
W. O'REILLY1968 Volume 20 Issue 4 Pages 381-386
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSAn empirical method is used to calculate the Curie temperatures of spinel materials containing Fe2+ and Fe3+ ions. The approach taken is to select three simple spinel oxides of known cation distribution and Curie temperature containing the paramagnetic ions Fe2+ and Fe3+. In this way the relative strengths of the Fe3+—Fe3+, Fe3+—Fe2+ and Fe2+—Fe2+ AB interactions are calculated. For titanomagnetites the calculated Curie temperatures agree with the observed values to within 20%. A Curie temperature of 770°C is calculated for maghemite. This is higher than the Curie temperature of magnetite. Similarly an increase in the Curie temperatures of titanomagnetites is predicted on oxidation. This is in agreement with experiment. Finally the method is applied to the ratio of the BB/AB interactions in the spinel structure. This predicts that the apparent ferrimagnetic P-type behaviour of titanium rich titanomagnetites is not explained by the Néel theory. However the behaviour of titanium rich oxidized titanomagnetites is shown to be of the Néel P-type.View full abstractDownload PDF (661K) -
M. G. ROCHESTER1968 Volume 20 Issue 4 Pages 387-402
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThe effect of electromagnetic core-mantle coupling on small changes in the length of day and the geographical location of the pole is treated by a simplified model which neglects the time required for magnetic diffusion through the lower mantle, and approximates the poloidal field by the centred dipole. The resulting formulae for the time constants of the coupling are more meaningful physically than, and give nearly the same numerical values as, those derived previously by more rigorous methods. It is shown that, despite the complexity of the electromagnetic interactions at the coremantle boundary, the two kinds of perturbation in the Earth's rotation can be treated independently. Simple expressions are given for the electromagnetic restoring torque on the accelerating mantle. The effect of the geomagnetic coupling on the diurnal wobble is discussed, and concluded to be negligible.View full abstractDownload PDF (1543K) -
Takesi YUKUTAKE1968 Volume 20 Issue 4 Pages 403-414
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSBased on the spherical harmonic analyses of the geomagnetic secular variation, the drift velocity of the earth's magnetic field is examined in three ways. In the first place, drift rates of phase angles of individual spherical harmonic components are calculated. Secondly the geomagnetic secular variations along parallel circles are expanded in Fourier series and drift velocities of harmonic components for various latitudes are estimated. Thirdly a rigid rotation is assumed for the westward drift of the secular variation along a parallel and the velocity is determined by calculating a correlation function between the distributions of the secular change at different epochs.
From these it has resulted in that there exists a dispersive relationship in the drift rate, at least between the harmonic component m=1 and m=2. The velocity of the westward drift is independent of the latitude except for a narrow zone near the equator, where an occasional eastward drift is observable.
It has been confirmed that the mean drift rate of the secular variation (0.3°/year for a rigid rotation model) is definitely larger than that of the non-dipole field itself (0.2°/year). The low mean velocity of the non-dipole field seems to arise from the coexistence of the stationary fields with the drifting ones.View full abstractDownload PDF (1096K) -
Tsuneji RIKITAKE, Yukio HAGIWARA1968 Volume 20 Issue 4 Pages 415-422
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSIn contrast to the non-steady states of a Bullard-Gellman dynamo model as studied in the previous paper ignoring the reaction to the fluid motion of the mechanical force of electromagnetic origin, a few examples of non-steady B-G model are studied taking the equation of motion coupled to the induction equation into account. The zonal flow is approximated by rotation of a rigid sphere in actual calculation. Computational difficulties are proved so serious that no results analogous to reversals of the geomagnetic field or the like are obtained. But it seems likely that the model is stable for a small disturbance.View full abstractDownload PDF (646K) -
A. I. I. ETTE1968 Volume 20 Issue 4 Pages 423-426
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
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T. YUKUTAKE1968 Volume 20 Issue 4 Pages 427-428
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
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R. W. JAMES1968 Volume 20 Issue 4 Pages 429-431
Published: December 20, 1968
Released on J-STAGE: March 12, 2010
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