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Volume 48, Issue 2
Displaying 1-6 of 6 articles from this issue
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W. Baumjohann, Y. Kamide, R. Nakamura1996 Volume 48 Issue 2 Pages 177-185
Published: February 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSMore than 50, 000 measurements made with the AMPTE IRM satellite in the magnetotail at radial distances between 10 and 19 RE during 40 substorms have been used in a super-posed epoch analysis, separating storm-time substorms from those occurring during intervals of low Dstt levels. It is found that most of the tail signatures reported previously as typical for substorms are strongly influenced by magnetic storm activity. The magnetic field dipolarization and the Earthward convection in the near-Earth tail are much more pronounced for substorms which occur during the main phase of magnetic storms than for non-storm substorms. Moreover, only for storm-time substorms the lobe magnetic pressure decreases during the expansion phase. These findings indicate that not all substorms are alike and that the near-Earth neutral line scenario may apply only to the storm-time substorms.View full abstractDownload PDF (1762K) -
Keith D. Cole1996 Volume 48 Issue 2 Pages 187-210
Published: February 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSA theory of equatorial thermosphere-ionosphere-plasmasphere (magnetosphere) disturbances creating field aligned irregularities is extended here. Further development is given of the hypothesis of the transfer of electrostatic fields and currents from the B-region dynamo to the conjugate F-region, topside ionosphere, and plasmasphere, involving field-aligned currents. Conditions are found such that dynamo action in the ionosphere controls the formation of large-scale magnetic field-aligned irregularities. Sporadic-E layers involving Fe+, and/or other long-lasting ions, may play a special role in the process. General conditions are found under which the discharge of ionospheric currents across the geomagnetic field in the magnetosphere is a significant factor. An energy analysis is conducted of the processes involved in the formation of the irregularities. This suggests that there is a large class of equatorial ionosphere-plasmasphere irregularities whose source of energy is in the conjugate -regions. Alternatively stated, winds and gravity waves in the conjugate point B-regions are a significant source of energy for the equatorial F-region and topside plasmasphere where it is dissipated as joule heat, viscous heating and compressional heating of plasma followed by heat conduction in the neutral gas. Dynamo processes in the conjugate B-regions are a significant source of energy also for the nightside equatorial thermosphere at F region and higher altitudes.View full abstractDownload PDF (5596K) -
Lalmani, Altaf Ahmad, Rajesh Singh1996 Volume 48 Issue 2 Pages 211-220
Published: February 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSParticular emphasis is laid on the application of whistlers recorded at low latitude ground station, Nainital during magnetically quiet times to estimate the eastward/westward electric field in the plasmasphere. The east-west components of electric field during quiet magnetic (average Kp = 1) are obtained for the first time from low latitude station on the basis of the available whistler data on March 7, 1971 (ΣKp = 8) in the 01:22 to 03:21 IST sector and 22:10 to 23:20 IST sector, April 18, 1971 (ΣKp = 19-) in the 22:15 to 23:44 IST sector and April 19, 1971 (ΣKp = 15) in the 01:26 to 03:31 IST sector. During above quiet times in the whistler activity period, a decrease in dispersion with time is observed. The method of measuring electric field from the observed cross-L motion of whistler ducts within the plasmasphere, indicated by changes in nose frequency of whistlers has been outlined. The nose frequency of the non-nose whistlers under consideration have been deduced by means of an accurate curve fitting method as developed by Tarcsai (1975). Our measurements demonstrate an average estimated electric field of ∼0.06 mVm-1 in the premidnight local time sector and an average westward electric field of ∼0.05 mVm-1 in the post-midnight local time sector. These values are in good agreement with similar results reported by earlier workers. Near midnight there is a sharp transition from eastward field to westward electric field. The electric fields during quiet days at low latitudes are thought to be generated by the dynamo mechanism.View full abstractDownload PDF (2053K) -
L. R. Newitt, C. E. Barton1996 Volume 48 Issue 2 Pages 221-232
Published: February 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSIn the spring of 1994, a survey was carried out to redetermine the position of the North Magnetic Pole (NMP). Observations of declination, inclination, and total intensity were made at eight sites around the expected location of the pole. All observations were corrected for transient variations using data from a variometer set up in the survey area, and data from magnetic observatories at Mould Bay and Resolute Bay. The NMP position was determined by performing a spherical cap harmonic analysis of the corrected data. The computed position of 78.3°N, 104.0°W for 1994.0 was 150 km northwest of the position previously determined in 1984, and showed that the NMP was moving more rapidly than anticipated. The motion of the NMP has changed from a uniform drift of about 9 km/yr, prior to mid-1971, to a uniform acceleration of approximately 0.34 km/yr2, after mid-1971. This change may be related to the widely-reported geomagnetic jerk that occurred in 1969/70.View full abstractDownload PDF (2115K) -
Kazuo Saito, Koichi Kato1996 Volume 48 Issue 2 Pages 233-246
Published: February 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSA detailed K-Ar and 40Ar-39Ar geochronological study was conducted on the Kinpu-san body, which is a part of the Kufu plutonic complex. We collected a sample from every 3 km × 3 km area in the body. The chronological study based on this high density sampling clearly illustrates that the body systematically becomes younger from north to south. The oldest age in the body could be considered to restrict the initiation time of the Philippine Sea plate subduction. Thus, we conclude that the subduction started 16 Ma age at latest. Previous paleomagnetic studies have revealed that the adjacent region north of the Kanto Mountains rotated 60° clockwise between 15 Ma and 12 Ma. Our data demonstrate that the Kinpu-san body cooled during this same interval. Hence, the Kinpu-san body is a candidate for providing information about the severe deformation accompanied with the collision between the Izu-Bonin and Honshu arcs.View full abstractDownload PDF (2461K) -
H. W. Dosso, J. Chen, C. J. Bromley1996 Volume 48 Issue 2 Pages 247-255
Published: February 20, 1996
Released on J-STAGE: May 25, 2007
JOURNAL FREE ACCESSThe geomagnetic coast effect is known to comprise a major component in magnetic field observations at coastal sites. As the New Zealand South Island is relatively narrow, significant induction effects of the surrounding oceans are expected at most on-land sites. Interpretations of the observations as the responses of anomalous conductors would be simplified if these coast effects were not present. In this work, the removal of the coast effects at sites on the South Island is accomplished by subtracting analogue model coast effect induction arrows from the field site induction arrows. With the coast effects removed, the resulting difference induction arrows at some of the 26 sites would appear to be attributable to the induction responses of some of the sedimentary basins and faults, structures that were not included in the analogue model simulations.View full abstractDownload PDF (30160K)
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