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Volume 41, Issue 5
Displaying 1-5 of 5 articles from this issue
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C. A. ONWUMECHILI, P. C. OZOEMENA, C. E. AGU1989 Volume 41 Issue 5 Pages 443-459
Published: 1989
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSLandmark values of the equatorial electrojet: the minimum intensity Jm A·km-1, its distance xm km and ratio to maximum intensity Jm/J0; the magnetic field constant K nT; the maximum northward magnetic field X0 nT, and the distance of zero northward magnetic field wX km; the minimum northward magnetic field Xm nT, its distance um km and ratio to maximum northward field Xm/X0; the vertical magnetic field Z0 nT at the dip equator and the distance of zero vertical field wZ km; the maximum vertical magnetic field ZM nT, its distance uM km and ratio to maximum northward field ZM/X0; have all been derived from September equinox satellite data and they compare favourably with their values from ground-based data. Our Jm/J0 agrees excellently with MUSMANN and SEILER (1978) and ANANDARAO and RAGHAVARAO (1979); while our xm agrees excellently with the location of CAHILL's (1959) westward current, and the findings of MUSMANN and SEILER (1978). The landmark distances xm, wX, um, uM, wZ and the ratios Jm/J0, Xm/X0 and ZM/X0 do not vary with longitude but the intensity Jm and magnetic fields, K, X0, Xm, Z0 and ZM have maxima around 90°E, 180°E and 270°E; and minima around 155°E and 225°E.View full abstractDownload PDF (1391K) -
C. A. ONWUMECHILI, C. E. AGU, P. C. OZOEMENA1989 Volume 41 Issue 5 Pages 461-467
Published: 1989
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSFrom the correlations of seven landmark distances, s, of the equatorial electrojet with its peak eastward current intensity J0 and its space gradient dJ0/ds, we find that the entire electrojet current system, with its magnetic field, tends to contract; consequently, the current and magnetic field foci, as well as contours of equal current intensity or of equal magnetic field, move towards the magnetic dip equator as the electrojet intensity increases. Furthermore, for a given increase in intensity, the greater the landmark distance the greater its contraction; and for movement of unit distance, the nearer the position to the dip equator the greater the increase in intensity required. Three causes which possibly contribute to the contraction are briefly discussed.View full abstractDownload PDF (573K) -
Masahiko TAKEDA, Yuji YAMADA1989 Volume 41 Issue 5 Pages 469-478
Published: 1989
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSA quasi two-day variation is determined from SdI in the geomagnetic field in the interval from May to August, 1958. Two peaks are found in the power spectrum at 45 and 58 hours in period. The amplitude of the 58 hour period variation increases with geographic latitude and the phase is almost the same at the observatories used in both hemispheres. A calculation of the geomagnetic field variation from winds antisymmetric with the geographic equator reproduces the observed distribution of the amplitude. However, the calculation shows that the phase is the same in both hemispheres except that it is reversed at certain meridians, while the observational results indicate the same phase everywhere.View full abstractDownload PDF (870K) -
Constraints on the Time of Lateral Bending of the Kanto SyntaxisMasaki TAKAHASHI, Satoshi NOMURA1989 Volume 41 Issue 5 Pages 479-489
Published: 1989
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSPaleomagnetic directions have been determined on Late Miocene diorite bodies in the Kanto Mountains in an effort to clarify the timing of lateral bending of the Kanto Syntaxis. A mean paleomagnetic direction (D=3.5°, I=64.4°, α95=5.1°) of the Chichibu Quartz Diorite, obtained from 21 samples, shows no significantly deflected declination. This indicates no tectonic rotation of the Kanto Mountains since intrusion of the Chichibu Quartz Diorite (6-8Ma). This result signifies that the cusp in the pre-Neogene zonal structure (Kanto Syntaxis) was formed in the Late Miocene or earlier.View full abstractDownload PDF (979K) -
Kin-ichiro KOIZUMI, Jiro SEGAWA, Hiroaki TOH, Jose L. OUBINA CARRETERO ...1989 Volume 41 Issue 5 Pages 491-506
Published: 1989
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSIn order to examine the instability of the three-component ocean bottom magnetometer, we have developed an ocean bottom proton magnetometer and made comparison measurements at the sea floor using both fluxgate and proton magnetometers. The comparison was made in 1987 at 30°57′.1N, 140°39′.1E near the Izu-Bonin Arc. We were able to obtain data from this measurement for as long as 77 days with two-minute sampling intervals. Although we tried to install the two meters as close together as possible, it was later found that the separation between the two meters was 487m. The difference in the absolute value between the fluxgate and the proton magnetometer was approximately 100nT, which may have been caused by the difference of the sites of installation. The result of comparison as to long-term changes shows that the three-component vector magnetometer used for the comparison was unstable for a few days after installation and then stabilized, and that the drift rate during the stable period was not larger than 0.27nT/day.View full abstractDownload PDF (1936K)
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