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Volume 32 (1980)
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Volume 33, Issue 10
Displaying 1-3 of 3 articles from this issue
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J. A. JACOBS1981 Volume 33 Issue 10 Pages 527-529
Published: 1981
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSMajor changes in the frequency of reversals of the Earth's magnetic field over the last 150myr are shown to occur at times when there are changes in the heat flow. This provides further evidence that certain processes in the upper mantle and those in the outer core may be coupled.View full abstractDownload PDF (234K) -
Hidefumi WATANABE1981 Volume 33 Issue 10 Pages 531-543
Published: 1981
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThe non-steady state of a simplified hydromagnetic αω-dynamo is investigated. The hydromagnetic α-effect is derived by taking into consideration Coriolis, Lorentz and viscous forces, based on a simple, nearly homogeneous and isotropic turbulence. The nonuniform rotation is also taken to be non-stationary and subjected to the above forces.
Numerical calculations of the initial value problem of the αω-dynamo equations have revealed that the dipole field undergoes relatively gradual variations and occasional polarity changes similar to the geomagnetic reversals. The reversal of the dipole field is caused essentially by the disruption of the non-uniform rotation. The time required for a complete decay of the dipole field is estimated to be about 3, 000 years which is consistent with paleomagnetic observations.
By taking into account the electrical conductivity of the bottom part of the mantle, electromagnetic coupling of the mantle to the core has also been studied. It is found that the field reversal is accompanied by the acceleration of the rotational speed of the mantle, and a change in l. o. d. of 95 msec.View full abstractDownload PDF (1178K) -
Goesta WOLLIN, William B. F. RYAN, David B. ERICSON1981 Volume 33 Issue 10 Pages 545-567
Published: 1981
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSMagnetic intensity and temperature data from 29 pairs of magnetic observatories and weather stations in the Northern Hemisphere were compared. Of these, 27 pairs lag correlate. The study covers mainly the period from 1935 to 1975. Annual surface air temperatures were used and both annual absolute values and rate of change values of horizontal component (H) and total intensity component (F) were plotted. Absolute values of H and F when plotted did not correlate with the temperature curves. Twenty-five curves of variations in the rate of change of H lag correlate with paired temperature curves. The 25 curves of variations in the rate of change of F based on data from the same observatories do not correlate with the temperature changes at the paired weather stations. Two curves of the variations in the rate of change of F based on data from two magnetic observatories lag correlate with the temperature records from nearby weather stations. No correlation was found between the records from 2 magnetic observatories and paired weather stations. The lag in temperature trends against magnetic variation ranges from 1 to 3 years. The correlation is inverse; that is, increase in the rate of change of magnetism is followed by decrease in temperature and vice versa. Statistically significant correlations between magnetic variations and temperature changes are reported. Neither the temperature curves nor the magnetic curves correlate with the sunspot number curve. We present two mechanisms which may be responsible for a relationship between annual ariations in the rate of change of magnetic intensity and those of surface air temperature.View full abstractDownload PDF (1964K)
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