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Geophysical Monograph Series




Morphology and some interpretation of geomagnetic variations in Antarctica

Takesi Nagata

Geophysical Institute, University of Tokyo, Tokyo, Japan

Geomagnetic charts over the Antarctic area are constructed based on all available data. The geomagnetic field strength in this area is appreciably smaller (by about 3 pct) than the value expected heretofore. According to analysis of recent geomagnetic secular variation in this area, the above-mentioned smallness of the geomagnetic strength is caused by a remarkably large rate of the secular variation in this area. In addition to the generally large rate of geomagnetic secular decrease, there are very strong local variations, which could be attributed to breaking out of a toroidal magnetic field system near the Earth core's surface beneath this area.
Generally speaking, geomagnetic activities in the southern polar region are well correlated with those in the northern one, the correlation coefficient being about 80 pct. It has been found, however, that there is remarkable geomagnetic variation in the sunlit polar cap even on geomagnetically quiet days, this new phenomenon being called solar radiation control of geomagnetic activity in the polar region. Geomagnetic variations at geomagnetic conjugate points in the north and the south polar regions are very well correlated to each other. It seems likely that the elementary corpuscular beam impinging on the north and the south polar regions simultaneously has dimensions of about 400 km in the N-S direction and 2000 km or more in the E-W direction.
The DS-current system over the Antarctic area can be considered just as a mirror image of that over the Arctic area with respect to the geomagnetic equatorial plane.
According to the results of observations of geomagnetic variation and relevant upper atmospheric phenomena in the southern auroral zone, there are very close connections amongst the magnitude of geomagnetic disturbances, auroral luminosity, sporadic ionization and black-out of the ionosphere. Most of the observed phenomena and their interrelations seem to be explained consistently by considering that a stream of electrons of 1 to 102 KeV in energy and of various flux intensities conies down to the auroral zone ionosphere, and by accepting the observed empirical law that the magnitude of the geomagnetic variation is proportional to that of the increase in the electric conductivity there owing to the anomalous ionization.

Citation: Nagata, T. (1962), Morphology and some interpretation of geomagnetic variations in Antarctica, in Antarctic Research: The Matthew Fontaine Maury Memorial Symposium, Geophys. Monogr. Ser., vol. 7, edited by H. Wexler, M. J. Rubin, and J. E. Caskey Jr., pp. 89–110, AGU, Washington, D. C., doi:10.1029/GM007p0089.


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