Development of Geomagnetic and Ionospheric Storms on July 8, 1958.
Nagai, M.
Abstract
An investigation was made on relation between the worldwide patterns of ionospheric storm and the corresponding current systems of geomagnetic storm which occurred at 07h 48m UT July 08, 1958.
Polar cap blackouts began to occur 30 hours before the sc. The horizontal component of the geomagnetic field was almost calm during 9 hours, until the whole polar cap region suffered from complete blackouts. And then, a sharp negative bay was formed suddenly at 21 hours before the sc, over the well-developed polar cap blackout region. These results seem to show some characteristics of polar geomagnetic disturbances in the case of the occurrence of fast onset type of PCA in this severe upper atmospheric disturbances.
The typical Pre-sc disturbance which was intensified with enhanced ionization in the midnight auroral zone was observed at 3 hours before the sc. The current pattern of the Spq-field resembles very much with that of the DP (Pre-sc) field, though the former is confined in the polar-cap area and there is no auroral zone enhancement of the currents.
After the sc, polar cap blackout developed its region to form the current system known as the initial phase. The polar cap blackout is known as the phenomenon caused by the invasion of highly energetic solar corpuscles without any appreciable geomagnetic disturbances. However, it is clarified that an apparent current system is already formed a few hours before the onset of a geomagnetic storm, the same as in the case of slow occurrence type PCA, which flows over the conductive region of polar cap blackout. Such a current system seems to be essentially identical with that of the initial phase, though it is strengthened and widened after the onset of the geomagnetic storm.
At the main phase, the ionospheric storm progressed to a world-wide scale; the regions of polar blackouts elongated to words the lower latitudes as the Dst field developed. It was shown that auroral currents at this stage, flowed over the conductive region of the disturbed lower ionosphere.
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