Abstract
The time variations of D s and D st for the geomagnetic storm of 4 September 1958 have been calculated using hourly values of the horizontal component of the geomagnetic field over the world. These D st and D s have been compared with the observation of the earth's exosphere by Explorer IV and that of auroral radio echoes during the same period, During this geomagnetic storm marked decrease in the intensity of trapped radiations was observed in the outer zone and brilliant auroral displays were observed at latitudes well below the auroral zone. The time variations of D s at geomagnetic latitudes of 57–58° have indicated the largest deviation of all ones at other latitudes. All peaks of D s at high latitudes and auroral radio echoes at Jodrell Bank occurred for the main phase of this geomagnetic storm. The time variations of D s at low latitudes have shown only a little deviation and have been almost relatively unvariable compared with ones at high latitudes during the geomagnetic storm. From the analyses of D s at high latitudes it is deduced that the exospheric region within the inner boundary of the outer zone, where is is located along the geomagnetic lines of force intersecting the earth's surface at geomagnetic latitudes of about 50°, was not so much disturbed by the invasion of solar plasma cloud. It is considered that the dumping of part of the contents of the outer earth's exosphere, which interprets well the reduction in the intensity of trapped radiations in the outer exosphere, produces regions of comparatively high ionization which are detectable as auroral radio echoes and D s of geomagnetic disturbances. It has been shown that the time variations of D s at the auroral and the sub-auroral zones represent reasonably well the extent of disturbance of trapped radiations in the outer exosphere during the geomagnetic storm. The equatorward shifting of latitude of the maximum strength of chorus and hiss during the geomagnetic storm may be due to the inaction of generation mechanism of v.l.f. emissions in the exospheric region where the geomagnetic lines of force intersecting the auroral zone pass through during the geomagnetic quiet period, in addition to the equatorward shifting of precipitation of auroral particles during the geomagnetic storm. Statistical results of v.l.f. emission suggest that the electron density distribution given by the gyrofrequency model may not exist along the geomagnetic lines of force intersecting the earth's surface at the auroral zone during the geomagnetic storm. D st at the auroral zone has shown larger deviation from the prestorm level for the main phase, sharper recovery after the main phase, and earlier recovery for the recovery phase than ones at the middle and the equatorial zones. This slow and late recovery of equatorial D st and small variation of equatorial D s may support the existence of the equatorial ring current around the earth. A simple model of the state of earth's exosphere during the main phase of the storm has been proposed.
Published Version
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