Magnetic storms and the Van Allen radiation belts-Observations from satellite 1958ε (Explorer IV)

Abstract

The changes in intensity of charged particles measured with two Geiger counters carried in Explorer IV, between 270 and 2200 km above the earth's surface in August and September 1958, were analyzed. During magnetic storms marked decreases in the intensity of trapped charged particles were observed above about 1000 km, at the friages of the outer Van Allen belt over North America and Australia; at lower altitudes, where little trapped radiation is usually observed, the Geiger counting rates increased underneath the outer zone at magnetically disturbed times. After the great magnetic storm of September 4- 5, 1958, there was a significant increase in the average energy of particles trapped in the outer zone. No changes of intensity of particles in the inner Van Allen belt were detected during the period of observation except after nuclear enplosions. It is suggested that the intensity decreases observed from Explorer IV in the outer radiation zone are due largely to increased scattering and absorption of trapped charged particles produced by atmospheric heating and expansion at fairly high latitudes during magnetic storms. The intensity increases observed at low altitudes beneath the outer zone are probably due to particles scattered down from the trapping region above.more » The average particleenergy increase in the outer Van Allen belt after a strong magnetic storm may be due either to injection of energetic particles from the sun into the trapping zone or to some acceleration process connected with the magnetic disturbance. The absence of noticeable intensity changes in the inner Van Allen belt argues in favor of a cosmic-ray albedo neutron rather than a solar origin of inner-zone protons, particularly since there was considerable solar activity during August and September 1958. (auth)« less