Magnetic storm inflation in the evening sector

Previous studies have indicated that the development of magnetic storms commences with an asymmetric inflation of the magnetosphere in the evening and afternoon sectors due to entry there of protons into the closed field lines from L= 7 to L = 3 [Akasofu and Chapman, 1964; Cahill, 1966, 1970; Cummings, 1966; Langel and Cain, 1968; Frank, 1967]. The Explorer 45 satellite was launched into the evening quadrant in November 1971 to investigate further, with an expanded inventory of field and particle observations, the development and subsequent stages of magnetic storms. In December 1971, there was, conveniently, a double magnetic storm; ground records are shown in Figure 1. The two periods of magnetic disturbance are quite different in appearance.