Abstract
This chapter presents observations of periodic substorms under different solar wind conditions and describes that periodic substorms can occur during stable or fluctuating interplanetary magnetic field (IMF). It also discusses the possible role played by the solar wind in the generation of substorms and the interpretation of the observations. The substorms last continuously for many cycles over an interval of up to 24 hours when the IMF is stable and does not show any northward turnings. When the IMF fluctuates rapidly between southward and northward, the substorms still occur every ∼3 hours and do not follow the rapid northward turnings of the IMF. A solar wind pressure impulse may play a role in triggering the first cycle of the periodic substorms while the substorms continue after the solar wind pressure has become stable. Each cycle of the substorms does not have to be triggered by a solar wind pressure impulse or by an IMF northward turning. The observations show that the period of substorms is not determined directly by variations in the solar wind. The merging rate between the IMF and magnetospheric magnetic field during strongly southward IMF is significantly different from that during small and fluctuating IMF, so the period of substorms is not determined indirectly by the energy transferred to the magnetosphere from the solar wind.
Published Version
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