Earth’s magnetotail variability during supersubstorms (SSSs): A study on solar wind–magnetosphere–ionosphere coupling

Abstract

Supersubstorm (SSS) events are associated with extremely intense westward auroral electrojet currents (the minimum SuperMAG AL or SML <-2500nT) resulting from the solar wind-magnetosphere coupling. We present, for the first time, variability of the Earth’s magnetotail and coupling from the solar wind to magnetotail, geosynchronous orbit and auroral ionosphere during the SSS events. Five intervals with multiple SSSs were identified when the Cluster spacecraft was well inside the inner magnetotail. The SSS events are found to be characterized by turbulent magnetotail plasma sheet and injection of energetic (∼100eV to ∼100keV) electrons and protons. Injection of energetic protons from the plasma sheet causes electromagnetic ion cyclotron waves that lead to pitch angle scattering of the outer radiation belt MeV electrons and loss to the atmosphere during the SSSs. The SSS events are found to be associated with interplanetary magnetic clouds characterized by slowly varying interplanetary magnetic fields. An overall increase in the turbulence is recorded from the solar wind to the inner magnetosphere-ionosphere system during the SSSs. From the wavelet and cross-wavelet analyses, the inner magnetosphere and ionosphere are found to respond quasi-periodically at ∼1.5-4hours, and sporadically at shorter timescales of ∼0.5-1.5hours.