Solar wind-magnetosphere energy coupling during supersubstorms

Supersubstorms (SSSs) are intense auroral zone geomagnetic activity associated with extremely intense westward auroral electrojet currents  (SML < -2500 nT). The nightside SSS onsets and auroral evolution were found to be substantially different than the Akasofu (1964) standard picture of auroral development for “typical” substorms. SSSs are the primary causes of intense geomagnetically induced currents (GICs) at the Mäntsälä gas pipeline, Finland, determined from a 21-year data study. From a statistical study of SSSs triggered by interplanetary shocks, during solar cycles 23 and 24, solar wind-magnetosphere energy coupling will be discussed. Magnetospheric shock compression greatly strengthens the upstream interplanetary magnetic field southward component, and thus, through magnetic reconnection at the Earth’s dayside magnetopause, greatly enhances the solar wind energy input into the magnetosphere and ionosphere during the SSS events. The additional solar wind magnetic reconnection energy input supplements the ∼1.5 hr precursor (growth-phase) energy input and both supply the necessary energy for the high-intensity, long-duration SSS events. The major part of the SSS energy is dissipated into Joule heating, distributed equally in the dayside and nightside ionosphere, giving a picture of the global energy dissipation in the magnetospheric/ionospheric system, not simply a nightside substorm effect.