Solar wind-magnetosphere energy coupling during supersubstorms

Supersubstorms (SSSs) are intense auroral zone geomagnetic activity associated with extremely intense westward auroral electrojet currents&#160; (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 &#8220;typical&#8221; substorms. SSSs are the primary causes of intense geomagnetically induced currents (GICs) at the M&#228;nts&#228;l&#228; 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&#8217;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 &#8764;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.