Interplanetary Shocks Inducing Magnetospheric Supersubstorms (SML < −2500 nT): Unusual Auroral Morphologies and Energy Flow

Overview & Synopsis

We present case studies of two interplanetary shock-induced supersubstorms (SSSs) with extremely high intensities (peak SML -4418 and -2668 nT) and long durations (similar to 1.7 and similar to 3.1 hr). The events occurred on 2005 January 21 and 2010 April 5, respectively. It is shown that these SSSs have a different auroral evolution than a nominal Akasofu-type substorm. The auroras associated with the SSSs did not have the standard midnight onset and following expansion. Instead, at the time of the SML index peak, the midnight sector was generally devoid of intense auroras, while the most intense auroras were located in the premidnight and postmidnight magnetic local times. Precursor energy input through magnetic reconnection was insufficient to balance the large ionospheric energy dissipation during the SSSs. It is argued that besides the release of stored magnetotail energy during the SSSs, these were powered by additional direct driving through both dayside magnetic reconnection and solar wind ram energy.