Sq current system during stratospheric sudden warming events in 2006 and 2009

Ionospheric Sq current systems during unusually strong and prolonged stratospheric sudden warming (SSW) events in January 2006 and January 2009 are examined by analyzing ground-magnetometer data for the American and Asian longitude sectors. During these SSW events, a significant decrease and increase of the Sq equivalent current intensity are observed in the Northern and Southern Hemispheres, respectively, along with a reduction in the longitudinal separation between the northern and southern current vortices. Numerical experiments using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General-Circulation Model show that changes in the solar anti-symmetric (2,3) semidiurnal tide can bring about similar changes in the Sq current system.