Case Studies of Ionospheric Effects of Stratospheric Sudden Warmings

Recent studies have shown large variations in low-latitude ionospheric electron density occurring after stratospheric sudden warming event. We use observations of GPS total electron content data in the Western Hemisphere for winters of 2009, 2008, and 2003 to illustrate main features of ionospheric changes related to stratospheric sudden warmings. The common feature in all events is the increase in the electron density during the morning hours and the decrease in the afternoon, related to amplification of 12-hour signature in low-latitude vertical ion drifts. This feature persists for several days after the peak in stratospheric temperature. As stratospheric warming event subsides, the feature shifts to later local times, indicating a phase shift in the 12-hour wave. Non-linear interaction of planetary waves with tides leading to increase in the amplitude of semidiurnal tide at low latitude lower thermosphere and modulation of E-region electric field with subsequent mapping along the magnetic field lines to the F-region is thought to be the primary mechanism responsible for the observed ionospheric response.