Phenomenology of the low-latitude ionosphere during northern winter and association with sudden stratospheric warmings

Abstract:

Large number of recent studies has demonstrated strong anomalies in the low-latitude ionosphere during sudden stratospheric warmings (SSW) that occur primarily during the northern winter period (December-February). Such events occurred with unusually high frequency during the last decade, making it possible to take advantage of increasingly available GPS TEC data to make significant progress in studies of atmosphere-ionosphere coupling. We focus on the American longitudinal sector, where good quality GPS TEC data is available for extended period of time, and examine three wintertime (November – February) periods marked by major sudden stratospheric warmings, 2005/06, 2008/09, and 2012/13. The selected events represent wide variety of stratospheric and geophysical conditions, including a vortex-shift (wave 1) SSW during solar minimum (2005/06), vortex-split (wave 2) SSW during extreme solar minimum (2008/09), and vortex-split (wave 2) SSW during moderate-to-high solar activity. To clearly separate ionospheric anomalies associated with SSW from other types of variations, we also examine the winter of 2006/07, which was characterized by less disturbed middle atmosphere. Comparison of ionospheric disturbances for three SSW cases shows remarkably consistent response to all events, albeit with varying magnitude. This response has primarily a tidal character and lasts for extended period of time. WACCM-X simulations of these events demonstrate amplification in global tidal energy for all major tides (diurnal, semidiurnal, terdiurnal), with strongest enhancement of semidiurnal tide.