Global Variations in GNSS-TEC During Storm Time Substorms on 23 December 2014

TEC disturbances have substantial impacts on communications and global positioning systems. Based on total electron content (TEC) observations from global navigation satellite systems and plasma observations from the Defense Meteorological Satellite Program, global variations in and mechanisms of the differential TEC (dTEC) during three successive substorms, which occurred on 23 December 2014 during the main phase of a geomagnetic storm, were investigated. The results show that TEC disturbances were not globally uniform but exhibited pronounced latitude and local time dependences. One prominent dTEC enhancement, reaching up to 25 TECU within 10 min, occurred over North America from the prenoon to dusk sector at subauroral and auroral latitudes, related to the ionization driven by particle precipitation and storm-enhanced density (SED) driven by an intensified convection electric field. Enhanced dTEC at high latitudes expanded to midlatitudes, forming the broad midlatitude SED, expanding poleward and developing a tongue of ionization (TOI), persisting for 100 min. In addition, over South America at premidnight, decreased dTEC at low latitudes and increased dTEC at equatorial latitudes with amplitudes of around 16 TECU were consistent with suppression of the equatorial ionization anomaly (EIA), driven by substorm-related westward prompt penetration electric fields (PPEFs). These results demonstrate that storm time substorms can simultaneously enhance and deplete TEC in different latitude and local time sectors through the combined effects of particle precipitation, convection electric fields, and PPEFs.