Ionospheric storm effects in the EIA region in the American and Asian-Australian sectors during geomagnetic storms of October 2016 and September 2017

Abstract

The interrelationships between a geomagnetic storm and Earth’s ionosphere are highly variable and complex. This paper studies the ionospheric storm effects (ISEs) and plasma redistributions in the American and Asian-Australian sectors during the geomagnetic storms of 13 October 2016 and 8 September 2017. The hourly NmF2 variations in the equatorial ionization anomaly (EIA) region and horizontal magnetic field (H) data in each sector were employed to unveil the plasma redistributions during the storms. The hourly analysis presents more revealing ISEs on EIA structures, showing evidence of sectorial difference during the two storms. During the SSC period, negative storm, NS, dominated as ISE around the magnetic equator, negative storm effects were less significant beyond the equator, and positive storm, PS, was significantly dominant at higher latitudes. During the main phase, the ionization is enhanced/depleted with time in the American/Asian-Australian sector for the 13 Oct. 2016 storm, and a reversed ISE is recorded for the 8 September 2017 storm. The ISE during the October 2016 storm, was negative at the equator and positive at the crest regions. However, these effects were reversed during the September 2017 storm in the American sector. The PS effect was more pronounced in the Asian-Australian sector than in the American sector in the northern hemisphere and was weaker near the equator. During the recovery phase, PS was dominant during the Oct 2016 storm in the American sector. NS was extensively observed during Sept. 2017 storm except for around 1200 – 2300 UT when PS was registered around the dip equator. The EIA structure is stronger with a noticeable PS impact in the American sector than it appears in the Asian-Australian sector during the storm of Oct. 2016. The differences in ISEs observed during the two storms could be attributed to differences in the properties of solar wind driver gases and associated ring current mechanisms. PPEF and DDEF are the primary causes of ISEs, but other storm-time forces were also discussed.