The current study aims at investigating and identifying the ionospheric effects of the geomagnetic storm that occurred during 17–19 March 2015. Incidentally, with SYM‐H hitting a minimum of −232 nT, this was the strongest storm of the current solar cycle 24. The study investigates how the storm has affected the equatorial, low‐latitude, and midlatitude ionosphere in the American and the European sectors using available ground‐based ionosonde and GPS TEC (total electron content) data. The possible effects of prompt electric field penetration is observed in both sectors during the main phase of the storm. In the American sector, the coexistence of both positive and negative ionospheric storm phases are observed at low latitudes and midlatitudes to high latitudes, respectively. The positive storm phase is mainly due to the prompt penetration electric fields. The negative storm phase in the midlatitude region is a combined effect of disturbance dynamo electric fields, the equatorward shift of the midlatitude density trough, and the equatorward compression of the plasmapause in combination with chemical compositional changes. Strong negative ionospheric storm phase is observed in both ionosonde and TEC observations during the recovery phase which also shows a strong hemispherical asymmetry. Additionally, the variation of equatorial ionization anomaly as seen through the SWARM constellation plasma measurements across different longitudes has been discussed. We, also, take a look at the performance of the IRI Real‐Time Assimilative Mapping during this storm as an ionospheric space weather tool.

The present work investigates ionospheric effects of the 21 August 2017 total solar eclipse, particularly targeting eclipse‐generated gravity waves in the ionosphere. Ionospheric total electron content (TEC) derived from Global Positioning System (GPS) data obtained from a number of stations located both along and across the path of eclipse totality has been utilized for this purpose. Distinct gravity wave‐like signatures with wave periods around 20–90 min (with dominant peak at 25–30 min wave period) have been observed at all locations both in the path of totality and away from it. The observed gravity waves are more intense at locations closer to the path of totality, and the wave amplitudes decrease gradually with increasing distance from the path of totality. Our result highlights the manifestation of eclipse‐generated waves in the variability of the terrestrial ionosphere.

An alternative scenario to the Ngwira et al. (2014, https://doi.org/10.1002/2013JA019661) high sheath densities is proposed for modeling the Carrington magnetic storm. Typical slow solar wind densities (~5 cm−3) and lower interplanetary magnetic cloud magnetic field intensities (~90 nT) can be used to explain the observed initial and main phase storm features. A second point is that the fast storm recovery may be explained by ring current losses due to electromagnetic ion cyclotron wave scattering.

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The present study investigates the effect of the major sudden stratospheric warming (SSW) event of 2009, on the small‐scale gravity wave (GW) activity in the ionosphere. Small‐scale fluctuations with time periods within the range of 10–90 min observed in Global Positioning System total electron content (TEC) data have been used as a proxy for GW activity in the ionosphere. TEC data from five longitudinally separated Global Positioning System stations located around 60∘N latitude have been utilized for this purpose. In the initial phase of the major warming, when the stratospheric conditions are similar to a minor warming during which the mean zonal flow starts to weaken, the ionopsheric GW activity tends to increase. However, during the peak phase of the SSW, as the zonal mean wind starts to reverse its direction, and after the peak warming, as the winds remain weak, conditions are less favorable for upward propagation of a spectrum of GWs, and thus the ionospheric GW activity is reduced, as seen from the behavior of the small‐scale TEC fluctuations during the latter period of the SSW. Similar reduction in GW activity is also observed in the middle atmosphere (65–100 km) as seen from GWs derived from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature profiles. The reductions in GW activity is more prominent during local daytime as compared to nighttime period. The reduction in GW activity shows a longitudinal variation with some locations showing relatively more reduction in the GW activity as compared to others.