First observations of poleward large‐scale traveling ionospheric disturbances over the African sector during geomagnetic storm conditions

Abstract

This paper presents first observations of poleward traveling ionospheric disturbances (TIDs) during strong geomagnetic conditions over the African sector. By analyzing different data sets we have observed both positive and negative ionospheric responses during the storm period of 08–10 March 2012. Considering the African region as a whole, three longitudinal sectors were strategically selected to establish the entire regional response. On both sides of the geomagnetic equator, results show poleward shift in peak total electron content (TEC) enhancements/depletions at different times which are associated to large‐scale TIDs. The observed phenomena are linked to the global ionospheric response and electrodynamics. The understanding has been established using data from International GNSS Service receiver network, radio occultation electron density profiles, derived E×B drift measurements from magnetometer observations and regional ground‐based and satellite data. Contrary to other related studies, generated regional TEC perturbation maps were not enough to show obvious directions of the large‐scale TIDs due to insufficient data over the northern hemispheric part of the African sector. There appears to be a switch between positive and negative storm phases during the same storm period especially in the Southern Hemisphere part of the African region where “enough” data were available. However, a detailed analysis revealed that the positive storm phase corresponded to the expansion of the equatorial ionization anomaly (EIA) toward some parts of midlatitude regions (and possibly with the contribution from low‐latitude electrodynamics associated to equatorial electrojet), while the other part recorded a negative storm phase due to storm‐induced changes from the auroral origin. We have observed a simultaneous occurrence of both poleward and equatorward propagating TIDs over the African sector during the same geomagnetic storm period. Our results show that short‐lived large‐scale TIDs are possibly launched by the equatorial electrojet, while the EIA expansion contributes (through modulation) to the poleward propagation of the disturbances. Temporal variation of TEC perturbations on a storm day over the entire African sector showed the existence of large‐scale TIDs during the main and recovery phases which can travel poleward up to 20° latitude. The amplitudes of the TIDs have range ±2 total electron content unit, 1 TECU = 1016 el m−2, period of 2 h and virtual velocities of 250 ± 59–750 ± 95 m/s in midlatitude regions and up to 990 ± 65 m/s within the EIA region.

Simultaneous storm time equatorward and poleward large‐scale TIDs on a global scale

“…TIDs originating from the geomagnetic equator during storms have been rarely reported, despite having been suggested and numerically shown by Chimonas [1969]. A link to direct observational evidence of poleward TIDs was recently presented in a region with sparse instrumentation over the low latitude region [Habarulema et al, 2015].…”

“…It has been previously shown that JULIA daytime vertical velocities agree well with F-region Incoherent Scatter Radar (ISR) observations [Chau and Woodman, 2004], and JULIA data is therefore a reliable dataset to provide a picture of the local time electrodynamics over Jicamarca during the period under consideration. First observational results showing possible poleward TIDs were first reported by Habarulema et al [2015] over the African sector putting forward the dynamics of EEJ as the primary mechanism through Lorentz forcing. We wish to restate that possibilities of EEJ's role in driving poleward TIDS were first suggested and numerically shown by Chimonas [1969].…”

Unexpected Southern Hemisphere ionospheric response to geomagnetic storm of 15 August 2015

“…Several decades of ionospheric studies have shown that the ionospheric response to geomagnetic storms can differ above different locations (Yizengaw et al, 2005;Pirog et al, 2006a, b;Habarulema et al, 2013;Buresova and Lastovicka, 2017). Due to the relatively dense global coverage of Global Navigation Satellite System (GNSS) receivers, measurements of the total electron content (TEC) are nowadays used as a key parameter to study the ionospheric response to geomagnetic storms (e.g., Borries et al, 2016;Habarulema et al, 2015;Horvath and Lovell, 2015;Liu et al, 2016) and to describe an impact of the state of ionization of the Earth's upper atmosphere on the radio wave propagation conditions, which is crucial for terrestrial and Earth-space communications. The results of (Yin et al, 2004) demonstrated the potential of the two-dimensional tomographic methods extended to three-dimensional timedependent imaging and applied to ground based GPS observations, which allows GPS data to be used for large-scale studies of the ionosphere under very disturbed geomagnetic conditions.…”

Dynamic Response of Ionospheric Plasma Density to the Geomagnetic Storm of 22‐23 June 2015

“…However, there has been a growing number of studies that identify these poleward TIDs (e.g., Ding et al, 2013;Habarulema et al, 2015;Habarulema et al, 2017;Jonah et al, 2018;Zakharenkova et al, 2016, and references therein). However, there has been a growing number of studies that identify these poleward TIDs (e.g., Ding et al, 2013;Habarulema et al, 2015;Habarulema et al, 2017;Jonah et al, 2018;Zakharenkova et al, 2016, and references therein).…”