During the sudden stratospheric warming (SSW) event in 2013, we investigated the American low latitude around 75°W. We used 12 Global Positioning System (GPS) receivers, a pair of magnetometers, and the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite airglow instrument to unveil the total electron content (TEC), inferred vertical drift, and the changes in the neutral composition, respectively. A major SSW characterized the 2013 SSW event with the main phase (7–27 January 2013) overlapped by a minor geomagnetic storm (17 January 2013). The late morning inferred downward‐directed E X B drift did not support the varying equatorial ionization anomaly (EIA) signature during the SSW onset (7 January 2013). The mid‐January (15–16 January 2013) witnessed enhancement in the varying inferred upward‐directed E X B drift at both hemispheres. On 17 January 2013, there were reductions in the varying inferred upward‐directed E X B drift at both hemispheres. Generally, the SSW effect on TEC around 15–16 January 2013 is more pronounced than the SSW onset. During the mid‐January (15–16 January 2013), the higher northern EIA crests are facilitated majorly by the SSW compared to the photo‐ionization that primarily enabled the southern crests. On 17 January 2013, the combined effect of photo‐ionization and SSW contribution was majorly responsible for the slight reduction in the northern crest. In the southern hemisphere, photo‐ionization played the lead role as the SSW, and the minor geomagnetic storm roles are secondary in enhancing the southern crest.

Scintillation and total electron content (TEC) are the two major examples of the top-side ionospheric parameters that are recorded differently by most Global Positioning System (GPS) receivers. The new GPS sensor created by the Atmospheric and Space Technology Research Associates (ASTRA), Cornell University, and the University of Texas, Austin have capability to record scintillation and TEC fluctuations simultaneously. Hence, the Connected Autonomous Space Environment Sensor (CASES) from ASTRA is a software-defined GPS receiver with the dual frequency of L1 C/A and L2C codes for space-weather monitoring and can be remotely programmed via an internet source. The receiver employs numerous novel techniques that make it suitable for space-weather studies compared to other nearby GPS receivers, such as different methods for eliminating local clock effects, an advanced triggering mechanism for determining scintillation onset, data buffering to permit observation of the prelude to scintillation, and data-bit prediction and wipe-off for robust tracking. Moreover, the CASES hardware is made up of a custom-built dual frequency, a digital signal processor board, and a “single board computer” with an ARM microcontroller. We have used the CASES GPS receiver newly installed at Bowen University, Iwo, Nigeria, to investigate the TEC and the rate of the TEC index (ROTI) around the equatorial region. Measurements of the TEC and ROTI showed similar variation trends in monthly, seasonal, and annual periods when compared to TEC and ROTI measurements from a nearby station, BJCO at Cotonou, Benin Republic. The newly installed GPS receiver looks promising for scientific use as it is the only one operational in Nigeria at the moment.

This study investigates the response of the Asian‐Australian low‐latitude ionosphere to the 2013 Sudden Stratospheric Warming (SSW) event. The equatorial ionization anomaly structures were built from the latitudinal distribution of Total Electron Content (TEC) measured from 10 Global Positioning System receivers along 115°E in the Asian‐Australian sector. A pair of magnetometers and NASA Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite airglow instrument were also employed to measure the equatorial electrojet strength (inferred E × B drift) and to unveil the changes in the neutral thermospheric O/N₂ ratio during the SSW event, respectively. The relocation of the northern crests to higher latitudes during the SSW compared to the non‐SSW periods was mainly attributed to the combined effect of enhanced magnetometer‐inferred upward‐directed E × B drift and increasing solar flux. The local time shift in the thermospheric O/N₂ ratio, a slight enhancement in the magnitude of the semi‐diurnal magnetometer‐inferred upward‐directed E × B drift, and changes in solar flux were primarily responsible for the hemispheric TEC enhancement during mid‐January compared to SSW onset. Additionally, the photo‐ionization effect due to increasing solar flux further enhances the TEC magnitude during the relaxing phase. On the other hand, the strong thermospheric equatorward wind played a crucial role in moving the plasma to lower latitudes during the zonal wind transition phases. A moderate geomagnetic storm of 17 January 2013 did not perturb the Asian‐Australian ionosphere. However, on 18 January 2013, the storm had a significant impact and greatly diminished the effect of the SSW.

In this study, the Total Electron Content (TEC) variability over Asian-Australian low-latitude sector is investigated during the 2013 Sudden Stratospheric Warming (SSW) event that overlapped with a moderate geomagnetic storm. These investigations are about the latitudinal distribution of ionospheric TEC measured from 10 Global Positioning System (GPS) receivers along 115° E in the Asian-Australian sector. We used a pair of magnetometers to reveal the equatorial electrojet (EEJ) strength equivalent to the magnetometer-inferred \(E \times B\) drift. Also, the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite airglow instrument was used to unveil the changes in the neutral thermospheric \({{\text{O}} \mathord{\left/ {\vphantom {{\text{O}} {{{{\text{N}}}_{2}}}}} \right. \kern-0em} {{{{\text{N}}}_{2}}}}\) ratio during the event. The current work was compared with a similar investigation in the American sector. During SSW onset (7 January 2013), the northern EIA crest that moved poleward in the Asian-Australian sector contradicted the equatorward movement of the crest observed in the American sector. At both the Asian-Australian and American longitudes in mid-January, the poleward northern crests are at higher latitudes in the American longitude than in the Asian-Australian longitude. This longitudinal difference in mid-January was evident in significant enhancement of the magnetometer inferred upward-directed \(E \times B\) drift in the American sector compared to the Asian-Australian sector. Compared to the American sector, the moderate geomagnetic storm that overlapped the ongoing major SSW on 17 January 2013 did not significantly affect the Asian-Australian sector. The storm-time effect on the TEC on 18 January 2013 in the Asian-Australian sector reduced (increased) the SSW (photo-ionization) effect in the northern (southern) hemisphere.

This study delved into the response of the equatorial ionosphere in the South American region to the geomagnetic storm in September 2017. Six global positioning system (GPS) receivers, positioned along 45° W and 70° W, were utilized to estimate the daily variation of total electron content (TEC). A pair of magnetometers measured the strength of the equatorial electrojet (EEJ) (inferred E × B drift), and the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite revealed changes in the thermospheric neutral composition before, during, and after the geomagnetic storm on September 8, 2017. The pre-storm effect and occurrence of solar flares, accompanied by solar bursts are responsible for the significant enhancement in TEC magnitudes days prior to geomagnetic storm event. However, the significant enhancement observed in the TEC magnitude during the main phase of the geomagnetic storm was primarily driven by DP2 (disturbance polar number 2), created by the daytime prompt penetration of electric field (PPEF) signature. Other mechanisms responsible for this enhancement included the increase in thermospheric neutral composition, O/N₂ ratio, and more ionization of electrons due to the increase in solar flux. Furthermore, the drastic increase in the amplitude of the morning-afternoon magnetometer-inferred upward-directed E × B drift during the main phase of the storm, compared to the quiet periods, was attributed to the magnetic signature (DP2) due to PPEF. Additionally, the inhibition of ionospheric irregularities at the equatorial ionosphere during the main phase of the geomagnetic storm may be associated with the storm-time occurrence.