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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 drift. Also, the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite airglow instrument was used to unveil the changes in the neutral thermospheric 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 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.

The prompt penetration electric field (PPEF) drives the DP2 currents composed of the two-cell Hall current vortices surrounding the Region-1 field-aligned currents (R1FACs), and the zonal equatorial electrojet (EEJ, Cowling current) at the dayside equator, which is connected to the R1FACs by the Pedersen currents at middle latitudes. The midlatitude H- and D-components of the disturbance magnetic field are caused by the DP2 currents, as well as by the magnetospheric currents, such as magnetopause currents, FACs, ring currents, and so on. If the DP2 current is the major source for the midlatitude geomagnetic disturbances, H and D are supposed to be caused by the Hall and Pedersen currents, respectively. The H-D correlation would be negative in both morning and afternoon sectors, and H/D-EEJ correlation would be negative/positive in the morning and positive/negative in the afternoon. We picked out 39 DP2 events in the morning and 34 events in the afternoon from magnetometer data at Paratunka, Russia (PTK, 45.58° N geomagnetic latitude (GML)), which are characterized by negative H–D correlation with correlation coefficient (cc) < −0.8. We show that the midlatitude H/D is highly correlated with EEJ at Yap, Micronesia (0.38° S GML) in the same local time zone, meeting the Pedersen–Cowling current circuit between midlatitude and equator in the DP2 current system. Using the global simulation, we confirmed that the ionospheric currents with north–south direction at midlatitude is the Pedersen currents developing concurrently with the Cowling current. We suggest that the negative H-D correlation provides a clue to detect the PPEF when magnetometers are available at middle latitudes.

Observations made in non-equatorial regions appear to support the hypothesis that the daytime scintillation of radio signals at gigahertz (GHz) frequencies is produced by the gradient-drift instability (GDI) in the presence of a blanketing sporadic E (E sb ) layer. However, the only evidence offered, thus far, to validate this notion, has been some observations of E sb in the vicinity of GHz scintillations. A more comprehensive evaluation requires information about electric field, together with the presence of a steep gradient, which is presumed to be that of E sb . In this regard, the region in the vicinity of the equatorial electrojet (EEJ) appears to be an ideal “laboratory” to conduct such experiments. The dominant driver of electron drift there is the same as that of the EEJ, the vertical polarization electric field, and indications are that the presence of E sb in that vicinity is controlled by a balance in horizontal transport of E sb , between the EEJ electric field and the neutral wind, as described in a model by Tsunoda (On blanketing sporadic E and polarization effects near the equatorial electrojet, 2008). In this paper, we present, for the first time, results from a comprehensive study of daytime GHz scintillations near the magnetic equator. The properties, derived from measurements, are shown, for the first time, to be consistent with a scenario in which E sb presence is dictated by the Tsunoda model, and the plasma-density irregularities responsible for GHz scintillations appear to be produced by the GDI.

This study utilized magnetic field records of the horizontal component obtained from magnetic data acquisition system at northern island of Malaysia to delineate the diurnal variations of SqH and their monthly mean MSqH for a period of 4 years. The results show that for the entire period of study, the daytime SqH amplitudes increase from ∼20 to ∼160 nT and their MSqH amplitudes increased from ∼40 to about 135 nT in 2008 to 2013, respectively. These variabilities of SqH and MSqH reached peak amplitudes between 10:00 and 12:00 LT hrs. The standard deviation fairly responds to the daily variability of SqH with a phase shift in January 2008 and 2013 which may likely have connection to the sudden stratospheric warming event that occurred in these months. We observed the extension of eastward field that continued beyond the sunset (18:00 LT) hours is more prevalent with higher magnitudes during the deep minimum solar activity and the probable causes are discussed. The observed counter equatorial electrojet associated with late reversal of night-time westward electric field (WEF) shows inverse relationship with increasing solar activity and those that are not associated to late reversal of night-time WEF seems to indicate linear relationship exception of deep minimum solar activity year (2008). We also observed a gradual shift of ECEJ to the morning sector with increasing solar activity. Throughout the years, days with stronger morning counter equatorial electrojet magnitudes generally weaken the expected strong eastward current and shifted its peak to earlier local time. The annual and seasonal variations of SqH show semiannual variation with equinoctial maxima and solstitial minima. About 40% of the SqH shows positive night-time to pre-sunrise variations which suggest the existence of weak electric currents not necessarily of ionospheric origin with appreciable influence at this longitude sector. The extension of eastward field beyond the sunset hours suggests likely modification of the evening side ionosphere over this region.

The equatorial electrojet (EEJ) is a prominent eastward geomagnetic current flowing at the dayside magnetic dip equator, peaking just before noon. Associated meridional currents also flow perpendicular to the main current, predicted through modeling and observed in rocket measurements. While these currents help explain some of the observed intensity of the EEJ, any further relationship between the two currents is poorly understood. This research proposes that the intensification of the EEJ is at least partially due to this meridional current system. To explore this hypothesis, data from several ground magnetic stations near the dip equator in Southeast Asia was analyzed. Principal component analysis was used to isolate the signature of the proposed meridional current structure. The analysis revealed a signal corresponding to the proposed meridional current structure that was also linked to the intensification of the EEJ. Future efforts will focus on elucidating mechanisms for the observed current system.

This study uses multiple ground and satellite‐based measurements to investigate the extreme ionospheric response to the Mother's Day storm on May 10–11, 2024. Prompt penetration electric field caused a significant enhancement in the ionospheric vertical drift (∼${\\sim} $95 m/s) and the equatorial electrojet strength (∼${\\sim} $  275 nT) over Jicamarca. These extreme eastward electric field perturbations, along with the large meridional wind, significantly altered the F‐region plasma fountain at different local times. The afternoon equatorial ionization anomaly (EIA) not only sustained for an exceptionally long duration (∼${\\sim} $12 hr) but also expanded spatially over time. The separation between the two peaks of EIA crests exceeded ∼48°${\\sim} 48{}^{\\circ}$and ∼70°${\\sim} 70{}^{\\circ}$in the morning and evening sectors, respectively. This study shows, for the first time, that unusually strong EIA can not only develop at different local times but can also sustain for long duration under favorable conditions, which has implications for space weather applications. Plain Language Summary The Earth's upper atmosphere is significantly influenced by space weather events, particularly geomagnetic storms. In this study, we investigate the impact of an intense geomagnetic storm that occurred on 10–11 May 2024 (popularly known as Mother's Day storm) on the equatorial and low‐latitude ionosphere. Using datasets from various ground and satellites‐based (SWARM, and GOLD satellites, Global GNSS receivers, Incoherent Scatter Radar (ISR), Fabry‐ Perot interferometers (FPI), and magnetometer) measurements, we show the impact of extreme prompt penetration of electric field on the development of plasma fountain during the storm. We observe a significant increase in electron density and TEC during the main phase of the storm. Our findings highlight the role of extreme space weather disturbances on the generation of EIA at different local times and the impact of the plasma distribution on the globe. We also observe different types of electric field perturbations on low latitude ionosphere during this severe geomagnetic storm. Key Points The plasma fountain during the Mother's Day storm was unusually strong across different local time sectors The combined effects of a strong penetration electric field and meridional wind sustained the plasma fountains for an extended period The EIA crest over the Jicamarca sector merged with the expanded auroral region

While the isolated effects of solar flares on low‐latitude ionospheric electrodynamics have been well documented, the coupled system response of the equatorial electrojet (EEJ), auroral electrojet (AEJ), field‐aligned currents (FACs), and asymmetric ring current (ASY‐H) remains poorly understood. This study statistically analyzes 1,657 X/M‐class flares (2001–2017) to quantify rapid electrodynamic changes across current systems. Our results indicate (a) flare intensity‐dependent enhancements in eastward EEJ, suppressed equatorial ionospheric vertical drift (Vz), and increased ASY‐H; (b) negligible flare influence on AEJ; and (c) R2 FACs intensification in the dusk sector, linking ionospheric dynamics to asymmetric ring current perturbations. These observations reveal transient electrodynamic coupling within the geospace associated with flares, independent of solar wind forcing, advancing understanding of flare‐driven ionosphere‐magnetosphere interactions.

Substorms are known to induce global magnetosphere‐ionosphere coupling. However, the specific response of the dayside ionospheric electric field and its influence on the equatorial electrojet (EEJ) remain controversial. This study investigates the electromagnetic field response in the dayside equatorial region during isolated substorms using ground magnetic field data. Statistical analysis revealed that the H component decreased at equatorial and low‐latitude stations during isolated substorms. These decreases were of similar magnitude on average, indicating that significant changes in the EEJ caused by penetrating electric fields were not observed. However, individual events showed slight positive and negative variations. These results suggest that substorm‐associated electric fields can reach equatorial regions, but additional conditions determine the positive and negative variations. This finding provides new insights into the spatial extent of substorm‐induced electric fields.

Equatorial electrojet (EEJ) and solar quiet (Sq) currents with one vortex each in either hemisphere are key components of the ionospheric dynamo currents, driving geomagnetic diurnal variations observed at Earth's surface. However, the physical coupling between EEJ and Sq westward currents on the polar side of the vortex focus remains poorly understood. Here, we present observational evidence that there are significant correlations between EEJ variability and Sq westward currents variability in both morning and afternoon sectors, with correlation coefficients of −0.87 during March in the afternoon and −0.67 during May in the morning, respectively. The seasonal variations of the correlations exhibit a morning‐afternoon asymmetry. Specifically, the correlations in the afternoon are stronger during the hemispheric summer season, whereas in the morning correlations show a slightly semiannual variation that are stronger approximately during the equinoxes. The results are helpful for understanding of current closure and global ionospheric electrodynamics.