Equatorial Electrojet Currents Research Articles

Longitudinal variability of complexities associated with equatorial electrojet and its coupling with Solar Quiet Daily variation Sq field

The large-scale solar quiet (Sq) current and the Equatorial Electrojet (EEJ) current are two structures produced by electric current in the Earth’s ionosphere. For a long time, the characteristics of these two currents, particularly whether the EEJ is an extended portion of the Sq current has been a hot topic within the community. This study examined magnetic data obtained from ground-based magnetometers at 6 representative stations for the year 2009 and for geomagnetically quiet days (Ap⩽3). The selected stations are along the magnetic equator in the South America (Huancayo), Africa (Ilorin; Addis Ababa), and the Philippines (Langkawi, dip latitude -2.32°; Davao, dip latitude -1.02°; Yap, dip latitude -1.49°). Results showed that both current systems are complex, and this complexity varies significantly from one longitudinal station to another. The strongest and weakest complexity were found in Huancayo and Ilorin, respectively. Afterwards, using four entropy quantifiers (Phase synchronization, Mutual Information, Ensemble Symbolic Coupling Traces, and S-independence), this study examined the relationship between the EEJ and Sq currents. Results revealed clearly a significant information exchange between both currents; that is, the Sq and EEJ currents are indeed coupled. As a step further, using the transfer entropy approach, a directional investigation was carried out to ascertain the direction of information flow between the Sq and EEJ stations. Observations revealed that due to the weak coupling obtained over the African sectors, only the currents over these stations exchanged information. This study further discussed the possible physical mechanisms responsible for the identified variabilities.

Average Ionospheric Mid‐ and Low‐Latitude Currents From E‐ and F‐Region Altitudes, Derived by the Swarm Constellation

AbstractBy utilizing magnetic field measurements from the Swarm constellation during the years 2014–2019, average characteristics of the height‐integrated ionospheric zonal and meridional currents at middle and low latitudes are investigated. We provide for the first time the detailed dependencies of these currents on location, local time, and season. The main results obtained are: (a) Large parts of the ionospheric currents flow in the F‐region, particularly on the nightside and in the winter hemisphere. (b) Clearly outstanding zonal current is the equatorial electrojet (EEJ) around noon, accompanied by currents in opposite direction at middle latitudes. At night, eastward currents are prevailing in the summer hemisphere, and westward in winter. During equinox the nighttime zonal currents show a lot of hemispheric similarity, with westward currents around pre‐midnight and eastward currents post‐midnight at mid latitudes. These features can be attributed to the meridional thermospheric wind effects. (c) The meridional currents are weak at night, exhibiting a preferred direction toward the summer hemisphere. At daytime the meridional currents flow toward equator in the pre‐noon sector and opposite current directions prevail in the afternoon, which is consistent with the closing of the EEJ current circuit. Large hemispheric differences in meridional currents are found during December solstice, suggesting that most of the EEJ current is closed through the winter, northern hemisphere. (d) The zonal and meridional currents at middle latitude exhibit clear signatures of solar tides at daytime. Most prominent are the non‐migrating tidal components DE3 in the zonal currents and SW5 in the meridional.

Robust least square modelling for selected daytime ionospheric parameters using geomagnetic observations at low latitudes

The east–west electric field and the characterized horizontal configuration of the geomagnetic fields around the equatorial region cause electron redistribution in the ionospheric bottomside F- region. This electric field E in turn causes the flow of current in a narrow band around this region called Equatorial Electrojet (EEJ) current. The paper discusses the robust least square modelling approach for modelling some selected ionospheric profile parameters below the maximum height of the F2 layer from the computed EEJ values at Jicamarca station (12°S, 76.9 °W) in the Southern American sector and Ilorin (8.50°N, 4.68°E) in the West African sector. The modelled parameters are the maximum electron density, NmF2, the maximum height, hmF2 and the thickness parameter, B0 of the F2- layer which were then compared with the recent ionospheric international standard model (IRI-2016). The proposed new model for ionospheric parameters based on ground-based magnetic field data at specific locations improved the model fit for hmF2 with RMSE value ∼ 30 km, an improvement to the IRI hmF2 model options. In addition, the derived NmF2 model performs poorly as compared to the IRI URSI and CCIR model options for NmF2. The model was however able to reproduce the temporal changes in the NmF2, for example, the semi-annual variation in the observational NmF2 value. The specific local features that were not fully reproduced in the IRI B0 model options can be seen in the derived model.

Current Understanding of the Equatorial E x B Drift velocities in the African Sector: A Short Review

A short review of the pattern and morphology of the equatorial plasma drift velocities, particularly during the evening-time Pre-reversal enhancement (PRE) period in the African region had been presented. The seasonal PRE peak values across some locations in the West-African region were considered and compared with other sectors of the world. While most plasma drift observations in the African region were calculated from ionosonde measurements, the observations from other sectors involved direct measurement from satellite and the Incoherent Scatter Radar (ISR) observations. The importance of the PRE in ionospheric electrodynamics was highlighted, the better in the use of either the virtual or real heights of the F-layer in inferring vertical drift velocities were enumerated, revealing the strengths and weakness of each method. The general observations revealed that PRE peak magnitude is commonly weaker in the African region in comparison with the American/Peruvian and Indian sectors, seasonal and solar activity dependent, and could be higher during either magnetic quiet or disturbed activity than when both magnetic activity conditions are combined. The first work to present a regional PRE model around the African equatorial ionization anomaly region (Adebesin et al model) was mentioned. The relevance of the E × B drift in quantifying the daytime equatorial electrojet (EEJ) current was also discussed.

INVESTIGATING THE VARIATIONS OF HORIZONTAL (H) AND VERTICAL (Z) COMPONENTS OF THE GEOMAGNETIC FIELD AT SOME EQUATORIAL ELECTROJET STATIONS

This research is monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. It presents the variations of Horizontal (H) and vertical (Z) component of the geomagnetic field at some Equatorial Electrojet (EEJ) Stations during quiet days. Data from five (5) observatories along the magnetic equator were used for the study. Daily baseline values for each of the geomagnetic element 𝐻 and Z were obtained. The monthly average of the diurnal variation and the seasonal variations were found. Results showed that the variations of the geomagnetic element of both H and Z differ in magnitudes from one stations to another along the geomagnetic Equator due to the differences of their geomagnetic latitude. The Amplitude curves for Z) are seen to be conspicuously opposite to that of H), and there is absence of CEJ in Z- Component but present in H- Components. The values during the pre-sunrise hours are low compare to daytime hours. Minimum variations of dH was observed during June solstice and maximum variations was observed during Equinox season. This study shows that daily variations of (H) and (Z) occur in all the stations. The enhancement in H is as a result of EEJ current

INVESTIGATING THE VARIATIONS OF HORIZONTAL (H) AND VERTICAL (Z) COMPONENTS OF THE GEOMAGNETIC FIELD AT SOME EQUATORIAL ELECTROJET STATIONS

This research is monitoring equatorial geomagnetic current which causes atmospheric instabilities and affects high frequency and satellite communication. It presents the variations of Horizontal (H) and vertical (Z) component of the geomagnetic field at some Equatorial Electrojet (EEJ) Stations during quiet days. Data from five (5) observatories along the magnetic equator were used for the study. Daily baseline values for each of the geomagnetic element 𝐻 and Z were obtained. The monthly average of the diurnal variation and the seasonal variations were found. Results showed that the variations of the geomagnetic element of both H and Z differ in magnitudes from one stations to another along the geomagnetic Equator due to the differences of their geomagnetic latitude. The Amplitude curves for Z) are seen to be conspicuously opposite to that of H), and there is absence of CEJ in Z- Component but present in H- Components. The values during the pre-sunrise hours are low compare to daytime hours. Minimum variations of dH was observed during June solstice and maximum variations was observed during Equinox season. This study shows that daily variations of (H) and (Z) occur in all the stations. The enhancement in H is as a result of EEJ current.

Investigation on longitudinal and decadal variations of the equatorial electrojet using a physical model

A detailed investigation on longitudinal and decadal variations of general characteristics (amplitude, width, peak altitude) of the equatorial electrojet (EEJ) is carried out using a physics-based model of electrojet. A few important aspects that emerge from this investigation include (i) changes in the half-width of EEJ with longitude and it’s dependence on the rate of change of dip-angle with latitude, (ii) changes in EEJ strength as large as 10–20% over the Peruvian and Brazilian sectors from 1960 to 2020 associated with significant changes in the local geomagnetic field, (iii) wave-4 structure in the EEJ current density and integrated EEJ current. In addition, it is shown that the peak EEJ current density over different longitudes inversely depends on the strength of geomagnetic field. More importantly, relationships of EEJ parameters (such as half-width, peak current density, integrated current) with ionospheric electric field, electron density, and geomagnetic field are brought out. These relationships are verified using EEJ observations carried out earlier using sounding rocket and ground based magnetometers. This comprehensive account of the longitudinal and decadal variations of EEJ along with the expressions to calculate EEJ characteristics can be used in observational and modelling studies to understand the low-latitude ionospheric electrodynamics in greater detail.

Coordinated Ground‐Based and Space‐Borne Observations of Ionospheric Response to the Annular Solar Eclipse on 26 December 2019

AbstractThis paper studies the ionosphere's response to the annular solar eclipse on 26 December 2019, utilizing the following ground‐based and space‐borne measurements: Global Navigation Satellite System (GNSS) total electron content (TEC) data, spectral radiance data from the Sentinel‐5P satellite, in situ electron density and/or temperature measurements from DMSP and Swarm satellites, and local magnetometer data. Analysis concentrated on ionospheric effects over low‐latitude regions with respect to obscuration, local time, latitude, and altitude. The main results are as follows: (1) a local TEC reduction of ∼4–6 TECU (30–50%) was identified along the annular eclipse path, with larger depletion and longer recovery periods in the morning eclipse compared to midday. (2) The equatorial electrojet current was significantly weakened when the eclipse trajectory crossed the magnetic equator in the morning (India) sector, which contributed to large and prolonged TEC depletion therein. (3) At midday, equatorial ionization anomaly exhibited enhancements of 20–40% as well as poleward shifting of 3–4°, likely triggered by modified neutral wind and electrodynamics patterns. (4) The behavior of equatorial ionospheric electron density showed considerable altitudinal differences in the topside, exhibiting ∼30% reduction around 500 km and ∼30% enhancement with 300–500 K Te reduction around 850 km, before the arrival of maximum eclipse. This may have been caused by the enhanced eastward electric field and equatorward neutral wind, and other possible factors are also discussed.

Evolution of the Geomagnetic Daily Variation at Tatuoca, Brazil, From 1957 to 2019: A Transition From Sq to EEJ

AbstractThe magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long‐term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day‐to‐day variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet‐time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day‐to‐day variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long‐term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation.

English

Variations of equatorial electrojet (EEJ) in six Magnetic Data Acquisition System (MAGDAS) stations (four stations within the magnetic equator region and two stations outside the region) on the 210oMagnetic Meridian (MM) chain were examined. Data of hourly values of horizontal component of magnetic field, H in the year 2007 for Cooktown (CKT), Amami-oh-Shima (AMA), Davao (DAV), Langkawi (LKW), Yap- Island (YAP) and Cebu (CEB) were used in the study. The electrojet current was studied using both the estimation method and Fambitakoye simulation model to determine the correlation between their results. The strength of equatorial electrojet in the stations were estimated with respect to Cooktown (CKT; 15.48°N, 145.25°E), a station located outside the electrojet region. The maximum electrojet strength was observed in the month of March in Davao (DAV), Cebu (CEB) and Langkawi (LKW) with values of 107.5, 88.5 and 64.08 nT, respectively. The model simulation of EEJ current presents maximum values of 237.9, 207 and 160 nT in DAV, CEB and LKW, respectively in the same month. This result establishes a similarity in the performance of the methods but with higher values in the model performance. A linear correlation analysis between them showed average correlation coefficient values of 0.81 in Yap-Island (YAP), 0.84 in LKW, 0.6 in DAV and 0.54 in CEB. The data also show variability in EEJ, with results showing higher EEJ current magnitude for stations closer to the dip equator. The Root Mean Square Error (RMSE) was carried out to determine the suitability of the model for in the four seasons for each station. Result shows that the model performed better for March equinox in Cebu (3.58) and Yap-Island (5.97), December solstice (8.96) and September equinox in Davao and Langkawi (6.55), respectively. Key words: Equatorial electrojet, dip equator, magnetic data acquisition system (MAGDAS), Fambitakoye model, E-region, solar quiet.

Can the Comprehensive Model (CM4) predict global features of sudden commencements?

We investigate the capability of the Comprehensive model CM4 to predict features of geomagnetic sudden commencements (SCs) focusing on observations from five ground-based observatories along the African chain. A list of 153 SC events has been selected within the period 2011–2015 to compare between modelled and observed SCs at different seasons and local times. The study reflects the degree of consistency between the CM4 model and the real physics occurring at each ground station. It also compares the characteristics of observed and modelled SC field to show how well the model performs for predicting the SC field variation. Results of feeding the CM4 model by the SYMH index data shows that the CM4 model provides a reasonable fit of the observed SC field at stations located closer to the average latitude of Dst index stations. Positive SC field variations during the day and night times for both CM4 modelled and observed fields are expected to be a signature of the magnetopause and field aligned currents rather than the axial ring current. The dawn-dusk asymmetry of the SC modelled field, which resembles the observed field at stations located poleward of the equatorial region, reveals a significant contribution from the partial ring current. At the magnetic equator, the equatorial ionospheric electrojet current plays a significant role in enhancing the observed SC field during daytime hours, which is not parameterized in the CM4 model. The latitudinal profile of the modelled field exhibits its maximum variation at the magnetic equator, decreasing towards the poles. This latitudinal profile resembles the observed field but is weaker. The modelled field at the latitudes of the Dst index stations has the same local time features of the observed field, but its strength is much smaller than the observed field and also it does not exceed its corresponding SYMH variations. In addition, the modelled SC field has a weak smooth variation with respect to local time, unlike the broad scattering of the observed field. Despite the substantial correlation between the modelled SC field and its associated SYMH field variations, the model always under-estimates the SYMH variations even at the magnetic equatorial station. Also, the CM4 model has no information about the SC seasonal variation, even at stations located within the same latitudes of the Dst index stations. These limitations should be considered when using the CM4 model to describe the external magnetospheric field.

Effects of solar activity on ionospheric current system in the Southeast Asia region

The equatorial ionospheric current system is composed of equatorial electrojet (EEJ) and solar quiet (Sq) that flow in the eastward direction. That being mentioned, this study looked into the changes in ionospheric currents stemming from geomagnetic storm disturbances at different levels of solar activity during solar cycle 24. This analysis was performed by employing an EEJ index known as EUEL, which is calculated from northward geomagnetic component data measured using ground-based magnetometer at five different latitudes across the Southeast Asia region. Based on the outcomes, the impacts of geomagnetic storm on EEJ currents were observed at 1200 LT and 1100 LT, respectively, during high and low solar activity levels. Time delay was associated with changes in EEJ peak time at varied activity levels. This case study reveals that EEJ value at peak time of high solar activity decreased significantly during the main phase of geomagnetic storm.

Altitude of Two‐Stream Irregularities in Equatorial E Region Using Sounding Rocket Experiments From Thumba

AbstractAmplitudes of two‐stream irregularities and equatorial electrojet (EEJ) current are known to peak around the same altitude. Sounding rocket‐borne magnetometer experiments have consistently shown that the EEJ current density maximizes around 105‐km altitude whereas the theoretical models predict the EEJ peak around 100 km. One of the propositions to bridge this difference in the altitude has been based on the inclusion of small‐scale turbulence (wavelength of <100 m) with the large‐scale dynamics (kilometer size). This proposition is examined based on in situ measurements of E region electron density and plasma irregularities (two‐stream and gradient‐drift irregularities) obtained at different times of the day and night. These measurements were obtained based on sounding rocket flight experiments conducted from Thumba Equatorial Rocket Launching Station (8.54° N, 76.86° E), a facility in the vicinity of the dip equator. Whenever two‐stream irregularities are present, the minimum electrojet current density is estimated based on the threshold velocity required for generation of these plasma irregularities. This method provides estimates of nighttime E region current also, which is difficult to measure. It is found that amplitudes of both two‐stream irregularities and the estimated EEJ current peak around 105‐km altitude irrespective of the presence or absence of the gradient‐drift irregularities at the base of electrojet (95‐ to 100‐km altitude).

Effect of moderate geomagnetic storms on equatorial plasma bubbles over eastern Africa in the year 2012: Evolution and electrodynamics

Equatorial plasma bubbles (EPBs) are common features of the equatorial and low-latitude ionosphere and are known to cause radio wave scintillation which leads to the degradation of communication and navigation systems. Although these structures have been studied for decades, a full understanding of their evolution and dynamics remains important for space weather mitigation purposes. In this study, we present cases of EPBs occurrences around April and July 2012 geomagnetic storm periods over the African equatorial sector. The EPBs were observed from the Communications/Navigation Outage Forecasting System (C/NOFS) and generally correlated well to the ionospheric irregularities observed from the Global Positioning System total electron content (GPS-TEC) measurements (rate of TEC change, ROT). This study revealed that the evolution of the EPBs during moderate storms is controlled by the strength of the daytime equatorial electrojet (EEJ) currents regardless of the strength of the equatorial ionization anomaly (EIA), the latter is observed during the July storm case in particular. These effects were more evident during the main and part of the early recovery phases of the geomagnetic storm days considered. However, the evening hours TEC gradients between regions of the magnetic equator and ionization crests also played roles in the existence of ionospheric irregularities.

A Method of Estimating Equatorial Plasma Vertical Drift Velocity and Its Evaluation Using C/NOFS Observations

AbstractTo understand the dynamics of the equatorial ionosphere and mitigate its effect on radio wave propagation, vertical ion drift velocity empirical models have been developed using limited ground‐based and/or space‐based observations. These models, however, have not yet been validated in detail using recent observations for sufficiently different longitudinal sectors. In this paper we have evaluated the performance of two empirical models and also propose a simplified vertical drift velocity model based on basic physics laws (i.e., Ampere's and Ohm's laws) that we call it parameterized drift velocity (PDV) model. These models have been applied to estimate the E region electric field and the associated F region E × B drift velocity using observed horizontal magnetic fields, due to equatorial electrojet current, as model driver input. Drift velocities obtained from these models are compared with the Communication/Navigation Outage Forecasting System (C/NOFS) satellite in situ vertical drift observations for different longitudinal sectors. It is found, for all longitudinal sectors considered in this study, that the vertical drift velocity obtained from a model based on physics laws has shown better agreement with C/NOFS observations as compared to the outputs of other empirical models. Moreover, it is shown that the Anderson empirical model performs better than the International Reference Ionosphere model.

Occurrences of counter electrojets and possible ionospheric TEC variations round new Moon and full Moon days across the low latitude Indian region

Abstract The present paper investigates the alterations in ionospheric Total Electron Content (TEC) over a low latitude location Bangalore (Geographic latitude 12.9 ∘ N {12.9^{\circ }}\hspace{2.38387pt}\text{N} and longitude 77.6 ∘ E {77.6^{\circ }}\hspace{2.38387pt}\text{E} ; Geomagnetic latitude 4 . 5 ∘ N 4.{5^{\circ }}\hspace{2.38387pt}\text{N} ) in India, corresponding to the new Moon and full Moon days which are associated with abnormality in the eastward Equatorial Electrojet (EEJ) currents. It has been well established that even during certain geomagnetic quiet days, the EEJ current direction is reversed, resulting in a westward electrojet current called Counter Electrojet (CEJ) which is more prominent around the new Moon and full Moon days, favored by Sun–Moon–Earth alignments and lunar orbital characteristics. The Global Positioning System (GPS) derived TEC at Bangalore is investigated for full Moon and new Moon and their adjacent days during the period 2008–2015. The presence of CEJ during these days suggests the foremost role of driving EEJ current over the equator in the alterations of spatiotemporal distributions of TEC over the low latitude region. The deviations in quiet time TEC during new Moon and full Moon days are quantified in this study that may give a thrust towards modeling of lunar tidal effects in the flipped ionospheric parameter over the Indian region. The study would also support analysis of future solar eclipse effects on ionosphere those involve additional photoionization production/recombination processes corresponding to the passage of lunar shadow and cooling effects. Moreover, the results underpin modeling and mitigation of ionospheric error in the satellite-based positioning, navigation, and communication applications.

Response of Ionospheric Profile Parameters to Equatorial Electrojet Over Peruvian Station

AbstractThe response of the ionospheric bottomside electron density profile parameters of the F2 layer, namely, the maximum electron density (NmF2), the maximum height of F2 layer (hmF2), and bottomside thickness (B0) parameter to the equatorial electrojet (EEJ) current is examined for a Peruvian location at the Jicamarca station (12 °S, 76.9 °W) in the South American sector. The results of the analysis show that both hmF2 and B0 increase for ~2 h before sunrise and exhibit a postsunset peak during the equinoctial and summer months. The increase in the peak height, hmF2, is observed to terminate before midday, while B0 continued to increase throughout the daytime. The apparent midday and postnoon peaks in NmF2 occur in all the seasons under study. It was demonstrated that a relationship exists between EEJ and the profile parameters hmF2 and B0 during low and moderate solar conditions. Conversely, the correlation coefficient between EEJ and NmF2 is statistically significant only during solar minimum conditions but correlates poorly, if at all, with EEJ during moderate solar activity.

Variability of the African equatorial ionization anomaly (EIA) crests during the year 2013

This paper discusses the variability of the position and magnitude of the crests of African Equatorial Ionization Anomaly during noon and post sunset periods. Total electron content data covered the year 2013, and were obtained from a chain of global positioning system receivers in both hemispheres around 37°E longitude. Local magnetometer data were used to infer the direction and magnitude of the E × B drift, while the solar extreme ultraviolet proxy index was used as a measure of solar activity. It was found that the time of formation of both crests varied from 1400 to 1700 local time. Additionally, the position of the crests was found to be asymmetric with respect to the magnetic equator. During the noon period, the position of the northern and southern crests varied from 4.91° to 7.36° and −9.17° to −12.62°, respectively. During the post-sunset period, it varied from 8° to 11.7° and −9° to −16°, respectively. Seasonally, with reference to the magnetic equator, both crests moved poleward during equinoxes and collapsed towards the equator during winter and summer. Equinoxes recorded the greatest crest magnitude followed by winter then summer over both hemispheres during the noon period. However, this trend persisted over the northern crest only during the post-sunset period. Overall, during the noon period, we recorded correlation coefficients of 0.67 and 0.68 between crest magnitudes and ΔH, a proxy for equatorial electrojet current, and 0.88 and 0.81 between crest positions and ΔH, for the northern and southern crests, respectively. During the Halloween day storm of 30 October 2013, a westward electric field inhibited the development of the post-sunset crests.

Geomagnetically Induced Currents Caused by Interplanetary Shocks With Different Impact Angles and Speeds

AbstractThe occurrence of geomagnetically induced currents (GICs) poses serious threats to modern technological infrastructure. Large GICs result from sharp variations of the geomagnetic field (dB/dt) caused by changes of large‐scale magnetospheric and ionospheric currents. Intense dB/dt perturbations are known to occur often in high‐latitude regions as a result of storm time substorms. Magnetospheric compressions usually caused by interplanetary shocks increase the magnetopause current leading to dB/dt perturbations more evident in midlatitude to low‐latitude regions, while they increase the equatorial electrojet current leading to dB/dt perturbations in dayside equatorial regions. We investigate the effects of shock impact angles and speeds on the subsequent dB/dt perturbations with a database of 547 shocks observed at the L1 point. By adopting the threshold of dB/dt = 100 nT/min, identified as a risk factor to power systems, we find that dB/dt generally surpasses this threshold when following impacts of high‐speed and nearly frontal shocks in dayside high‐latitude locations. The same trend occurs at lower latitudes and for all nightside events but with fewer high‐risk events. Particularly, we found nine events in equatorial locations with dB/dt > 100 nT/min. All events were caused by high‐speed and nearly frontal shock impacts and were observed by stations located around noon local time. These high‐risk perturbations were caused by sudden strong and symmetric magnetospheric compressions, more effectively intensifying the equatorial electrojet current, leading to sharp dB/dt perturbations. We suggest that these results may provide insights for GIC forecasting aiming at preventing degradation of power systems due to GICs.

Effects of Electric Field and Neutral Wind on the Asymmetry of Equatorial Ionization Anomaly

AbstractThe zonal electric field and the meridional neutral wind are the principal drivers that define the geometry and characteristics of the equatorial ionization anomaly (EIA). Here we present the response of the EIA to the variability of the zonal electric field based on measurements of the equatorial electrojet (EEJ) currents and trans‐equatorial neutral winds for the generation and control of the asymmetries of the EIA crests of total electron content (TEC) in the western side of the South American continent. The EEJ strengths are determined using a pair of magnetometers. The 24‐hr trans‐equatorial neutral wind profile is measured using the Second‐Generation, Optimized, Fabry‐Perot Doppler Imager (SOFDI) located near the geomagnetic equator. The EIA is evaluated using TEC data measured by Global Positioning System (GPS) receivers from the Low‐Latitude Ionospheric Sensor Network and several other networks in South America. A physics‐based numerical model, Low‐Latitude Ionospheric Sector, and SOFDI data are used to study the effects of daytime meridional neutral winds on the consequent evolution of an asymmetry in equatorial TEC anomalies during the afternoon and onward for the first time. We find that the configuration parameters such as strength, shape, amplitude, and latitudinal width of the EIAs are affected by the eastward electric field associated with the EEJ under undisturbed conditions. The asymmetries of EIA crests are observed more frequently during solstices and the September equinox than in the March equinox season. Importantly, this study indicates that the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. This result suggests that a precise observation of the latitudinal TEC profile at low latitudes can be used to derive the meridional wind.