Equatorial Ionization Anomaly Crest Research Articles

Temporal Variability of Equatorial Ionization Anomaly Crest Locations Extracted From Global Ionospheric Maps

AbstractThe Equatorial Ionization Anomaly (EIA) crest location is known to vary over a variety of temporal scales. For the first time we perform a statistical survey of the temporal variation of the EIA crest location viewed globally and spanning 20 years. We extract the crest location for double‐peaked EIAs from a data set of total electron content intensifications identified on global ionospheric maps from 2003 to 2022. We show that the dominant temporal variations of the crest latitude are annual and semi‐diurnal for the northern crest, and annual and diurnal for the southern crest. For the annual variation, we find that both crests move poleward in local summer and equatorward in local winter, which is more pronounced for the southern crest than the northern crest, and more pronounced at solar minimum than solar maximum. For the diurnal and semi‐diurnal variations in universal time, both crests dip southward around 15UT and the northern crest additionally dips southward around 2.5UT. We consider apparent universal time dependence to be a proxy for the longitudinal distribution of the crest geomagnetic latitude, which exhibits the known wave‐number‐four longitudinal structure of EIA crests. In local time, the EIA crests form earlier than 10LT and move poleward to their maximum distance at 14LT, and remain at constant latitude until 18LT. Solar cycle modulation on the diurnal/semi‐diurnal variations and the local time evolution of the crest latitude is minimal.

Variability of the equatorial ionization anomaly over the South American sector: Effects of electric field and effective meridional wind

Vertical Total Electron Content (VTEC) Maps over the South American Continent were utilized to investigate the temporal and longitudinal climatology of Equatorial Ionization Anomaly (EIA) using more than 350 Global Navigation Satellite Systems (GNSS) receivers. At a temporal resolution of 10 min, the EIA motions, morphologies, and evolutions were mapped using VTEC keogram along magnetic meridians lines. Between 2014 and 2019, characteristics of the EIA were studied at two different South American magnetic meridians (i.e., 3.36° E and 7.58° E) separated by ∼555 km at an altitude of 300 km. The aim of this study is to examine the EIA’s variability, monthly variations and occurrences at evenly spaced longitudinal sectors. The effects of effective meridional winds component and E × B drift velocity on the daytime asymmetry of EIA anomalies were studied using a physics-based numerical model, Sheffield University Plasmasphere-Ionosphere model at Instituto Nacional de Pesquisas Espaciais (SUPIM-INPE). We found that the EIA parameters such as strength, shape, intensity, and latitudinal positions are affected by the eastward electric field and effective meridional wind. The monthly variations in the EIA over two magnetic meridian sectors demonstrate a semiannual variation. The EIA crests were more symmetric in equinox than in solstice seasons. The asymmetries of the EIA observed during the December solstice are more intense than during the June solstice, whereas September equinox is less symmetric than March equinox seasons. Moreover, this study indicates that the vertical drift and the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. There was a notable contraction of the EIA southern hemispheric (SH) crests from the December solstice to the June solstice. Meanwhile, the EIA crest positions in the northern hemisphere (NH) expand from the December solstice to the June solstice. According to our observations, the March equinox season had the most EIA occurrences, which were then followed by the September equinox, the December and June solstices. The intensities of the EIA crests also considerably decreased with solar descending phases. Through modeling, this work provides the scientific community with new insights into the evolution/development of EIA and their latitudinal asymmetry, as well as the role of E × B drift and thermospheric neutral wind in assessing the statistical analysis of EIA variability using the largest VTEC database over the South American sector.

The X‐Pattern Merging of the Equatorial Ionization Anomaly Crests During Geomagnetic Quiet Time

AbstractA unique phenomenon—A geomagnetically quiet time merging of Equatorial Ionization Anomaly (EIA) crests, leading to an X‐pattern (EIA‐X) around the magnetic equator—has been observed in the night‐time ionospheric measurements by the Global‐scale Observations of the Limb and Disk mission. The pattern is also reproduced in an ionospheric model that assimilates slant Total Electron Content from Global Navigation Satellite System and Constellation Observing System for Meteorology, Ionosphere, and Climate 2. A free‐running whole atmospheric general circulation model simulation reproduces a similar pattern. Due to the similarity between measurements and simulations, the latter is used to diagnose this heretofore unexplained phenomenon. The simulation shows that the EIA‐X can occur during geomagnetically quiet conditions and in the afternoon to evening sector at a longitude where the vertical drift is downward. The downward vertical drift is a necessary but not sufficient condition. The simulation was performed under constant low‐solar and quiescent‐geomagnetic forcing conditions, therefore we conclude that EIA‐X can be driven by lower‐atmospheric forcing.

The Third Plasma Density Peak at Poleward of EIA Crest: Swarm and ICON Observations

AbstractIn this study, we focus on the presence of the ionospheric third plasma density peak associated with the equatorial ionization anomaly (EIA) based on observations from the ESA's Swarm constellation. By statistically analyzing the third peaks observed by the Swarm A and B at two different altitudes, we found that such structure appears mainly around ±20° magnetic latitude (Mlat), namely the poleward of the EIA crests. In the meanwhile, the third peak shows prominent season and local time dependences, that are mainly observed in the summer hemisphere during solstice seasons and with the highest occurrence in the afternoon hours. However, no clear solar flux and magnetic activity dependences are found. By further analyzing the simultaneous neutral wind measurements from the ionospheric connection explorer satellites, we found that the summer‐to‐winter hemispheric meridional wind is responsible for causing the third peak as well as its seasonal dependence (higher occurrence in the summer hemisphere). In addition, the third‐peak structure shows prominent longitudinal dependence. In regions where the magnetic declination directs eastward, it has a larger occurrence in the southern hemisphere, while in regions where the magnetic declination reverses, it has a larger occurrence in the northern hemisphere. Such a longitudinal dependence suggests that the zonal wind, which has a magnetic field‐aligned component at favorable magnetic declination regions, contributes also to the formation of the third‐peak structure.

Controlling Factors of the Seasonal Variation of the Latitudinal Location of the Equatorial Ionization Anomaly Crest

AbstractThe latitudinal location of the Equatorial Ionization Anomaly (EIA) crest has seasonal variation, and there are disagreements on the interpretation of such seasonal characteristic in previous studies. Some studies suggested that this seasonal characteristic is determined by the seasonal characteristic of the equatorial electric field. Others suggested that this seasonal characteristic is determined by the seasonal changes of the thermospheric wind. The current paper uses Total Electron Content (TEC) data and the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) to analyze the seasonal variation of the northern EIA crest in the eastern Asian sector under low solar activity. Our results show that the monthly averaged latitudinal location of the northern EIA crest has a good linear relationship (r = 0.74) with the monthly averaged Equatorial Electrojet (EEJ) intensity, which is a commonly used proxy of the eastward electric field. However, TIEGCM simulations with and without F‐region wind indicate that such a relationship might be attributed to wind effects. Additionally, the linear relationship between the EEJ intensity and the northern‐southern EIA crest distance is not significant (r = 0.47) in the eastern Asian sector. Our results suggest that a good correspondence between the eastward electric field and the latitudinal location of the EIA crest is not assured annually, as the seasonally varying F‐region wind significantly influences EIA evolution.

IonosphericTotal Electron Content Changes during the 15 February 2018 and 30 April 2022 Solar Eclipses over South America and Antarctica

This is one of the first papers to study the ionospheric effects of two solar eclipses that occurred in South America and Antarctica under geomagnetic activity in different seasons (summer and autumn) and their impact on the equatorial ionization anomaly (EIA). The changes in total electron content (TEC) during the 15 February 2018 and 30 April 2022 partial solar eclipses will be analyzed. The study is based on more than 390 GPS stations, Swarm-A, and DMSP F18 satellite measurements, such as TEC, electron density, and electron temperature. The ionospheric behaviors over the two-fifth days on both sides of each eclipse were used as a reference for estimating TEC changes. Regional TEC maps were created for the analysis. Background TEC levels were significantly higher during the 2022 eclipse than during the 2018 eclipse because ionospheric levels depend on solar index parameters. On the days of the 2018 and 2022 eclipses, the ionospheric enhancement was noticeable due to levels of geomagnetic activity. Although geomagnetic forcing impacted the ionosphere, both eclipses had evident depletions under the penumbra, wherein differential vertical TEC (DVTEC) reached values <−40%. The duration of the ionospheric effects persisted after 24 UT. Also, while a noticeable TEC depletion (DVTEC ∼−50%) of the southern EIA crest was observed during the 2018 eclipse (hemisphere summer), an evident TEC enhancement (DVTEC > 30%) at the same crest was seen during the eclipse of 2022 (hemisphere autumn). Swarm-A and DMSP F18 satellite measurements and analysis of other solar eclipses in the sector under quiet conditions supported the ionospheric behavior.

Dynamic Processes Associated With Prominent Ionospheric Variations in a Narrow Longitudinal Zone Near the EIA Crest Region as Revealed by ICON Satellite and Ground Beidou Receiver Observations Over South Asia

AbstractNeutral winds and plasma motions from the Ionospheric Connection Explorer mission were used to investigate dynamic processes associated with large regional total electron content (TEC) differences in a narrow longitudinal zone exceeding ∼45 TECU obtained from dense Beidou geostationary receivers at low latitudes over South Asia. The TEC east‒west asymmetry was defined to quantify this difference, which exceeded ∼5 TECU per 1° longitude distance and occurred around the equatorial ionization anomaly (EIA) crest on 31 March 2021 under geomagnetically quiescent conditions. Moreover, the magnetic meridional ion velocity exhibited a large longitude difference around the EIA crest during periods with strong ionospheric east‒west asymmetry. Furthermore, the longitude difference variation was consistent with the TEC east‒west asymmetry variation during 11–21 March 2020 and 27 March–4 April 2021. No significant correlations between TEC east‒west asymmetry and longitude differences under conditions with neutral winds and magnetic zonal ion drifts were observed in either case. The different vertical plasma drifts could contribute to ionospheric changes with a zonal range of a few hundred kilometers.

Effects of the Relative Dynamics of Ionospheric Irregularities and GPS Satellites on Receiver Tracking Loop Performance

AbstractTransionospheric satellite signals are exposed to perturbation, caused by irregularities generated in the ionosphere. However, the characteristics of the satellite motion can have an additional impact on signal perturbation, in addition to the effects of irregularity structures, that drift from west to east during geomagnetic quiet conditions. This paper reports the effect of Global Positioning System satellite geometry, on tracking loop performance of ground‐based receivers, during occurrence of ionospheric scintillations. Observations are made from station Calcutta (22.58°N, 88.38°E geographic; magnetic dip 34.54°), located near the northern crest of Equatorial Ionization Anomaly, during three different solar activity periods (March 2014, March 2015, and March 2022). Efforts have been made to study the correlation of east‐west component of satellite velocity at Ionospheric Pierce Point (IPP) with duration of loss‐of‐lock and rate of signal fading (<−10 dB), from ground scintillation pattern observations. Results of this study show 75%–78% correlation between duration of loss‐of‐lock and eastward component of satellite velocity, for all three period of observation. Subsequently, shorter duration of loss‐of‐lock has been observed corresponding to satellite velocity being westward. Signal fading rate is found to decrease with increasing satellite velocity, having median value of the fading rate cumulative distribution percentage, corresponding to satellite velocity of 16.69, 31.76, and 19.14 m/s respectively during March 2014, March 2015, and March 2022. Results of this study also indicate direction and component of satellite velocity at IPP to be a dominant cause of signal outage, even during periods of weak to moderate scintillations.

Response of the ionosphere to equatorial electrojet at latitudes near the northern EIA crest in the East African longitudinal sector

Equatorial Electrojet (EEJ) and Equatorial Ionization Anomaly (EIA) are two distinct ionospheric phenomena which are caused by the horizontal configuration of the geomagnetic field at the equator. On the day side of the earth, these activities are controlled by a common zonal electric field, and their interactions must be researched for a number of scientific reasons. In this study, we used multiple Global Navigation Satellite System (GNSS) stations at Al Wajh, Sola village, Nama, and Sheba in 2012 to investigate the correlations between the instantaneous and integrated equatorial electrojet (EEJ) and the variations of vertical total electron content (vTEC) at the northern crest of EIA in the East Africa and Middle East longitudinal sector. The equinoctial and solstitial months have the highest and lowest values of the monthly mean EEJ and vTEC, respectively, and as a result, both parameters show a semi-annual variability. The monthly mean vTEC also demonstrates equinoctial and solstitial asymmetries, resulting in vTEC values that are higher at the September equinox and the December solstice than at the March equinox and the June solstice, respectively. These asymmetries have been also observed in the composition of [O]/[N2] ratio. On days with strong counter electrojet (CEJ), EEJ peaks are smaller and occur later than on days with weak CEJ. Additionally, when CEJ is high, EIA is suppressed and vTEC exhibits low values at all crest points. In the early hours (10:00–12:00 Lt), Nama and Sheb showed higher correlation coefficient values with significant levels than Alwj and Sola. According to the correlation analysis, the anomaly crest develops at the lower latitude stations between 10:00 and 12:00 Lt and then moves to the higher latitude stations later. Generally, the correlations are higher and more significant in the equinoxes than the solstices. The correlations between integrated EEJ (IEEJ) and vTEC were also found to be strong and significant at the lower latitude stations throughout all seasons. These findings suggest that both the instantaneous and integrated EEJ can be used as a proxy for the eastward zonal equatorial electric field and must be considered in regional and global models of total electron content of equatorial and low latitude ionosphere.

Significant Mid‐ and Low‐Latitude Ionospheric Disturbances Characterized by Dynamic EIA, EPBs, and SED Variations During the 13–14 March 2022 Geomagnetic Storm

AbstractThis work investigates mid‐ and low‐latitude ionospheric disturbances over the American sector during a moderate but geo‐effective geomagnetic storm on 13–14 March 2022 (π‐Day storm), using ground‐based Global Navigation Satellite System total electron content data, ionosonde observations, and space‐borne measurements from the Global‐scale Observations of Limb and Disk (GOLD), Swarm, the Defense Meteorological Satellite Program (DMSP), and the Ionospheric Connection Explorer (ICON) satellites. Our results show that this modest but geo‐effective storm created a number of large ionospheric disturbances, especially the dynamic multi‐scale electron density gradient features in the storm main phase as follows: (a) The low‐latitude equatorial ionization anomaly (EIA) exhibited a dramatic storm‐time deformation and reformation, where the EIA crests evolved into a bright equatorial band for 1–2 hr and then quickly separated back into the typical double‐crest structure with a broad crest width and deep equatorial trough. (b) Strong equatorial plasma bubbles (EPBs) occurred with an abnormally high latitude/altitude extension, reaching the geomagnetic latitude of ∼30°, corresponding to an Apex height of 2,600 km above the dip equator. (c) The midlatitude ionosphere experienced a conspicuous storm‐enhanced density (SED) plume structure associated with the subauroral polarization stream (SAPS). This SED/SAPS feature showed an unusual temporal variation that intensified and diminished twice. These distinct mid‐ and low‐latitude ionospheric disturbances could be attributed to the storm‐time electrodynamic effect of electric field perturbation, along with contributions from neutral dynamics and thermospheric composition change.

Multi‐Wavelength (L and S Band) Study of Ionospheric Irregularities From an Anomaly Crest Location

AbstractThis paper reports observation of moderate to intense scintillations, at S band of Indian Regional Navigation Satellite System (IRNSS). During current solar cycle 25, these occurrences are probably being reported for the first time, from a low‐latitude station Calcutta (22.58°N, 88.38°E geographic; magnetic dip 34.54°), located near the northern crest of Equatorial Ionization Anomaly. Efforts have been made to analyze irregularity dynamics at IRNSS S band, along with a comparative study at GNSS L1 to characterize occurrence and evolution of multiscale irregularity structures. Power spectral analysis technique has been applied on recorded C/NO, during scintillation patches, to measure east‐west zonal drift velocity. Efforts are also made to study intensity of signal perturbation at L5 frequency of IRNSS, compared to S band, when observed simultaneously, during period of ionospheric scintillation. Concurrent irregularity dynamics at L1, L5, and S band, particularly from a low‐latitude station, has not been extensively reported earlier. Data is recorded during vernal equinox (February–April 2022) of current solar cycle. Results of this study show occurrence of simultaneous night‐time scintillation at L1, L5, and S band. East‐west zonal drift velocity of irregularity, obtained from S band observations are found to decrease with the progress of time during 20–23 LT having a maximum value of 125 m/s. At GNSS L1, hourly average value of the velocity, is observed to maximize during 20–21 LT. Simultaneous observation of scintillation effects at L5 and S band of IRNSS led to loss‐of‐lock at L5, while no such occurrence was noted at S band.

Longitudinal, Latitudinal, and Local Time Variations of the 14.5‐Day Periodic Oscillation in the Ionosphere During 2014–2015 SSW

AbstractBased on global total electron content (TEC) maps from the International Global Navigation Satellite Systems Service (IGS), the ionospheric perturbations during the 2014–2015 sudden stratospheric warming (SSW) event were investigated. The analyses revealed both phase‐shifted semidiurnal perturbations and 14.5‐day periodic signal with zonal wavenumber 0 in the IGS TEC, indicating an enhanced lunar tidal impact on the ionosphere during the 2014–2015 SSW period. The 14.5‐day periodic oscillation in the IGS TEC presents an obvious latitudinal variation, with the maximum appearing in Equatorial Ionization Anomaly crest regions, which is due to the modulation of the equatorial ionospheric fountain effect by wind perturbations modulated by the lunar tide. Additionally, the 14.5‐day periodic oscillation presents a longitudinal pattern with three peaks in the northern hemisphere and four peaks in the southern hemisphere. Local time dependence of the 14.5‐day periodic perturbation is also significant.

Investigation of the GOLD Observed Merged Nighttime EIA With WACCM‐X Simulations During the Storm of 3 and 4 November 2021

AbstractDuring the storm on 3 and 4 November 2021, the Global‐scale Observations of the Limb and Disk (GOLD) mission observed well separated equatorial ionization anomaly (EIA) crests post sunset on 3 November, but merged EIA on 4 November. We used the Whole Atmosphere Community Climate Model‐eXtended to simulate the EIA structures during the two nights. The simulations show two separated post sunset EIA crests on 3 November but merged post sunset EIA crests on 4 November, which are qualitatively consistent with the GOLD observations. Numerical simulations and Ionospheric Connection Explorer neutral wind observations illustrate that the formation of merged EIA crests was due to several hours of downward E B drifts before and after sunset. Further diagnostic analysis revealed that it was mainly driven by westward electric fields caused by the disturbance dynamo electric field during the recovery phase of the storm.

Equatorial Ionization Anomaly Discontinuity Observed by GOLD, COSMIC‐2, and Ground‐Based GPS Receivers' Network

AbstractWe report a new ionosphere phenomenon: Equatorial ionization anomaly (EIA) discontinuity (EIAD), based on OI 135.6 nm radiance observations from the Global Observations of Limb and Disk (GOLD), ground‐based total electron content maps and in‐situ ion density data from Constellation Observing System for Meteorology, Ionosphere, and Climate‐2. The EIAD occurs when the OI radiance of the EIA crest has a local minimum, at a fixed UT, with the radiance in the local longitude region being weaker than that on the east and west sides. In the GOLD field‐of‐view, EIAD follows the seasonal variations of EIA. EIAD appears more often over the Atlantic Ocean and Africa than over South America. It occurs more in the southern crest during the December solstice, and more in the northern crest during both equinoxes. EIAD can occur under both quiet and disturbed times.

Geomagnetic storm-induced perturbations over Indian equatorial ionosphere

This study reveals the geomagnetic storm-induced ionospheric perturbations observed over the near-equatorial Indian stations - Cochin and Changanacherry in 2021. The 205 MHz VHF radar at Cochin University of Science and Technology (CUSAT) detected the storm-induced E- and F- region echoes during the moderate (28th February − 6th March 2021) and weak (19th − 25th March 2021) storm events. The fast-fluctuating northward interplanetary magnetic field (IMF BZ) and inhibition of the equatorial ionization anomaly (EIA) observed on 1st March indicate the suppression of daytime eastward electric field by the westward electric field associated with the counter electrojet (CEJ). Concurrent equatorward shift in the EIA crest and minor positive storm enhancement in the vertical total electron content were observed. The CEJ could have helped in the accumulation of photo-generated plasma at the near-equatorial region by pushing the daytime F-layer downward. During the moderate storm phase, post-sunset E-region echoes were detected during 1st − 3rd March, attributed to the disturbance dynamo electric field (DDEF). Nevertheless, during the main phase of the weak storm, a poleward shifting of the EIA crest occurred on 20th March, indicating the presence of a prompt penetration electric field (PPEF), which enhanced the upwardE×Bdrift. A major positive ionospheric storm enhancement that lasted for 7 h occurred on 20th March due to the DDEF. Bottom-type F-region echoes were observed over Cochin during the recovery phase of the weak storm. This work highlights the observation of equatorward and poleward shifting of the EIA using a 205 MHz radar.

Wavenumber-4 Structure in COSMIC-2 Observations: Vertical Plane Perspective

High-rate radio occultation (RO) in COSMIC-2 (FORMOSAT7) enables us to investigate the finer details of the ionosphere owing to the measurements being made at a significantly high spatiotemporal resolution, which was unthinkable a decade ago. In the vertical plane, local-time ionospheric wavenumber-4 (WN4) structures display tilted phase-fronts over the equatorial ionization anomaly (EIA) belt. The longitudinal extent of a tilted WN4 phase-front approximates the zonal wavelength of nonmigrating DE3 tide in the local-time frame of reference, i.e., ~900. The WN4-filtered (residual) component indicates a greater tilt (when visible), with a larger longitudinal extent of a wavenumber structure in the vertical plane. The WN4 structure over the EIA crest region is found to be out of phase (in phase) with respect to that over the EIA trough region during daytime (nighttime), which also depended on the altitude under consideration. Intriguingly, above 400 km, the WN4 structures in the EIA crest and trough regions are seen to be in phase with each other at all local times. The phenomenon of the “longitudinal co-location” of WN4 over the EIA crest and trough regions at altitudes above ~400 km at all local times remains unexplained. Results also highlight that the formation of WN4 is governed by a complex interplay of direct forcing of nonmigrating tides and the zonal electric field whose characteristics within the EIA belt vary drastically with latitude and altitude under consideration.

GOLD Observations of Longitudinal Variations in the Nighttime Equatorial Ionization Anomaly (EIA) Crests' Latitudes

AbstractEach day the Global‐scale Observations of the Limb and Disk imager observes the equatorial ionization anomaly (EIA) near sunset from ∼10°E to ∼80°W geographic longitude. Most images cover ∼45° of longitude (∼3 hr), and most longitudes are observed multiple times. Monthly averages of EIA crests' latitude (EIA lats) versus longitude during March, September, and December 2020 have been analyzed. The EIA lats reflect the combined influence of winds, solar radiation, and fields (electric and magnetic) in the equatorial region. Winter solstice differs significantly from the equinoxes, which are similar, but there are notable similarities between all three. The similarities in the EIA lats during the seasons examined indicates that the magnetic equator to subsolar point separation influences them in all three seasons and that it has a more distinct, possibly more significant, influence than winds on the average latitudes.

Forecasting hourly [formula omitted] over Sonmiani using an artificial neural network algorithm

This article describes the efforts made to forecast daily hourly critical frequency foF2 of the ionosphere over a station at the crest of equatorial ionization anomaly (EIA) region by using artificial neural network (ANN) technique. The ANN based model is developed to forecast foF2 1-h in advance over Sonmiani (25.19°N, 66.74°E) by making use of ionosonde data of 2018–2020. The input parameters of the model include day of year (DOY), local time (Hour), 27- day running mean of solar radio flux (F10.7), running mean of 8 previous values of geomagnetic planetary Ap index (AP8) and 1-h prior value of ionosonde foF2 (foF2pObs). The model is comprising of one hidden layer with 27 neurons, tangent hyperbolic as activation function, adaptive movement estimation (Adam) as optimization algorithm and mean squared error (MSE) as cost function. The optimal configuration is obtained by training the model on 500 epochs using above-mentioned inputs and configuration. The model is then validated over unseen data of 2021. It is found that the developed ANN based model predicts 1-h ahead values of foF2 with an average RMSE of 1.0 MHz on comparing with ionosonde measurements. For the same unseen data set RMSE of 1.6 MHz is found between ionosonde measurements and IRI-Plas 2020 estimations. The developed space weather model may be further improved by incorporating long time series data in future to capture geomagnetically as well as atmospherically induced short-term variations.

Characterization and Climatological Modeling of Equatorial Ionization Anomaly (EIA) Crest Position

AbstractThe Equatorial Ionization Anomaly (EIA) is characterized by strong ionospheric gradients that complicate ionospheric modeling and mitigation of ionospheric impact on Global Navigation Satellite System applications. In this study, the variation of EIA crest locations as a function of longitude and solar radio flux index F10.7 has been derived and modeled. Seven years (2013–2019) of ionospheric NmF2 and in‐situ ion density data from Constellation Observing System for Meteorology Ionosphere and Climate and Swarm‐A satellites have been used. We find that the distance between the northern and southern crest of EIA grows slightly with increase of solar flux. The position of the crests of EIA follows a wave number 4 structure with peak values at around −130°, 0°, and 100°E. At the altitude of Swarm‐A (∼460 km), the equatorial crests are found closer to the geomagnetic dip equator than they are at the peak density height hmF2 (∼310 km) which may be due to the spatial variations of geomagnetic field strength. Accordingly, two Crest Position climatological Models have been developed, one for the F2 Peak height (CPM_F2P) and the other one for Swarm‐A height (CPM_SAH).

Daily Dynamo Electric Fields Derived by Using Equatorial Ionization Anomaly Crests of the Total Electron Content

AbstractLatitudinal distances between the two equatorial ionization anomaly (EIA) crests in total electron content (TEC) of global ionosphere map (GIM) are used to derive the daily dynamo eastward electric field by comparing the eastward electric field calculated by ROCSAT‐1 vertical ion velocity in four seasons. The electric fields derived by the EIA crests of GIM TEC, ROCSAT‐1 ion velocity, and the incoherent scatter radar (ISR) observations at Jicamarca are generally in good agreement in longitudes and seasons. Meanwhile, the electric fields derived by the EIA crests agree well with those by ROCSAT‐1, FORMOSAT‐7/COSMIC‐2, and Jicamarca ISR on individual days. A long‐term study of the GIM‐TEC crest distance reveals obvious solar activity dependency of the daily dynamo electric field during 1999–2020. These agreements confirm that the EIA crest can be used to derive the daily eastward dynamo electric field and the associated vertical ion velocity which is responsible to the strength of equatorial plasma fountain and the latitudinal extend of the EIA. Moreover, the vertical ion velocity derived by the GIM‐TEC crest distance is further used to improve the SAMI2 model for space weather applications.