Bibliography

On the impact of meridional wind circulation changes in the electron density distribution over the Indian equatorial and low latitude ionospheric region during a severe geomagnetic storm

Using a suite of instruments, which included a chain of ground-based dual-frequency GPS receivers, and magnetometers, we have studied the importance of thermospheric meridional wind circulation in controlling the distribution of plasma over the Indian low latitude ionospheric regions during the period of a severe geomagnetic storm. The storm on 15 May 2005, which had its onset coinciding with the local noon time sector for the Indian ionospheric zone, was a severe geomagnetic storm with symH ∼ - 305 nT. A steep increase in the Total Electron Content (TEC) of the ionosphere over the entire Indian ionospheric region was observed on May 15. The enhancement in the TEC was well correlated with the increase in ΔH at the dip-equator due to the prompt penetration of the convection electric field associated with the storm. However, contrary to the previous studies on the storm impact over low latitude regions, a clear signature of disturbance dynamo was absent on the day after the storm. Enhancements in the TEC were observed on May 16, a day after the storm, as well, though the ΔH at the dip-equator was quite below the quite-time mean. The TEC remained well above its monthly mean over the entire Indian ionospheric region during the storm recovery period. We suggest that the TEC enhancement on May 16, even though it looked like due to a prompt penetration effect, was directly related to the compositional disturbances as given by the O/N2 ratio. We conclude that the meridional wind circulation plays an important role in the distribution of electron density over the equatorial and low latitudinal region during the period of a geomagnetic storm.

Ambili, K.; Choudhary, R.;

Published by: Advances in Space Research      Published on: oct

YEAR: 2022     DOI: 10.1016/j.asr.2022.06.027

Compositional disturbances; Equatorial ionosphere; geomagnetic storm; total electron content

Solar and interplanetary events that drove two CIR-related geomagnetic storms of 1 June 2013 and 7 October 2015, and their ionospheric responses at the American and African equatorial ionization Anomaly regions

This study investigates the sequence of solar and interplanetary events that drove the 1 June 2013 and October 2015 geomagnetic storms and how the American (68°–78oE) and African (32°–42oE) Equatorial Ionization Anomaly (EIA) regions responded to them. We constructed the EIA structures by using Total Electron Content (TEC) and ionospheric irregularities derived from Global Navigation Satellite System (GNSS) receivers along with the study locations. We also analyzed disturbed time ionospheric electric field and model data alongside the GNSS data. The 1 June 2013 geomagnetic storm was driven by a combination of a weak CME and HSSs from solar coronal holes, while the 7 October 2015 storm was solely driven by HSSs. Storm-time hemispherical asymmetry in ionospheric TEC and irregularities distributions was consistently observed. Storm with minimum SYM-H value at day-side locations caused enhancement in plasma ionization and pole-ward movement of EIA crests, while storm with minimum SYM-H value at night-side locations caused reduction in plasma ionization and equator-ward movement of EIA crests. The phase of responses of the ionosphere to geomagnetic storms depends on the local time of storm’s onset and local time of the storm’s main phase minimum which also determine the orientation of Prompt Penetration Electric Field (PPEF). At storm’s onset time in the low latitude regions, the main storm-induced electric field is PPEF. Daytime eastward PPEF intensified plasma fountain to increase the EIA crests locations, while nighttime westward PPEF reversed plasma fountain to cause equator-ward collapse of the EIA crests. However, around the storm’s recovery phase, under southward turning of IMF Bz, depending on their orientations, PPEF and Disturbed Dynamo Electric Field (DDEF) collectively influenced low latitude ionosphere. Eastward PPEF at the Pre-Reversal Enhancement (PRE) time enhanced irregularities generation, while westward DDEF at PRE time inhibited irregularities generation. The season of storm’s occurrence is also a factor that dictates ionospheric response to a storm, for instance, the 7 October storm (SYM-H −124 nT) influenced the ionosphere more than the 1 June storm (SYM-H −137 nT). Both storms had long recovery phase. On pre-storm days, we observed stronger and well-developed EIA crests over the American sector than over the African sector.

Oyedokun, Oluwole; Amaechi, P.; Akala, A.; Simi, K.; Ogwala, Aghogho; Oyeyemi, E.;

Published by: Advances in Space Research      Published on: mar

YEAR: 2022     DOI: 10.1016/j.asr.2021.12.027

geomagnetic storm; total electron content; Corotating Interacting Region; ionospheric irregularities

Climatology of global, hemispheric and regional electron content variations during the solar cycles 23 and 24

We present the results of study on the variations of ionospheric total electron content (TEC) by using global, hemispheric, and regional electron contents computed from the global ionospheric maps (GIMs) for the period from 1999 to 2020. For a low and moderate solar activity, the global and regional electron contents vary linearly with solar 10.7 cm radio flux and EUV flux. While a saturation effect in the electron content verses EUV and F10.7 is found during the high solar activity periods at all regions, the maximum effect is observed at low-latitudes followed by high and mid-latitudes region. The extent of saturation effect is more pronounced for F10.7 as compared to EUV. A wavelet transform is applied to global and hemispheric electron contents to examine the relative strength of different variations. The semi-annual variations dominate in the northern hemisphere, whereas annual variations dominate in the southern counterpart. The amplitude of annual variations in southern hemisphere is found to be higher than northern counterpart at all latitudes. This asymmetry in the amplitude of annual variation is maximum at low-latitudes, followed by mid and high-latitudes, respectively. The semi-annual variations are in-phase in both hemisphere and follow the solar cycle. The northern hemisphere depicts relatively large amplitude of semi-annual variations and exhibit the maximum effect at high-latitudes.

Younas, Waqar; Amory-Mazaudier, C.; Khan, Majid; Amaechi, Paul;

Published by: Advances in Space Research      Published on: jul

YEAR: 2022     DOI: 10.1016/j.asr.2022.07.029

annual variation; global electron content; Ionosphere; semi-annual variation; total electron content

Responses of the Indian Equatorial Ionization Anomaly to two CME-induced geomagnetic storms during the peak phase of solar cycle 24

This work analyzes the geo-effectiveness of Coronal Mass Ejection- (CME-) induced storms by investigating the responses of ionospheric Vertical Total Electron Content (VTEC) and the Equatorial Ionization Anomaly (EIA) over the Indian sector to two storms. One of the storms occurred on February 19, 2014 (SYM-H: −120 nT), while the other occurred on June 23, 2015 (SYM-H: −204 nT). Both storms were driven by full halo CMEs. Global TEC maps were used to characterize VTEC variations during the storms. June 23, 2015 storm was characterized with stronger solar progenitors, right from its origin, although the VTEC response to the storm was not influenced by their strong progenitors. The CMEs that caused the selected storms are large (Halo CMEs). We inferred that irrespective of the strength of solar origin of a storm, the response of ionization distribution over equatorial and low-latitude regions to it depends on the season of storm occurrence, local time of the storm onset, and PPEF orientation. From the VTEC variations for the three Indian stations namely, Trivandrum (geographic latitude: 8.52°N, geographic longitude: 76.94°E, magnetic latitude: 0.37°N), Hyderabad (17.39°N, 78.49°E, 10.15°N) and Delhi (28.70°N, 77.10°E, 22.70°N), we observed that EIA disturbances were more prominent over Hyderabad than over Delhi. The February 19, 2014 storm was characterized by a localized EIA crest at latitude a little above Hyderabad, while in June 23, 2015 storm localized EIA crest was observed directly on Hyderabad. IRI-2016 model generally underestimated VTEC at the three Indian equatorial and low-latitude locations. Solar cycle 24 was characterized with low heliospheric pressure due to its weak polar field strength. The lower pressure allowed CMEs to expand greatly as they transit through space. As they expand, the strengths of the magnetic field inside them decrease, and such lower-strength magnetic fields cause geomagnetic storms that are less geoeffective, even when their solar/interplanetary progenitors are strong and healthy. This associated weak polar field strength of solar cycle 24 caused weak fountain effect with the attendant inability to exhibit storm-time super-fountain effect in the dayside of the equatorial/low-latitude regions.

Simi, K.; Akala, A.; Krishna, Siva; Amaechi, Paul; Ogwala, Aghogho; Ratnam, Venkata; Oyedokun, O.;

Published by: Advances in Space Research      Published on: oct

YEAR: 2021     DOI: 10.1016/j.asr.2021.06.013

Coronal mass ejection; Disturbance dynamo electric field; geomagnetic storm; prompt penetration electric field; total electron content

Assessment of the predictive capabilities of NIGTEC model over Nigeria during geomagnetic storms

The Nigerian Total Electron Content (NIGTEC) is a regional neural network-based model developed by the Nigerian Centre for Atmospheric Research to predict the Total Electron Content (TEC) at any location over Nigeria. The addition of the disturbance storm time (Dst) index as one of NIGTEC s input layer neurons raises a question of its accuracy during geomagnetic storms. In this paper, the capability of NIGTEC in predicting the variability of TEC during geomagnetic storms has been assessed. TEC data predicted by NIGTEC is compared with those derived from Global Navigation Satellite System (GNSS) over Lagos (6.5oN, 3.4oE) and Toro (10.1oN, 9.12oE) during the intense storms in March 2012 and 2013. The model s predictive capability is evaluated in terms of Root Mean Square Error (RMSE). NIGTEC reproduced a fairly good storm time morphology in VTEC driven by the prompt penetration electric field and the increase in thermospheric O/N2. Nevertheless, it failed to predict the increase in TEC after the intense sudden impulse of 60 nT on 8 March 2012. And it could not capture the changes in VTEC driven by the storm time equatorward neutral wind especially during 18:00–24:00 UT. Consequently, the RMSEs were higher during this time window, and the highest RMSE value was obtained during the most intense storm in March 2012.

Amaechi, Paul; Humphrey, Ibifubara; Adewoyin, David;

Published by: Geodesy and Geodynamics      Published on: nov

YEAR: 2021     DOI: 10.1016/j.geog.2021.09.003

geomagnetic storm; global navigation satellite system; Nigerian Total Electron Content (NIGTEC); total electron content

Effects of the 12 May 2021 Geomagnetic Storm on Georeferencing Precision

In this work, we present the positioning error analysis of the 12 May 2021 moderate geomagnetic storm. The storm happened during spring in the northern hemisphere (fall in the south). We selected 868 GNSS stations around the globe to study the ionospheric and the apparent position variations. We compared the day of the storm with the three previous days. The analysis shows the global impact of the storm. In the quiet days, 93\% of the stations had 3D errors less than 10 cm, while during the storm, only 41\% kept this level of accuracy. The higher impact was over the Up component. Although the stations have algorithms to correct ionospheric disturbances, the inaccuracies lasted for nine hours. The most severe effects on the positioning errors were noticed in the South American sector. More than 60\% of the perturbed stations were located in this region. We also studied the effects produced by two other similar geomagnetic storms that occurred on 27 March 2017 and on 5 August 2019. The comparison of the storms shows that the effects on position inaccuracies are not directly deductible neither from the characteristics of geomagnetic storms nor from enhancement and/or variations of the ionospheric plasma.

Valdés-Abreu, Juan; Díaz, Marcos; Báez, Juan; Stable-Sánchez, Yohadne;

Published by: Remote Sensing      Published on: jan

YEAR: 2021     DOI: 10.3390/rs14010038

Geomagnetic storms; total electron content; global navigation satellite system; Global positioning system; precise point positioning; rate of change of the tec index

B2 Thickness Parameter Response to Equinoctial Geomagnetic Storms

The thickness parameters that most empirical models use are generally defined by empirical relations related to ionogram characteristics. This is the case with the NeQuick model that uses an inflection point below the F2 layer peak to define a thickness parameter of the F2 bottomside of the electron density profile, which is named B2. This study is focused on the effects of geomagnetic storms on the thickness parameter B2. We selected three equinoctial storms, namely 17 March 2013, 2 October 2013 and 17 March 2015. To investigate the behavior of the B2 parameter before, during and after those events, we have analyzed variations of GNSS derived vertical TEC (VTEC) and maximum electron density (NmF2) obtained from manually scaled ionograms over 20 stations at middle and low latitudes of Asian, Euro-African and American longitude sectors. The results show two main kinds of responses after the onset of the geomagnetic events: a peak of B2 parameter prior to the increase in VTEC and NmF2 (in \textasciitilde60\% of the cases) and a fluctuation in B2 associated with a decrease in VTEC and NmF2 (\textasciitilde25\% of the cases). The behavior observed has been related to the dominant factor acting after the CME shocks associated with positive and negative storm effects. Investigation into the time delay of the different measurements according to location showed that B2 reacts before NmF2 and VTEC after the onset of the storms in all the cases. The sensitivity shown by B2 during the studied storms might indicate that experimentally derived thickness parameter B2 could be incorporated into the empirical models such as NeQuick in order to adapt them to storm situations that represent extreme cases of ionospheric weather-like conditions.

Migoya-Orué, Yenca; Alazo-Cuartas, Katy; Kashcheyev, Anton; Amory-Mazaudier, Christine; Radicella, Sandro; Nava, Bruno; Fleury, Rolland; Ezquer, Rodolfo;

Published by: Sensors      Published on: jan

YEAR: 2021     DOI: 10.3390/s21217369

Geomagnetic storms; total electron content; ionospheric empirical models; NeQuick model; thickness parameter

Improved model of ionosphere variability and study for long-term statistical characteristics

Ionospheric variability is influenced by many factors, such as solar radiation, neutral atmosphere composition, and geomagnetic disturbances. Mainly characterized by the total electron content (TEC) and electron density, the climatology of the ionosphere features temporal and spatial changes. Establishing a multivariant regression model helps substantially in better understanding the ionosphere characteristics and their long-term variability. In this paper, an improvement of the existing ionosphere multivariate linear fitting regression model is proposed and investigated using data from both the ionosonde and the global ionosphere map (GIM) derived from ground-based Global Navigation Satellite System (GNSS) observations. The proposed method gives more consideration to the impact of the solar activity and adds modeling of the annual periodic fluctuations and half-year periodic fluctuations for the F10.7 index. The improved model is verified to have a better correlation with the real observations and can help reduce the calculation uncertainty. Moreover, the proposed model is used to evaluate the fitting accuracy of the GIMs produced by five authorized data analysis centers from the International GNSS Service (IGS). The results show that there is a fixing hole in the North America region for the GIM model where the correlation between the GIM and the proposed model always returns lower values compared to other places.

Bin, Xueheng; Liu, Yang;

Published by: Chinese Journal of Aeronautics      Published on: feb

YEAR: 2021     DOI: 10.1016/j.cja.2020.03.018

total electron content; Analysis of anomalies; Long-term statistics; Regression model

The Delayed Ionospheric Response to the 27-day Solar Rotation Period Analyzed With GOLD and IGS TEC Data

The delayed ionospheric response is analyzed for two well-defined 27-day solar rotation periods in the year 2019 with solar radio flux index F10.7 and Global-scale Observations of the Limb and Disk (GOLD) data, like solar extreme ultraviolet (EUV) flux proxy, O/N2 column density ratio and peak electron density, as well as International Global Navigation Satellite System Service rapid high-rate total electron content (TEC) map data. Although the correlation between GOLD solar EUV flux proxy and TEC is similar to the correlation between F10.7 and TEC, it is shown that the estimated delays based on GOLD data are in much better agreement with recent studies using EUV measurements compared to the delays based on F10.7 data. The GOLD peak electron density correlates well with TEC and allows insight to a local time interval when the ionosphere is not controlled by solar activity changes (17:00 LT to 21:00 LT). The present study investigates the impact of the solar activity (F10.7, GOLD EUV flux proxy) and O/N2 column density ratio on the ionospheric delay for two representative solar rotation periods. The capabilities of GOLD data for future research on the ionospheric response to the 27-day solar rotation period are demonstrated and discussed. These results are crucial information for precise ionospheric models and forecasts.

Schmölter, Erik; Berdermann, Jens; Codrescu, Mihail;

Published by: Journal of Geophysical Research: Space Physics      Published on:

YEAR: 2021     DOI: 10.1029/2020JA028861

Ionosphere; solar proxies; time delay; total electron content

Equatorial Ionospheric Electrodynamics

The low-latitude ionosphere is one of the most dynamic regions of the Earth s upper atmosphere. The morphology of this region is controlled by radiative and coupled chemical, neutral, and plasma transport processes. Equatorial electrodynamics plays a fundamental role on the low-latitude plasma density, total electron content (TEC), and plasma structures and waves extending from the E-region to the protonosphere. Ground-based and satellite measurements over the last six decades determined the climatology of quiet- and storm-time equatorial electrodynamic processes. Extensive theoretical and numerical simulations, particularly in the last two decades, investigated the main electrodynamic driving mechanisms. These combined studies have led to major advances in the understanding of the short-term variability of equatorial electrodynamics, which is essential for the accurate forecast of low-latitude ionospheric weather, and its effects on ground- and space-based technological systems. In this work, we review the main properties of low-latitude electrodynamics, focusing on recent results of the equatorial ambient plasma drifts, which are the main drivers of low-latitude ionospheric weather. We also briefly mention some outstanding questions and suggest possible future directions for their more complete understanding.

Fejer, Bela; Maute, Astrid;

Published by:       Published on:

YEAR: 2021     DOI: 10.1002/9781119815617.ch9

total electron content; equatorial ionospheric electrodynamics; low-latitude plasma density; quiet-time equatorial plasma drifts; storm-time equatorial electric fields

The global morphology of the plasmaspheric electron content during Northern winter 2009 based on GPS/COSMIC observation and GSM TIP model results

We studied the contribution of the global plasmaspheric and ionospheric electron content (PEC and IEC) into total electron content (TEC). The experimental PEC was estimated by comparison of GPS TECobservations and FORMOSAT-3/COSMIC radio occultation IEC measurements. Results are retrieved for the winter solstice (January and December 2009) conditions. Global maps of COSMIC-derived IEC, PECand GPS TEC were compared with Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) results. In addition, we used GSM TIP model results in order to estimate the contribution of plasmaspheric electron content into TEC value at the different altitudinal regions. The advantages and problems of the outer ionospheric/plasmaspheric parameters (O⁺/H⁺ transition height,TEC and electron density at height above F2 layer peak) representation by the IRI (International Reference Ionosphere) model are discussed.

Klimenko, M.V.; Klimenko, V.V.; Zakharenkova, I.E.; Cherniak, Iu.V.;

Published by: Advances in Space Research      Published on: 06/2014

YEAR: 2015     DOI: 10.1016/j.asr.2014.06.027

FORMOSAT-3/COSMIC; GPS; Numerical modeling; Plasmasphere; total electron content

Ionospheric symmetry caused by geomagnetic declination over North America

We describe variations in total electron content (TEC) in the North American sector exhibiting pronounced longitudinal progression and symmetry with respect to zero magnetic declination. Patterns were uncovered by applying an empirical orthogonal function (EOF) decomposition procedure to a 12 year ground-based American longitude sector GPS TEC data set. The first EOF mode describes overall average TEC, while the strong influence of geomagnetic declination on the midlatitude ionosphere is found in the second EOF mode (or the second most significant component). We find a high degree of correlation between spatial variations in the second EOF mode and vertical drifts driven by thermospheric zonal winds, along with well-organized temporal variation. Results strongly suggest a causative mechanism involving varying declination with longitude along with varying zonal wind climatology with local time, season, and solar cycle. This study highlights the efficiency and key role played by the geomagnetic field effect in influencing mesoscale ionospheric structures over a broad midlatitude range.

Zhang, Shun-Rong; Chen, Ziwei; Coster, Anthea; Erickson, Philip; Foster, John;

Published by: Geophysical Research Letters      Published on: 10/2014

YEAR: 2013     DOI: 10.1002/grl.v40.2010.1002/2013GL057933

geomagnetic field; midlatitude ionosphere; thermospheric winds; total electron content

Ionospheric response to the geomagnetic storm on 13\textendash17 April 2006 in the West Pacific region

This paper presents an investigation of geomagnetic storm effects in the equatorial and middle-low latitude F-region in the West Pacific sector during the intense geomagnetic storm on 13\textendash17 April, 2006. The event, preceded by a minor storm, started at 2130 UT on April 13 while interplanetary magnetic field (IMF)\ B_zcomponent was ready to turn southward. From 14\textendash17 the ionosphere was characterized by a large scale enhancement in critical frequency, foF2 (4\~6\ MHz) and total electron content (TEC) (\~30TECU, 1TECU=1\texttimes10¹⁶el/m²) followed by a long-duration negative phase observed through the simultaneous ionospheric sounding measurements from 14 stations and GPS network along the meridian 120\textdegreeE. A periodic wave structure, known as traveling ionospheric disturbances (TIDs) was observed in the morning sector during the initial phase of the storm which should be associated with the impulsive magnetospheric energy injection to the auroral. In the afternoon and nighttime, the positive phase should be caused by the combination of equatorward winds and disturbed electric fields verified through the equatorial F-layer peak height variation and modeled upward drift of Fejer and Scherliess [1997. Empirical models of storm time equatorial electric fields. Journal of Geophysical Research 102, 24,047\textendash24,056]. It is shown that the large positive storm effect was more pronounced in the Southern Hemisphere during the morning-noon sector on April 15 and negative phase reached to lower magnetic latitudes in the Northern Hemisphere which may be related to the asymmetry of the thermospheric condition during the storm.

Zhao, Biqiang; Wan, Weixing; Liu, Libo; Igarashi, K.; Yumoto, K.; Ning, Baiqi;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: Jan-01-2009

YEAR: 2009     DOI: 10.1016/j.jastp.2008.09.029

Magnetic storm; total electron content; Mid-low latitude

Ionospheric response to the geomagnetic storm on 13–17 April 2006 in the West Pacific region

This paper presents an investigation of geomagnetic storm effects in the equatorial and middle-low latitude F-region in the West Pacific sector during the intense geomagnetic storm on 13–17 April, 2006. The event, preceded by a minor storm, started at 2130 UT on April 13 while interplanetary magnetic field (IMF) Bz component was ready to turn southward. From 14–17 the ionosphere was characterized by a large scale enhancement in critical frequency, foF2 (4∼6MHz) and total electron content (TEC) (∼30TECU, 1TECU=1×1016el/m2) followed by a long-duration negative phase observed through the simultaneous ionospheric sounding measurements from 14 stations and GPS network along the meridian 120°E. A periodic wave structure, known as traveling ionospheric disturbances (TIDs) was observed in the morning sector during the initial phase of the storm which should be associated with the impulsive magnetospheric energy injection to the auroral. In the afternoon and nighttime, the positive phase should be caused by the combination of equatorward winds and disturbed electric fields verified through the equatorial F-layer peak height variation and modeled upward drift of Fejer and Scherliess [1997. Empirical models of storm time equatorial electric fields. Journal of Geophysical Research 102, 24,047–24,056]. It is shown that the large positive storm effect was more pronounced in the Southern Hemisphere during the morning-noon sector on April 15 and negative phase reached to lower magnetic latitudes in the Northern Hemisphere which may be related to the asymmetry of the thermospheric condition during the storm.

Zhao, Biqiang; Wan, Weixing; Liu, Libo; Igarashi, K.; Yumoto, K.; Ning, Baiqi;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on:

YEAR: 2009     DOI: https://doi.org/10.1016/j.jastp.2008.09.029

Magnetic storm; total electron content; Mid-low latitude