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

Local Persistent Ionospheric Positive Responses to the Geomagnetic Storm in August 2018 Using BDS-GEO Satellites over Low-Latitude Regions in Eastern Hemisphere

We present the ionospheric disturbance responses over low-latitude regions by using total electron content from Geostationary Earth Orbit (GEO) satellites of the BeiDou Navigation Satellite System (BDS), ionosonde data and Swarm satellite data, during the geomagnetic storm in August 2018. The results show that a prominent total electron content (TEC) enhancement over low-latitude regions is observed during the main phase of the storm. There is a persistent TEC increase lasting for about 1–2 days and a moderately positive disturbance response during the recovery phase on 27–28 August, which distinguishes from the general performance of ionospheric TEC in the previous storms. We also find that this phenomenon is a unique local-area disturbance of the ionosphere during the recovery phase of the storm. The enhanced foF2 and hmF2 of the ionospheric F2 layer is observed by SANYA and LEARMONTH ionosonde stations during the recovery phase. The electron density from Swarm satellites shows a strong equatorial ionization anomaly (EIA) crest over the low-latitude area during the main phase of storm, which is simultaneous with the uplift of the ionospheric F2 layer from the SANYA ionosonde. Meanwhile, the thermosphere O/N2 ratio shows a local increase on 27–28 August over low-latitude regions. From the above results, this study suggests that the uplift of F layer height and the enhanced O/N2 ratio are possibly main factors causing the local-area positive disturbance responses during the recovery phase of the storm in August 2018.

Tang, Jun; Gao, Xin; Yang, Dengpan; Zhong, Zhengyu; Huo, Xingliang; Wu, Xuequn;

Published by: Remote Sensing      Published on: jan

YEAR: 2022     DOI: 10.3390/rs14092272

BDS-GEO; differential code biases; geomagnetic storm; Ionospheric disturbance; TEC

Ionospheric response to the 26 August 2018 geomagnetic storm along 280° E and 316° E in the South American sector

This paper studies the response of the ionospheric parameters critical frequency (foF2), their height (hmF2), and Total Electron Content (TEC) at mid, low, and near-equatorial latitudes of the South American sector during the intense geomagnetic storm of 26 August 2018. The ionospheric response at the beginning of the main phase was different depending on latitude (in general, there were decreases in foF2 at near-equatorial and low latitudes and small increases at mid-latitudes). During the recovery, positive storm effects in foF2 and TEC were observed almost all day on 26 August 2018 overall the stations along all the latitudes and also on 27 August. The initial effects were possibly caused by a weak prompt penetration electric field while the enhanced ratio of thermosphere neutral composition i.e. [O]/[N2] was considered as the main cause for the positive storm effects during the recovery phase.

Mansilla, Gustavo; Zossi, Marta;

Published by: Advances in Space Research      Published on: jan

YEAR: 2022     DOI: 10.1016/j.asr.2021.08.002

geomagnetic storm; Ionosphere; South America

Responses of Mesosphere and Lower Thermosphere Temperature to the Geomagnetic Storm on 7–8 September 2017

The variations of neutral temperature in the mesosphere and lower thermosphere (MLT) region, during the 7–8 September 2017 intense geomagnetic storm, are studied using observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. They are also studied using simulations by the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIMEGCM). The neutral temperature data cover the altitudes from 80 km to 110 km between 83° N and 52° S latitude, obtained from both SABER observations and model simulations. The SABER observations reveal that temperature increases (the maximum increase is larger than 35 K at \textasciitilde108 km) and decreases (the maximum decrease is larger than 20 K at \textasciitilde105 km) during the geomagnetic storm. The storm effects penetrate down to \textasciitilde80 km. In observations, temperature variations corresponding to the storm show hemispheric asymmetry. That is, the variations of temperature are more prominent in the northern hemisphere than in the southern hemisphere. Conversely, the TIMEGCM outputs agree with the observations in general but overestimate the temperature increases and underestimate the temperature decreases at high and middle latitudes. Meanwhile, the simulations show stronger temperature decreases and weaker temperature increases than observations at low latitudes. After analyzing the temperature variations, we suggest that vertical winds may play an important role in inducing these significant variations of temperature in the MLT region.

Sun, Meng; Li, Zheng; Li, Jingyuan; Lu, Jianyong; Gu, Chunli; Zhu, Mengbin; Tian, Yufeng;

Published by: Universe      Published on: feb

YEAR: 2022     DOI: 10.3390/universe8020096

geomagnetic storm; temperature; the mesosphere and lower thermosphere (MLT); TIMEGCM

FUV observations of variations in thermospheric composition and topside ionospheric density during the November 2004 magnetic superstorm

We revisited the November 2004 superstorm by analyzing TIMED/GUVI data. The 135.6 nm limb radiances at 520-km are mainly due to the O+ and electron radiative recombination and represent the daytime ionosphere density at the altitude. The 135.6 nm radiances clearly showed a signature of ionospheric equatorial arcs and their variations during the November 2004 magnetic superstorm. When an intense eastward Interplanetary Electric Field (IEF) occurred, the dayside equatorial arcs were enhanced and their latitude separation increased. The enhanced equatorial arcs were hemispherically symmetric or asymmetric in the region with non-depleted O/N2 or hemispherically asymmetric O/N2 depletion, respectively. When O/N2 depletion reached the magnetic equator, there was no observable enhancement in the equatorial arcs regardless the IEF conditions, indicating O/N2 condition significantly modulated the variations in storm-time equatorial arcs. GUVI observations also showed that a westward IEF and/or disturbance dynamo electric field could also suppress the dayside equatorial arcs.

Zhang, Yongliang; Paxton, LarryJ.; Huang, Chaosong; Wang, Wenbin;

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

YEAR: 2022     DOI: 10.1016/j.jastp.2022.105832

geomagnetic storm; penetration electric field; Thermosperic composition; topside ionosphere

Significant Variations of Thermospheric Nitric Oxide Cooling during the Minor Geomagnetic Storm on 6 May 2015

Using observations by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on board the TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) satellite and simulations by the TIEGCM (Thermosphere-Ionosphere-Electrodynamics General Circulation Model), we investigate the daytime variations of thermospheric nitric oxide (NO) cooling during the geomagnetic storm on 6 May 2015. The geomagnetic storm was minor, as the minimum Dst was −28 nT, the maximum Kp was 5+ and the maximum AE was 1259 nT. However, significant enhancements of peak NO cooling rate and prominent decreases in the peak NO cooling altitude were observed from high latitudes to low latitudes in both hemispheres on the dayside by the SABER instrument. The model simulations underestimate the response of peak NO cooling and have no significant variation of the altitude of peak NO cooling rate on the dayside during this minor geomagnetic storm. By investigating the temporal and latitudinal variations of vertical NO cooling profiles inferred from SABER data, we suggest that the horizontal equatorward winds caused by the minor geomagnetic storm were unexpectedly strong and thus play an important role in inducing these significant daytime NO cooling variations.

Li, Zheng; Sun, Meng; Li, Jingyuan; Zhang, Kedeng; Zhang, Hua; Xu, Xiaojun; Zhao, Xinhua;

Published by: Universe      Published on: apr

YEAR: 2022     DOI: 10.3390/universe8040236

geomagnetic storm; thermosphere; nitric oxide cooling

Response of the Ionospheric TEC to SSW and Associated Geomagnetic Storm Over the American Low Latitudinal Sector

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

Fashae, J.; Bolaji, O.; Rabiu, A.;

Published by: Space Weather      Published on:

YEAR: 2022     DOI: 10.1029/2021SW002999

equatorial ionization anomaly (EIA); geomagnetic storm; low-latitude ionosphere; sudden stratospheric wind (SSW)

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

Features of the Ionospheric Storm on December 21--24, 2016

The purpose of this work is to investigate the response of the F region and topside ionosphere to the moderate geomagnetic storm on December 21, 2016 (Kp max = 6). The subject of the study is the height–time variations in the parameters of the ionospheric plasma over Kharkiv. Experimental data were obtained using vertical sounding and incoherent scatter methods by the ionosonde and incoherent scatter radar. The presented results are based on the correlation analysis of the incoherent scattered signal. The ion and electron temperatures, as well as the ionospheric plasma velocity, were determined from a set of measured correlation functions of the incoherently scattered signal. The electron density was calculated using the following parameters measured for a number of ionospheric heights: power of the incoherent scatter signal, ion and electron temperatures, and the electron density at the ionospheric F2 layer peak, which is calculated from the critical frequency measured by the ionosonde. The moderate geomagnetic storm was accompanied by an ionospheric storm over Kharkiv with sign-variable phases (first positive and second negative). The peak increase in the electron density was 1.8 times and decrease was 3.4 times. The negative phase was accompanied by a slight rise of the F2 layer (by 20–28 km), which could be due to a decrease in the vertical component of the plasma velocity and an increase in the electron temperature by 600–800 K and ion temperature by 100–160 K. Effects of strong negative ionospheric disturbances were registered during the subsequent magnetospheric disturbance of December 22–24, 2016, with a decrease in electron density at the F2 layer peak up to 2.5–4.9 times. The effects of negative disturbances manifested themselves in the variations of temperatures of electrons and ions. In general, the moderate magnetic storm caused significant changes in the electron density in the ionospheric F2 layer peak, which were accompanied by heating of the ionospheric plasma as well as changes in variations of the vertical component of the ionospheric plasma velocity and the height of ionization during the main phase of the magnetic storm.

Katsko, S.; Emelyanov, Ya.; Chernogor, L.;

Published by: Kinematics and Physics of Celestial Bodies      Published on: mar

YEAR: 2021     DOI: 10.3103/S0884591321020045

geomagnetic storm; Electron density; Ionospheric storm; space weather; ionosonde; electron and ion temperatures; incoherent scatter radar; plasma velocity; positive and negative storm phases

Longitudinal variations of geomagnetic and ionospheric parameters in the Northern Hemisphere during magnetic storms according to multi-instrument observations

We present a joint analysis of longitude-temporal variations of ionospheric and geomagnetic parameters at middle and high latitudes in the Northern Hemisphere during the two severe magnetic storms in March and June 2015 by using data from the chains of magnetometers, ionosondes and GPS/GLONASS receivers. We identify the fixed longitudinal zones where the variability of the magnetic field is consistently high or low under quiet and disturbed geomagnetic conditions. The revealed longitudinal structure of the geomagnetic field variability in quiet geomagnetic conditions is caused by the discrepancy of the geographic and magnetic poles and by the spatial anomalies of different scales in the main magnetic field of the Earth. Variations of ionospheric parameters are shown to exhibit a pronounced longitudinal inhomogeneity with changing geomagnetic conditions. This inhomogeneity is associated with the longitudinal features of background and disturbed structure of the geomagnetic field. During the recovery phase of a storm, important role in dynamics of the mid-latitude ionosphere may belong to wave-like thermospheric disturbances of molecular gas, propagating westward for several days. Therefore, it is necessary to extend the time interval for studying the ionospheric effects of strong magnetic storms by a few days after the end of the magnetospheric source influence, while the disturbed regions in the thermosphere continues moving westward and causes the electron density decrease along the trajectories of propagation.

Chernigovskaya, M.; Shpynev, B.; Yasyukevich, A.; Khabituev, D.; Ratovsky, K.; Belinskaya, Yu.; Stepanov, A.; Bychkov, V.; Grigorieva, S.; Panchenko, V.; Kouba, D.; Mielich, J.;

Published by: Advances in Space Research      Published on: jan

YEAR: 2021     DOI: 10.1016/j.asr.2020.10.028

Chain of GPS/GLONASS receivers; Geomagnetic field variations; geomagnetic storm; Ionosonde chain; ionospheric disturbances

Latitudinal Dependence of the Ionospheric Slab Thickness for Estimation of Ionospheric Response to Geomagnetic Storms

The changes in the ionosphere during geomagnetic disturbances is one of the prominent Space Weather effects on the near-Earth environment. The character of these changes can differ significantly at different regions on the Earth. We studied ionospheric response to five geomagnetic storms of March 2012, using data of Total Electron Content (TEC) and F2-layer critical frequency (foF2) along the meridian of 70° W in the Northern Hemisphere. There are few ionosondes along this longitudinal sector: in Thule, Sondrestrom, Millstone Hill and Puerto Rico. The lacking foF2 values between the ionosondes were determined by using the experimental latitudinal dependences of the equivalent ionospheric slab thickness and TEC values. During geomagnetic storms, the following features were characteristic: (a) two-hours (or longer in one case) delay of the ionospheric response to disturbances, (b) the more prominent mid-latitude trough and (c) the sharper border of the EIA northern crest. During four storms of 7–17 March, the general tendency was the transition from negative disturbances at high latitudes to intense positive disturbances at low latitudes. During the fifth storm, the negative ionospheric disturbance controlled by O/N2 change was masked by the overall prolonged electron density increase during 21–31 March. The multiple correlation analysis revealed the latitudinal dependence of dominant Space Weather parameters’ impacts on foF2.

Sergeeva, Maria; Maltseva, Olga; Caraballo, Ramon; Gonzalez-Esparza, Juan; Corona-Romero, Pedro;

Published by: Atmosphere      Published on: feb

YEAR: 2021     DOI: 10.3390/atmos12020164

foF2; geomagnetic storm; Ionospheric disturbance; ionospheric equivalent slab thickness; statistical analysis; TEC

Responses of the African equatorial ionization anomaly (EIA) to some selected intense geomagnetic storms during the maximum phase of solar cycle 24

This study investigates the morphology of the GPS TEC responses in the African Equatorial Ionization Anomaly (EIA) region to intense geomagnetic storms during the ascending and maximum phases of solar cycle 24 (2012–2014). Specifically, eight intense geomagnetic storms with Dst ≤ −100 nT were considered in this investigation using TEC data obtained from 13 GNSS receivers in the East African region within 36–42°E geographic longitude; 29°N–10°S geographic latitude; ± 20°N magnetic latitude. The storm-time behavior of TEC shows clear positive and negative phases relative to the non-storm (median) behavior, with amplitudes being dependent on the time of sudden commencement of the storm and location. When a storm starts in the morning period, total electron content increases for all stations while a decrease in total electron content is manifested for a storm that had its sudden commencement in the afternoon period. The TEC and the EIA crest during the main phase of the storm is significantly impacted by the geomagnetic storm, which experiences an increase in the intensity of TEC while the location and spread of the crest usually manifest a poleward expansion.

Oyedokun, O.; Akala, A.; Oyeyemi, E.;

Published by: Advances in Space Research      Published on: feb

YEAR: 2021     DOI: 10.1016/j.asr.2020.11.020

African equatorial ionization anomaly; geomagnetic storm; GNSS; Ionosphere

Assessing the performance of a Northeast Asia Japan-centered 3-D ionosphere specification technique during the 2015 St. Patrick’s day geomagnetic storm

This paper demonstrates and assesses the capability of the advanced three-dimensional (3-D) ionosphere tomography technique, during severe conditions. The study area is northeast Asia and quasi-Japan-centred. Reconstructions are based on total electron content data from a dense ground-based global navigation satellite system receiver network and parameters from operational ionosondes. We used observations from ionosondes, Swarm satellites and radio occultation (RO) to assess the 3-D picture. Specifically, we focus on St. Patrick’s day geomagnetic storm (17–19 March 2015), the most intense in solar cycle 24. During this event, the energy ingested into the ionosphere resulted in Dst and Kp and reaching values \textasciitilde − 223 nT and 8, respectively, and the region of interest, the East Asian sector, was characterized by a \textasciitilde 60\% reduction in electron densities. Results show that the reconstructed densities follow the physical dynamics previously discussed in earlier publications about storm events. Moreover, even when ionosonde data were not available, the technique could still provide a consistent picture of the ionosphere vertical structure. Furthermore, analyses show that there is a profound agreement between the RO profiles/in-situ densities and the reconstructions. Therefore, the technique is a potential candidate for applications that are sensitive to ionospheric corrections.

Nicholas, Ssessanga; Mamoru, Yamamoto; Susumu, Saito;

Published by: Earth, Planets and Space (Online)      Published on: dec

YEAR: 2021     DOI: 10.1186/s40623-021-01447-8

geomagnetic storm; Ground-GNSS-STEC tomography; Ionosonde data assimilation

Effect of intense geomagnetic storms on low-latitude TEC during the ascending phase of the solar cycle 24

The results presented in this paper are obtained from low-latitude ionospheric total electron content (TEC) variation during the chosen geomagnetic storm events happening during the solar cycle 24. We include the four intense geomagnetic storms that occurred on 26 September 2011, 15 July 2012, 19 February 2014 and 20 December 2015, depending upon the availability of TEC data. For this, we have used the TEC data from low-latitude station Varanasi (geographic latitude 25°, 16′N, geographic longitude 82°, 59′E and geomagnetic latitude 16°, 24′N) and an equatorial station Bengaluru (geographic latitude 13°, 02′N, geographic longitude 77°, 34′E and geomagnetic latitude 04°, 68′N). The storm-induced TEC changes at chosen stations have been discussed in terms of local time, storm wind effect, neutral wind, composition changes and variation in the dawn–dusk component of the interplanetary electric field (IEF Ey).

Singh, Abha; Rathore, Vishnu; Kumar, Sanjay; Rao, S.; Singh, Sudesh; Singh, A.;

Published by: Journal of Astrophysics and Astronomy      Published on: aug

YEAR: 2021     DOI: 10.1007/s12036-021-09774-8

geomagnetic storm; Global positioning system; low latitude; total electron contents

Solar flares and geomagnetic storms of September 2017: Their impacts on the TEC over 75°E longitude sector

This study investigates the ionospheric Total Electron Content (TEC) responses over 75°E longitude to the solar flares and geomagnetic storms of September 6–9, 2017. The results of this study provide the impacts of solely solar flares on the ionosphere and such impact when the effects of solar flares and geomagnetic storm are combined. On September 6, two X class solar flares, namely X2.2 at 0857 UT and X9.3 at 1153 UT, were recorded with quiet geomagnetic conditions. The EUV/X-ray intensity of X9.3 flare was significantly greater than that of X2.2 flare, and the recovery phase of both the flares was slower than their respective impulsive phase. The slower recovery rate in EUV/X-ray intensity is reflected as a delayed TEC response. A nearly 8\% higher crest to trough TEC change on flare day than the pre-flare day suggests an enhanced level of the equatorial electrojet. The overall weak TEC response to X9.3 solar flare is attributed to solar zenith angle dependency and shifting of solar flare location from disk center to west limb. The solar flares on September 7–8 were co-occurred with geomagnetic storms and observed large increments in TEC are additionally induced by prompt penetration electric field and the enhanced level of thermospheric compositional changes. On September 9, an increase in TEC is observed during M class solar flares under effect of solar flares and disturbed dynamo electric field.

Chakraborty, Monti; Singh, A.; Rao, S.;

Published by: Advances in Space Research      Published on: aug

YEAR: 2021     DOI: 10.1016/j.asr.2021.04.012

TEC; geomagnetic storm; EUV; Solar flare; X-ray

A Statistical Analysis of Plasma Bubbles Observed by Swarm Constellation during Different Types of Geomagnetic Storms

Based on the observations of Ionospheric Bubble Index (IBI) data from the Swarm mission, the characteristics of plasma bubbles are investigated during different types of geomagnetic storms recorded from 2014 to 2020. The geometrical constellation of the Swarm mission enabled us to investigate the altitudinal profile of the IBIs during different activity levels in a statistical mean. Results show that the majority of IBIs associated with moderate storms are observed at low altitudes and the probability of observing IBIs at high altitudes (Swarm-B) increases with the increase in storm level. This is confirmed by observing the F2 layer peak height (hmF2) during super storm events at larger altitudes using COSMIC data. The maximum number of IBIs is recorded within the South Atlantic Anomaly (SAA) region with a long duration time and tends to increase only during dusk time. Both the large duration time and number of IBIs over the South Atlantic Anomaly (SAA) suggest that the gradient in the electron density and the depression in the magnetic field are the main factors controlling IBI events. Also, the IBIs at high altitudes are larger at sunset and at low altitudes pre-midnight. In addition, the occurrence of IBIs is always larger in the northern hemisphere than in the southern hemisphere irrespective of the type of storm, as well as during the summer months. Moreover, there is no correlation between the duration time of IBIs and both the altitudinal observation of the IBIs and the storm type. Seasonal occurrence of IBIs is larger during equinoxes and vice versa during solstices irrespective of both the type of storm and the altitude of the satellite. The large number of IBIs during equinoxes agrees with the previous studies, which expect that the large electron density is a developer of steeper ∇n. Large occurrences of super storm IBIs observed within the pre-midnight during summer and at sunset during equinoxes are a novel observation that needs further investigation. Also, the majority of IBIs are observed a few hours after geomagnetic substorms, which reflects the role of the Disturbance Dynamo Electric Field (DDEF) as a main driver of IBIs.

Hussien, Fayrouz; Ghamry, Essam; Fathy, Adel;

Published by: Universe      Published on: apr

YEAR: 2021     DOI: 10.3390/universe7040090

geomagnetic storm; ionospheric irregularity; plasma bubble; Swarm mission

Periodic Variations in Solar Wind and Responses of the Magnetosphere and Thermosphere in March 2017

TIMED/GUVI observed thermospheric column ∑O/N2 depletion in both hemispheres between March 1 and 21, 2017 which was caused by large periodic variations in interplanetary magnetic field (IMF) and a high solar wind speed, likely in a solar wind. The dominant periods seen in the solar wind and magnetosphere coupling function (CF) were around 1.9, 3.0, 4.7, 7.6, 14.0 and 22.0 h on March 1 and 2. The major AE variations were around 3.0, 4.7, 7.6, 10.7, 14.0 and 22.0 h. Auroral hemispheric power (HP) also showed periodic variations similar to that of AE, except for the absence of the 3.0 h variation due to a low sampling rate in HP data. SymH data didn t show the periodic variations seen in AE but a weak 12-h periodic variation which was seen in the solar wind dynamic pressure. A weak AE and HP variation at 10.7-h period was not observed in CF or any individual solar wind parameters or IMF components. These results suggest that (a) the oscillating IMF pumped energy and mass periodically into the magnetosphere and the polar ionosphere, creating a long lasting (20-days) storm and O/N2 depletion, (b) the high latitude AE and HP responded to the solar wind and IMF variations directly, (c) SymH did not show any direct periodic responses, likely due to the fact that the ring current response resulted from the cumulative effect of solar wind and IMF drivers, (d) the 10.7-h variations in AE and HP were likely due to magnetospheric internal processes.

Zhang, Yongliang; Paxton, Larry; Wang, Wenbin; Huang, Chaosong;

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

YEAR: 2021     DOI: 10.1029/2021JA029387

AE index; geomagnetic storm; hemispheric power; periodic variation; solar wind and magnetosphere coupling; thermospheric composition

An Unusually Large Electron Temperature Increase Over Arecibo Associated With an Intense Geomagnetic Storm

We present an investigation of the F-region electron temperature to an intense geomagnetic storm that occurred on 5 August 2011. The investigation is based on the incoherent scatter radar measurements at Arecibo Observatory, Puerto Rico (18.3°N, 66.7°W). The electron temperature exhibits a rapid and intensive enhancement after the commencement of the geomagnetic storm. The electron temperature increases by ∼800 K within an hour, which is seldomly reported at Arecibo. At the same time, a depletion of the electron density is also observed. The daytime perturbations of electron density and temperature are anticorrelated with the correlation coefficient, which is −0.88 and −0.91 on the day and the following day of the geomagnetic storm, respectively. According to the Global Ultraviolet Imager measurements, the ratio of atomic oxygen to molecular nitrogen concentration () decreases dramatically during the storm. Our analysis suggests that the enhancement of the electron temperature is due to the depletion of the electron density, which is likely associated with the decrease of . The reduction of maybe caused by a prompt upward plasma motion after the commencement of the geomagnetic storm.

Lv, Xiedong; Gong, Yun; Zhang, ShaoDong; Zhou, Qihou; Ma, Zheng;

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

YEAR: 2021     DOI: 10.1029/2021JA029836

Arecibo; F-region electron temperature; geomagnetic storm; incoherent scatter radar

Dependence of the high-latitude plasma irregularities on the auroral activity indices: a case study of 17 March 2015 geomagnetic storm

The magnetosphere substorm plays a crucial role in the solar wind energy dissipation into the ionosphere. We report on the intensity of the high-latitude ionospheric irregularities during one of the largest storms of the current solar cycle\textemdashthe St. Patrick\textquoterights Day storm of 17 March 2015. The database of more than 2500 ground-based Global Positioning System (GPS) receivers was used to estimate the irregularities occurrence and dynamics over the auroral region of the Northern Hemisphere. We analyze the dependence of the GPS-detected ionospheric irregularities on the auroral activity. The development and intensity of the high-latitude irregularities during this geomagnetic storm reveal a high correlation with the auroral hemispheric power and auroral electrojet indices (0.84 and 0.79, respectively). Besides the ionospheric irregularities caused by particle precipitation inside the polar cap region, evidences of other irregularities related to the storm enhanced density (SED), formed at mid-latitudes and its further transportation in the form of tongue of ionization (TOI) towards and across the polar cap, are presented. We highlight the importance accounting contribution of ionospheric irregularities not directly related with particle precipitation in overall irregularities distribution and intensity.

Cherniak, Iurii; Zakharenkova, Irina;

Published by: Earth, Planets and Space      Published on: 12/2015

YEAR: 2015     DOI: 10.1186/s40623-015-0316-x

Auroral hemispheric power index Auroral precipitation; geomagnetic storm; GPS; Ionosphere irregularities; ROTI

The response of the ionosphere to intense geomagnetic storms in 2012 using GPS-TEC data from East Africa longitudinal sector

The response of the ionosphere to intense magnetic storms has been studied using total electron content (TEC). TEC data recorded by a series of GPS receivers at a longitude\~35\textdegreeE\ covering a wide range of latitudes (32\textdegreeS\ to\ 68\textdegreeN, geographic) is analyzed to study spatio-temporal modifications of the vertical TEC (vTEC) during storms on 07 and 09 March 2012 and on 14 July 2012. We have observed main phase positive response at equatorial ionization anomaly (EIA) crests and mid latitude regions in all the storms. These main phase positive responses are associated with vertical drift enhancement (intensified equatorial electrojet (EEJ)) and the mechanical effect of equatorward neutral wind after an auroral activity. A daytime substantial depletion of TEC at low latitude region was observed on 08 March 2012. This is due to the combined effects of oversheilding and disturbance dynamo electric field that drive large downward drifts during the day. The low latitude and equatorial ionospheric response in the recovery phase days of March storm is found to be largely associated with the disturbance dynamo field that suppressed the upward\ E\texttimesB\ drift from EEJ observations. The summer negative and winter positive response in July storm as well as mid latitude positive response in March storm was associated with the composition changes as depicted by the\ O\ to\ N₂\ ratio from GUVI measurements.

Tesema, F.; Damtie, B.; Nigussie, M.;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 12/2015

YEAR: 2015     DOI: 10.1016/j.jastp.2015.10.021

Equatorial Electrojet; geomagnetic storm; Ionosphere

Ionospheric response to the 2015 St. Patrick's Day storm: A global multi-instrumental overview

We present the first multi-instrumental results on the ionospheric response to the geomagnetic storm of 17\textendash18 March 2015 (the St. Patrick\textquoterights Day storm) that was up to now the strongest in the 24th solar cycle (minimum SYM-H value of -233 nT). The storm caused complex effects around the globe. The most dramatic positive ionospheric storm occurred at low latitudes in the morning (~100\textendash150\% enhancement) and postsunset (~80\textendash100\% enhancement) sectors. These significant vertical total electron content increases were observed in different local time sectors and at different universal time, but around the same area of the Eastern Pacific region, which indicates a regional impact of storm drivers. Our analysis revealed that this particular region was most concerned by the increase in the thermospheric O/N₂\ ratio. At midlatitudes, we observe inverse hemispheric asymmetries that occurred, despite the equinoctial period, in different longitudinal regions. In the European-African sector, positive storm signatures were observed in the Northern Hemisphere (NH), whereas in the American sector, a large positive storm occurred in the Southern Hemisphere, while the NH experienced a negative storm. The observed asymmetries can be partly explained by the thermospheric composition changes and partly by the hemispherically different nondipolar portions of the geomagnetic field as well as by the IMF By component variations. At high latitudes, negative ionospheric storm effects were recorded in all longitudinal regions, especially the NH of the Asian sector was concerned. The negative storm phase developed globally on 18 March at the beginning of the recovery phase.

Astafyeva, Elvira; Zakharenkova, Irina; Förster, Matthias;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2015

YEAR: 2015     DOI: 10.1002/2015JA021629

geomagnetic storm; hemispheric asymmetry; Ionosphere; negative storm; positive storm; Swarm mission

Dynamics of the high-latitude ionospheric irregularities during the 17 March 2015 St. Patrick's Day storm: Ground-based GPS measurements

We report first results on the study of the high-latitude ionospheric irregularities observed in worldwide GPS data during the St. Patrick\textquoterights Day geomagnetic storm (17 March 2015). Multisite GPS observations from more than 2500 ground-based GPS stations were used to analyze the dynamics of the ionospheric irregularities in the Northern and Southern Hemispheres. The most intense ionospheric irregularities lasted for more than 24 h starting at 07 UT of 17 March. This period correlates well with an increase of the auroral Hemispheric Power index. We find hemispheric asymmetries in the intensity and spatial structure of the ionospheric irregularities. Over North America, the ionospheric irregularities zone expanded equatorward below ~45\textdegreeN geographic latitude. Additionally, the strong midlatitude and high-latitude GPS phase irregularities in the auroral oval were found to be related to the formation of storm enhanced density and deepening of the main ionospheric trough through upper atmosphere ionization by energetic particle precipitation. Significant increases in the intensity of the irregularities within the polar cap region of both hemispheres were associated with the formation and evolution of the storm enhanced density/tongue of ionization structures and polar patches.

Cherniak, Iurii; Zakharenkova, Irina; Redmon, Robert;

Published by: Space Weather      Published on: 09/2015

YEAR: 2015     DOI: 10.1002/swe.v13.910.1002/2015SW001237

auroral precipitation; geomagnetic storm; Ionosphere; irregularities; rate of TEC

E-region ionospheric storm on May 1\textendash3, 2010: GSM TIP model representation and suggestions for IRI improvement

his paper presents the model simulation results of ionospheric E-region parameters during geomagnetic storm on May 2\textendash3, 2010. For this investigation we used the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in West Department of IZMIRAN. GSM TIP model simulations were performed using empirical model of high-energy electron precipitation. The temporal and spatial distributions of the lower ionosphere parameters and minor neutral species are presented. GSM TIP model results of E-region parameters are compared with IRI-2012 model. The differences between model results are discussed.

Bessarab, F.S.; Korenkov, Yu.N.; Klimenko, V.V.; Klimenko, M.V.; Zhang, Y.;

Published by: Advances in Space Research      Published on: 08/2014

YEAR: 2015     DOI: 10.1016/j.asr.2014.08.003

E-region; Electric field; geomagnetic storm; Ionospheric modeling; IRI-2012; Nitric oxide density

Effects of geomagnetic storm on low latitude ionospheric total electron content: A case study from Indian sector

The effect of geomagnetic storms on low latitude ionosphere has been investigated with the help of Global Positioning System Total Electron Content (GPS-TEC) data. The investigation has been done with the aid of TEC data from the Indian equatorial region, Port Blair (PBR) and equatorial ionization anomaly region, Agartala (AGR). During the geomagnetic storms on 24th April and 15th July 2012, significant enhancement up to 150\% and depression up to 72\% in VTEC is observed in comparison to the normal day variation. The variations in VTEC observed from equatorial to EIA latitudes during the storm period have been explained with the help of electro-dynamic effects (prompt penetration electric field (PPEF) and disturbance dynamo electric field (DDEF)) as well as mechanical effects (storm-induced equatorward neutral wind effect and thermospheric composition changes). The current study points to the fact that the electro-dynamic effect of geomagnetic storms around EIA region is more effective than at the lower latitude region. Drastic difference has been observed over equatorial region (positive storm impact) and EIA region (negative storm impact) around same longitude sector, during storm period on 24th April. This drastic change as observed in GPS-TEC on 24th April has been further confirmed by using the O/N₂\ ratio data from GUVI (Global Ultraviolet Imager) as well as VTEC map constructed from IGS data. The results presented in the paper are important for the application of satellite-based communication and navigational system.

Chakraborty, Monti; Kumar, Sanjay; De, Barin; Guha, Anirban;

Published by: Journal of Earth System Science      Published on: 07/2015

YEAR: 2015     DOI: 10.1007/s12040-015-0588-3

geomagnetic storm; Ionospheric total electron content; low latitude ionosphere

Using IRI and GSM TIP model results as environment for HF radio wave propagation model during the geomagnetic storm occurred on September 26–29, 2011

This paper analyses the geomagnetic storm on September 26–29, 2011. We compare the calculation results obtained using the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) and IRI-2012 (Bilitza et al., 2014) model with ground-based ionosonde data of stations at different latitudes and longitudes. We examined physical mechanisms responsible for the formation of ionospheric effects during the main phase of geomagnetic storm that occurred at the rising phase of the 24th solar cycle. We used numerical results obtained from IRI-2012 and GSM TIP models as propagation environment for HF signals from an equatorial transmitter during quiet and disturbed conditions. We used the model of HF radio wave propagation developed in I. Kant Baltic Federal University (BFU) that is based on the geometrical optics approximation. We compared the obtained radio paths in quiet conditions and during the main and recovery storm phases and evaluated radio wave attenuation in different media models.

Kotova, D.S.; Klimenko, M.V.; Klimenko, V.V.; Zakharov, V.E.; Ratovsky, K.G.; Nosikov, I.A.; Zhao, B.;

Published by: Advances in Space Research      Published on:

YEAR: 2015     DOI: 10.1016/j.asr.2015.05.009

HF radio wave propagation model; IRI model; First principles model; ionosonde; 3 layer; geomagnetic storm

The responses of ionospheric topside diffusive fluxes to two geomagnetic storms in October 2002

O⁺ field-aligned ambipolar diffusive velocities V_d and fluxes Ф_d in the topside ionosphere have been calculated from the observed profiles of electron density, ion, and electron temperatures during a 30 day incoherent scatter radar experiment conducted at Millstone Hill (288.5\textdegreeE, 42.6\textdegreeN) from 4 October to 4 November 2002. Two geomagnetic storms took place during this period. During the negative phases (depleted electron densities) of these two storms, the magnitudes of the daytime upward V_d and Ф_d were less than their averaged quiet time values. Whereas at nighttime, the downward V_d and Ф_d were sometimes larger than the averaged quiet time values. The variations in diffusive velocity and flux during the storm main and recovery phases were caused by changes in the ionospheric scale height or the shapes of ionospheric density profiles. The negative storm effect further reduced daytime diffusive flux. During these two storms, positive ionosphere phases (enhanced electron densities) were also observed. The diffusive velocity was much smaller during the period of positive storm effect, which led to a smaller diffusive flux than the quiet time one, although electron density was higher. It appears that storm time variations in diffusive velocity were more the results of storm time changes in the plasma vertical profile, rather than the cause of these plasma density changes.

Chen, Guang-Ming; Xu, JiYao; Wang, Wenbin; Lei, Jiuhou; Zhang, Shun-Rong;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2014

YEAR: 2014     DOI: 10.1002/2014JA020013

diffusion; geomagnetic storm; scale height; topside ionosphere

Storm-time behaviors of O/N2 and NO variations

Algorithms have been developed to extract net nitric oxide (NO) radiances in the wavelength range of 172\textendash182\ nm from the dayside TIMED/GUVI spectrograph data and convert them to NO column density (100\textendash150\ km). The thermospheric O/N₂ column density ratios (referenced from an altitude ~135\ km with a N₂column density of 10¹⁷\ cm^-2) are also obtained from the spectrograph data. The spatial resolution of the NO and O/N₂ products along the GUVI orbit is 240\ km. The coincident O/N₂ ratio and NO column density maps during a few geomagnetic storms reveal two major features: (1) Storm-time O/N₂ depletion and NO enhancement extend from high to mid and low latitudes. They are anti-correlated on a global scale, (2) the NO enhancement covers a wider longitude and latitude region than O/N₂ depletion on a local scale. The similarity between O/N₂ depletion and NO enhancement on global scale is due to storm-time equatorward meridional wind that brings both O/N₂ depleted and NO enhanced air from high to low latitudes. The altitude dependence of the storm-time meridional wind, different peaks altitudes of the local O/N₂ and NO variations, and long life time of NO (one day or longer) may explain the different behaviors of O/N₂ and NO on a local scale.

Zhang, Y.; Paxton, L.J.; Morrison, D.; Marsh, D.; Kil, H.;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 07/2014

YEAR: 2014     DOI: 10.1016/j.jastp.2014.04.003

geomagnetic storm; Thermospheric nitric oxide; Thermospheric O/N2 ratio

Traveling ionospheric disturbances observed at South African midlatitudes during the 29--31 October 2003 geomagnetically disturbed period

This paper presents traveling ionospheric disturbances (TIDs) observations from GPS measurements over the South African region during the geomagnetically disturbed period of 29\textendash31 October 2003. Two receiver arrays, which were along two distinct longitudinal sectors of about 18\textdegree-20\textdegree and 27\textdegree-28\textdegree were used in order to investigate the amplitude, periods and virtual propagation characteristics of the storm induced ionospheric disturbances. The study revealed a large sudden TEC increase on 28 October 2003, the day before the first of the two major storms studied here, that was recorded simultaneously by all the receivers used. This pre-storm enhancement was linked to an X-class solar flare, auroral/magnetospheric activities and vertical plasma drift, based on the behaviour of the geomagnetic storm and auroral indices as well as strong equatorial electrojet. Diurnal trends of the TEC and foF2 measurements revealed that the geomagnetic storm caused a negative ionospheric storm; these parameters were depleted between 29 and 31 October 2003. Large scale traveling ionospheric disturbances were observed on the days of the geomagnetic storms (29 and 31 October 2003), using line-of-sight vertical TEC (vTEC) measurements from individual satellites. Amplitude and dominant periods of these structures varied between 0.08\textendash2.16 TECU, and 1.07\textendash2.13\ h respectively. The wave structures were observed to propagate towards the equator with velocities between 587.04 and 1635.09\ m/s.

Katamzi, Zama; Habarulema, John;

Published by: Advances in Space Research      Published on: 01/2014

YEAR: 2014     DOI: 10.1016/j.asr.2013.10.019

geomagnetic storm; Substorm; Total electron content (TEC); Traveling ionospheric disturbances (TIDs)

The effect of geomagnetic-storm-induced enhancements to ionospheric emissions on the interpretation of the TIMED/GUVI O/N ₂ ratio

[1]\ We examine the consequence of enhanced atomic oxygen (OI) 135.6 nm emissions due to the recombination of O⁺ with electrons on the column number density ratio of atomic oxygen to molecular nitrogen (O/N₂ ratio) provided by Global Ultraviolet Imager (GUVI) on board the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics satellite. GUVI O/N₂ ratio is derived from the measurements of OI 135.6 nm and N₂ Lyman-Birge-Hopfield airglow emissions. The OI 135.6 nm emission arises from two sources: photoelectron impact excitation of neutral atomic oxygen and the radiative recombination of O⁺ with electrons. We estimate the O/N₂ ratio disturbance associated with the O⁺ density enhancement during geomagnetic storms through the case study of the storms on 20 November 2003 and 8 November 2004. The OI 135.6 nm emission enhancement originating from the ionosphere is derived using the Utah State University Global Assimilation of Ionospheric Measurements model ionosphere. Our results show that the O/N₂ ratio increase from the equator to middle latitudes during the storm periods is primarily associated with thermospheric neutral composition disturbances. However, the contribution of the OI 135.6 nm emission originating from the ionosphere to the storm time O/N₂ ratio increase is substantial in the northern low-middle latitude regions where severe plasma density enhancements occur during the main phase of the storms. Therefore, the ionospheric contribution should be considered for an accurate assessment of the storm time O/N₂ ratio increase at low-middle latitudes during these large storm events.

Lee, Woo; Kil, Hyosub; Paxton, Larry; Zhang, Yongliang; Shim, Ja;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2013

YEAR: 2013     DOI: 10.1002/2013JA019132

geomagnetic storm; GUVI O/N2 ratio; ionospheric effect

Storm time spatial variations in TEC during moderate geomagnetic storms in extremely low solar activity conditions (2007--2009) over Indian region

The total electron content (TEC) measurements from a network of GPS receivers were analyzed to investigate the storm time spatial response of ionosphere over the Indian longitude sector. The GPS receivers from the GPS Aided Geo Augmented Navigation (GAGAN) network which are uniquely located around the \~77\textdegreeE longitude are used in the present study so as to get the complete latitudinal coverage from the magnetic equator to low mid-latitude region. We have selected the most intense storms but of moderate intensity (-100\ nT\ \<\ Dst\ \<\ -50\ nT) which occurred during the unusually extremely low solar activity conditions in 2007\textendash2009. Though the storms are of moderate intensity, their effects on equatorial to low mid-latitude ionosphere are found to be very severe as TEC deviations are more than 100\% during all the storms studied. Interesting results in terms of spatial distribution of positive/negative effects during the main/early recovery phase of storms are noticed. The maximum effect was observed at crest region during two storms whereas another two storms had maximum effect near the low mid-latitude region. The associated mechanisms like equatorial electrodynamics and neutral dynamics are segregated and explained using the TIMED/GUVI and EEJ data during these storms. The TEC maps are generated to investigate the storm time development/inhibition of equatorial ionization anomaly (EIA).

Sunda, Surendra; Vyas, B.M.; Khekale, P.V.;

Published by: Advances in Space Research      Published on: 07/2013

YEAR: 2013     DOI: 10.1016/j.asr.2013.03.006

Electrodynamics; Equatorial and low-latitude; geomagnetic storm; Total electron content (TEC)

Ionospheric response to a geomagnetic storm during November 8--10, 2004

This paper investigates the response of the equatorial, and near equatorial, ionosphere to geomagnetic disturbances during the period November 8-10, 2004. Ionosonde data from Trivandrum (8.5\textdegreeN 77\textdegreeE and dip 0.5\textdegreeN) and SHAR (13.5\textdegreeN, 80.2\textdegreeE, dip \~5.5\textdegreeN), magnetic field data from Tirunelveli (8.7\textdegreeN, 76.9\textdegreeE, dip latitude 0.5\textdegreeS) and Alibag (18.64\textdegreeN, 72.87\textdegreeE), and GUVI O/N₂ data in the Indian longitude sector, are used for the study. The behavior of interplanetary parameters is also examined in conjunction with the ionospheric data. On 8 November, the EIA around noontime is not fully inhibited even though the electrojet strength an indicates inhibition of EIA due to a disturbance dynamo electric field effect. It is the enhanced O/N₂ over TRV and SHAR, with a larger increase over SHAR, which results in a larger (than expected) value of the EIA proxy parameter. On 9 November, the comparable values of f_oF₂ at TRV and SHAR around noon time is due to the combined effect of a weakened anomaly in the presence disturbance dynamo electric field effects leading to the EIA crest being near SHAR, and increased O/N₂ values at TRV and SHAR with a larger increase at TRV. On 10 November, the very strong values of the EIA proxy-SHAR parameter is attributed to the combined effects of prompt penetration electric field related modulations of EIA, and significant O/N₂ changes at the equatorial, and near equatorial, latitude. Thus, the study reveals the important role of storm-induced O/N₂ changes, along with prompt penetration electric fields and disturbance dynamo electric fields in modulating the ionization distribution in the equatorial ionization anomaly (EIA) region during this period.

Simi, K.; Manju, G.; Haridas, M.; Nayar, S.; Pant, Tarun; Alex, S.;

Published by: Earth, Planets and Space      Published on: 05/2013

YEAR: 2013     DOI: 10.5047/eps.2012.09.005

Equatorial Electrojet; Equatorial ionization anomaly; geomagnetic storm; O/N2 ratio

Disturbance dynamo, prompt penetration electric field and overshielding in the Earth's ionosphere during geomagnetic storm

This paper presents a result of model calculation of the disturbance dynamo electric field, prompt penetration, overshielding and their ionospheric effects during geomagnetic storm on December 14\textendash15, 2006. The calculations were carried out with use of the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP model) developed in WD IZMIRAN. Simulations were performed for quiet and disturbed conditions with took into account the magnetospheric convection electric field with and without took into account dynamo electric field. It has allowed to neglecting thermospheric and ionospheric effects of the disturbance dynamo electric field. The analysis of model calculation results was carried out. We have made conclusions about the role of the disturbance dynamo electric field, prompt penetration electric field and overshielding effects in thermospheic and ionospheric parameters during geomagnetic storm.

Klimenko, M.V.; Klimenko, V.V.;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 12/2012

YEAR: 2012     DOI: 10.1016/j.jastp.2012.02.018

Disturbance dynamo electric field; geomagnetic storm; Numerical modeling; Overshielding; prompt penetration electric field

Effects observed in the equatorial and low latitude ionospheric F-region in the Brazilian sector during low solar activity geomagnetic storms and comparison with the COSMIC measurements

The main objective of the present investigation has been to compare the ionospheric parameters (NmF2 and hmF2) observed by two ground-based ionospheric sounders (one at PALMAS- located near the magnetic equator and the other at Sao Jose dos Campos-located in the low-latitude region) in the Brazilian sector with that by the satellite FORMOSAT-3/COSMIC radio occultation (RO) measurements during two geomagnetic storms which occurred in December 2006 and July 2009. It should be pointed out that in spite of increasing the latitude (to 10\textdegree) and longitude (to 20\textdegree) around the stations; we had very few common observations. It has been observed that both the peak electron density (NmF2) and peak height (hmF2) observed by two different techniques (space-borne COSMIC and ground-based ionosondes) during both the geomagnetic storm events compares fairly well (with high correlation coefficients) at the two stations in the Brazilian sector. It should be pointed out that due to equatorial spread F (ESF) in the first storm (December 2006) and no-reflections from the ionosphere during nighttime in the second storm (July 2009), we had virtually daytime data from the two ionosondes.

Sahai, Y.; de Jesus, R.; Fagundes, P.R.; Selhorst, C.L.; de Abreu, A.J.; Ram, Tulasi; Aragon-Angel, A.; Pillat, V.G.; Abalde, J.R.; Lima, W.L.C.; Bittencourt, J.A.;

Published by: Advances in Space Research      Published on: 11/2012

YEAR: 2012     DOI: 10.1016/j.asr.2012.07.006

COSMIC satellite; F-region; geomagnetic storm; Ionosphere; Low solar activity

GPS-TEC variations during low solar activity period (2007--2009) at Indian low latitude stations

The paper is based on the ionospheric variations in terms of vertical total electron content (VTEC) for the low solar activity period from May 2007 to April 2009 based on the analysis of dual frequency signals from the Global Positioning System (GPS) satellites recorded at ground stations Varanasi (Geographic latitude 25\textdegree16 \ N, Longitude 82\textdegree59 \ E), situated near the equatorial ionization anomaly crest and other two International GNSS Service (IGS) stations Hyderabad (Geographic latitude 17\textdegree20 \ N, longitude 78\textdegree30 \ E) and Bangalore (Geographic latitude 12\textdegree58 \ N, longitude 77\textdegree33 \ E) in India. We describe the diurnal and seasonal variations of total electron content (TEC), and the effects of a space weather related event i.e. a geomagnetic storm on TEC. The mean diurnal variation during different seasons is brought out. It is found that TEC at all the three stations is maximum during equinoctial months (March, April, September and October), and minimum during the winter months (November, December, January and February), while obtaining intermediate values during summer months (May, June, July and August). TEC shows a semi-annual variation. TEC variation during geomagnetic quiet as well as disturbed days of each month and hence for each season from May 2007 to April 2008 at Varanasi is examined and is found to be more during disturbed period compared to that in the quiet period. Monthly, seasonal and annual variability of GPS-TEC has been compared with those derived from International Reference Ionosphere (IRI)-2007 with three different options of topside electron density, NeQuick, IRI01-corr and IRI 2001. A good agreement is found between the GPS-TEC and IRI model TEC at all the three stations.

Kumar, Sanjay; Priyadarshi, S.; Krishna, Gopi; Singh, A.;

Published by: Astrophysics and Space Science      Published on: 05/2012

YEAR: 2012     DOI: 10.1007/s10509-011-0973-6

geomagnetic storm; GPS; Ionospheric total electron contents; IRI model

The source of the steep plasma density gradient in middle latitudes during the 11--12 April 2001 storm

A steep plasma density gradient has been observed in the middle-latitude F region during large geomagnetic storms. This phenomenon can be understood as a special form of the middle-latitude ionization trough (hereafter trough), but its causal linkage has not yet been clarified. We investigate the association of the steep density gradient and the trough by comparing their morphologies and occurrence locations using the satellite and ground observation data during the 11\textendash12 April 2001 storm. Steep density gradients are detected in the dusk sector at the equatorward edges of the aurora by the Defense Meteorological Satellite Program (DMSP) F13 spacecraft. The locations of the steep density gradients coincide with the locations of the ionospheric footprints of the plasmapause identified by the Imager for Magnetopause-to-Aurora Global Exploration satellite. These observations demonstrate that the steep density gradient is created at the typical location of the trough. However, the steep density gradient is not produced by the formation of an intense trough during the storm. The temporal evolution of the total electron content maps shows that the steep density gradient observed at dusk by DMSP is associated with the plasma density enhancement in the dayside and its corotation into the dusk sector. The severe plasma density enhancement in middle latitudes, in combination with the trough and presumably the plasma depletion in high latitudes by the neutral composition change, produces the steep density gradient in the subauroral region during the storm.

Park, S.; Kim, K.-H.; Kil, H.; Jee, G.; Lee, D.-H.; Goldstein, J.;

Published by: Journal of Geophysical Research      Published on: 05/2012

YEAR: 2012     DOI: 10.1029/2011JA017349

geomagnetic storm; plasma trough; steep density gradient

Disturbances in the ionospheric F-region peak heights in the American longitudinal sector during geomagnetic storms of September 2005

In this paper, we use the modified GSM TIP model to explore how the thermosphere–ionosphere system in the American longitudinal sector responded to the series of geomagnetic storms on September 9–14, 2005. Comparison of modeling results with experimental data at Millstone Hill, USA (42.6°N, 71.5°W), Ramey, Puerto Rico (18.3°N, 66.8°W) and Jicamarca, Peru (11.9°S, 76.9°W) has shown a good agreement of ionospheric disturbances in the F-region maximum height. We examine in detail the formation mechanisms of these disturbances at different latitudes and describe some of the important physical processes affecting the behavior of the F-region. In addition, we consider the propagation of thermospheric wind surge and the formation of additional layers in the low-latitude ionosphere during geomagnetic storms.

Klimenko, M.V.; Klimenko, V.V.; Ratovsky, K.G.; Goncharenko, L.P.;

Published by: Advances in Space Research      Published on:

YEAR: 2011     DOI: https://doi.org/10.1016/j.asr.2011.06.002

geomagnetic storm; Ionospheric modeling; F-region maximum height; Electric field; F3-layer; Thermospheric wind surge

Observations of the ionospheric response to the 15 December 2006 geomagnetic storm: Long-duration positive storm effect

The long-duration positive ionospheric storm effect that occurred on 15 December 2006 is investigated using a combination of ground-based Global Positioning System (GPS) total electron content (TEC), TOPEX and Jason-1 TEC, and topside ionosphere/plasmasphere TEC, GPS radio occultation, and tiny ionospheric photometer (TIP) observations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. This multi-instrument approach provides a unique view of the ionospheric positive storm effect by revealing the storm time response in different altitude regions. The ground-based GPS TEC, TOPEX/Jason-1 TEC, and topside ionosphere/plasmasphere TEC all reveal significant enhancements at low latitudes to midlatitudes over the Pacific Ocean region during the initial portions of the storm main phase from 0000–0400 universal time (UT) on 15 December. At low latitudes, the topside ionosphere/plasmasphere TEC increase represents greater than 50\% of the TEC enhancement that is observed by ground-based GPS receivers. Moreover, electron density profiles obtained using the technique of GPS radio occultation demonstrate that the F layer peak height increased by greater than 100 km during this time period. The effects of soft particle precipitation are also apparent in the COSMIC observations of topside ionosphere/plasmasphere TEC. The positive storm effects over the Pacific Ocean region remain present in the equatorial ionization anomaly crest regions beyond 1200 UT on 15 December. This long-lasting positive storm effect is most apparent in ground-based GPS TEC and COSMIC TIP observations, while only a small increase in the topside ionosphere/plasmasphere TEC after 0400 UT is observed. This indicates that the long-lasting positive storm effect occurs predominantly at F region altitudes and, furthermore, that refilling of the topside ionosphere and plasmasphere is not the primary mechanism for producing the long-lasting positive storm phase during this event. The observations suggest that the enhanced eastward electric field and equatorward neutral wind are likely to play a significant role in the generation of long-lasting positive storm effects.

Pedatella, N.; Lei, J.; Larson, K.; Forbes, J.;

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

YEAR: 2009     DOI: https://doi.org/10.1029/2009JA014568

Ionosphere; geomagnetic storm

GPS observations of the ionospheric F2-layer behavior during the 20th November 2003 geomagnetic storm over South Korea

The ionospheric F2-layer peak density (NmF2) and its height (hmF2) are of great influence on the shape of the ionospheric electron density profile Ne (h) and may be indicative of other physical processes within the ionosphere, especially those due to geomagnetic storms. Such parameters are often estimated using models such as the semiempirical international reference ionosphere (IRI) models or are measured using moderately priced to expensive instrumentation, such as ionosondes or incoherent scatter radars. Global positioning system (GPS) observations have become a powerful tool for mapping high-resolution ionospheric structures, which can be used to study the ionospheric response to geomagnetic storms. In this paper, we describe how 3-D ionospheric electron density profiles were produced from data of the dense permanent Korean GPS network using the tomography reconstruction technique. These profiles are verified by independent ionosonde data. The responses of GPS-derived parameters at the ionospheric F2-layer to the 20th November 2003 geomagnetic storm over South Korea are investigated. A fairly large increase in the electron density at the F2-layer peak (the NmF2) (positive storm) has been observed during this storm, which is accompanied by a significant uplift in the height of the F2 layer peak (the hmF2). This is confirmed by independent ionosonde observations. We suggest that the F2-layer peak height uplift and NmF2 increase are mainly associated with a strong eastward electric field, and are not associated with the increase of the O/N₂ ratio obtained from the GUVI instruments aboard the TIMED satellite. It is also inferred that the increase in NmF2 is not caused by the changes in neutral composition, but is related to other nonchemical effects, such as dynamical changes of vertical ion motions induced by winds and E\ \texttimes\ B drifts, tides and waves in the mesosphere/lower thermosphere region, which can be dynamically coupled upward to generate ionospheric perturbations and oscillations.

Jin, Shuanggen; Luo, O.; Park, P.;

Published by: Journal of Geodesy      Published on: 03/2008

YEAR: 2008     DOI: 10.1007/s00190-008-0217-x

F2-layer; geomagnetic storm; GPS; Ionosphere; Tomography

Observations of a positive storm phase on September 10, 2005

In this study, we present multi-instrument observations of a strong positive phase of ionospheric storm, which occurred on September 10, 2005 during a moderate geomagnetic storm with minimum D_st=-60\ nT and maximum K_p=6\textendash. The daytime electron density measured by the Millstone Hill incoherent scatter radar (42.6\textdegreeN, 288.5\textdegreeE) increased after 13\ UT (\~8\ LT) compared with that before the storm. This increase is observed throughout the daytime, lasts for about 9\ h, and covers F-region altitudes above \~230\ km. At the altitude of 300\ km, the maximum increase in N_e reaches a factor of 3 by 19:30\textendash20:00\ UT and is accompanied by a \~1000\ K decrease in electron temperature, a \~100\textendash150\ K increase in ion temperature, and a strong upward drift. Observations by Arecibo ISR (18.3\textdegreeN, 293.3\textdegreeE) reveal similar features, with the maximum increase in electron density reaching a factor of 2.5 at 21:30\ UT, i.e. 1.5\textendash2\ h later than over Millstone Hill. The GPS TEC data show that the increase in electron density observed at Millstone Hill and Arecibo is only a part of a global picture reflected in TEC. The increase in TEC reaches a factor of 2 and covers middle and low latitudes at 19\ UT. At later times this increase moves to lower latitudes. A combination of mechanisms were involved in generation of positive phase. The penetration electric field resulted in N_e enhancements at subauroral and middle latitudes, the TAD/TID played an important role at middle and lower latitudes, and increase in O/N₂ ratio could contribute to the observed positive phase at middle and lower latitudes. The results show the importance of an upward vertical drift at \~140\textendash250\ km altitude, which is observed for sustained period of time and assists in the convergence of ionization into the F-region.

Goncharenko, L.P.; Foster, J.C.; Coster, A.J.; Huang, C.; Aponte, N.; Paxton, L.;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 07/2007

YEAR: 2007     DOI: 10.1016/j.jastp.2006.09.011

F-region; geomagnetic storm; Ionosphere; positive phase

Ionospheric disturbances during the magnetic storm of 15 July 2000: Role of the fountain effect and plasma bubbles for the formation of large equatorial plasma density depletions

We investigate the role of the fountain effect and plasma bubbles for the formation of the large equatorial plasma depletions during the geomagnetic storm of 15 July 2000. The large equatorial plasma depletions are detected in the Atlantic sector on the night of the 15th by the Defense Meteorological Satellite Program (DMSP) F15 and the first Republic of China Satellite (ROCSAT-1). The observations show discontinuous drop of the plasma density at the walls of the depletions, flat plasma density inside the depletions, and persistence or growth of the depletions over night. These properties are not consistent with the trough morphology induced by the fountain effect. The coincident ionospheric observations of DMSP F15 and ROCSAT-1 demonstrate that the large depletions are created in the longitude regions where plasma bubbles are present. The occurrence of the large depletions after sunset, elongation in the north-south direction, formation of steep walls, and colocation with plasma bubbles at lower altitudes or earlier times suggest that the large depletions are closely associated with plasma bubbles.

Kil, Hyosub; Paxton, Larry;

Published by: Journal of Geophysical Research      Published on: 12/2006

YEAR: 2006     DOI: 10.1029/2006JA011742

Equatorial ionosphere; geomagnetic storm; ionospheric disturbances

Characteristics of the storm-induced big bubbles (SIBBs)

Large equatorial plasma depletions, referred to as storm-induced big bubbles (SIBBs), are detected from the Defense Meteorological Satellite Program F15 and from the first Republic of China Satellite during the large magnetic storms of 31 March 2001, 29 October 2003, and 20 November 2003. They occur in the equatorial region at night, are elongated in the north-south direction, have steep walls, and always coexist with plasma bubbles. These observations are consistent with the SIBB characteristics described in the companion paper by Kil and Paxton [2006] and corroborate that the SIBBs are associated with bubbles. We discuss the common characteristics of the SIBBs and the role of the E \texttimes B drift for the formation of the SIBBs.

Kil, Hyosub; Paxton, L.; Su, Shin-Yi; Zhang, Yongliang; Yeh, Hweyching;

Published by: Journal of Geophysical Research      Published on: 10/2006

YEAR: 2006     DOI: 10.1029/2006JA011743

Equatorial ionosphere; geomagnetic storm; irregularities

First look at the 20 November 2003 superstorm with TIMED/GUVI: Comparisons with a thermospheric global circulation model

The NASA TIMED/GUVI experiment obtained unprecedented far ultraviolet images of thermospheric composition and temperature during the intense geomagnetic storm on 20\textendash21 November 2003. Geographic maps of the atomic oxygen to molecular nitrogen column density ratio show severe depletions that extend to the equator near the peak of the storm. This ratio is a key indicator of how the thermospheric composition is disrupted at high latitudes and how the perturbed air moves globally as a result of dynamical forcing. For example, migrating regions of low oxygen-to-nitrogen air are invariably found to correlate with high thermospheric temperatures. As well, GUVI obtained altitudinal-latitudinal (limb) images of temperature and composition, which show how the disturbances vary at different heights. The ASPEN thermospheric global circulation model was used to test our understanding of these remarkable images. The resulting simulations of thermospheric response show good agreement with GUVI data prior to the peak of the storm on 20 November. During the peak and recovery phases, serious discrepancies between data and model are seen. Although this initial attempt to model the storm is encouraging, much more detailed analysis is required, especially of the high-latitude inputs. The GUVI images demonstrate that far ultraviolet imaging is becoming a crucial component of space weather research and development.

Meier, R.; Crowley, G.; Strickland, D.; Christensen, A.; Paxton, L.; Morrison, D.; Hackert, C.;

Published by: Journal of Geophysical Research      Published on: 09/2005

YEAR: 2005     DOI: 10.1029/2004JA010990

dayglow; geomagnetic storm; GUVI; remote sensing; thermospheric composition; TIMED