Total Electron Content Depletions Research Articles

Supersonic Waves Generated by the 18 November 2023 Starship Flight and Explosions: Unexpected Northward Propagation and a Man‐Made Non‐chemical Depletion

AbstractOn 18 November 2023, SpaceX launched the Starship, the tallest and the most powerful rocket ever built. The Super Heavy engine separated from the Starship spacecraft and exploded at 90 km of altitude, while the main core Starship continued to rise up to 149 km and exploded after ∼8 min of flight. In this work, we used data from ground‐based GNSS receivers and we analyzed total electron content (TEC) response to the Starship flight and the two explosions. For the first time, we observed large‐distance northward propagation of intensive 2,000 km V‐shaped ionospheric disturbances from the rocket trajectory. The observed perturbations, most likely, represent shock waves propagating with the cone angle of ∼14° on the North and ∼7° on the South against the flight track that corresponds to the Mach angle of the shock waves in the lower atmosphere. The Starship explosion also produced a non‐chemical depletion in the ionospheric TEC.

Monitoring the ionospheric conditions during the annular solar eclipse December 2019: A case study

This study investigates the ionospheric response to the December 26, 2019 annular solar eclipse over the southern tip of the Asia region, focusing on Malaysia, Sumatra, and Singapore. Utilizing data from GPS stations and ionosondes along the eclipse path, variations in Total Electron Content (TEC) and ionospheric foF2 parameters were analysed to assess the eclipse's impact. Results indicate a slight northward depletion of TEC, possibly linked to the Equatorial Ionization Anomaly (EIA), with up to −30% of depletions observed across all sites. Time delays in TEC and foF2 parameter responses suggest the influence of recombination and photochemical processes. Differences in depletion percentages between TEC and foF2 parameters may stem from production rate reductions during the eclipse. Post-sunset enhancements in TEC and foF2 parameters suggest the formation of ionospheric plasma blobs associated with Travelling Ionospheric Disturbances (TIDs) during the eclipse. While consistent with trends observed in prior studies, the study's findings highlight regional variations in ionospheric effects. This study enhances our understanding of ionospheric dynamics during solar eclipses and paves the way for further exploration in this area.

TEC disturbances caused by CME-triggered geomagnetic storm of September 6–9, 2017

This study investigates the ionospheric response to a geomagnetic storm triggered by a Coronal Mass Ejection (CME) during 6–9 September 2017, across GPS stations located in diverse geographical regions. We analyze the changes in the magnetic field component (ΔH), the Prompt Penetration Electric Fields (PPEF), and the Total Electron Content (TEC). We find that ΔH exhibits latitude-dependent responses during the storm, with high-latitude stations experiencing more significant reductions compared to low-latitude stations. The PPEF behavior is found to be directly correlated with solar wind disturbances. Particularly during the main phase of the storm, fluctuations in PPEF were clearly associated with negative values in the Dst index. The KIRU station, located at a high latitude, shows the most pronounced PPEF effects, indicating the increased susceptibility of high-latitude regions to solar wind interactions. The time series plot of TEC, covering a full month at different stations, shows a distinct diurnal pattern driven by solar ionization. Equatorial stations such as HYDE, BOU, HON (HNLC), and DODM exhibit the highest daily TEC values. During the geomagnetic storm, TEC disturbances are evident across all stations, with significant disturbances and varying trends in TEC depletion rate observed at different locations. The TEC values differ by 5–25 TECU during the storm period, suggesting intricate ionospheric responses to geomagnetic storms at different stations. This highlights the importance of considering different geographical regions to fully understand the ionospheric dynamics related to solar activities.

Assessment of the Origin of a Plasma Depletion Band Over the United States During the 8 September 2017 Geomagnetic Storm

AbstractThe development of an intense total electron content (TEC) depletion band over the United States during the 8 September 2017 geomagnetic storm was understood as the extension of an equatorial plasma bubble (EPB) to midlatitudes in previous studies. However, this study reports non‐EPB aspects within this phenomenon. First, the simultaneous emergence of the TEC depletion band at midlatitudes and EPBs in the equatorial region indicates that the midlatitude TEC depletion band is not initiated by an EPB. Second, the intensification of TEC depletion at midlatitudes during the decay of TEC depletion at intermediate latitudes is anomalous. Third, the location of the TEC depletion band at midlatitudes is inconsistent with the EPB location estimated from zonal plasma motion. Given ionospheric perturbations in North America from the beginning of the storm, it is plausible that the TEC depletion band was locally generated in association with these perturbations.

Statistical Characteristics of Total Electron Content Intensifications on Global Ionospheric Maps

AbstractGlobal ionospheric total electron content (TEC) maps exhibit TEC intensifications and depletions of various sizes and shapes. Characterizing key features on TEC maps and understanding their dynamic coupling with external drivers can significantly benefit space weather forecasting. However, comprehensive analysis of ionospheric structuring over decades of TEC maps is currently lacking due to large data volume. We develop feature extraction software based on image processing techniques to extract TEC intensification regions, that is, contiguous regions with sufficiently elevated TEC values than surrounding areas, from global TEC maps. Applying the software to the Jet Propulsion Laboratory Global Ionospheric Map data, we generate a TEC intensification data set for years 2003–2022 and carry out a statistical study on the number and strength of TEC intensifications. We find that the majority of the TEC maps (about 86%) are characterized with one or two intensification(s), while the rest of the TEC maps have three or more intensifications. Both the number and strength of TEC intensifications exhibit semi‐annual variation that peaks near equinoxes and dips near solstices, as well as an annual asymmetry with larger values around December solstice compared to June solstice. The number and strength of intensifications increase with enhanced solar extreme‐violet irradiance. The strength of intensifications also increases with elevated geomagnetic activity, but the number of intensifications does not. In addition, the number of intensifications is not correlated with the strength of intensifications.

The Relation Among the Ring Current, Subauroral Polarization Stream, and the Geospace Plume: MAGE Simulation of the 31 March 2001 Super Storm

AbstractThe geospace plume, referring to the combined processes of the plasmaspheric and the ionospheric storm‐enhanced density (SED)/total electron content (TEC) plumes, is one of the unique features of geomagnetic storms. The apparent spatial overlap and joint temporal evolution between the plasmaspheric plume and the equatorial mapping of the SED/TEC plume indicate strong magnetospheric‐ionospheric coupling. However, a systematic modeling study of the factors contributing to geospace plume development has not yet been performed due to the lack of a sufficiently comprehensive model including all the relevant physical processes. In this paper, we present a numerical simulation of the geospace plume in the 31 March 2001 storm using the Multiscale Atmosphere‐Geospace Environment model. The simulation reproduces the observed linkage of the two plumes, which, we interpret as a result of both being driven by the electric field that maps between the magnetosphere and the ionosphere. The model predicts two velocity channels of sunward plasma drift at different latitudes in the dusk sector during the storm main phase, which are identified as the sub‐auroral polarization stream (subauroral polarization streams (SAPS)) and the convection return flow, respectively. The SAPS is responsible for the erosion of the plasmasphere plume and contributes to the ionospheric TEC depletion in the midlatitude trough region. We further find the spatial distributions of the magnetospheric ring current ions and electrons, determined by a delicate balance of the energy‐dependent gradient/curvature drifts and the E × B drifts, are crucial to sustain the SAPS electric field that shapes the geospace plume throughout the storm main phase.

Unveiling the combined effects of neutral dynamics and electrodynamic forcing on dayside ionosphere during the 3–4 February 2022 “SpaceX” geomagnetic storms

Geomagnetic storms of G1-class were observed on 3 and 4 February 2022, which caused the loss of 38 out of 49 SpaceX satellites during their launch due to enhanced neutral density. The effects of storm-time neutral dynamics and electrodynamics over the American sector during this minor storm have been investigated using Global Positioning System—total electron content (TEC) and Global‐scale Observations of the Limb and Disk (GOLD) mission measured thermospheric composition and temperature. Results revealed an unexpected feature in terms of increase in O/N2 and depletion in TEC over the American low-latitudes. This feature is in addition to the classic storm time ionospheric variations of enhancement in ionospheric electron density in presence of enhanced O/N2 and an intense equatorial electrojet (EEJ). Further, significant morning-noon electron density reductions were observed over the southern mid-high latitudes along the American longitudes. Results from Multiscale Atmosphere-Geospace Environment (MAGE) model simulations elucidated storm-induced equatorward thermospheric wind which caused the strong morning counter electrojet by generating the disturbance dynamo electric field. This further explains the morning TEC depletion at low-latitudes despite an increase in O/N2. Sub-storm related magnetospheric convection resulted in significant noon-time peak in EEJ on 4 February. Observation and modelling approaches together suggested that combined effects of storm-time neutral dynamic and electrodynamic forcing resulted in significant ionospheric variations over the American sector during minor geomagnetic storms.

Ionospheric Super Bubbles Near Sunset and Sunrise During the 26–28 February 2023 Geomagnetic Storm

AbstractIonospheric equatorial plasma bubbles (EPBs) are usually generated around sunset over equatorial to low latitudes. In this study, super EPBs extending to middle latitudes were observed, which were freshly generated at both post‐sunset and near‐sunrise periods over East/Southeast Asia during the geomagnetic storm on 26–28 February 2023. The post‐sunset (near‐sunrise) EPB persisted ∼4 (8) hours, drifting eastward (westward) and extending up to ∼35°N. Strong L‐band scintillations, deep total electron content (TEC) depletions and significant positioning errors were caused by the post‐sunset EPB. However, the scintillations and TEC depletions linked with the near‐sunrise EPB were relatively weaker, and no apparent positioning error was caused. Before the onsets of the post‐sunset EPBs, rapid upward vertical plasma drifts of ∼60 m/s, which could be linked with storm‐time prompt penetration electric fields, were observed at magnetic equator. The upward vertical drifts could amplify the F‐region bottomside perturbation via increasing the growth rate of Rayleigh‐Taylor (R‐T) instability and lead to the generation of post‐sunset EPBs. On the other hand, before the onset of near‐sunrise EPBs, the uplift of F layer was more significant at higher latitudes than that at magnetic equator, probably indicating the presence of equatorward neutral wind. Both the equatorial F layer uplift and equatorward neutral wind could contribute to the growth of R‐T instability and favor the generation of near‐sunrise EPBs.

Trailing Equatorial Plasma Bubble Occurrences at a Low-Latitude Location through Multi-GNSS Slant TEC Depletions during the Strong Geomagnetic Storms in the Ascending Phase of the 25th Solar Cycle

The equatorial plasma bubbles (EPBs) are depleted plasma density regions in the ionosphere occurring during the post-sunset hours, associated with the signal fading and scintillation signatures in the trans-ionospheric radio signals. Severe scintillations may critically affect the performance of dynamic systems relying on global navigation satellite system (GNSS)-based services. Furthermore, the occurrence of scintillations in the equatorial and low latitudes can be triggered or inhibited during space weather events. In the present study, the possible presence of the EPBs during the geomagnetic storm periods under the 25th solar cycle is investigated using the GNSS-derived total electron content (TEC) depletion characteristics at a low-latitude equatorial ionization anomaly location, i.e., KL University, Guntur (Geographic 16°26′N, 80°37′E and dip 22°32′) in India. The detrended TEC with a specific window size is used to capture the characteristic depletion signatures, indicating the possible presence of the EPBs. Moreover, the TEC depletions, amplitude (S4) and phase scintillation (σφ) indices from multi-constellation GNSS signals are probed to verify the vulnerability of the signals towards the scintillation effects over the region. Observations confirm that all GNSS constellations witness TEC depletions between 15:00 UT and 18:00 UT, which is in good agreement with the recorded scintillation indices. We report characteristic depletion depths (22 to 45 TECU) and depletion times (28 to 48 min) across different constellations confirming the triggering of EPBs during the geomagnetic storm event on 23 April 2023. Unlikely, but the other storm events evidently inhibited TEC depletion, confirming suppressed EPBs. The results suggest that TEC depletions from the traditional geodetic GNSS stations could be used to substantiate the EPB characteristics for developing regional as well as global scintillation mitigation strategies.

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

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

On the quiet-time occurrence rates, severity and origin of L-band ionospheric scintillations observed from low-to-mid latitude sites located in Puerto Rico

In December 2021 three Global Navigation Satellite System (GNSS) ionospheric scintillation and Total Electron Content (TEC) monitors were installed in Puerto Rico (∼24.5° N dip latitude). The installation is part of an effort to better understand the occurrence of ionospheric irregularities and scintillation at mid-latitudes. Puerto Rico (PR) is commonly referred to as being located at mid-latitudes or at the boundary between low and mid-latitudes. Previous reports already presented observations of ionospheric irregularities and scintillation detected from PR. These observations, however, were limited in number. Additionally, the reports related the observed scintillation and irregularities events with different types of mid-latitude ionospheric disturbances. Here we present results from the analyses of the first three months of observations, December 21st, 2021 to March 20th, 2022. The analyses focus on the occurrence rate, severity and origin of scintillation detected on the signals tracked by the PR monitors during geomagnetically quiet times. We show that, out of the 43 geomagnetically quiet nights, 34 (∼80%) showed the occurrence of L-band scintillation. The results also indicate the recurrent existence of severe scintillation (S4 ∼ 1.0) accompanied by large TEC depletions. The temporal evolution of the observed scintillation showed that scintillation-causing plasma irregularities first occurred near the magnetic equator and propagated towards PR (reaching up to ∼22o dip latitude). Simultaneous space-based observations of the ionospheric F-region peak electron densities made by the GOLD mission confirmed that the quiet-time scintillation observed by the monitors in PR was associated with equatorial plasma bubbles. GOLD observations also show enhanced background F-region densities at the location of the Ionospheric Pierce Points of the affected GNSS signals, indicating conditions that favor the occurrence of intense scintillation.

Regional ionospheric TEC modeling during geomagnetic storm in August 2021- data fusion using multi-instrument observations

Regional ionospheric Total Electron Content (TEC) models are most significant to investigate the variability of ionosphere during all-weather conditions. Since the ground-based TEC measurements are not available in oceanic and polar regions, space-based observations are incorporated to increase the positional accuracy and reliability of Global Ionospheric TEC Maps (GIMs). Therefore, data fusion techniques are necessary to enhance the prediction capability of regional ionospheric models by considering multi-source data. In view of this, an attempt is made to investigate Equatorial Ionization Anomaly (EIA) structures in low-latitudinal Indian region using multi-instrument data. Data observations from background model CODEGIM, available International GNSS Service (IGS) stations in India, GNSS receivers at KLEF and Tripura stations, FORMOSAT/COSMIC radio occultation and SWARM during geomagnetic storm period August 26–28, 2021 are used for the study. Spherical Harmonics Function (SHF) of order 4 is employed along with Weighted Least Squares analysis (WLS), where separate weight constraint is computed for each data source. TEC maps of spatial resolution 5° x 5° and temporal resolution of 1 h are generated to illustrate the dynamic behavior of ionosphere. The standard deviation for 3 days is obtained as 0.42, 0.61 and 1.43 TECU respectively. TEC depletions and enhancements are observed on August 27 and 28, with mean values of 12.74 and 15.27 TECU respectively, demonstrating negative and positive storm effects.

Response of the Ionospheric Total Electron Content During St. Patrick's Day Geomagnetic Storm in 2015 over the Philippine-Taiwan Region

The ionospheric total electron content (TEC) response during the St. Patrick's Day geomagnetic storm of 2015 (max Kp = 8) is an interest of study in the field of space weather since it is the strongest geomagnetic storm of Solar Cycle 24. The cause of this storm is a coronal mass ejection (CME) from the Sun on 15 Mar 2015 recorded by SOHO/LASCO and arrived at ~ 05:00 UT 17 Mar 2015. The CME speed is estimated at ~ 668 km/s. At the initial phase of the storm, the disturbance storm time (Dst) index rose from 15 nanoteslas nT at 03:21–56 nT at 05:31 UT. The main phase of the storm caused the Dst index to drop to the minimum value of –223 nT from 05:31–22:33 UT on 17 Mar 2015. In the Philippine-Taiwan sector, TEC during the main phase was enhanced by ~ 25 TECU on 10 GNSS receiver stations and was depleted afterward with a maximum depletion of ~ 33 TECU on PBAS. The recovery phase showed a TEC depletion on all stations for the whole day. The minimum dTEC (differential TEC) is observed at PBAS (Basco, Batanes, Philippines), and the maximum percent depletion is observed at TWTF (Taoyuan, Taiwan) during the early hours of photoionization. Results from this study verified that GNSS TEC measurements along Asian sectors dropped significantly during St. Patrick's geomagnetic storm.

Machine learning approach for detection of plasma depletions from TEC

Ionospheric delay is of concern for trans-ionospheric radio communication, especially for the navigation systems relying on these satellite signals. Most of the ionospheric delays are estimated to a degree of first-order using dual frequency global navigation satellite system (GNSS) receivers except during irregularities and equatorial plasma bubbles. The plasma bubbles are observed as a decrease or reduction in total electron content (TEC) as a result of large-scale irregularities that are generated at the equatorial ionosphere. These plasma bubbles can be detected from TEC values visually or by using mathematical algorithms. The mathematical algorithms may have limitations based on assumptions made for the current dataset. Therefore, various machine learning (ML) techniques were tried by training them with selected TEC depletions that are verified for accuracy. From this study, the Random Forest Method (RFM) has performed well compared to other ML methods. The RFM is trained to use for the detection of TEC depletions from the Indian low-latitude region. The training accuracy obtained is 97.6%, with a minimum classification error of 0.023%. The result obtained from the confusion matrix ascertained that the proportion of positively classified cases that are truly positive that is the positive predictive value (PPV) is 96.8%. These statistical results are validated after plotting the observed TEC depletion patch obtained from the ML method. There are cases in which depletions detected by the ML method are appreciable over the mathematical algorithm. The ML technique once trained will not have inherent limitations, as there are no assumptions or threshold values needed to set as required by most of the mathematical algorithms. Thus, the results are encouraging and have scope for further improvement and advancement.

Ionospheric TEC Variation and Gravity Waves Signatures During the Solar Eclipse on 21 June 2020 Over Southern China

AbstractThe total electron content (TEC) derived from ground‐based BeiDou geostationary orbit (GEO) satellite receivers lying on both sides of the eclipse path is used to study the ionospheric variations in southern China, particularly targeting eclipse‐induced gravity waves in the ionosphere during the annular solar eclipse on 21 June 2020. Eclipse‐induced gravity waves (GWs) signatures with periods of about 70 min, from wavelet analysis, were identified on both sides of TEC observations, which are most likely to be induced in the thermosphere. However, there were significant differences in the intensity of the gravity waves on both sides of the eclipse path, gravity waves are stronger on the northern side of the eclipse path than on the southern side. Moreover, a postponement of TEC depletion shows on the northern side of the eclipse path which is caused by the convergence effect of the wind field. And at the same obstruction rate, GWs possibly can slightly adjust the postponement of TEC depletion on a small scale.

Convergence Effects on the Ionosphere During and After the Annular Solar Eclipse on 21 June 2020

AbstractIn this study, we analyze the observations of the ionosondes at Wuhan (30.4°N, 114.4°E, 82.4% obscuration), Xiamen (24.2°N, 118.07°E, 97.8% obscuration), and Nanning (22.7°N, 109.25°E, 81.1% obscuration), as well as the total electron content (TEC) from the global ionosphere maps (GIMs) to examine the ionospheric behaviors in the F‐region on 21 June 2020 solar eclipse day. The observations show that a TEC enhancement occurred after the major depression near the center path of the solar eclipse, and it lasts to midnight on the solar eclipse day. Notes that the occurrence of the TEC enhancement is accompanied by the prominent TEC depletion in the southern side of the center path in the nighttime. The independent in situ electron density (Ne) observation from the Swarm‐B satellite and the calibrated TEC profile from the radio occultation technique onboard the FORMOSAT‐7/Constellation Observing System for Meteorology, Ionosphere, and Climate‐2 satellites also observed the long‐lasting enhancement in the F2 region near midnight. The solar eclipse‐induced convergence effects can result in the long‐lasting ionospheric perturbations, which may further cause the spread‐F in the nighttime.

Multifrequency Observations of Postmidnight Ionospheric Irregularities From an Anomaly Crest Location

AbstractThe paper reports occurrences of postmidnight to early morning ionospheric depletions in total electron content (TEC) observed using the Low Earth Orbiting satellite beacon from Calcutta (22.57°N, 88.36°E geographic, and 32°N magnetic dip) situated around the northern crest of the equatorial ionization anomaly (EIA) in the Indian longitude sector for the period 2015–2016. These results are novel and contrary to the usual scenario of equatorial ionospheric irregularities being dominant during the early evening to pre‐midnight hours of equinoctial months. The TEC depletions, commonly called “bite‐outs,” exhibit amplitudes of 1–2.5 TECU, with maximum depletion found near the northern crest of the EIA around subionospheric coordinates 25.8°N and 82.2°E. These bite‐outs exhibited seasonal variabilities, with maximum occurrences found during local summer months. The observed TEC depletions during postmidnight hours point toward irregularities, which are not generated over the magnetic equator and drifted along magnetic field lines. A case study of the observation of these ionospheric disturbances has also been presented across a spectrum of frequencies, namely 150 and 400 MHz (Low Earth Orbit satellites), 250 MHz (Geostationary satellites), and 1.5 GHz (GPS—Medium Earth Orbit satellites) to establish the presence of irregularities of different scale sizes even during postmidnight hours.

Ionospheric Disturbances in Low‐ and Midlatitudes During the Geomagnetic Storm on 26 August 2018

AbstractPlasma density depletions at midlatitudes during geomagnetic storms are often understood in terms of equatorial plasma bubbles (EPBs) due to their morphological similarity. However, our study reports the observations that reveal the generation of plasma depletions at midlatitudes by local sources. During the geomagnetic storm on 26 August 2018, the Defense Meteorological Satellite Program and Swarm satellites detected plasma depletions at midlatitudes in the Asian sector in the absence of EPBs in the equatorial region. This observation and the total electron content (TEC) maps over Japan demonstrate that traveling ionospheric disturbances (TIDs) are the sources of midlatitude plasma depletions in the Asian sector. Near the west coast of the United States, the development of a narrow TEC depletion band was identified from TEC maps. The TEC depletion band, which is elongated in the northwest–southeast direction, moves toward the west with a velocity of approximately 240 m/s. The TEC at the TEC depletion band is about 5 TEC units (1016 m−2) smaller than the ambient TEC. As this band is confined to the midlatitudes, this phenomenon is not associated with an EPB. The characteristics of the TEC depletion band are consistent with those of medium‐scale TIDs. Observations in the Asian sector and the TEC depletion band over the United States demonstrate that plasma depletions can develop at midlatitudes by local sources. Therefore, the morphological similarity between midlatitude irregularities and EPBs or their coincident occurrence does not provide corroborating evidence of their connection.

Statistical Behavior of Large‐Scale Ionospheric Disturbances From High Latitudes to Mid‐Latitudes During Geomagnetic Storms Using 20‐yr GNSS‐TEC Data: Dependence on Season and Storm Intensity

AbstractTo establish the statistical behavior of ionospheric TEC variations from high latitudes to mid‐latitudes during the main and recovery phases of geomagnetic storms, we conducted a superposed epoch analysis of interplanetary magnetic field, solar wind, geomagnetic indices (AE and SYM‐H), and global navigation satellite system (GNSS)‐total electron content (TEC) data for 20 yr (2000–2019). In this study, we identify 663 geomagnetic storm events with the minimum SYM‐H value of less than −40 nT and investigate the characteristics of the TEC variations for the weak (−60 ≤ SYM‐Hmin < −40 nT), moderate (−100 ≤ SYM‐Hmin < −60 nT), and strong (−150 ≤ SYM‐Hmin < −100 nT) geomagnetic storms. The main results obtained from the present study are as follows: (a) The TEC enhancements related to the tongue of ionization (TOI), auroral oval, and storm‐enhanced density (SED) plume are more dominant in winter than in summer during the main phase of geomagnetic storms. (b) The structure of the mid‐latitude trough in the nighttime sector becomes unclear in winter. (c) The TEC depletion at auroral and mid‐latitudes (40°–70° GMLAT: geomagnetic latitude) starts to appear in the morning sector (8–10 hr GMLT: geomagnetic local time) during the main phase of geomagnetic storms and the decreased region extends in the lower latitude and GMLT directions with time. The negative storm activity tends to be enhanced significantly as the storm intensity becomes larger. The activity of the TEC depletion is dominant in summer than in winter, which is agreement with the classical ionospheric storm scenario.

Ionospheric and geomagnetic response to the total solar eclipse on 21 August 2017

Solar eclipses provide an excellent opportunity to study the effects of a sudden localized change in photoionization flux in the Earth's ionosphere and its consequent repercussion in the Geomagnetic field. We have focused on a subset of the data available from the North American 2017 eclipse in order to study VTEC measurements from GNSS data and geomagnetic field estimations from INTERMAGNET observatories near the eclipse path. Our simultaneous analysis of both datasets allowed us to quantify the ionosphere and magnetic field reaction to the eclipse event with which allowed us to compare how differently these take place in time. We found that studying the behaviour of VTEC differences with respect to reference values provides better insight of the actual eclipse effect and were able to characterize the dependence of parameters such as time delay of maximum depletion and recovery phase. We were also able to test models that link the ionospheric variations in a quantitative manner. Total electron content depletion measured from GNSS were fed into an approximation of Ashour-Chapman model at the locations of geomagnetic observatories and its predictions match the behaviour of magnetic field components in time and magnitude strikingly accurately.