Ionospheric Response Research Articles

Unexpected STEVE Observations at High Latitude During Quiet Geomagnetic Conditions

AbstractStrong Thermal Emission Velocity Enhancement (STEVE), is a captivating optical phenomenon typically observed in the mid‐latitude ionosphere. This paper presents an intriguing observation of a STEVE event at high‐latitudes, approximately 10 degrees poleward of previously documented observations. This event was recorded in Yellowknife, Canada, by a TREx RGB imager and a citizen scientist. Swarm satellites traversed the latitude of the observation, measuring extreme westwards ion drift velocities exceeding 4 km/s. Such velocities are more typically associated with the subauroral region located at mid‐latitudes, rather than at the high‐latitudes reported here. Significantly, this event occurred without a substorm, which differs from previous STEVE observations. While high‐latitude radars detected fast ionospheric equatorward flows, GOES satellite did not record any injections. These observations suggest that the inner magnetosphere is highly inflated. This unique case study raises new questions surrounding subauroral dynamics and the influence of magnetospheric configurations on ionospheric responses.

Ionospheric Total Electron Content Response to the Intense Geomagnetic Storm of 10th -11th May 2024 over Low, Mid and High Latitude Regions

In this paper, we investigated the response of ionospheric Total electron content (TEC) to the intense geomagnetic storm of 10th - 11th May 2024 using 6 Global Navigation Satellite System (GNSS) stations: BAKE (Geog. Lat.64.33o N; Geog. Lon. 96.02o W), BELE (Geog. Lat. 1.41o S; Geog. Lon. 48.46o W), MBAR (Geog. Lat. 0.60o S; Geog. Lon. 30.74o E), SUTH (Geog. Lat. 32.38o S; Geog. Lon. 20.81o E), BJFS (Geog. Lat. 39.61o N; Geo. Lon. 115.89o E) and DUND (Geog. Lat. 45.88o S; Geog. Lon.170.60o E) situated over low, mid and high latitude regions. The GPS-TEC data was extracted, processed and used to plot vertical total electron content (VTEC) verses universal time (UT) from 8th to 13th May 2024 for each GNSS receiver station. A contour plot of TEC variation was also plotted for each station from 8th to 13th May 2024. The results showed TEC enhancing significantly at the beginning of the storm, during daytime at the geomagnetic equator, with the exception of MBAR, where TEC increased at night. This was attributed to the effect of prompt penetration of electric field (PPEF). A reduction in TEC was also noted on 11th May 2024, during the recovery phase over all the GNSS receiver stations. This was attributed to the effect of the disturbance dynamo electric field (DDEF) and composition change. The contour plots showed diurnal variation in TEC concentration over each GNSS receiver station. The TEC concentration however reduced during the storm period.

Detecting covolcanic ionospheric disturbances using GNSS data and a machine learning algorithm

Many natural and man-made phenomena cause ionospheric responses that can be captured in total electron content data obtained from Global Navigation Satellite System observations. However, the increasing volume of the data poses challenges for its analysis. This study provides an algorithm for detecting covolcanic ionospheric disturbances in total electron content time series based on machine learning. Using the Sarychev Peak eruption (June 11–16, 2009) as an example, we identified and labeled the observational data, proposed data features, and generated datasets. The design and number of features were chosen considering the computational efficiency of the algorithm and its potential applicability in monitoring systems. A machine learning model based on a gradient boosting technique was trained and achieved a Matthews correlation coefficient of 0.86 on the test dataset, indicating the high quality. The proposed algorithm detects 96% of the disturbances in the datasets with a minimal number of false positives (48 out of 200 test files), exhibiting a significant improvement compared with the conventional STA\\LTA algorithm, which detected only 11% of the disturbances. The validation of the algorithm on data corresponding to the Calbuco (2015) and Hunga Tonga-Hunga Ha’apai (2022) volcanoes eruptions showed 94% and 81% of the disturbances detected, respectively.

Impacts of Extreme Ultraviolet Late Phase of the Solar Flare on Ionospheric Electrodynamics

Previous investigations of ionospheric electrodynamical responses to solar flares primarily focused on the main phases (MPs) of solar flares. Typical solar irradiance models for driving global ionosphere models do not include the extreme ultraviolet (EUV) late phase (ELP) of flares, which was recently observed with new high-quality solar EUV spectra. Thus, it is still unclear how ionospheric electrodynamics respond to the flare ELP. Here, we analyzed the ionospheric electrodynamical response to the MP and ELP of the X9.3 flare on 2017 September 6, using observations from ground magnetometers, along with simulation results from an ionosphere–thermosphere coupled model. Observations indicated an intensification of the dayside eastward equatorial electrojet (EEJ) by approximately 12 nT at the ELP peak as compared to the quiet day reference. Additionally, the dayside eastward electric field increased due to the ELP, which is different from the reduction of dayside electric fields during MP. The upward E × B plasma drifts decreased by 2.5 m s–1 during MP but increased by 0.75 m s–1 during the ELP. Altitude-dependent responses of ionospheric conductivities to the ELP modulated the relative contribution of the E- and F-region wind dynamo to zonal electric fields, resulting in an overall increase in the daytime eastward electric fields. Furthermore, combined effects of electric fields and conductivities enhancements contributed to EEJ intensification during the ELP. This study enhances our understanding of how solar flares with ELP change global ionospheric electric fields and currents.

Ionospheric response to the 08 April 2024 total solar eclipse over United States: a case study

Ionospheric response to the 08 April 2024 total solar eclipse over United States: a case study

The High Latitude Ionospheric Response to the Major May 2024 Geomagnetic Storm: A Synoptic View

AbstractThe high latitude ionospheric evolution of the May 10‐11, 2024, geomagnetic storm is investigated in terms of Total Electron Content and contextualized with Incoherent Scatter Radar and ionosonde observations. Substantial plasma lifting is observed within the initial Storm Enhanced Density plume with ionospheric peak heights increasing by 150–300 km, reaching levels of up to 630 km. Scintillation is observed within the cusp during the initial expansion phase of the storm, spreading across the auroral oval thereafter. Patch transport into the polar cap produces broad regions of scintillation that are rapidly cleared from the region after a strong Interplanetary Magnetic Field reversal at 2230UT. Strong heating and composition changes result in the complete absence of the F2‐layer on the eleventh, suffocating high latitude convection from dense plasma necessary for Tongue of Ionization and patch formation, ultimately resulting in a suppression of polar cap scintillation on the eleventh.

Study of Chinese regional ionospheric TEC response to magnetic storms during April 23–25, 2023

Study of Chinese regional ionospheric TEC response to magnetic storms during April 23–25, 2023

Persistent high-latitude ionospheric response to solar wind forcing

The solar wind continuously transfers energy into the Earth’s thermosphere-ionosphere system and variations in the solar wind properties modify the state of the system. The modifications are best visible during storm conditions when the ingestion of extreme amounts of solar wind energy into the thermosphere-ionosphere system causes global changes in thermosphere as well as large deviations in the ionospheric electron density from its quiet conditions. This study shows that there exists a persistent impact of the solar wind on the high-latitude electron density. A data set of 22 years of Total Electron Content (TEC) and 15 years of ionosonde data (critical frequency foF2 and height of maximum electron density hmF2) at Tromsø (70°N, 19°E) are used for correlation analyses with different solar wind parameters derived from measurements of the Advanced Composition Explorer (ACE). The results show that the ionospheric parameters systematically respond with an increase or decrease depending on local time, season and solar cycle. TEC and foF2 increase with solar wind energy during winter night conditions and decrease with increasing solar wind energy during summer daytime. The summer negative ionospheric response is more intense during solar maximum conditions, while the winter positive ionospheric response is stronger during solar minimum. An anomaly is observed around 10 UT (noon), when TEC and foF2 respond with an increase during solar minimum conditions. Cross polar cap plasma convection, particle precipitation and Joule heating are considered to be the main drivers of the electron density changes at Tromsø. Local time, season and solar cycle changes in the background ionosphere-thermosphere conditions lead to different effects of theses driving processes. The results help to better understand the variability of the high-latitude electron density and show that solar wind forcing causes a systematic and persistent response of the ionosphere which alternates depending on local time, season and solar cycle.

East–West Difference in the Ionospheric Response During the Recovery Phase of May 2024 Super Geomagnetic Storm Over the East Asian

AbstractIn this study, we offer an extensive examination of the F‐region ionospheric disturbances during the May 2024 superstorm, focusing primarily on the middle‐low latitude regions of East Asia. Our analysis is grounded in a wealth of data sources including Total Electron Content (TEC), ionospheric parameters NmF2 and hmF2, Electron Density Profile (EDP) retrieved from Radio Occultation (RO) data, and ∑[O]/[N2] from the Global Ultraviolet Imager (GUVI), among others, complemented by model simulations. The observed negative ionospheric storm effect, characterized by a significant and long‐lasting reduction in electron density across the entire China, commenced immediately following the sudden storm commencement (SSC) on 10 May and continued through the main and early recovery phase of the storm on 11 May. On 11–12 May, positive ionospheric storm impacts were initially observed in a restricted geographical area from the post‐midnight to sunrise, first manifesting over the eastern regions of China and then shifting to the central regions. Subsequently, a pronounced negative storm effect persisted throughout the later stages of recovery phase. In contrast, the western regions of China experienced a positive storm effect on 12 May followed by a comparatively mild negative storm phase. This persistent extensive zonal gradient in electron density across the East Asian region resembles the scenarios depicted in prior superstorms attributed to the thermospheric circulation patterns. The disparity in the ionospheric response from east to west in this area is probably a common feature during superstorms, potentially resulting from an arch‐shaped structure of elevated ∑[O]/[N2].

Influence of the October 14, 2023, Ring of Fire Annular Eclipse on the Ionosphere: A Comparison Between GNSS Observations and SAMI3 Model Prediction

AbstractCelestial phenomena such as solar eclipses disrupt the ionosphere's inherent photochemical, dynamic, and electrodynamic processes and can be viewed as a natural experiment that provides a unique opportunity to study ionospheric perturbations. We investigate the spatiotemporal ionospheric response induced by the 14 October 2023 annular eclipse using ground‐based Global Navigation Satellite System (GNSS) receivers located over the continental region of North and South America. The largest total electron content (TEC) change (∼22 TECU decrease) is observed over the path of the eclipse at around 16°–18°N which lies just before the greatest eclipse location. However, the percentage change in TEC here is ∼44% (of the background value), which is less than that observed at midlatitudes around 30°–35°N (∼18.7 TECU, ∼50%). We observed a latitudinal dependency of TEC variation and time delay in ionospheric response to the eclipse with midlatitudes experiencing greater TEC changes and longer time delays compared to low‐latitude and equatorial regions. The SAMI3 model used to simulate the impact of the eclipse, captures the large decrease in VTEC along the eclipse path. Interestingly, increases in the TEC are also observed in several GNSS sites and it varied from 4.5 to 6.5 TECU in the Northern Hemisphere and 7 to 12 TECU in the Southern Hemisphere. The SAMI3 model results also show an enhancement in TEC but significantly less than that observed. Moreover, the SAMI3 model simulations for individual GNSS site coordinates within the conjugate regions failed to predict accurately, the TEC enhancement recorded by the GNSS sites.

Exploring AI Progress in GNSS Remote Sensing: A Deep Learning Based Framework for Real‐Time Detection of Earthquake and Tsunami Induced Ionospheric Perturbations

AbstractGlobal Navigation Satellite System Ionospheric Seismology investigates the ionospheric response to earthquakes and tsunamis. These events are known to generate Traveling Ionospheric Disturbances (TIDs) that can be detected through GNSS‐derived Total Electron Content (TEC) observations. Real‐time TID identification provides a method for tsunami detection, improving tsunami early warning systems (TEWS) by extending coverage to open‐ocean regions where buoy‐based warning systems are impractical. Scalable and automated TID detection is, hence, essential for TEWS augmentation. In this work, we present an innovative approach to perform automatic real‐time TID monitoring and detection, using deep learning insights. We utilize Gramian Angular Difference Fields (GADFs), a technique that transforms time‐series into images, in combination with Convolutional Neural Networks (CNNs), starting from VARION (Variometric Approach for Real‐time Ionosphere Observation) real‐time TEC estimates. We select four tsunamigenic earthquakes that occurred in the Pacific Ocean: the 2010 Maule earthquake, the 2011 Tohoku earthquake, the 2012 Haida‐Gwaii, the 2015 Illapel earthquake. The first three events are used for model training, whereas the out‐of‐sample validation is performed on the last one. The presented framework, being perfectly suitable for real‐time applications, achieves 91.7% of F1 score and 84.6% of recall, highlighting its potential. Our approach to improve false positive detection, based on the likelihood of a TID at each time step, ensures robust and high performance as the system scales up, integrating more data for model training. This research lays the foundation for incorporating deep learning into real‐time GNSS‐TEC analysis, offering a joint and substantial contribution to TEWS progression.

Multi‐Instrument and SAMI3‐TIDAS Data Assimilation Analysis of Three‐Dimensional Ionospheric Electron Density Variations During the April 2024 Total Solar Eclipse

AbstractThis paper conducts a multi‐instrument and data assimilation analysis of the three‐dimensional ionospheric electron density responses to the total solar eclipse on 08 April 2024. The altitude‐resolved electron density variations over the continental US and adjacent regions are analyzed using the Millstone Hill incoherent scatter radar data, ionosonde observations, Swarm in situ measurements, and a novel TEC‐based ionospheric data assimilation system (TIDAS) with SAMI3 model as the background. The principal findings are summarized as follows: (a) The ionospheric hmF2 exhibited a slight enhancement in the initial phase of the eclipse, followed by a distinct reduction of 20–30 km in the recovery phase of the eclipse. The hmF2 in the umbra region showed a post‐eclipse fluctuation, characterized by wavelike perturbations of 10–25 km in magnitude and a period of 30 min. (b) There was a substantial reduction in ionospheric electron density of 20%–50% during the eclipse, with the maximum depletion observed in the F‐region around 200–250 km. The ionospheric electron density variation exhibited a significant altitude‐dependent feature, wherein the response time gradually delayed with increasing altitude. (c) The bottomside ionospheric electron density displayed an immediate reduction after local eclipse began, reaching maximum depletion 5–10 min after the maximum obscuration. In contrast, the topside ionospheric electron density showed a significantly delayed response, with maximum depletion occurring 1–2.5 hr after the peak obscuration.

Contributions of Ionospheric Migrating Tides to Ionospheric Intra‐Annual Variations

AbstractThe Earth's ionosphere undergoes regular intra‐annual variations (IAVs) characterized by two peaks and troughs around the equinoxes and solstices. This phenomenon is crucial for analyzing the ionospheric response to geomagnetic storms. This study presents a comprehensive analysis of the IAVs contributed by diurnal and semidiurnal migrating tides (DW1 and SW2) using Global Ionospheric Maps (GIMs) data from 2017 to 2021. Through data stacking techniques, the seasonal variability and splitting phenomenon of DW1 and SW2 across different latitudes are examined. The findings indicate that the splitting of these tides can be attributed to their quasi‐periodic variations, predominantly composed of annual oscillation (AO) and semiannual oscillation (SAO). The combination of DW1, SW2, and their side‐band harmonics results in beats with annual and semiannual periodicities, enabling the restoration of the seasonal variations in DW1 and SW2. The ionospheric day‐to‐day variations were reconstructed by superimposing DW1 and SW2, and their IAVs were evaluated using the envelope method. Comparison with IAVs driven by Earth's orbital geometry reveals that tide‐driven IAVs are more significant, and both exhibit solar activity dependence. The results advance the understanding of ionospheric variability, emphasizing the critical role of tidal contributions.

Ionosonde Measurement Comparison during an Interplanetary Coronal Mass Ejection (ICME)- and a Corotating Interaction Region (CIR)-Driven Geomagnetic Storm over Europe

A comparison of three types of ionosonde data from Europe during an interplanetary coronal mass ejection (ICME)- and a corotating interaction region (CIR)-driven geomagnetic storm event is detailed in this study. The selected events are 16–20 March 2015 for the ICME-driven storm and 30 May to 4 June 2013 for the CIR-driven one. Ionospheric data from three European ionosonde stations, namely Pruhonice (PQ), Sopron (SO) and Rome (RO), are investigated. The ionospheric F2-layer responses to these geomagnetic events are analyzed with the ionospheric foF2 and h’F2 parameters, the calculated deltafoF2 and deltahF2 values, the ratio of total electron content (rTEC) and Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite Global Ultraviolet Imager (GUVI) thermospheric [O]/[N2] measurement data. The storm-time and the quiet-day mean values are also compared, and it can be concluded that the quiet-day curves are similar at all the stations while the storm-time ones show the latitudinal dependence during the development of the storm. As a result of the electron density comparison, during the two events, it can be concluded that the sudden storm commencement (SSC) that characterized the ICME induced a traveling atmospheric disturbance (TAD) seen in the European stations in the main phase, while this is not seen in the CIR-driven ionospheric storm, which shows a stronger and more prolonged negative effect in all the stations, probably due to the season and the depleted O/N2 ratio.

Time‐Lagged Effects of Ionospheric Response to Severe Geomagnetic Storms on GNSS Kinematic Precise Point Positioning

AbstractThis paper investigates time‐lag effects of ionospheric response to two severe geomagnetic storms (Kp = 8) on the degradation of kinematic precise point positioning (PPP) solutions, utilizing over 5500 Global Navigation Satellite Systems (GNSS) stations distributed worldwide. Focusing on these two severe geomagnetic storms that occurred during solar cycle 24, the study employs an open‐source positioning software package, namely RTKLIB, to derive the PPP solutions. The findings reveal significant variations in time lags across different magnetic latitudes. These variations are driven by ionospheric responses to a southward interplanetary magnetic field and subsequent decreases in the SMY‐H index during the 2015 St. Patrick's Day Storm and the 2017 September 7–8 Storm. Specifically, at high latitudes, PPP degradation primarily manifests during the main phase of the storm, resulting in delays spanning from several minutes to 1–2 hr after the sudden onset of the storm. In contrast, mid‐ and low latitudes exhibit a wider range of delays extending up to tens of hours. Notably, rapid positioning degradation is observed predominantly at the magnetic local time noon and midnight sectors. The study discusses these time lag effects concerning the intensity of various ionospheric disturbances triggered by the interactions among the solar wind, magnetosphere, and ionosphere during geomagnetic storms. The insights obtained from this research have the potential to be integrated into physics‐based and machine‐learning models to enhance forecasting capabilities of space weather impacts.

Assessment of Satellite Differential Code Biases and Regional Ionospheric Modeling Using Carrier-Smoothed Code of BDS GEO and IGSO Satellites

The geostationary earth orbit (GEO) represents a distinctive geosynchronous orbit situated in the Earth’s equatorial plane, providing an excellent platform for long-term monitoring of ionospheric total electron content (TEC) at a quasi-invariant ionospheric pierce point (IPP). With GEO satellites having limited dual-frequency coverage, the inclined geosynchronous orbit (IGSO) emerges as a valuable resource for ionospheric modeling across a broad range of latitudes. This article evaluates satellite differential code biases (DCB) of BDS high-orbit satellites (GEO and IGSO) and assesses regional ionospheric modeling utilizing data from international GNSS services through a refined polynomial method. Results from a 48-day observation period show a stability of approximately 2.0 ns in BDS satellite DCBs across various frequency signals, correlating with the available GNSS stations and satellites. A comparative analysis between GEO and IGSO satellites in BDS2 and BDS3 reveals no significant systematic bias in satellite DCB estimations. Furthermore, high-orbit BDS satellites exhibit considerable potential for promptly detecting high-resolution fluctuations in vertical TECs compared to conventional geomagnetic activity indicators like Kp or Dst. This research also offers valuable insights into ionospheric responses over mid-latitude regions during the March 2024 geomagnetic storm, utilizing TEC estimates derived from BDS GEO and IGSO satellites.

GOLD Observations of the Merging of the Southern Crest of the Equatorial Ionization Anomaly and Aurora During the 10 and 11 May 2024 Mother's Day Super Geomagnetic Storm

AbstractUsing NASA's Global‐scale Observations of the Limb and Disk (GOLD) imager, we report nightside ionospheric changes during the G5 super geomagnetic storm of 10 and 11 May 2024. Specifically, the nightside southern crest of the Equatorial Ionization Anomaly (EIA) was observed to merge with the aurora near the southern tip of South America. During the storm, the EIA southern crest was seen moving poleward as fast as 450 m/s. Furthermore, the aurora extended to mid‐latitudes reaching the southern tips of Africa and South America. The poleward shift of the equatorial ionospheric structure and equatorward motion of the aurora means there was no mid‐latitude ionosphere in this region. These observations offer unique insights into the ionospheric response to extreme geomagnetic disturbances, highlighting the complex interplay between solar activity and Earth's upper atmosphere.

Low-latitude ionospheric responses and positioning performance of ground GNSS associated with the geomagnetic storm on March 13–14, 2022

Interplanetary coronal mass ejections (ICMEs) and the driven geomagnetic storms have a profound influence on the ionosphere, potentially leading to a degradation in positioning performance. In this study, we made a comprehensive analysis of the entire process of the impact of a typical ICME and its driven geomagnetic storm on the low-latitude ionosphere during March 13–14, 2022 (π-day storm) and the positioning performance of Global Navigation Satellite System (GNSS). During the passage of the ICME event, significant ionospheric scintillation, and TEC (total electron content) disturbances were observed in the low-latitude Hong Kong region. The ICME sheath region intensively compressed the magnetosphere via solar wind dynamic pressure enhancement and subsequently drove the storm main phase. It is found that both the magnetospheric compression that formed the storm initial phase and the storm main phase caused ionospheric scintillation. In comparison, the intensity of the ionospheric scintillation caused by the intense magnetospheric compression just before the storm main phase is even more pronounced. We also analyzed the impact of storms on standard point positioning (SPP), precise point positioning (PPP) and real-time kinematic (RTK) techniques. The positioning accuracies of single-frequency SPP and PPP experienced the most severe decline, and there was a noticeable increase in the initialization time for dual-frequency static PPP and RTK during the event. RTK demonstrated a shorter convergence time and higher accuracy during this event, but it was limited to short-baseline RTK (<30 km).

Ionospheric and meteorological response to total solar eclipses

Studies concerning solar eclipses have been rising significantly, yet, different circumstances during their occurrence provide uniqueness to every study. This paper studies the ionospheric and meteorological response to the total solar eclipses of August 21, 2017, March 20, 2015 and August 1, 2008. The ionospheric total electron content (TEC) was calculated from the signals beamed by the dual-frequency Global Positioning System (GPS) satellites and accessed from University NAVSTAR Consortium (UNAVCO) data archive. Similarly, the data of meteorological parameters were accessed from the historical climate archive of respective countries. The TEC drop of ∼2–7 TECU with a lag of ∼15–30 min is observed at varying latitudes which correspond with the findings of numerous past research. We analyzed the data of 15 stations under ∼100% obscuration to rule out the varying effects of different obscuration rates. Yet, given the turbulent nature of climate, we found varying changes at observed locations. A good relationship, however, was observed in 8 of the stations, where temperature drop ranged from 0.4 °C to 6.11 °C, and rise in relative humidity ranged from 0 to ∼77%. Wind speed has shown the most turbulent behavior. Their change was largely impacted by the eclipse on 5 of the stations, while the local factor was dominant on the others. In spite of this, the stations under observation showed distinct responses to the ionospheric change during the total solar eclipses, thus demonstrating the relation of meteorological parameters with eclipses.

ELF emission in the topside ionosphere from the ZEVS transmitter detected by CSES satellite

The extremely-low-frequency (ELF) response in the upper ionosphere to ground large-scale transmitter ZEVS on the Kola Peninsula has been detected by low-Earth orbiting satellite CSES (∼500 km altitude). When the satellite was in the vicinity of the ZEVS transmitter above the White Sea (horizontal distance ∼400–900 km), the electric and magnetic sensors detected a narrowband 82 Hz emission with amplitudes E≃1-3μV/m and B≃0.5-1.0 pT. We modeled the ELF wave field spatial structure in the upper ionosphere excited by an oscillating 82 Hz linear current with the 60 km length suspended above a high-resistive ground. Realistic altitudinal profiles of the plasma parameters during events under study have been reconstructed with the use of the IRI ionospheric model. The modeled amplitudes of electromagnetic response of the upper ionosphere are in reasonable agreement with the 82-Hz emission power recorded by the CSES satellite for a typical transmitter current intensity >100 A.