Ionospheric Density Research Articles

Improvement of topside ionosphere and plasmasphere estimation in ionospheric simulation system

This work is based on the results for a complete solar cycle of 11 years (2011–2021) from the ionospheric simulation system used in the Brazilian Space Weather program. The electron density profiles generated were integrated in height and compared to the International GNSS Service (IGS) vertical total electron content (vTEC) data. Experiments have shown an inadequate electron concentration decay with height which led to an overestimation in TEC values. We propose an improvement for the topside ionosphere and plasmasphere modeling in the system, considering recent advances in empirical modeling through observational data. The idea is to combine bottomside ionosphere estimates from the physical-based core model with NeQuick analytical formulation for ionospheric profile above hmF2. Our approach also calculates the ionospheric parameters for topside modeling using bottomside estimates. The ionospheric density profile decay obtained with the proposed approach was smoother and sharper, reaching a reduction of approximately 1 to 2 orders of magnitude of electron concentration in plasmasphere. It was observed a coherent reduction of high altitudes ionosphere/plasmasphere contribution to TEC. Also, the TEC values obtained using this hybrid solution were much closer to the International GNSS Service (IGS) data for the considered dataset, with root mean squared error (RMSE) of only 2.64 TECU for the entire period.

Low Ionosphere Density Above the Earthquake Epicentre Region of Mw 7.2, El Mayor–Cucapah Earthquake Evident from Dense CORS Data

Low Ionosphere Density Above the Earthquake Epicentre Region of Mw 7.2, El Mayor–Cucapah Earthquake Evident from Dense CORS Data

Ionospheric density depletions around crustal fields at Mars and their connection to ion frictional heating

Abstract. Mars' ionosphere is formed through ionization of the neutral atmosphere by solar irradiance, charge exchange, and electron impact. Observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft have shown a highly dynamic ionospheric layer at Mars impacted by loss processes including ion escape, transport, and electron recombination. The crustal fields at Mars can also significantly modulate the ionosphere. We use MAVEN data to perform a statistical analysis of density depletions of ionospheric species (O+, O2+, and electrons) around crustal fields. Events mostly occur when the crustal magnetic fields are radial, outward, and with a mild preference towards east in the planetocentric coordinates. We show that events near crustal fields are typically accompanied by an increase in suprathermal electrons within the depletion, either throughout the event or as a short-lived electron beam. However, no correlation between the changes in the bulk electron densities and suprathermal electron density variations is observed. Our analysis indicates that the temperature of the major ionospheric species, O2+, increases during most of the density depletion events, which could indicate that some ionospheric density depletions around crustal fields are a result of ion frictional heating.

Thermospheric Wind Response to March 2023 Storm: Largest Wind Ever Observed With a Fabry‐Perot Interferometer in Tromsø, Norway Since 2009

AbstractSolar cycles 24–25 were quiet until a geomagnetic storm with a Sym‐H index of −170 nT occurred in late March 2023. On March 23–24, a Fabry‐Perot interferometer (FPI; 630 nm) in Tromsø, Norway, recorded the highest thermospheric wind speed of over 500 m/s since 2009. Comparisons with magnetometer readings in Scandinavia showed that a large amount of electromagnetic energy was transferred to the ionosphere‐thermosphere system. Total electron content maps suggested an enlarged auroral oval and revealed that the FPI observed winds near the polar cap instead of inside the oval for a long period during the storm main phase. The FPI wind had a strong equatorward component during the storm, likely because of the powerful anti‐sunward ionospheric plasma flow in the polar cap. The positive Y‐component of the IMF for 6 days before the storm caused a successive westward component of the FPI‐measured wind during the storm main phase. On March 24, the first day of the storm recovery phase, thermospheric wind disturbed and the ionospheric density decreased significantly at high latitudes. This density depression lasted for several days, and a large amount of electromagnetic energy during the storm modified the thermospheric dynamics and ionospheric plasma density.

Energy Deposition into the Ionosphere during a Solar Flare with Extreme-ultraviolet Late Phase

Solar extreme-ultraviolet (EUV) irradiance is the dominant energy source for ionizing and heating the Earth’s upper atmosphere. It is common to assume that the spectra of different EUV lines have the same trend to fill the solar EUV irradiance gap for modeling purposes due to inadequate EUV irradiance measurements. However, the spectra across the EUV bands may not vary in the same trend. The flare radiation energy release in the EUV (10–120 nm) is about twice as much as X-rays (0.1–10 nm) during flare interval ∼03–06 UT on 2012 October 23. By assimilating the observed nonuniform varying, time-dependent, and high-resolution solar spectrum from the Solar Dynamics Observatory mission into the modeling framework, we provide the first direct evidence of nonuniform varying solar EUV fluxes during the solar flare EUV late phase (ELP) having appreciable effects on the dayside ionosphere. The total EUV radiation energy release (5.838 × 1028 erg) during the flare ELP is larger than that (5.698 × 1028 erg) during the flare main phase. The ELP of an X1.8-class solar flare on 2012 October 23 can increase the dayside ionospheric density at the subsolar point by ∼5 TECU and the ionospheric density enhancements extend from the bottom to the peak of the F2 region at low latitudes with relative changes ranging from ∼20% to ∼100%. Our results highlight the importance of incorporating a realistic, high spectral and temporal resolution solar irradiance spectrum into numerical models to capture the observed time-varying ionospheric response to solar flares.

Ionospheric response to PPEF events in the Indian region during high and low intense geomagnetic storms

Space weather variations can significantly affect ionospheric electron density, which can, in turn, adversely affect various navigational and communication technologies. One such phenomenon is the prompt penetration electric field. The convective electric field from a magnetospheric origin penetrates the lower ionosphere during a geomagnetic storm. The electric field penetrating the ionosphere can challenge space-based technologies. Thus, understanding the convectional electric field from higher latitudes to the low-latitudinal region during geomagnetic disturbance is critical. The ionosphere over the Indian region consists of equatorial and low latitude dynamics, such as equatorial ionization anomaly, that are highly dynamic even during the quiet days. Therefore, understanding the effects of prompt penetration electric field observed in the Equatorial Electrojet is of utmost importance over the Indian region. In the current study, two geomagnetic storms, the St. Patrick's Day storm of 17th March 2015 and another low intense storm of 8th June 2014, were chosen to understand the effects of PPEF over equatorial ionization anomaly. The ionospheric density was enhanced during the relatively less intense geomagnetic storm compared to the St. Patrick's Day storm. In these two events, large-scale ionospheric irregularities were observed from ROTI values during the local daytime hours, but no ionospheric scintillation was detected (S4 index).

Giant ionospheric density hole near the 2022 Hunga-Tonga volcanic eruption: multi-point satellite observations

A giant ionospheric hole was simultaneously detected in the in situ measurements of FORMOSAT-7/COSMIC-2 (F7/C2), Ionospheric Connection Explorer (ICON), Swarm missions, and ground-based total electron content (TEC) by global navigation satellite system receivers, and F7/C2 Global Ionosphere Specification (GIS) data near Tonga, following the explosive volcano eruption on 15 January 2022. The TEC maps displayed the huge depletions that developed near Tonga after the eruption and gradually evolved. The ICON IVM, F7/C2 IVM and Swarm-LP detected large depletions not only near Tonga, but also in the EIA trough region. The GIS observations clearly show the ionospheric hole that extends spatially near Tonga, especially strongly south/southward. The simultaneous observations showed that the ionosphere hole near Tonga combined with the EIA trough and finally evolved into a giant ionosphere hole around 07 UT. The ionospheric hole, which occurred at 05 UT near Tonga, extended over a wide area of 160°-200°E and 25°S-20°N and lasted for about 11 h. The F7/C2 and ICON satellites overpasses showed large ion density depletions by the hole at orbit altitudes, accompanied by enhancements in ion temperature and field-aligned and perpendicular ion drift. Such a long-lasting giant ionospheric hole by a seismic event has not been reported earlier, creating a unique ionospheric environment near Tonga after the eruption. The strong successive impulses by multiple volcano eruptions, together with O/N2 decrease in the summer hemisphere, interhemispheric wind, and water vapor injection into high altitudes apparently yielded such a giant ionospheric hole, 4–6 times larger than that observed during the Tohoku earthquake.Graphical

Estimation of dusk time F-region electron density vertical profiles using LSTM neural networks: A preliminary investigation

The vertical profile of the ionosphere density plays a significant role in the development of low-latitude Equatorial Plasma Bubbles (EPBs), that in turn lead to ionospheric scintillation which can severely degrade precision and availability of critical users of the Global Navigation Satellite System (GNSS). Accurate estimation of ionospheric delays through vertical electron density profiles is vital for mitigating GNSS errors and enhancing location-based services. The objective of this study is to propose a neural network, trained with radio occultation data from the COSMIC-1 mission, that generates average ionospheric electron density profiles during dusk, focusing on the pre-reversal enhancement of the zonal electric field. Results show that the estimated profiles exhibit a clear seasonal pattern, and reproduce adequately the climatological behavior of the ionosphere, thus presenting strong appeal on ionospheric error attenuation.

Performance Analysis of a Strong Constraint 4DVar and 4DEnVar on Regional Ionosphere Imaging

AbstractData assimilation (DA) techniques have recently gained traction in the ionospheric community, particularly at regional operational centers where more precise data are becoming prevalent. At center stage is the argument over which technique or scheme merits realization. At 4DSpace, we have in‐house developed and assessed the performance of two regional flavors of short‐term forecast strong constraint four‐dimensional (4D, space and time) variational (SC4DVar) DA schemes; the orthodox incremental (SC4DVar‐Inc) and ensemble‐based (SC4DEnVar) approach. SC4DVar‐Inc is bottled‐necked by expensive Tangent Linear Models (TLMs) and model Ad‐joints (MAs), while SC4DEnVar design mitigates these limitations. Both schemes initialize from the same background (IRI‐2016), and electron densities forward propagated (30‐min) by a Gauss Markov filter‐ the densities take on a log‐normal distribution to assert the mandatory ionosphere density positive definiteness. Preliminary assimilation is performed only with ubiquitous Global Navigation Satellite System observables from ground‐based receivers, with a focus on moderately stable mid‐latitudes, specifically the Japanese archipelago and neighboring areas. Using a simulation analysis, we find that under model space localization, 30 member Ensembles are sufficient for regional SC4DEnVar. Verification of reconstructions is with independent observations from ground‐based ionosonde and satellite radio occultations: the performance of both schemes is fairly adequate during the quiet period when the background has a better estimation of the hmF2. SC4DVar‐Inc is slightly better over areas densely populated with measurements, but SC4DEnVar estimates the overall 3D ionosphere picture better, particularly in remote areas and during severe conditions. These results warrant SC4DEnVar as a better candidate for precise short‐time regional forecasts.

Limits on the Density of the Lunar Ionosphere: ARTEMIS Observations

The Moon of our Earth has a tenuous atmosphere, known as an exosphere. The ionization of this exosphere is speculated to possibly form a weak ionosphere. Some radio occultation (RO) experiments have suggested the presence of a dense ionosphere with an electron density on the order of hundreds of cm−3 near the surface. Using in situ measurements from the ARTEMIS mission during 2012–2021, we conduct statistical analyses and case studies to investigate the plasma density at near-surface altitudes. ARTEMIS measurements reveal no plasma densities at altitudes between 10 and 50 km that exceed 35 cm−3, and therefore they provide no evidence for a steady-state or global lunar ionosphere at the level suggested by some RO observations. Density profiles with local time and altitude show higher density in the sunlit sector than in the shadowed sector. These observations suggest that the natural variation of solar wind plasma flux with solar zenith angle plays a critical role in controlling the plasma population near the surface. This research provides a reference for a comparison with RO observations and a statistical view of the low-altitude plasma environment near the lunar surface.

Ionospheric Plasma Density Gradients Associated With Night‐Side Energetic Electron Precipitation

AbstractEnergetic electron precipitation from the equatorial magnetosphere into the atmosphere plays an important role in magnetosphere‐ionosphere coupling: precipitating electrons alter ionospheric properties, whereas ionospheric outflows modify equatorial plasma conditions affecting electromagnetic wave generation and energetic electron scattering. However, ionospheric measurements cannot be directly related to wave and energetic electron properties measured by high‐altitude, near‐equatorial spacecraft, due to large mapping uncertainties. We aim to resolve this by projecting low‐altitude measurements of energetic electron precipitation by ELFIN CubeSats onto total electron content (TEC) maps serving as a proxy for ionospheric density structures. We examine three types of precipitation on the nightside: precipitation of <200 keV electrons in the plasma sheet, bursty precipitation of <500 keV electrons by whistler‐mode waves, and relativistic (>500 keV) electron precipitation by EMIC waves. All three types of precipitation show distinct features in TEC horizontal gradients, and we discuss possible implications of these features.

Martian M2 peak behavior in the dayside near-terminator ionosphere during interplanetary coronal mass ejections

The interplanetary coronal mass ejections (ICMEs) can pose significant impacts on the Martian ionosphere, resulting in plasma depletion, variability, and escape to space. However, the connections between the ICMEs and the associated responses of the dayside near-terminator Martian ionospheric primary peak (M2) are not well understood. The present study primarily investigates the behavior of the ionospheric peak density (Nm) and height (hm) during the passage of ICMEs using observations from the Radio Occultation Science Experiment (ROSE) aboard MAVEN spacecraft. We have selected 8 such ICMEs (during 2017–2022) at Mars from the existing catalogs and studied the ROSE electron density profiles during quiet and disturbed time (ICMEs) for identical solar zenith angle range. We observed the elevation of the M2 peak (hm ∼ 4–16 km) during disturbed time (ICMEs) with a decrease in Nm (0.41–2.8 × 1010 m−3) in comparison to the quiet time. The present study, for the first time, addressed the influence of ICMEs on the M2 peak parameters (Nm and hm). We have proposed that the development of large vertical pressure gradient and electron temperature enhancement are plausible causes for ionospheric variability. Therefore, the present study provides new insights to understand peak plasma behavior in the dayside near-terminator ionosphere during ICMEs.

Quality assessment of the ionospheric density profiles based on long-term COSMIC 1 and 2 radio occultation observations

Quality assessment of the ionospheric density profiles based on long-term COSMIC 1 and 2 radio occultation observations

Classification of the equatorial plasma bubbles using convolutional neural network and support vector machine techniques

Equatorial plasma bubble (EPB) is a phenomenon characterized by depletions in ionospheric plasma density being formed during post-sunset hours. The ionospheric irregularities can lead to disruptions in trans-ionospheric radio systems, navigation systems and satellite communications. Real-time detection and classification of EPBs are crucial for the space weather community. Since 2020, the Prachomklao radar station, a very high frequency (VHF) radar station, has been installed at Chumphon station (Geographic: 10.72° N, 99.73° E and Geomagnetic: 1.33° N) and started to produce radar images ever since. In this work, we propose two real-time plasma bubble detection systems based on support vector machine techniques. Two designs are made with the convolutional neural network (CNN) and singular value decomposition (SVD) used for feature extraction, the connected to the support vector machine (SVM) for EPB classification. The proposed models are trained using quick look (QL) plot images from the VHF radar system at the Chumphon station, Thailand, in 2017. The experimental results show that the combined CNN-SVM model, using the RBF kernel, achieves the highest accuracy of 93.08% while the model using the polynomial kernel achieved an accuracy of 92.14%. On the other hand, the combined SVD-SVM models yield the accuracies of 88.37% and 85.00% for RBF and polynomial kernels of SVM, respectively.Graphical

Machine learning approach for prediction of total electron content and classification of ionospheric scintillations over Visakhapatnam region

Ionospheric scintillations, which are due to ionospheric plasma density anomalies, negatively impact trans-ionospheric signals and the positioning accuracy of the global navigation satellite system (GNSS). One of the crucial variables for comprehending space weather conditions is the total electron content (TEC) of the ionosphere. It is vital to predict the ionospheric TEC before making efforts to enhance the GNSS system. In this article, the long short-term memory machine learning approach for TEC prediction is presented, based on which the ionospheric phase scintillations are identified and classified using popular classifiers: support vector machines and decision trees. In this article, the comparative analysis of these classifiers is presented using the standard performance metrics: accuracy, recall, precision, and F1 score.

Simultaneous Global Ionospheric Disturbances Associated With Penetration Electric Fields During Intense and Minor Solar and Geomagnetic Disturbances

AbstractA new observational phenomenon, named Simultaneous Global Ionospheric Density Disturbance (SGD), is identified in GNSS total electron content (TEC) data during periods of three typical geospace disturbances: a Coronal Mass Ejection‐driven severe disturbance event, a high‐speed stream event, and a minor disturbance day with a maximum Kp of 4. SGDs occur frequently on dayside and dawn sectors, with a ∼1% TEC increase. Notably, SGDs can occur under minor solar‐geomagnetic disturbances. SGDs are likely caused by penetration electric fields (PEFs) of solar‐geomagnetic origin, as they are associated with Bz southward, increased auroral AL/AU, and solar wind pressure enhancements. These findings offer new insights into the nature of PEFs and their ionospheric impact while confirming some key earlier results obtained through alternative methods. Importantly, the accessibility of extensive GNSS networks, with at least 6,000 globally distributed receivers for ionospheric research, means that rich PEF information can be acquired, offering researchers numerous opportunities to investigate geospace electrodynamics.

Large-scale traveling ionospheric disturbances over central and eastern Europe during moderate magnetic storm period on 22–24 September 2020

We present the results of ground based remote sensing observations of large-scale traveling ionospheric disturbances (LSTIDs) occurring during the moderate magnetic storm evolution (22–24 September 2020) over central and eastern Europe. Three ionosondes located in Juliusruh, Pru˚honice and near Kharkiv, and the Kharkiv incoherent scatter radar were employed to study temporal and spatial LSTID signatures in ionospheric F2 peak density and height and electron density variations at the heights of 100–300 km. Two types of LSTIDs are detected, which are originated during enhancement in auroral activity (2 events) and local sunrise terminator passage (3 events) from the ionosonde data. The magnetic storm-related LSTIDs exhibit equatorward propagation with the horizontal phase velocities of 546 m/s and 576 m/s, similar dominant periods of 135–150 min and 165–180 min over all three sites and a longitudinal dependence in fractional (relative) amplitudes of electron density perturbation. The solar terminator induced LSTIDs demonstrate the variety in both relative amplitudes and dominant periods over different locations. They have a westward apparent horizontal phase velocities of 288–345 m/s, which are close to the solar terminator velocity at ionospheric heights. Employment of incoherent scatter data enabled the detection of additional LSTIDs over Ukraine with the periods in a broader range of 41–168 min, an establishment of phase and onset differences for the oscillations in the ionospheric F2 peak electron density and height.

Driving Source of Change for Ionosphere before Large Earthquake -Vertical Ground Motion-

This paper discusses the relationship between the vertical ground motion and ionospheric disturbances before the Kumamoto earthquake on 16 April 2016, in Kyushu, Japan, using the vertical ground motion measured by slant gauges widely distributed in Kyushu, and the NmF2 observed by ionosondes in Japan and another region. We provide evidence that vertical ground motion excites internal gravity waves (IGWs) that disturb changes in the ionospheric plasma density. From the spectral analysis results of the vertical ground motion data, the summation of various period (frequency) components analyzed from the original data of the slant gauge shows a possible correlation with the change of NmF2 before the earthquake. On the other hand, the influence of the geomagnetic disturbance on vertical ground motion seems to exist. However, we cannot confirm that vertical ground motion is influenced by the geomagnetic disturbance (Kp index) and that the earthquake is triggered by the geomagnetic disturbance. There are two conditions for the vertical ground motion to disturb variations in the ionospheric plasma density: (1) The effective vertical ground motion period should be shorter than 5 h. In addition, (2) vertical ground motion should continue to exist so that wave energy can be continuously injected into the atmosphere. A possible mechanism with which to modify the ionosphere is discussed. The results of this study can provide a basis for the future ionospheric precursors of earthquakes by using the vertical ground motion.

Polar Vortex Strength Impacts on the Longitudinal Structure of Thermospheric Composition and Ionospheric Electron Density

AbstractThis work examines the weak stratospheric polar vortex event in late February 2008 and the strong polar vortex event in late February 2021 to understand the potential influence of polar vortex strength on midlatitude thermospheric composition and ionospheric plasma density. The weak polar vortex event shows a reduction in thermospheric O/N2 at all longitudes, changes in the ionospheric total electron content (TEC) that vary with longitude, and an intensification of the semidiurnal tides. The strong polar vortex event shows O/N2 elevated by up to 25% in the Asian sector and a 25% decrease in semidiurnal tidal amplitude. The TEC response during the strong polar vortex event is complex and shows enhanced TEC in the Asian sector where O/N2 is elevated. These are the first observations of anomalies in the thermospheric composition and ionospheric plasma associated with a strong polar vortex event.

Effects of the 10 September 2017 Solar Flare on the Density and Composition of the Ionosphere of Mars: Significance of Thermospheric Changes

AbstractThe impact of solar flares on the upper atmosphere of Mars presents an opportune environment for investigating the ionosphere's response to the rapid and high‐energy dynamics of our Sun, with implications for characterizing atmospheric escape and evolution. The ionosphere of Mars is strongly influenced both by the levels of ionizing solar irradiance it receives and the associated behavior of the neutral thermosphere within which it is embedded. Here, we characterize density and composition changes in the topside ionosphere of Mars due to the X8.2‐class solar flare on 10 September 2017 from MAVEN spacecraft observations roughly 90 min after the onset of flare irradiance at Mars, by which time the neutral thermosphere had experienced significant thermal expansion. By contrasting altitude and pressure‐based representations of the ionospheric changes during the flare with the neutral thermospheric changes in both representations and basic photochemical expectation, we interpret and quantify the ionospheric behavior through a lesser explored lens of the neutral thermosphere's response to a flare. We find that the high‐altitude ionospheric density enhancements during this flare are larger than many identified from other flares, and that the neutral thermosphere's expansion accounts for a majority of the cumulative ion density changes observed. The ion density and compositional changes exhibit corresponding behavior with the neutral thermosphere's changes from both thermal expansion and photochemical effects. The identified characteristics of the ionosphere's response to a solar flare provide observational benchmarks for assessing and aiding numerical modeling efforts in accurately reproducing the behavior of the environment of Mars.