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Experimental rate coefficients for the quenching of vibrational levels 0 and 1 of the N 2 + A 2 Π u state by N2 are presented. The experiments were performed using near-infrared observations of the N 2 + Meinel bands excited by electron impact at several pressures of the N2 target/quenching gas. The total removal rate coefficients were derived from a Stern–Volmer analysis of the Meinel band intensities as a function of N2 density and yielded rate coefficients of (2.5 ± 0.5 × 10−10) and (5.6 ± 0.6 × 10−10) cm3⋅molecule−1⋅s−1 for vibrational levels 0 and 1, respectively. It is shown that rate coefficients increase with increasing vibrational level and decreasing energy gap. Our results impact modeling studies of the disturbed atmosphere and ionosphere as the reduced quenching rate coefficients for the preferentially excited A-state vibrational levels <2 lower the quenching altitude in the atmosphere by one scale height, or about 6 km. [ABSTRACT FROM AUTHOR]

The ionosphere, partially ionized by solar radiation, is rich in free electrons and ions, affecting satellite navigation signals by altering their speed and path. This interaction often leads to signal delays of 5–10 m, complicating accurate positioning in satellite-based systems. This paper investigates the influence of global ionospheric models (GIMs) with varying Temporal Resolutions (TR) on satellite positioning accuracy and convergence time under different solar activities, represented by the years 2009 (low solar activity) and 2014 (high solar activity). The study utilizes Global Positioning System (GPS) data from three GIMs: CODG, representing the Center for Orbit Determination in Europe (CODE) GNSS model with a 2-h TR; bcom, with a 1-h TR; and b5mg, with a 5-min TR. Analysis was conducted using the GNSS Analysis Software for Multi-constellation and Multi-frequency Precise Positioning across 46 international GNSS service stations under single and dual-frequency strategies. The results indicate that precise point positioning convergence time improved by approximately 18 % and 78 % using single and dual frequencies, depending on the GIM applied. Consequently, positioning accuracy after convergence improved by about 16 % and 27 % in the horizontal and up components for ionospheric-constrained single-frequency PPP models and by 68 % and 79 % in the horizontal and up components for dual-frequency PPP models. Furthermore, vertical total electron content analysis at the MARS station revealed significant variations correlating with solar activity, underscoring the importance of selecting appropriate GIMs for accurate GNSS positioning. Future studies, including multi-solar events, are recommended for comprehensive analysis. [ABSTRACT FROM AUTHOR]

Despite routine detection of coseismic acoustic‐gravity waves (AGWs) in Global Navigation Satellite System (GNSS) total electron content (TEC) observations, models of the earthquake‐atmosphere‐ionosphere dynamics, essential for validating data‐driven studies, remain limited. We present the results of three‐dimensional numerical simulations encompassing the entire coupling from Earth's interior to the ionosphere during the Mw ${M}_{w}$ 7.8 2016 Kaikoura earthquake. Incorporating the impact of data/model uncertainties in estimating the ionospheric state, the results show a good agreement between observed and simulated slant TEC (sTEC) signals, assessed through a set of metrics. The signals exhibit intricate waveforms, resulting from the integrated nature of TEC and phase cancellation effects, emphasizing the significance of direct signal comparisons along realistic line‐of‐sight paths. By comparing simulation results initialized with kinematic and dynamic source models, the study demonstrates the quantifiable sensitivity of sTEC to AGW source specifications, pointing to their utility in the analysis of coupled dynamics. Plain Language Summary: Earthquakes launch acoustic‐gravity waves (AGWs) into the atmosphere, spanning periods from seconds to minutes, that can reach the ionosphere at ∼ ${\sim} $100–400 km altitude. The majority of AGW detections in the ionosphere are performed with the use of GNSS signals collected with ground‐based receivers that nowadays comprehensively cover seismically active regions. However, the modeling of earthquake‐atmosphere‐ionosphere processes together, essential for validating and supporting data‐driven studies, remains rare. We present the outcomes of three‐dimensional numerical modeling of interconnected processes, spanning from Earth's interior to the ionosphere. We conducted a case study focused on the 2016 Mw ${M}_{w}$ 7.8 earthquake in New Zealand, renowned for its complexity and comprehensive observations of coseismic AGWs recorded with GNSS signals. Our results demonstrate a high level of accuracy of simulated GNSS signals, also revealing the high sensitivity to the chosen earthquake model and the complexity of resulting ionospheric signals, highlighting the necessity of attributing realistic geometries of GNSS TEC observations. The findings highlight the potential for using GNSS signals to investigate coseismic AGWs to infer characteristics of earthquakes. Key Points: Acoustic‐gravity wave‐driven slant total electron content (sTEC) signals are analyzed in terms of amplitude, waveform, and onset timeIntricate sTEC signal waveforms result from ionospheric fluctuations measured along lines‐of‐sight between satellites and receiversHigh sensitivity of sTEC signals to acoustic‐gravity wave source specification provides additional basis for earthquake characterization [ABSTRACT FROM AUTHOR]

The magnetopause is the boundary between the Earth's magnetosphere and the solar wind. Magnetosheath high‐speed jets can impact the magnetopause, causing local indentation and subsequently rebound. However, the comprehensive response of the magnetopause to the impact of a high‐speed jet remains unclear. In this study, we establish that the full spatiotemporal response pattern of the magnetopause to the impact of an isolated magnetosheath high‐speed jet can be characterized as an "Indentation‐Rebounce‐Relaxation" sequence from a statistical view. Based on the pressure balance, we estimate the spatial and temporal scales of the entire response process to range from 0.5 to 3.2 Earth radii and 0.9–4.7 min, respectively. Furthermore, we find that the interaction between the magnetopause and the high‐speed jet during the rebounce phase distorts the magnetopause, subsequently generating pairs of field‐aligned currents. These generated field‐aligned currents may flow to the ionosphere, potentially contributing to magnetosphere‐ionosphere coupling. Plain Language Summary: The Earth's magnetopause, separating the Earth's magnetosphere from the solar wind, is usually distorted by upstream magnetosheath pressure perturbations. One of these is the magnetosheath high‐speed jets, which are localized dynamic pressure enhancements that can induce the local deformation of the magnetopause. Previous studies have found that magnetosheath high‐speed jets can interact with the magnetopause, causing local indentation and subsequent rebound. However, due to the limitations of in‐situ spacecraft observations, the complete response of the magnetopause to the impact of a high‐speed jet remains unknown. Using Magnetospheric Multiscale satellite data, we establish a comprehensive response pattern of the magnetopause to an HSJ for the first time based on the statistical analysis of multiple cases, which is described as a sequence of "Indentation‐Rebounce‐Relaxation". This study will help us better understand the solar wind‐magnetosphere coupling process. Key Points: The spatiotemporal response of the magnetopause to an isolated HSJ can be sequenced as 'Indentation‐Rebounce‐Relaxation'The estimated spatial and temporal scales of the magnetopause response range from 0.5 to 3.2 Earth radii and 0.9–4.7 min, respectivelyThe high‐speed jet induces deformation of the magnetopause, subsequently generating pairs of field‐aligned currents [ABSTRACT FROM AUTHOR]

Intense ionization enhancements in the Earth's ionosphere, known as sporadic-E ( E s ), can degrade and severely disrupt the propagation of radio signals. Although many previous studies have analyzed the characteristics and morphologies of sporadic-E, few efforts have attempted to model global E s occurrence rates (ORs) at high time resolutions. This study develops a global empirical model of blanketing sporadic-E occurrence rates using a Karhunen–Loéve Expansion (KLE) of a global OR climatology built with Global Navigation Satellite System radio occultation (GNSS-RO) and ionosonde observations. Using an fbE ≥ threshold of 3 MHz, the model outputs a blanketing sporadic-E OR for a given geomagnetic latitude, longitude, day of year, and local solar time. The model outputs are compared to digisonde observations at four sites with varying geomagnetic latitudes, resulting in correlation coefficients ranging from 0.5 to 0.9 for monthly averaged observations and an uncertainty of 11%. Furthermore, the average uncertainty is estimated to be 12%. This Global Empirical Model of Sporadic-E Occurrence Rates (GEMSOR) is capable of providing blanketing sporadic-E OR estimates for global radio frequency (RF) operations. [ABSTRACT FROM AUTHOR]

• ELF response to large-scale transmitter ZEVS has been detected by satellite CSES. • CSES sensors detected narrowband 82 Hz emission with amplitudes E∼2 μV/m and B∼0.5 pT. • Wave spatial structure excited by 82 Hz horizontal 60 km current has been modeled. • Modeling shows that CSES recorded response corresponds to transmitter current >100 A. 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 - 3 μ V/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. [ABSTRACT FROM AUTHOR]

During the 2013 SSW, ionospheric disturbances were observed at eighteen stations on three meridional chains of 100°E, 110°E and 120°E ranging from 19.03°N to 49.21°N at latitudes over the East Asia region. The total electron content (TEC) response showed evident semidiurnal disturbances with TEC enhancement in the morning and depletion in the afternoon. The maximum TEC increased by more than 220 % along the 120°E longitude. In addition, the semidiurnal disturbance of the TEC was enhanced and indicated evident latitudinal and longitudinal dependence. The wavelet spectra of semidiurnal disturbance in TEC presented quasi-16-day planetary wave-like oscillations at middle latitudes and quasi-10-day planetary wave-like oscillations near Sanya at low latitudes. Moreover, the zonal winds and meridional winds at altitudes of 92 km and 96 km showed quasi-16-day planetary waves at the Mohe station located at middle latitudes and quasi-10-day planetary waves at the Sanya station located at low latitudes, which maybe relate to the semidiurnal disturbance of the TEC. In particular, the 12hrs oscillation of the TEC showed a quasi-16-day periodic component at middle latitudes and a quasi-10-day periodic component at low latitudes, indicating that the modulated semidiurnal tides may transmit these 10-day and 16-day planetary wave-like oscillations to the ionosphere. The coupling between the atmosphere and ionosphere may be strengthened by quasi-16-day waves at middle latitudes and quasi-10-day waves at low latitudes (near Sanya). This finding can further confirm the PW-tide interaction theory during the 2013 SSW event, and it is of significance in the middle and low latitude ionospheric response to SSW. [ABSTRACT FROM AUTHOR]

• Three TEC techniques gave consistent values of shell height over East Africa. • New method suggested agree with that of Nava et al.,. (2007) and Li et al.,. (2017). • Over East Africa the value of the effective height is about 400 km. The ionosphere over the low latitude region, where East Africa falls, is associated with high perturbations arising from numerous phenomenon such as Equatorial Ionization Anomaly (EIA), plasma bubbles, electrostatic instabilities etc. All these together, make it difficult to determine the actual values of important parameters used to characterize the ionosphere of the region in order to mitigate its negative contribution to technology. One such parameter is the effective height which is used among others to map the Total electron Content (TEC) over a given region, in argumentation, calibration of Global Navigation Satellite System (GNSS) observations etc. The value of the effective height of a place is got by radiosounders installed in a given location. However, these sounders are not readily available in many places, especially East Africa where the few that are available are currently malfunctioning and also their ionospheric spatial coverage is very limited. Alternative techniques that use TEC from GNSS receivers to estimate effective height of the ionosphere have been suggested and employed in different places, giving results that in some instances conflict with each other. This study has done a comparative analysis of the suggested GNSS-TEC techniques to determine their reliability over low latitude region of East Africa and has found out that some of them do not give consistent results over the region. To supplement the existing methods, a new method is proposed that relates IRI TEC to TEC obtained from the difference between sTEC recorded simultaneously by a given receiver on ground and the receiver on board Swarm satellite when swarm is over head the ground receiver. The results obtained using the new suggested technique gives consistent results over East African region which is in agreement with two other techniques among the four methods discussed. [ABSTRACT FROM AUTHOR]

We present the first simultaneous observations of a traveling ionosphere wave (TID) event, measuring electron concentration ( N e ), vertical plasma drift ( V z ), and ion and electron temperatures ( T i , T e ) using the Arecibo incoherent scatter radar. A TID with a period of 135 min was evident in all four state variables in the thermosphere. The amplitudes of V z and relative T i fluctuations show only small height variations from 200 to 500 km and their vertical wavelengths increase with altitude. The T e fluctuation shows different characteristics from EISCAT in both phase and amplitude. When the geomagnetic dip angle is 45°, half of the driving gravity wave's (GW's) equatorward velocity is mapped to V z . This meridional-to-vertical velocity coupling amplifies GW's effect in N e through vertical transport. The amplifying and anisotropic effects of the geomagnetic field explain the ubiquitous presence of TIDs and their preferred equatorward propagation direction in the geomagnetic mid-latitudes, as well as the midnight collapse phenomenon observed at Arecibo. [ABSTRACT FROM AUTHOR]

The main idea of the present study is to investigate in detail the time evolution of the spatial inhomogeneities connected with the ionospheric response to the geomagnetic storm registered in the period of 10–11 May 2024. The obtained ionospheric anomalies represented by the relative deviations of the global Total Electron Content (TEC) data have been utilized in the analysis. The used global TEC data have been converted to a coordinate system with a modip latitude and geographical longitude. In addition to the maps illustrating the global spatial distribution of the geomagnetically forced ionospheric anomalies, a presentation of the observed longitudinal structures by sinusoidal approximation has also been used. The resulting positive and negative responses have been studied depending on the magnetic latitude, local times and the behavior of the geomagnetic activity parameters during the considered event. The interpretation takes into account the known mechanisms for the effect of the geomagnetic storm on the electron density. A special attention is focused on the differences in the two hemispheres at high and mid latitudes, where a simultaneous direct impact of the particle precipitation and the change in the temperature regime of the neutral atmosphere has been assumed. The low-latitude response as a result of the Equatorial Ionization Anomaly (EIA) associated with Disturbed Dynamo Electric Fields (DDEFs) and its relationship with local time has also been considered. [ABSTRACT FROM AUTHOR]

A novel method was developed based on the amplitude data of the EM waves measured by Digisondes to calculate and investigate the relative ionospheric absorption changes. The effect of 13 solar flares (>C8) that occurred from 4 to 10 September 2017 were studied at three European Digisonde stations (Juliusruh (54.63°N, 13.37°E), Průhonice (49.98°N, 14.55°E) and San Vito (40.6°N, 17.8°E)). The present study compares the results of the amplitude method with the absorption changes measured by the Finnish Riometer Network and determined by the NOAA D-RAP model during the same events. The X-class flares caused 1.5–2.5 dB of attenuation at 30–32.5 MHz based on the riometer data, while the absorption changes were between 10 and 15 dB in the 2.5–4.5 MHz frequency range according to the amplitude data. The impact caused by energetic particles after the solar flares are clearly seen in the riometer data, while among the Digisonde stations it can be observed only at Juliusruh in some certain cases. Comparing the results of the amplitude method with the D-RAP model it seems evident that the observed absorption values almost always exceed the values given by the model both at 2.5 MHz and at 4 MHz during the investigated period. According to the comparison between the riometer data with the D-RAP, generally, the model underestimates the absorption values obtained from the riometers during solar flares except at the highest latitude stations, while D-RAP overestimates the impact during the particle events. [ABSTRACT FROM AUTHOR]

Geomagnetic storms can cause large variations in the ionosphere, but their impacts on the mesosphere and lower thermosphere (MLT) are not well understood. Based on the Total Electron Content (TEC) data and the meteor neutral winds data over Mohe (53.5°N, 122.3°E) and Beijing (40.3°N, 116.2°E), we analyze the tidal variations during six intense geomagnetic storms from 2016 to 2021. According to the six intense geomagnetic storms, we found that intense geomagnetic storms can lead to diurnal and semidiurnal tidal enhancements in TEC, while their influences on tidal variations in the MLT region are not always captured. Responses of tidal enhancement in the MLT region to the intense geomagnetic storms are more obvious at a lower latitude at Beijing, but the tidal amplitude changes are not proportional to the Dst indices. Some semidiurnal tides are significantly enhanced prior to the onset of geomagnetic storms, which needs to be statistically investigated in the future based on additional observations. [ABSTRACT FROM AUTHOR]

The article discusses the collection of physics teaching apparatus housed in the museum wing of the Greenslade house in Ohio, dating from 1850 to 1950. Various apparatus named after academic ancestors such as Barker, Boys, Thacher, Sommerfeld, Edison, Braun, Ritchie, Sturgeon, and Poynting are highlighted, each with unique historical significance and contributions to the field of physics. The article provides detailed descriptions and historical context for each apparatus, shedding light on the evolution of physics education and experimentation over time. [Extracted from the article]

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Parker Solar Probe (PSP) uses Venus gravity assists (VGA) to achieve the closest orbits to the Sun by a spacecraft. During the third (VGA3) and fourth (VGA4) Venus gravity assists, the PSP entered the Venusian ionosphere. The core electrons could not be detected as they were below the SWEAP/SPAN electrostatic analyzer instrument energy threshold. However, there is another way to estimate the core temperature using quasi‐thermal noise (QTN) data measured by the PSP/FIELDS Radio Frequency Spectrometer instrument. QTN spectroscopy offers an effective tool for measuring electron temperature and density when the electrons are too cold for other instruments to measure, as is the case with VGA3 and VGA4. Low‐frequency plasma wave data from the closest approach during VGA3 and VGA4 was analyzed with the QTN spectroscopy technique to determine the density and first‐ever in‐situ thermal electron temperature of the Venusian ionosphere at solar minimum. Plain Language Summary: Parker Solar Probe is a NASA mission designed to collect solar wind data closer to the Sun than any spacecraft has before. It uses Venus' gravity to achieve its close orbit, collecting data at Venus while doing so. Quasi‐thermal noise spectroscopy was used to determine the thermal electron properties of the Venusian ionosphere during these gravity assists when other instruments could not. This analysis provides insights into how Venus' ionosphere reacts to the solar cycle and how the ionosphere is losing mass. Key Points: Thermal electron properties of Venus' ionosphere can be determined using quasi‐thermal noise spectroscopyVenusian ionospheric electron temperatures are found to be colder at solar minimum than maximumAmbipolar fields, not wave heating, may be the main source of outfield flow in Venusian tail rays [ABSTRACT FROM AUTHOR]

The second generation of the Global navigation satellite system Receiver for Atmospheric Sounding (GRAS-2) is a radio occultation (RO) instrument which is capable of providing 2000 atmospheric profiles per day. The instrument is hosted on all satellites in the MetOp Second Generation (MetOp-SG) series for polar orbit operation. The GRAS-2 instruments provide occultation measurements from the Galileo, GPS, and BeiDou satellites at their common frequencies centred at 1575.42 MHz (L1) and 1176.45 MHz (L5). Using high-gain antennas and an ultra-stable oscillator, neutral bending angles are measured at an unprecedented accuracy of 0.3–0.4 µrad , which is better than the requirement of less than 0.5 µrad. The RO signal will be measured deep into the troposphere using a novel open-loop tracking scheme utilizing multiple correlator outputs for operation with a tailored ground processing algorithm optimized for extracting signals with low amplitudes, approaching the noise floor limitation. Ionosphere measurements to an altitude of 600 km are also acquired. [ABSTRACT FROM AUTHOR]

As devastating natural disasters, typhoons pose a tremendous threat to human society, making effective typhoon early warning and monitoring crucial. To address this challenge, High Frequency Surface Wave Radar (HFSWR), which can observe oceanic parameters such as typhoon wind fields in real time and even capture the dynamic changes in the ionosphere, has become an effective tool for typhoon monitoring. This paper investigates the interaction mechanisms about Typhoon-Acoustic Gravity Waves (AGWs)-Ionosphere, as well as Typhoon-Ocean Waves for HFSWR, and simulates these interaction processes within HFSWR. Then a typhoon early warning and monitoring scheme for HFSWR has been proposed: In the first stage, the S-shaped ionospheric disturbances observed by HFSWR are utilized as precursor signals for early typhoon warnings. In addition, the second stage involves analyzing changes in first-order oceanic echo spectral peak ratio to pinpoint when the typhoon eye enters the radar detection range, thus initiating the typhoon monitoring phase. Subsequently, the measured data from HFSWR collected during Typhoon "Muifa" (2212) in conjunction with the proposed scheme are evaluated in detail. The results indicate that AGWs generated by typhoons can propagate into non-typhoon areas within the detection range, causing S- shaped ionospheric disturbances and providing approximately 6 h of early warning. At around 8:05 (UTC+8), an increasing trend in the first-order spectral peak ratio was noted, indicating the entry of the typhoon eye into the detection range, which closely aligns with the official typhoon path and marks the transition to the monitoring phase. The proposed scheme is expected to enhance the capability for typhoon early warning and real-time monitoring in specific sea areas and mitigate the risks associated with typhoon-related disasters. [ABSTRACT FROM AUTHOR]

We proposed, for the first time, that the angle between the horizontal projection of the magnetic field line and the sunrise line (AMFS) is a crucial factor that controls predawn heating. Through quantitative analysis, we determined that both the AMFS and the length of the magnetic field line (LMF) significantly affect predawn heating. We found that an increased AMFS intensifies predawn heating, while an increased LMF counteracts it. Our research indicates that the optimal conditions for peak predawn heating occur at an AMFS of approximately 30 degrees and an LMF of about 4000 km, where the effect surpasses 400 K. Additionally, we observed that the effects of both the AMFS and the LMF on predawn heating exhibit a saturation effect. This study provides a clearer understanding of the factors driving predawn ionospheric heating, with implications for topside ionosphere research. [ABSTRACT FROM AUTHOR]

The 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. Plain Language Summary: The intense geomagnetic storm of May 2024 caused a plethora of different responses within the Earth's ionosphere. In the early phases of the storm, the auroral oval quickly expands to upper midlatitudes and induces strong variations in Global Navigation Satellite System (GNSS) phase measurements. Concurrently, midlatitude plasma is repeatedly lifted by 100–300 km on timescales of about an hour resulting in enhanced plasma densities. This intensified and lifted plasma is then drawn into the polar cap inducing variations in GNSS amplitude and phase. As the storm evolves, heating drives mixing of the thermosphere and causes an extreme depletion in ionospheric plasma. After 24 hr, despite severe geomagnetic conditions persisting, the depleted plasma environment results in only relatively weak plasma transport into the polar cap and significantly reduced impacts on GNSS. Key Points: Plasma lifting during the storm caused midlatitude displacements of ionospheric peak height by as much as 300 km over the course of 1 hourSporadic‐E is observed at the sub‐auroral convective boundary edge of the storm‐enhanced density with strong plasma drift shears presentSevere depletion of electron density at mid and high latitudes significantly reduced the impact of subsequent geomagnetic activity on GNSS [ABSTRACT FROM AUTHOR]

Using the SuperThermal Electron Transport (STET) model coupled with the Super‐thermal Proton Electron Atomic Hydrogen—tRansport in the Ionosphere and Thermosphere (SPEAH‐RIT) codes, we demonstrate that temporal variability of ionospheric conductance is defined by several time scales: the temporal variations of the magnetospheric source, the start time of electron precipitation, and the termination of the corresponding source. In these cases, the time scales are defined by dissipation of energetic electrons and effective recombination processes. The results presented in this paper were applied in the regions of pulsating aurora and polar arcs, demonstrating the fact that ionospheric conductance requires some time to form and decay. These time delays constitute an effective "inertia" in the conductance calculation which is not accounted for in many global models which assume an instantaneous connection between precipitation and conductance. Ionospheric conductance inertia influences the temporal variation in ionospheric and magnetospheric electric fields, and as a result, impacts magnetosphere‐ionosphere (MI) dynamics on a global scale. Plain Language Summary: We demonstrate in this manuscript that temporal variability of ionospheric conductance is defined by several temporal scales and has inertias to its development and decay. Ionospheric conductance inertia influences the temporal variation in ionospheric and magnetospheric electric fields, and as a result, the further reconfiguration of electron precipitation dynamics. The results presented in this paper were applied in the regions of pulsating aurora and polar arcs clearly demonstrate an effective "inertia" of ionospheric system to electron precipitation dynamics. Key Points: Ionospheric conductance is the system response to electron precipitation in the regions of pulsating and discrete aurorasIonospheric conductance carries the inertias of its development and decayConductance formation in pulsating aurora and discrete auroral arcs are defined by multiple temporal scales [ABSTRACT FROM AUTHOR]

Total Electron Content (TEC) forecasting using machine learning has been extensively preferred in characterizing the spatio-temporal variability of the ionosphere, to support space communication and navigation applications. Although, a variety of machine learning methods have been evolved, still, there is a greater persistence in the prediction of ionospheric TEC due to adverse space weather impacts and the complex behavior of ionosphere. And hence, more sophisticated short-term ionospheric TEC forecasting models should be developed for better prediction accuracy. The present study investigated and evaluated the performance of three models – Light Gradient Boosting Machine (LightGBM), Extreme Gradient Boosting (XGBoost), and Gradient Boost Regression (GBR) algorithms using the data set for 25 years (1997–2021) GNSS Earth Observation Network System (GEONET) Global mean TEC time-series data. For better prediction accuracy, the data of geomagnetic storm indices Dst and Mg-II index were also utilized in training the three models. One year of data for both high (2015) and low (2020) solar activity were used to test the three models. The prediction plots are used to visualize the level of prediction error for the three algorithms. The statistical results illustrate that the LightGBM model performed better in predicting TEC with an RMSE value of 2.25 TECU (2015) and 0.52 TECU (2020) for high and low solar activity years respectively for global mean TEC data and with an RMSE of 2.34 TECU at Japan grid point location of (34.95°N and 134.05°E). In turn the XGBoost and GBR models provide an absolute TEC forecasting with an RMSE of 2.76 and 2.59 TECU (2015) and 0.60 and 0.55 TECU (2020) correspondingly for global data and as 2.39 and 2.93 TECU for grid point location. [ABSTRACT FROM AUTHOR]

The Triple Ionosophere PhotoMeter (TRIPM) is designed to make the disk observations of the Earth airglow emissions at OI 135.6 nm and N 2 Lyman-Birge-Hopfield (LBH) band that flew aboard the newly launched early morning satellite Fengyun-3E (FY-3E) which was launched on July 5th, 2021. This is the first attempt to obtain the global twilight airglow data in the far ultraviolet band using Ionosophere PhotoMeter. The seasonal behavior of the twilight airglow at the OI 135.6 nm and N 2 LBH band is exhibited and interpreted in the paper. Validity of the TRIPM data is analyzed by comparison with the simulation results of the Global Airglow (GLOW) and the simulation results reveal good consistency with the observational results. Furthermore, based on the ionospheric contributions calculated by GLOW model, we extract the ionospheric information from the TRIPM 135.6 nm emissions. This means the ionospheric signature in the 135.6 nm radiance at the dawn and dusk times can be provided. Comparison between the ionospheric 135.6 nm radiance due to O+ and electron radiative recombination with GPS TEC data shows a similar morphology of equatorial arcs and seasonal variation of the ionosphere. [ABSTRACT FROM AUTHOR]

At an altitude of 1000 - 2000 km in the Venusian upper ionospheric region, the plasma is composed of H + ions, O + ions, and solar wind (SW) protons with electrons distributed according to the kappa distribution. This research delves into the exploration of nonlinear solitary and periodic waves, including the behavior of two-soliton. The Reductive Perturbation Technique (RPT) is used to derive the Korteweg-de Vries (KdV) equation for studying these nonlinear waves. Subsequently, a travelling wave transformation is employed to establish a planar dynamical system for the obtained KdV equation. Phase portrait is drawn and the associated nonlinear waves are examined adjusting the values of the parameters temperature ratio, unperturbed number density ratios, spectral index and travelling wave speed. Two-soliton solution of the KdV equation is investigated using the Hirota's direct approach. The influence of parameters like the spectral index, unperturbed number density ratios, and temperature ratio on the two-soliton is demonstrated, including the change in the phase shift. The findings from this research provide valuable insights into the dynamics of two-soliton solutions and nonlinear waves in the upper ionosphere of Venus. [ABSTRACT FROM AUTHOR]

We statistically study 10 weak to moderate geomagnetic storms that occurred since the 25th solar activity cycle to evaluate the quality of satellite signal and positioning accuracy of Beidou Navigation Satellite System (BDS). The results show that the PAS (Percentage of Affected Satellites) index, which integrates three scenarios: satellite signal loss, satellite signal loss of lock, and carrier phase signal anomaly, appears significant anomaly changes during weak and moderate geomagnetic storms, and its changing trend is closely related to the geomagnetic storm Kp index and Dst index, the correlation coefficient is greater than 0.75. Based on the results of PAS signal quality evaluation, the effect of PAS on the positioning error of Precision Point Positioning (PPP) of BDS-2/BDS-3 systems is analyzed and verified in conjunction with PAS. The results show that there is a strong agreement between the time of PAS anomaly and the time of PPP positioning accuracy anomaly. The positioning error of PPP increases by 9 to 44 times compared to the quiet period. The statistical results indicate that the PAS index is useful for the signal quality evaluation of the Beidou Navigation Satellite System under different space weather conditions. [ABSTRACT FROM AUTHOR]

The Equatorial Ionization Anomaly (EIA), a manifestation of Ionospheric plasma irregularities, is closely linked to the equatorial fountain, influenced by solar activity and Earth's geomagnetic field. While previous studies on EIA have predominantly focused on specific regional analyses using TEC data from GPS stations, revealing correlations between peaks, discrepancies with models, and temporal variations, there exists a gap in comprehensive global statistics, consideration of different solar activity years, and exploration of EIA characteristics across various local time scales. To address these, this study employs high spatiotemporal data from the Global Ionospheric Map (GIM) to comprehensively analyze EIA across different periods of the day during high solar activity in 2014 and low solar activity in 2020. The study delves into the subtle variations of EIA under different solar activity levels and seasonal conditions, focusing on changes in occurrence rate, intensity, and geomagnetic latitude positions concerning longitude, month, and local time. Our study reveals several findings: (1) EIA exhibited more frequent and intense trends during high solar activity years, with higher occurrence rates and intensity observed during the equinoxes; (2) EIA exhibits significant variations across different longitudes and local times, showing systematic patterns in its occurrence rates over time; (3) The crest-to-trough TEC Ratio (CTR) effectively characterizes nighttime EIA intensity, while the crest-to-trough TEC Difference (CTD) is suitable for representing daytime EIA intensity; (4) The temporal changes in EIA positions may be related to electric fields and wind patterns, while differences in longitudes are attributed to variations in the geomagnetic field. [ABSTRACT FROM AUTHOR]

A total solar eclipse occurred on April 8, 2024, across the United States, with obscuration rates ranging from 20–100% at different locations. We study the ionospheric Total Electron Content (TEC) response to the eclipse using data from 51 ground-based GPS stations. We find a significant depletion in TEC of up to 65%, with larger depletion rates occurring along the path of totality. We also observe a time delay between the maximum TEC depletion and the time of maximum obscuration, ranging from 8 to 80 minutes, with longer delays occurring at stations with lower obscuration rates. Both time delay and TEC depletion rates are found to vary with latitude, with slightly longer delays at lower latitudes and higher TEC depletion rates at mid-latitudes. The TEC depletion rate also increased with local time, showing a higher decrement after noon compared to before. The spatiotemporal variation in TEC closely followed the eclipse's path, indicating a positive correlation with the movement of the moon's shadow. Monitoring rate of TEC change during such rare events is crucial for enhancing our understanding of ionospheric dynamics, which can be very helpful to improve the accuracy of global communication and navigation systems. [ABSTRACT FROM AUTHOR]

Accurate determination of the ionospheric parameters is one of the important objectives of the Ionospheric Connection Explorer (ICON) mission. Recent analyses of the current ICON Level 2.5 (L2.5) data product have shown that the ionospheric parameters (e.g., the peak electron density, n m F 2 , and the peak height, h m F 2 ) that are retrieved from the nighttime OI 135.6 nm emission observed by ICON's Far Ultraviolet (FUV) imager exhibit a systematic bias when compared to external radio measurements. In this study, we demonstrate that the bias was introduced by Tikhonov regularization that was used for the FUV Level 1 data inversion to generate the L2.5 data product. To address the bias, we develop a Bayesian framework for accurate determination of the nighttime ionospheric parameters through the Maximum A Posteriori (MAP) estimation. We show through analysis of synthetic observations that the key to an accurate MAP estimation is to construct a series of prior distributions associated with different h m F 2 using climatological empirical models. Implementation of the MAP estimation with this series of prior distributions to the ICON FUV observations and comparison of the ionospheric retrievals with external radio measurements verify that the Bayesian method can reduce the systematic bias to a negligible level of ∼1% in the retrieved n m F 2 and ∼1 km in the retrieved h m F 2 . Our study provides a novel method for FUV remote sensing data analysis and an improved data set for ionospheric research. [ABSTRACT FROM AUTHOR]

The influence of the ionospheric wind on internal gravity waves is considered. It is shown that interaction of wind in the ionosphere with the geomagnetic field leads to occurrence of the Ampére force, the vertical gradient of which modifies the properties of internal gravity waves. Such interaction results in the discrete spectrum of ionospheric fluctuations with the main period about 30 min. The increase in the Ampére force due to an electric field of seismic origin leads to the appearance of a maximum with shorter periods of about 10 and 22 min in the spectrum of ionosphere fluctuations. Observations of phase and amplitude fluctuation of a radio wave reflected from the ionosphere during increasing seismic activity are confirmed by the results of the considered model. [ABSTRACT FROM AUTHOR]

On October 9, 2022, orbiting X-ray and γ-ray telescopes registered the most powerful explosion ever observed in the Universe—the GRB221009A γ-ray burst at a distance of 2.4 billion light years. The response of the Earth's ionosphere to this unique event was detected in the received signals of very-low-frequency (VLF) radio paths passing through both the daytime and nighttime ionosphere. A disturbance in the night sector was observed as a sudden decrease in amplitude up to 7 dB and a sharp jump in the signal phase up to 20°‒30°. Less pronounced amplitude jumps up to 1.5 dB were found in the daytime sector. At the time of the flare, magnetometers showed only the appearance of a weak burst of the geomagnetic field ∼0.5 nT at the time of the flare. In the daytime, an isolated geomagnetic pulse with an amplitude of up to 1 nT was observed. The appearance of a geomagnetic response to a γ-ray flare is surprising, because its radiation creates additional ionization in the stratosphere, significantly below the conducting E-layer of the ionosphere. The recorded event showed that extragalactic γ-ray bursts cause a noticeable perturbation in the Earth's ionosphere, and the network of VLF radio paths covering the lower ionosphere can be considered as a giant γ-ray detector. [ABSTRACT FROM AUTHOR]

Satellite-borne electromagnetic pulse (EMP) detection technology plays an important role in military reconnaissance, space environment monitoring, and early warning of natural disasters. However, the complex ionosphere greatly distorts the waveform during propagation and poses a challenge to EMP detection. Therefore, it is necessary to conduct theoretical research on EMP propagation in the ionosphere. Conventional second-order pseudo-spectral time-domain (PSTD-2) algorithm has difficulties in keeping the stability and accuracy of waveforms in calculations over hundreds of kilometers of propagation. To overcome the difficulties, a fourth-order PSTD algorithm incorporating the moving window technique (MWPSTD-4) is proposed. In the numerical examples, the performance of MWPSTD-4 is compared with PSTD-4 and PSTD-2 in the long-distance propagation of EMP. The results show that the MWPSTD-4 improves efficiency while guaranteeing accuracy and is suitable for large-scale electromagnetic field simulation. The proposed method provides a basic algorithm to eliminate the numerical dispersion interference for calculating the long-distance propagation of EMP in complex spaces and is helpful for the design and calibration of satellite-borne EMP detectors. [ABSTRACT FROM AUTHOR]

The modeling and forecasting of Total Electron Content (TEC) play a major role in influencing signals from satellite-based navigation systems and impact the performance of diverse satellite-dependent technologies. The intensity of solar ionizing radiation and the state of geomagnetic field activity influence the Global Navigation Satellite System (GNSS)-TEC. This paper uses a Linear TEC Function (LTF) climatology model to understand ionospheric behavior under solar and geomagnetic activities that cause variations in the electron distribution of the ionosphere medium. The LTF model integrates representations of solar EUV photon (MgII) and geomagnetic (SYMH) activities, incorporating solar-modulated oscillations (periodic variations) at four seasonal cycles and a linear trend. The LTF model examined the time series of GPS-TEC at a location (geographic 34.95° N, 134.05° E) with a time resolution of 1 h, from 1997 to 2016, covering solar cycles 23 and 24. The Root Mean Square Deviation (RMSD) and correlation coefficient between the GNSS-TEC and model TEC (LTF) was 5.30 TECU and 95 %. The results indicate that solar components, as well as annual and semi-annual variations, have a significant impact on the daily average TEC. Solar activity appears to be the predominant determining factor of TEC during the solar phases of cycles 23 and 24. In contrast, periodic influences primarily outline TEC during periods characterized by minimal solar activity. The geomagnetic component presents an increased influence, particularly during storm periods. The model demonstrates superior performance in Total TEC modeling compared to other state-of-the-art approaches. [ABSTRACT FROM AUTHOR]

Multiple constellations and their combinations in the global navigation satellite systems (GNSS) provide a great opportunity for single-station precise point positioning (PPP) models. The PPP models are of more importance for GNSS users as they are cost-effective with reasonable accuracy. There are abundant models in the market that use different data processing techniques based on the location and constellations used. In this study, we used the precise point positioning (PPP) software Net_Diff to verify the positioning accuracy at a low latitude Indian location using individual global satellite constellations (GPS, GLONASS, Galileo, BeiDou) and their combinations with GPS fixed. The ionospheric correction models such as GIM and Klobuchar are applied in the post-processing to determine the positioning accuracy. The Kalman filter method is applied to model the input data along with including the noise to derive the position solution. The results revealed that the GPS showed constant residual error for both quiet and disturbed days. In terms of single constellation Galileo produced less residuals in WGS 84 and ECEF coordinate systems whereas in the multi-constellation combination GPS, Galileo and GLONASS resulted in residuals of lesser magnitudes compared to the other combinations considered in this study. The RMS and STD of the residuals confirmed the high precision for Galileo and low precision for BeiDou constellations at the location. [ABSTRACT FROM AUTHOR]

The technological advancements in the current era have highlighted the increasing significance of satellite-based positioning, navigation, and timing services in a wide range of dynamic and critical applications. This has led to significant efforts towards enhancing the performance of global navigation satellite systems (GNSS) operating under challenging ionospheric conditions. The Sri Lankan ionosphere region is a focal point of equatorial aeronomy scientists, being situated in the southernmost landmass of the Indian longitude sector within the vicinity of the magnetic equator where a combination of electric, wind, and temperature dynamics exerts a substantial influence on the ionosphere but was relatively unexplored in the past. In the present work, we employed a Kriging interpolation technique on the total electron content (TEC) variables from ten GNSS receivers operating under the Continuously Operating Reference Stations (CORS) network in Sri Lanka first ever of its kind to deliver two-dimensional regional ionospheric TEC maps at hourly intervals, both during quiet and disturbed ionospheric conditions in the equinoctial March and April months of 2022. The latitudinal variation patterns are discernable from the hourly TEC maps. Furthermore, a comparative analysis of the performance of GNSS-derived TEC with that of the routinely published Global Ionospheric Maps (GIMs) confirms overestimation characteristics of the latter irrespective of the local time of observation. The generated regional ionospheric maps are fairly responsive to the onset of the storm and the recovery phase thereafter. The extent of nighttime ionospheric irregularity is also probed through the rate of TEC index (ROTI) variations, demonstrating that the irregularities were insignificant during the selected storm event. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite Systems (GNSS) have become an integral part of modern life, supporting various applications, from precise positioning and navigation to timing and synchronization. However, GNSS signals are vulnerable to natural interferences including various atmospheric disturbances, with ionospheric scintillations being a significant challenge. Ionospheric scintillations, caused by irregularities in the Earth's ionosphere, introduce rapid fluctuations in the amplitude and phase of GNSS signals. These fluctuations can severely degrade the accuracy and reliability of GNSS receivers, leading to positioning errors and navigation failures. Hence, it is crucial to develop effective mitigation strategies. One of the promising approaches to mitigate ionospheric scintillations is the utilization of Software Defined Radio (SDR) technology in GNSS receivers. SDR allows for real-time adaptation to changing signal conditions, enabling the receiver to detect scintillations and adjust its signal processing accordingly. This adaptability enhances the receiver's stability against ionospheric disturbances, ensuring more robust and accurate positioning and navigation. In this paper, preliminary results of GNSS SDR (Make: iP-Solutions, Japan) installed at Koneru Lakshmaiah Education Foundation (KLEF), Vaddeswaram (Guntur) (16.44° N, 80.62° E) are presented. Amplitude scintillation index (S4) variations for different PRNs and subsequent positioning results are interpreted from April to September 2023. The results are compared and validated with those of the co-located Novatel GNSS receiver and NAVIC receiver. Most of the S4 variations correlate well with the S4 values from the Novatel and NAVIC receivers. S4 observations from the Septentrio receiver at Daytona Beach (Florida) are also presented. The results of SDR will be extended further for the development of scintillation mitigation algorithms. We plan to install an SDR and employ similar mitigation strategy at this location in the near future. [ABSTRACT FROM AUTHOR]

In order to study the coupling relationship between earthquakes and ionospheric disturbances, TEC data during the Mw 7.3 earthquake that occurred near Fukushima, Japan on March 16, 2022, were processed using global ionospheric data provided by the Center for Orbit Determination in Europe (CODE). In this paper, the sliding quartile interval method is used to eliminate solar activity in a 27-day window, including sunspot number (SSN), F10.7 cm radio flux (F10.7), total solar irradiation (TSI), solar wind velocity (Vsw) and geomagnetic activity. The impact of disturbance storm time index (DST) and global geomagnetic activity index (KP) on TEC anomaly disturbance can obtain more accurate TEC anomaly information. The results indicate that when the solar and geomagnetic activity cycles are inconsistent with the TEC anomalies on fifth day before the earthquake, the TEC anomalies above the epicenter are significantly greater than those observed in other regions, and the corresponding magnetic conjugate region is accompanied by anomalies, which is the characteristic of TEC anomalies caused by earthquakes. This means that the detected TEC anomalies can be used as a potential ionospheric precursors, indicating that the Fukushima earthquake is imminent. [ABSTRACT FROM AUTHOR]

A climatological survey of Martian ionospheric plasma density irregularities was conducted by exploring the in-situ measurements of the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. The irregularities were first classified as enhancement, depletion, and oscillation. By checking the simultaneous magnetic field fluctuation, the irregularities have been classified into two types: with or without magnetic signatures. The classified irregularities exhibit diverse global occurrence patterns, as those with magnetic signatures tend to appear near the periphery of the crustal magnetic anomaly (MA), and those without magnetic signatures prefer to appear either inside of the MA or outside of the MA, depending on the type and solar zenith angle. Under most circumstances, the irregularities have a considerable occurrence rate at altitudes above the ionospheric dynamo height (above 200 km), and the magnetization state of the ions seems irrelevant to their occurrence. In addition, the irregularities do not show dependence on magnetic field geometry, except that the enhancement without magnetic signatures favors the vertical field line, implying its equivalence to the localized bulge. Other similarities and discrepancies exist in reference to previous studies. We believe this global survey complements previous research and provides crucial research clues for future efforts to clarify the nature of the Martian ionospheric irregularities. [ABSTRACT FROM AUTHOR]

A solar eclipse is a fascinating event that gives a unique opportunity to study the ionospheric characteristics in a controlled blockage of solar radiation. We present the upper atmosphere's response, mostly F-layer, during the annular eclipse on October 14, 2023. This eclipse was mostly visible from the North and South American regions with a maximum obscuration of around 91%. We study the response of the ionospheric Total Electron Content (TEC) and the critical frequency of the F2 layer (f 0 F 2) for three consecutive days (October 13 to 15, 2023) using ground and space-based techniques. We present the ionospheric response for a large area that covers the path of the solar eclipse of latitude and longitude range from 50 ° N to 10 ° S and 30 ° W to 150 ° W. For the ground-based observation, we use fifty-five International GNSS Service (IGS) stations and eleven Global Ionospheric Radio Observatory (GIRO) Digisonde stations that cover the annular and partial solar eclipse and are in the close vicinity of the annularity belt. We compute the vertical TEC (VTEC) and f 0 F 2 from this database and check their temporal and spatial variations. It is found that the VTEC, as computed from the IGS stations, mostly shows decrements during the partial blockage of the sun by the lunar disc. The VTEC, as computed from the GIRO database, also shows a decreasing trend but with comparatively more oscillating in nature. The f 0 F 2 shows a similar decreasing trend due to the solar eclipse. For space-based observation, we use the Swarm satellite data for the tracks that have gone through the annularity belt. Also, a spatiotemporal study is executed using the Global Ionospheric Map (GIM) database. For both cases, the VTEC shows a prominent depletion. We investigate the variation in the percentage change in VTEC as a function of obscuration and observe a positive correlation between them. We also compute the time difference between the maximum eclipse and the maximum TEC modulation to investigate the response time profiles of the ionosphere at different receiving stations. All the methods give satisfactory and consistent outcomes that corroborate the physical mechanism of ionospheric variabilities due to the effect of the solar eclipse. We check the geomagnetic condition to eliminate the scope of contamination and observe that their values are normal during the study. [ABSTRACT FROM AUTHOR]

The earthquake (EQ) precursors from satellites data portray an image of the energy propagation from the lithosphere to atmosphere and then to the ionosphere. Previous studies have often presented detailed discussion on different precursors at various altitudes. However, this study aimed to investigate the anomalies at various altitudes associated with the Hotan China EQ (hypocentral depth: 10 km, latitude 35.5°N, longitude 82.4°E). The goal was to identify pre-and post-seismic anomalies statistically in the conjunction with the wavelet transformation. We observed possible precursors in the atmosphere such as variations in aerosol optical depth, tropopause pressure, relative humidity, latent heat flux, and outgoing longwave radiation in a window of 5–10 days before the seismic event. Moreover, the total electron content had precursors during quiet geomagnetic storm conditions (−20 < Dst ≤ − 40 nT, Kp ≤ 3) beyond the bound within 5–10 days. These findings highlight the potential of using atmospheric and ionospheric parameters to detect seismic anomalies as EQ precursors for improved EQ early warning systems. [ABSTRACT FROM AUTHOR]

The injection of energy into the Earth's magnetosphere during geomagnetic storms and substorms has a direct impact on the ionosphere in the auroral and sub-auroral regions. This influence can be observed through phenomena such as the expansion of the auroral oval, and fluctuations in plasma density and the intensity of the field-aligned current (FAC) system. Changes in the geomagnetic environment significantly affect the main ionospheric trough (MIT) and field-aligned currents (FACs). In this study, we analysed two geomagnetic storms of different origins—October 2015 and September 2017 that occurred during solar cycle 24. Both storms were characterised by two minima of the Dst index and classified as two-step storms. In this work, we investigate the evolution of FACs density, the displacement of MIT and FACs during the development of geomagnetic storms, and we quest for the relationship between field-aligned currents and the main ionospheric trough. We noticed a connection between the positions of the main ionospheric trough minima and the Dst index, found cases especially during the main and recovery phase of the storms when FACs increase after leaving the ionospheric trough, and observed the predominance of downward currents in the area of the MIT which suggest their influence on the formation of this region of depleted plasma density. [ABSTRACT FROM AUTHOR]

On 6 February 2023, the destructive earthquakes (EQs) occurred in Kahramanmaras Turkey with the maximum magnitude 7.8. In this paper, based on multi-source satellite observations, we investigated the pre-seismic anomalies of infrared radiation and ionosphere, and analyzed the coupling features of multi-parameter anomalies in temporal evolution and spatial distribution. Analysis results indicated that in the vicinity of the epicenter, the outgoing longwave radiation (OLR) anomalies observed from NOAA-18 satellite were very obvious in January 2023, and the ionospheric plasma anomalies observed from CSES and SWARM satellites were significantly detected on 30 January 2023, which were probably the precursor signals of the impending main shock. Combined with the analysis results of crustal deformation and atmospheric compositions for the Turkey EQs in published articles, we believed that crustal stress changes and rock ruptures in the boundaries between the Arabian and African plates and the Anatolian block were more likely to cause the pre-seismic anomalies in infrared radiation, atmosphere and ionosphere. The observed anomalies had a clear coupling relationship, and represented the stage changes of seismogenic process for the Turkey EQs. In addition, the satellite remote sensing technology is very helpful for us to monitor the multi-parameter variations in lithosphere, atmosphere and ionosphere, better verify the correlation of pre-seismic anomalies in Earth's multi-sphere structures, and further promote the research on the multi-sphere anomaly coupling mechanism. [ABSTRACT FROM AUTHOR]

Understanding ionospheric irregularities and their dynamics is crucial, with the rate of change of the total electron content index (ROTI) serving as a significant metric for this purpose. However, inconsistencies in ROTI magnitudes have been noted when sampled at one‐second interval across various Global Navigation Satellite System (GNSS) receivers. This study presents a detailed statistical analysis to investigate inconsistencies in ROTI using multi‐GNSS observations in conjunction with four distinct GNSS receiver types. Various factors affecting the ROTI inconsistencies among receivers were examined, including differences in sampling rates (1, 5, 15, and 30 s), and varying time window widths (1, 2, and 5 min). By examination of data obtained from GNSS receivers with zero or short baselines on a global scale, the analysis uncovered substantial variations in multi‐GNSS ROTI values across the four assessed receiver types. The main findings suggest that reducing the sampling rate reduces the inconsistencies in the magnitude of ROTI, particularly at lower sampling rates. This reduction can be attributed to the exclusion of high‐frequency components in the ROTI spectrum. Interestingly, the width of the time window is found to have minimal impact on the ROTI magnitude. The study also shows a direct correlation between a larger magnitude of ROTI and the increased noise in the signals tracked by receivers. These results emphasize the importance of considering sampling rates and GNSS receiver types when utilizing ROTI to investigate ionospheric irregularities. Plain Language Summary: Studying the changes in the ionosphere is important, and the rate of change of total electron content index (ROTI) is a key measure used for this purpose. ROTI is calculated using data from Global Navigation Satellite Systems (GNSS). However, variations in ROTI values were seen when measured at one‐second interval using different types of GNSS receivers. This study looked at these variations by analyzing ROTI data from multiple GNSS systems (BeiDou, GPS, GLONASS, and Galileo) and different types of GNSS receivers (Septentrio, Javad, Trimble, and Leica). Factors like sampling rates (1, 5, 15, and 30 s) and time window widths (1, 2, and 5 min) were considered during the analysis. The research found notable differences in multi‐GNSS ROTI values among the receiver types, with the Septentrio and Trimble receiver showing the most significant variations. Lowering the sampling rate led to fewer inconsistencies at slower rates, which is caused by a decrease in the multi‐GNSS ROTI values due to missing high‐frequency components. It was interesting to discover that the duration of the time window had little impact on ROTI values. These results stress the importance of paying attention to sampling rates and the type of GNSS receiver when using ROTI to study ionospheric irregularities. Key Points: Differences in multi‐GNSS ROTI values were observed across various receiver types at zero/short‐baseline stations globallyLowering the sampling rate decreased inconsistencies in the multi‐GNSS ROTI values among diverse receiversTime window width had a minimal impact on both the consistency and magnitude of multi‐GNSS ROTI values [ABSTRACT FROM AUTHOR]

In this work, we analyze data collected by an HF transmitter/receiver radio link, operating as an oblique ionosonde between the McMurdo Station (transmitter) and South Pole Station (receiver) at 4.1, 5.1, 6.0, 6.4, and 7.2 MHz between 28 February and 14 March 2019. To help contextualize the link's data we have performed numerical raytrace simulations to help understand the observations. By considering both the data and simulations, we have identified both single‐ and two‐hop E‐ and F‐region propagation modes in the data, where the multi‐hop modes were observed in the hours around sunrise and sunset in the 4.1 and 5.1 MHz channels. This is an unexpected result given the accepted wisdom that multi‐hop modes, which require a ground scatter component, cannot be supported in Antarctica because of the highly absorptive ice covering much of the continent. Our results show that multi‐hop propagation modes can be supported in the region under specific ionospheric conditions—around sunrise and sunset—if the mode's ground scatter component is collocated with the Transantarctic Mountains. The mountains are located along the great‐circle path between the link's transmitter and receiver. However, the combination of favorable ionospheric and ground scattering conditions makes the detection of the multi‐hop mode a rare occurrence in the data set analyzed here. These findings are critical to data analysis efforts of any current or future oblique ionosonde systems operating in Antarctica and other regions such as the Arctic. Plain Language Summary: The ionosphere is a region of plasma located above approximately 60 km in altitude that affects the propagation of High Frequency (HF; 3–30 MHz) radio waves. An HF radio transmitter and a receiver link is commonly used as a remote sensing tool for analyzing the characteristics of the ionosphere over vast and inaccessible regions such as Antarctica. In this work, we analyze data collected by an HF which operated from 28 February–14 March 2019 in Antarctica. The experiment consisted of an HF transmitter located at the McMurdo Station and a receiver located at the South Pole Station. An important finding of this work is the identification transmission pathways in the link that are supported by reflections between the Antarctic ground and the Earth's ionosphere, commonly referred to as a "multi‐hop mode." This is an unexpected result because conventional wisdom says that the Antarctic ice should absorb the radio transmissions when they interact with the ice on the ground, preventing a multi‐hop mode. Our analysis shows that in the hours around sunrise and sunset, the HF link's ground reflections points can be collocated with the Transantarctic Mountains which act as a good reflector because the mountains are exposed rock. Key Points: Raytracing simulation results are compared to transmitter/receiver link observations between the McMurdo and South Pole StationsEvidence of a two‐hop propagation mode between the stations is observed in the data and supported in the modelingMulti‐hop modes in Antarctica are rare but possible under specific ionospheric conditions [ABSTRACT FROM AUTHOR]

The ionosphere shows regular changes such as daily, 27 days, seasonal, semi-annual, annual, and 11 years. These changes can be modeled and their effects largely determined. However, in addition to regular changes, irregular changes occur in the ionosphere due to space weather conditions, natural disasters, and human-induced irregularities. GNSS is one of the instruments along with many others that can give a piece of information on the ionospheric state. Various indices/parameters are used to determine the effect of space weather conditions. The well-known ones are solar activity indices, geomagnetic storm indices, magnetic field components, proton density, and proton flux parameters. It is important to take all of these indices into consideration when investigating the source of the anomaly. Considering only some of them may lead to incorrect inferences about the source of possible anomalies. To carry out comprehensive research in this field, it is necessary to analyze a very large data set. This indicates the requirement for an automatic system. With the Global and Regional Ionosphere Monitoring System (GRIMS) designed within the scope of this study, the ionosphere can be monitored globally and regionally. The GRIMS is online at https://www.online-grims.com/. By using Global ionospheric maps and GNSS receiver data, global, regional, and station-specific anomalies can be detected regularly through methods such as HDI (Highest Density Interval) and ARIMA (Autoregressive Integrated Moving Average). GRIMS gathers space weather-related parameters from ionospheric data centers to help users interpret the situation, and it allows users to download the results and request data for specific days. The details of the experimental results and output products of the system designed during the geomagnetic active days of March 17, 18, 2015 are given in this paper. Moreover, geomagnetic active days that occurred between 2000 and 2023 are given in the GRIMS. [ABSTRACT FROM AUTHOR]

The terrestrial ionosphere is a birefringent medium that allows radio waves to propagate in two modes: the ordinary (O‐mode) and the extraordinary (X‐mode). A difference in the index of refraction of the two modes results in differential delay (mode delay) between the O‐ and X‐modes of radio waves propagating through the ionosphere. Mode delays of transionospheric high frequency radio waves are determined using the Radio Receiver Instrument (RRI) onboard the Enhanced Polar Outflow Probe (e‐POP) on the CASSIOPE/Swarm‐E satellite. Experiments between RRI and the SuperDARN radar at Saskatoon, Canada show large variabilities in mode delays. The mode delays are nearly constant in some experiments but other experiments have large variations. The mode delay observations could not be explained by the distance between the e‐POP satellite and the radar, the foF2 values along the satellite track, nor whether the satellite track was across or along a SuperDARN radar beam. A combination of RRI observations and ray‐trace modeling are used to investigate the mode delay of transionospheric radio waves. Key Points: Observations and modeling of differential delay between the O‐ and X‐modes (mode delay) of transionospheric radio wavesMode delays strongly depend on the magnitude and distribution of foF2 through which radio waves propagateAdditional gradients in foF2 lead to larger changes in mode delays [ABSTRACT FROM AUTHOR]

Effects of Hurricane Grace in August 2021 are studied in the thermosphere and ionosphere, using data from the COSMIC‐2, ICON, and GOLD satellites. Significant impacts on electron density, thermospheric winds, and temperature are observed after the onset of the hurricane, compared to the pre‐hurricane phase. Comparison of the observations during the hurricane with the ones during a non‐hurricane year clearly provides further evidence for substantial hurricane‐induced thermospheric and ionospheric changes. We reveal an enhancement in electron density during the hurricane's rapid intensification and pronounced changes in thermospheric winds. Additionally, the low‐latitude thermosphere exhibits considerable warming of up to 70 K around 150 km during this period. These changes highlight the long‐range vertical coupling mechanisms between hurricanes and the upper atmosphere, and provide valuable insights into the profound influence of meteorological events on upper atmospheric dynamics, emphasizing the need for further exploration. Plain Language Summary: Our research investigates how hurricanes, specifically Hurricane Grace in 2021, affect Earth's upper atmosphere. The hurricane was able to influence layers of the atmosphere that are critical for satellite communication and GPS. We used data from different satellites to study changes in the number of free electrons per unit volume of air (electron density), neutral winds, and temperature. We found that during the intensification of the hurricane, electron density increased in the ionosphere, which is the layer of Earth's atmosphere containing a high concentration of ions and free electrons. We also observed substantial changes in the winds high up in the atmosphere and found that a region of the upper atmosphere around 150 km warmed significantly. This research helps us understand how weather events on the Earth's surface can impact conditions hundreds of kilometers above the surface in Earth's atmosphere. Key Points: 2021 Hurricane Grace's impact on electron density, thermospheric winds, and temperature are analyzed using COSMIC‐2, ICON, and GOLDIonospheric electron density showed notable variations, predominantly increasing with the hurricane's intensificationSignificant thermospheric warming and circulation changes are observed [ABSTRACT FROM AUTHOR]

The Martian ionosphere has many similarities and differences compared to Earth, attracting significant attention. This paper utilizes radio occultation data from the Mars Global Surveyor (MGS), Mars Atmosphere and Volatile Evolution Mission (MAVEN), and ESA Mars Express mission (MEX), associated with the measurements from Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) aboard MEX, to investigate the seasonal variation of the Martian dayside ionosphere. Data preprocessing is performed first to isolate the influence of solar zenith angle and solar radiation, the seasonal variation of the Martian dayside ionosphere explored in this study. The results suggest that the peak electron density reaches its minimum and maximum at LS = 70.2° and LS = 250.2°, respectively, with an amplitude of 16.5% concerning the average (LS is referred to as the solar longitude of Mars). The peak altitude experiences its minimum at LS = 78.4° and maximum at LS = 258.4°, and its relative amplitude is 12.1%. The outcomes suggest that the seasonal variations in the Martian ionosphere are primarily attributed to the Mars‐Sun distance change, which is different from the situation on Earth. This study will benefit both Martian ionosphere modeling and Earth's ionosphere understanding in the future. Plain Language Summary: The Martian ionosphere shares many similarities with Earth's, which has attracted considerable attention. The Martian ionosphere is primarily driven by solar radiation, including the solar zenith angle and solar radiation strength. So far, missions of MGS, MEX, and MAVEN have collected thousands of measurements about the Martian ionosphere over decades. Based on data preprocessing and systematic error correction, this study explored the seasonal variation in the dayside Martian ionosphere's peak electron density and altitude. The primary results suggest that the seasonal variation in the Martian ionosphere is mainly driven by the Sun‐Mars distance changing, and the mechanisms are distinguished for peak electron density and altitude. In particular, the peak electron density is directly driven by solar radiation, while the peak altitude is due to the lower boundary perturbation. These findings are quite different from Earth and shed light on further understanding in the future. Key Points: The seasonal variability of the Martian dayside ionosphere is studied using multi‐source dataBoth the peak electron density and peak altitude exhibit notable seasonal variationsThe mechanisms are different between the seasonal variations in the peak electron density and altitude [ABSTRACT FROM AUTHOR]

The cusp ion outflow on Earth has been extensively studied for decades. However, the energy flux associated with the ion outflow, which is of equivalent importance to the number flux or mass flux, has been rarely studied. Here, we present the first systematic study on the cusp ion energy flux and the energy budget along the cusp magnetic flux tube using quasi‐conjunction observations from the Polar and Fast satellites. Significant ion energy fluxes (several 10s mW/m2 ${\mathrm{m}}^{2}$ mapped to 100 km altitude) away from the Earth are frequently observed in the mid‐altitude cusp (3–6 Re). Observations at low altitudes (< ${< } $2 Re) show that the upward ion energy flux is associated with ion outflows originating from the ionosphere. In addition, we show that the ion outflows experience intense energization well above the ionosphere. The only possible energy source for this energization is the earthward Poynting flux in mid‐altitude. The electrons are accelerated downward and are another energy sink (not source). The altitude profile of the energy fluxes suggests a transition region between 2 and 4 Re where both ion heating and electron acceleration primarily occur and where significant Poynting flux is dissipated. Analysis of the E/B ratio shows that the Poynting flux is carried by both the Alfven waves and quasi‐static structures. The above results place important constraints on possible local ion energization mechanisms. Key Points: Significant ion energy outflows are frequently observed in the mid‐altitude cusp (|R| in 3–6 Re)Significant ion energization and Poynting flux dissipation occur well above the ionosphere (|R| in 2–4 Re)The earthward Poynting flux is the most likely energy source for the ion energization [ABSTRACT FROM AUTHOR]

A comprehensive pattern of localization of ionization troughs has been constructed for all local time hours. It includes high‐latitude troughs (HLT), main (or sub‐auroral) troughs (MIT), mid‐latitude ring ionospheric troughs (RIT), low‐latitude troughs (LLT), and quasi‐troughs. The CHAMP satellite data recorded in the southern hemisphere for quiet geomagnetic conditions under high solar activity were used. The separation of HLT and MIT was based on the model of auroral diffuse precipitation (Vorobjev et al., 2013). This model describes zone I of diffuse precipitation at the equatorward edge of the auroral oval and zone II of diffuse precipitation at its poleward edge. To distinguish between MIT and RIT the dynamics of both troughs during geomagnetic disturbances was examined. Because the position of all ionospheric structures, including the auroral oval, depends on longitude, the analysis in each local time sector was conducted within the framework of the longitudinal effect. Each local time sector exhibits specificity. (a) The noon sunlit ionosphere is strongly influenced by the dayside cusp; MIT occurs only at shadow longitudes. (b) In the daytime, strong plasma peaks are observed at latitudes of diffuse precipitation in zone I. (c) In the afternoon/evening sector, the plasma peaks are often observed equatorward of the auroral oval. Both peaks are sometimes accompanied by a quasi‐trough. (d) In the evening, HLT sometimes appears slightly equatorward of auroral oval. (e) In the nighttime, at longitudes of America and the Atlantic, a wide electron density minimum is formed near the Polar circle, which masks the MIT minimum. Plain Language Summary: Several ionization troughs are formed in the ionosphere: high‐latitude (HLT), main ionospheric trough (MIT), ring ionospheric trough (RIT) and low‐latitude trough (LLT). HLT is by definition located inside the auroral oval, MIT is located equatorward of oval. The problem of separation MIT and HLT arises because the position of the equatorward edge of the auroral oval is usually unknown, and both troughs are widely dispersed in latitude, so that HLT can appears equatorward of oval, and MIT inside of oval. To separate HLT and MIT the model of auroral diffuse precipitation is used. According this model, zone I forms the poleward wall of MIT, while zone II forms the poleward wall of HLT. This is a key factor for distinguishing between MIT and HLT. Another trough is associated with hot particle precipitation from the magnetospheric ring current and was, therefore, named the ring ionospheric trough (RIT). RIT, on average, is located equatorward of MIT, however, in general, areas of existence of MIT and RIT overlap. MIT and RIT is distinguishing using thorough analysis of the dynamics of both troughs over time. LLT is observed at low‐latitudes, its identification does not cause large problems, however it was discovered quite recently. Key Points: The pattern of localization of different ionospheric troughs for all local time hours in the southern winter hemisphere was createdThe main (sub‐auroral), high‐latitude, low‐latitude, ring ionospheric troughs and quasi‐troughs were rigorously identified and classifiedThe CHAMP data for high solar activity (7,000 cases) and modeled auroral diffuse precipitation were analyzed within the longitudinal effect [ABSTRACT FROM AUTHOR]

A necessary condition for the generation of Geomagnetically Induced Currents (GICs) that can pose hazards for technological infrastructure is the occurrence of large, rapid changes in the magnetic field at the surface of the Earth. We investigate the causes of such dB/dt $dB/dt$ events or "spikes" observed by SuperMAG at auroral latitudes, by comparing with the time‐series of different types of geomagnetic activity for the duration of 2010. Spikes are found to occur predominantly in the pre‐midnight and dawn sectors. We find that pre‐midnight spikes are associated with substorm onsets. Dawn sector spikes are not directly associated with substorms, but with auroral activity occurring within the westward electrojet region. Azimuthally‐spaced auroral features drift sunwards, producing Ps6 (10–20 min period) magnetic perturbations on the ground. The magnitude of dB/dt $dB/dt$ is determined by the flow speed in the convection return flow region, which in turn is related to the strength of solar wind‐magnetospheric coupling. Pre‐midnight and dawn sector spikes can occur at the same time, as strong coupling favors both substorms and westward electrojet activity; however, the mechanisms that create them seem somewhat independent. The dawn auroral features share some characteristics with omega bands, but can also appear as north‐south aligned auroral streamers. We suggest that these two phenomena share a single underlying cause. The associated fluctuations in the westward electrojet produce quasi‐periodic negative excursions in the AL index, which can be mis‐identified as recurrent substorm intensifications. Plain Language Summary: Sudden changes in electrical currents flowing in the auroral ionosphere produce magnetic perturbations on the ground, large dB/dt $dB/dt$ "spikes," which can lead to damaging Geomagnetically Induced Currents (GICs) in technological infrastructure. It is known that these spikes occur preferentially in the pre‐midnight local time sector and near dawn, though their exact cause is still poorly understood. In this study we show that pre‐midnight spikes are associated with the well‐known auroral substorm phenomenon which produces sudden southward‐directed perturbations in the magnetic field. Dawn spikes are associated with east‐west spaced auroral features which drift eastwards and produce wave‐like fluctuations in the magnetic field in the east‐west direction. The magnitude of dB/dt $dB/dt$ will depend on the speed at which the forms drift. Pre‐midnight and dawn spikes are not directly related, but can occur together when geomagnetic activity is high. Key Points: Pre‐midnight and dawn spikes in dB/dt $dB/dt$ occur independently; pre‐midnight spikes are associated with substorm onsetsDawn spikes are associated with sunward‐propagating, azimuthally‐spaced auroral features embedded in the westward electrojetFluctuations in AL associated with the dawn sector activity is often mis‐identified as recurrent substorm intensifications [ABSTRACT FROM AUTHOR]

The occurrence of small‐scale and intense ionospheric currents that can contribute to geomagnetically induced currents have recently been discovered. A difficulty in their characterization is that their signatures are often only observed at single widely spaced (typically 200–400 km) ground geomagnetic stations. These small‐scale structures motivate the examination of the maximum station separation required to fully characterize these small‐scale signatures. We analyze distributions of correlation coefficients between closely spaced mid‐latitude and auroral zone ground magnetometer stations spanning day to month long intervals to assess the separation distance at which geomagnetic signatures appear in only one station. Distributions were analyzed using periods that included low and high geomagnetic activity. We used data from pairs of magnetometer stations across North America within 200 km of each other, all of which were separated primarily latitudinally. Results show that while measurements remain largely similar up to separations of 200 km, large and frequent differences appear starting at around 130 km separation. Larger differences and lower correlations are observed during high geomagnetic activity, while low geomagnetic activity leads to frequent high correlation even past 200 km separation. Small but identifiable differences can appear in magnetometer data from stations as close as 35 km during high geomagnetic activity. We recommend future magnetometer array deployment in the auroral and sub‐auroral zone to have separations of 100–150 km. This enables the monitoring of large scale effects of geomagnetic storms, better temporal and spatial resolution of substorms, and observations of small‐scale current signatures. Plain Language Summary: Magnetic field data, gathered by magnetometer stations, are used to observe currents in the ionosphere and throughout the magnetosphere. Magnetometer stations are generally separated by 200–400 km. High‐frequency (1 s) data have become the norm in recent years. These data have uncovered that this spacing is too large to fully observe small currents in the ionosphere, which can damage technology on the ground if undetected. We looked at correlations between magnetometer stations separated by < ${< } $200 km across northern North America to analyze how observations change over various distances. We found that at high latitudes (>63° ${ >} 63{}^{\circ}$ magnetic latitude) and during high geomagnetic activity, substantial differences can appear over intervals < ${< } $150 km. Because of these findings, we suggest that future magnetometer stations placed at high latitudes should be separated by < ${< } $150 km. Key Points: The conventional wisdom for ground magnetometer station separation is based on outdated assumptionsCurrent magnetometer arrays do not sufficiently measure small‐scale geomagnetic disturbancesRecommendation for spacing of future ground magnetometers in the auroral zone is 100–150 km [ABSTRACT FROM AUTHOR]