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• HF & VHF radars, making measurements of resident space objects, detect Doppler oscillations. • The Doppler oscillations are interpreted as waves propagating in the ionosphere. • Statistical analysis shows the waves have a frequency distribution in the 0.2–1 Hz range. • The waves are most likely observed during day with higher frequencies in weaker ionospheres. • The wave frequency and occurrence distributions suggest the most likely waves are EMIC waves. Radars performing observations of resident space objects (RSO) measure Doppler variations in wave events of several minutes duration, with frequencies in the 0.2–1 Hz range peaking near 0.5–0.7 Hz, consistent with variations in electron density induced by waves in the intervening ionosphere. The two mid-latitude radars used were a Very High Frequency (VHF) radar operating at 55 MHz, and a High Frequency (HF) radar operating at 30 MHz, both in southern Australia. The VHF radar wave observations exibited a peak in wave occurrence in the post-dawn sector (0600–1200 local solar time). The seasonal occurrence of the waves had a strong minimum during winter compared with the other seasons. Comparison between observations in 2018/19 (near solar minimum) and 2021/22 (mid-rise to cycle 25 peak) suggests wave occurrence is anti-correlated with sunspot number and hence with EUV and ionospheric strength. Generally the waves had higher frequencies during night than day, and low sunspot number than mid solar cycle, when there was a weaker ionosphere. Given the oscillation frequency of the wave events, the most likely geophysical phenomena that is consistent with the observations are electro-magnetic ion cyclotron (EMIC) plasma waves in the Pc1 (0.2–5 Hz) frequency range. No other candidate geophysical disturbance appears to fit the wave characteristics. The majority of geomagnetic field-guided transverse Pc1 EMICWs project from the outer magnetosphere down onto the polar ionosphere, where they can convert to compressional fast-mode waves propagating parallel to the Earths surface in the ionospheric F2 layer waveguide, both equatorwards to mid-latitudes and polewards. It is likely the majority of the Doppler oscillations in the Pc1 frequency range observed by the radars at mid-latitudes are these ducted compressional waves. However, sources of transverse EMICWs from the magnetosphere onto the mid-latitude ionosphere do exist, and these may cause some of the observed oscillations. The micro-physics of these compressional waves causing Doppler oscillations in radio observations is not inconsistent with the history of ionospheric Doppler measurements and theory, although the radar trans-ionospheric radio propagation and the observed waves being higher frequency than previous studies is different. If the observed Doppler oscillations are compressional EMICW in the ionospheric waveguide then several of the statistical results can be explained. The anti-correlation of the wave occurrence with sunspot number (and resultant ionospheric strength) can be attributed to lower ionospheric attenuation at the higher latitudes, between where geomagnetically field-guided transverse EMIC waves initially enter the high-latitude ionospheric waveguide from the magnetosphere above, and their observation at mid-latitudes. The observation of higher frequency waves during low sunspot number may also be explained by a source effect in the magnetosphere that preferentially selects the higher frequency field-guided transverse EMIC waves to propagate down to the ionosphere. Comparisons will be shown with results from ground and space based magnetometers of compressional waves in the waveguide, highlighting consistent results and areas where the measurement techniques differ. Theory suggests the radar Doppler measurements are far more sensitive to variations in in-situ ionospheric electron density than magnetic field variations. This agrees with existing literature which highlights the very strong contribution from the compressional component. Theory also suggests that the Doppler sensitivity of a radar to ionospheric electron density variations is frequency dependent, with lower frequencies being more sensitive. This is borne out by the measurements, with the HF radar being more sensitive than the VHF radar. [ABSTRACT FROM AUTHOR]

Equatorial Plasma Bubbles (EPBs) can generate ionospheric scintillation at GHz frequencies used in the Global Navigation Satellite System (GNSS). Emerging at any longitude following sunset and typically moving eastward, monitoring the EPBs is essential for space weather services. Using three GNSS receivers positioned at the same latitude (∼0°N) but separated in longitudes (∼9°, ∼16°, and ∼25°) and the 47 MHz Equatorial Atmosphere Radar (EAR) in Indonesia, our study delineates the zonal extent of eastward‐traveling post‐sunset EPB inducing ionospheric GNSS scintillation. Typically, the scintillation occurrences detected by a ground receiver concentrate between 19 and 01 local time (LT), with a peak incidence observed at 21 LT. Furthermore, an experiment combining EAR observations with GNSS receiver data allowed for the determination of the linear change in the speed of eastward‐traveling EPB inducing scintillation during this time period. Interestingly, the longitudinal range of eastward‐traveling EPBs increased with higher solar flux (F10.7) levels. Our findings suggest that EPB can induce scintillation up to a longitudinal distance of approximately 25° from the onset location at sunset to the eastern midnight region, particularly in F10.7 ranging from 90 to 150 solar flux units. Moreover, experiments using longitudinally separated GNSS receivers indicated that scintillations during 19–01 LT originate from post‐sunset EPBs within a longitudinal range extending 25° to the west. In conclusion, our research provides valuable insight into the ability of eastward‐traveling EPB to induce GNSS scintillation within a longitudinal range of 25°, thereby enhancing EPB and scintillation monitoring and prediction in regional space weather services. Plain Language Summary: Many modern technologies rely on Global Navigation Satellite Systems (GNSS). GNSS refers to satellites constellations, including Global Positioning Systems, that send signals from space to the receivers on the ground, providing positioning and timing data. However, GNSS signals can be disrupted by natural phenomena in the Earth's ionosphere, a layer of charged particles in the upper atmosphere. One such phenomenon is the Equatorial Plasma Bubble (EPB) occurring at night, which can cause fluctuations or scintillations in GNSS signals, leading to errors in positioning and timing. Understanding how EPBs affect GNSS is essential for maintaining the reliability of navigation systems and ensuring the smooth operation of various technological applications that rely on GNSS data. EPBs usually move eastward and can cause scintillation in the longitude where they are generated and in other longitudes. Previous studies have not determined how far eastward‐traveling EPB can induce scintillation. Our recent discovery shows that EPBs can induce scintillation within a longitudinal range of up to 25°. This insight is essential for mitigating the adverse effects of EPBs on GNSS applications in regional or longitudinal sectors. Key Points: A ground GNSS receiver typically detects scintillations due to Equatorial Plasma Bubbles (EPBs) from 19 to 01 local time (LT) with the peak occurrence at 21 LTThe furthest longitudinal range of EPB inducing GNSS scintillation depends on solar flux (F10.7) levelEPBs can cause GNSS scintillation within a 25° longitudinal range at F10.7 levels of 90–150 solar flux units [ABSTRACT FROM AUTHOR]

The strip‐like bulge is a storm‐time conjugate ionospheric plasma density enhancement, constituted by the plasmaspheric H+/He+, that extends widely (over 150° in longitude) in the zonal dimension but occupies only 1°–5° in latitude. Based on in‐situ measurements of 11 low earth orbit satellites, this study statistically investigates the bulge structures of geomagnetic storms driven by 136 interplanetary coronal mass ejections during 2000–2021. The statistical results show that the strip‐like bulges are observed at the end of the storm main phase and can persist for more than 60 hr. The spatial and temporal coverage of the strip‐like bulge varies from storm to storm. However, the bulges do exhibit occurrence preferences: stronger storms (for the ICME‐driven) during solar minimum periods, the Asian‐Pacific sector (with eastward magnetic declination), and the nightside of the dawn‐dusk terminator. A quiet time density enhancement called mid‐latitude enhancement could be recognized as a precursor of the strip‐like bulge. The evolution features of the plasmapause height exhibit similarities with the strip‐like bulge, indicating a field‐aligned downward and cross‐L inward intrusion of the plasmaspheric ions. The local net ion drifts partly support this scenario with downward/inward being the most dominant but not unique pattern, the other diverse net ion drift configurations exist but their impact on the strip‐like bulges remains unclear. Plain Language Summary: A geomagnetic storm is a major disturbance of Earth's magnetic field when energy from the solar wind is effectively injected into the space environment surrounding Earth. During a storm, the ionosphere from 80 to 1,000 km is affected, and a sharp increase in ionospheric ion density with a narrow latitudinal range could be observed at low‐mid latitudes. The main ions constituting the sharp increase are H+/He+, which are the primary ions in the plasmasphere. We called this increase the "bulge." Toward a better understanding of the principal nature as well as the formation mechanisms of the structure, we extracted a number of samples snapshotted by many satellites to conduct a statistical investigation. It is found that the bulges prefer to appear in the Asian‐Pacific region, at 18:00‐06:00 LT, during strong storms, and under solar minimum conditions. Before their appearance, a smoother density peak structure is often observed, which could be recognized as the precursor. We suggested a substantial transfer of ions from higher to lower altitudes and the storm‐induced disturbance neutral wind, causing the smoother density peak structure to evolve into the bulge. Key Points: Occurrence of bulge has no strict limitation but shows some dependences on longitude, storm intensity, local time, and solar activityMidlatitude extra density peak could be recognized as a precursor of the strip‐like bulgeIon drift within the flux tube of the bulges is mainly in the field‐aligned downward/cross‐L inward pattern [ABSTRACT FROM AUTHOR]

Winds in the nighttime upper thermosphere are often observed to mimic the ionospheric plasma convection at polar latitudes, and whether the same is true for the daytime winds remains unclear. The dayside sector is subject to large temperature gradient set up by solar irradiance and it also contains the cusp, which is a hotspot of Poynting flux and a region with the strongest soft particle precipitation. We examine daytime winds using a Scanning Doppler Imager (SDI) located at the South Pole, and investigate their distribution under steadily positive and negative IMF By conditions. The results show that daytime winds exhibit significant differences from the plasma convection. Under negative IMF By conditions, winds flow in the same direction as the plasma zonally, but have a meridional component that is strongest in the auroral zone. As a result, winds are more poleward-directed than the plasma convection within the auroral zone, and more westward-directed in the polar cap. Under positive IMF By conditions, winds can flow zonally against the plasma in certain regions. For instance, they flow westward in the polar cap despite the eastward plasma convection there, forming a large angle relative to the plasma convection. The results indicate that ion drag may not be the most dominant force for daytime winds. Although the importance of various forcing terms cannot be resolved with the utilized dataset, we speculate that the pressure gradient force in the presence of cusp heating serves as one important contributor. [ABSTRACT FROM AUTHOR]

Ionospheric plasma density irregularities, which are one of the primary sources of disturbance for the Global Navigation Satellite System, significantly impact the propagation of electromagnetic signals, leading to signal degradation and potential interruptions. In the equatorial ionospheric F region after sunset, certain plasma density irregularities, identified as equatorial plasma bubbles, encounter optimal conditions for their formation and development. The energy spectra of electron density fluctuations associated with these irregularities exhibit a power-law scaling behavior qualitatively similar to the Kolmogorov power law observed in fluid turbulence theory. This intriguing similarity raises the possibility that these plasma density irregularities may possess turbulent characteristics. In this study, we analyzed electron density, temperature, and pressure data obtained from the China Seismo-Electromagnetic Satellite (CSES-01) to delve into the spectral properties of equatorial plasma depletions in the ionospheric F region at an altitude of about 500 km. This research marks the first exploration of these properties utilizing CSES-01 data and focuses on 14 semi-orbits that crossed the equator after midnight (01:00–03:00 LT), characterized by a geomagnetic quiet condition (Kp < 1). The analysis of electron temperature, density and pressure within equatorial plasma depletions revealed power-law scaling behavior for all the selected parameters. Notably, the spectral index values of these parameters are different from each other. The significance of these findings in terms of investigating plasma depletions via magnetic field signatures, as well as their relationship to the occurrence of Rayleigh–Taylor convective turbulence, is examined and discussed. [ABSTRACT FROM AUTHOR]

ANCHOR is a novel assimilative model developed at the U.S. Naval Research Laboratory, which was designed for rapid assimilative runs. ANCHOR uses recently developed PyIRI model for the background and for the formation of the background covariance matrix. It only takes a few minutes for ANCHOR to complete the data assimilation (DA) for one day, including data pre‐processing and model set up. ANCHOR extracts ionospheric parameters from radio occultation (RO) and ionosonde data using PyIRI formalism and assimilates them as point measurements into maps of the background parameters using a Kalman Filter approach. This paper introduces the ANCHOR algorithm, discusses its coordinate system and background, explains the background covariance formation, discusses the extraction of the ionospheric parameters from the data and the assimilation process, and, finally, shows the results of the observing system simulation experiment with synthetic data simulated using the SAMI3 model. ANCHOR reduces the root mean square errors in the analysis by more than a half for all of the ionospheric parameters in comparison to the background. Finally, this paper discusses advantages and limitations of the parametrized ionospheric DA, highlighting the avenues for its future improvement. Plain Language Summary: ANCHOR is a novel data assimilation model developed at the U.S. Naval Research Laboratory. It combines estimates of the electron density in the Earth's ionosphere from climatological model with observations, producing a better model representation that matches the data. It extracts ionospheric parameters from radio occultation and ionosonde data and assimilates them as point measurements into the maps of the background parameters using Kalman Filter approach. This paper introduces the ANCHOR algorithm, discusses its coordinate system and background, explains the background covariance formation, discusses the extraction of the ionospheric parameters from the data and the assimilation process, and, finally, shows the results of the observing system simulation experiment. Key Points: Novel approach for rapid ionospheric data assimilation (DA) using anchor pointsGlobal ionospheric DA for plasma density parametersExtraction of the anchor points from the ionospheric data [ABSTRACT FROM AUTHOR]

The ground‐based, high‐frequency radars of the Super Dual Auroral Radar Network (SuperDARN) observe backscatter from ionospheric field‐aligned plasma irregularities and features on the Earth's surface out to ranges of several thousand kilometers via over‐the‐horizon propagation of transmitted radio waves. Interferometric techniques can be applied to the received signals at the primary and secondary antenna arrays to measure the vertical angle of arrival, or elevation angle, for more accurate geolocation of SuperDARN observations. However, the calibration of SuperDARN interferometer measurements remains challenging for several reasons, including a 2π phase ambiguity when solving for the time delay correction factor needed to account for differences in the electrical path lengths between signals received at the two antenna arrays. We present a new technique using multi‐frequency ionospheric and ground backscatter observations for the calibration of SuperDARN interferometer data, and demonstrate its application to both historical and recent data. Key Points: Calibration of Super Dual Auroral Radar Network (SuperDARN) interferometer angle of arrival data remains an outstanding challengeAnalysis of data at multiple frequencies can overcome the inherent 2π measurement ambiguity in the time delay correction factor (tdiff)Example applications are shown for historical and contemporary multi‐frequency SuperDARN observations [ABSTRACT FROM AUTHOR]

The ability to understand and model ionospheric plasma flow on all spatial scales has important implications for operational space weather models. This study exploits a recently developed method to statistically separate large‐scale and meso‐scale contributions to probability density functions (PDFs) of ionospheric flow vorticity measured by the Super Dual Auroral Radar Network (SuperDARN). The SuperDARN vorticity data are first sub‐divided depending on the Interplanetary Magnetic Field (IMF) direction, and the separation method is applied to PDFs of vorticity compiled in spatial regions of size 1° of geomagnetic latitude by 1 hr of magnetic local time, covering much of the high‐latitude ionosphere in the northern hemisphere. The resulting PDFs are fit by model functions using maximum likelihood estimation (MLE) and the spatial variations of the MLE estimators for both the large‐scale and meso‐scale components are presented. The spatial variations of the large‐scale vorticity estimators are ordered by the average ionospheric convection flow, which is highly dependent on the IMF direction. The spatial variations of the meso‐scale vorticity estimators appear independent of the senses of vorticity and IMF direction, but have a different character in the polar cap, the cusp, the auroral region, and the sub‐auroral region. The paper concludes by discussing the sources of the vorticity components in the different regions, and the consequences for the fidelity of ionospheric plasma flow models. Plain Language Summary: The ability to accurately model the flow of ionized gases (plasma) in the Earth's ionosphere (the ionized region of the Earth's upper atmosphere) has important implications for operational space weather models. Large‐scale variations in this plasma flow are modeled well, but fluctuations on the meso‐scale and small scale are typically ignored in these models. This study uses measurements from a high‐latitude ground‐based radar network to measure the ionospheric plasma flow in terms of its vorticity (how straight or curved the flow is). The measured vorticity is separated into components related to both the large and meso‐scale fluctuations. The paper discusses the origins of the meso‐scale component, and what needs to be done before it can be confidently added to ionospheric plasma flow models. Key Points: The spatial variation of meso‐scale ionospheric flow vorticity is independent of the prevailing IMF By directionMeso‐scale ionospheric flow vorticity is strongest in the cusp and the auroral regionMeso‐scale ionospheric flow vorticity is most intermittent in the polar cap and the sub‐auroral region [ABSTRACT FROM AUTHOR]

We present broadband ionospheric scintillation observations of highly defined symmetric quasi‐periodic scintillations (QPS: Maruyama, 1991, https://doi.org/10.1029/91rs00357) caused by plasma structures in the mid‐latitude ionosphere using the LOw Frequency ARray (LOFAR: van Haarlem et al., 2013, https://doi.org/10.1051/0004‐6361/201220873). Two case studies are shown, one from 15 December 2016, and one from 30 January 2018, in which well‐defined main signal fades are observed to be bounded by secondary diffraction fringing. The ionospheric plasma structures effectively behave as a Fresnel obstacle, in which steep plasma gradients at the periphery result in a series of decreasing intensity interference fringes, while the center of the structures largely block the incoming radio signal altogether. In particular, the broadband observing capabilities of LOFAR permit us to see considerable frequency dependent behavior in the QPSs which, to our knowledge, is a new result. We extract some of the clearest examples of scintillation arcs reported in an ionospheric context, from delay‐Doppler spectral analysis of these two events. These arcs permit the extraction of propagation velocities for the plasma structures causing the QPSs ranging from 50 to 00 m s−1, depending on the assumed altitude. The spacing between the individual plasma structures ranges between 5 and 20 km. The periodicities of the main signal fades in each event and, in the case of the 2018 data, co‐temporal ionosonde data, suggest the propagation of the plasma structures causing the QPSs are in the E‐region. Each of the two events is accurately reproduced using a thin screen phase model. Individual signal fades and enhancements were modeled using small variations in total electron content (TEC) amplitudes of order 1 mTECu, demonstrating the sensitivity of LOFAR to very small fluctuations in ionospheric plasma density. To our knowledge these results are among the most detailed observations and modeling of QPSs in the literature. Plain Language Summary: Quasi‐periodic scintillations (QPS) are repeated variations in radio signals received on the ground from radio sources beyond the Earth's atmosphere. As these signals pass through plasma structures in the ionosphere they undergo refractive lensing which is seen at the receiver as a distinct signal fade, bounded on both sides by diffraction fringing. Analysis of these QPS using 2D Fourier transforms produced very clear examples of "scintillation arcs" which were used to extract the velocity of the ionospheric plasma producing these patterns. These symmetric quasi‐periodic oscillations form a distinct category of radio signals which were reproduced in this study using a phase screen model with very small changes in amplitude, corresponding to variations in ionospheric plasma density along the raypath of <<1% of ionospheric plasma density along the raypath. These features are seen across the wide bandwidth from 24 to 64 MHz, with frequency dependent variation in the width of the signal fade and fringing all being visible. Consequently we see how even these very small changes in ionospheric plasma density are nonetheless able to produce quite distinct variations in received signal strength. The observations in this paper thus demonstrate some of the fundamental physical processes of radio scattering in the ionosphere. Key Points: These are the first reported broadband ionospheric scintillation observations of symmetric quasi‐periodic scintillations (QPS)The QPS are very highly defined showing the clearest reported examples of ionospheric scintillation arcs in delay‐Doppler spectraThe observations are successfully reproduced using a phase screen model in which plasma density is varied by <1 mTECu [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 novel optimization algorithm integrating random and grid search mechanisms as function calls. • A cost-effective low inference time deep learning model for detecting 2D ionospheric plasma structures from all-sky airglow images. • The issue of uncertainty quantification has been addressed using the approach of bootstrapping. The ionosphere, part of the Earth's atmosphere, where different plasma irregularities/structures are generated through various electrodynamical processes. Airglow imaging is one of the tools to observe various morphological features of these irregularities. We aim to help all-sky airglow imaging-based ionospheric research by proposing novel deep learning at the edge framework for the detection of different types of mid-latitude ionospheric plasma structures (medium scale traveling ionospheric disturbances with single and multiple bands, and plasma bubbles). The primary challenge was to find an optimal deep neural network by considering the trade-off between accuracy and inference time. In order to address this, a novel hyperparameter optimization technique has been used that integrates the approaches of random and grid search mechanisms as a compact function. The random function generates the subspace for hyperparameters to check the convergence of the model while the grid search creates possible combinations to tune these hyperparameters. Our novel optimization method for deep learning inference at the edge led us to a low-cost, high-accuracy convolutional neural network (CNN) model, which outperformed the complex state-of-the-art deep learning models such as Inception-v3, DenseNet169, VGG16, and VGG19. For airglow image-based plasma structure detection, the proposed model recorded an accuracy of 99.9% with an inference time of 5.8 s. This was an improvement of about 4% in accuracy while 85% reduction in inference time over the best-performing baseline. There was about 93% reduction in the number of model parameters with respect to the best-performing baseline. Uncertainty quantification has also been performed in the present work through bootstrapping to validate the robustness of the proposed model. The findings of our study show the promise of deep learning at the edge for all-sky airglow imaging systems by demonstrating an alternate low-cost, high-accuracy deep neural network. [ABSTRACT FROM AUTHOR]

The ionosphere can be artificially modified by employing ground-based high-power high-frequency electromagnetic waves to irradiate the ionosphere. This modification is achieved through the nonlinear interaction between the electromagnetic waves and the ionospheric plasma, leading to changes in the physical properties and structure of the ionosphere. The degree of artificial modification of the ionosphere is closely related to the heating energy density of high-frequency pump waves. Due to the high density of neutral constituents in the lower ionosphere and the high frequency of electron-neutral collisions, the energy of heating pump waves will be absorbed and attenuated during the penetration of the low ionosphere, seriously affecting the heating effect. This paper proposes a method to reduce the absorption of ionospheric heating pump waves by releasing electron attachment chemicals into low ionosphere to form a large-scale electron density hole. A model for mitigating pump waves absorption based on SF6 release is established, and the absorption at different frequencies is quantitatively calculated. The propagation characteristics of high-frequency signals in ionospheric holes are studied using a three-dimensional ray tracing method, and the results demonstrate that the chemical release method not only reduces the absorption attenuation of heating pump waves but also forms spherical electron density holes, which exhibit a focusing effect on the heating beam and enhance the heating effect. The results are of great significance for understanding the nonlinear interaction between electromagnetic wave and ionospheric plasma and improving the ionospheric heating efficiency. [ABSTRACT FROM AUTHOR]

The prediction of post‐sunset equatorial plasma depletions (EPDs), often called ionospheric plasma bubbles, has remained a challenge for decades. In this study, we introduce the Ionospheric Bubble Probability (IBP) model, an empirical model to predict the occurrence probability of EPDs derived from 9 years of CHAMP and 9 years of Swarm magnetic field measurements. The model predicts the occurrence probability of EPDs for a given longitude, day of year, local time and solar activity, for the altitude range of about 350–510 km, and low geographic latitudes of ±45°. IBP has been found to successfully reconstruct the distribution of EPDs as reported in previous studies from independent data. IBP has been further evaluated using 1‐year of untrained data of the Ionospheric Bubble Index (IBI). IBI is a Level 2 product of the Swarm satellite mission used for EPD identification. The relative operating characteristics (ROC) curve shows positive excursion above the no‐skill line with Hanssen and Kuiper's Discriminant (H&KSS) score of 0.52, 0.51, and 0.55 at threshold model output of 0.16 for Swarm A, B, and C satellites. Additionally, the reliability plots show proximity to the diagonal line with a decent Brier Skill Score (BSS) of 0.249, 0.210, and 0.267 for Swarm A, B, and C respectively at 15% climatological occurrence rate. These tests indicate that the model performs significantly better than a no‐skill forecast. The IBP model offers compelling glimpses into the future of EPD forecasting, thus demonstrating its potential to reliably predict EPD occurrences. The IBP model is publicly available. Plain Language Summary: Post‐sunset equatorial plasma depletions (EPDs), often called ionospheric plasma bubbles, are a severe threat for reliable radio wave communication. However, their predictability has remained a challenge for the scientific community for decades. In this study, we introduce the Ionospheric Bubble Probability (IBP) model predicting the occurrence probability of post‐sunset EPDs for a given longitude, day of year, local time and solar activity, for the altitude range of about 350–510 km, and low geographic latitudes of ±45°. To this aim we have used 9 years of CHAMP and 9 years of Swarm magnetic field measurements. The IBP model predictions have been found to agree well with climatologies derived from independent data and performs largely better than unskilled forecasts. The IBP model is made publicly available. Key Points: The Ionospheric Bubble Probability (IBP) model estimates the occurrence probability of post‐sunset equatorial plasma depletions (EPDs)IBP shows high performance in predicting EPD occurrence for longitude, local time, day of year, solar activity, at altitudes of about 350–510 kmThe IBP model is publicly made available with documentation [ABSTRACT FROM AUTHOR]

Low‐cost instrumentation combined with volunteering and citizen science educational initiatives allowed the deployment of L‐band scintillation monitors to remote sense areas that are geomagnetically conjugated and located at low‐to‐mid latitudes in the American sector (Quebradillas in Puerto Rico and Santa Maria in Brazil). On 10 and 11 October, 2023, both monitors detected severe scintillations, some reaching dip latitudes beyond 26°N. The observations show conjugacy in the spatio‐temporal evolution of the scintillation‐causing irregularities. With the aid of collocated all‐sky airglow imager observations, it was shown that the observed scintillation event was caused by extreme equatorial plasma bubbles (EPBs) reaching geomagnetic apex altitudes exceeding 2,200 km. The observations suggest that geomagnetic conjugate large‐scale structures produced conditions for the development of intermediate scale (few 100 s of meters) in both hemispheres, leading to scintillation at conjugate locations. Finally, unlike previous reports, it is shown that the extreme EPBs‐driven scintillation reported here developed under geomagnetically quiet conditions. Plain Language Summary: The ionosphere is a region of the Earth's upper atmosphere characterized by a relatively large density of free ions and electrons produced, mainly, by solar photoionization. Ionospheric equatorial plasma bubbles (EPBs) are drastic decreases in ionospheric density known to develop near the equator during nighttime and expand to low latitudes. EPBs cause fluctuations in transionospheric signals transmitted by global navigation satellite systems (GNSS) such as the GPS (global positioning system). In this report, we present the results of a study made possible by low‐cost, GNSS‐based sensors hosted by volunteers and citizen science educational initiatives. The study evaluated the behavior of scintillation in the northern and southern hemispheres at low‐to‐mid latitudes. We found similar spatio‐temporal behavior in the scintillation events observed by monitors deployed in geomagnetically conjugate areas in the northern and southern hemispheres. We also found that the observed scintillation events were associated with EPBs that reached low‐to‐mid latitudes (extreme EPBs). Although these events are more likely to occur under disturbed geophysical conditions, the case presented here took place during a quiet period. The results indicate that GNSS systems at low‐to‐mid latitudes can be affected by EPBs‐driven scintillation more often than previously anticipated. Key Points: Citizen science initiatives allowed simultaneous observations of scintillation over geomagnetic conjugate areas at low‐to‐mid latitudesThe observations show a conjugacy in the spatio‐temporal evolution of intermediate scale size ionospheric irregularitiesLow‐to‐mid latitude scintillations were associated with extreme EPBs (reaching dip latitudes >26°) during quiet conditions [ABSTRACT FROM AUTHOR]

Plasma Depletion Events (PDEs) are characterized by abrupt, localized reductions in ionospheric plasma density at least by an order of magnitude decrease. These events are observed over a limited range of altitudes, typically spanning a few tens of kilometers. We use Mars Atmosphere and Volatile Evolution spacecraft data to investigate the properties and possible formation mechanism of daytime PDEs, typically observed at altitudes above 250 km. We show, using two example events and statistical analysis, that the depletion events are associated with electrostatic fluctuations and increased electron temperatures. The events are further accompanied by enhanced fluxes of suprathermal electrons and light energetic ions. These are indicative of local plasma heating, possibly mediated by the electrostatic fluctuations. The heated plasma may eventually escape from the depletion region through the ambipolar diffusion. Plain Language Summary: The Martian ionosphere, consisting of ions and electrons, is embedded in the planet's thin atmosphere. Density variations in the ionosphere, occurring on both large and small scales, can significantly impact the atmospheric loss process on Mars. One particular type of these ionospheric anomalies involves sudden reductions in ion density, often by tenfold or more. Although we have a basic understanding of these depletion events, their detailed characteristics and origins are not yet fully understood. We use data from various instruments onboard the Mars Atmosphere and Volatile Evolution spacecraft to investigate these phenomena, particularly on the dayside. We find that these depletion events are accompanied by increased electron temperatures and enhanced electric field fluctuations, while the magnetic field remains virtually unchanged. These observations suggest localized plasma heating within the depleted region. Furthermore, the fluxes of energetic light ions (mostly protons) and electrons are increased during the events. This increase in energetic particles could potentially serve as the energy source driving the heating process. We propose that the depletion events form when the heated ionospheric plasma escapes from the heated region. Key Points: Large scale plasma density depletions in the Martian dayside ionosphere are linked with electrostatic fluctuationsIncreased electron temperatures, enhanced suprathermal electron fluxes, and energetic light ions are observed within the depleted regionsLocal plasma heating possibly drives electron escape, forming an ambipolar field and causing plasma depletions through ambipolar diffusion [ABSTRACT FROM AUTHOR]

Molecular ions are relatively cold in the E region ionosphere; however, they can upwell to the magnetosphere during geomagnetically active times. Resonance between electrostatic ion cyclotron (EIC) waves is a potential pathway to energize molecular ions. In this work, the E region ionospheric plasma was modeled in the laboratory, and EIC waves were excited by a nonuniform field‐aligned current. The EIC wave was excited even when the ion neutral collision frequency is much higher than the ion cyclotron frequency, and the fundamental frequency was observed to be below the ion cyclotron frequency. In addition, the wave dispersion of the collisional EIC wave was calculated, which shows a consistent trend with experimental results as the collisions increasing. Therefore, this work suggests that EIC waves can be excited in the E region ionospheric‐like plasma, which can support the explanation of the energization of molecular ions in the E region ionosphere. Plain Language Summary: Spacecraft observed the presence of molecular ions in the topside ionosphere (600–1,000 km) and the magnetosphere during geomagnetically active times, and the potential mechanisms responsible for the acceleration of these molecular ions are still not fully understood. The resonance between electrostatic ion cyclotron (EIC) waves and molecular ions is a potential pathway to energize the molecular ions. However, most previous works on EIC waves were studied in collisionless plasma similar to the magnetospheric plasma, which is different from the E region ionospheric plasma. A typical characteristic of E region ionospheric plasma is the partially ionized effect, which introduces new physical processes that do not occur in collisionless plasmas. In this work, strong collisions that occurred in the E region ionosphere were simulated in the laboratory, and the current‐driven electrostatic ion cyclotron waves were observed in the modeled ionosphere. It is found that electrostatic ion cyclotron waves can be generated in the E region ionospheric‐like plasma. This work provides solid experimental evidence that electrostatic ion cyclotron instability can exist in weakly ionized plasmas of the E region ionosphere, and can be applied to explain the transverse ion heating of bulk ions in the bottomside ionosphere. Key Points: The E region ionospheric‐like collisional plasma was modeled in the laboratoryEIC waves were excited by field aligned current in the ionospheric‐like plasmaThis work can be applied to explain the energization of molecular ions in the E region ionosphere [ABSTRACT FROM AUTHOR]

The Super Dual Auroral Radar Network (SuperDARN) consists of more than 30 monostatic high‐frequency (HF, 8–20 MHz) radars to study dynamic processes in the ionosphere. SuperDARN provides maps of global‐scale ionospheric plasma drift circulation from the mid‐latitudes to the poles. The conventional SuperDARN radars consecutively scan through 16 beam directions with a lower limit of 1 minute to sample the entire field of view. In this work, we use the advanced capabilities of the recently developed Borealis digital SuperDARN radar system. Combining a wide transmission beam with multiple narrow reception beams allows us to sample all conventional beam directions simultaneously and to speed up scanning of the entire field‐of‐view by up to 16 times without noticeable deterioration of the data quality. The wide‐beam emission also enabled the implementation of multistatic operations, where ionospheric scatter signals from one radar are received by other radars with overlapping viewing areas. These novel operations required the development of a new model to determine the geographic location of the source of the multistatic radar echoes. Our preliminary studies showed that, in comparison with the conventional monostatic operations, the multistatic operations provide a significant increase in geographic coverage, in some cases nearly doubling it. The multistatic data also provide additional velocity vector components, increasing the likelihood of reconstructing full plasma drift velocity vectors. The developed operational modes can be readily implemented at other fully digital SuperDARN radars. Plain Language Summary: The Super Dual Auroral Radar Network (SuperDARN) consists of more than 30 high‐frequency (HF, 8–20 MHz) radars that observe the ionized part of the Earth's atmosphere to study Space Weather phenomena, like magnetic storms and the aurora. Each SuperDARN radar transmits a radio wave at a particular frequency and receives the returns scattering from ionized structures. The returns are analyzed to extract information about processes in near‐Earth space. Conventionally, these radars scan 16 azimuthal directions consecutively, dwelling for 3.5 s in each direction, which restricts a scan of the field‐of‐view to 1 minute. In this work, we use a recently developed digital SuperDARN radar system called Borealis to shorten the scan duration by an order of magnitude by illuminating the whole field of view with a broad transmitter beam and receiving radar returns from all 16 directions simultaneously using narrow receiver beams. We also implemented a technique to receive signals sent from one radar by other radars with overlapping viewing areas. This provides a significant increase (nearly doubles) the geographic area of coverage, compared with using the same radar for both transmission and reception. Key Points: We developed wide‐beam transmission to probe an entire Super Dual Auroral Radar Network (SuperDARN) field of view simultaneously and to enable bistatic operationsNew multistatic operation of SuperDARN radars provides additional measured velocity vector componentsNew wide‐beam and multistatic operations significantly improve temporal resolution and spatial coverage by SuperDARN [ABSTRACT FROM AUTHOR]

The ion upflow has great significance for the transport and exchange of particles during magnetosphere‐ionosphere coupling process. Previous studies focus on the ion upflow in the polar region, and find that ion upflow has hemispheric asymmetries. In subauroral region, the ion upflow is closely related with subauroral ion drift (SAID). However, the characteristics of ion upflow associated with SAID in both northern and southern hemispheres are still unknown. Based on the observation of DMSP satellites F16‐F18 from 2010 to 2020, we investigate the north‐south hemisphere distributions of ion upflow associated with SAID during quiet and disturbed time. The ion upflow rate presents localized features in both hemispheres. The ion upflow rate in the southern hemisphere is slightly higher/lower than that in the northern hemisphere before/after 1900 MLT. The ion upflow velocity in the southern hemisphere shows a clear dependence on magnetic local time (MLT). Furthermore, We find that the hemispheric asymmetry of ion upflow is closely related to the asymmetric configuration of the ionospheric parameters such as plasma density, conductance and solar elevation angle during magnetosphere‐ionosphere coupling process. The result also indicates that SAID and sunlight condition play important roles in the ion upflow in subauroral region. Key Points: Ion upflow occurrence rate in the southern hemisphere is slightly higher/lower than that in the northern hemisphere before/after 1900 MLTThe ion upflow velocity exhibits a strong dependence on MLT, which was observed in the southern hemisphere in this studyBesides subauroral ion drift, the sunlight condition also affects the occurrence rate and velocity of ion upflow in both hemispheres [ABSTRACT FROM AUTHOR]

In this study, we utilize ICON observations from 2019 to 2022 to analyze the variability of vertical plasma drift and its relationship with the neutral winds. The results reveal that there are 19% of downward plasma drifts at 13–17 LT, which changes with seasons and longitudes. The downward plasma drift occurs less frequently compared to the contemporaneous counter electrojet during solstices. We identify the relationship between vertical plasma drifts and north foot magnetic zonal and meridional wind profiles at 90–300 km altitudes. As the vertical plasma drifts become small or downward, the zonal winds display diverse variations at the altitudes; that is, the disturbances are eastward at 95–120 km altitudes, westward at 120–160 km altitudes, and eastward above 180 km altitudes, while the meridional winds present weak changes in all altitudes. Additionally, we discuss the possible roles of the E‐ and F‐region dynamos on the vertical plasma drifts. Plain Language Summary: The neutral wind in the Earth's upper atmosphere drives the ionospheric ions to cross the geomagnetic field lines and produces the dynamo effects in the E‐ and F‐regions. The electric field is created due to the divergence free of the total electrical current. The zonal electric field drives the ionospheric plasma to drift upward and downward due to the horizontal field lines, and influences the structures of low latitude ionosphere. One open question is that the vertical plasma drift shows the significant day‐to‐day variability and sometimes remarkably deviates from the climatological pattern during the quiet times. The ICON satellite provides the simultaneous observations of the plasma drifts and neutral winds in low latitudes, which provides us a good chance to investigate the day‐to‐day variability of the vertical plasma drift and its relationship to the neutral wind, as we discuss in the manuscript. Key Points: The equatorial vertical plasma drifts show large variability and 19% downward plasma drift at 13–17 LTThe occurrence of the downward plasma drift presents a significant longitudinal and seasonal variationsThe E‐ and F‐region zonal winds play vital roles on the large variability and the occurrence of the downward plasma drift [ABSTRACT FROM AUTHOR]

During magnetospheric substorms in the F region of the ionosphere and up to altitudes of ~1000 km, a polarization jet (PJ) is developed. Measurements of energetic ring current ions on the AMPTE/CCE satellite and driftmeter data on the DMSP satellites evidence that the formation of PJ is associated with the injection of energetic ions (10–100 keV) into the inner magnetosphere during substorms. In the region of PJ development, the characteristics of the ionospheric plasma change: the plasma density decreases, sometimes by an order of magnitude, and at the same time, the plasma temperature increases significantly. In addition, simultaneously with the westward plasma drift, upward plasma drift is usually observed. The upward ion flux from the region of PJ development of ~109 cm–2 s–1 is an order of magnitude greater than the average daytime ion flux from the ionosphere to the plasmasphere. Measurements on the MAGION-5 satellite in the plasmasphere on the same L-shells, where the polarization jet is recorded in the ionosphere, show an increase in the cold ion density. The density "humps" observed near the plasmapause are apparently formed due to plasma flows from the ionosphere accompanying the formation of the polarization jet. Thus, the consequences of substorms are observed throughout almost the entire magnetosphere. [ABSTRACT FROM AUTHOR]

In our exploration, we aimed at identifying seismic anomalies using limited ionospheric data for earthquake forecasting and we meticulously compiled datasets under conditions of minimal geomagnetic disturbance. Our systematic evaluation affirmed the ITransformer as a potent tool for the feature extraction of ionospheric data, standing out within the domain of transformer-based time series prediction models. We integrated the maximum entropy principle to fully leverage the available information, while minimizing the influence of presuppositions on our predictions. This led to the creation of the MaxEnt SeismoSense Model, a novel composite model that combines the strengths of the transformer architecture with the maximum entropy principle to improve prediction accuracy. The application of this model demonstrated a proficient capability to detect seismic disturbances in the ionosphere, showcasing an improvement in both recall rate and accuracy to 71% and 69%, respectively, when compared to conventional baseline models. This indicates that the combined use of transformer technology and the maximum entropy principle could allow pre-seismic anomalies in the ionosphere to be sensed more efficiently and could offer a more reliable and precise approach to earthquake prediction. [ABSTRACT FROM AUTHOR]

Irregularities in ionospheric plasma distribution can result in severe scintillation and disruption to the radio frequencies utilized for satellite communications and navigation. In the low and mid latitudes, these irregularities can include Equatorial Plasma Bubbles (EPBs) and Travelling Ionospheric Disturbances (TIDs). EPBs are irregularities manifesting in low latitude nighttime ionosphere plasma density that can extend along magnetic field lines with zonal scales on the order of 100 km or less, while TIDs are propagating wave disturbances. High frequency in-situ measurements of ionospheric plasma aboard spacecraft in Low Earth Orbit (LEO) are a direct measurement of irregularities in plasma density and are therefore valuable for resolving EPB and TID occurrences, variability, and relation to other ionospheric parameters that are believed to play a driving role in the formation of such irregularities. In this study, we utilize observations taken over a three-year period between 2017 and 2020 by the Advanced Ionospheric Probe (AIP) carried aboard the FORMOSAT-5 satellite to examine the spatial, seasonal, and interannual variability of equatorial to mid latitude ionospheric irregularities and vertical ion drift during this time. AIP provides in-situ measurements of ion density and vertical ion drift in the equatorial to mid latitude ionosphere at approximately 720 km altitude with local times between 22:00 – 23:00 local time. Our global scale results resolve distinct and inter-annually recurrent seasonal patterns in the distribution of nighttime ionospheric irregularities and vertical plasma drift during this time. Elevated occurrences of ion density irregularities are resolved along the Equatorial Ionization Anomaly (EIA) latitudes, while notable occurrences with variability consistent with EPBs also observed along the low and equatorial magnetic latitudes. Zonal variability of equatorial irregularities consistent with the signatures of nonmigrating atmospheric tides are observed. It is also notable that the occurrences and geographic distribution of ion density irregularities showed a considerable level of interannual variability, especially at mid latitudes over the South Atlantic and Southern African sectors, which showed much higher levels of irregularities in 2017–––2018, compared to 2019 and 2020. In comparison, the spatial and interannual variation of the co-located vertical ion drifts were much more consistent during the years examined, indicating that the driver for the observed interannual variability in ion density irregularities cannot be attributed to the vertical ion drift at the same time and location of the observations. This highlights the need for in-situ instruments distributed across multiple satellites in different local time zones. [ABSTRACT FROM AUTHOR]

• Three characteristically different plasma structures viz. EMSTID, plasma depletion and non-electrified MSTID were observed simultaneously. • The individual structures underwent evolution, distortion, and dissipation separately. • The lack of mutual interaction between these three structures, despite existing simultaneously, is highly unusual. An unusual event of three characteristically different plasma structures on a geomagnetically quiet night (Ap = 4) of 08 July 2018 has been investigated in this paper using an all-sky imager installed at Hanle, Ladakh (32.7°N, 78.9°E; Mlat. ∼ 24.1°N), India. These structures include a freshly generated electrified medium scale traveling ionospheric disturbances (EMSTID), ambiguous plasma depletions, and a northward propagating non-electrified MSTID. One of the most fascinating aspects of this event was the lack of mutual interaction between the three structures, even though they existed simultaneously and propagated in different directions. They individually underwent evolution, distortion, and dissipation separately. One of the structures was an EMSTID, which got generated within the imager's field-of-view (FOV) and evolved with time. As time progressed, different strip-like structures travelled southwestward, merged with each other to form the EMSTID. The second structure was plasma depletions which appeared in the southeastern part of the FOV. They eventually merged into a single band, which propagated nearly westward. The merged band evolved with time, extended further northward, and dissipated later. Along with these, a very rare non-electrified MSTID structure with east–west aligned fronts was observed which propagated northward. Its fronts underwent distortion, became curved and dissipated. In this study, we have explored the role of electrodynamics behind the observed unique features of the three plasma structures. [ABSTRACT FROM AUTHOR]

Ionospheric irregularities remain as a challenging concern among space scientists and engineers as it can pose severe threats to satellite-based services by introducing amplitude and phase scintillations in the transionospheric radio signals. The scintillations may cause degradation of the positioning, navigation, and timing (PNT) services or even complete system failure under extreme conditions. The present work focuses on understanding the ionospheric irregularities during the space weather event on May 12, 2021, witnessing the first strong geomagnetic storm in the 25th solar cycle. This particular event commenced around 13.00 UT, apparently altering the regular development of equatorial plasma bubbles around the local post-sunset terminator. We selected three global positioning system (GPS) stations, one at the near-magnetic equator (CUSV) and two at far low-latitude locations with a longitudinal separation (THKK and HWKS) over the Southeast Asian longitudes to investigate the characteristics of ionospheric plasma irregularities on the storm day. The results showed that the amplitude of ROTI was highest at the low-latitude CUSV, followed by the THKK and HKWS stations. The increased ROTI at CUSV is due to its latitudinal location close to the geomagnetic equator in the equatorial ionization anomaly (EIA) region which often witnesses more fluctuations than the inter-mediate latitudes. The strong TEC fluctuation occurrences were comparatively minimal at HWKS station on the storm day (May 12, 2021), whereas both intermediate and relatively higher TEC fluctuation occurrences were found at THKK and CUSV stations, respectively. Moreover, the occurrence rate of moderate irregularities was the highest at CUSV, followed by THKK and HKWS, while that of weak irregularities was maximum at HKWS, followed by THKK and CUSV. This happens because the systematic longitudinal time delay observed at the onset of ionospheric scintillations corresponds to the rise of PBs velocity at the magnetic equator that strongly depended upon the F-region dynamo electric fields in the east–west direction. Furthermore, the three-dimensional (3-D) positioning errors were estimated at a 30-sec interval to understand the impact of storm-induced irregularity on the positioning solution. An excellent agreement is realized between the ROTI pattern and positioning errors at all stations, irrespective of latitudinal extent from the magnetic equator. In order to model the amplitude of the scintillation index against the SNR measurements, the linear, quadratic, and cubic regression curve fittings are utilized that indicate the cubic polynomial manifesting the best fitted SNR measurements with the weak as well as moderate scintillation index. The continuous wavelet transformation (CWT) method was implemented to mitigate the ionospheric scintillation effects on positioning accuracy. The CWT estimation reveals the hidden information in positioning error due to the scintillation index, which makes it easy to understand the ionospheric scintillation effects on positioning. The attempt in this work is aligned with the efforts towards reliable PNT operations over equatorial and low latitudes. [ABSTRACT FROM AUTHOR]

Medium-scale traveling ionospheric disturbances (MSTIDs) are one of the ionospheric plasma density structures and are observable through 630-nm airglow images. Previous studies using airglow images at Tromso (69.6°N, 19.2°E; magnetic latitude: 66.7°N), Norway, reported high-latitude MSTIDs (here we call them as polar-type MSTIDs) whose propagation direction changes associated with auroral brightening and magnetic field disturbances. However, there has been little statistical analysis on the connection of MSTIDs occurring at high and middle latitudes. In this study, we statistically analyzed the MSTIDs observed by an airglow imager at Nyrola (62.3°N, 25.5°E; magnetic latitude: 59.4°N), Finland, which is located ~7° south of Tromso, corresponding to subauroral latitudes. The period analyzed was from 23 January 2017, to 30 September 2021. We found 11 cases of MSTIDs during this period. Eight cases were found to be the polar-type MSTIDs whose motion changes associated with auroral brightening and magnetic field disturbances. We found that 9 cases of MSTID show the low-latitude boundary at 61° ± 2°N for geographic latitude and 58° ± 2°N for magnetic latitude, indicating disconnection between high- and mid-latitude MSTIDs. We also derived occurrence probability, velocity, wavelength, period, wave front direction, and propagation direction of these MSTIDs. The occurrence probability of MSTIDs at Nyrola is 1.9%, which is much lower than those at high (Tromsoe, more than 50%) and middle (Japan, ~30%) latitudes. We discuss these MSTID characteristics at subauroral latitudes based on possible difference of generation mechanisms of nighttime MSTIDs at high and middle latitudes. [ABSTRACT FROM AUTHOR]

Ionospheric scintillation causes errors in radio signals. One potential source in the polar region is polar cap patches. Using a polar cap patch database from Ren et al. (2018), https://doi.org/10.1029/2018ja025621 and data provided by a scintillation receiver at Resolute Bay, we evaluated the polar cap patch impact on ionospheric scintillation. In a statistical analysis, we found that 92% of the maximum patch scintillation was under 0.3 for both phase (in the unit of radian) and amplitude scintillations. Of the remaining 8%, less than 1% could be classified as severe phase scintillation (>0.5 radians), while none could be classified as severe amplitude scintillation. Magnetic Local Time (MLT) dependence of the patch phase scintillation shows higher scintillation values near noon MLTs. Patches are classified into cold, hot-Te and hot-Te-Ti types based on their plasma temperatures. The dependence of scintillation on the patch density prominence showed a positive correlation between phase scintillation and cold patches near noon MLT and hot-Te patches everywhere except midnight MLT. In the event analysis, two events were studied. The first event with large phase scintillation was located in the polar cap with weak polar rain precipitation and large, uniform, antisunward convection flows. The second event with large amplitude scintillation was located in a region with active soft particle precipitation and velocity shear, classical ionospheric signatures of plasma sheet boundary layer. The statistical and event analysis improve understanding of the location and characteristics of patch-related scintillations. [ABSTRACT FROM AUTHOR]

Heavy cold ions at Mars are gravitationally bound to the planet unless some process provides energy to them. Observations show that cold (<20 eV) and dense (∼>1 cm−3) O+/O2+ ions with bulk velocities equal to energies ∼1 keV can reach deep into the nightside Martian magnetosheath. These ions are co‐located with a change of the sign of the sunward component of the magnetic field. This magnetic field topology implies the persistence of a localized planetary ions escape channel associated with draped magnetic field lines that are convecting tailward. The observed ion populations propagate approximately in the same direction as surrounding magnetosheath flow and are likely to be almost unheated ionospheric ions from low altitudes. The paper discusses planetary ion energization via Hall electric field originated from ions and electron separation associated with magnetic field curvature. Plain Language Summary: In‐situ observations above the nightside of Mars show the presence of localized dense planetary ion fluxes at altitudes exceeding 2,000 km and escaping from the planet at high energies, comparable to that of the solar wind. These fluxes are accompanied by the reversal of sunward component of magnetic field. Unlike most atmospheric escape channels, the reported phenomenon is characterized by an increase in heavy to light ions density ratio with the distance from the planet at the observed altitudes up to nearly 5,000 km, as well as an increase in overall plasma number density inside this escape channel relative to the ambient sheath environment. This behavior is consistent with acceleration process initiated by a bent magnetic flux tube. Key Points: Ions of different species gain similar energies in the Martian magnetosheath by Hall electric fields associated with magnetic curvatureA high concentration of ionospheric ions correlates with a near void of shocked solar wind protons and a magnetic field reversalNumber density at the reversal increases with distance from Mars in comparison to the surrounding sheath at least till two Martian radii [ABSTRACT FROM AUTHOR]

Ionospheric plasma introduces nonlinear perturbations in regular EM wave propagation which in turn affects the signal transmission in a highly nonlinear manner. Often the signals are distorted by a varied degree of nonlinearity. The wireless communication mechanism is affected by small perturbations which take gigantic rogue wave structures with the possibility of damaging sophisticated equipments. To study the evolution of rogue wave-type solitons starting from initial small-amplitude perturbations, we have considered a three-component electron–ion plasma system with degeneracy pressure as well as quantum diffraction effects. A solitary wave structure is formed due to the interplay of nonlinear and dispersive forces. Such a formation under an external force gets modified and the stability criteria are altered. The interesting fact thus obtained here shows that relativistic and thermal degeneracy favour stability whereas quantum diffraction leads to instability. In this paper, we have studied how solitary wave structures behave under an external force. Next, we study how the nonlinear effects cause an amplitude modulation and the envelope soliton is formed. Such an envelope soliton is studied by the nonlinear Schrödinger equation that we derive in the later part of the work. We have carried out simulation studies and compared our results with the analytical findings of other workers. [ABSTRACT FROM AUTHOR]

• Results of ionosphere observations during solar eclipse on 25.10.2022 are presented. • F2-layer vertical sounding was used for this. • Solar eclipse led to changes in state and dynamics of the ionosphere. • Features: eclipse coincided with daytime dip in electron density diurnal variation. • Effects of preceding magnetic storm were partially superimposed on eclipse effects. The results of observations of the critical frequency (f o F2), ionospheric F2 peak electron density (N m F2) and peak height (h m F2) of the ionosphere over Kharkiv (Ukraine, 49.6° N, 36.3° E) during a partial solar eclipse (SE) on 25 October 2022 are presented. The data analysis showed a clear effect in the variations of f o F2 (and, accordingly, N m F2): during the SE, f o F2 decreased, and 5 min after the time of maximum eclipse, began to increase to its usual level. From the beginning of the SE, h m F2 decreased from 285 to 255 km, and then it began to grow with a maximum near the time of maximum obscuration. To study longitudinal effects and clarify contributions of different factors to the observed temporal variations of the ionospheric parameters, the results of observations of the ionosphere over Kharkiv were compared with the data obtained by the ionosonde in Pruhonice (Czech Republic, 50.0° N, 14.6° E). The N m F2 electron density decreased due to SE by the factor of 1.46 in Kharkiv, in contrast to 1.33 times in Pruhonice. Comparison of data in universal time (UT) showed a coincidence in the nature and time of fluctuations in both f o F2 and h m F2 observed in Kharkiv and Pruhonice on 25 October. Variations in h m F2 caused by SE in Kharkiv and Pruhonice were identical. The SE was accompanied by a plasma flow from the plasmasphere to the ionosphere. The flux density change was about –2 × 1013 m–2s−1 and about 0 for Kharkiv and Pruhonice, respectively. The obtained value of the vertical velocity (tens of meters per second) for Kharkiv is the typical velocity for the mid-latitude F2 layer of the ionosphere. It was confirmed that in addition to typical SE effects, results of observations of the ionosphere over Kharkiv on October 25, 2022 had individual features. [ABSTRACT FROM AUTHOR]

THE TERRESTRIAL IONOSPHERE IS MAINLY A PLASMA REGION which is very sensitive to different disturbances. A wide range of plasma instabilities can develop in this region, which are often nonlinear processes and leading to the development of plasma turbulence. Turbulence plays a crucial role in the dynamics of the space plasma processes. The turbulence appears when some physical parameter exceeds a certain level. It can have place during strong thunderstorms. The ionosphere is sometimes treated as plasma physics laboratory with unique possibility to study fundamental plasma processes. The use of ionospheric satellite gives the chance to perform insitu measurements of plasma parameters during dynamic processes. For our analysis we used a set of selected data of the electric and magnetic fields variations in ELF (Extra Low Frequency 10-1250 Hz) and VLF (Very Low Frequency 100-20000 Hz) ranges originated from the French microsatellite DEMETER which was operating on the circular orbit with inclination of about 80° at altitude of 660km from July 2004 until December 2010. The Fourier, wavelet and bispectral analyses of these signals are given in this paper. Three wave processes have been identified during few very strong strokes. In some cases the nonlinear interactions of whistlers with the VLF signals of ground based transmitters have been registered. The character of spectra suggests the pres- ence of Richardson's cascade. Our conclusion is that in few cases these results are related to whistler turbulence. [ABSTRACT FROM AUTHOR]

This study focuses on modeling the characteristics of nighttime topside Ionospheric Plasma Irregularities (PI) on a global scale. We utilize Random Forest (RF) and a one‐dimensional Convolutional Neural Network (1D‐CNN) model, incorporating data from the Swarm A, B, and C satellites, space weather data from the OMNIWeb data center, as well as zonal and meridional wind model data. Our objective is to simulate monthly global PI characteristics using a multilayer 1D‐CNN model trained on 12 space weather and ionospheric parameters. In addition, we investigate the most influential input parameters for predicting global nighttime PI characteristics. Our findings indicate that non‐equinox months exhibit the highest equatorial PI magnitude over the American‐African longitudinal sector, contrary to the expected higher Rayleigh‐Taylor instability growth rate during equinox months. Winter months display the most intense and widespread vertically and horizontally distributed equatorial PI patterns. We also observe double peaks across geomagnetic latitudes and longitudinally varying wavelike irregularity structures, particularly in May, August, and predominantly in September. Furthermore, north‐south hemispherical asymmetry in PI observed across different seasons. Through the RF parameter importance analysis method, we determine that temporal, geographical, and magnetic disturbance‐related factors play a crucial role in predicting global PI variabilities. These findings emphasize the significance of these variables in controlling the strongest PI characteristics observed in the Atlantic sector, which has garnered considerable attention in PI research. The employed 1D‐CNN model demonstrates exceptional predictive capabilities, exhibiting a strong correlation of 0.98 for global PI characteristics across all months and satellites. Plain Language Summary: This study aimed to understand the characteristics of nighttime Ionospheric Plasma Irregularities (PI) on a global scale. To achieve this, we used advanced machine learning techniques called RF and a one‐dimensional Convolutional Neural Network (1D‐CNN). We collected data from the Swarm A, B, and C satellites, as well as space weather data and wind model data. The goal is to create a model that could simulate monthly global PI characteristics using 12 different space weather and ionospheric parameters. We found that during non‐equinox months, the equatorial PI magnitude is highest over the American‐African longitudinal sector. It is expected that the equinox months would have a higher growth rate of Rayleigh‐Taylor instability (RTI). We also observed that winter months had the most intense and widespread equatorial PI patterns, both vertically and horizontally distributed. Across different seasons, we noticed a north‐south hemispherical asymmetry in PI. We also identified specific months where double peaks observed across geomagnetic latitudes and irregularity structures that varied along longitudes, particularly in May, August, and mainly in September. Using the RF parameter importance analysis method, we determined that factors related to time, location, and magnetic disturbances played a crucial role in predicting global PI variabilities. These findings highlight the importance of these variables in controlling the strongest PI characteristics observed in the Atlantic sector, which is an area of significant interest in PI research. The 1D‐CNN model used in this study demonstrated exceptional predictive capabilities, showing a strong correlation of 0.98 for global PI characteristics across all months and satellites. This suggests that the model is highly reliable in simulating and predicting PI behavior on a global scale. Key Points: Winter months exhibit the most intense and widespread vertically and horizontally dispersed PI patterns simultaneously on all the three Swarm satellitesThe 1D‐CNN model demonstrates remarkable predictive capabilities, with a strong correlation of 0.98 for all global PI characteristicsTemporal, geographical, and factors related to magnetic disturbance were found to play a crucial role on PI occurrence based on Random Forest importance score [ABSTRACT FROM AUTHOR]

Solar 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. Plain Language Summary: Magnetospheric energy flows into the polar ionosphere. One example of this is the aurora that can be seen at high latitudes. During geomagnetic storms, the energy increases and the auroral oval expands toward the equator. Solar cycles 24 and 25 were quiet until a moderate geomagnetic storm occurred in late March 2023. On March 23–24, a Fabry‐Perot interferometer in Tromsø, Norway, recorded the highest thermospheric wind speed of over 500 m/s since 2009. An immense amount of electromagnetic energy entered the ionosphere‐thermosphere system at night. During the storm main phase, the FPI observed winds near the polar cap rather than in the auroral oval. The FPI‐measured thermospheric wind was strongly equatorward, likely accelerated by the strong anti‐sunward ionospheric plasma flow in the polar cap. The ionospheric density decreased on March 24, which was linked to thermospheric wind disturbances that lasted for several days. The storm's large energy input altered the thermospheric dynamics and ionospheric plasma density. Key Points: Fabry‐Perot interferometer in Tromsø, Norway, recorded the largest thermospheric wind since 2009 at the main phase of the Mar.2023 stormTromsø was located near the polar cap during the storm main phase, showing strong, continuous anti‐sunward windsSpatiotemporal changes in the pressure gradient resulting from the ionospheric current led to a sudden acceleration in the wind [ABSTRACT FROM AUTHOR]

Electron density (Ne) and electron temperature (Te) observations collected by Langmuir Probes on board the European Space Agency (ESA) Swarm B satellite are used to characterize their correlation in the topside ionosphere at an altitude of about 500 km. Spearman correlation coefficient values (RSpearman) are calculated on joint probability distributions between Ne and Te for selected conditions. The large data set of Swarm B observations at 2‐Hz rate, covering the years 2014–2022, allowed investigating the correlation properties of the topside ionospheric plasma on a global scale, for different diurnal and seasonal conditions, with both a coverage and a detail never reached before. Results are given as maps of RSpearman as a function of the Quasi‐Dipole (QD) magnetic latitude and magnetic local time (MLT) coordinates. The characterization of the correlation at high latitudes, along with the description of the diurnal trend at all latitudes, are the new findings of this study. The main correlation features point out a negative correlation at the morning overshoot, during daytime at mid latitudes, and during nighttime at the ionospheric trough and subauroral latitudes. Conversely, a positive correlation dominates the nighttime hours at mid and low latitudes and, to a minor extent, the low latitudes from 09 MLT onwards. A seasonal dependence of the correlation is noticeable only at very high latitudes where the general pattern of the negative correlation does not hold around ±75° QD latitude in the summer season. Results from Swarm B have been statistically compared and discussed with observations from the Arecibo, Jicamarca, and Millstone Hill incoherent scatter radars. Key Points: The correlation between the electron density and temperature in the topside ionosphere has been investigated through 9 years of Swarm B in‐situ observationsThe latitudinal, diurnal, and seasonal variations of the correlation have been studied on a global scale at an unprecedented spatial and temporal resolutionFirst ever study of the correlation at high latitudes, which highlighted a general pattern of negative correlation except for the summer season at the polar cusp [ABSTRACT FROM AUTHOR]

This study investigates the diurnal variation of topside ionospheric plasma density using the Ionospheric Connection Explorer (ICON) observations from May to July in 2020 and 2021. The total ion density exhibits daytime double‐maxima (DDM) patterns, also known as "bite‐out" at magnetic latitudes from 10°S to 20°N and longitudes of 180°–276°E, but a single peak in other longitudes. The total ion density between 180° and 276°E reaches its first peak around 12 LT (Local Time) in both hemispheres and the second peak at 14–15 LT in the Northern Hemisphere, gradually shifting to around 16–17 LT in the Southern Hemisphere. The formation of the first peak is mainly influenced by vertical plasma drift, while the second peak is associated with both neutral wind and vertical plasma drift. Furthermore, this study provides direct observational evidence for the influence of neutral winds on the longitude and latitude differences of the topside DDM. Stronger southward magnetic meridional winds and vertical plasma drifts are observed at approximately 11–15 LT in the longitude sector with DDM compared to other longitudes, leading to a valley of ion density in the Southern Hemisphere around 15 LT. In the Northern Hemisphere, ion density continues to accumulate to form a second peak at 15 LT. Key Points: Diurnal double maxima (DDM) occur in the daytime topside ionosphere around 180°–276°E in June SolsticeThis study presents probably evidence that neutral trans‐equatorial winds cause the formation of the topside ionospheric DDMSimulations analyzed the respective contributions of neutral winds and E × B drift to the topside ionospheric DDM [ABSTRACT FROM AUTHOR]

We study the magnetosonic waves (MWs) propagating in magnetized plasmas comprising light warm ions, cold heavy ions and hot electrons at the Earth's ionosphere. The dispersion relation is given and the effects of different physical parameters on the frequency of fast and slow MSWs are shown. We derive a KdV equation for the MSWs in multi-ion plasma and study the two-soliton and three-soliton overtaking collision of KdV MSWs by Hirota's bilinear method. We show the trajectories and amplitude of solitons in this process, and the phase shift after collision. It is found that when solitons merge, it will form a new soliton whose amplitude first decreases then increases. The effects of physical parameters on the phase shift of multi-soliton collision are presented. It is worth noting that the solitons' interaction can result in the redistribution of momentum and energy in the plasmas. [ABSTRACT FROM AUTHOR]

We investigate the role of auroral particle precipitation in small‐scale (below hundreds of meters) plasma structuring in the auroral ionosphere over the Arctic. In this scope, we analyze together data recorded by an Ionospheric Scintillation Monitor Receiver (ISMR) of Global Navigation Satellite System (GNSS) signals and by an All‐Sky Imager located in Longyearbyen, Svalbard (Norway). We leverage on the raw GNSS samples provided at 50 Hz by the ISMR to evaluate amplitude and phase scintillation indices at 1 s time resolution and the Ionosphere‐Free Linear Combination at 20 ms time resolution. The simultaneous use of the 1 s GNSS‐based scintillation indices allows identifying the scale size of the irregularities involved in plasma structuring in the range of small (up to few hundreds of meters) and medium‐scale size ranges (up to few kilometers) for GNSS frequencies and observational geometry. Additionally, they allow identifying the diffractive and refractive nature of fluctuations on the recorded GNSS signals. Six strong auroral events and their effects on plasma structuring are studied. Plasma structuring down to scales of hundreds of meters is seen when strong gradients in auroral emissions at 557.7 nm cross the line of sight between the GNSS satellite and receiver. Local magnetic field measurements confirm small‐scale structuring processes coinciding with intensification of ionospheric currents. Since 557.7 nm emissions primarily originate from the ionospheric E‐region, plasma instabilities from particle precipitation at E‐region altitudes are considered to be responsible for the signatures of small‐scale plasma structuring highlighted in the GNSS scintillation data. Plain Language Summary: We investigate the role of auroral particle precipitation in plasma structuring in the auroral ionosphere over the Arctic. For this we use Ionospheric Scintillation Monitor Receiver of Global Navigation Satellite System (GNSS) signals to detect plasma structuring and an All‐Sky‐ Camera to monitor the Aurora. Six strong auroral events are studied. Plasma structuring down to scales of hundreds of meters are seen when strong gradients in green auroral emissions cross the line of sight between the GNSS satellite and receiver. Intensification of ionospheric currents are observed to coincide with small‐scale structuring processes. Green auroral emissions originate from the ionospheric E‐region, which is considered the source of plasma instabilities causing the signatures of small‐scale plasma structuring as observed in the GNSS scintillation data. Key Points: Enhanced values of the GNSS‐based 1–s amplitude scintillation index are observed at auroral intensity gradientsThe IFLC is often elevated at the same time as the S4 index, confirming the diffractive nature of observed scintillation eventsSignificant increases in the auroral particle precipitation result in joint signatures of increased ionospheric currents and plasma structuring below the Fresnel's scale [ABSTRACT FROM AUTHOR]

This paper introduces the Peak Density Thickness (PDT) formalism, a novel approach to representing the F2 layer's vertical electron density profile in the ionosphere. It diverges from the conventional "pointed‐peak" model by suggesting a "broad‐peak" or "flat‐nose" profile where plasma density remains constant within an altitude interval χ. This theory is backed by independent observations, including a comprehensive data set from the Millstone Hill Incoherent Scatter Radar at the MIT Haystack observatory, spanning from 1993 to 2023, which illustrates the presence and diurnal variation of PDT. A single‐day intensive cross‐verification using Digisonde Portable Sounder DPS4D soundings of the sub‐peak ionosphere has shown remarkable agreement in the measurements of the lower boundary of the χ interval and the peak density. This study suggests incorporating the flat‐nose section χ into the F‐region profile formalism. Such a shift could improve the accuracy of topside specifications derived from ground‐based ionosonde measurements, enhancing our understanding of ionospheric plasma dynamics. Key Points: Peak Density Thickness (PDT) formalism that allows the plasma density at the F2 layer profile peak to remain constant with height for tens of kmCombined Incoherent Scatter Radar (ISR) and Digisonde measurements at mid‐latitudeUsing Millstone Hill ISR measurements from 1993 to 2023 to study the ionosphere Peak Plasma Density Thickness (PDT) [ABSTRACT FROM AUTHOR]

On 26 December 2022 the solar wind density dropped by over an order of magnitude and remained low for about a day. We have utilized in‐situ plasma measurements made by the Mars Atmosphere and Volatile EvolutioN mission to determine how this change affected the Mars‐solar wind interaction. During this time period, on inbound orbit segments, MAVEN sampled the terminator ionosphere, which switched from a magnetized to unmagnetized state immediately following the minimum in solar wind density. The magnetic field amplitude was typically 5–10 nT within the upper ionosphere prior to the event and consistently <1 nT after. During the event the magnetic pressure dominated immediately above the ionosphere while within the ionosphere the ionospheric plasma pressure dominated. The high altitude terminator ionosphere remained in this unmagnetized state throughout the event, suggesting that it was the new equilibrium state of the system. The terminator upper ionosphere returned to its original magnetized state once the solar wind density had recovered. The outbound orbit segments sampled the dayside subsolar region which remained magnetized throughout the event: the magnetization state of the ionosphere varied locally, dependent upon the solar zenith angle and corresponding incident solar wind dynamic pressure. Such conditions are different to the commonly reported unmagnetized ionospheric state at Venus during solar maximum conditions, where the interplanetary magnetic field is repelled from the entire dayside ionosphere. Drastic changes in the upstream solar wind are able to change the Mars‐solar wind interaction state on timescales less than one MAVEN orbit (∼3.5 hr). Plain Language Summary: Our Sun emits a continuous stream of charged particles radially outward into our solar system, known as the solar wind. Much like flowing water in a river is deflected around rocks and other objects in the river, the solar wind is also deflected around most obstacles in our solar system, including the planets. The physical forces that control this deflection differ depending upon the characteristics of the planet and the solar wind as it encounters the obstacle. We have studied a rare event at the planet Mars when the solar wind density dropped to very low values over the course of a day. Using orbiting spacecraft observations we have shown that the physical processes that control how the solar wind flows around the planet change directly in response to this event. These processes reverted back to their prior states once the solar wind density recovered a few days later, demonstrating that the planet‐wide system responds to large changes in the solar wind density on timescales of a few hours or less. Key Points: The Mars terminator ionosphere transitioned to an unmagnetized state in response to the 'disappearing solar wind event' in December 2022The Mars‐solar wind interaction system responds to changes in the solar wind density on timescales <3.5 hrThe event shares similarities with when the Venus ionosphere is unmagnetized, but the localized nature is an important difference [ABSTRACT FROM AUTHOR]

From August to October 2018, a series of strong earthquake (EQ) events occurred in southeast Asia and northern Oceania (22°S to 0°N, 115°E to 170°E) within 50 days. In this paper, we analyze the features of ionospheric plasma perturbations, recorded by the Plasma Analyzer Package (PAP) and Langmuir probe (LAP) onboard the China Seismo-Electromagnetic Satellite (CSES-01), before four EQs with magnitudes of Ms 6.9 to Ms 7.4. The ion parameters such as the oxygen ion density (No+), the ion drift velocity in the vertical direction (Vz) under the conditions of geomagnetic storms, and strong EQs are compared. The results show that within 1 to 15 days before the strong EQs, the No+ and the electron density (Ne) increased while the electron temperature (Te) decreased synchronously. Meanwhile, the Vz significantly increased along the ground-to-space direction. The relative variation of No+ and Vz before the strong EQs is more prominent, and the Vz is not easily influenced by the geomagnetic storm but is susceptible to the seismic activities. Our results suggest that the anomaly of ionospheric plasma perturbations occurring in this area is possibly related to the pre-EQ signatures. [ABSTRACT FROM AUTHOR]

The Swarm satellite mission has been used for numerous studies of the ionosphere. Here we use a global product, based on electron density measurements from Swarm that characterises ionospheric variability. The IPIR (Ionospheric Plasma IRregularities product) provides characteristics of plasma irregularities in terms of their amplitudes, gradients and spatial scales and assigns them to geomagnetic regions. Ionospheric irregularities and fluctuations are often the cause of errors in position, navigation, and timing (PNT) based on the Global Navigation Satellite Systems (GNSS), in which signals pass through the ionosphere. The IPIR dataset also provides an indication, in the form of a numerical value index (IPIR index), of the severity of irregularities affecting the integrity of trans -ionospheric radio signals and hence, the accuracy of GNSS positioning. We analysed datasets from Swarm A and ground-based scintillation receivers. Time intervals (when Swarm A passes over the field of view of the ground-based GPS receiver) are compared to ground-based scintillation data, collecting an azimuthal selection of the GNSS data relevant to the Swarm satellite overpass. We provide validations of the IPIR product against the ground-based measurements from 23 ground-based receivers, focusing on GPS TEC and scintillation data in low-latitude, auroral and polar regions, and in different longitudinal sectors. We have determined the median, mean, maximum and standard deviation of the parameter values for both datasets and each conjunction point. We found a weak correlation of the intensity of both phase and amplitude scintillation with the IPIR index. [ABSTRACT FROM AUTHOR]

Based on the double probe method, we investigated the ionospheric preseismic electric effects for the strong Chile earthquake of magnitude M = 8.8 that occurred on February 27, 2010, at 06:3414 universal time (UT). To correlate the electrical disturbance to natural geophysical activities in the ionosphere associated with the earthquake, we used a new approach to analyze these disturbances a few days before the event, based on DEMETER spacecraft collected data in the ultra low frequency (ULF) band. The double probes method and the calculated preseismic ionospheric electric field resulting from the potential difference between two electrical probes of ICE (Instrument Champ Electrique) onboard the DEMETER satellite are investigated. Once the effect of the satellite motion is canceled, it is found that the disturbance is caused only by the telluric activity. Moreover, the investigation of the collected data illustrates a clear correlation between preseismic electrical disturbances and ionospheric plasma parameters recorded near the future epicenter. The strongest ionospheric electrical disturbances are located near the future epicenter and close to the geomagnetic conjugate points. [ABSTRACT FROM AUTHOR]

The results of a study of the small-scale internal structure of a polarization jet/SAID (Subauroral Ion Drift) based on satellite data using the wavelet transform of ionospheric plasma parameters are presented. The minimum sizes of small-scale temperature and electron density irregularities are determined. Most likely, any polarization jet/SAID is stratified, as follows from the sample used in this work. It is shown that the wavelet transform is a convenient tool for studying the internal small-scale structure of the polarization jet/SAID, and the irregularities are better seen in the electron temperature power spectrograms than in the electron density spectrograms. [ABSTRACT FROM AUTHOR]

The plasma in situ detector is a multi-sensor package designed to in situ measure the bulk parameters of the local ionospheric plasma. The plasma in situ detector is comprised of three sensors: Langmuir probe (LP), retarding potential analyzer (RPA) and ion drift meter (IDM). LP measures electron density and temperature. RPA measures ion density, temperature and ion horizontal velocity. IDM measures the transverse horizontal component of the ram velocity. The plasma in situ detector has been installed outside the wentian module cabin, and the boom has been successfully deployed which extends the spherical sensor of LP beyond the sheath of the cabin. RPA and IDM were installed at the front of the experiment package, with the horizontal axis direction along the forward flight direction of the space station. This paper discusses the general performance characteristics of the in situ detector, the functional performance of each sensor, and initial results of some classical ionospheric features being observed. [ABSTRACT FROM AUTHOR]

A simple technique designed to automatically identify and characterize wave structures from total electron content (TEC) data obtained from Global Navigation Satellite System (GNSS) satellites and multiple receiver stations is presented. We used 11 years of GNSS data (one complete solar cycle) to detect and characterize the traveling ionospheric disturbances (TIDs) (or wave structures) over high latitude (65°N ± 5°, 147°W ± 5°—Poker Flat, AK) and middle latitude (40°N ± 5°, 117°W ± 5°—Mt. Moses, NV) regions. The algorithm is capable of automatically detecting basic wave parameters such as wave period, horizontal phase velocity, amplitude, wave propagation direction, and wavelength. The designed algorithm can be applicable in the following areas: (a) global GNSS‐TEC (b) climatology of waves (c) input into innovative machine learning algorithms, such as ABCGAN (e.g., Valentic, 2023, https://doi.org/10.5281/zenodo.7747377 designed to characterize background ionospheric plasma and predict wave‐like high/low‐frequency perturbations) (d) anomaly detection for real‐time scenarios. Furthermore, we apply the developed wave detect and characterization technique to investigate three rockets launched on 26 and 28 January 2015. We examine the distribution of different scales of TIDs, and how they varied from high (Poker Flat) to middle (Mt. Moses) latitudes. Lastly, we show that the wave structures at the high‐latitude regions of Poker Flat are substantially affected by auroral processes and those from the middle‐latitude regions of Mt. Moses are impacted by AGWs coupling from below. Key Points: The computation approach and characterization of wave parameters using Global Navigation Satellite System‐total electron content (GNSS‐TEC) dataMorphological statistical distribution of large‐scale traveling ionospheric disturbances and medium‐scale traveling ionospheric disturbances from 11 years of GNSS‐TEC data over Poker Flat and Mount MosesResults also show ionospheric perturbation induced by rocketing lunching [ABSTRACT FROM AUTHOR]

We investigate in detail the occurrence and evolution of ionospheric equatorial plasma bubbles (EPBs) during a moderate storm on 17 September 2021, using Global‐scale Observations of the Limb and Disk (GOLD) observations and Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X) simulations. GOLD observations show that there were no EPBs on 16 September before the storm but EPBs occurred after the storm commencement on 17 September. The EPBs extended to ∼30° magnetic latitude. A diagnostic analysis of WACCM‐X simulations reveals that the rapid enhancement of prompt penetration electric fields (PPEFs) after the sudden storm commencement is the main reason that triggered the occurrence of the EPBs. Further quantitative analysis shows that vertical plasma drifts, which are enhanced by the PPEF, played a dominant role in strengthening the Rayleigh‐Taylor instability, leading to the occurrence of the EPBs and the large latitudinal extension of the EPBs to ∼30° magnetic latitude during the night of 17 September. Plain Language Summary: Equatorial plasma bubbles (EPBs) are frequently observed in the equatorial region after sunset and have been the focus of ionospheric research. They are an important space weather phenomenon that often significantly impact trans‐ionospheric radio wave signals. During geomagnetic storms, the occurrence and evolution of EPBs are more complicated, and their physical mechanisms are worthy of further investigation. In this study, we used Global‐scale Observations of the Limb and Disk (GOLD) observations and Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X) simulations to study the occurrence and evolution of EPBs during a moderate storm on 17 September 2021. GOLD observations show that EPBs occurred after the storm commencement on 17 September, whereas no EPBs were observed on 16 September. Additionally, these EPBs extend to ∼30° magnetic latitude. According to the WACCM‐X simulation analysis, the rapid enhancement of the prompt penetration electric fields (PPEFs) after the sudden storm commencement resulted in a significant Rayleigh‐Taylor instability (RTI) on 17 September, triggering the occurrence of EPBs. Furthermore, quantitative analysis revealed that PPEF induces enhanced vertical plasma drifts, which are the main reason for the strengthening RTI and the large latitudinal extension of the EPBs on 17 September. Key Points: Equatorial plasma bubbles (EPBs) extended poleward to ∼30° magnetic latitude during a moderate storm on 17 September 2021Diagnostic analysis reveals that occurrence of EPBs was due to rapidly enhanced eastward prompt penetration electric field (PPEF) after the sudden storm commencementPPEF‐driven upward drifts are the main factor causing large Rayleigh‐Taylor instability, and thus the formation and large latitudinal extension of the EPBs [ABSTRACT FROM AUTHOR]

The numerical forecast methods used to predict ionospheric convective plasma instabilities associated with Equatorial Spread‐F (ESF) have limited accuracy and are often computationally expensive. We test whether it is possible to bypass first‐principle numeric simulations and forecast irregularities using machine learning models. The data are obtained from the incoherent scatter radar at the Jicamarca Radio Observatory located in Lima, Peru. Our models map vertical plasma drifts, time, and solar activity to the occurrence and location of clusters of echoes telltale of ionospheric irregularities. Our results show that these models are capable of identifying the predictive power of the tested inputs, obtaining accuracies around 75%. Plain Language Summary: Equatorial Spread‐F (ESF) is a phenomenon that happens in the ionosphere and it can create disturbances that affect communication and navigation systems, such as GPS or satellite phones. Scientists have been trying to predict when and where ESF will happen using numerical forecast methods, but these methods are not very accurate and can be expensive. In this study, we tested a new way to predict ESF using machine learning models. We used data from a radar in Lima, Peru, and looked at information such as how the plasma in the ionosphere moves vertically and how active the sun was. The models were able to predict where and when ESF would occur with about 75% accuracy, which is a promising development. Key Points: Clusters of radar echo bins associated with Equatorial Spread‐F can be identified using the DBSCAN algorithm from coherent scatter dataA random forest model showed that the day of year and vertical plasma drifts previous to sunset are good predictors of high SNR clustersA convolutional neural network was able to predict ionospheric irregularities with an accuracy of more than 70% despite scarce data [ABSTRACT FROM AUTHOR]

Mars is typically regarded as a non‐magnetic planet. Currents in the Martian ionosphere generate a Venus‐like induced magnetosphere which deflects the solar wind flows and piles up the interplanetary magnetic fields. However, crustal magnetic fields in the southern hemisphere influence local plasma properties. Using observations from the MAVEN mission, we characterize the distinguishing plasma characteristics of a mini‐magnetosphere that forms on the Martian dayside. We establish three criteria to differentiate this mini‐magnetosphere from the induced magnetosphere. Notably, the mini‐magnetosphere exhibits higher plasma beta (values near 1), with a balance between planetary ions, crustal magnetic fields, and the solar wind at the magnetopause. Observations show that the crustal magnetosphere reaches an altitude of 1,300 km, larger than one‐third of the Martian radius, indicating a dichotomy between the induced northern and the crustal southern magnetospheres. These findings offer novel insights into the distinctive properties of hybrid magnetospheres in the near‐Mars space. Plain Language Summary: Mars lacks a global intrinsic magnetic field. Currents in the Martian ionosphere generate a Venus‐like induced magnetosphere which deflects the solar wind flow and piles up the interplanetary magnetic field. However, local crustal magnetic fields in Mars' southern hemisphere significantly influence the nearby plasma. With the support of the MAVEN mission, this work analyses observations from passes of the spacecraft through the mini‐magnetosphere during suitable orbits and investigates plasma pressures in both single orbit data and by a 4‐year statistical analysis. We present an observation of a mini‐magnetosphere filled by trapped heavy ions above the crustal magnetic fields on the Martian dayside. Furthermore, we establish three criteria to distinguish this mini‐magnetosphere from the induced magnetosphere. Observations show that the mini‐magnetosphere reaches an altitude of 1,300 km, larger than one‐third of the Martian radius. The observed mini‐magnetosphere and the dichotomy between the crustal southern and induced northern Martian magnetosphere forms a distinct environment that may help us to test the interactions between stellar winds and magnetic or nonmagnetic bodies. Key Points: The crustal magnetic fields trap ionospheric plasma to form a mini‐magnetosphere in the near‐Mars plasma environmentThe mini‐magnetosphere reaches 1,300 km on the Martian daysideThe mini‐magnetosphere balances the solar wind through contributions from plasma thermal pressure and the crustal magnetic pressure [ABSTRACT FROM AUTHOR]

Energetic 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. Plain Language Summary: Bursty precipitation of energetic electrons, via pitch‐angle scattering by whistler‐mode waves from the magnetosphere to the ionosphere, is an important factor in the global magnetosphere‐ionosphere coupling. It induces local modifications of ionospheric density and chemical composition. A recurrent problem in the investigation of this process is the presence of large uncertainties in the field‐line mapping between ionospheric density structures and high altitude satellites measuring electron fluxes in the magnetosphere. In the present study, such uncertainties are significantly reduced by making use of precipitating electron fluxes recorded by ELFIN CubeSats at low altitudes (450 km) just above the ionosphere and comparing them with maps of the corresponding ionospheric density structures. We identify three different types of electron precipitation on the nightside, corresponding to low, moderate, and high energy precipitating electrons. We show that each type of the precipitation is characterized by particular plasma density gradients in the ionosphere, suggesting a key role of wave ducting by plasma density gradients in fostering the precipitation of 300–500 keV electrons by whistler‐mode waves, and the potential importance of midnight plasma injections in generating EMIC waves that can further precipitate 0.5–2 MeV electrons far away from the plasmasphere. Key Points: Total electron content (TEC) maps are examined during energetic electron precipitation at the conjugate low altitudeNight‐side whistler‐mode wave driven precipitation is often associated with local horizontal TEC gradientsNight‐side EMIC wave driven precipitation is often poleward of the TEC minima associated with the plasmapause projection [ABSTRACT FROM AUTHOR]