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Air plasma induced by ultrafast laser pulses is an extraordinary source of electromagnetic waves, emitting microwave, terahertz (THz) radiation, and cavityless lasing in the near‐infrared and visible ranges. The temporal dynamics of the electron density have been revealed by optical pump‐probe techniques, while the evolution of the electron temperature remains elusive due to a lack of suitable methods. Here, it is demonstrated that the intense THz‐field‐enhanced fluorescence emission from the excited molecules of nitrogen is a novel tool that allows to explore the complex dynamics of the plasma density and electron temperature simultaneously. Two relaxation times of electrons in air plasma are observed and interpreted as a competition between the excitation of a triplet state by laser or THz‐field‐heated electrons and the dissociative recombination of nitrogen molecular ions. Based on the theoretical simulations, the tens of picoseconds relaxation process is attributed to the ultrafast temperature decrease, while the longer relaxation in the range of hundreds of picoseconds is ascribed to the decay of electron density. The temporal relaxation of both the electron density and temperature revealed by applying an intense THz field provides further insights into the laser‐air plasma interaction and will benefit the engineering of this exceptional source. [ABSTRACT FROM AUTHOR]

The high‐density transient plasma, streaming from a pulsed plasma accelerator (PPA), was diagnosed with a Triple Langmuir probe (TLP) for spatial mapping of the stream in terms of plasma density and temperature. A contour plot for density and temperature shows a distinct form of a highly dense island of plasma with varied plasma temperatures. The formation of such highly dense islands can be correlated with the formation of distinct plasma structures, as observed in astrophysical plasmas and fusion plasma. The results of TLP were supported by the intensity variation derived from signals of a photodetector system. The plasma stream imaged with high‐speed video camera also showed the density fluctuation inside the plasma stream. The estimated maximum density and temperature were ∼7.2 × 1020 m−3 and ∼28 eV, respectively. [ABSTRACT FROM AUTHOR]

The impact of spatial and temporal evolution of nonlinear mixing of two Gaussian laser pulses propagating in plasma on generation of terahertz (THz) radiation have been investigated taking into account the ponderomotive nonlinearity. By calculating the modified electron density of plasma caused by the finite ponderomotive force of the pump lasers and using wave equation and paraxial ray approximation, two coupled governing equations for temporal and spatial pulse‐width parameters have been derived. The electric field of the THz wave as a result of nonlinear current density induced by the beat ponderomotive force of the pulses was extracted. Combined effects of initial laser and plasma parameters on the behavior of self‐compression and self‐focusing as well as THz radiation generation were investigated. The numerical results indicated a considerable spatiotemporal compression takes place within a specific range of laser intensity, exhibiting a saturation intensity point where the compression process reaches its maximum extent. It is observed that the generated THz radiation also strongly depends on the spatiotemporal dynamics of the pump pulses. The maximum THz amplitude corresponds to the strongest pump pulse compression extent. [ABSTRACT FROM AUTHOR]

This study investigated the latitudinal variations of post‐sunset enhancements in the ionospheric electron density during the geomagnetic quiet period in May 2021 with a combination of high‐precision ionospheric parameters obtained from four ionosondes, Beidou geostationary satellite (BD‐GEO) receiver network and Sanya incoherent scatter radar (SYISR). We identified four categories of post‐sunset enhancement phenomena (Types 1–4), each with unique spatial and temporal evolutions, yet uniformly accompanied by a decrease in hmF2. Measurements of plasma drift vector velocities from SYISR and hmF2 gradients across various latitudes provided pivotal insights, confirming that the ionospheric post‐sunset enhancements can result from downward plasma motion due to westward electric field, downward field‐aligned drift, or a combination of both. For Type 1, dominated by field‐aligned drift, plasma density enhancements not only intensify at low latitudes but may also extend to mid‐latitudes, exhibiting a distinct temporal delay with increasing latitude. In contrast, Type 4, primarily driven by the westward electric field, is characterized by modest increases in plasma density confined to localized low‐latitude regions, with no observable latitudinal time delay in the peak of enhancements. Types 2 and 3, which are subject to the combined influence of the westward electric field and field‐aligned drift, exhibit plasma density increases at certain low‐latitude areas, with Type 2 presenting a delayed pattern and Type 3 showing none with rising latitude. Meanwhile, neutral winds can partially account for the observed post‐sunset enhancement from low to middle latitudes. These findings offer new insights into the factors influencing ionospheric behavior after sunset. Key Points: Four types of distinctive latitudinal variations of post‐sunset enhancements were identified with multiple data sets during the quiet periodAccompanying the increase in the electron density at sunset, the decrease in hmF2 is favorable for the formation of post‐sunset enhancementDownward field‐aligned drift and westward electric field govern the spatial scale of post‐sunset enhancements at low and middle latitudes [ABSTRACT FROM AUTHOR]

The energy of ring current protons is believed to influence the pitch angle scattering due to electromagnetic ion cyclotron (EMIC) waves and is typically analyzed using quasi‐linear theory. However, nonlinear behavior becomes significant as the wave amplitude intensifies. In this study, we aim to explore how the nonlinear behavior depends on the initial proton energy under various background plasma density conditions. The frequency of EMIC waves is 0.96ΩHe (where ΩHe is the gyrofrequency of He+ at the equator). It is found that the higher energy protons with nonlinear phase trapping experience more resonances, causing these trapped protons to move away from the loss cone more quickly compared to lower energy protons. However, the proportion of phase‐trapped protons significantly decreases as the initial proton energy increases. This declining trend is more pronounced for a background plasma condition in the plasmapause than within the plasmasphere. The number of phase‐trapped protons goes to zero as initial proton energy increases to above approximately 60 keV. Additionally, nonlinear phase bunching is more pronounced for lower energy protons (e.g., below 60 keV) compared to higher energy protons. As a result, both nonlinear phase trapping and phase bunching contribute to larger standard deviations in the net changes of equatorial pitch angle (Δαeq), suggesting a larger pitch agnel diffusion coefficient compared to the prediction of quasi‐linear theory. Key Points: The proportion of phase‐trapped protons is sensitive to changes in initial proton energy, and decreases as the initial proton energy increasesHigher energy protons with phase trapping experience more resonances, which will move quickly away from the loss coneTest‐particle pitch angle diffusion is more pronounced in lower energy protons (e.g., below 60 keV) compared to higher energy protons [ABSTRACT FROM AUTHOR]

We analyze data from multiple flybys by the Solar Orbiter, BepiColombo, and Parker Solar Probe (PSP) missions to study the interaction between Venus' plasma environment and the solar wind forming the induced magnetosphere. Through examination of magnetic field and plasma density signatures we characterize the spatial extent and dynamics of Venus' magnetotail, focusing mainly on boundary crossings. Notably, we observe significant differences in boundary crossing location and appearance between flybys, highlighting the dynamic nature of Venus' magnetotail. In particular, during Solar Orbiter's third flyby, extreme solar wind conditions led to significant variations in the magnetosheath plasma density and magnetic field properties, but the increased dynamic pressure did not compress the magnetotail. Instead, it is possible that the increased EUV flux at this time rather caused it to expand in size. Key findings also include the identification of several far downstream bow shock (BS), or bow wave, crossings to at least 60 RV ${\mathrm{R}}_{V}$ (1 RV ${\mathrm{R}}_{V}$ = 6,052 km is the radius of Venus), and the induced magnetospheric boundary to at least ∼ ${\sim} $ 20 RV ${\mathrm{R}}_{V}$. These crossings provide insight into the extent of the induced magnetosphere. Pre‐existing models from Venus Express were only constrained to within ∼ ${\sim} $ 5 RV ${\mathrm{R}}_{V}$ of the planet, and we provide modifications to better fit the far‐downstream crossings. The new model BS is now significantly closer to the central tail than previously suggested, by about 10 RV ${\mathrm{R}}_{V}$ at 60 RV ${\mathrm{R}}_{V}$ downstream. Plain Language Summary: We studied data from the missions Solar Orbiter, BepiColombo, and Parker Solar Probe to understand Venus' magnetotail. We focused on how Venus' magnetic environment interacts with the solar wind to create its magnetosphere. By looking at magnetic fields and plasma density, we figured out the size and movement of Venus' magnetotail, and found where its boundaries are. We noticed that these boundaries change a lot between missions, showing that Venus' magnetotail is very dynamic. Our main discoveries include finding boundary crossings like the bow shock 60 times Venus' radius downstream, and the magnetospheric boundary about 20 times Venus' radius downstream. This helps us understand how far the magnetosphere extends and improve our models of its shape. We also saw that the solar wind affects the magnetotail: during one mission, even though the solar wind was strong, it didn't squish the magnetotail; instead, it made it bigger because of increased solar radiation. Key Points: Venus' magnetotail is observed during nine spacecraft flybys revealing a dynamic structure reaching at least 60 RV downstreamAn improved bow shock model is presented for the deep tail regionThe pre‐existing model of the induced magnetospheric boundary is valid downstream to at least 20 RV [ABSTRACT FROM AUTHOR]

A proton (H+) channel, Otopetrin 1 (OTOP1) is an acid sensor in the sour taste receptor cells. Although OTOP1 is known to be activated by extracellular acid, no posttranslational modification of OTOP1 has been reported. As one of the posttranslational modifications, glycosylation is known to modulate many ion channels. In this study, we investigated whether OTOP1 is glycosylated and how the glycosylation affects OTOP1 function. Pharmacological and enzymatic examinations (using an N‐glycosylation inhibitor, tunicamycin and peptide: N‐glycanase F [PNGase F]) revealed that overexpressed mouse OTOP1 was N‐glycosylated. As the N‐glycans were Endoglycosidase H (Endo H)‐sensitive, they were most likely high‐mannose type. A site‐directed mutagenesis approach revealed that both two asparagine residues (N238 and N251) in the third extracellular loop between the fifth transmembrane region and the sixth transmembrane region (L5‐6) were the glycosylation sites. Prevention of the glycosylations by the mutations of the asparagine residues or by tunicamycin treatment diminished the whole‐cell OTOP1 current densities. The results of cell surface biotinylation assay showed that the prevention of the glycosylations reduced the surface expression of OTOP1 at the plasma membrane. These results indicate that mouse OTOP1 is N‐glycosylated at N238 and N251, and that the glycosylations are necessary for OTOP1 to show the maximum degree of H+ current densities at the plasma membrane through promoting its targeting to the plasma membrane. These findings on glycosylations of OTOP1 will be a part of a comprehensive understanding on the regulations of OTOP1 function. [ABSTRACT FROM AUTHOR]

The coupling of transport code SOLPS with the turbulence code BOUT++ was reported in Reference [D. R. Zhang et al., Phys. Plasmas 26, 012508 (2019)], while the grids of SOLPS and BOUT++ are not completely consistent with each other, especially in the divertor region. In the present work, a method of replacing the grids of BOUT++ with the grids of SOLPS is proposed to make the simulation region fully consistent with each other for the SOLPS/BOUT++ coupling. A SOLPS grid file is generated with an MHD equilibrium and used in BOUT++ code to simulate the profiles of plasma density, ion temperature, and electron temperature with the six‐field two‐fluid model. The profiles of the main plasma parameters simulated with the SOLPS grids are similar with the profiles simulated with the BOUT++ grids at the midplane, while the profiles are deformed compared with the profiles simulated with the BOUT++ grids at the outer divertor target because of the differences of the distributions of SOLPS grids and BOUT++ grids in the divertor region. The radial particle transport coefficient and heat transport coefficients are also calculated by using the BOUT++ code with the two grids, and the comparisons of the radial particle transport coefficient and heat transport coefficients simulated with the two grids at the midplane and outer divertor target plate are discussed. [ABSTRACT FROM AUTHOR]

The processes in far scrape‐off layer (SOL) and the plasma interaction with the first‐wall (FW) elements may notably affect the tokamak discharge, since they define fuel and impurity recycling, material erosion and redeposition, wall surface heating, etc. For a long time, the far SOL description in most plasma edge transport codes was insufficient or absent at all, and so particle and heat fluxes onto the FW (except divertor plates) were out of consideration. Recently some codes, for example, SOLEDGE and SOLPS‐ITER are upgraded allowing for the extension of the computational grid up to real walls and for corresponding account of the vacuum vessel shape and all in‐vessel elements. The new release of SOLPS‐ITER (the version 3.2.0) required a development of a new code data structure and new approach to numerical approximation of fluid equations compatible with unstructured non‐orthogonal computational grid. Intensive testing of the new code in different conditions is still required. In the present contribution, such a testing is performed for the EAST disconnected double null (DDN) L‐mode discharge. For the first time, the SOLPS‐ITER 3.2.0 modeling results with drifts and currents turned on are presented, and a comparison to former SOLPS‐ITER version (3.0.8) is performed. The far SOL transport and its effects on the discharge performance are studied by comparing the computational results obtained on several meshes which differ by their width in equatorial midplane. A single null (SN) one (with mesh width limited by distance to the secondary separatrix) was examined versus two DDN meshes (one with actual and one with artificially extended targets to make mesh wider) and a true unstructured (the widest) mesh. The notable difference in results obtained on different meshes appears in those places where plasma density does not vanishes at the computational domain boundaries. For the cases on true unstructured (the widest) mesh, the particle and heat fluxes onto central column, limiters, far SOL part of targets, dome umbrella and other EAST far SOL in‐vessel structures are calculated for the first time by SOLPS‐ITER, allowing assessment of the plasma interaction with those surfaces. [ABSTRACT FROM AUTHOR]

Background: Hair loss profoundly affects women's physical appearance and psychological health. Platelet‐rich plasma (PRP) therapy has gained attention as a potential treatment for female hair loss. This systematic review and meta‐analysis aim to evaluate the efficacy and safety of PRP in treating different forms of female hair loss. Methods: A comprehensive search was conducted across PubMed, EMBASE, Scopus, Cochrane Library, Web of Science, and ClinicalTrials.gov from January 2000 to May 2024. The focus was on randomized controlled trials investigating PRP treatment for various types of hair loss in women. The research protocol is registered with International Prospective Register of Systematic Reviews (CRD42024556190). The quality of the studies was evaluated using the Cochrane risk of bias tool (RoB 2). Results: A total of 21 studies comprising 628 participants were included in the analysis. PRP treatment was found to significantly enhance hair density and thickness. Additionally, there was a significant reduction in the number of hairs pulled in the PRP group. Adverse effects were generally mild and transient, with no notable difference in pain or discomfort between the PRP and control groups (risk ratio: 1.01; 95% CI: 0.87–1.18). Conclusion: PRP therapy effectively enhances hair density and thickness in women with hair loss, with a favorable safety profile. However, the effects of PRP on hair density and thickness vary with dosage, injection duration, and ethnicity, indicating the need for tailored treatment protocols. [ABSTRACT FROM AUTHOR]

We use the full NASA Van Allen Probes mission (2012–2019) to extract the electron plasma density from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) and Electric Field and Waves (EFW) instruments and discuss the evolution of the plasmasphere. We generate new statistics including mean and standard deviations of the plasma density with respect to L‐shell, magnetic local time (MLT), and various geomagnetic indices. These statistics are generated to be applied in radiation belt physics and space weather codes (with fits provided). The mean plasmasphere is circular around Earth with respect to MLT for Kp < 1. The mean 100 cm−3 level line is above L = 5 and mean 10 cm−3 level expands above the Van Allen Probes apogee for Kp < 1. The outer electron belt lies within the plasmasphere for 60% of all times. As activity increases (Kp > 2), a gradual MLT asymmetry forms with higher mean density in the afternoon sector due to plumes expanding outward. Conversely, the mean density decreases on the dawn and night sectors. The mean density is between ∼500 and ∼50 cm−3 between L ∼ 4 and L ∼ 6 during quiet and moderately active times (Kp < 3), representing ∼80% of all times. Statistics in regions of high density below L = 2 are underdefined for intense activity. The highest standard deviation of density represents a factor 2.5 to 3 times the mean above L = 5 and for active times. We find the percent difference between the EFW and EMFISIS densities is bounded by ±20% for quiet and moderate activity (Kp < 5) and goes up to ±100% for extreme activity. Plain Language Summary: The Earth's plasmasphere, discovered in the 1950s, is a region of cold plasma made of ions and electrons of a few electronvolts in energy, originating from upwelling ionized gas from the ionosphere and forming a rotating torus around the Earth. The radial profile of the electron cold plasma density within the plasmasphere decays from 10,000 electrons per cubic centimeter at ∼1,000 km altitude to 10s electrons per cubic centimeter at its outer edge, sometimes exceeding ∼36,000 km in altitude at the equator. The state of the plasmasphere is highly dependent on geomagnetic conditions, with geomagnetic storms and substorms eroding parts of this plasma. Here, we analyze 7 years of NASA Van Allen Probes measurements of the electron plasma density and generate statistics with respect to L‐shell, magnetic local time, and geomagnetic indices. In this way, we show statistical variations of the plasmasphere, a strong magnetic local time dependence, and erosion with increasing geomagnetic activity. New mean electron densities and their standard deviation are generated and fitted with model functions that can be incorporated into space weather codes. This is important because the electron density is a key parameter influencing the strength of wave‐particle interactions that accelerate and scatter energetic particles in the inner magnetosphere. Key Points: Generation of new statistics of mean and standard deviation of the plasma density from Electric Field and Waves and Electric and Magnetic Field Instrument Suite and Integrated Science of RBSP for the whole missionEmpirical density models made of fits are provided versus L‐shell, magnetic local time (MLT), and geomagnetic indices to be used in radiation belt codesAn extensive analysis of the cold plasma statistics is provided with respect to L‐shell, MLT, and geomagnetic activity [ABSTRACT FROM AUTHOR]

Recent studies have shown that the measurements of Langmuir Probes (LPs) onboard ESA's Swarm mission overestimate ion densities on the nightside by up to 50%. The overestimation is due to the assumption of oxygen‐only plasma for ion density calculations, which is often violated at mid‐latitudes on the nightside. In this study, we present a calibration model that resolves the nighttime overestimation by Swarm LPs. Using observations by Swarm FacePlate (FP) as a reference, we develop a neural network (NN) model that adjusts LP data to the FP measurements. The model incorporates dependence on solar and geomagnetic conditions, parameterized by the P10.7 and Hp30 indices, location, day of the year and local time. Our model reveals a distinct double‐crest pattern in nighttime density overestimation by LPs, centered at ∼30° quasi‐dipole latitude in both hemispheres. This overestimation intensifies during low solar activity and shows strong seasonal dependence. During solstices, the crests are more pronounced in the local winter hemispheres, while during equinoxes the crests are weaker and exhibit hemispheric symmetry. This morphology aligns with the presence of light ions diffusing downward from the plasmasphere. Validating the LP data in conjunctions with Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) observations showed a much stronger agreement after applying the developed correction: for Swarm B, nighttime correlation with COSMIC increased from 0.74 to 0.93. The NN‐calibrated LP data set has numerous applications in ionospheric research, and the developed model can provide useful insights into the ion composition in the topside ionosphere. Plain Language Summary: Operating since late 2013, ESA's Swarm mission has provided an extensive data set of plasma densities in the topside ionosphere, frequently used in space weather research. Recent studies have shown that the Langmuir Probes (LPs) onboard the Swarm mission overestimate ion densities during nighttime by up to 50%. This overestimation is due to the presence of light ions not accounted for in the ion density calculations. In this study, we develop a new NN‐based calibration model for Swarm observations, which resolves the nighttime overestimation by the LPs for the first time. Our results reveal a distinct double‐crest pattern on the nightside, centered at ∼30° quasi‐dipole latitude in both hemispheres, which corresponds to decreased effective ion masses and thus causes the overestimation of ion densities. This pattern closely mimics the behavior of light ions diffusing downwards from the plasmasphere. The developed NN‐based calibration improves the quality of the LP observations and allows using them for improving the existing models of the topside ionosphere, among other applications. Furthermore, the developed model provides insights into the ion composition and light ion dynamics in the topside ionosphere. Key Points: We present a neural network‐based calibration model that resolves the nighttime overestimation of ion densities by Swarm Langmuir Probes (LPs)This overestimation, peaking at 30°QDLat in both hemispheres, mimics the morphology of light ions diffusing downward from the plasmasphereThe corrected LP ion densities are in excellent agreement with COSMIC radio occultation data [ABSTRACT FROM AUTHOR]

Electron fluxes in the keV energy range can cause significant spacecraft surface charging, which in turn can affect the functioning of spacecraft components. In this paper, the geostationary electron fluxes measured by the satellites GOES 13‐18 in the energy range 2–200 keV are analyzed in order to look for their dependence on solar wind conditions. For this purpose, a range of solar wind parameters, IMF parameters and geomagnetic indices are examined, to look for the parameters which most significantly affect the electron flux. The analysis includes fluxes in the lower energy range of 2–40 keV, measured by GOES 16‐18, which have not been analyzed before. The measured electron fluxes are averaged over all directions, and high‐pass filtered to isolate variations shorter than 1 month. The analysis concentrates of the dawn sector, where variations are largest. A number of solar wind parameters and magnetic indices are analyzed concurrently with the electron flux data, to look for the most significant correlations between them. Most parameters have the highest correlation with electron flux when shifted in time by a certain delay. In addition to the different solar wind parameters and magnetic indices, combinations of different parameters are also examined for their best correlation with the electron flux. The most significant driving parameters are found to be the auroral electrojet index, combined with either the solar wind plasma velocity or the plasma density. The relative contribution of each of these parameters depends on electron energy, and differs between periods of high and low flux. Plain Language Summary: In the geostationary satellite orbit, there is a constant flux of particles from the solar wind. Of these particles, electrons in the energy range between about 1 and 1,000 keV can cause surface charging of satellites, which in turn can affect the functioning of spacecraft components. The strength of the electron flux can vary strongly, mainly with variations in the solar wind, but is hard to predict. This paper uses measured data of this electron flux, and examines a large set of solar wind parameters and magnetic indices which are regularly available, and looks for the parameters which most significantly indicate the variations of the electron flux. It is found that the auroral electrojet index, together with the solar wind speed or the solar wind density, can be the best indicators. Key Points: The most effective drivers of electron flux of keV energies in the geostationary orbit are searched from a range of environment parametersThe electron flux variations are largest around dawn and most correlated with solar wind density and velocity and auroral electrojet indexThe relative contribution of each these parameters depends on electron energy, and differs between periods of high and low flux [ABSTRACT FROM AUTHOR]

Phase separations in strongly coupled fine particles in plasmas are discussed and two‐component mixtures are simulated by molecular dynamics with the background plasma being treated as continuum. The system size of laboratory experiments is assumed and separations into phases with a common electron density of the background plasma are analyzed. Since the charge on fine particles increases approximately in proportion to the size, we expect the larger component with stronger coupling condensates from the mixture. Results expressed in terms of strengths of Coulomb coupling and screening of the larger component seem to be mostly similar to the one‐component case, at least in cases where the ratio of fine particle sizes is 2, and the mixing ratio is in the range from 0.25 to 0.75. [ABSTRACT FROM AUTHOR]

This study presents a recent finding of magnetic shelf structures and packages of whistler‐mode waves in the data obtained from the Magnetospheric Multiscale (MMS) mission satellite in the equatorial magnetosphere. These observations are compared with the waves observed on density shelves by the NASA Van Allen Probes (aka RBSP) mission. By employing simulations of the electron‐MHD model, we explain that similar to the density shelf ducting, magnetic shelves effectively guide whistler‐mode waves along the ambient magnetic field with little attenuation. The parameters of the guided waves depend on the parameters of the shelves. We discuss the similarities and differences of the wave guided by the density and magnetic field shelf‐like structures. The simulations successfully reproduce the parameters of the observed waves. Key Points: Observations show that whistler‐mode waves can be guided by shelf‐like structures of the plasma density and the magnetic fieldWe numerically investigate shelf‐like structures' characteristics and the guided whistler‐mode wavesSimulations reproduce parameters of the waves observed on density and magnetic shelves by the RBSP and Magnetospheric Multiscale satellites [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]

Different from power line harmonic radiation (PLHR) events at high harmonics (∼kHz) in the ionosphere and inner magnetosphere, the wave dynamics of power line emission (PLE) (the fundamental frequency 50/60 Hz or PLHR at low harmonics) can be significantly affected by various ion species. In order to investigate the evolution of the wave properties of PLE from power lines to satellite altitudes in a dipole field, a numerical model is developed to perform full‐wave simulations, in which the lithosphere and atmosphere are characterized by electrical conductivity and the ionosphere (inner magnetosphere) is treated as collisional (collisionless) cold plasma consisting of electron, H+, He+, O+, and NO+. Our simulation results show that the spatial distribution and wave properties of PLE are determined by the magnetic latitudes of power lines and plasma densities. PLE from power lines at middle and high magnetic latitudes (|MLAT| > 40°) can propagate to high L shells as whistler waves; PLE from power lines at |MLAT| < 30° usually propagate at low L shells below local He+ cyclotron frequency as left‐handedly polarized or right‐handedly He+ band electromagnetic ion cyclotron (EMIC) waves. The amplitude of PLE is usually stronger with smaller electron density in the space plasma medium. With power lines at |MLAT| < 30°, the coupling efficiency between different right‐handedly polarized EMIC wave modes of PLE decreases significantly with electron density. Wave properties of PLE including Poynting vector direction, wave normal angle and wave polarization obtained from our simulation results are consistent with some of the recent observations using Van Allen Probes. Key Points: Model incorporating the effects of lithosphere, atmosphere and space plasma is developed to study the propagation of PLE in a dipole fieldPLE propagate to high L shells as whistlers at |MLAT| > 40° while propagate as left (or right)‐handedly polarized He+ band EMIC at |MLAT| < 30°The PLE amplitude and the coupling efficiency of EMIC wave modes at |MLAT| < 30° decrease with electron density in the space plasma medium [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 plasma density is one of the most fundamental quantities of any plasma yet measuring it in space is exceptionally difficult when the density is low. Measurements from particle detectors are contaminated by spacecraft photoelectrons and methods using plasma wave emissions are hampered by natural plasma instabilities which dominate the wave spectrum. Here we present a new method which calculates the density from magnetosonic waves near the lower hybrid resonance frequency. The method works most effectively when the ratio of the plasma to cyclotron frequency is fpe/fce < 3.5. The method provides a lower bound on the plasma density. Using the new method we show that wave acceleration of electrons to relativistic energies is increased by orders of magnitude. The method enables years of satellite data to be re‐analyzed for the Earth and the effectiveness of wave acceleration at the Earth, Jupiter and Saturn to be re‐assessed. Plain Language Summary: The electron plasma density is a fundamental quantity of any plasma, but it is very difficult to measure in space using satellites. Satellites charge to different potentials with repel or attract electrons making the true measurement very difficult. The plasma density can be determined from wave oscillations at the plasma frequency, but the waves are difficult to identify as the wave spectrum is often dominated by other much stronger waves. Here we analyze satellite data and show that magnetosonic waves near the lower hybrid resonance frequency can be used to calculate the plasma density. This method provides a lower bound on the density. We show that this lower density leads to much faster electron acceleration by wave‐particle interactions, accelerates electrons to much higher energies and increases the electron flux at one MeV by two orders of magnitude or more. The method enables the importance of electron acceleration at the Earth, Jupiter and Saturn to be re‐evaluated. Key Points: New method to calculate plasma density from magnetosonic waves near the lower hybrid resonance frequencyMethod enables low densities to be measured near the magnetic equatorLow density increases wave acceleration of electrons by orders of magnitude [ABSTRACT FROM AUTHOR]

Based on correlated magnetosphere‐ionosphere (M‐I) conjugate observations of seven events, we study the hot zone developed under short‐circuiting conditions leading (a) to the development of outward Subauroral Polarization Streams (SAPS) or Subauroral Ion Drifts (SAID) electric (E) field and (b) to the various subauroral arcs' absence or presence. Results show (a) the close relations of the hot zone earthward extent and peak ion temperature (Ti) to the magnitude of outward SAPS/SAID E field and (b) the hot zone's high Ti (∼11,000 eV) developed under enhanced plasma turbulence that was (c) generated by the amplified narrow hot ion and electron plasma density peaks, (d) sometimes in plasmaspheric plumes, and that was (e) sometimes further enhanced by the strong auroral kilometric radiation (AKR) waves (f) leading to the development of enhanced SAPS/SAID E field. From these (a–f) findings we conclude for the seven events investigated that (a) the hot zone's development under short‐circuiting conditions was regulated by the kinetic energy of mesoscale plasma flows and that (b) the hot zone created the favorable inner‐magnetosphere conditions during short circuiting (c) for stable auroral red (SAR) arc development by plasma turbulence, which is the common source of heat/suprathermal particles accelerated downward, and (d) in the plasmaspheric plume scenario for SAR arc and Strong Thermal Emission Velocity Enhancement (STEVE) arc development by the plumes' enhanced cold plasma populations leading to strong shear flows and thus shear‐flow instabilities well‐known associated with the SAPS/SAR arc and recently regarded as a potential driver mechanism of the STEVE arc. Key Points: The hot zone's development under short‐circuiting conditions was regulated by the kinetic energy of mesoscale plasma flowsThe hot zone created favorable inner‐magnetosphere conditions for the development of stable auroral red arc by plasma turbulenceStrong Thermal Emission Velocity Enhancement arc development was favored by the plasmaspheric plume related shear flows [ABSTRACT FROM AUTHOR]

This study focuses on the causes for the generation of equatorial plasma bubbles (EPBs) over the Indian subcontinent and their correlation with atmospheric‐ionospheric disturbances resulting from the eruption of the Tonga volcano on 15 January 2022. Concurrent ionosonde observations obtained from Tirunelveli (8.67°N, 77.81°E) and Prayagraj (25.41°N, 81.93°E) show the presence of spread‐F traces in ionograms. Notably, the EPBs are also accompanied by plasma blobs (PBs), with their pronounced occurrence during midnight at Prayagraj and Tirunelveli. Analysis of in situ electron density observations obtained from the Swarm B and C satellites reveals substantial plasma density depletions associated with EPBs. An intriguing observation is the intensification of Pre‐Reversal Enhancement (PRE) immediately preceding the onset of spread‐F at Tirunelveli due to enhanced eastward F region zonal winds by Tonga Volcano, as seen in the satellite observations. Furthermore, the isofrequency analysis from Tirunelveli shows the presence of gravity wave‐like oscillations in the equatorial F‐region over India. The investigation of Total Electron Content (TEC) obtained from a Pseudo Random Number (PRN)‐14 over Indian longitudes suggests the presence of two dominant modes of Traveling Ionospheric Disturbances (TIDs) with speeds ∼452 m/s and ∼406 m/s having periods in the range of ∼65–75 min. These observations reaffirm that volcano triggered atmospheric/ionospheric disturbances can propagate long distances for several hours and can provide necessary seeding conditions for the generation of EPBs. Key Points: Concurrent observation of EPBs at equatorial (Tirunelveli) and low mid‐latitude (Prayagraj) stationsTonga eruption‐induced gravity waves provide the seed perturbation for EPBsTEC perturbations provide evidence for two modes of TIDs with speeds of ∼452 m/s and ∼406 m/s over the Indian region [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]

Plasmaspheric density structures are considered to control the propagation trajectories of fast magnetosonic (MS) waves in the inner magnetosphere. However, whether the plasmaspheric plume can effectively alter the propagation of MS waves remains unknown. Based on the analytical model of plasma density, ray tracing simulations are performed to investigate the propagation of exactly perpendicular MS waves in the equatorial plane in the magnetosphere containing a plasmaspheric plume. We find that plasmatrough and plume MS waves propagating toward the plasmaspheric plume can be reflected into the plasmaspheric core by the plume, then potentially migrating globally and thus quasi‐trapped inside the plasmaspheric core. The simulations also indicate that lower‐frequency MS waves approaching the plasmaspheric plume are more easily reflected and quasi‐trapped inside the plasmaspheric core. Our findings illustrate a previously unexplored way that plasmatrough MS waves could access and be trapped inside the plasmaspheric core via azimuthal plasmaspheric density structures. Plain Language Summary: Fast magnetosonic (MS) waves are one of the most common and intense electromagnetic emissions observed both inside and outside the plasmasphere. Portions of MS waves observed inside the plasmasphere are supposed to come from the propagation of those waves outside the plasmasphere. It is well known that the radial plasmaspheric density structures can strongly alter the propagation trajectories of MS waves in the inner magnetosphere. However, a typical azimuthal plasmaspheric density structure, the plasmaspheric plume, can form in the magnetosphere during the geomagnetic disturbed times. How the plasmaspheric plume affects the propagation of MS waves remains unknown. Based on the ray tracing simulations, we show that MS waves generated outside the plasmapause and inside the plume can be reflected into the plasmaspheric core by the plasmaspheric plume and a few of the reflected waves can migrate globally inside the plasmaspheric core. Our findings provide a new potential way for MS waves to access and be trapped inside the plasmaspheric core. Key Points: Propagation of magnetosonic waves in the magnetosphere containing a plasmaspheric plume is examined using the ray tracing simulationsPlasmatrough and plume magnetosonic waves can be reflected into the plasmaspheric core by the plasmaspheric plumeThose reflected magnetosonic waves can be quasi‐trapped inside the plasmaspheric core or propagate radially down to low altitudes [ABSTRACT FROM AUTHOR]

Based on High Magnetic field Helicon eXperiment, considering the parabolic distribution and Gaussian distribution of radial plasma density, HELIC code was used to study the influence of temperature and pressure gradient on power deposition, electric field, and current density of Helicon Wave Plasma. Three different gradients (positive, negative, and zero gradient) were selected. The results show that positive temperature gradient is beneficial to increase the relative absorption power at the center of plasma. Compared with negative and zero pressure gradients, positive pressure gradient increases the relative absorption power and weakens the current density at the center of plasma, and increases the electric field intensity at the edge of plasma. Larger edge heating will cause the relative absorption power at edge to rise rapidly, which is not conducive to the coupling at the center of plasma. In practical experiments, it is particularly important to reduce the heating effect at edge by cooling the antenna itself. Three different gradients of temperature and pressure have little effect on electric field intensity and current density in plasma, and the variation trend is basically similar, which proves the stability of the antenna mode: m = 1. [ABSTRACT FROM AUTHOR]

The self‐organization of a magnetized multi‐ion plasma, composed of inertialess electrons and inertial H+, He+, and O+ ions, leads to the formation of quadruple Beltrami (QB) field structures. The QB self‐organized state is a linear combination of four single Beltrami fields, and it is a non‐force‐free state that shows strong magnetofluid coupling. Moreover, the QB state is characterized by four relaxed state structures of different length scales. The investigation reveals that the generalized helicities of plasma species and the densities of ion species have a significant impact on the characteristics of the self‐organized vortices in the QB state. The study also highlights the potential consequences of QB field structures on earth's inner magnetosphere, including diamagnetic and paramagnetic trends as well as heating effects resulting from disparate length scales. [ABSTRACT FROM AUTHOR]

The discharge properties of post‐cathode plasma generated by grid electrode discharge were investigated. Post‐cathode plasma is the plasma, generated in an open discharge, at the other side of the cathode that is different from the electrode gap. Based on the unique electron transport, discharge chamber parameters were adjusted to compare their impact on the electron density of the post‐cathode plasma. The peak of the electron flow in the grid cathode hole and the peak of the post‐cathode plasma thickness appear in the same diameter of the grid electrode holes, which shows the crucial influence of the electron transport within the grid cathode on the post‐cathode plasma. The study also investigated the combined effects of cathode thickness and gas pressure on post‐cathode plasma thickness. The findings suggest that the primary factor influencing post‐cathode plasma thickness is the electron transport within the grid cathode. [ABSTRACT FROM AUTHOR]

A nonthermal, pulsed spark discharge is applied to three polymer powders in Ar and Ar–H2 ${{\rm{H}}}_{2}$ gas mixtures. Hydrogen is introduced to assess plasma‐driven decomposition. Gaseous decomposition products, including methane, acetylene, and ethylene, are observed with Fourier‐transform infrared (FTIR). Surface modifications are observed on the residual polymer via attenuated total internal reflection‐FTIR. Time‐averaged rotational, vibrational, and excitation temperatures are characterized in the discharge. The plasma density is found to be around 3×1022 m−3 $3\times 1{0}^{22}\unicode{x0200A}{{\rm{m}}}^{-3}$, with rotational and vibrational temperatures ranging from 1500 to 2200 K and an excitation temperature of 1–2 eV. While spark properties did not change with either gas composition or polymer composition, it was determined that the addition of hydrogen promoted higher concentrations of gaseous phase products (promoting hydrogenolysis). [ABSTRACT FROM AUTHOR]

Using an in–house developed Quasi Two–Dimensional (QTD) physics–based ionospheric model, the impact of E × B drift velocity on the vertical distribution of the electron density over the equatorial latitude has been investigated. The vertical drift measurements from (a) drift analysis software of Digisonde (b) derived from Digisonde ionograms (c) calculated from the Scherliess–Fejer (SF) model, and (d) obtained from the magnetometer ΔH measurements have been used in this study. Four quiet days in a low solar activity year, representing four seasons of the year 2010, have been chosen for the study. The model–derived electron density profiles using the vertical drifts from all four methods matched well with the Digisonde observation below ∼150 km at all the Local Times (LTs) for all 4 days. However, since the Digisonde–derived drifts were very low, centered mostly around zero, it led to the overestimation/underestimation of the F–region peak plasma density (nmF2)/height (hmF2). The model simulated electron density profiles using the SF model, and ΔH derived vertical drifts showed good agreement with the observation up to an altitude of ∼350 km. The study showed that vertical drift is a factor that controls the nmF2 trough around noon over the equatorial latitude. It is seen that plasma diffusion occurs only beyond an altitude of 350 km, while the range of altitudes between 320 and 350 km acts as the "diffusion threshold height." This finding has significant implications for understanding plasma dynamics in the equatorial ionosphere. Plain Language Summary: The present study employed a quasi–two–dimensional theoretical ionospheric model to investigate the impact of vertical drift on the electron density distribution over the equatorial ionosphere. Utilizing vertical drift values derived from Digisonde, Scherliess–Fejer (SF) model calculations, and magnetometer readings, the model was simulated for four distinct days of 2010 representing the four seasons of the year. The electron density profiles generated using all four techniques exhibited a close match to the observed values for all 4 days. However, when very low Digisonde–derived drifts were employed, an overestimation of the F–region density and an underestimation of peak F–region plasma density heights were observed. The study demonstrated that the model–simulated electron density profiles, generated using the SF model and magnetometer–derived vertical drifts, exhibited excellent agreement with the observed profiles at altitudes up to approximately 350 km. Similar variations of the calculated and observed nmF2 values led to the conclusion that vertical drift is a crucial factor in controlling the equatorial noon–time nmF2 trough. Furthermore, the study revealed that plasma diffusion occurred only beyond an altitude of 350 km as the altitude range of 320–350 km acts like a "diffusion threshold height." Key Points: This paper studies the impact of vertical drift on the vertical distribution of the electron densityThe plasma vertical drift plays an important role in the noon time nmF2 troughThe altitude range 320–350 km can be called as the plasma "diffusion threshold height" [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]

During geomagnetic storms, the increase in energy input into the ionosphere in the form of Poynting flux and electron precipitation leads to an enhanced ionospheric outflow that results in an increase of the O+ content in the magnetosphere. Using different missions and instrumentation, two main ionospheric sources have been identified for the oxygen ions reaching the inner magnetosphere during geomagnetic storms: the dayside cusp, and the night side auroral region. Evidence of both pathways have been presented in the literature. However, the relative contribution of each of these pathways to the enhancement of O+ observed in near‐Earth plasma sheet, as well as the dynamics involved during the development of geomagnetic storms remains an open question. Here, we present the first statistical study to date to address this question, in the form of a superposed epoch analysis of O+ and H+ moments obtained by the Magnetospheric Multiscale (MMS) mission throughout the main phase of 90 geomagnetic storms with a minimum SYM‐H of at least −50 nT. The results show a clear increase in the oxygen density in the near‐Earth plasma sheet, with values further from Earth remaining low. Temperature values for both species show an increase with the progress of the storms. These results combined suggest that, during the main phase of geomagnetic storms, most of the oxygen ions observed in the near‐Earth plasma sheet are traveling directly from the nightside auroral region. Key Points: Superposed epoch analysis shows dynamic evolution of O+ ions during geomagnetic stormsSignificant enhancement of the O+‐to‐H+ number density ratio observed at radial distances less than 12 REScalar temperature for both species show the arrival of heated ions far from Earth throughout the analyzed period [ABSTRACT FROM AUTHOR]

The coupling between the ionosphere and plasmasphere is not known well during the quiet and storm times. The topside ionosphere ion composition reflects the exchange between the ionosphere and plasmasphere. We used the DMSP satellite observations to show the changes of the 840 km altitude H+ and O+ ions at ~3-6 LT in the mid- and low-latitudes on 20-31 August 2018 where a storm occurred on 25 August. The H+ was the main ion at 3-4 LT, and its concentration presented two peaks around 40°N/S magnetic latitudes on 20-24 August. The H+ concentration strongly lessened for more than five days around 40°N/S magnetic latitudes in the recovery phase of the storm on 26-30 August. Further, the enhancement and reduction of the H+ concentration persisted mainly in the Pacific and Asian sectors. The O+ density increased in Northern Hemisphere at 6:36 LT, and the H+ concentration showed the maximum around the magnetic equator during the quiet times, while the H+ concentration still mainly reduced around 40°N/S and stronger at 40°S in the recovery phase. The plasmaspheric total electron content showed a peak around the magnetic equator on 20-24 August, and the peak was weakened or disappeared on 26-30 August. The plasmasphere might be the principal sources for the mid-latitude H+ enhancement along the geomagnetic field lines during the quite times and the storm-time suppressed plasmasphere plasma density would weaken the supply of the H+ at 840 km altitude. [ABSTRACT FROM AUTHOR]

In this study we used the Level-2 product of field-aligned currents (FACs) from the Swarm satellites, to check the distribution characteristics of small-scale FACs (SSFACs) of intense amplitude. Data applied covers 9 years from December 2013 to April 2023. Based on the statistical analysis on the amplitude, the SSFACs in this study is defined with amplitude larger than 20 µA/m², which is also by two orders larger than the well-known large-scale R1 and R2 FACs (about 0.2 µA/m²). Such an intense amplitude indicates that it should play an important role in the magnetosphere-ionosphere coupling. The location of the SSFACs observed is general between 60°~80° and - 80°~-60° magnetic latitude, which is coincidently inside the auroral oval. The occurrence of the SSFACs depends on both solar activity and geomagnetic activity, and the influence of geomagnetic activity is more important than that of solar activity. By further checking the simultaneous in situ plasma density measured by Swarm, we find that the SSFACs are always associated with clear plasma density fluctuations. This suggests that the SSFACs play an important role for causing the small-scale plasma density irregularities at auroral latitude. [ABSTRACT FROM AUTHOR]

We present results from the investigation of a transition between two whistler-mode waves with the same frequency and the parallel wavelength but different perpendicular wavenumbers in the inhomogeneous media consisting of the plasma density and the background magnetic field. We consider transverse inhomogeneities of these quantities. We demonstrate that there are critical values of the plasma density and the magnetic field (which depend on the wave frequency and the parallel wavelength) and the switching between two whistler-mode waves occurs in the vicinity of these values. We analyze this problem assuming that these critical values are reached inside the finite-size transition layer between two regions where all the background quantities are homogeneous. We found analytical criteria for the mode switching and we confirmed our results with time-dependent simulations of the electron-MHD equations describing whistler-mode waves in the magnetospheric plasma. We also investigate numerically the dependency of various parameters of the wave switching on the size of the transition region containing critical values of the plasma density and the magnetic field. [ABSTRACT FROM AUTHOR]

During geomagnetic storms relativistic outer radiation belt electron flux exhibits large variations on rapid time scales of minutes to days. Many competing acceleration and loss processes contribute to the dynamic variability of the radiation belts; however, distinguishing the relative contribution of each mechanism remains a major challenge as they often occur simultaneously and over a wide range of spatiotemporal scales. In this study, we develop a new comprehensive model for storm-time radiation belt dynamics by incorporating electron wave-particle interactions with parallel propagating whistler mode waves into our global test-particle model of the outer belt. Electron trajectories are evolved through the electromagnetic fields generated from the Multiscale Atmosphere-Geospace Environment (MAGE) global geospace model. Pitch angle scattering and energization of the test particles are derived from analytical expressions for quasi-linear diffusion coefficients that depend directly on the magnetic field and density from the magnetosphere simulation. Using a study of the 17 March 2013 geomagnetic storm, we demonstrate that resonance with lower band chorus waves can produce rapid relativistic flux enhancements during the main phase of the storm. While electron loss from the outer radiation belt is dominated by loss through the magnetopause, wave-particle interactions drive significant atmospheric precipitation. We also show that the storm-time magnetic field and cold plasma density evolution produces strong, local variations of the magnitude and energy of the wave-particle interactions and is critical to fully capturing the dynamic variability of the radiation belts caused by wave-particle interactions. [ABSTRACT FROM AUTHOR]

In this study, we focus on the presence of the ionospheric third plasma density peak associated with the equatorial ionization anomaly (EIA) based on observations from the ESA's Swarm constellation. By statistically analyzing the third peaks observed by the Swarm A and B at two different altitudes, we found that such structure appears mainly around ±20° magnetic latitude (Mlat), namely the poleward of the EIA crests. In the meanwhile, the third peak shows prominent season and local time dependences, that are mainly observed in the summer hemisphere during solstice seasons and with the highest occurrence in the afternoon hours. However, no clear solar flux and magnetic activity dependences are found. By further analyzing the simultaneous neutral wind measurements from the ionospheric connection explorer satellites, we found that the summer-to-winter hemispheric meridional wind is responsible for causing the third peak as well as its seasonal dependence (higher occurrence in the summer hemisphere). In addition, the third-peak structure shows prominent longitudinal dependence. In regions where the magnetic declination directs eastward, it has a larger occurrence in the southern hemisphere, while in regions where the magnetic declination reverses, it has a larger occurrence in the northern hemisphere. Such a longitudinal dependence suggests that the zonal wind, which has a magnetic field-aligned component at favorable magnetic declination regions, contributes also to the formation of the third-peak structure. [ABSTRACT FROM AUTHOR]

The relative motion of an artificial plasma stream in an ambient plasma background transverse to the geomagnetic field produces a polarization current and an ... drift in the direction of the injected photoionized neutral cloud. The polarization current couples the ion cloud momentum to the ambient plasma causing the stream to brake or "skid" before coming to rest. A multi-fluid five-moment resistive magnetohydrodynamic (MHD) model has been previously developed and is used in this study to simulate an artificial barium cloud released at 8 km/s in the lower ionosphere transverse to the magnetic field. The MHD model's governing equations are used to derive 2D analytical solutions to the equations of motion that capture oscillatory behavior relating the cloud ion cyclotron frequency, artificial and ambient plasma density, initial release velocity, and photoionization rate. The analytical solutions are compared to the MHD results for time t < 1 s and previous 1D momentum coupling models. It is shown that motion in the cloud release direction is consistent with previous models while motion in the polarization direction is consistent with numerical results. [ABSTRACT FROM AUTHOR]

Magnetosonic (MS) waves are electromagnetic emissions from a few to 100 Hz primarily confined near the magnetic equator both inside and outside the plasmasphere. Previous studies proved that MS waves can transport equatorially mirroring electrons from an equatorial pitch angle of 90° down to lower values by bounce resonance. However, the dependence of the bounce resonance effect on wave or background plasma parameters is still unclear. Here, we applied a test particle simulation to investigate electron transport coefficients, including diffusion and advection coefficients in energy and pitch angle, due to bounce resonance with MS waves. We investigate five wave field parameters, including wave frequency width, wave center frequency, latitudinal distribution width, wave normal angle root-mean-square of wave magnetic amplitude, and two background parameters, L-shell value and plasma density. We find different transport coefficient peaks resulting from different bounce resonance harmonics. Higher-order harmonic resonances exist, but the effect of fundamental resonance is much stronger. As the wave center frequency increases, higher-order harmonics start to dominate. With wave frequency width increasing, the energy range of effective bounce resonance broadens, but the effect itself weakens. The bounce resonance effect will increase when we decrease the wave normal angle, or increase the wave amplitude, latitudinal distribution width, L-shell value, and plasma density. The parametric study will advance our understanding of the favorable conditions of bounce resonance. [ABSTRACT FROM AUTHOR]

The narrowband kilometric radiation (nKOM) is a Jovian low-frequency radio component identified as a plasma emission produced in the region of the Io plasma torus. Measurements from the Waves instrument onboard the Juno spacecraft permitted to establish the distribution of nKOM occurrence and intensity as a function of frequency and latitude. We have developed a 3D geometrical model that can simulate at large scale the plasma emissions occurrence observed by a spacecraft based on an internal Jovian magnetic field model and a diffusive equilibrium model of the plasma density in Jupiter's inner magnetosphere. With this model, we propose a new method to discriminate the generation mechanism, wave mode, beaming and radio source location of plasma emissions. Here, this method is applied to the study of the nKOM observed from all latitudes by the Juno/Waves experiment to identify which conditions reasonably reproduce the observed occurrence distribution versus frequency and latitude. The results allow us to exclude the two main nKOM models published so far, and to show that the emission is produced at the local plasma frequency and then beamed anti-parallel to the local density gradient into free space. We also propose that depending on its latitude, Juno observes two distinct kinds of nKOM: the low frequency nKOM in ordinary mode at high latitudes, and the high frequency nKOM on extraordinary mode at low latitudes. Both radio source locations are found to be distributed near the centrifugal equator ranging from the outer edge to the inner edge of the Io plasma torus. [ABSTRACT FROM AUTHOR]

This study investigates the propagation characteristics of Saturn's Narrowband (NB) emissions using a 3D ray‐tracing code incorporating Saturn's magnetic field and electron density parameters. The potential source regions and propagation zones of the L‐O mode, Z mode and whistler mode NB emissions are distinguished. The L‐O mode NB emissions, generated along local electron plasma frequency surfaces through mode conversion, exhibit straight‐line propagation but undergo reflections between the ionosphere, the plasma torus, and the magnetosheath. The slot region, characterized by a lower electron density distributed around the plasma torus boundary, significantly influences emission propagation, potentially leading to trapping and depolarization. The 5 kHz Z mode NB emissions propagate and fill the trapping region delineated by lower cut‐off and upper hybrid resonance frequencies. In contrast, the 20 kHz Z mode NB emissions are primarily confined near source regions at the north and south edges of the plasma torus, with the possibility of escaping under variable plasma conditions. Plain Language Summary: Scientists have discovered low‐frequency radio waves near Saturn, roughly at 5 and 20 kHz, using data from the Voyager and Cassini spacecrafts. These waves are referred to as narrowband (NB) emissions. The NB emissions are thought to originate from Saturn, but exhibit a puzzling propagation pattern when they propagate far away from their source region. Recent studies propose that the 5 kHz waves might be bouncing off a dense plasma area in Saturn's magnetosheath, introducing intriguing yet not fully understood propagation characteristics. This study employs a numerical approach, that is, the ray‐tracing technique, to trace the likely paths of these waves. Drawing on earlier theoretical studies, we pinpoint the potential origins of these waves. Our results indicate that most of these waves, particularly the so‐called L‐O mode emissions, tend to travel toward Saturn's high latitudes. This directional preference is due to interference from a dense plasma torus in Saturn's equatorial region. The boundary of this torus can trap these waves. Meanwhile, the so‐called Z mode waves are confined to a specific region near Saturn. Our study unveils intricate features such as multiple reflections and refractions of these waves near Saturn, shedding light on various data observations. Key Points: A 3D ray‐tracing analysis is conducted for Saturn Narrowband (NB) emissionsThe L‐O mode NB emissions propagate toward high latitudes and the Z mode NB emissions are trapped near SaturnSmall electron density structures on the plasma torus can lead to trapping and depolarization of NB emissions [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]

Jupiter's plasma sheet has been understood to be primarily composed of Io‐genic sulfur and oxygen, along with protons at lower mass density. These ions move radially away from Jupiter, filling its magnetosphere. The material in the plasma sheet interacts with Europa, which is also a source of magnetospheric pickup ions, primarily hydrogen and oxygen. Juno's thermal plasma instrument JADE, the Jovian Auroral Distributions Experiment, has provided comprehensive in situ observations of the composition of Jupiter's plasma sheet ions with its Time‐of‐Flight mass‐spectrometry capabilities. Here, we present observations of the magnetospheric composition in the Europa‐Ganymede region of Jupiter's magnetosphere. We find material from Europa is intermittently present at comparable densities to Io‐genic plasma. The intermittency of Europa‐genic signatures suggests Europa's neutral oxygen toroidal cloud is more localized to Europa's vicinity than its hydrogen cloud. These observations reveal a more complex and compositionally diverse magnetosphere than previously thought. Plain Language Summary: Jupiter's charged particle environment is overwhelmingly driven by material lost from Io. This material interacts with the icy moon Europa, which can also inject charged particles into the environment. We find that Europa appreciably contributes to and modifies its local charged particle environment, revealing a more complex and compositionally diverse magnetosphere than previously thought. Key Points: Three distinct heavy ion populations observed in Jupiter's plasma sheet: Io‐genic plasma, Europa‐genic plasma, and Io‐genic energetic particlesThe mixture of Io‐genic and Europa‐genic plasma varies greatly throughout the Europa‐Ganymede regionWe find evidence Europa's oxygen neutral toroidal clouds are more localized than its hydrogen cloud [ABSTRACT FROM AUTHOR]

The effects of plasma density on the plasmaspheric hiss amplitude and its spatial and temporal scale sizes are investigated using data from Van Allen Probes A and B. The plasmaspheric hiss amplitude and scale sizes are found to be more affected by the small‐scale density variations than the overall density profile of the plasmasphere. In detail, our results suggest that both the hiss wave amplitude and its scale sizes are (a) related to the total electron density when the density is less than ∼1,000 cm−3; (b) independent of the total electron density when the density is greater than ∼1,000 cm−3; and (c) better correlated with the detrended density (removing the background plasmasphere density profile from the total electron density) regardless of the density value. Key Points: Effects of plasma density on the spatial and temporal scale sizes of plasmaspheric hiss amplitude is statistically investigatedThe plasmaspheric hiss amplitude is better correlated with the detrended electron density than the total electron densityThe spatial and temporal scale sizes of plasmaspheric hiss are mainly related to that of the relatively small‐scale density variations [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]

In this study, multiple instrumental observations including Global Navigation Satellite System total electron content (TEC), plasma drift velocity measured by Sanya (18.3°N, 109.6°E, dip latitude 12.6°N) Incoherent Scatter Radar (SYISR) and F2‐layer peak electron density (NmF2) and peak height (hmF2) from ionosonde and SYISR have been used to investigate ionospheric responses during a minor yet highly geo‐effective geomagnetic storm on 26–27 May 2021. Our findings revealed a significant time delay in the post‐sunset plasma density enhancement peak across different latitudes over East Asia, that is, the lower the geographic latitude, the earlier the peak appeared. The plasma density enhancement was accompanied by a decrease in hmF2 prior to NmF2 peak around sunset. The newly built SYISR measurements around sunset verified that the field‐aligned drift decreased the ionosphere with a notable time delay at latitude, beneficial to electron density enhancements at lower altitudes within the 16–30°N latitudinal band but a small TEC change. While at 30–50°N, it is possible that the competition between storm‐induced equatorward winds and downward field‐aligned drift depressed hmF2 decline and the buildup increased both NmF2 and TEC. The ICON observations suggested that the meridional wind during this minor storm event modulated the direction of plasma transport near sunset, playing a dominant role in post‐sunset plasma density enhancement from low to middle latitudes. These results provide fresh insight into the electrodynamic mechanisms of post‐sunset enhancements at middle and low latitudes over East Asia, and also enhance our understanding of the intricate behaviors within the ionosphere‐thermosphere system in response to a minor storm. Key Points: The local time of post‐sunset plasma density enhancement peak had a notable time delay with increasing latitude during a minor stormThe plasma drift during postsunset hours observed by Sanya incoherent scatter radar exhibited strong response to the minor geomagnetic stormThe meridional winds changing from equatorward to poleward explained the post‐sunset enhancement from low to middle latitudes [ABSTRACT FROM AUTHOR]

A Van Allen Probes observation of a high‐density duct alongside whistler‐mode wave activity shows several distinctive characteristics: (a)—within the duct, the wave normal angles (WNA) are close to zero and the waves have relatively large amplitudes, this is expected from the classic conceptualization of ducts. (b)—at L‐shells higher than the duct's location a large "shadow" is present over an extended region that is larger than the duct itself, and (c)—the WNA on the earthward edge of the duct is considerably higher than expected. Using ray‐tracing simulations it is shown that rays fall into three categories: (a) ducted (trapped and amplified), (b) reflected (scattered to resonance cone and damped), and (c) free (non‐ducted). The combined macroscopic effect of all these ray trajectories reproduce the aforementioned features in the spacecraft observation. Plain Language Summary: The near‐earth space environment is a complex system that is dominated by the interaction of radio waves with charged particles. A class of radio waves known as "whistler‐mode" waves, have a drastic impact on energetic particles; understanding properties of whistler waves is thus of considerable interest. It is well‐known that whistler‐mode waves can be trapped within "ducts," which are perturbations in plasma density. Ducts act like pipes that guide waves over thousands of kilometers and routinely connect one hemisphere to the other. Although ducting has been studied for over 75 years, prior research has primarily focused on this guiding effect. Instead, we use spacecraft observations alongside computer simulations to show that ducts have a dramatic effect on waves that are never directly confined to the duct. It is found that a "shadow" region extends far outside the duct caused by trapped waves that leave behind a gap in power. Furthermore, external waves also collide with the duct and ride along the edge at an unexpectedly oblique angle. The results of the work indicate that wave propagation in the vicinity of ducts is more complex than previously thought and must be carefully examined for an accurate understanding of the space environment. Key Points: A Van Allen Probes duct observation shows that whistler waves are field aligned inside, absent on one side, and oblique on the otherRaytracing shows that rays are either trapped in the duct, reflected toward the resonance cone, or free (non‐ducted)Power density and wave normal angle distribution constructed from 10,000 rays reproduces the observed wave properties [ABSTRACT FROM AUTHOR]

Numerical forecasts of plasma convective instability in the postsunset equatorial ionosphere are made based on data from the Ionospheric Connections Explorer satellite (ICON) following the method outlined in a previous study. Data are selected from pairs of successive orbits. Data from the first orbit in the pair are used to initialize and force a numerical forecast simulation, and data from the second orbit are used to validate the results 104 min later. Data from the IVM plasma density and drifts instrument and the MIGHTI red‐line thermospheric winds instrument are used to force the forecast model. Thirteen (16) data set pairs from August (October), 2022, are considered. Forecasts produced one false negative in August and another false negative in October. Possible causes of forecast discrepancies are evaluated including the failure to initialize the numerical simulations with electron density profiles measured concurrently. Volume emission 135.6‐nm OI profiles from the Far Ultraviolet (FUV) instrument on ICON are considered in the evaluation. Plain Language Summary: Numerical forecasts of disruptions in the postsunset equatorial ionosphere are made from data from the Ionospheric Connections Explorer (ICON) satellite using the method outlined in a previous study. Data are selected from pairs of successive orbits–the first providing data for the numerical forecast model, and the second providing a means of validation. Specifically, measurements of vertical plasma drifts and horizontal wind profiles are used. Thirteen (16) orbital pairs from August (October) of 2022 are considered. The forecasts were accurate in the main but produced one false negative in August and another false negative in October. Reasons for the forecast discrepancies are analyzed including the failure to include electron density profile measurements in the forecast model initialization. Data from the Far Ultraviolet instrument on Icon are considered in the analysis. Key Points: ICON‐based numerical forecasts of plasma convective instability in the equatorial ionosphere extended through 2022Results mainly consistent with earlier ICON‐based forecastsICON FUV profiles used to investigate forecast discrepancies further [ABSTRACT FROM AUTHOR]

Dual‐frequency (DF) dual‐antenna inductively coupled plasma (ICP) sources have been proposed as one of the methods to produce large‐area uniform plasma. In this study, a hybrid model, consisting of a fluid module and an electron Monte Carlo (eMC) module, is used to further investigate the modulation of the plasma characteristics (i.e., induced electric field, electron energy distribution, electron heating mechanism, electron temperature, and plasma density) by the low‐frequency (LF) and high‐frequency (HF) currents in a DF argon discharge. When the inner LF current increases from 12 to 22 A at a fixed outer HF current of 10 A, the induced electric field is strengthened near the LF coil and weakened near the HF coil. The fraction of high‐energy electrons at different spatial positions increases with the increase of LF current, which is caused by the sufficient collision heating in the skin layer of LF source, leading to an increase in electron temperature. When the outer HF current rises from 7 to 13 A with the inner LF current fixed at 17 A, the induced electric field is enhanced near the HF coil and weakened near the LF coil. The fraction of low‐energy electrons at different positions increases with the increase of HF current since the energetic electrons from the skin layer of HF source are cooled due to the ionization, excitation, and stepwise ionization collisions between electrons and neutral particles, as well as the weakened induced electric field near the LF coil. As a result, the electron temperature drops with the increase of HF current. Moreover, when the LF and HF currents increase, the plasma density increases, and the distribution of plasma density is also significantly modulated. [ABSTRACT FROM AUTHOR]

In this article, a plasma‐metal model is studied as an electromagnetic absorber for stealth application. Epstain distribution is considered for plasma and the electromagnetic reflection of the structure is analyzed by the Green's function volume integral equation method. The attenuation of microwaves in plasma depends on microwave frequency, plasma electron density, spatial distribution of plasma, collision frequency, and plasma thickness. Using a metaheuristic optimization method, it is possible to change the parameters simultaneously in the specified domains to obtain conditions for which microwaves can be absorbed effectively in the specified frequency. In this paper, optimized plasma parameters related to ideal attenuation in desired frequency band are determined by this method. The advantage of this method is that the intervals related to the plasma parameters are selecting according to the practical conditions and in many cases prevent the production of high volume with high density plasma to achieve effective attenuation. The proposed method can be useful for designing adjustable devices in stealth applications. Proper management of power consumption in these devices is one of the results of adjustment. [ABSTRACT FROM AUTHOR]

This paper conducts a multi‐instrument analysis of a latitudinal plasma density peak at the middle latitudes during the early recovery phase of the April 2023 geomagnetic storm. The total electron content (TEC), peak density of the F layer, and the in situ plasma density from Swarm and Defense Meteorological Satellite Program (DMSP) satellites all capture this peak feature. This narrow latitudinal peak structure appeared around 50°N and extended from 40°E to 150°E in longitude with a prolonged duration of about 8 hr from sunset to midnight. This mid‐latitude peak reveals a noticeable equatorward motion and a slight westward shift. According to the plasma composition observations from DMSP satellites, this peak structure shows an O+ ions dominance, which means that this peak is more likely to be formed by an internal rather than an external source from the plasmasphere. Meanwhile, the middle latitude Fabry–Perot interferometer (FPI) observed strong equatorward thermospheric winds, and the peak height of the F layer presented a visible elevation, which suggests that the equatorward wind lifting caused the plasma density enhancement. Besides, the O/N2 ratio significantly decreased at lower and middle latitudes, and ion drift observations showed a distinct subauroral westward channel. Based on these simultaneous measurements, this structure's sharp equatorward and poleward boundaries might be related to the O/N2 ratio change and the subauroral polarization stream (SAPS) flow separately. Plain Language Summary: The ionospheric response to geomagnetic storm disturbances exhibits diverse plasma density structures. During the early recovery phase of the April 2023 geomagnetic storm, a distinct latitudinal plasma density peak is observed at middle latitudes. The formation of the mid‐latitude plasma density peak structure is not settled yet, even though some homologous structures have been reported. This study investigates the spatial and temporal features of this mid‐latitude peak structure and the dominant ion composition. The investigation is achieved by utilizing the total electron content, F layer parameters, and in situ plasma observations. Furthermore, the observations of neutral wind, thermospheric composition, and ion drift observations show a good correlation with the spatial‐temporal characteristics of this peak structure. These clues suggest that the formation of the mid‐latitude peak structure during the April 2023 geomagnetic storm may be attributed to a combined effect involving equatorward neutral winds, thermospheric composition change, and subauroral polarization stream flow. Key Points: A mid‐latitude peak is present in total electron content, F layer peak density, and in situ plasma density during the storm recovery phaseThe mid‐latitude peak covers 40°–150°E in longitude with a noticeable equatorward motion and slight westward shiftThe peak structure may be associated with the thermospheric equatorward wind, composition change, and subauroral polarization stream [ABSTRACT FROM AUTHOR]

STEVE, Strong Thermal Emission Velocity Enhancement, was often observed by ground‐based imagers in visible wavelengths and rarely detected by global FUV imagers. We present a new event, and revisit two reported STEVE events, that were observed by the DMSP/SSUSI FUV imager at O 135.6 nm, N2 LBHS, and LBHL emissions. Coincident particle and plasma drift observations showed that the events were associated with high ion drift speed, low ion density and no energetic particle precipitation. This is consistent with earlier findings (e.g., MacDonald et al., 2018, https://doi.org/10.1126/sciadv.aaq0030; Gallardo‐Lacourt et al., 2018a, https://doi.org/10.1029/2018ja025368, 2018b, https://doi.org/10.1029/2018gl078509; Archer et al., 2019). In this paper, several new features are identified: (a) Detection rates of FUV STEVE are much lower than that of visible STEVE; (b) The STEVE on 27 March 2008 covers 3‐hr local time with a length up to 2,700 km around 60° magnetic latitudes; (c) Different widths of STEVE observed in O 135.6 nm and N2 LBH images indicate a large altitude range in the STEVE FUV emissions; (d) The true ion (assuming O+) drift speeds during the 27 March 2008 STEVE event could be up to 20 km/s, well above the DMSP SSIES sensor limit. The kinetic energy of the high speed ions is larger than the excitation potential of the observed FUV emissions; (e) The requirement of such extreme high ion drift speed explains why FUV STEVE have been rarely observed, compared to the visible STEVE; (f) The three FUV STEVE events occurred during moderate geomagnetic activity; (g) Theses events were conjugate in both hemispheres. Plain Language Summary: STEVE, Strong Thermal Emission Velocity Enhancement, was discovered by ground‐based imagers in visible wavelengths. We present examples of STEVE detected by FUV imager at O 135.6 nm, N2 LBHS (140–150 nm), and LBHL (165–180 nm) emissions. These FUV STEVE events were associated with high plasma drift speed and low plasma density in the ionosphere, and no energetic particle precipitation. These FUV STEVE events show several new features: (a) Detection rates of FUV STEVE are much lower than that of visible STEVE; (b) The STEVE length is up to 2,700 km; (c) There is a large altitude range of the FUV emission; (d) The true ion (assuming O+) drift speeds could be up to 20 km/s. Ions with such a high drift speed would carry sufficient kinetic energy to excite FUV emissions; (e) The FUV STEVE events occurred during moderate geomagnetic activity; and (f) The FUV STEVE events were conjugate in both hemispheres. Key Points: In addition to the visible emissions, STEVE is also observed in far ultraviolet emissionsThe STEVE on 27 March 2008 has a horizontal length up to 2,700 km and a large altitude extensionEstimated O+ ion drift speed for some STEVE events is ∼20 km/s and the ions' kinetic energy is greater than the FUV excitation potential [ABSTRACT FROM AUTHOR]