Search

Led by the Institute of Geology and Geophysics, Chinese Academy of Sciences, we have built a brand‐new modular active digital phased array, with all solid‐state transmission and digital receiving incoherent scatter radar (ISR) in Sanya (18.3°N, 109.6°E), a station in low latitude China called Sanya ISR (SYISR) since 2015. The development of SYISR involved the indoor design and development of key components, an outdoor prototype test, and the production and debugging of the entire array. The unique features of SYISR include a single‐channel directly connected T/R unit and antenna, a radar array monitoring and calibration network, environmental adaptability design and open architecture. The entire radar has 4,096 channels and 5,930 modules in total. All the technical indices, mainly including a >2 MW peak power, a 43 dBi antenna gain and a <120 K noise temperature, either meet or are superior to the designed value through an independent evaluation. Waveforms of single pulse, linear frequency modulation, Barker code, long pulse and alternating code have been implemented to meet multiple purposes. Four observational modes for ionospheric experiments, including zenith stare, perpendicular to geomagnetic field, meridian scan, and all sky scan, have been developed. We have implemented time domain decoding, frequency domain decoding, and statistical inversion methods in calculating the autocorrelation function and power spectra in signal processing. The preliminary experimental results on ionospheric parameters, plasma lines, irregularities and hard targets are reasonable and encouraging, which greatly enhances our confidence in achieving our scientific goals in the future. Plain Language Summary: The Earth's ionosphere (∼60–1,000 km above the sea level) is composed of dense plasma, which shows complicated variations versus altitude, geographic location, and solar activity level. When a ground‐based radio wave is transmitted onto these plasmas, it will generate stimulated radiation, with a small portion of them radiating back to the ground. If this backscattered radiation is collected by a ground‐based radar, a variety of ionospheric parameters, including plasma density, temperature, and movement speed, can be derived through a complicated signal processing algorithm. An ionospheric monitoring method called incoherent scatter radar (ISR) was therefore developed. However, since this backscattered radiation is very weak, the ISR should be built with sufficiently large power (usually megawatts) and apertures (usually hundreds of square meters). This leads to the high cost of building an ISR, with only a few having been built in the world thus far. In this paper, we describe a newly built ISR, called Sanya ISR (SYISR), in low latitude China by applying modern radar technologies, such as modular active digital phased arrays, all solid‐state transmitting and digital receiving. The development of SYISR followed the principle of a gradual and orderly progress, including indoor design, outdoor prototype testing and the entire radar construction and debugging. The radar technical indices have been evaluated, and all meet the designed value. We also developed a signal processing algorithm and a variety of observational modes. Finally, preliminary experimental results are shown, which are reasonable and encouraging. In the future, we will gradually achieve our scientific goals via effective data accumulation and analysis. Key Points: Sanya incoherent scatter radar (SYISR) is a newly built incoherent scatter radar in low latitude China with modular active electronic scanning, digital phased array, solid‐state transmitting, and digital receivingThis paper details the hardware, key parameters, data processing and preliminary experimental results of SYISRThe key parameters meet or are superior to the original design, and the preliminary observations are encouraging [ABSTRACT FROM AUTHOR]

The Mid‐latitude All‐sky‐imaging Network for Geophysical Observations (MANGO) employs a combination of two powerful optical techniques used to observe the dynamics of Earth's upper atmosphere: wide‐field imaging and high‐resolution spectral interferometry. Both techniques observe the naturally occurring airglow emissions produced in the upper atmosphere at 630.0‐ and 557.7‐nm wavelengths. Instruments are deployed to sites across the continental United States, providing the capability to make measurements spanning mid to sub‐auroral latitudes. The current instrument suite in MANGO has six all‐sky imagers (ASIs) observing the 630.0‐nm emission (integrated between ∼200 and 400 km altitude), six ASIs observing the 557.7‐nm emission (integrated between ∼90 and 100 km altitude), and four Fabry‐Perot interferometers measuring neutral winds and temperature at these wavelengths. The deployment of additional imagers is planned. The network makes unprecedented observations of the nighttime thermosphere‐ionosphere dynamics with the expanded field‐of‐view provided by the distributed network of instruments. This paper describes the network, the instruments, the data products, and first results from this effort. Plain Language Summary: A network of cameras and optical sensing instruments is deployed across the continental United States and is used to study the processes in the earth's upper atmosphere. These processes range from response to explosive events on the sun, as well as, response to strong events in the troposphere like thunderstorms or hurricanes. This paper describes this network, how it works, how the data are being produced, and initial scientific results. Key Points: A network of red and green line cameras and Fabry‐Perot interferometers is being developed in mid‐latitude USAThe network observes dynamics in two altitude regions of the upper atmosphereThe data are used to understand the upper atmospheric response to energetic events generated in the lower atmosphere or the sun [ABSTRACT FROM AUTHOR]

The ionosphere of Titan hosts a complex ion chemistry leading to the formation of organic dust below 1,200 km. Current models cannot fully explain the observed electron temperature in this dusty environment. To achieve new insight, we have re‐analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science package. A first paper (Chatain et al., 2021) introduces the new analysis method and discusses the identification of four electron populations produced by different ionization mechanisms. In this second paper, we present a statistical study of the whole LP dataset below 1,200 km which gives clues on the origin of the four populations. One small population is attributed to photo‐ or secondary electrons emitted from the surface of the probe boom. A second population is systematically observed, at a constant density (∼500 cm−3), and is attributed to background thermalized electrons from the ionization process of precipitating particles from the surrounding magnetosphere. The two last populations increase in density with pressure, solar illumination and Extreme ultraviolet flux. The third population is observed with varying densities at all altitudes and solar zenith angles (SZA) except on the far nightside (SZA > ∼140°), with a maximum density of 2,700 cm−3. It is therefore certainly related to the photo‐ionization of the atmospheric molecules. Finally, a fourth population detected only on the dayside and below 1,200 km reaching up to 2000 cm−3 could be photo‐ or thermo‐emitted from dust grains. Key Points: Four cold electron populations are detected by the Cassini Langmuir probe in Titan's ionosphere below 1,200 km altitudeThree populations are likely produced by particle precipitation ionization and photo‐ionization in the atmosphere and on the probe boomThe fourth electron population, observed on dayside below 1,200 km, could be photo‐ or thermo‐emitted from dust grains [ABSTRACT FROM AUTHOR]

The Floating Potential Measurement Unit onboard the International Space Station includes a Wide sweeping Langmuir Probe that has been operating in the F‐region of the ionosphere at ∼400 km since 2006. While traditional Langmuir probe estimates include critical plasma parameters like electron density and temperature, we have also extracted the O+ percentage from the total ion constituents. This O+ composition data set from the recent minimum in the Solar Cycle 24 reveals orbits with dropouts in O+ to below 80% of the total background ion density at International Space Station orbital altitudes. The observed O+ percentages during these dropouts are much lower than the values predicted by the International Reference Ionosphere 2016 (IRI2016) empirical model. In this paper, we present the climatology of these O+ dropouts with their dependency on season, local time and geographical location. The results show that the lowered O+ percentages are more significant in the winter hemispheres and are routinely observed for orbits in the pre‐sunrise periods. The patterns in O+ dropouts can be explained in part from the lowering of the O+/H+ transition height during solar minimum along with patterns in neutral wind variation. Plain Language Summary: The plasma environment experienced by the International Space Station (ISS) is of key importance to the space physics community. A suite of instruments on the ISS has been operating since 2006 that consist of a spherical Langmuir probe, called the Wide sweeping Langmuir Probe, which is a sensor that periodically collects information about the density and energy of the ambient electrons. Recently, we presented a technique to also infer the composition of O+ ions relative to the total ion density which is an important parameter in understanding the interaction between the terrestrial atmosphere with the exosphere. Results from the most recent period of solar minimum reveal dropouts in O+ densities compared to predictions from empirical models. We show global climatology plots from 2018 to 2019 and observe that these large dropouts in O+ are more prevalent in the post‐midnight region of the winter hemisphere. Past studies have discussed increased presence of lighter H+ ions at higher orbital altitudes, but the fact that O+ dropouts are observed even at ISS altitudes is striking and one of the prominent features of solar minimum. Key Points: O+ percentages often drop below 80% at International Space Station altitudes during solar minimumThe dropouts in O+ abundance are common in post‐midnight sector in winter hemisphereThe climatology of the dropouts is governed by neutral wind variations and lowered O+/H+ transition height [ABSTRACT FROM AUTHOR]

Normally, auroral kilometric radiation (AKR) which is emitted in the auroral zones escapes from the Earth. But since a few decades very similar radiations are observed by ground‐based receivers and by satellites at altitudes below the AKR generation area. They are called leaked AKR or AKR‐like emissions because it is expected that there are linked to AKR. This paper deals with observations of such AKR‐like emissions observed in the auroral zones (in the North and in the South) by the low‐altitude satellite DEMETER. In total, 2,526 events have been recorded during 6.5 years. These events are not very rare as they occur at least 2% of the time. Although this data set has a severe flaw due to a latitudinal constraint, it was possible to draw interesting properties of these emissions. In fact they are very similar to usual AKR observed at much higher altitudes during auroral activities (the same frequency range, magnetic local time (MLT) sector, and invariant latitude). The main difference concerns a strong asymmetry between the Northern and the Southern hemispheres: (a) the number of AKR‐like emissions in the Northern hemisphere is 32% larger than in the Southern hemisphere but this percentage decreases when the auroral activity increases, and (b) there is an important seasonal effect because the number of events decreases during the winter season both in the North and in the South. Plain Language Summary: Auroral kilometric radiation (AKR) is the strongest terrestrial radio emission generated between 30 and 800 kHz along the auroral field lines and associated with a discrete auroral arc. This emission is generated by superthermal electrons (several keV) which are injected from the magnetotail when the solar activity increases. Typical location of the source is ∼22 hr of magnetic local time (MLT), ∼70° of invariant latitude, and (2–10)103 km of altitude. AKR propagates from the Earth and should not be able to reach low altitudes because of the ionospheric frequency cutoff. But a few decades ago, AKR‐like emissions have been recorded by low orbiting satellites and even by ground‐based receivers. It was explained by a mode conversion of the wave propagating in inhomogeneous plasma. Up to now, only studies of some AKR‐like events have been reported, and this paper presents the statistical properties of such emissions recorded by the low altitude satellite DEMETER during 6.5 years. AKR‐like emissions display similar characteristics of AKR in terms of frequency, MLT, and invariant latitude. It is shown that more events are observed in the North than in the South, and that there is a seasonal effect (the number of events decreases in winter hemispheres). Key Points: Numerous auroral kilometric radiation‐like events have been recorded by the low‐altitude satellite DEMETER during moderate and high magnetic activityThere are more events in the Northern than in the Southern hemisphere but this difference decreases when the auroral activity increasesThe number of events decreases in winter in each hemisphere [ABSTRACT FROM AUTHOR]

In this paper we present an algorithm which identifies ion energy dispersion events in low altitude cusp observations. Such an algorithm is suitable for implementation to prioritize data for downlink, or to be run on the ground for data mining. The energy dispersion events, sometimes known as dispersed particle precipitation, have been interpreted as due to time‐of‐flight effects of energized ions from magnetopause reconnection sites. Our algorithm utilizes a novel method of integrating a scoring function across moving time windows to capture the dispersion structure. The algorithm is implemented and prototyped with Defense Meteorological Satellite Program data but specified in terms that apply to other missions for both ions and electrons. Two new types of dispersion events are uncovered with the algorithm, consisting of a cold inverse double dispersion event where one population dominates, and a V‐type dispersion event during northward interplanetary magnetic field. Plain Language Summary: Ion energy dispersion events occur in the low altitude cusp region, originating from reconnection at the magnetopause. This paper presents an algorithm for automatically detecting these events in data from the Defense Meteorological Satellite Program (DMSP) satellites. Though the algorithm is demonstrated with DMSP, the algorithm can work with other satellites. The algorithm is also used to search for new types of dispersion, and two new types of dispersion events are presented in this paper. Key Points: A novel method for capturing the energy dispersion structure is developed and applied to the DMSP dataThe algorithm is applied and validated against a G2‐class Moderate StormNew types of ion dispersion events are uncovered with the algorithm and their relevance is stated [ABSTRACT FROM AUTHOR]

We associate new data from icebear, a coherent scatter radar located in Saskatchewan, Canada, with scale‐dependent physics in the ionosphere. We subject the large‐scale icebear 3D echo patterns (treated as 2D point clouds) to a data analysis technique hitherto never applied to the ionosphere, a technique that is widely applied in cosmological red‐shift surveys to characterize the spatial clustering of galaxies. The technique results in a novel method to calculate the spatial power spectral density of the greater ionospheric irregularity field. We compare results from this method to in‐situ plasma density and magnetic field observations from the Swarm mission. We show that there is a remarkable similarity between echo clustering spectra in the E‐region and the field‐aligned current structuring spectrum observed in the F‐region: a clear and characteristic preferred scale (5 km) both in the E‐ and F‐region spectra. We discuss the possibility that this represents evidence of an energy injection into the ionospheric irregularity field via energetic particle precipitation, but offer alternative interpretations with wider connotations for the ionosphere‐magnetosphere system. These findings open new and promising avenues of research for the study of the location of ionospheric scatter echoes with 3D information. It constitutes a novel way to consider the pattern of ionospheric irregularities over wide fields of view when there is an abundance of radar echoes, which allows for the analysis of radar data as point clouds. Plain Language Summary: With the advent of precision radar data from the aurora containing detailed information about radar echo locations, we are in a position to apply statistical methods from cosmology to extract information about plasma turbulence in the ionosphere. This interdisciplinary paper presents some birds‐eye view discussions about the use of correlation functions in physics, showing how it can be used to understand physics on virtually all spatial scales in the observable universe. We present results pertinent to the ionosphere, shedding light on plasma turbulence and its relation to energetic particles in the aurora. Here, we use observations both from space, by the orbiting satellites in the European Space Agency's Swarm mission, and using an experimental auroral radar in Saskatchewan, Canada. Key Points: Clustering Statistics are used to extract large scale turbulence information from 3‐m structures in the E‐regionE‐region clustering spectra are remarkably similar to in‐situ spectra from field‐aligned currents in the F‐regionA preferential 5‐km scale is simultaneously observed in the E‐region and in the F‐region field‐aligned currents [ABSTRACT FROM AUTHOR]

Geomagnetic conjugate mid‐latitude nighttime ionospheres are frequently simultaneously populated with electrified nighttime medium‐scale traveling ionospheric disturbances (MSTIDs). Earlier observations and theoretical analysis have underscored the ionosphere E‐F coupling and the postulation of coupled conjugate hemispheres, playing a pivotal role in the formation of electrified MSTIDs. In this paper, the conjugate MSTIDs are studied to elucidate the causes and effects of E‐F coupling in the interhemispheric coupled ionosphere. The hemisphere‐coupled ionospheres over Japan and Australia are observed and analyzed using total electron content (TEC) measurements, supplemented with multi‐source observations from ionosondes, Ionospheric Connection Explorer (neutral wind), Constellation Observing System for Meteorology, Ionosphere, and Climate (electron density), and Swarm (magnetic field). A double‐thin‐shell model is introduced to analyze the ionospheric responses in E and F regions during the coupling process. For the first time, observation results provide the evidence that F‐region geomagnetic conjugate irregularities in both hemispheres are mainly driven by the Es layers in the summer hemisphere. The Es layer in the summer hemisphere subsequently triggers local E‐F coupling and inter‐hemispheric coupling. In the winter hemisphere, Es layers show amplitude reduction or even dissipation during the interhemispheric coupling process. Furthermore, thermospheric winds, non‐equipotential magnetic field lines, and background TEC are presumed candidates for the inter‐hemispheric asymmetry in MSTIDs amplitudes and growth rates. Key Points: The F‐region geomagnetic conjugate medium‐scale traveling ionospheric disturbances (MSTIDs) in both hemispheres are mainly driven by the Es layers in the summer hemispherePreexisting Es layers in the winter hemisphere show intensity reduction or even dissipation after the interhemispheric couplingThe amplitude and growth rate of hemispheric conjugate MSTIDs are smaller in the winter hemisphere [ABSTRACT FROM AUTHOR]

Surface waves on Earth's magnetopause have a controlling effect upon global magnetospheric dynamics. Since spacecraft provide sparse in situ observation points, remote sensing these modes using ground‐based instruments in the polar regions is desirable. However, many open conceptual questions on the expected signatures remain. Therefore, we provide predictions of key qualitative features expected in auroral, ionospheric, and ground magnetic observations through both magnetohydrodynamic theory and a global coupled magnetosphere‐ionosphere simulation of a magnetopause surface eigenmode. These show monochromatic oscillatory field‐aligned currents (FACs), due to both the surface mode and its non‐resonant Alfvén coupling, are present throughout the magnetosphere. The currents peak in amplitude at the equatorward edge of the magnetopause boundary layer, not the open‐closed boundary as previously thought. They also exhibit slow poleward phase motion rather than being purely evanescent. We suggest the upward FAC perturbations may result in periodic auroral brightenings. In the ionosphere, convection vortices circulate the poleward moving FAC structures. Finally, surface mode signals are predicted in the ground magnetic field, with ionospheric Hall currents rotating perturbations by approximately (but not exactly) 90° compared to the magnetosphere. Thus typical dayside magnetopause surface modes should be strongest in the East‐West ground magnetic field component. Overall, all ground‐based signatures of the magnetopause surface mode are predicted to have the same frequency across L‐shells, amplitudes that maximize near the magnetopause's equatorward edge, and larger latitudinal scales than for field line resonance. Implications in terms of ionospheric Joule heating and geomagnetically induced currents are discussed. Plain Language Summary: Waves on the boundary of the magnetosphere, the magnetic shield established by the interplay of the solar wind with Earth's magnetic field, play a controlling role on energy flow into our space environment. While these waves can be observed as they pass over satellites in orbit, due to the small number of suitable satellites available it would be helpful to be able to detect these waves from the surface of the Earth with instruments that measure the northern/southern lights, motion of the top of our atmosphere, or magnetic field on the ground. However, we do not currently understand what the signs of these waves should look like in such instruments. In this paper we develop theory and use computer simulations of these boundary waves to predict key features one might expect to measure from the ground. Based on these predictions, we also discuss how the waves might contribute to the hazards of space weather. Key Points: Theory and global simulations of magnetopause surface waves' effects on the aurorae, ionosphere, and ground magnetic field are investigatedWe predict poleward‐moving periodic aurora, convection vortices, and ground pulsations, with larger latitudinal scales than Alfvén modesAmplitudes of all signals peak near the projection of the inner/equatorward edge of the magnetopause rather than the open–closed boundary [ABSTRACT FROM AUTHOR]

Releasing diffuse artificial clouds into the space environment using a rocket or spacecraft can modify the natural plasma state. This uses space itself as a laboratory for studying plasma phenomena that cannot be reproduced on the ground. The Space Measurement of A Rocket‐released Turbulence (SMART) mission will inject a beam of barium neutral vapor into the ionosphere and perpendicular to the Earth's magnetic field. Barium atoms will be photoionized, forming an ion ring distribution that is unstable to lower hybrid waves. Large amplitude lower hybrid waves nonlinearly scatter to whistler and magnetosonic waves that can propagate out to the magnetosphere. This paper details the theory, modeling, and simulation we used to design this release experiment to optimize the energy in the plasma waves under a variety of constraints. A product of this analysis is quantitative predictions for some in situ and remote measurements. Hydrocode simulations of barium vapourization and acceleration via shaped charge provide the initial state of the neutral beam. We optimize the apogee, orientation, and position of the payload and instruments. Cloud dynamics are simulated with a direct simulation Monte Carlo technique, which includes photoionization with metastable barium states, collisions with the neutral background atmosphere, optical line emission, gravity, and electromagnetic forces. We predict the plasma density measured by the instrument payload and the remotely measured optical intensity. We also examine how the plasma wave growth differs at the measurement location compared to the bulk of the barium cloud. Key Points: A variety of models and simulations are combined to optimize plasma wave energy in a neutral beam injection experimentModeling provides quantitative predictions of measurements (e.g., plasma density, beam velocity, total barium produced, optical intensity)We discuss the many details that arose between concept and implementation of the experiment, and how these affected mission design [ABSTRACT FROM AUTHOR]

In this paper, the internal structuring of Polarization Jet (PJ)/Subauroral Ion Drift (SAID) is studied. It is shown that PJ/SAID consists of several Polarization Jet Strata (PJS) of electron density and temperature. A new type of phenomena has been discovered called Stratified Subauroral Ion Drift (SSAID), which is a PJ/SAID containing small‐scale PJS. Internal small‐scale structure of SSAIDs is measured during various geomagnetic events using data from NorSat‐1, DMSP F‐17 and F‐18 satellites. High resolution measurements on the Norsat‐1 satellite make it possible to detect and study small‐scale structures inside the PJ/SAID, that is, SSAID. The data from DMSP satellites is used to determine explicitly the presence of PJ/SAID during the considered geomagnetic events. Results show that SSAID consist of 2–4 large PJS and from a few units to several tens of small PJS. Large PJS have a size of 0.2°–0.3° latitude and small PJS have a size of <0.1°. Several suggestions regarding possible physical mechanisms of production of SSAID and PJS are presented. Plain Language Summary: In the subauroral zone, narrow fluxes of fast subauroral ion drifts are observed near the projection of the plasmapause at heights of the F‐layer of the ionosphere, which are most noticeable during geomagnetic activity against the background of large‐scale plasma convection, called polarization jet (PJ) or subauroral ion drifts (SAID). Despite the importance of using a variety of ground‐based observation facilities for studying and analyzing PJ/SAID properties, as well as developing analytical models and numerical modeling, in situ observations are most valuable. These observations can be obtained only during the satellite flyby through the subauroral zone during the PJ/SAID development. Small‐scale processes inside PJ/SAID were practically not studied and many open questions remain here due to lack of high‐resolution satellite measurements. In this work, using NorSat‐1 satellite high sampling rate data, we report that there are Stratified Subauroral Ion Drifts (SSAIDs) which consist of small‐scale Polarization Jet Strata (PJS) of electron density and temperature. Key Points: We explore the internal structuring of subauroral polarization jets/ion drifts (SSAID ‐ Stratified Subauroral Ion Drift)SSAIDs consist of 2–4 large Polarization Jet Strata (PJS) and from a few units to several tens of small PJSLarge PJS have a size of 0.2°‐0.3° latitude and small PJS have a size of <0.1° [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]

The work is devoted to modeling and verification of the dynamics of charged components of the Earth's lower ionosphere, obtained using different values of the background neutral atmosphere parameters. Long‐term experimental data on temperature and concentration of neutral components from the Aura satellite and Mass Spectrometer Incoherent Scatter Radar (MSIS) model were used as input data. The average relative difference between the electron concentration values obtained using Aura and MSIS data (11 June 2014, 6–18 UT, h = 50–90 km, 41°N 10°E) was 34%. Obtained results were verified with use of very low frequency (VLF) signals propagation data, which were collected on Mikhnevo Geophysical Observatory (GPO) and A118 station from GBZ, GQD, DHO, TBB, and ICV transmitters. Based on the results of the verification, it was found that the response of the lower ionosphere to X‐ray flares, that occurred on 9–11 June 2014, is better described by the Aura satellite data in 4 out of 5 cases. Consequently, they are more preferable for predicting the state of ionospheric parameters below the reflection height of signals of the considered frequencies (∼75 km). It is also shown that taking into account the ion concentration for calculation the amplitude‐phase characteristics of the VLF‐signals makes it possible to describe the dynamics of parameters better. Plain Language Summary: Due to the small amount of direct experimental measurements, the lower ionosphere still remains the least studied. At the same time, it is responsible for the distortion of the amplitude and phase of the very low frequency (VLF) signals and the absorption of high frequency radio waves during strong disturbances. The correctness of the existing plasma‐chemical models of the lower ionosphere depends on the values of the input parameters, many of which are known with low accuracy. In this paper, we compare and verify results of the plasma‐chemical model with different values of the background neutral atmosphere parameters—experimental data on the temperature and concentration of neutral components from the Aura satellite and the Mass Spectrometer Incoherent Scatter Radar (MSIS) model results. These two sets of neutral atmospheric input data were used to simulate the response of the lower ionosphere to solar flares that occurred on 9–11 June 2014. Verification is carried out according to the VLF‐signals propagation from GBZ, GQD, DHO, TBB, and ICV transmitters to the Mikhnevo Geophysical Observatory and A118 station. It is shown that in 80% of cases the measurements of the Aura satellite make it possible to describe the state and dynamics of the medium more correctly than the results of the MSIS model. Key Points: Simulation of the ionospheric response to X‐ray flares using Aura satellite data is more accurate than using the Mass Spectrometer Incoherent Scatter Radar model resultsAccounting for the ion concentration when calculating very low frequency (VLF)‐signals propagation improved agreement with experiment in 38% of the casesVerification of the model results was carried out on 10 different VLF‐paths with use of data from the A118 station and Mikhnevo Geophysical Observatory [ABSTRACT FROM AUTHOR]

The geospace plume, referring to the combined processes of the plasmaspheric and the ionospheric storm‐enhanced density (SED)/total electron content (TEC) plumes, is one of the unique features of geomagnetic storms. The apparent spatial overlap and joint temporal evolution between the plasmaspheric plume and the equatorial mapping of the SED/TEC plume indicate strong magnetospheric‐ionospheric coupling. However, a systematic modeling study of the factors contributing to geospace plume development has not yet been performed due to the lack of a sufficiently comprehensive model including all the relevant physical processes. In this paper, we present a numerical simulation of the geospace plume in the 31 March 2001 storm using the Multiscale Atmosphere‐Geospace Environment model. The simulation reproduces the observed linkage of the two plumes, which, we interpret as a result of both being driven by the electric field that maps between the magnetosphere and the ionosphere. The model predicts two velocity channels of sunward plasma drift at different latitudes in the dusk sector during the storm main phase, which are identified as the sub‐auroral polarization stream (subauroral polarization streams (SAPS)) and the convection return flow, respectively. The SAPS is responsible for the erosion of the plasmasphere plume and contributes to the ionospheric TEC depletion in the midlatitude trough region. We further find the spatial distributions of the magnetospheric ring current ions and electrons, determined by a delicate balance of the energy‐dependent gradient/curvature drifts and the E × B drifts, are crucial to sustain the SAPS electric field that shapes the geospace plume throughout the storm main phase. Key Points: The first whole geospace simulation to demonstrate coherent storm‐time evolution of plasmaspheric and total electron content (TEC) plumesThe model demonstrates plasmasphere erosion and TEC depletion by the subauroral polarization streams (SAPS)SAPS is sustained by magnetospheric ion and electron distributions formed by a delicate balance of energy‐dependent and E × B drifts [ABSTRACT FROM AUTHOR]

This paper reports a large‐scale magnetospheric line radiation (MLR) event during a moderate geomagnetic storm on 11 September 2018, which was well recorded by the China‐Seismo‐Electromagnetic Satellite (CSES) in the upper ionosphere. The event shows a symmetrical propagation feature at the conjugated locations between the two hemispheres, exhibiting a large spatial extension roughly from the latitudes 54°N to 53°S. The parallel structures are visible both in the electric and magnetic fields at a frequency band ranging from the local proton cyclotron frequency to ∼1.6 kHz. The wave intensity of parallel spectral lines was primarily enhanced in high latitude regions, gradually weakening at mid‐low latitudes, and then got absorbed in the equatorial region, presenting a distinct V‐shaped structure. The frequency spacings between neighboring spectral lines roughly vary from ∼80 to 110 Hz at the high latitudes and ∼80–130 Hz at the low latitudes, suggesting a slight variation feature with latitude. The parallel spectral structures of MLR drift between ∼0.39 and 0.57 Hz/s at high latitudes and ∼0.18–0.19 Hz/s at low latitudes. The wave vector analysis shows that the MLR waves are right‐hand polarized, obliquely propagating toward the Earth and in the azimuthal direction, where the Poynting flux is primarily oriented perpendicular to the ambient magnetic field. The other large‐scale MLR events all exhibit similar parallel structures and polarization characteristics, suggesting the universality of such a phenomenon. However, the azimuthal angles differ among different events, showing complex features. Plain Language Summary: Magnetospheric line radiation (MLR) is a unique electromagnetic wave distinguished by parallel spectral lines. This study reports a large‐scale MLR event that occurred in the dayside ionosphere. The event shows a symmetrical propagation feature, with a large spatial extension between latitudes 54°N and 53°S. The parallel structures are visible both in the electric and magnetic spectrogram, ranging from the local proton cyclotron frequency to ∼1.6 kHz. The MLR structures were primarily enhanced in high latitude regions, gradually weakening at mid‐low latitudes, and then got absorbed in the equatorial region, presenting a distinct V‐shaped structure. The frequency spacings of MLR roughly vary from ∼80 to 110 Hz in the high latitudes and from ∼80 to 130 Hz in the mid‐low latitude region, slightly varying with latitude. The MLR structures drift between ∼0.39 and 0.57 Hz/s at high latitudes and ∼0.18–0.19 Hz/s at low latitudes. This MLR event is right‐hand polarized, obliquely propagating toward the Earth and in the azimuthal direction, and the Poynting flux is primarily oriented perpendicular to the ambient magnetic field. However, the azimuthal angles differ among different events, indicating the complexity of the wave propagation feature. Key Points: A large‐scale magnetospheric line radiation (MLR) event shows a symmetrical propagation feature in two hemispheres, presenting a distinct V‐shaped structureBoth the frequencies of the parallel spectral lines and their frequency spacings slightly drift with latitudesThe MLR waves are right‐hand polarized, obliquely propagating toward the Earth and azimuthal direction [ABSTRACT FROM AUTHOR]

This paper reports the first high‐resolution 4‐dimensional ionospheric disturbance caused by hurricane Matthew on 7 October 2016. The temporal as well as vertical and horizontal variations of the concentric traveling ionospheric disturbances (CTIDs) were reconstructed using 3‐dimensional computerized ionospheric tomography (3DCIT) technology, based upon the Global Navigation Satellite System data from the dense receiver network over North America. The frequency range of disturbances was determined by spectrum analysis, and a Butterworth band‐pass filter was used to de‐trend the total electron content (TEC) sequences to determine TIDs. A remarkable CTID segment was detected at a distance of 1,000–1,500 km from the hurricane eye at ∼5:40–6:10 UT on 7 October 2016, moving westward with the horizontal phase velocity of ∼153.4 m/s, the period of ∼30 min and the horizontal wavelength of ∼276.1 km. The positive and negative wavefronts dominated the CITD at different times during the event. From 4:00 to 8:00 UT, the altitudinal variation of the CTIDs in electron density exhibited clear downward phase progression predominately in the range of 150–400 km altitudes; however, the percentage of electron density disturbances was larger below 250 km. The inverted cone‐like geometry of CTID wavefronts was presented. The vertical phase velocities of the CTIDs ∼1,100 km away from the hurricane eye in the northwest direction near 88°W, 34°N were ∼203.7–277.8 m/s, and at the same location, the horizontal phase velocities at 300 km altitude were ∼149.1–181.5 m/s, slightly larger than those at 200 km altitude (∼145.1–178.5 m/s). Key Points: The propagation features of concentric traveling ionospheric disturbances (CTID) caused by Hurricane Matthew on 7 October 2016 were analyzedFirst 4‐dimensional CTIDs caused by hurricane were reconstructed using ionospheric tomographyThe horizontal phase velocities at different altitudes and the vertical phase velocities of the ionospheric disturbances were estimated [ABSTRACT FROM AUTHOR]

In this paper, the ionospheric quiet‐time disturbances otherwise known as Pre‐Magnetic Storm Signatures (PMS) have been studied using the F2‐layer peak electron density (NmF2) data obtained from 12 Digisonde/ionosonde stations distributed across equatorial, low and mid‐latitudes. The datasets used spans the years 2010–2012. Results from this study reveals strong PMS in NmF2 with percentage deviations (ΔNmF2) ranging from −91% to 500% at the equatorial, low and mid‐latitudes, with maxima occurring at the equatorial region. Significant effects on the peak height of the F2‐layer (hmF2) were also observed, and they are correlated with the variations in NmF2 particularly at the equatorial station during the PMS. The duration of a PMS is found to be 12–48 h. Although, it was difficult to state clearly the connection between the PMS and the geomagnetic storm that usually follows within 24–48 h; but the NmF2 and hmF2 responses during the PMS were quite similar to those observed during geomagnetic storms. A slight increase in the Solar‐wind‐plasma speed (>20 km/s) was also observed during PMS. The PMS occur under a southward IMF‐Bz, moderate aurora activity (AE ranging from 114 to 560 nT) and quiet ring current (Dst >−10 nT). Therefore, it is pertinent to consider a certain threshold of the aurora indices (AE, AL, and AU) in addition to the Dst, ap, and Kp in the definition of a geomagnetically quiet day. This may eliminate the ambiguity in explaining the ionospheric variability that occurs few days before Sudden Storm Commencement (SSC). Key Points: Pre‐Magnetic Storm Signatures (PMS) on NmF2 were observed to be maximum at the equatorial ionosphereIonospheric Responses during PMS were observed to be similar to the effect of geomagnetic stormsThere is a need to consider a certain threshold of the aurora indices (AE, AL, and AU) in the definition of a geomagnetic quiet day [ABSTRACT FROM AUTHOR]

Current models of Titan's ionosphere have difficulties in explaining the observed electron density and/or temperature. In order to get new insights, we re‐analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science (RPWS) instrument. This is the first of two papers that present the new analysis method (current paper) and statistics on the whole data set. We suggest that between two and four electron populations are necessary to fit the data. Each population is defined by a potential, an electron density and an electron temperature and is easily visualized by a distinct peak in the second derivative of the electron current, which is physically related to the electron energy distribution function (Druyvesteyn method). The detected populations vary with solar illumination and altitude. We suggest that the four electron populations are due to photo‐ionization, magnetospheric particles, dusty plasma and electron emission from the probe boom, respectively. Key Points: The Cassini Langmuir probe dataset in Titan's ionosphere is re‐analyzed with a specific interest on the electron density and temperature2 to 4 cold electron populations with distinct potentials are observedElectron populations vary with altitude and solar illumination suggesting origins linked to solar photons, magnetospheric particles and dust [ABSTRACT FROM AUTHOR]

Inside the magnetosheath, the IBEX‐Hi energetic neutral atom (ENA) imager measures a distinct background count rate that is more than 10 times the typical heliospheric ENA emissions observed when IBEX is outside the magnetosheath. The source of this enhancement is magnetosheath ions of solar wind (SW) origin that deflect around the Earth's magnetopause (MP), scatter and neutralize from the anti‐sunward part of the IBEX‐Hi sunshade, and continue into the instrument as neutral atoms, behaving indistinguishably from ENAs emitted from distant plasma sources. While this background pollutes observations of outer heliospheric ENAs, it provides a clear signature of IBEX crossings over the magnetospheric boundaries. In this study, we investigate IBEX encounters with the magnetosheath boundaries using ∼8 yr of orbital data, and we determine the MP and bow shock (BS) locations derived from this background signal. We find 280 BS crossings from XGSE ∼ 11 Re to XGSE ∼ −36 Re and 241 MP crossings from XGSE ∼ 6 Re to XGSE ∼ −48 Re. We compare IBEX BS and MP crossing locations to those from IMP‐8, Geotail, Cluster, Magion‐4, ISEE, and Magnetospheric Multiscale Mission, and we find that IBEX crossing locations overlap with the BS and MP locations inferred from these other data sets. In this paper, we demonstrate how IBEX can be used to identify magnetosheath crossings, and extend boundary observations well past the terminator, thus further constraining future models of magnetosheath boundaries. Furthermore, we use the IBEX data set to show observational evidence of near‐Earth magnetotail squeezing during periods of strong interplanetary magnetic field By. Plain Language Summary: The Interstellar Boundary Explorer (IBEX) spacecraft is designed to use remote‐sensing to examine the outer reaches of the solar system, yet it has been shown to have many magnetospheric applications as well. The primary interaction between the SW and the Earth's magnetosphere is the creation of a comet‐tail like structure known as the magnetosheath. The magnetosheath is highly dynamic, and its size and shape changes in response to changing SW conditions, with the exact details presently unknown. In this paper, we demonstrate how the IBEX's highly eccentric orbit allows for hundreds of encounters with both the inner and outer magnetosheath boundaries, and we use these crossings to create a new magnetosheath boundary data set. We then compare our new data set with data sets from previous magnetospheric missions. Finally, we use our new data set to provide observational evidence for a poorly understood phenomenon known as magnetotail squeezing. Key Points: We demonstrate a technique for producing both Bow Shock and Magnetopause data sets using the Interstellar Boundary ExplorerWe introduce new boundary crossings further tailward than previously used data sets into underexplored magnetosheath regionsWe provide observational evidence of magnetotail squeezing during periods when the interplanetary magnetic field has a strong y‐component [ABSTRACT FROM AUTHOR]

Jupiter has a strong magnetic field, and a huge magnetosphere is formed through the solar wind-Jupiter interaction. The generated magnetosphere-ionosphere system is reproduced based on the 9-component Magnetohydrodynamics (MHD) and the current conservation in the ionosphere. Assuming Io plasma emission rate 1.4 t/sec, this paper reproduces self-consistently global magnetic configuration, generations of the field-aligned current (FAC) and aurora, formation of the Io plasma disk at 8-20 RJ, plasma corotation, instability in the plasma disk, transition from the Io plasma disk to the plasma sheet at 20-150 RJ, and the plasmoid ejection. The rotating Io plasma in the disk forms instabilities that promotes radial diffusion. H+ is supplied from the ionosphere along high-latitude magnetic field lines and mixed with heavy ions around 15-20 RJ. Beyond 20 RJ, mixed plasma diffuses further outward by the centrifugal force that can exceed magnetic tension. In the ionosphere, the main oval occurs at 13.7°-15.5° colatitude. The Io disk is inner side of magnetic field lines traced from the low-latitude edge of the main oval. Along magnetic field lines, the main oval is mapped from the outer edge of the Io disk to the entire plasma sheet accompanying rotation delay. Due to the corotation limit, convection is accompanied by plasmoid ejection. Back reaction of plasmoid ejection affects even transport process in the Io disk. The downward FAC occurs in the polar cap showing variability. The region of externally driven Dungey convection seems quite narrow. [ABSTRACT FROM AUTHOR]

We present the first observational determination of statistical limits on the rise of equatorial plasma bubbles as a function of solar flux. We analyzed in situ electron density data collected onboard the Communications/Navigations Outage Forecasting System (C/NOFS) satellite to characterize the distribution of peak altitudes of equatorial ionospheric plasma bubbles. We first describe our algorithm for detecting ionospheric irregularities within the observations and then use a series of statistical simulations to identify and compensate for the sampling biases inherent in observations from a single satellite in a low‐inclination elliptical orbit. The simulations also confirmed that space‐based orbital platforms such as the C/NOFS satellite undersample the existing irregularities in the ionosphere and provide a measure of the satellite's inefficiency in observing those naturally occurring irregularities. In deducing the variation of the peak‐height distributions of the irregularities with solar activity, we find that the median maximum height of the bubbles increases linearly from about 490 km at the solar minimum (2008) to 740 km during the (2014) solar maximum in the longitude sector 80°W–10°E. The results will be valuable for the development of improved scintillation mapping models for both real‐time and postprocessing applications. We also confirm our observational findings with modeling results from a physics‐based model, allowing us to identify field‐line‐integrated Pedersen conductance as the key determinant of terminal bubble altitude: a bubble will cease to rise further when the conductance inside the bubble is equal to that of the background ionosphere. Plain Language Summary: In this study, we take a new approach of data analysis in determining the peak heights at the magnetic equator, or the peak apex heights, of the equatorial ionospheric irregularities from the ion‐density observations made by a sensor onboard Communications/Navigations Outage Forecasting System (C/NOFS) satellite. The variation of these peak‐height distributions with solar activity is studied over the years of operation of C/NOFS mission (2008–2014). We use numerical simulations to confirm the approach used in determining the peak‐height distributions from the observed height distributions and, in the process, discovered that the efficiency of C/NOFS for detecting equatorial irregularities was less than 50% throughout the solar cycle. We find that the median maximum height of the equatorial ionospheric irregularities increases linearly from about 490 km at the solar minimum to 740 km during solar maximum in the longitude sector 80°W–10°E. The results will be valuable for the development of space‐weather forecasting models. We also confirm the observational findings presented in this paper with modeling results from a physics‐based model. In the model, we identify conductance as the key parameter controlling the peak heights of the equatorial irregularities. Key Points: Quantitative distributions of equatorial plasma bubble peak apex heights as a function of solar fluxField‐line‐integrated Pedersen conductance as the key determinant of terminal bubble altitude of the equatorial plasma bubbles using the physics‐based modelEstimation of the meridional extent of scintillation activity as a function of solar flux [ABSTRACT FROM AUTHOR]

The ionosphere exhibits enhanced semidiurnal lunitidal (M2) perturbations during sudden stratospheric warming (SSW) events, of which the manifestation and mechanism are not well documented and understood. This paper studies the latitudinal and inter‐hemispheric variations of the ionospheric M2 perturbations during the 2021 major Arctic SSW with total electron content (TEC) data in the American, Asian‐Australian, and African‐European sectors. Results show that the M2 perturbations in the three sectors all enhanced during the SSW, with the strongest M2 perturbations in the Northern and Southern Hemispheres at about 10°∼15°N and 25°∼30°S geomagnetic latitudes, respectively. Also, clear M2 perturbations in the three sectors all extended to middle latitudes during the SSW only in the Southern Hemisphere. Comparatively, the inter‐hemispheric asymmetry of the magnitude of the M2 perturbations during the SSW was more complex. The inter‐hemispheric asymmetry of the crest locations of the low‐latitude M2 perturbations in the three sectors during the SSW was probably due to the F‐region meridional wind effect on the diffusion process of the low‐latitude plasma fountain. Meanwhile, the longitudinal differences were also obvious. The TEC M2 amplitude in the American sector was obviously larger than those in the Asian‐Australian and African‐European sectors during the SSW. The M2 characteristics in the southern middle latitude in the American sector were significantly different from those in the other two sectors during the SSW, which may be related to the differences of the combined effects of the local wind and geomagnetic configuration. In addition, a moderate geomagnetic activity occurred during the 2021 SSW, which brings difficulties to the analysis of the SSW‐related TEC variation. Key Points: The latitudinal differences of the ionospheric semidiurnal lunitidal (M2) perturbations during the 2021 sudden stratospheric warming were studied with total electron contentThe low‐latitude M2 perturbations exhibited similar latitudinal and inter‐hemispheric variations in the American, Asian and African sectorsThe M2 perturbation in the southern middle latitude was obviously different in the American from those in the Asian and African sectors [ABSTRACT FROM AUTHOR]

This paper uses a regional simulation of plasma convective instability in the postsunset equatorial ionosphere together with a global atmosphere/ionosphere/plasmasphere GCM (WAM‐IPE) to forecast irregularities associated with equatorial spread F (ESF) for 1–2 hr after sunset. First, the regional simulation is initialized and forced using ionosphere state parameters derived from campaign data from the Jicamarca Radio Observatory and from empirical models. The irregularities produced by these simulations are found to be quantitatively similar to those observed. Next, the aforementioned state parameters are replaced with parameters from WAM‐IPE, and the resulting departures between the simulated and observed irregularities are noted. In one of five cases, the forecast failed to accurately predict ESF irregularities due to the late reversal of the zonal thermospheric winds. In four of five cases, significant differences between the observed and predicted prereversal enhancement (PRE) of the background vertical drifts resulted in degraded forecast accuracy. This highlights the need for improved PRE forecasting in the global‐scale model. Key Points: Equatorial ionospheric F‐region stability can be reproduced quantitatively using a regional data‐driven direct numerical simulation (DNS)DNS model runs become forecasts when initialized and driven with parameters from a comprehensive GCM such as Whole Atmosphere Model with Ionosphere, Plasmasphere, ElectrodynamicThe post‐sunset background vertical plasma drift and zonal thermospheric wind profile are the most critical forecast parameters [ABSTRACT FROM AUTHOR]

Based on the data of magnetic field and electronic density of SWARM, and Total Electron Content, this paper screened six typhoons that died out on the sea. We studied how typhoons affected the ionosphere when they died out without the influence of topography and other factors. The statistical results show that during the extinction of typhoons, the magnetic disturbances all appeared, and the electron density disturbances were observed in five typhoons. The frequency of the electronic density disturbance is slightly higher than the magnetic disturbance. The range of the electronic density disturbance is mostly five or six hundred kilometers and relatively concentrated. The range of the magnetic disturbance can reach about two thousand kilometers and is relatively scattered. Our results indicate that the extinction of typhoon may affect the ionosphere through acoustic gravity waves (AGWs). The AGWs is not generated by friction, but may be from the typhoon itself or a new phenomenon when the typhoon dies out. Key Points: Our statistics show that the extinction process of typhoon on the sea can cause ionospheric disturbanceThe amplitude of magnetic disturbance is more obvious than disturbance of electron densityThe magnetic disturbance and disturbance of electron density in ionosphere may be caused by acoustic gravity waves [ABSTRACT FROM AUTHOR]

The ionospheric variabilities are influenced by various drivers, and quantifying their relative contributions is beneficial to ionospheric modeling and ionospheric forecasting, but this is still a significant challenge in the ionospheric community. In present paper, the global ionosphere maps, solar indices, solar wind and interplanetary parameters, geomagnetic indices, and lower atmospheric parameters from 2001 to 2021 are collected, and the Liang‐Kleeman information flow is used to measure the amount of information exchanges from external drivers to ionospheric TEC at different geographical regions, and the normalized Liang‐Kleeman information flow is adopted to quantify their relative information contributions. The results show that the geographical distribution of information flow has prominent hemispheric asymmetry, and overall, the information flows from solar indices (solar wind and interplanetary parameters, geomagnetic indices) to ionospheric TEC in the northern hemisphere are larger than those in the southern hemisphere. Ionospheric self‐influence (i.e., internal processes of the ionosphere) has the largest information contribution to ionospheric TEC, accounting for about 46.78%. Solar activity manifested as P index has the second largest contribution (nearly 35.29%). Solar wind and interplanetary activity represented as IMF magnitude contributes around 2.94%, geomagnetic activity characterized as ASYH index accounts for about 1.52%, lower atmospheric forcing contributes nearly 7.75%, and noise accounts for approximately 5.73%. What's more, the performances of the IRI‐2020 model are evaluated from the perspective of information flow. Key Points: The Liang‐Kleeman information flow is used to measure the rates of information exchanges from external drivers to ionospheric TECThe geographical distribution of information flow shows a prominent hemispheric asymmetryIonospheric self‐influence has the largest information contribution to ionospheric TEC, followed by solar activity [ABSTRACT FROM AUTHOR]

Electron injections are critical processes associated with magnetospheric substorms, which deposit significant electron energy into the ionosphere. Although wave scattering of <10 keV electrons during injections has been well studied, the link between magnetotail electron injections and energetic (≥100 keV) electron precipitation remains elusive. Using conjugate observations between the Electron Loss and Fields Investigation (ELFIN) and Magnetospheric Multiscale (MMS) missions, we present evidence of tens to hundreds of keV electron precipitation to the ionosphere potentially driven by kinetic Alfvén waves (KAWs) associated with magnetotail electron injections and magnetic field gradients. Test particle simulations adapted to observations show that dipolarization‐front magnetic field gradients and associated ∇B drifts allow Doppler‐shifted Landau resonances between the injected electrons and KAWs, producing electron spatial scattering across the front which results in pitch‐angle decreases and subsequent precipitation. Test particle results show that such KAW‐driven precipitation can account for ELFIN observations below ∼300 keV. Plain Language Summary: Energetic electron precipitation from magnetospheric injections has a major impact on magnetosphere‐ionosphere coupling. This energy deposition is largely in the form of electron precipitation driven by wave‐particle interactions in the magnetotail. Although wave‐driven precipitation with energies less than approximately ∼10 keV has been studied extensively, the link between energetic electron precipitation (≥∼100 keV) and electron injections remains elusive. Combining observations and simulations, this paper provides evidence of such precipitation driven by kinetic Alfvén waves, which have been previously observed to be ubiquitously associated with magnetospheric electron injections but have not been considered as an important driver for precipitation of such electrons. Key Points: Conjugate Electron Loss and Fields Investigationand Magnetospheric Multiscale observations reveal evidence of tens to hundreds of keV electron precipitation associated with kinetic Alfvén wavesDipolarized magnetic field gradients and perpendicular magnetic drifts allow Landau resonance between waves and injected electronsAdiabatic transport and spatially varying E × B and grad‐B drifts induce perpendicular momentum scattering and electron losses [ABSTRACT FROM AUTHOR]

Ground‐based facilities make an important contribution to our understanding of the magnetospheric system. Coordination with ground‐based facilities has been embedded within the Cluster mission since before launch, and this has given rise to a large number of studies which have exploited data from both Cluster and one or more of the diverse range of ground‐based instrumentation that have been available during the mission timespan. In this paper, we review the advances that have been made to our understanding of the magnetosphere‐ionosphere system, in which insight has been enhanced by combining ground‐based observations with observations from Cluster. Topics covered span from the bow shock to the magnetotail and down to the aurora. Key Points: Space‐ and ground‐based measurements strongly complement each other, and combining the two further enhances the insight they provideStudies exploiting ground‐based observations have been a key aspect of the Cluster mission, yielding approximately 100 papersWe review these studies, covering the full range of solar wind/magnetosphere/ionosphere coupling and dynamics [ABSTRACT FROM AUTHOR]

Measurement of the dense cold thermal plasma in planetary ionospheres via orbiting spacecraft is challenging because ion energies are small (0–4 eV), densities can vary by four orders of magnitude, composition varies with altitude, spacecraft charging varies in time and must be measured very accurately, and instrumental effects (e.g., detector dead‐time and background) can be significant. The SupraThermal And Thermal Ion Composition instrument team has recently released a new set of data products that contain density moments of the primary ion species at Mars, including those derived at periapsis, subject to the full suite of calibration factors required. This article discusses the challenges associated with deriving these densities and provides examples of the key caveats that users of the data should be aware of. A preliminary statistical study of this new data set focuses on the structure and variability of Mars' ionosphere, demonstrating that solar zenith angle effects, the crustal magnetic fields, and electron precipitation on the nightside, drive the strongest structural features, consistent with photochemical theory and previous studies. Dayside ionospheric density profiles are highly repeatable below altitudes of 200 km, marking the region where photochemistry and collisions dominate. In the upper dayside ionosphere (altitudes >300–400 km) changes in the solar wind dynamic pressure on timescales of Mars Atmosphere and Volatile EvolutioN's orbit (hr) drive the largest (factors of 1–3) variability in ionospheric density. In contrast variability in ionospheric density peaks between 150 and 250 km altitude on the nightside (factors of 1–2), consistent with electron precipitation driving ionization in this region. Plain Language Summary: Making accurate measurements of the ions present in planetary atmospheres via orbiting spacecraft is difficult due to the large changes in conditions encountered throughout spacecraft orbits. This paper describes the techniques implemented to address the full array of difficulties associated with measuring planetary ions at Mars using measurements made by the SupraThermal And Thermal Ion Composition instrument. These techniques are used to calculate ion densities in Mars' atmosphere and we perform a preliminary investigation of this new data set, revealing several important characteristics of how ions behave in Mars' atmosphere. In particular, we find that on the dayside of the planet, there is a transition region between the upper and lower atmosphere where planetary ions behave differently. Above this transition region planetary ions are influenced by forces that arise in the space environment about Mars, while below this transition region, planetary ions are well shielded from these effects. Our results provide insight into the processes that shape Mars' atmosphere and tell us how energy is transported through the Mars system. Key Points: The calibration challenges and caveats of ion densities derived from SupraThermal And Thermal Ion Composition observations are discussedSolar zenith angle effects and the crustal magnetic fields drive the strongest structural features in ionospheric densityA variety of processes drive ionospheric variability throughout different regions of the Martian ionosphere [ABSTRACT FROM AUTHOR]

The ionosphere experiences strong diurnal and seasonal changes. The longitudinal variations of electron density (Ne) in the ionosphere at the middle latitudes also show strong diurnal and seasonal changes. In this paper, we use in situ Ne measurements from the DEMETER satellite and electron density profiles retrieved from the COSMIC data to study the local time (LT) and seasonal dependence of the longitudinal variations of topside Ne at middle latitudes during 2007–2009. With regard to the diurnal trend, the reversal phase of longitudinal peaks/valleys of topside Ne with a 12 hr interval occurred in less than half of the cases, and there were less cases with eastward phase shift of the longitudinal variations of topside Ne with LT in winter than those in other seasons. The seasonal trends of transition longitudes of topside Ne might be westward from winter to summer and eastward from summer to winter in the daytime and in the opposite direction at night in both hemispheres in some cases and sometimes they were located within 20° of longitude at 52°N in other cases. The longitudinal peaks/valleys of hmF2 and/or NmF2 and the longitudinal peaks/valleys of topside Ne were within 30° of longitude in most cases at all local times, in all seasons, and in both hemispheres. Exceptions to this were independent of season or LT. Key Points: Reversal phase of longitudinal peaks/valleys of topside Ne with a 12 hr interval occurred in less than half of the casesLess cases with eastern phase shift of longitudinal variations of topside Ne during a day in winter than those in other seasonsSeasonal trends of the transition longitudes of topside Ne in the daytime and at night were in the opposite direction in both hemispheres [ABSTRACT FROM AUTHOR]

The location of the polar cap boundary is typically determined by using low‐orbit satellite measurements in which the boundary is identified by its unique signature of a sharp decrease in energy and particle flux poleward of the auroral oval. In principle, this decrease in precipitating particles should appear as a concomitant sharp change in auroral luminosity. Based on a few events, Blanchard et al. (1995, https://doi.org/10.1029/94JA02631) suggested that a dramatic gradient in redline aurora may also be an indicator of the polar cap boundary. In recent years, advances in capabilities and the deployment of ground‐based all‐sky imagers have ushered in a new era of auroral measurements. Auroral imaging has moved well beyond the capabilities of the instrumentation in the previous study in terms of both spatial and temporal resolution. We now have access to decades of optical data from arrays spanning a huge spatial range, enabling a fresh examination of the relationship between redline aurora, particle precipitation, and the polar cap open closed boundary. In this study, we use data from the Defense Meteorological Satellite Program satellites in conjunction with the University of Calgary's Redline Emission Geospace Observatory (630.0 nm) data to assess the viability of automated detection of the 2‐dimensional polar cap boundary. Our results exhibit good agreement between the optical and particle polar cap boundary and suggest that a luminosity in redline emission could serve as a reasonable proxy for the location of the electron poleward boundary, while providing both high temporal and spatial resolution maps of the open‐closed boundary. Plain Language Summary: Named for its shape, the auroral oval is an oval‐shaped region located near the north and south poles where the aurora is formed. Studying the location of the equatorward and poleward limits of the auroral oval is fundamental to evaluate the dynamics and responses of the near‐Earth space environment. In particular, the poleward boundary corresponds to a region in which Earth's magnetic field transitions from closed (connected to Earth on both sides) to open field lines (connected to the solar wind on one side); because of this topological change in magnetic field, the location of this boundary is fundamental to understand mass and energy transport in the whole magnetosphere‐ionosphere system. While satellite data can determine the exact location of this boundary, they only provide point measurements. Auroral images are capable of detecting the luminosity around this boundary; however, many qualitative studies consider the region immediately poleward of this luminosity as the oval's poleward boundary. In this paper, we analyze the location of this boundary in a case study by using satellite data combined with auroral imaging data. Key Points: Polar cap boundary determined with Defense Meteorological Satellite Program particle data allows for examination of the boundary in optical redline dataWe find good agreement between the auroral boundary determined by auroral luminosity and those determined by particle fluxLuminosity method can be applied during active geomagnetic conditions, providing high spatial and temporal resolution polar cap boundary [ABSTRACT FROM AUTHOR]

Small‐scale magnetic structures have been observed in the induced Martian ionosphere by magnetometers onboard the Mars Global Surveyor (MGS) and the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. The origin and evolution of these structures remain poorly understood and the goal of the current paper is to better characterize them and their distribution in the dayside ionosphere using Mars Atmosphere and Volatile EvolutioN (MAVEN) data. Mars Atmosphere and Volatile EvolutioN (MAVEN) Langmuir probe data is used to find thermal pressures in the ionosphere. The structures studied range in size from about 20 km up to a couple of hundred km. We constrain our investigation to the northern hemisphere, dayside Martian ionosphere in order to minimize crustal magnetic field interference. Magnetic pressure spikes (and/or field component variations), along with thermal pressure behavior can also sometimes characterize small‐scale structures. In addition to pressures and field components, minimum variance analyses are carried out for each structure in order to help classify them (e.g., horizontal slabs, ionopause‐like structures, flux tube and flux ropes). A "statistical" catalog of properties (pressure, field amplitude, ellipticity, width, etc.) is generated for about 1,000 structures. One conclusion we reached from this survey is that slab‐like features are more likely to be found than rope‐like features for altitudes above 250 km. Key Points: The magnetic barrier connection to the lower ionosphere is exploredWe characterize and examine the evolution of small‐scale magnetic structureMars Atmospheric and Volatile EvolutionN (MAVEN) data is analyzed for magnetic and thermal structure [ABSTRACT FROM AUTHOR]

In 27 October 2012 an Alfvén wave of the Pc4 range was observed with Van Allen Probe A. The parallel Poynting flux of the wave was directed toward the Northern ionosphere. Assuming that this may be caused by the asymmetry of the ionospheric conductivity between the Northern and Southern hemispheres, its effect on the standing structure of the Alfvén wave was investigated. For this purpose, the analytical model with straight magnetic field lines was used. As a result, the method for estimation of the Northern and Southern ionospheric conductivity was developed. It allows to reconstruct the parallel structure of Alfvén waves under various conditions of the ionospheric conductivity. With the method developed, the ionospheric conductivity for the 27 October 2012 event was evaluated and compared with ionosphere model IRI‐2016 results. Plain Language Summary: The most commonly observed ultra low frequency waves in the magnetosphere are Alfvén waves standing along a magnetic field line between magnetically conjugated points of the ionosphere located in opposite hemispheres. In this paper, we considered how the north‐south asymmetry of the ionospheric conductivity influences standing Alfvén wave's parallel structure. The model predicts that the structure of the Alfvén waves may differ depending on the conductivity values of the Northern and Southern ionospheres. Based on the model we developed a method of a qualitative estimation of the ionospheric height‐integrated Pedersen conductivity. The method is used parameters of Alfvén waves observed with spacecraft in the magnetosphere. As a result, for the 27 October 2012 event the parallel structure of the observed Alfvén wave was reconstructed, and the ionospheric conductivity was estimated. We found a significant difference in the conductivity values of the Northern and Southern ionospheres. The mean is that the magnetically conjugated footprints of the spacecraft trajectory, where the event was observed, were located on the opposite sides of the terminator line (a line dividing day and night sides of a planet). Key Points: A method for estimating the ionospheric conductivity based on spacecraft observations of Alfvén waves in the magnetosphere is proposedThe parallel structure of an Alfvén wave under various conditions of the ionospheric conductivity is reconstructedThe height‐integrated Pedersen conductivity of the ionosphere were estimated for the 27 October 2012 event [ABSTRACT FROM AUTHOR]

Dusty plasma is generally defined as a plasma system containing a large number of nano‐ or micron‐sized dust particles. Its plasma properties and propagation properties of wave travel through it is of great scientific significance to the understanding of many fundamental problems in space physics and astrophysics. Based on previous studies on rocket exhaust and Polar Mesosphere Summer Echoes, fluid mechanics and dust microphysics are combined to simulate the ionospheric plasma structure generated by neutral gases and charged aerosols using fluid theory and kinetic theory. The Total Electron Content of the in‐situ detection beacon is simulated and compared with the experimental phenomenon given in Charged Aerosol Release Experiment by Bernhardt et al. The ray tracing algorithm is used to simulate the path deflection of the radio wave when it passes through the artificial disturbance area generated by the gas‐solid mixture, and the simulation results of ionosonde and analysis are given. Since the neutral gas expands substantially isotropically after being released, the resulting depleted structure is an approximately isotropic sphere, or an acorn‐like structure. The solid particles are constrained by the nozzle, and particles will distribute within a spray angle, and the depletion structure will appear as a "broom‐like" or "cone‐like" structure. If the size of dust particles is small enough, the particle movement will be restricted by the geomagnetic field, resulting in a "squid‐like" ionospheric structure. Because of the fishtail‐like sharp boundary, radio waves passing through it are deflected in a specific path, which is markedly different from the effect of pure neutral gas injected into the ionosphere. Plain Language Summary: Many studies have focused on ionospheric disturbances caused by natural dust of polar mesospheric clouds or by ionospheric pollutants. However, practical physical scenarios usually have both neutral gases and charged aerosols, whose total contribution to the plasma after injection into the ionosphere and wave propagation through the disturbance have rarely been studied. In this paper, the fluid theory and kinetic theory are used to simulate the ionospheric plasma disturbance structure by combining the fluid mechanics and the dust microphysics. The Total Electron Content of the in‐situ detection, the path of radio waves through the disturbance and the vertical ionogram produced by the injection of neutral gas and dust particles are also simulated. Key Points: An analytic solution model of the ionospheric disturbance produced by artificial neutral gas‐dust particles mixture injection is establishedThe motion of charged dust particles and evolution of ionospheric depletion caused by mixture injection are simulatedThe perturbed Total Electron Content and the path deflection of radio wave passing through the disturbance region are simulated and analyzed [ABSTRACT FROM AUTHOR]

The effect of radial interplanetary magnetic field (IMF BX ${\mathrm{B}}_{\mathrm{X}}$) has been ignored in the solar wind‐magnetosphere‐ionosphere (S‐M‐I) coupling. We present a statistical study of IMF Bx effects on the Heppner‐Maynard Boundary (HMB) midnight latitude calculated from SuperDARN measurements between January 2002 and December 2017. The HMB represents the equatorward extent of the ionospheric convection pattern and can be used as a proxy for the equatorward boundary of the auroral oval. That is, the HMB expands toward lower latitude when the level of S‐M‐I coupling is enhanced. It is found that the averaged HMB midnight latitudes during both sunward and antisunward radial IMFs are around 64–65° magnetic latitude (MLAT). HMB midnight latitude is negatively correlated with the magnitude of IMF Bx as well as solar wind speed, while no significant trend is found between HMB midnight latitude and IMF Bz or By during radial IMF. For antisunward radial IMF, the relationship between upstream parameters and HMB is more dependent than in sunward radial direction. As the first long‐term statistical study focused on HMB during radial IMF conditions, this work provides observational evidence that the IMF Bx plays an important role in the coupling process and the traditional coupling function could not be applicable in the case of radial IMF. Plain Language Summary: The magnetic reconnection between solar wind and magnetosphere can drive a convection structure in the high‐latitude ionosphere. Heppner and Maynard developed a method to calculate the equatorward boundary of the ionospheric convection, which is called Heppner‐Maynard Boundary (HMB). HMB could be used as the monitor of the interaction process between the solar wind and geomagnetic field. In this paper, we report the effects of the radial (sunward or antisunward) interplanetary magnetic field (IMF) on HMB in the northern hemisphere. For normal cases, the Bz component o IMF is the most important. But our statistical results indicate that there is a decreasing trend between the strength of IMF Bx and HMB latitudes at midnight. No significant trend is found between HMB midnight latitude and IMF Bz or By during radial IMF. Moreover, the results provide observational evidence the Bx term should be considered in the coupling function during radial IMF. Key Points: The HMB midnight latitude has a negative trend on the IMF Bx, especially for negative IMF BxThe averaged values of HMB during radial IMFs are larger than those for substorm periods and a long‐term period of 17 yearsThe traditional coupling function may not be applicable in the case of radial IMF [ABSTRACT FROM AUTHOR]

In this paper, we present a case study of the radial interplanetary magnetic field (IMF Bx)‐induced asymmetric solar wind‐magnetosphere‐ionosphere (SW‐M‐I) coupling between the northern and southern polar caps using ground‐based and satellite‐based data. Under prolonged conditions of strong earthward IMF on 5 March 2015, we find significant discrepancies between polar cap north (PCN) and polar cap south (PCS) magnetic indices with a negative bay‐like change in the PCN and a positive bay‐like change in the PCS. The difference between these indices (PCN‐PCS) reaches a minimum of −1.63 mV/m, which is approximately three times higher in absolute value than the values for most of the time on this day (within ±0.5 mV/m). The high‐latitude plasma convection also shows an asymmetric feature such that there exists an additional convection cell near the noon sector in the northern polar cap, but not in the southern polar cap. Meanwhile, negative bays in the north‐south component of ground magnetic field perturbations (less than 50 nT) observed in the nightside auroral region of the Northern Hemisphere are accompanied with the brightening and widening of the nightside auroral oval in the Southern Hemisphere, implying a weak, but clear energy transfer to the nightside ionosphere of both hemispheres. After the hemispheric asymmetries in the polar caps disappear, a substorm onset takes place. All these observations indicate that IMF Bx‐induced single lobe reconnection that occurred in the Northern Hemisphere plays an important role in hemispheric asymmetry in the energy transfer from the solar wind to the polar cap through the magnetosphere. Key Points: Hemispheric asymmetries in magnetic activity and ionospheric convection in the polar cap are observed under strong interplanetary magnetic field (IMF) Bx conditionsWeak, but clear energy transfer to the nightside auroral region is observed in both hemispheres during the same periodIMF Bx‐induced single lobe reconnection may give rise to hemispheric asymmetry in SW‐M‐I coupling in the polar cap [ABSTRACT FROM AUTHOR]

The ionospheric scale height is a key parameter that defines the shape of the electron density profile. Given that its direct calculation requires knowledge of the physical and chemical state of the plasma, the concept of the effective scale height was proposed to facilitate its application. It is defined as the scale height that fits the electron density profiles with the α‐Chapman function. Its main characteristics, including the diurnal and altitudinal variation are still under investigation. This paper focuses on the specification of its key characteristics at middle latitudes based on coincident Digisonde and Swarm A satellite data. Based on the assumption that the topside electron density profile is approximated with the α‐Chapman model of variable scale height, the effective scale height at the Swarm A altitude is calculated and compared with the effective scale height at hmF2 $hmF2$. A general conclusion is that the topside effective scale height at ∼450 km exhibits a diurnal variation with highest values in the early morning and evening sectors, while at hmF2 $hmF2$ it gets its maximum values at noon. At night, the effective scale height tends to increase with altitude, however in the daytime, its behavior is more complex. On a local scale, evidence for connection between spread F irregularities and high variability in the topside effective scale height is reported. These preliminary results indicate the potential to further exploit Swarm and Digisonde data for the development of a model for the effective scale height, able to support realistic electron density reconstruction models. Key Points: A clear diurnal pattern is identified in the topside effective scale height with peak values in the early morning and evening sectorsAt night, the topside effective scale height tends to increase with altitude, while in the daytime its altitudinal dependence is complexEvidence for connection between spread F irregularities and high variability in the topside effective scale height is reported [ABSTRACT FROM AUTHOR]

Newly built Jiamusi (JME) radar and Hokkaido East (HOK) radar data reveal statistical features of the mid-latitude ionospheric irregularities during quiet times. In this paper, the distribution features and seasonal variations of the scattering occurrence rate and convection velocity of the ionospheric, F-region irregularities between 45°N and 60°N magnetic latitude (MLAT) during geomagnetic quiet times are studied by using one-year observation data from the JME radar and HOK radar. The results show that the scattering occurrence rate is strongest in summer and weakest in winter in this region, and the highest value always appears on the dusk side, especially in summer and the equinox. Line-of-sight (LOS) velocity also shows significant seasonal variation. It is stronger in winter and the equinox than in summer, which is in good agreement with previously reported observations from six midlatitude Super Dual Auroral Radar Network radars in the North American sector. An interesting new finding is that on the night side, LOS velocity decreases first and then increases as the MLAT increases from 45°N to 56°N, particularly in summer and the equinox. This implies that there is a velocity reversal region during the geomagnetic quiet time in regard to night side, mid-latitude, ionospheric convection. Plain Language Summary The distribution features and seasonal variations of the scattering occurrence rate and convection velocity of the F-region irregularities between 45° to 56° magnetic latitude during the geomagnetically quiet time are studied by using one-year observation data from the Jimausi radar and the Hokkaido East radar. [ABSTRACT FROM AUTHOR]

This paper reports the characteristics of the topside ionospheric O+ diffusive flux (ΦO+) during both geomagnetically quiet (0 ≤ Kp ≤ 2) and moderate (2 < Kp ≤ 4) times using incoherent scatter radar observations at Millstone Hill (42.6°N, 288.5°E) for solar minimum from 1970 to 2018. ΦO+ partially characterizes plasma mass exchange between the upper and lower part of the topside ionosphere through diffusion and sometimes serves as upper boundary conditions for ionosphere‐thermosphere models. The altitude where the flux sign changes (mainly during daytime) is termed the transition height and the time when the flux sign changes (mainly at dawn and dusk) is termed the transition time. At quiet times, the daytime transition height is ∼100 km above the F2 peak height (hmF2) in summer, and it is about 50 km above hmF2 in other seasons; the transition time is before 18 solar local time (SLT) in spring and winter, but after 18 SLT in summer and autumn. The daytime average upward ΦO+ above the transition height shows a significant seasonal variation with a minimum of 2.2×108cm−2s−1 in summer and a maximum of 3.7×108cm−2s−1 in autumn. Under geomagnetically moderate conditions, the transition height increases by ∼20 km in spring, winter, and autumn, but moves up by about 20–50 km in summer. The transition time occurs later by ∼1 hr in summer but ∼1 hr earlier in other seasons. The mean upward ΦO+ peaks in summer and minimizes in spring. Plain Language Summary: The topside ionospheric O+ diffusive flux (ΦO+) is a part of the total plasma flux that is a critical parameter to characterize the plasma exchange between the upper and lower part of the topside ionosphere, but has been poorly known due to lack of direct measurements. Using long‐term incoherent scatter radar (ISR) data observed at Millstone Hill for nearly five decades, this study investigates ΦO+ variations as a function of the altitude above the F2 peak height (hmF2), local time, and season in both geomagnetically quiet and moderate times, and further explores the physical mechanism causing these variations. During quiet times, the summer daytime transition height where ΦO+ changes from downward to upward along magnetic field lines occurs at ∼hmF2+100 km. However, it is usually near hmF2+50 km in other seasons. In addition, the transition time when ΦO+ changes from upward to downward at a fixed height is earlier than 18 SLT in spring and winter, but later than 18 SLT in summer and autumn. We also found that an increase in geomagnetic activity decreases the vertical gradient of plasma density during the daytime in all seasons, resulting in a ∼20 km increase in the transition height and an earlier transition time near dusk in spring, autumn, and winter, but a larger transition height change of about 20–50 km and a later transition time in summer. The change in the seasonal variations of the upward ΦO+ results from the competition between the variations of plasma diffusive velocity and density when the geomagnetic activity increases, as well as the changes in plasma vertical density profiles. Key Points: Topside ionospheric O+ diffusive flux (ΦO+) climatology at solar minimum is derived from incoherent scatter radar data at Millstone HillO+ diffusive flux has seasonal, local time, and altitude dependenceGeomagnetic activity changes the spatiotemporal variations of Φ(O+) by modulating the vertical gradient of the plasma density [ABSTRACT FROM AUTHOR]

Computerized ionospheric tomography (CIT) based on Global Navigation Satellite System (GNSS) data is a worthwhile project. However, predominant issues like unevenly distributed stations, lack of data, and high‐elevation GNSS signals could affect the precise information about the ionosphere. To address this problem, many previous studies were mainly improving tomographic algorithms, rather than incorporating multisource data such as data from rapidly developed upcoming Low‐Earth‐Orbit (LEO) satellites. In this paper, the potential improvements of GNSS‐based ionospheric tomography at a global scale by combining the upcoming LEO constellations is investigated. On this basis, some numerical experiments were conducted to evaluate the performances of LEO‐augmented GNSS ionospheric tomography. Specifically, the slant total electron contents (STEC) required for ionospheric tomography from ground receivers to GNSS (including GPS, GLONASS, BDS, and Galileo) and LEO satellites are simulated by the international reference ionosphere (IRI‐2016) model during low and high solar activity in 2018 and 2014, respectively. The simulated STEC values from single‐, double‐ and quad systems of GNSS constellations were first used for ionospheric tomography. Afterward, the GNSS‐based STEC values were combined with the LEO‐based simulated STEC values. The STEC values directly derived from the IRI‐2016 model that have not been used in ionospheric tomography were used as independent references. The results showed that the GNSS + LEO solutions outperform the GNSS‐only solutions overall, the STEC values obtained by GNSS + LEO solutions are more consistent with the STEC references during both high and low years of solar activity. In comparison with the STEC references, the RMS values of the CIT‐derived STEC for GNSS‐only solutions can be decreased by 15% and 20.3% at most during low and high years of solar activity, respectively. Key Points: A method of Global Navigation Satellite System (GNSS)‐based ionospheric tomography augmented by Low‐Earth‐Orbit (LEO) satellite constellations is proposedObservations of multi‐GNSS and 192 LEO satellites are simulated for three‐dimensional ionospheric electron density reconstructionCombining LEO satellite constellations improves GNSS‐only ionospheric tomographic results [ABSTRACT FROM AUTHOR]

The Ionospheric Data Assimilation Four‐Dimensional (IDA4D) technique has been coupled to Sami3, which is another model of the ionosphere (SAMI3). In this application, ground‐based and space‐based GPS total electron content (TEC) data have been assimilated into SAMI3, while in‐situ electron densities, autoscaled ionosonde NmF2, and reference GPS stations have been used for validation. IDA4D/SAMI3 shows that night‐time ionospheric localized enhancements (NILE) are formed following geomagnetic storms in November 2003 and August 2018. The NILE phenomenon appears as a moderate, longitudinally extended enhancement of NmF2 at 30°–40°N MLAT, occurring in the late evening (20–24 LT) following much larger enhancements of the equatorial anomaly crests in the main phase of the storms. The NILE appears to be caused by upward and northward plasma transport around the dusk terminator, which is consistent with eastward polarization electric fields. Independent validation confirms the presence of the NILE, and indicates that IDA4D is effective in correcting random errors and systematic biases in SAMI3. In all cases, biases and root‐mean‐square errors are reduced by the data assimilation, typically by a factor of 2 or more. During the most severe part of the November 2003 storm, the uncorrected ionospheric error on a GPS 3D position at 1LSU (Louisiana) is estimated to exceed 34 m. The IDA4D/SAMI3 specification is effective in correcting this down to 10 m. Plain Language Summary: Geomagnetic storms have important effects on signals of different frequencies, including GPS and HF, because they modify the ionosphere. This paper presents a new data assimilation modeling technique for specifying the ionospheric response to geomagnetic storms, and highlights poorly understood aspects of these events. One such feature is a localized night‐time enhancement of the ionosphere that occurs at midlatitudes. The new technique provides major improvements in terms of correcting GPS position estimates and maximum usable frequencies in the HF band. Key Points: The IDA4D data assimilation scheme has been coupled to the SAMI3 ionospheric modelIDA4D/SAMI3 shows night‐time ionospheric localized enhancements (NILE) at midlatitudes after stormsFormation of the NILE appears to be caused by upward/northward plasma transport near the dusk terminator [ABSTRACT FROM AUTHOR]

Medium‐scale traveling ionospheric disturbances (MSTIDs) are a phenomenon widely and frequently observed over the ionosphere from high to low latitudes. Night time MSTIDs are caused generally by the polarization electric field in the ionosphere. However, propagation of this polarization electric field to the magnetosphere has not yet been identified. Here, we report the first observation of the polarization electric field and associated density variations of a night time MSTID in the magnetosphere. The MSTID event was observed by an all‐sky airglow imager at Gakona (geographical latitude: 62.39°N, geographical longitude: 214.78°E, magnetic latitude: 63.20°N), Alaska. The Arase satellite passed over the MSTID in the inner magnetosphere at 0530–0800 UT (2030–2300 LT) on November 3, 2018. This MSTID, observed in 630 nm airglow images, was propagating westward with a horizontal wavelength of ∼165 km, a north–south phase front, and a phase velocity of ∼80 m/s. The Arase satellite footprint on the ionosphere crossed the MSTID in the direction nearly perpendicular to the MSTID phase fronts. The electric field and electron density observed by the Arase satellite showed periodic variation associated with the MSTID structure with amplitudes of ∼2 mV/m and ∼150 cm−3, respectively. The electric field variations projected to the ionosphere are mainly in the east‐west direction and are consistent with the direction of the polarization electric field expected from MSTID growth by E × B drift. This observation indicates that the polarization electric field associated with the MSTID in the ionosphere is projected onto the magnetosphere, causing plasma density fluctuations in the magnetosphere. Plain Language Summary: Medium‐scale traveling ionospheric disturbances (MSTIDs) are propagation of electron density fluctuation in the ionospheric F‐layer. MSTIDs are a common phenomenon from high to low latitudes. From simultaneous observations of airglow imagers in both hemispheres, MSTIDs are known to have a mirror structure at magnetic conjugate hemispheres. If an MSTID is generated by ionospheric instabilities, the polarization electric field associated with the MSTID should propagate along the magnetic field lines. In this paper, we report the first simultaneous observation of an MSTID using a ground‐based airglow imager and the Arase satellite in the magnetosphere. The electric field variations and plasma density fluctuations observed by Arase showed periodic variations associated with the MSTID structure. This result indicates that the spatial inhomogeneity of the ionospheric Pedersen conductivity associated with the MSTID yields the polarization electric field in the ionosphere, and that this polarization electric field was projected onto the magnetosphere. Key Points: First simultaneous observation of an medium‐scale traveling ionospheric disturbance (MSTID) using a ground‐based airglow imager and the Arase satellite in the magnetosphereThe polarization electric field associated with the MSTID in the ionosphere was projected to the magnetosphere and observed by AraseThe electric field and electron density observed by the Arase satellite showed a periodic variation associated with the MSTID structure [ABSTRACT FROM AUTHOR]

Trans‐ionospheric high frequency (HF: 3–30 MHz) signals experience strong attenuation following a solar flare‐driven sudden ionospheric disturbance (SID). Solar flare‐driven HF absorption, referred to as short‐wave fadeout, is a well‐known impact of SIDs, but the initial Doppler frequency shift phenomena, also known as "Doppler flash" in the traveling radio wave is not well understood. This study seeks to advance our understanding of the initial impacts of solar flare‐driven SID using a physics‐based whole atmosphere model for a specific solar flare event. First, we demonstrate that the Doppler flash phenomenon observed by Super Dual Auroral Radar Network (SuperDARN) radars can be successfully reproduced using first‐principles based modeling. The output from the simulation is validated against SuperDARN line‐of‐sight Doppler velocity measurements. We then examine which region of the ionosphere, D, E, or F, makes the largest contribution to the Doppler flash. We also consider the relative contribution of change in refractive index through the ionospheric layers versus lowered reflection height. We find: (a) the model is able to reproduce radar observations with an root‐median‐squared‐error and a mean percentage error (δ) of 3.72 m/s and 0.67%, respectively; (b) the F‐region is the most significant contributor to the total Doppler flash (∼48%), 30% of which is contributed by the change in F‐region's refractive index, while the other ∼18% is due to change in ray reflection height. Our analysis shows lowering of the F‐region's ray reflection point is a secondary driver compared to the change in refractive index. Plain Language Summary: Sudden eruption of electromagnetic radiation from the Sun, also known as a solar flares, alters the physical properties of the ionosphere, creating ionospheric perturbations, commonly referred to as a sudden ionospheric disturbance (SID). The ionosphere perturbation following a solar flare disrupts the over the horizon radio communication channels on the dayside of the Earth, also known as shortwave fadeout. The ionospheric radio wave absorption effect during a solar flare‐driven SID is a well known and understood phenomena. However, the initial Doppler frequency shift, also known as "Doppler flash," in the traveling radio wave is a newly discovered phenomena and not yet fully understood. This paper seeks to advance our understanding of the initial impacts of solar flares on the ionospheric properties. Key Points: Doppler flash is predominantly driven by changes in ionospheric refractive indexThe F‐region ionosphere contributes significantly to the Doppler flashLowering of the F‐region reflection height is due to the flare‐driven weakening of upward ion‐drift [ABSTRACT FROM AUTHOR]

Few observations investigated the interaction between an electrical medium‐scale traveling ionospheric disturbance (EMSTID) and an equatorial plasma bubble (EPB). This paper presents another interaction between a southwestward propagating EMSTID and an eastward drifting EPB in the equatorial ionization anomaly (EIA) crest region of China. When the EMSTID and the EPB touched each other, several depletions of the EMSTID (EPB) showed the eastward (westward) velocity disturbances of the EPB (EMSTID) depletions. Besides, phase elongations of the EPB depletions contrarotated as the EMSTID propagated southwestward. However, of important finding is that the interaction of the EMSTID and the EPB could have polarized one depletion of the postmidnight EPB that should have become a fossilized bubble. Inside that polarized EPB depletion were meter‐scale irregularities that caused activated radar echoes and enhanced ranged spread F (RSF). The interaction occurred in descending ionosphere and the lower density regions got filled up with an enhanced density plasma. We propose that the EMSTID and the EPB could have electrically coupled with each other, causing an enhanced polarization electric field (PEF) that polarized that EPB depletion; the E × B gradient drift instability (Kelley, 1989) could have caused the meter‐scale irregularities when that enhanced PEF was imposed on that reactivated EPB depletion surrounded by that enhanced density plasma. This study provides observational evidence that how an electrical couple of EMSTID and EPB events can activate a postmidnight EPB depletion that should become a fossilized structure. Plain Language Summary: Otsuka et al. (2012, https://doi.org/10.1029/2012GL052286) provided the first report indicating the disappearance of an equatorial plasma bubble (EPB) airglow depletion after interaction with an electrical medium‐scale traveling ionospheric disturbance (EMSTID) airglow enhancement. For comparison, the current study reports a postmidnight airglow event in which an electrical coupling of an EMSTID and an EPB could have polarized one EPB airglow depletion that caused the activated radar echoes of very high frequency (VHF) radar and the enhanced ranged spread F (RSF) in descending ionosphere filled with an enhanced density plasma. Key Points: Interaction between an electrical medium‐scale traveling ionospheric disturbance (EMSTID) and an equatorial plasma bubble (EPB) in the equatorial ionization anomaly (EIA) crest region over ChinaElectrical coupling of the EMSTID and the EPB polarized one EPB depletion that caused activated radar echoes and enhanced ranged spread F (RSF)The interaction occurred in descending ionosphere and the lower density regions got filled up with an enhanced density plasma [ABSTRACT FROM AUTHOR]

Accurate representation of ensemble members of coupled Ionosphere‐Thermosphere (I‐T) is crucial to the ionosphere forecast in the ensemble Kalman filter (EnKF) data assimilation system. In this paper, besides the model drivers used in previous studies, including the solar 10.7 cm radio flux (F10.7), auroral hemispheric power (HP) and cross‐tail potential drop (CP), the eddy diffusion coefficient (ED), and nighttime vertical O+ flux at the top boundary are also perturbed to generate ensemble members. Based on our developed EnKF data assimilation system, the impact of perturbing different model external forcing parameters on ensemble generation and forecast capability of ionosphere and thermosphere has been investigated in detail through a series of sensitivity tests and data assimilation experiments. This system uses the National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) as a background model. The findings are summarized as follows: (a) Associated with perturbing two additional model forcing parameters, better ensemble members of ionosphere and thermosphere states of the background model can be generated during both daytime and nighttime. (b) The improvement of the forecast capability of the ionosphere and thermosphere variables can be further enhanced. This study can provide a reference for ensemble generating strategy for the coupled I‐T EnKF data assimilation in the future. Plain Language Summary: The ensemble member of EnKF data assimilation considering as much as possible variabilities existed in the coupled I‐T system should represent model uncertainties better. In the previous researches on EnKF ionosphere forecast, ensemble members are mainly generated by perturbing solar and geomagnetic activity index common model drivers (e.g., F10.7, KP). However, solely perturbing those indices is not sufficient to distribute the ionosphere and thermosphere states at all local times. In this study, in addition to perturbing those indices, the key model forcing parameters of the lower and upper boundary of the TIEGCM are also perturbed to generate the ensemble member of the coupled I‐T system. We found that an improved ensemble spread can be obtained at all local times in this way, which can further contribute to the forecast capability of the ionosphere and thermosphere states. Key Points: The eddy diffusion and upper boundary are additionally perturbed to generate ensembles in EnKF I‐T assimilation systemEnsemble members can be better obtained at no matter daytime or nighttimeThe forecasting capability of I‐T states can be further improved [ABSTRACT FROM AUTHOR]

Results from a dynamo electric field model are presented to examine the consistency of the widely used empirical models of low‐latitude plasma drifts and thermospheric neutral winds. The sector defined by the Jicamarca Radar measured plasma drifts is used due to the greater certainty of the empirical vertical plasma drifts. The plasma drifts produced by the Horizontal Wind Model (HWM) in a coupled ionosphere‐electric field model for geomagnetically quiet and moderate solar conditions are compared against empirical models of equatorial plasma drifts for the Peruvian sector. The HWM generates reasonable sunset prereversal enhancement of the vertical drift in all but May, June, July, and August when no prereversal enhancement exists in the empirical results. The daytime vertical drifts are deficient during all seasons. A solar diurnal and semi‐diurnal tidal forcing are required in the E region (100–150 km) to bring the HWM into better agreement as a dynamo driver for the daytime electric fields associated with the broad Solar Quiet current system. Plain Language Summary: Empirical models of the thermosphere neutral winds and of the plasma drifts are used in physics‐based models of the ionosphere to obtain reasonable day‐to‐day variations of the ionosphere through season and solar cycle. This paper examines the consistency of these empirical models by solving for the plasma drifts generated by empirical thermosphere neutral winds in a physics‐based model of the ionosphere and dynamo electric fields. We demonstrate the current inconsistency of the empirical wind model as a dynamo driver for obtaining the empirical low‐latitude plasma drifts. We provide future directions of for changes to the thermosphere neutral tidal winds within the empirical wind model to bring the two empirical models of winds and plasma drifts into better agreement for daytime winds and plasma drifts. Key Points: A survey of low‐latitude plasma drifts produced by the Horizontal Wind Model (HWM) and a dynamo electric field model in the Peruvian sectorA stronger diurnal solar‐driven neutral tide is required within the HWM to reproduce empirical vertical plasma driftsEquatorial zonal winds should be adjusted to improve zonal plasma drifts and the prereversal enhancement of May through August [ABSTRACT FROM AUTHOR]

Alfvén mode Pc1 waves undergo mode conversion to the fast mode due to induced Hall current in the ionosphere. The fast mode Pc1 waves are trapped and propagate across the magnetic field through the ionospheric waveguide. This process is called Pc1 wave ducting (PWD). Ducting is expected to be in any direction, but most of the existing literature investigated only PWDs toward the equator. In this paper, we report the rare observations of PWD propagating from sub-auroral latitudes and pervading the polar cap using Swarm satellites, ground magnetometers, and Defense Meteorological Satellite Program (DMSP) satellites. We first identify the injection region of Pc1 wave where localized broadband transverse waves, isolated aurora, and energetic proton precipitations are concurrently observed. Then, we compare ducting characteristics in the ionosphere between the two hemispheres. For the three events investigated here, PWDs in the Southern Hemisphere (SH) pervaded the polar cap while Pc1 waves in the Northern Hemisphere (NH) did not. This hemispheric asymmetry is attributed to the plasma density in the SH sufficient to form the Pc1 waveguide. However, a sharp plasma density gradient on the propagation path still interrupts the ducting even in higher plasma density (105cm-3) regions. The observation of two intersecting Swarm satellites indicates the PWD is not only elongated meridionally, but also can have a significant zonal extent beyond that of the injection region. [ABSTRACT FROM AUTHOR]

During the magnetic storm starting on September 7, 2017, the MEP‐i instrument onboard the Arase (ERG) satellite observed molecular ions (O2+/NO+/N2+) in the ring current. The molecular ions were observed by Arase in four orbits during this magnetic storm. This indicates that there was a continuous molecular ion supply from the ionosphere. During the storm main phase around the second Dst minimum (∼−100 nT) on September 8, 2017, the European Incoherent Scatter (EISCAT) radar observed the ion upflow (∼50–150 m s−1) in the low‐altitude (250–350 km) ionosphere together with strong ion heating up to >2,000 K. The convective electric field derived from the electron heating observed by EISCAT at an altitude of approximately 110 km was also enhanced by a factor of 2. The observations suggest that the additional ion heating at low altitudes helps to cause the fast upflow and transport molecular ions upward. The flux decreases from 280 to 350 km altitudes due to the dissociative recombination was estimated to be approximately two orders of magnitude. This resulted in significant molecular ion flux remaining at 350 km altitude. These results suggest that the low‐altitude ion upflow caused by the ion frictional heating enables molecular ions to escape to space against rapid loss by the dissociative recombination. Plain Language Summary: Molecular ions (O2+/NO+/N2+) in the ring current are sometimes observed during magnetic storms. These molecular ions come from the deep ionosphere and considered good tracers of escape mechanisms from the Earth's ionosphere to the magnetosphere. However, it has not been revealed how these molecular ions are transported upward, especially by ion upflows in the low‐altitude ionosphere (∼250–350 km). It is difficult to transport sufficient flux of molecular ions due to deceleration by the strong gravitational force and rapid decrease by dissociative recombination even during magnetic storms. In this paper, we report the analysis results of the fast ion upflow (∼100 m s−1) event in the low‐altitude ionosphere observed by the European Incoherent Scatter (EISCAT) radar, while the Arase (ERG) satellite observed molecular ions in the inner magnetosphere during the magnetic storm starting on September 7, 2017. The results suggest that ion frictional heating created the ion upflow and could be a source of outflows at higher altitudes in the ionosphere to supply the molecular ions into the magnetosphere. Key Points: Arase satellite observed molecular ions in the ring current during the magnetic storm starting on September 7, 2017An ion upflow from the deep ionosphere was observed with enhancements of electric field and ion temperature by EISCATThe fast upflow caused by the ion frictional heating enables molecular ions to escape to space against dissociative recombination [ABSTRACT FROM AUTHOR]

This study investigates the field‐aligned currents (FACs) and ionospheric equivalent currents for interplanetary coronal mass ejection (ICME)‐driven storms by considering 45 events with a minimum Dst ≤ −50 nT. The FACs and ionospheric equivalent currents are studied by applying a superposed epoch analysis to data from AMPERE and SuperMAG with the zero epoch (t0) centered at the onset of the storm main phase. The currents and number of substorm onsets begin to increase 3 hr before t0 and maximizes about 1 hr after t0. The currents and number of substorm onsets remain high throughout the entire storm main phase, until at t0 + 14 hr they start to slowly relax back to quiet time conditions. The storms were separated into two groups based on the solar wind dynamic pressure pdyn around t0. High pdyn storms are mostly driven by the sheath region ahead of the ejecta. These storms have short main phase durations and larger currents early in the main phase which maximize at t0 + 50 min. The low pdyn group contains storms that start during the magnetic clouds (MC) and have gradually increasing currents that maximize at t0 + 11 hr, close to the end of the storm main phase. For the first 4 hr of the storm main phase, the currents in sheath‐driven storms are larger than for MC‐driven storms. The Russell‐McPherron effect is less important for ICME‐driven storms where only 44% have a contribution, compared to 82% of high speed stream/stream interaction driven storms. Plain Language Summary: Geomagnetic storms are responsible for the largest magnetospheric and ionospheric disturbances and can last up to several days. During storms, field‐aligned currents (FACs) that couple the magnetosphere and the ionosphere intensify, increasing in magnitude by millions of ampere and are connected to large enhancements in the horizontally flowing ionospheric currents. In this study, the FACs and ionospheric currents have been studied statistically using data from 45 interplanetary coronal mass ejection (ICME) driven storms. It is found that the currents peak about 1 hr after the storm main phase onset and remain strongly intensified for the next 14 hr, before slowly decreasing back to normal time conditions. It is also shown that the solar wind dynamic pressure can to a large extent separate storms driven by the sheath region versus magnetic cloud (MC) region of the ICME. Sheath‐driven storms have an abrupt increase in the currents shortly after the storm main phase onset, while MC‐driven storms have gradual increase in currents that reach maximum 11 hr after onset. Sheath‐driven storms drive larger currents than MC‐driven storms for the first 4 hr after main phase onset. Afterward, the currents become larger for MC than sheath‐driven storms. Key Points: High pdyn storms are mainly driven by sheath regions ahead of the interplanetary coronal mass ejection (ICME) ejecta and low pdyn storms are mainly driven by magnetic clouds (MC)Sheath (high pdyn) storms have field‐aligned current (FAC) that peak 1 hr after t0, while MC (low pdyn) storms develop gradually and have FAC that peak 11 hr after t0Russell‐McPherron effect is less frequently observed in ICME storms (44%) than in high speed streams/stream interaction regions storms (82%) [ABSTRACT FROM AUTHOR]

Enhanced precipitation of magnetospheric energetic electrons during substorms increases ionospheric electron density and conductance. Such enhancements, which have timescales of a few hours, are not reproduced by the existing ionospheric models. We use the linear prediction filter (LPF) method to reconstruct the substorm‐related response of electron densities and integral conductances from long‐term ionospheric observations made by the European Incoherent SCATer radar located at Tromsø. To characterize the intensity of substorm dipolarization at a 5 min time step, we use the midlatitude positive bay index. We build response functions (LP filters) as a function of substorm time between T0−1 h and T0 + 4 h (T0 is a substorm onset time) in different magnetic local time (MLT) sectors to estimate the magnitude and delays of the ionospheric density response at different altitudes. Systematic and large relative changes are mostly observed in the D‐ and E regions. The duration of the response is about 3 h. It starts and reaches maximum magnitude near midnight, propagating from there toward the east and decaying after passing into the noon‐evening sector. The reliability of LPF results is confirmed by the consistency of D‐region response with independently derived response of the auroral absorption. Whereas strong ionization increases are seen in both E‐ and D‐regions on the nightside, the D‐region response is stronger in the morning‐dayside sector. Such MLT variation corresponds to the drift motion and precipitation of the high‐energy electrons injected in the nightside magnetosphere during substorm dipolarization. The inferred ionization changes result in strong enhancements of integral Hall (and Pedersen) conductance in the nightside auroral zone, where intense auroral currents are known to occur during substorms Key Points: Substorm‐related relative increase of electron density is small in F‐ and large in D and E regions, it mainly increases Hall conductanceThe electron density and conductance response starts near midnight at substorm onset, propagates eastward and decays after passing noonStrongest D‐region response in the pre‐noon MLT sector suggesting hard electron precipitation is observed [ABSTRACT FROM AUTHOR]

The spatial and temporal dynamics of ionospheric currents are among the most evident manifestations of the interaction between the magnetized plasma of solar origin and the magnetosphereionosphere system. In this context, a special role is played by field-aligned currents (FACs), which drive energy and momentum exchanges between the magnetosphere and the ionosphere, deeply affecting the energy balance of the latter. One of the most relevant physical quantities that may help to fully characterize FACs is the ionospheric electrical conductivity. Understanding the features associated with this quantity may contribute to the advancement of knowledge on the mechanisms of solar windmagnetosphere-ionosphere interaction as well as energy storage and dissipation involved in the space weather phenomena. By extending a previous study, we investigate the dependence of the electrical conductivity parallel to the geomagnetic field on solar and geomagnetic activity. To this aim, we considered a six-year long data set of in-situ electron density and temperature values recorded by the Langmuir probes on board the Swarm satellites in the topside ionosphere. With this large data set, we computed global maps of the parallel electron conductivity under both quiet and disturbed conditions, and for different solar activity levels. In both cases, the International Reference Ionosphere (IRI) model allowed estimating the contribution of particle precipitation to electrical conductivity. [ABSTRACT FROM AUTHOR]