JGR:Space physics

When solar wind and interplanetary magnetic field (IMF) disturb, thermospheric winds change accordingly. Among the momentum forces driving high-latitude thermospheric winds, ion drag is supposed to greatly affect wind variations through ion-neutral coupling when abrupt and strong changes in ion drifts occur. However, due to the great inertia of thermospheric winds it needs a certain period of time for the wind changes to be prominent both in speed and direction. How long the neutral winds take to change from one steady state to another through the ion-neutral coupling process is currently still a controversial issue. In this paper, we examine the high latitudinal ion-neutral coupling time scale based on the Thermosphere Ionosphere Electrodynamics General Circulation Model simulations, which can determine whether wind variations are dominantly driven by ion drag by analyzing the relative contribution of each momentum force. It is found that the spatial variation of ion-neutral coupling time scale is primarily determined by local electron density, but also varies with neutral density and ion-neutral collision frequency. Simulations during periods of medium solar activity at ∼250 km altitude show that the ion drag-dominated region is generally located at the dayside convection inverse boundary and the coupling time scale (e-folding time) is ∼1 hr when IMF B y is the dominant component of the IMF and changes direction. Meanwhile, the southward component of IMF B z enlarges the ion drag-dominated region. When IMF B z is southward with a large magnitude, ion drag-dominated region is primarily located in the nightside auroral oval with ∼2 hr coupling time scale.

Energetic particle injections are commonly observed in Jupiter's magnetosphere and have important impacts on the radiation belts. We evaluate the roles of electron injections in the dynamics of whistler-mode waves and relativistic electrons using Juno measurements and wave-particle interaction modeling. The Juno spacecraft observed injected electron flux bursts at energies up to 300 keV at M shell ∼11 near the magnetic equator during perijove-31. The electron injections are related to chorus wave bursts at 0.05–0.5 f ce frequencies, where f ce is the electron gyrofrequency. The electron pitch angle distributions are anisotropic, peaking near 90° pitch angle, and the fluxes are high during injections. We calculate the whistler-mode wave growth rates using the observed electron distributions and linear theory. The frequency spectrum of the wave growth rate is consistent with that of the observed chorus magnetic intensity, suggesting that the observed electron injections provide free energy to generate whistler-mode chorus waves. We further use quasilinear theory to model the impacts of chorus waves on 0.1–10 MeV electrons. Our modeling shows that the chorus waves could cause the pitch angle scattering loss of electrons at <1 MeV energies and accelerate relativistic electrons at multiple MeV energies in Jupiter's outer radiation belt. The electron injections also provide an important seed population at several hundred keV energies to support the acceleration to higher energies. Our wave-particle interaction modeling demonstrates the energy flow from the electron injections to the relativistic electron population through the medium of whistler-mode waves in Jupiter's outer radiation belt.

We evaluate average wave intensities at frequencies up to 10 kHz measured by two ground stations in Canada and two others in Finland at auroral and subauroral latitudes over a full year, as well as by the low-altitude DEMETER spacecraft during the years 2004–2010. Lightning location and energy data obtained by the World Wide Lightning Location Network, along with geomagnetic activity characterized by the Kp index, are further used. Latitudinal, diurnal, and annual variations are analyzed, and the global intensities measured on the ground and by the spacecraft are systematically compared for the first time. We show that lightning-generated waves often dominate the measured wave intensities, particularly during the night, in summer, and at higher frequencies. DEMETER observations, supported by ray-tracing analysis, reveal a significant role of nonducted lightning-generated whistler propagation between the hemispheres. Finally, the wave intensity response to geomagnetic activity variations is quite different on the ground compared to in space. While spacecraft-measured wave intensities are considerably larger during periods of enhanced geomagnetic activity, the ground-based intensities are only sporadically enhanced during geomagnetically active periods.

We present broadband ionospheric scintillation observations of highly defined symmetric quasi-periodic scintillations (QPS: Maruyama, 1991, https://doi.org/10.1029/91rs00357) caused by plasma structures in the mid-latitude ionosphere using the LOw Frequency ARray (LOFAR: van Haarlem et al., 2013, https://doi.org/10.1051/0004-6361/201220873). Two case studies are shown, one from 15 December 2016, and one from 30 January 2018, in which well-defined main signal fades are observed to be bounded by secondary diffraction fringing. The ionospheric plasma structures effectively behave as a Fresnel obstacle, in which steep plasma gradients at the periphery result in a series of decreasing intensity interference fringes, while the center of the structures largely block the incoming radio signal altogether. In particular, the broadband observing capabilities of LOFAR permit us to see considerable frequency dependent behavior in the QPSs which, to our knowledge, is a new result. We extract some of the clearest examples of scintillation arcs reported in an ionospheric context, from delay-Doppler spectral analysis of these two events. These arcs permit the extraction of propagation velocities for the plasma structures causing the QPSs ranging from 50 to 00 m s−1, depending on the assumed altitude. The spacing between the individual plasma structures ranges between 5 and 20 km. The periodicities of the main signal fades in each event and, in the case of the 2018 data, co-temporal ionosonde data, suggest the propagation of the plasma structures causing the QPSs are in the E-region. Each of the two events is accurately reproduced using a thin screen phase model. Individual signal fades and enhancements were modeled using small variations in total electron content (TEC) amplitudes of order 1 mTECu, demonstrating the sensitivity of LOFAR to very small fluctuations in ionospheric plasma density. To our knowledge these results are among the most detailed observations and modeling of QPSs in the literature.

Despite more than half a century of Collisionless shock (CS) research, our understanding of the processes of the shock energy dissipation into the charge particle heating and acceleration remains incomplete. To help to address the problem of the rate of the data analysis on CSs being well below of the rate of the data acquisition, an open-source high-level database of shocks and a centralized source of advanced tools for the purpose of analyzing shock structure and dynamics have been developed. The database is called SHARP shock database by the name of the project SHARP (Shocks: structure, AcceleRation, dissiPation) funded by the European Union's Horizon 2020 program. The SHARP shock database contains shock crossings and corresponding parameters obtained from Cluster and MMS (Magnetospheric Multiscale) missions for terrestrial bow shocks, THEMIS (Time History of Events and Macroscale Interactions during Substorms)/ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun) missions for interplanetary shocks, and MAVEN (Mars Atmosphere and Volatile EvolutioN) and VEX (Venus Express) missions for shocks at non-magnetized planets. The SHARP shock database can be accessed via https://sharp.fmi.fi/shock-database/.

The OI 630.0 nm airglow emission variability provides salient information on the dynamical changes taking place in the upper atmosphere at around 250 km. The emission rates vary with the changes in the ambient electron densities and the neutral constituents that are associated with these emissions. On several occasions, enhancements in these emissions are observed during post-sunset hours, around 21 local time (LT), as measured from Mt. Abu (24.6°N, 72.7°E, 19°N Mag), a low-latitude location at Indian longitudes. These enhancements occur following the typical monotonic decrease in emission intensity after sunset. The presence of poleward meridional wind preceded by cessation and reversal of equatorward wind at the post-sunset hours was shown to be the cause for such observed emission enhancements in an earlier study. In this study, the cause of such reversal in meridional winds during post-sunset hours has been investigated using the variation in electron densities and meridional winds simulated by the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X), which also shows enhancements in electron densities similar to those observed in the post-sunset OI 630.0 nm nightglow emissions, and simultaneous reversal in meridional winds as well. The amplitudes and phases of different components of tides obtained from WACCM-X meridional winds reveal a significant contribution of higher-order tides, especially, quarter-diurnal tides, to the observed reversal in the meridional winds during post-sunset hours.

Stable Auroral Red (SAR) arcs are enhanced OI 630.0 nm emissions formed due to an increased electron temperature (Te) near the equatorward wall of mid-latitude trough during geomagnetic disturbances. The Te enhancement associated with SAR arcs is driven by electron heating through heat flux precipitation from near plasmapause region to ionospheric F-region via heat conduction. Although Te enhancements have been reported by radar/satellite measurements along with increased 630.0 nm brightness during SAR arc events, measurements of corresponding heat flux are sparse, and almost none in the daytime. This work presents the results on the estimation of electron heat flux incident during SAR arcs formed during daytime obtained by a comprehensive suite of measurements, and forward modeling. We present observations of several SAR arc events when the ground-based OI 630.0 nm emissions were larger than the model values during disturbed periods and were found to be existing in conjunction with increased Te at the altitude of DMSP (∼840 km). Forward modeling was carried out to determine the values of Te that would cause an enhancement in these emissions during daytime at much lower altitudes (∼400–500 km). These values of Te were used to estimate the required electron heat flux varying in the range of ∼1.0–4.6 × 1010 eV-cm−2-s−1. These results present the first estimates of F-region heat flux enabled using ground-based OI 630.0 nm emissions and open a new approach in the investigations of energy released into the ionosphere through heat conduction for daytime conditions during geomagnetically disturbed periods.

A statistical study has been made of dynamic small-scale auroral events in order to understand the drivers of the large variability in the electrodynamics of auroral arcs at fine scales. We used the Auroral Structure and Kinetics (ASK) instrument, located on Svalbard, in order to measure various electrodynamic properties of fine scale auroral arcs. We performed Spearman and Kendall statistical tests and found two significant correlations. The first is between the mean precipitation flux and the variability of flux, which we assume is because of the dynamic and bursty nature of the acceleration mechanism and its dependence on Alfvén waves. The second correlation is between the variability of the precipitating electron flux and the variability of the tangential component of the electric field close to the arc and perpendicular to the magnetic field. We propose that both variabilities occur because of the variability of the upward (field-aligned) current sheet in and around the arc, which is dynamic and non-uniform. The correlation between the two variabilities can therefore be explained by their common source.

During periods of increased geomagnetic activity, perturbations within the terrestrial magnetosphere are known to induce currents within conducting materials, at the surface of Earth through rapid changes in the local magnetic field over time (dB/dt). These currents are known as geomagnetically induced currents and have potentially detrimental effects on ground based infrastructure. In this study we undertake case studies of five geomagnetic storms, analyzing a total of 19 days of 1-s SuperMAG data in order to better understand the magnetic local time (MLT) distribution, size, and occurrence of “spikes” in dB/dt, with 131,447 spikes in dB/dt exceeding 5 nT/s identified during these intervals. These spikes were concentrated in clusters over three MLT sectors: two previously identified pre-midnight and dawn region hot-spots, and a third, lower-density population centered around 12 MLT (noon). The noon spike cluster was observed to be associated with pressure pulse impacts, however, due to incomplete magnetometer station coverage, this population is not observed for all investigated storms. The magnitude of spikes in dB/dt are determined to be greatest within these three “hot-spot” locations. These spike occurrences were then compared with field-aligned current (FAC) data, provided by the Active Magnetospheric Planetary Electrodynamic Response Experiment. Spikes are most likely to be co-located with upward FACs (56%) rather than downward FACs (30%) or no FACs (14%).

The Nitric Oxide (NO) emission at 5.3 μm wavelength is a well-known coolant above 100 km. It effectively regulates thermospheric temperature during space weather events. We studied NO cooling emission over Tromsø (geographic:69.59°N, 19.22°E; cgm:66.58°,102.94°), Norway by using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) simulation driven by both Heelis and Weimer models as sources of geomagnetic forcing during October–November 2003 storm. The Weimer driven TIEGCM significantly overestimates thermospheric Nitric Oxide and Atomic Oxygen densities and underestimates temperature as compared to the Heelis driven simulation. The density ratio between the Weimer and Heelis driven estimations decreases with increasing altitude for both NO and atomic oxygen densities. The Heelis driven Joule heating rate agrees very well with the European incoherent scatter (EISCAT) radar measurements. It peaks during the main phase of the storm with magnitude about 4–5 times higher than that driven by Weimer model which peaks during the recovery phase. The difference in Joule heating rates between the Heelis and Weimer driven models increases with storm intensity, reaching a peak discrepancy of about an order of magnitude during the October-November 2003 storm. An early and stronger NO cooling enhancement is predicted by Heelis driven TIEGCM simulation. It overestimates NO cooling emission by about 2–3 times as compared to SABER observations and about 4–5 times the Weimer driven calculation. This strong difference between the two models can be attributed to the model calculations of high latitude electric field and convection patterns.

This paper presents the results of a nearly 2-year long campaign to detect and analyze meteor persistent trains (PTs)—self-emitting phenomena which can linger up to an hour after their parent meteor. The modern understanding of PTs has been primarily developed from the Leonid storms at the turn of the century; our goal was to assess the validity of these conclusions using a diverse sample of meteors with a wide range of velocities and magnitudes. To this end, year-round observations were recorded by the Widefield Persistent Train camera, 2nd edition (WiPT2) and were passed through a pipeline to filter out airplanes and flag potential meteors. These were classified by visual inspection based on the presence and duration of trains. Observed meteors were cross-referenced with the Global Meteor Network (GMN) database, which independently detects and calculates meteor parameters, enabling statistical analysis of PT-leaving meteors. There were 4,726 meteors codetected by the GMN, with 636 of these leaving trains. Among these were a large population of slow, dim meteors that left PTs; these slower meteors had a greater train production rate relative to their faster counterparts. Unlike prior research, we did not find a clear magnitude cutoff or a strong association with fast meteor showers. Additionally, we note several interesting trends not previously reported, which include PT eligibility being primarily determined by a meteor's terminal height and an apparent dynamical origin dependence that likely reflects physical meteoroid properties.

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

Along the I24, I27, and I31 flybys of Io (1999–2001), the Energetic Particle Detector (EPD) onboard the Galileo spacecraft observed localized regions of energetic protons losses (155–1,250 keV). Using back-tracking particle simulations combined with a prescribed atmospheric distribution and a magnetohydrodynamics (MHD) model of the plasma/atmosphere interaction, we investigate the possible causes of these depletions. We focus on a limited region within two Io radii, which is dominated by Io's SO2 atmosphere. Our results show that charge exchange of protons with the SO2 atmosphere, absorption by the surface and the configuration of the electromagnetic field contribute to the observed proton depletion along the Galileo flybys. In the 155–240 keV energy range, charge exchange is either a major or the dominant loss process, depending on the flyby altitude. In the 540–1,250 keV range, as the charge exchange cross sections are small, the observed decrease of the proton flux is attributed to absorption by the surface and the perturbed electromagnetic fields, which divert the protons away from the detector. From a comparison between the modeled losses and the data we find indications of an extended atmosphere on the day/downstream side of Io, a lack of atmospheric collapse on the night/upstream side as well as a more global extended atmospheric component (>1 Io radius). Our results demonstrate that observations and modeling of proton depletion around the moon constitute an important tool to constrain the electromagnetic field configuration around Io and the radial and longitudinal atmospheric distribution, which is still poorly understood.

The statistics of day-to-day tidal variability within 35-day running mean windows is obtained from Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI)/Ionospheric Connection Explorer (ICON) observations in the 90–107 km height region for the year 2020. Temperature standard deviations for 18 diurnal and semidiurnal tidal components, and for four quasi-stationary planetary waves are presented, as function of latitude, altitude, and day-of-year. Our results show that the day-to-day variability (DTDV) can be as large as 70% of the monthly mean amplitudes, thus providing a significant source of variability for the ionospheric E-region dynamo and hence for the F-region plasma. We further validate our results with COSMIC-2 ionospheric observations and present an approach to extend the MIGHTI/ICON results to all latitudes using Hough Mode Extension fitting, to produce global tidal fields and their statistical DTDV that are suitable as lower boundary conditions for nudging and ensemble modeling of TIE-GCM. In the future, this will likely help to establish a data-driven perspective of space weather variability caused by the tidal weather of the lower atmosphere.

The Earth's magnetosphere is filled with a collisionless plasma that exhibits non-Maxwellian particle distributions which are well described by Kappa functions. In contrast to the Maxwellian, the Kappa contains not only density and temperature but also the kappa index that allows us to characterize the energetic tails. In this study, we analyze the response of the ion and electron Kappa distributions, obtained by fitting ion and electron fluxes measured by the five THEMIS satellites, to changes of the solar wind dynamic pressure. It was found that the solar wind dynamic pressure strongly affects the values of the kappa index, and that its impact depends on the magnetic local time (MLT). In particular, there is a significant dawn-dusk asymmetry for low P SW values which is enhanced in the night side. Further, we observe a narrow partial ring-shaped structure at different azimuthal extension that divides the plasma into two clearly defined domains. The results obtained reflect the global reconfiguration of the magnetosphere caused by variations of the solar wind dynamic pressure. Kappa distribution parameters and their average values for different ranges of P SW and MLT are provided, which we believe will contribute as realistic inputs to the modeling of the magnetosphere.

In the present study, the influence of the solar wind dynamic pressure on the plasma and magnetic pressures of the magnetosphere is studied. We use 11-year Time History of Events and Macroscale Interactions during Substorms (THEMIS) instruments for plasma and magnetic field measurements in the magnetosphere and the OMNI database for solar wind dynamic pressure and IMF data. We focus on the effects of the solar wind dynamic pressure (P SW ) and consider only times in which the interplanetary magnetic field (IMF) components are within ±5 nT. We find that the plasma pressure inside the magnetosphere follows the solar wind dynamic pressure and that an increase in P SW also influence the day-night pressure asymmetry. Our analysis also reveals the existence of ion and electron drifts from midnight toward the dusk and dawn sectors, respectively. We observe a local magnetic pressure minimum located near a plasma pressure maximum at around 11 R E on the nightside. Comparing the effect of P SW on both plasma and magnetic pressures, we observe trends which are consistent with the diamagnetic properties of plasmas. In general, the distribution of plasma pressure within the Earth's magnetosphere is an important criterion for evaluating the magnetostatic equilibrium and electric current system. The outcome of this study should provide additional methodologies for the characterization of key plasma characteristics within the magnetosphere.

We present a physical mechanism for generating ∼GeV ions in the Jovian radiation belts. The mechanism is called relativistic turning acceleration (RTA) and involves a special form of nonlinear wave trapping by electromagnetic ion cyclotron (EMIC) waves. Necessary conditions for RTA include a near-equatorial source of EMIC waves, strong wave amplitudes (of the order of a few percent of the background magnetic field strength), and a source of ions of sufficiently high energy. RTA occurs when a fraction of equator-ward moving ions encounters pole-ward moving waves, and, in so doing, becomes entrapped and undergoes a turning motion. The trapped ions then move poleward in the same direction as the waves and eventually become detrapped, but during the turning motion the ions undergo significant acceleration. We rigorously verify this process by providing the theory of nonlinear interactions between relativistic protons and coherent EMIC waves. The RTA process has been previously established for the analogous whistler mode wave-electron interaction. We carry out particle simulations for protons at R = 2R J (where R J  = Jovian radius) interacting with EMIC waves of amplitude B w  = 0.02B 0eq (where B 0eq  = background magnetic field strength at the equator). We confirm that a large portion of test protons experience RTA and that some protons of critical energy 240 MeV can be accelerated to 10 GeV in a period of 5 s. The nonlinear acceleration process is crucially controlled by the trapping condition 0 < S < 1 where S is the inhomogeneity factor.

The paper presents the effects of the storm-time prompt penetration electric fields (PPEF) and traveling atmospheric disturbances (TADs) on the total electron content (TEC), foF2 and hmF2 in the American sector (north and south) during the geomagnetic storm on 23–24 April 2023. The data show a poleward shift of the Equatorial Ionization Anomaly (EIA) crests to 18°N and 20°S in the evening of 23 April (attributed to eastward PPEF) and the EIA crests remaining almost in the same latitudes after the PPEF reversed westward. The thermospheric neutral wind velocity, foF2, hmF2, and TEC variations show that TADs from the northern and southern high latitudes propagating equatorward and crossing the equator after midnight on 23 April. The meridional keograms of ΔTEC show the TAD structures in the north/south propagated with phase velocity 470/485 m/s, wave length 4,095/4,016 km and period 2.42/2.30 hr, respectively. The interactions of the TADs also appear to modify the wind velocities in low latitudes. The eastward PPEF and equatorward TADs also favored the development of a clear/not so clear F3 layer in northern/southern regions of the equator.

The 1859 Carrington event is the most intense geomagnetic storm in recorded history, and the literature provides numerous explanations for what drove the negative H perturbation on the Earth. There is debate on what dominated the event. Our analysis shows a combination of causes of similar orders of magnitude. Previous analyses generally rely upon the observed H perturbation at Colaba, India; historic newspaper reports; and empirical models. We expand the analysis using two Space Weather Modeling Framework simulations to examine what drove the event. We compute contributions from currents and geospace regions to the northward B field on Earth's surface, B N . We examine magnetospheric currents parallel and perpendicular to the local B field, ionospheric currents, and gap region field–aligned currents (FACs). We also evaluate contributions from the magnetosheath, near–Earth, and neutral sheet regions. A combination of currents and geospace regions significantly contribute to B N on the Earth's surface, changing as the storm evolves. At storm onset, magnetospheric currents and gap–region FACs dominate in the equatorial region. At auroral latitudes, gap–region FACs and ionospheric currents are the largest contributors. At storm peak, azimuthal magnetospheric currents and gap–region FACs dominate at equatorial latitudes. Gap–region FACs and ionospheric currents dominate in the auroral zone, down to mid-latitudes. Both the magnetosheath and FACs contribute at storm peak, but are less significant than that from the near–Earth ring current. During recovery, the near–Earth ring current is the largest contributor at equatorial latitudes. Ionospheric currents and gap–region FACs dominate in the auroral zone.

Electron density irregularities in the ionosphere can give rise to scintillations, affecting radio wave phase and amplitude. While scintillations in the cusp and polar cap regions are commonly associated with mesoscale density inhomogeneities and/or shearing, the auroral regions exhibit a strong correlation between scintillation and density structures generated by electron precipitation (arcs). We aim to examine the impact of electron precipitation on the formation of scintillation-producing density structures using a high-resolution physics-based plasma model, the “Geospace Environment Model of Ion-Neutral Interactions,” coupled with a radio propagation model, the “Satellite-beacon Ionospheric-scintillation Global Model of the upper Atmosphere.” Specifically, we explore the effects of varying spatial and temporal characteristics of the precipitation, including electron total energy flux and their characteristic energies, obtained from the all-sky-imagers and Poker Flat Incoherent Scatter Radar observations, on auroral scintillation. To capture small-scale structures, we incorporate a power-law turbulence spectrum that induces short wavelength features sensitive to scintillation. Finally, we compare our simulated scintillation results with satellite-observed scintillations, along with spectral comparisons.