JGR:Space physics

Using radars and C/NOFS satellite observations we studied the spatio-temporal evolution of Equatorial Plasma Bubbles (EPBs) and estimated its onset location across a wide longitudinal sector over Indian and Southeast Asian longitudes. The vertical E × B drift velocity measurements obtained from the Ion Velocity Meter (IVM) on board the C/NOFS satellite and collocated ionosonde observations were used to examine the background ionospheric conditions. Our study shows that the periodic EPBs were present in those longitudes where periodic wave structure in the E × B drift and elevated F layer were observed. In this case study, the comprehensive analysis using the observations from radars and satellite data provides a better understanding on the longitudinal preference of the EPB occurrence and its responsible background mechanisms. This understanding of the onset location and background conditions of EPBs over a large longitudinal area for an extended period can contribute to the development of accurate EPB forecasting models, which are essential to mitigate the detrimental effects of EPBs on communication and navigation systems.

Traveling quasi-5-day oscillations (Q5DOs) with different wavenumbers are independently observed in the mesosphere and the lower thermosphere during many recent sudden stratospheric warming (SSW) events, but their common activities during SSWs are still unclear. Based on the geopotential height data measured by the Aura/Microwave Limb Sounder (MLS) from August 2004 to March 2021, we statistically investigate the characteristics of the Q5DOs during eight Arctic major SSW events. The amplitudes of the Q5DOs are obtained by a new fitting method, which inhibits the effect of rapid changes in stationary planetary waves during SSWs. Our results reveal a robust feature that Q5DOs were enhanced during all interested SSW events. Our analysis indicates that eastward and westward propagating Q5DOs can be simultaneously enhanced during SSWs. Additionally, the wavenumbers of the enhanced Q5DOs are found to be associated with the geometry of polar vortices. Extremely strong westward Q5DOs with wavenumber 2 are consistently observed during split-type major SSWs.

The Jovian Auroral Distributions Experiment Ion sensor (JADE-I) on NASA’s Juno mission provides in-situ measurements of ions from 0.1 to 46.2 keV/q inside Jupiter’s magnetosphere. JADE-I is used to study the plasma with two types of datasets from the same measurement: Time-of-flight (TOF) and SPECIES. The TOF dataset provides mass-per-charge measurements with a range of 1–64 amu/q but oversamples particles over 6π steradian viewing per spacecraft spin and has little directional information. On the other hand, the SPECIES dataset can provide a good measurement of the flow direction but does not provide mass-per-charge information due to the telemetry limit. In this study, we developed a 2-step forward modeling method that combines the advantages and avoids the disadvantages of TOF and SPECIES data to derive the 3-D properties of heavy ions. Assuming that the ion velocity distribution can be described with the kappa distribution, we first perform the forward model fit of the TOF data to calculate the relative abundance of heavy ion species. Then we fix the relative abundance and perform the second forward model fit on the SPECIES data. Using this method, we obtain the densities of different heavy ions, the shared temperature and kappa value, and the 3-D flow velocity vector. Some data examples of the equatorial plasma disk before Perijove 24 are included to demonstrate the method. Plasma properties can then be mapped to explore spatial and temporal variabilities in Jupiter’s magnetosphere.

The auroral arc is the typical track of the interaction between the solar wind and the Earth's magnetosphere. A sketch of skeletons for arc-like aurora is usually used to describe auroral structures, such as vortex, fold and curl structures, etc. With artificial intelligence technologies, sketching auroral skeleton structure (AuroSS) in all-sky images enables automatic detection and measurement of aurora arcs in very large amounts of ground-based auroral observation data. The skeleton is a highly characterizing topological structure that has been extensively studied in the field of computer vision. However, AuroSS is not the medial axis of auroral shapes and a large number of accurate AuroSS annotations are not available. It is difficult to detect AuroSS by using an unsupervised or fully-supervised method. In this paper, we formulate the automatic AuroSS extraction to learn a mapping from an all-sky auroral image to a ridge style AuroSS. Without accurate AuroSS annotations, emission ridge and coarse localization of aurora are incorporated to generate pseudo-labels of AuroSS. A series of functional weakly supervised models are trained and cascaded to achieve AuroSS detection. Experimental results on auroral images obtained from all-sky imagers at Yellow River Station (YRS) show that the detected AuroSS is consistent with that of human visual perception. Based on the obtained AuroSS, the orientations and lengths of auroral arcs can be estimated automatically. By browsing the temporal variation in arc orientation from dusk to dawn, we can acquire synoptic observations of auroral activities at YRS.

Heavy particles are extensively detected in the space environment, especially in the solar wind and interplanetary magnetosphere. Various physical processes can be affected by the physical dynamics of heavy particles. One of the processes is magnetic reconnection, which converts the energy from the magnetic field to the particles. In the present study, we investigate the impact of heavy particles with increasing mass (i.e., mass-loading effect) on energy conversion rate during magnetic reconnection. The declined reconnection rate and energy conversion rates by this effect are captured as reported previously. After considering three major regions in reconnection, it reveals that the mass-loading effect decreases more energy conversion rate of positive species at the separatrix, affects the heavier species less in the inner electron diffusion region (EDR), and propels the formation of a non-zero electric field at reconnection front (RF). Our results provide a more comprehensive understanding of the magnetic reconnection with complicated plasma components.

Outward transport of plasma in the inner and middle magnetospheres of gas giants results from an interplay between mass loading from the inner dominant mass sources (volcanic moons), flux tube interchange in the centrifugally unstable magnetospheric plasma disk, turbulent heating of the plasma, and coupling between the equatorial plasma and the planetary upper atmosphere through magnetic field-aligned current loops and/or Alfvén waves. We present a new analytical formalism describing large scale transport in gas giant systems, combining two historical approaches: radial diffusion of mass and energy through flux tube interchange, and angular momentum transport through corotation enforcement. Under the hypotheses of axisymmetry, steady-state, and multi-fluid plasma, we provide transport equations for total contents of flux tubes. They feature new transport parameters accounting for the latitudinal extent of the disk, and self-consistently include field-aligned potential drops in the magnetosphere-ionosphere coupling. Our general formalism has a wealth of applications, two of which are presented, corresponding to the cases of the two gas giants: the effect of interhemispheric asymmetries in the resistive and magnetic properties between the northern and southern ionospheres on the transport of angular momentum at Jupiter, and the influence of the plasma disk thickness on transport at Saturn. We apply our formalism to derive ionospheric parameters and reproduce the Juno and Cassini data. Further work will allow for more complete numerical solutions of our equations, with the aim of capturing the broad complexity of fast rotating magnetospheric systems which can be found inside and outside the Solar System.

Electron resonant interaction with ultra-low-frequency (ULF) waves is considered to be a driver of electron radial transport in Earth’s inner magnetosphere. Traditional concept of such interaction assumes the electron slow diffusive scattering by a broad-band ULF spectrum, but recent spacecraft observations reported a possibility for electrons to resonate nonlinearly with intense coherent ULF waves. This study proposes a theoretical model describing the main elements of such nonlinear resonant interactions. We implement a Hamiltonian approach to describe equatorial electron motion in a dipole magnetic field and electric ULF wavefield and demonstrate the ULF-electron interactions has two basic nonlinear resonant regimes: phase bunching and phase trapping. Finally, we discuss possible applications of the proposed theoretical approach and the importance of ULF-electron nonlinear resonances.

Observations from Van Allen Probes are analyzed to obtain the statistical wave normal distribution of lightning-generated whistlers (LGWs). An automatic algorithm is developed to identify burst mode waveform data with LGW signals and analyze the wave polarization information for these LGW signals. The spatial distribution of the LGW occurrence and the probabilities of different propagation types demonstrate that most LGWs can be observed in the low L-shell region (L < 3), where the dominant propagation type is oblique outward. Parallel propagation dominates in the high L-shell region, but the LGW occurrence is very small. Additionally, a small group of oblique but inwardly propagating LGWs are observed at low altitudes (<0.2R E ). A ray tracing simulation is performed not only to confirm predominant oblique and outward wave vectors in the vast region of the plasmasphere but also to verify the existence of these inward propagating LGW signals at low altitudes near the topside ionosphere.

A thorough understanding of collisionless shocks requires knowledge of how different ion species are accelerated across the shock. We investigate a bow shock crossing using the Magnetospheric Multiscale spacecraft after a coronal mass ejection crossed Earth, which led to solar wind consisting of protons, alpha particles, and singly charged helium ions. The three species are resolved upstream of the shock. The low Mach number of the bow shock enabled the ions to be partly distinguished downstream of the shock due to the relatively low ion heating. Some of the protons are specularly reflected and produce quasi-periodic fine structures in the velocity distribution functions downstream of the shock. Heavier ions are shown to transit the shock without reflection. However, the gyromotion of the heavier ions partially obscures the fine structure of proton distributions. Additionally, the calculated proton moments are unreliable when the different ion species are not distinguished by the particle detector. The need for high time-resolution mass-resolving ion detectors when investigating collisionless shocks is discussed.

High-power large-aperture radar instruments are capable of detecting thousands of meteor head echoes within hours of observation, and manually identifying every head echo is prohibitively time-consuming. Previous work has demonstrated that convolutional neural networks (CNNs) accurately detect head echoes, but training a CNN requires thousands of head echo examples manually identified at the same facility and with similar experiment parameters. Since pre-labeled data is often unavailable, a method is developed to simulate head echo observations at any given frequency and pulse code. Real instances of radar clutter, noise, or ionospheric phenomena such as the equatorial electrojet are additively combined with synthetic head echo examples. This enables the CNN to differentiate between head echoes and other phenomena. CNNs are trained using tens of thousands of simulated head echoes at each of three radar facilities, where concurrent meteor observations were performed in October 2019. Each CNN is tested on a subset of actual data containing hundreds of head echoes, and demonstrates greater than 97% classification accuracy at each facility. The CNNs are capable of identifying a comprehensive set of head echoes, with over 70% sensitivity at all three facilities, including when the equatorial electrojet is present. The CNN demonstrates greater sensitivity to head echoes with higher signal strength, but still detects more than half of head echoes with maximum signal strength below 20 dB that would likely be missed during manual detection. These results demonstrate the ability of the synthetic data approach to train a machine learning algorithm to detect head echoes.

The Van Allen Probes mission contributed to the discovery of the relativistic (∼500 keV–2 MeV) and ultra-relativistic (∼>2 MeV) electron three-belt structure in Earth's radiation belts. This structure results from the partial depletion of the preexisting outer belt and the replenishment of a new outer belt. Ultra-low frequency and very-low frequency waves are believed to play important roles in these processes, and substorm injections are usually not responsible for the formation of the external outer belt. In this study, based on observations from the Arase and NOAA-18 (National Oceanic and Atmospheric Administration-18) satellites, we report an electron three-belt event in the energy range of ∼100–200 keV (i.e., sub-relativistic electrons). According to the evolution of the phase space density and the dawn-dusk asymmetric flux enhancement during this event, we conclude that the depletion of the upper part of the original outer belt was due to outward radial diffusion accompanied by magnetopause shadowing effect and convection, and the formation of the external outer belt was due to increased electron flux from convection as well as substorm injections. This discovery and its preliminary explanation may help understand the electron three-belt structure in radiation belts more comprehensively.

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

Much of the longitude/local time dependence of the thermosphere is controlled by non-migrating tides. Observations of semidiurnal (12-hr) tides between 120 and 200 km altitude, that is, the middle thermosphere, are rare owing to the lack of systematic measurements in this region. Since late 2018, the Global-scale Observations of the Limb and Disk (GOLD) Mission has provided unique measurements of thermospheric disk temperature and the column density ratio of atomic oxygen to molecular nitrogen ratio (ΣO/N2) from geostationary orbit. In this paper, we present an approach to deduce the strongest semidiurnal non-migrating tides in the middle thermosphere by adapting the method of Krier et al. (2021, https://doi.org/10.1029/2021ja029563) that deduces diurnal non-migrating tides in simultaneous observations of temperature and ΣO/N2 made by GOLD. Testing of this approach suggests that the principal sources of uncertainties in the derived semidiurnal non-migrating tides are the limitation on the longitudes sampled, such that uncertainties are higher for tides with longer horizontal wavelength, and contamination of the local time sums by stationary planetary waves, which causes amplitudes to be overestimated. Our approach is applied to GOLD data during solstice conditions in 2019–2021. Comparison to models yield disagreements which are likely due to uncertainties intrinsic to the method and/or misrepresentation of tidal dynamics in the models. These results are the first observations of semidiurnal non-migrating tides in the middle thermosphere from a geostationary observational platform.

No abstract is available for this article.

We present first results derived from the largest collection of contemporaneously recorded Jovian sodium nebula and Io plasma torus in [S II] 6731 Å images assembled to date. The data were recorded by the Planetary Science Institute's Io Input/Output observatory and provide important context to Io geologic and atmospheric studies as well as the Juno mission and supporting observations. Enhancements in the observed emission are common, typically lasting 1–3 months, such that the average flux of material from Io is determined by the enhancements, not any quiescent state. The enhancements are not seen at periodicities associated with modulation in solar insolation of Io's surface, thus physical process(es) other than insolation-driven sublimation must ultimately drive the bulk of Io's atmospheric escape. We suggest that geologic activity, likely involving volcanic plumes, drives escape.

Auroral particle precipitation is usually assumed to be equally strong for both signs of the B y component of the interplanetary magnetic field (IMF). This is also the case in most currently used precipitation models, which parameterize solar wind driving by empirical coupling functions. However, recent studies have showed that geomagnetic activity is significantly modulated by the signs and amplitudes of IMF B y and the Earth's dipole tilt angle Ψ. This so called explicit B y dependence is not yet included in any current precipitation models. In this paper, we quantify this B y dependence for auroral electron precipitation for the first time. We use precipitation measurements of the Defense Meteorological Satellite Program (DMSP) Special Sensor J instruments from years 1995–2022. We show that the dawnside electron precipitation at energies 13.9–30 keV is greater at auroral latitudes for opposite signs of B y and Ψ in both hemispheres, while the dusk sector is mostly unaffected by B y and Ψ. For energies below 6.5 keV the B y dependence is strong poleward of the auroral oval in the summer hemisphere, also exhibiting a strong dawn-dusk asymmetry. We also show that B y dependence of precipitation modulates ionospheric conductance.

We report an unusual event on absence of high frequency (HF) echoes in ionosonde observations from the ionospheric F2 region during the geomagnetic storm of 23–25 April 2023. This event was observed in both southern and northern hemispheres over two stations, Grahamstown (33.3°S, 26.5°E), South Africa and Pruhonice (50.0°N, 14.6°E), Czech Republic. Significant O/N2 depletion over the stations was observed by TIMED/GUVI, indicating a strong negative ionospheric storm. This is unique since absence of echoes in ionosonde measurements is usually due to strong radio absorption in the ionosphere associated with solar flares. However, there was no flare activity during the periods of “absent” F2 HF echoes. On the other hand, the ionosonde detected echoes from E-layer. TIEGCM simulation reproduced TIMED/GUVI O/N2 depletion and showed that NmE was larger than NmF2 on dayside over Pruhonice. TIMED/GUVI O/N2 also showed a clear spatial gradient in the O/N2 depleted regions, suggesting F-region ionosphere was tilted. By estimating the critical frequency of the F2 layer using GNSS observations, we have shown that it wasn't possible for the ionospheric electron density to reach depletion levels prohibiting reflection of HF echoes from ionosondes. We suggest that this phenomena may have been caused by either (a) maximum electron density of E layer exceeding that of F2 layer and/or (b) ionospheric tilting which made the signals to be reflected far away from the ionosonde locations.

The day-to-day variability (“weather”) associated with the diurnal- and zonal-mean (DZM) circulation, O/N2 ratio and electron density (Ne) of the I-T system due to tidal “forcing from below” and solar flux and magnetosphere (SM) “forcing from above” during 2021 are delineated, diagnosed and quantitatively compared using a series of model simulations designed to separate these responses with respect to their origins. The external forcings are driven by actual tidal, solar wind, and solar flux observations. Both circulation systems occupy the full extent of the I-T, and the SM-forced DZM circulation is 2–3 times more vigorous in terms of vertical and meridional wind magnitudes. Tidal-driven DZM Ne reductions of up to 30%–40% with respect to those of the fully forced I-T system occur, mainly between ±30° latitude, compared to SM-driven increases of up to 15%–20%. In terms of annual variances over this latitude range, tidal-driven DZM Ne variances exceed or equal those of the SM-driven variances. The former is mainly controlled by O/N2 ratio vis-a-vis tidal-forced temperature variations above 150 km. While a similar cause-effect relation exists for the latter, this is superseded by Ne variability associated with solar production. However, DZM I-T system variability forced from below is underestimated in the simulations in two respects: the effects of gravity waves are omitted, and tidal forcing is represented by 45-day running means, as compared with the more realistic actual daily variability of SM forcing. These shortcomings should be ameliorated once multi-satellite missions planned for the future come to fruition.

The present study uncovers the fine structures of magnetosonic waves by investigating the EFW waveforms measured by Van Allen Probes. We show that each harmonic of the magnetosonic wave may consist of a series of elementary rising-tone emissions, implying a nonlinear mechanism for the wave generation. By investigating an elementary rising-tone magnetosonic wave that spans a wide frequency range, we show that the frequency sweep rate is likely proportional to the wave frequency. We studied compound rising-tone magnetosonic waves, and found that they typically consist of multiple harmonics in the source region, and may gradually become continuous in frequency as they propagate away from source. Both elementary and compound rising-tone magnetosonic waves last for ∼1 min which is close to the bounce period of the ring proton distribution, but their relation is not fully understood.

Besides the significant effects of a variety of naturally occurring magnetospheric waves on the electron dynamics in the magnetosphere, the important contribution of ground-based very-low-frequency (VLF) transmitter waves also has been gradually discovered. The VLF transmitter's wave penetrating into the topside ionosphere is its energy source injected into the magnetosphere and has been extensively investigated. In the VLF wave trans-ionospheric propagation, the main energy attenuation occurs in the lower ionosphere which is controlled by solar short-wave radiation. However, the investigation on the variation of the VLF transmitters' energy in the topside ionosphere and ionospheric reflection height with solar activity is lacking. We use 4 years electric field measurements performed by DEMETER satellite and full-wave simulations to address these concerns. The results show the electric field radiated from NWC was relatively similar from May 1 to July 31 in 2006, 2008, and 2009 in daytime and nighttime, stronger than that in 2005, because the solar activity was similar and extremely low in these years compared with that in 2005. The nighttime and daytime ionospheric reflection heights are also relatively similar in these 3 years, with about 6 km higher than that in 2005. The difference in the simulated electric field based on the electron density profile from the IRI-2016 model between 2005 and 2009 is lower compared with the observation results. However, considering 6 km added in ionospheric reflection height in 2009, the simulation results are much more consistent with the observation results both in daytime and nighttime.