The Light Ion Analyzer (LIA) instrument, part of the Solar-wind-Magnetosphere–Ionosphere-link- Explorer (SMILE) mission, is designed to measure the ion velocity distribution function within an energy range of 5 eV up to 25 keV. LIA provides in-situ measurements of the ion velocity distribution functions of the solar-wind and magnetosheath, from which the moments can be derived on ground, serving as an upstream input for the magnetosphere-ionosphere downstream responses. Two identical 2π sr field-of-view LIA instruments are mounted on two opposite sides of the spacecraft platform, offering a combined 4π sr instantaneous field-of-view. Each LIA consists of a top-hat electrostatic analyzer, electrostatic aperture deflectors, and a microchannel plate detector for analyzing the energy, direction, and flux of ions. Depending on operation mode, the angular resolution ranges from 22.5° to 5.625° in elevation and from 30° to 7.5° in azimuth, and the time resolution spans from 0.25 to 2 seconds. This paper describes the design of the LIA, its performance, ground calibration, operation procedures, and resultant data products. 

How to cite: Kong, L., Dai, L., Zhang, A., Nicolaou, G., Berthomier, M., Gao, J., Su, B., Escoubet, P., Wang, C., Li, L., Ren, Y., Wang, W., Lv, Y., Kataria, D., Wurz, P., Raab, W., Vey, S., and Echim, M.: The Light Ion Analyzer (LIA) for SMILE mission: design, ground calibration and data products, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9904, https://doi.org/10.5194/egusphere-egu25-9904, 2025.

Supersubstorms (SSSs) are intense auroral zone geomagnetic activity associated with extremely intense westward auroral electrojet currents  (SML < -2500 nT). The nightside SSS onsets and auroral evolution were found to be substantially different than the Akasofu (1964) standard picture of auroral development for “typical” substorms. SSSs are the primary causes of intense geomagnetically induced currents (GICs) at the Mäntsälä gas pipeline, Finland, determined from a 21-year data study. From a statistical study of SSSs triggered by interplanetary shocks, during solar cycles 23 and 24, solar wind-magnetosphere energy coupling will be discussed. Magnetospheric shock compression greatly strengthens the upstream interplanetary magnetic field southward component, and thus, through magnetic reconnection at the Earth’s dayside magnetopause, greatly enhances the solar wind energy input into the magnetosphere and ionosphere during the SSS events. The additional solar wind magnetic reconnection energy input supplements the ∼1.5 hr precursor (growth-phase) energy input and both supply the necessary energy for the high-intensity, long-duration SSS events. The major part of the SSS energy is dissipated into Joule heating, distributed equally in the dayside and nightside ionosphere, giving a picture of the global energy dissipation in the magnetospheric/ionospheric system, not simply a nightside substorm effect.

How to cite: Hajra, R., Tsurutani, B., Lu, Q., and Du, A.: Solar wind-magnetosphere energy coupling during supersubstorms, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1897, https://doi.org/10.5194/egusphere-egu25-1897, 2025.

Magnetospheric substorms, characterized by the rapid release of energy stored in the magnetotail, play a central role in space weather dynamics. These events are typically triggered by enhanced magnetic reconnection between the Earth’s magnetic field and the interplanetary magnetic field (IMF). While substorms are often associated with southward IMF orientations, studies have also shown that they can occur even during northward IMF conditions, particularly when solar wind pressure pulses or strong IMF By components are present. In these cases, the location of substorm onsets and expansions can occur far from the usual midnight sector.

Notably, while the presence of an IMF By component tends to cause only small shifts in the local time sector of substorm onset (typically between ~22 MLT and ~01 MLT), solar wind pressure pulses can induce much larger shifts, potentially moving substorm onsets as far as the dawn or dusk sectors. This phenomenon suggests that ground-based observations of substorms centered around the dawn or dusk sectors could provide a unique signature of substorms triggered by pressure-induced impulses.

We provide examples of pressure-induced events exhibiting atypical onsets, with plasma splitting and propagating sunward in both pre-and post-midnight sectors. These findings suggest a likely cause for the large shifts in substorm onset locations during pressure pulses. The study highlights the need for further investigation into multiple reconnection sites and the role of solar wind pressure in shaping substorm evolution.

How to cite: Sinha, S., Sibeck, D., Fok, M.-C., and Oliveira, D.: Anomalous Substorm Signatures During Sudden Solar-Wind Pressure Enhancements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7407, https://doi.org/10.5194/egusphere-egu25-7407, 2025.

The response of the outer radiation belt to large-scale variations in the solar wind is an active field of research. In this work, we use electron flux measurement from the full 7 years of the Van Allen probes mission along with solar wind properties measurements from the OMNI database at L1 and THEMIS/ARTEMIS spacecraft to investigate how the electron flux in the outer radiation belt responds to variations in the solar wind parameters across temporal scales. We find that electron flux has multiple periodicities correlated with those of the solar wind. At the largest temporal scales, we observe 0.5-year, 27-days, and 13.5-days periodicities which are most prominent near the declining phase of the solar cycle. This is consistent with the Axial Effect where the solar magnetic field is aptly modeled as a tilted dipole and the Earth encounters the fast solar wind at the observed periodicities. In addition, we observe modulations in the electron flux at lower time scales (<= 1 day). The interpretation of the higher frequency periodicity and the study of the effects of various mesoscale structures such as HFAs, foreshock bubbles, and magnetosheath jets, on the electron flux in the outer radiation belt, is still under investigation.

How to cite: Lalti, A., Rae, J., and Watt, C.: Solar wind - radiation belt coupling across scales, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15721, https://doi.org/10.5194/egusphere-egu25-15721, 2025.

The Earth's outer radiation contains plenty of high-energy electrons. These electron populations exhibit high dynamics, with their fluxes varying by several orders of magnitude during magnetospheric disturbances. The enhancement of these high-energy electrons greatly increases the likelihood of spacecraft malfunction or failure and significantly influences the solar-terrestrial system's energy and mass coupling, highlighting the importance of fully understanding the mechanisms governing these dynamics from both theoretical and practical perspectives. The radial diffusion acceleration driven by ULF waves and local acceleration due to the interaction with whistler mode chorus waves were proposed to explain the enhancement of the radiation belt high-energy electrons. Recent work indicates that the magnetospheric convection, as a key dynamic process within the Earth's magnetosphere, is closely related to the dynamics of high-energy electrons in the radiation belt. Under fast solar wind conditions, the enhanced magnetospheric convection excites intense substorms, which are thought to induce rapid substorm injections of high-energy electrons, leading to relativistic electron enhancements in the outer radiation belt. Case studies and statistical analyses indicate that these injections predominantly enhance electrons in the range of hundreds of keV to 1-2 MeV beyond L ~ 4. Furthermore, in the plasmasphere, where the loss of radiation belt high-energy electrons has been traditionally believed to be dominant due to wave-particle interaction-induced scattering, we have find remarkable MeV electron enhancements. Our analysis shows that this enhancement is related to the magnetospheric convection. The research results are helpful for deepening the understanding of the formation and evolution mechanisms of high-energy electrons in the radiation belt, and also provide an important theoretical basis for further accurately predicting changes in the radiation belt environment and ensuring the safety of spaceflight activities.

How to cite: Yang, X., Dai, L., and Wang, X.: Enhancements of Radiation Belt High-Energy Electrons Driven by the Magnetospheric Convection, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5806, https://doi.org/10.5194/egusphere-egu25-5806, 2025.

Across the magnetopause, the velocity difference between the magnetospheric plasma and the shocked plasma of the solar wind gives rise to the Kelvin-Helmholtz instability. This instability can develop into large-scale surface waves and vortices at the magnetopause, causing the different plasma regions to mix, which plays an important role in the transfer of energy across the magnetopause. We know from spacecraft observations and simulations that the way Kelvin-Helmholtz waves grow and evolve can be different at dawn and dusk. However, very few studies have directly observed this phenomenon on both flanks of the magnetopause simultaneously. By combining measurements from the THEMIS and Cluster missions, we can report here on an event where such a simultaneous observation of the Kelvin-Helmholtz waves is possible.
    
For this event, we investigate and compare the typical wave parameters and in particular the difference in plasma mixing on the two flanks. The results presented here may help to improve our understanding of the energy transport during Kelvin-Helmholtz intervals, and may also provide new insights into the proposed dawn-dusk asymmetry of these waves.

How to cite: Grimmich, N., Pöppelwerth, P., Blasl, K.-A., Settino, A., Nakamura, R., Plaschke, F., Archer, M. O., and Nykyri, H. K.: Comparison of Kelvin-Helmholtz waves observed simultaneously at the dawn and dusk flanks of the Earth's magnetopause, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13281, https://doi.org/10.5194/egusphere-egu25-13281, 2025.

Using particle and electromagnetic field data from Magnetospheric Multiscale Spacecraft (MMS), we investigate energetic O⁺ ion characteristics in the strong velocity shear regions in the dusk-side low-latitude boundary layer (LLBL) during the main phase of an intense storm on 13 October 2016. In the large velocity reversal regions, O⁺ ion number density is very high, N_o+ ~ 0.3 cm^-3. The pitch angle distributions of these energetic O⁺ ions vary distinctly across different energy ranges. The pitch angles of the lower energetic (3 keV to 10 keV) O⁺ ions are mostly less than 45 degrees and show a quasi-parallel distribution. Conversely, the pitch angles of the higher energetic (20 keV to 40 keV) O⁺ ions are dominantly in the range from 45 to 135 degrees, suggesting a quasi-perpendicular distribution. The quasi-parallel distribution of lower energetic O⁺ ions implies that these O⁺ ions are outflow along the magnetic field line from the dayside high-latitude ionosphere. Intense electric fields in the strong shear flow region can accelerate O⁺ ions to higher energy, altering their motion from along the magnetic field to the transverse direction in the dusk-side LLBL. Our studies present evidence for strong shear flow in the dusk-side LLBL driving energetic O⁺ ions to traverse the magnetic field motion. The quasi-perpendicular distribution of higher energetic O⁺ ions, in the inner edge of the dusk-side LLBL, may provide a new source of ring current energetic particles during the main phase of the intense storm.

How to cite: Duan, S., Zhang, A., Dai, L., Hou, Y., He, Z., and Wang, C.: Observations of energetic O+ ions with strong velocity shear in the low latitude boundary layer during an intense storm main phase, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3066, https://doi.org/10.5194/egusphere-egu25-3066, 2025.

Atmospheric loss processes together with sources and sinks at the surface govern the evolution of the atmospheric composition. At present-day Earth, the main dominant escape process is polar wind, which predominantly removes ionized oxygen atoms from the polar regions of the Earth. Although a multitude of observations that cover atmospheric escape for different activity conditions of the Sun exist, theoretical and numerical aspects of the polar outflow are still not entirely understood.

In this work, we investigate the role different magnetospheric conditions play in governing the polar wind escape rates from the Earth. We use the Space Weather Modeling Framework and the BATS-R-US code to determine the magnetospheric structure in the polar areas of the Earth for quiet and storm conditions. The code output includes the configuration of the magnetic field in the vicinity of an exoplanet (using the Solar Corona and Inner Heliosphere modules) for a given stellar magnetic field and plasma parameters in the vicinity of the planet. The code offers significant flexibility and allows to study a wide range of quiet and storm conditions.

Using the magnetic and electric fields distributions calculated with the SWMF, we apply the test particle approach to track individual ions along the magnetic field lines and collect static on atmospheric ions that are lost. Depending on their energy, cold ions can end up in different regions of the magnetosphere, such as the magnetopause, the distant tail, and the ring currents, or fall down to the atmosphere. The idea of the test particle approach is to numerically calculate the trajectory of independent and non-interacting charged/uncharged particles, where external forces are well known. Particularly, for applications of the test particle approach for planetary magnetospheres it is common to use the magnetic and electric fields from global models such as the SWMF. To obtain a general picture of the percentage of particles that escape, we will study multiple test particles with different parameters such as initial energies, locations, and pitch angles (that can be inferred from the DSMC model) to accumulate statistics. As a result, we will obtain the distribution of locations, speeds and final destinations of ions in magnetospheres and/or ionospheres of planets. One of the main advantages of the test particle approach is that it avoids very expensive calculations (in terms of computational time and computer resources) and at the same time can reproduce the main features of the studied phenomena.

We show that magnetospheric parameters together with the current solar conditions play an important role for atmospheric escape. We discuss the influence of atmospheric loss processes on the Earth’s atmosphere over it’s history, and discuss the importance of preexisting modeling for stellar missions such as the SMILE satellite (Solar wind Magnetosphere Ionosphere Link Explorer).

How to cite: Kislyakova, K., Sasunov, Y., Metodieva, Y., Johnstone, C., Lammer, H., and Scherf, M.: Escape of ions from Earth under various magnetospheric conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9713, https://doi.org/10.5194/egusphere-egu25-9713, 2025.

The important early positive part of main phase (MP) from positive main phase onset (MPO) to 0‑level of SYM-H (and Dst, up to over 200 nT) was somehow missed in the treatment of geomagnetic storms. In this paper, we include the missed positive part in MP for over 1000 (out 1360) storms (SYM-HMin ≤-25 nT) having positive MPO identified in the SYM-H index in 1981-2024 by a computer algorithm using 5 selection criteria. The missed part is included by raising the 0-level of SYM-H to MPO-level, which increases the revised storm intensity (SYM-HMin^r) by up to -145 nT and revised storm impulsive strength (IpsSYM-H^r) by up to -139 nT. The inclusion of the positive part of MP therefore seems important for all aspects of global space weather. For example, IpsSYM-H^r identifies all 3 severe space weather (SvSW) events that caused power outage with a large separation of 52 nT and identifies all 9 minor-system-damage space weather (MSW) events that caused capacitor stripping and high induced voltage in power transformers from over 1000 normal space weather (NSW) events that did not cause any such damages since 1981. The included positive part of MP is explained statistically using long-term simultaneous SYM-H, solar wind dynamic pressure P and Y-component of interplanetary electric field IEFy (or VBz computed from solar wind velocity V and Bz component of IMF) data available for 156 storms since 1998. In addition, a 1-minute resolution SYM-H model developed from the existing Dst models is used to investigate the combined and relative contributions of P and IEFy on the included positive part of MP. The data statistics and model results reveal that the positive part of MP in majority (74%) of storms is contributed mainly (≥75%) by positive IEFy or increase in ring current; in a small number (6%) of storms, it is contributed mainly (≥75%) by sudden decrease in P; and in the remaining 20% of storms, it is contributed by both decrease in P and positive IEFy with major contribution from positive IEFy. In short, the important positive part of MP is caused mainly by the increase in ring current.

How to cite: Varghese, M., Raj, J., Nanan, B., Zhang, Q., and Xing, Z.: Including and explaining the important early positive part of main phase in the treatment of geomagnetic storms, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1362, https://doi.org/10.5194/egusphere-egu25-1362, 2025.

The aurora is the optical manifestation of the global magnetospheric dynamics. Optical imaging of aurora provide insight into the large-scale convections and wave-particle interactions in the magnetosphere, thus provide important information on the mass and energy flow in the solar wind-magnetosphere coupling system. The Ultraviolet Imager (UVI) onboard the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) satellite will image the entire auroral oval in N₂ Lyman-Birge-Hopfield (LBH) band (160–180 nm) while effectively mitigating contamination from dayglow, achieving a spatial resolution of approximately 100 km or better. The SMILE spacecraft operates in a highly eccentric orbit characterized by an orbital period of approximately 50 hours. This orbit configuration is particularly well-suited for long-term continuous monitoring of northern auroras. Such insights will significantly enhance our research into energy deposition processes occurring within the ionosphere and upper atmosphere during solar wind-magnetosphere interactions. Here, we will introduce in detail the instrument, laboratory calibrations, in-flight calibration plan, and data products of SMILE UVI.

How to cite: He, F., Wang, Y.-M., Zhang, X.-X., Liu, X.-H., Du, G.-J., Mao, J.-H., Li, P.-D., Huang, W.-P., Wang, T.-F., Liu, J., Yu, S., Wang, Z.-Y., Li, J., Li, L., Dai, L., Vey, S., Berlich, R., Forsyth, C., Escoubet, C. P., and Wang, C.: The Ultraviolet Imager (UVI) for SMILE mission: Instrument, Calibration, and Products, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7633, https://doi.org/10.5194/egusphere-egu25-7633, 2025.

Bursty Bulk Flows (BBFs) are high-speed plasma flows that occur within the magnetotail plasma sheet. BBFs are known to play a crucial role in transporting energy, mass, and magnetic flux across the magnetotail, as well as to the coupled ionosphere. Understanding the ionospheric signatures of BBFs is therefore essential to advance our understanding of the coupling processes between the Earth’s magnetosphere and ionosphere. Currently, most insights into the ionospheric signatures of BBFs come from individual case studies that include simultaneous observations of BBFs in the magnetotail and field-aligned currents (FACs) in the nightside ionosphere. In this study, we utilized the 6D Vlasiator simulations to study the ionospheric signatures of BBFs in the near-Earth magnetotail. Vlasiator is a global hybrid-Vlasov model designed to simulate near-Earth space plasmas and has recently been complemented with an ionosphere model, allowing the study of magnetosphere-ionosphere coupling.

In the magnetotail, the simulation results show that a BBF with V_x ≥400,km/s emerges shortly after magnetic reconnection occurs on the dusk-side at a radius between 11 and 14 R_E (where R_E= 6371 km, radius of the Earth) in the current sheet plane. As the BBF moves Earthward and azimuthally dusk-ward (as seen from above the current sheet plane), clockwise (counterclockwise) flow vortices are induced on the dawn(dusk) sides of it. These vortical flows generate FACs flowing upward (out of the current sheet plane) on the dawn-side and downward (into the current sheet plane) on the dusk-side flanks, respectively.

The mapping of BBF structures onto the ionosphere shows that BBFs are primarily aligned in the East-West direction, with their ionospheric signatures appearing as enhancements in FACs, ionospheric conductances, horizontal ionospheric currents, and the formation of localized plasma flow channels. The upward and downward FACs associated with BBFs in the magnetotail consistently map to enhanced Region 2 (R2) and Region 1 (R1) FAC structures at ionospheric altitude, which are then closed in the ionosphere by north-west flowing Pedersen currents. The Earthward motion of the BBF maps to an equator-ward flow channel, while the dusk-side counterclockwise (and dawn-side clockwise) magnetotail vortical flows correspond to evening-side clockwise (and midnight-side counterclockwise) flow channels in the ionosphere. Overall, the Vlasiator simulation results show that the emergence of BBFs in the near-Earth magnetotail drives enhancements in the currents and conductances of the nightside ionosphere, while the westward drift of these enhanced structures corresponds to the dusk-ward movement of BBFs in the magnetotail.

How to cite: Workayehu, A., Palmroth, M., Juusola, L., Alho, M., Horaites, K., Grandin, M., Koikkalainen, V., Zaitsev, I., Pfau-Kempf, Y., Ganse, U., Battarbee, M., and Suni, J.: Ionospheric signatures of Bursty Bulk Flows in the 6D Vlasiator simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13216, https://doi.org/10.5194/egusphere-egu25-13216, 2025.

With increasing solar activity, both auroral precipitation region and ionospheric convection of high-latitude proper expand to lower geomagnetic latitudes, leading to difficulties in monitoring the disturbances using the pre-existing observation instruments designed for high-latitude ionospheric dynamics. The Super Dual Auroral Radar Network (SuperDARN) was originally developed for studying high-latitude phenomena, but since the early 2000s, it has expanded toward lower geomagnetic latitudes, enabling the monitoring of sub-auroral and mid-latitude phenomena. The SuperDARN Hokkaido Pair of (HOP) radars, operated by Nagoya University, Japan, are located at the lowest geomagnetic latitude (=36.9 AACGM geomagnetic latitude and are most suitable for monitoring the ionospheric and magnetospheric dynamics during geomagnetic storms including recent huge storms such as the May 2024 storm. In this paper, we report the spatial and temporal evolution of ionospheric convection associated with the auroral precipitation during huge geomagnetic storms using the SuperDARN HOP radars data, together with ground-based camera data and the particle precipitation data at Low-Earth Orbit (LEO) satellites. The majority of low latitude auroral precipitation is accompanied by the sheared zonal ionospheric flows in its vicinity, but detailed flow patterns vary from event to event. Details of the multi-event analysis result will be presented.

How to cite: Nishitani, N., Hori, T., Hosokawa, K., Shinbori, A., Obana, Y., Teramoto, M., Shiokawa, K., and Kataoka, R.: A study of ionospheric convection pattern in the vicinity of low latitude auroral precipitation during huge geomagnetic storms, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14291, https://doi.org/10.5194/egusphere-egu25-14291, 2025.

An international campaign that encompassed diverse arrays of ground observations, including incoherent scatter radars and observational chains around the 60W~120E Meridian Circle, during the 10-11 Oct 2024 superstorm, was conducted to observe global upper atmospheric responses. This superstorm was driven by the arriving ICMEs which were associated with several solar eruptions on 7 and 8 Oct, 2024, respectively. Significant geomagnetic disturbances were observed as solar wind speeds elevated from 400 km/s to 800km/s, Bz turned southward reaching -24 nT initially then -41 nT at 22 UT on 10 Oct. SymH dropped to a minimum of 330 nT and Kp was above 8- for 21 hours which provided opportunities to watch spectacular auroras over around the world. These conditions triggered multi-scale global ionospheric disturbances. These disturbances are characterized by the sudden onset of the ionospheric perturbations in GNSS TEC observations, and the immediate launch of traveling ionospheric disturbances which propagated both equatorward into low latitudes (sometimes into the other hemisphere), and poleward across the polar cap from dayside to nightside. Subauroral disturbances exhibited characteristic storm-enhanced density (SED) plumes in the American longitudes, which convected sunward from dusk to noon and entered the cusp region contributing to the polar cap Tongue of Ionization (TOI) structure. Substantial equatorial ionization anomaly (EIA) poleward extension contributing to the density enhancement at the low latitude base of SED. A significant density depletion channel spanning between midlatitudes over the two hemispheres was found, accompanying the equatorial plasma bubble (EPB) development. This presentation provides a quick overview of the key observations with a focus primarily on TEC global responses.

How to cite: Zhang, S.-R., Erickson, P., Coster, A., and Goncharenko, L.: Global ionospheric disturbances during the 10-11 Oct 2024 superstorm, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12276, https://doi.org/10.5194/egusphere-egu25-12276, 2025.

Techniques developed in the past few years enable the derivation of multi-scale regional ion convection and particle precipitation patterns from the Super Dual Auroral Radar Network (SuperDARN) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) All-Sky Imager (ASI) observations, respectively. Our previous simulations driven by these multi-scale geomagnetic forcing suggest that both meso-scale ion convection and particle precipitation can intensify ionospheric and thermospheric disturbances with prominent structures and notable magnitudes. In this study, the global ionosphere–thermosphere model (GITM) is utilized to simulate the March 27^th, 2014 substorm event, and simulated F-region neutral winds have been compared with scanning Doppler imagers (SDI) wind measurements at Toolik Lake (68.6°N, 149.6°W). Neutral wind variations have been further separated into large (>500 km) and meso (<500) scales. The correlation between meso-scale ion-convection and neutral wind in a localized region has been qualified through the vortices and the speed. The meso-scale neutral wind response and ramp-up time show a strong dependence on the geomagnetic conditions.

How to cite: Deng, Y., Sheng, C., Bristow, W., Nishimura, Y., and Conde, M.: F-region Neutral Wind Response to the Multi-scale Geomagnetic Forcing During the March 27th, 2014 Substorm Event , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20463, https://doi.org/10.5194/egusphere-egu25-20463, 2025.

Strong Thermal Emission Velocity Enhancement (STEVE) is a fascinating optical phenomenon typically observed in the mid-latitude ionosphere. Recent observations reveal an exceptional STEVE event occurring at high latitudes, approximately 10 degrees poleward of previously documented cases. This event, recorded in Yellowknife, Canada, by a TREx RGB imager and a citizen scientist, coincided with Swarm satellite measurements of extreme westward ion drift velocities exceeding 4 km/s. Such velocities are generally associated with subauroral regions at mid-latitudes, making this high-latitude occurrence particularly striking.
Notably, this event unfolded in the absence of a substorm, a departure from previous STEVE and extreme drift velocity observations. High-latitude radars detected rapid equatorward ionospheric flows, while GOES satellites recorded no particle injections, suggesting a highly inflated inner magnetosphere.
This unique case study challenges existing paradigms of subauroral dynamics and highlights the significant influence of magnetospheric configurations on ionospheric responses. In this talk, we will discuss the characteristics of this event and examine the associated solar wind, magnetosphere, and ionosphere interactions.

How to cite: Gallardo-Lacourt, B., Nishimura, Y., Kepko, L., Spanswick, E. L., Gillies, D. M., Knudsen, D. J., Burchill, J. K., Skone, S. H., Pinto, V. A., Chaddock, D., Kuzub, J., and Donovan, E. F.: Unexpected STEVE Observations at High Latitude During Quiet Geomagnetic Conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12469, https://doi.org/10.5194/egusphere-egu25-12469, 2025.

Field-aligned currents (FACs) can be generated in the magnetosphere due to dynamic pressure variations associated with foreshock transients. The mechanisms may include: a) compressions or rarefactions causing divergence or convergence of diamagnetic or inertial currents in the magnetosphere, and b) compressions or rarefactions exciting shear Alfvénic waves associated with FACs. However, whether these FACs can further affect ions and neutral particles in the coupled ionospheric-thermospheric system remains unclear.

In this study, we utilized coordinated observations from THEMIS probes, (near-)polar-orbiting satellites (DMSP and SWARM), and ground-based optical imaging to identify FACs induced by foreshock transients and investigate their effects on ions and neutral particles. Ground-based all-sky imagers show that foreshock transients can generate traveling convection vortices (TCV) auroras near the equatorial boundary of the auroral oval and field line resonance (FLR) arcs at relatively lower latitudes. Events with conjugate DMSP observations reveal that the corresponding upward FACs were associated with ionospheric ion outflows, Poynting fluxes, and low-energy electron precipitation. Events with conjugate SWARM and optical observations indicate that these FACs were also associated with neutral wind divergence at ~250 km and enhanced neutral density at SWARM altitudes. This suggests that energy heating from foreshock-induced FACs can cause neutral wind perturbations and elevate neutral particles to higher altitudes.

How to cite: Wang, B., Zhi, Y., Xu, X., Nishimura, Y., Kajdic, P., Wang, Y., and Feng, X.: Field-aligned currents induced by foreshock transients and their effects on ions and neutral particles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15218, https://doi.org/10.5194/egusphere-egu25-15218, 2025.

The dusk-side mid-latitude ionosphere is characterized by fast, sunward flow channels of a few degrees in width, known as Subauroral Polarization Streams (SAPS). Occasionally, these regions exhibit distinct, latitudinally narrow enhancements in velocity, referred to as double-peak Sub-auroral Ion Drifts (DSAIDs). SAPS are associated with Region 2 Field-Aligned Currents (R2 FACs) that flow into the low-conductance sub-auroral ionosphere, while DSAIDs have been linked to the presence of a double-conductance trough in this region. Nishimura et al. (2022) demonstrated that sub-auroral ion drifts intensify in the presence of electromagnetic waves, with local plasma structures exerting greater control over the velocity characteristics of these westward flows than solar wind or global magnetospheric conditions. This study investigates the occurrence of westward ion flows in the dusk-side sector during a geomagnetic storm event, utilizing simulations from the RAM-SCB model. To explore the relationships between R2 FACs, electric fields, EMIC wave-particle interactions, proton precipitation, ionospheric conductance, and westward flows in the dusk-side sub-auroral ionosphere, we conducted two simulation studies, one with and one without EMIC waves. The simulations confirmed that EMIC wave-induced proton precipitation leads to localized enhancements in conductivity, which, in turn, generates high-speed westward flows in the dusk-side sub-auroral ionosphere. Our findings reveal the significant role of wave-particle interactions in shaping ionospheric behavior during disturbed conditions.

How to cite: Porunakatu Radhakrishna, S., Miyoshi, Y., Yu, Y., and Jordanova, V.: Westward ion drifts in the dusk-side sub auroral ionosphere: Role of EMIC wave-particle interactions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3419, https://doi.org/10.5194/egusphere-egu25-3419, 2025.

Previously we found that the inner radiation belt (IRB) shrinks and stretches in solar minimum and maximum. A natural problem comes up that how solar cycle effects the near-Earth space regions including plasmasphere, IRB, ionosphere, mesosphere and lower thermosphere (MLT). We present a thorough analysis of the extent of solar cycle effect on four regions by using mesospheric and thermospheric geopotential height and temperature from SABER on TIMED, ionospheric hmF2 from Chinese Meridian Project, high-energy protons in IRB and electron density in plasmasphere from Van Allen Probes within 2013-2018 intervals. By analyzing evolutions of these quantities, we find that entire IRB, ionosphere and MLT region shrink at solar minimum and stretch at solar maximum by ~10³ km, 50~10² km and 1 km scales, respectively, while plasmapause shows an opposite trend. Fourier spectra of these quantities have been investigated by Lomb–Scargle periodogram. The mid-term periodic oscillations (13.5-day, 45-day, and 52-day) have been observed in MLT region, matching well with plasmapause locations and geomagnetic indices, which have not been observed in solar EUV radiation and IRB. This may indicate that those oscillations facilitate energy exchange and mass transportation between MLT region and plasmasphere due to magnetic storms and substorms. The oscillation periods of higher energy (102.6MeV) in IRB have not been observed in MLT region except for annual variations. The impact of higher energy protons on MLT regions may not be significant, although they could penetrate deeper into MLT region. Our results reveal relationships between some quantities and solar cycle multi-scale modulation, which may provide assistance and monitors for mass transportation in the near-Earth space regions.

How to cite: He, Z., Xu, J., Dai, L., Duan, S., Gao, H., Wang, G., Roth, I., and Wang, C.: Solar Activity Effects on the Near-Earth Space RegionsDuring the Descending Phase of Solar Cycle 24, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2476, https://doi.org/10.5194/egusphere-egu25-2476, 2025.