Solar wind–driven disturbances excite Alfvénic perturbations in the Earth’s magnetosphere that propagate along geomagnetic field lines toward Earth, with the ionosphere being the inner boundary where field-aligned currents close. Horizontal gradients in the Hall and Pedersen conductances have previously been invoked to explain rotations of the convection pattern in response to magnetospheric forcing (Lotko et al., 2014).

We employ a time-dependent 2D model of the ionosphere driven by the magnetosphere. The radial magnetic field perturbations are generated inductively, numerically solving the induction equation  along with the two-fluid equations, allowing us to capture the gradual formation of the convection pattern and to understand the role of the ionization/recombination processes or pressure gradients.

We investigate the temporal evolution of the system under a range of realistic and hypothetical high-latitude Hall and Pedersen conductance distributions. We find that gradients in either Hall or Pedersen conductance can alter the convection pattern, in contrast to earlier results suggesting that only Hall conductance gradients play a role.

How to cite: Popescu Braileanu, B., M. Laundal, K., and M. Hatch, S.: The role of Hall and Pedersen conductivity profiles in the ionospheric response to magnetospheric driving, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14069, https://doi.org/10.5194/egusphere-egu26-14069, 2026.

Alfvén waves with small perpendicular scale lengths are dispersive and can carry parallel electric fields. In the Earth's magnetosphere, they capture and accelerate electrons in a resonant process along the magnetic field lines down into the high-latitude ionosphere. These wave-particle interactions are considered to be a significant driver of auroral particle acceleration and as such an important coupling process between the magnetospheric and ionospheric systems. However, studying these waves and their associated auroral precipitations remains challenging due to the short temporal and spatial scales involved. As a result, their role in auroral dynamics continues to be an active area of research.

Here, we present data from one of the VISIONS-2 (Visualizing Ion Outflow via Neutral Atom Sensing-2) sounding rocket launched in December 2018 from Ny-Ålesund, Svalbard, in the active dayside auroral region. Numerous time-energy dispersed structures, indicative of particle acceleration by Alfvén waves, were observed by the top-hat ESA instrument. We present the high-resolution measurements of several of these structures and analyse their time-of-arrival in energy and pitch-angle. We discuss the implications of these observations for understanding the acceleration region.

How to cite: Gavazzi, E., Spicher, A., Gustavsson, B., Clemmons, J., and Rowland, D.: Auroral electron acceleration by dispersive Alfvén waves – insights from the VISIONS-2 rocket mission, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19919, https://doi.org/10.5194/egusphere-egu26-19919, 2026.

Omega bands are an auroral structure which consist of upward and downward field aligned currents (FACs) which are formed in the boundary between the region 1 and region 2 FACs in the dawn sector. They are characterised by their wave-like structure, which is often described as looking like a chain of the Greek letter Ω, with luminous extensions of the aurora protruding poleward. Omega bands cause ground based perturbations as they drift eastward, which can have large dB/dt values and hence are a potential source of geomagnetically induced currents (GICs). GICs are a hazard to our infrastructure, as currents can be induced in power grids, railways and pipelines. In this study, we investigate several cases of omega bands using ground and spaced based observations to examine their properties. Observations from the European Incoherent SCATter (EISCAT) radar show enhancements in electron density, which alongside measurements of FACs from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) can be used to study the intensity of different events. We use the IMAGE magnetometer network across Scandinavia to explore the latitudinal extend of omega bands as well as see their drift speed and dB/dt strength. SuperDARN and DMSP ion drift meter measurements help us to determine if the omega bands are embedded in the convection flow. Data from the DMSP Special Sensor Ultraviolet Spectrographic Imager (SSUSI) show the auroral data associated with omega bands. We present a study of omega bands from 2010 onwards.

How to cite: Hodnett, R., Milan, S., Gjerloev, J., Vines, S., Paxton, L., Nozawa, S., and Raita, T.: Omega bands as a source of dB/dt in the auroral dawn sector, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20143, https://doi.org/10.5194/egusphere-egu26-20143, 2026.

This paper presents GNSS radio occultation (RO) observational analyses on deducing the relationships and dependences between post-sunset EPB occurrences and EIA strength variability. The RO data were acquired from the FS7/COSMIC2 Program from 2020 to 2025. In this study, we incorporate both effects from crest peak electron density (N_emax) and crest-to-trough N_emax ratio and propose a new EIA strength parameter defined as the mean of northern and southern crest-to-trough N_emax differences to recognize and characterize the post-sunset EIA features. Both seasonal–longitudinal appearances of intense post-sunset EPB occurrences and strong EIA events occurred on more or less 30 days expanded from when and where magnetic flux tubes align with the sunset terminator at the magnetic equator but have more intense EPB and/or strong EIA days during southern (northern) hemispheric summers in the South American area (the Central Pacific area and the Africa area). It is well consistent with Tsunoda’s hypothesis during the evening pre-reversal enhancement (PRE) and reveals more informationt on day-to-day variability, intensities and extents of post-sunset EPB occurrences and EIAs subject to seasonal, longitudinal, and solar cycle variability. Moreover, the local-time evolutions of peak post-sunset EIAs occurred during 19~20 LT which is earlier than that of the obtained experimental peak (i.e., 20:20 LT) of post-sunset EPB occurrences. We expect that the post-sunset EIA detection could be a potential precursor for post-sunset EPB occurrence.

How to cite: Tsai, L.-C., Su, S.-Y., Lv, J.-X., Schuh, H., Alizadeh, M. M., and Wickert, J.: Evolution of post-sunset equatorial plasma bubbles: relationships to the equatorial ionospheric anomaly induced by pre-reversal enhancement electric fields, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-474, https://doi.org/10.5194/egusphere-egu26-474, 2026.

An automatic scheme to detect equatorial plasma bubbles had been developed for Ionospheric Plasma and Electrodynamics Instrument (IPEI) onboard ROCSAT-1 satellite which was in a 35° inclination orbit at 600 km altitude (Su et al., 2006).  However, some mis-identifications could be found in the southern hemisphere of the negative magnetic declination longitudinal region during June solstice when the scheme was applied for data measured by Advanced Ionospheric Probe (AIP) onboard the FORMOSAT-5 satellite which was in a 98.28° inclination sun-synchronous circular orbit at 720 km altitude.  The mis-identifications seems to relate to mid-latitude ring ionospheric troughs (Karpachev, 2019).  In this presentation, global seasonal patterns of the equatorial plasma bubbles from FORMOSAT-5/AIP data during 2018 to 2025 were re-generated by a revised scheme like the rate of change of density index (RODI) by Jin et al. (2019) and are similar to the patterns obtained by ROCSAT1/IPEI data during 1999-2003.

How to cite: Chao, C.-K.: A Revised Automatic Detection Scheme to Identify Equatorial Plasma Bubbles Observed by Advanced Ionospheric Probe Onboard FORMOSAT-5 Satellite, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4198, https://doi.org/10.5194/egusphere-egu26-4198, 2026.

Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) is used to investigate underlying physical processes of the thermospheric and ionospheric vortex-like structure over East Asia region in November 2003 superstorm. Horizontal neutral winds with a vortex configuration modulate the composition (O/N₂) perturbations, forming the two-dimensional vortex-like structure. Vertical winds also have a positive contribution to the final shape of this structure in the altitude distribution. The ionospheric vortex-like structure below the ionospheric peak height (hmF2) is dominated by chemical effects (O/N₂ enhancements) and neutral wind transport, while it is directly controlled by the neutral wind transport above the hmF2. Decreases of plasma density within the core region of this structure, driven by E×B drifts at all altitudes, also contribute to its formation. Analysis of the forcing terms driving the wind vortex in the middle thermosphere reveals the dominant role of pressure gradients, alongside the combined action from Coriolis force and horizontal momentum advection. In the upper thermosphere, the ion drag becomes significant, but only partially offsets the substantial positive effects of pressure gradients. Furthermore, controlled numerical experiments demonstrate that the storm intensity is not the single trigger mechanism for this structure. Instead, the asymmetrical prevailing circulation is more beneficial to the formation of the vortex-like structure. The storm onset time also affects the formation and location of this structure, although it is more liable to appear near the magnetic poles primarily in the American and East Asia sector.

How to cite: Yu, T., Zhao, B., Ren, Z., and Guo, X.: The underlying physical processes of the vortex-like structure over the East Asia region during the recovery phase of the November 2003 superstorm, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17147, https://doi.org/10.5194/egusphere-egu26-17147, 2026.

The ionosphere is the ionized region of the atmosphere extending from 50 km to 1000 km. During solar flares, the near-Earth space environment is subjected to enhanced high-energy X-ray and EUV radiation, which significantly impacts ionospheric conditions. Variations in ionospheric parameters measured by ionosondes, specifically the fmin and foF2 values, were examined during solar flares occurring under geomagnetically quiet conditions (Dst > −40 nT, Kp < 4) between 2023 March and 2024 June . The required data were obtained from manually evaluated ionograms recorded by the Czech DPS4D ionosonde at Pruhonice (PQ052).

The degree of variation was determined by comparison with monthly mean values, allowing the calculation of deviations in the studied parameters (dfmin, dfoF2). Time series of these deviations were analysed. Furthermore, the relationship between the ionospheric deviations and a flare “geoeffectiveness” parameter was investigated. This parameter was defined by considering the X-ray flux, the solar zenith angle at the station at the time of the event, and the position of the flare on the solar disk. A positive correlation was found between dfmin and the flare geoeffectiveness parameter, which proved to be stronger than the correlation obtained for dfoF2. In addition, a cumulative dfmin parameter was introduced, and its correlation with integrated X-ray flux values was examined. In this case as well, the flares were separated by intensity classes, similarly to the non-integrated analysis. The strongest correlation was obtained for flares above M6, reaching a maximum correlation coefficient of 0.97. 

The relationship between EUV radiation and the ionospheric parameters was also investigated; however, these correlations were found to be considerably weaker and did not reach comparable levels of statistical significance.

How to cite: Erdey, J., Barta, V., Buzás, A., and Lichtenberger, J.: The Impact of Solar Flares on the Ionosphere During Geomagnetically Quiet Periods, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14193, https://doi.org/10.5194/egusphere-egu26-14193, 2026.

Space weather events such as solar flares and energetic particle events cause enhanced absorption of radio waves in the lower ionosphere, posing difficulties to radio communication at certain frequencies. Increases in ionospheric absorption are due to enhancement of the ionisation in the D region which can be related to the following sources: (1) increases in hard X-rays during solar flares, which affects the day-lit side of the earth especially at lower latitudes, (2) impacts by high-energy solar protons, which can reach the D region in the polar cap were the field lines of the geomagnetic field are open , and (3) precipitation of electrons due to recombination events in the magnetotail, which can produce D-region ionisation in the auroral oval region.

Determination of the changes in ionospheric absorption is possible using ionosounding techniques in which the ionosonde actively emits radio pulses towards the ionosphere over a selected frequency sweep (typically between 1.5 and 14 MHz), and the passive antenna system of the same instrument receives the reflected echoes. The absorption can be defined by the minimum frequency reflected by the ionosphere what can be recorded on the ionograms (fmin parameter, Barta el a. 2019). It can also be quantified based on the received amplitudes of the echoes (Buzás et al. 2023). An alternative approach to analyze the signal-to-noise ratio  of radio waves recorded on ionograms during solar events (de Paula et al. 2022). Another method to determine the absorption variation is to use the instrument in "listening mode" and analyze the background noise observed in the HF band (practically in 10–30 MHz range) during solar events.

The main purpose of the current study is to investigate the ionospheric absorption changes over Europe during the Mother’s Day Superstorm, determined from different type of data recorded by ionosondes at midlatitudes. A detailed analysis of the probable sources of the absorption changes —solar flare effects, polar cap and/or auroral absorption— will be discussed. Furthermore, we will compare the advantages and disadvantages of the different methods based on the results.

References:

Barta, V., Sátori, G., Berényi, K. A., Kis, Á., & Williams, E. (2019). Effects of solar flares on the ionosphere as shown by the dynamics of ionograms recorded in Europe and South Africa. Ann. Geophys. 37, 747-761. https://doi.org/10.5194/angeo-37-747-2019.

Buzás, A., Kouba, D., Mielich, J., Burešová, D., Mošna, Z., Koucká Knížová, P., & Barta, V. (2023). Investigating the effect of large solar flares on the ionosphere based on novel Digisonde data comparing three different methods. Front. Astron. Space Sci., 10:1201625. https://doi.org/10.3389/fspas.2023.1201625.

de Paula, V., Segarra, A., Altadill, D., Curto, J. J., & Blanch, E. (2022). Detection of solar flares from the analysis of signal-to-noise ratio recorded by Digisonde at mid-latitudes. Remote Sens., 14, 1898. https://doi.org/10.3390/rs14081898.

How to cite: Barta, V., Verhulst, T., Altadill, D., Mosna, Z., Segarra, A., Szárnya, C., de Paula, V., and Buzás, A.: Ionospheric absorption variation during the Mother Day Superstorm in May 2024 as observed by different types of ionosonde data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9555, https://doi.org/10.5194/egusphere-egu26-9555, 2026.

• Magnetosphere-Ionosphere-Thermosphere coupling response to the 1st December 2023 geomagnetic storm at low- and middle-latitude regions

Syed Faizan Haider<sup>1*

1*</sup> Space Education and GNSS Lab, National Center of GIS & Space Applications, Department of Space Science, Institute of Space Technology, Islamabad 44000, Pakistan
Faizanhaider92110@gmail.com

Abstract:

We investigate the global effects of the December 1, 2023 geomagnetic storm on the magnetosphere, ionosphere and thermosphere by utilizing data from the Magnetometer, Global Navigation Satellite System (GNSS), Swarm Mission and Global Ultraviolet Imager (GUVI). We found distinct vTEC patterns across different latitudes during various storm phases. Stations in Asia, Africa, North America, and Central America showed vTEC peaks during the main phase. In contrast, stations at mid-latitudes demonstrated both positive and negative ionosphere storms. These variations are attributed to changes in the Prompt Penetration Electric Field (PPEF), influenced by oscillations in the Interplanetary Magnetic Field (IMF) Bz component and interactions with solar winds and Earth's magnetosphere. Moreover, both the meridional and zonal winds provided by Horizontal Wind Model 2014 (HWM14) displayed positive correlation with vTEC variations of multiple GNSS stations throughout the storm. This correlation was especially strong over the Asian stations during both the main and recovery phases, while stations in Africa, America, and Oceania showed more prominent correlations during the recovery phase. In addition, low latitude regions in Asia, as well as mid latitude regions in New Zealand, South Africa, and South America, all showed a negative ionosphere storm as a result of the modification of the thermosphere winds. Strong correlations between the Swarm satellite data, GNSS stations, and vTEC variations confirm storm-penetrated ionospheric disturbances. Furthermore, significant variations in Earth's magnetic field, including the H-component and Diono, are observed, highlighting the complex dynamics of ionospheric perturbations during geomagnetic storms across diverse latitudinal and longitudinal contexts.

Keywords: Ionosphere, Thermosphere, Magnetosphere, Geomagnetic Storm, GNSS, Remote Sensing, vTEC, PPEF, GUVI

How to cite: Haider, S. F.: Magnetosphere-Ionosphere-Thermosphere coupling response to the 1st December 2023 geomagnetic storm at low and middle latitude regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13708, https://doi.org/10.5194/egusphere-egu26-13708, 2026.

Understanding the variability of the thermosphere–ionosphere (T–I) system across different conditions is especially important, as its state critically affects the operation and safety of numerous low Earth orbit (LEO) satellites. In the absence of routine thermospheric monitoring, ionosonde measurements and satellite data can be used to retrieve key aeronomic parameters at mid-latitudes during noontime via the THERION (THERmospheric parameters from IONosonde observations) method.

This study applies the THERION technique to analyze the T–I response in the European and American longitudinal sector to two recent severe geomagnetic storms (October 2024 and January 2025). Validated ionosonde data from Rome, Juliusruh, Millstone Hill and Eglin were used to assess ionospheric variability and derive thermospheric parameters such as neutral composition, temperature, and wind. Results are compared with outputs from the MSISE00 empirical model, highlighting THERION's improved capability in capturing thermospheric dynamics under storm conditions.

Additional datasets—including co-located GNSS-derived TEC, geomagnetic field data from the INTERMAGNET network, and interplanetary/magnetospheric conditions—were integrated to provide a comprehensive view of the events and the unique T-I coupling processes associated with each storm.

This study is carried out within the Space It Up project funded by the Italian Space Agency, ASI, and the Ministry of University and Research, MUR, under contract n. 2024-5-E.0 - CUP n. I53D24000060005.

How to cite: Sabbagh, D., Perrone, L., Scotto, C., Ippolito, A., Spogli, L., Regi, M., and Bagiacchi, P.: Comparing Northern Hemisphere Mid-Latitude Thermosphere-Ionosphere Response to Two Recent Geomagnetic Storms, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19800, https://doi.org/10.5194/egusphere-egu26-19800, 2026.

Anthropogenic greenhouse gas (GHG) emissions are the ongoing major driver of Earth’s climate change. While the increasing concentration of GHG causes a warming of the lower atmosphere, it leads to a cooling of the upper atmosphere, which is expected to result in a thermal contraction. These changes in the neutral atmosphere have been demonstrated to also influence the ionosphere. In fact, the contraction of the whole upper atmosphere should induce a downward displacement of the ionospheric layers due to the changes in the vertical distribution of the different ion species in the ionosphere.

To study the ionosphere changes in response to climate change, we investigate the long-term trends of the ionospheric equivalent slab thickness (τ). τ represents the thickness of an ideal ionospheric slab of constant electron density equal to that of the F2-layer peak (NmF2) with a vertical total electron content (vTEC) value equivalent to that of the entire ionosphere. To achieve this, we derive τ time series from a selection of globally distributed and co-located ionosondes (providing NmF2) and ground-based GNSS receivers (providing vTEC), focusing on stations with at least two solar cycles of continuous data. For trend and coherent structures extraction and analysis, we use the Empirical Mode Decomposition (EMD), an advanced data-adaptive decomposition method. EMD is particularly suited for preserving nonlinearity in time series and for processing non-stationary data, offering a more accurate representation of long-term variations compared to traditional statistical methods. We present preliminary results showing a global long-term decrease of τ, but with magnitudes dependent on latitude, pointing out a general shrinking of the ionosphere in the last two decades.

How to cite: Pignalberi, A. and Alberti, T.: Long-Term Trends in the Ionospheric Equivalent Slab Thickness: Is the ionosphere really shrinking?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5150, https://doi.org/10.5194/egusphere-egu26-5150, 2026.

Machine learning (ML) has shown growing promise for space weather applications. However, its performance is often limited by the scarcity of rare-event observations and a lack of physical consistency. In this study, we investigate plasmaspheric cold electron density modeling using approaches that span the spectrum from purely physics-based [1] to purely data-driven [4], with a focus on three hybrid physics–machine learning strategies. These strategies incorporate physical information through discrepancy correction, physics-informed input augmentation, and physics-based regularization. Each hybrid model combines density outputs from the VERB-CS [1] simulation with a neural network to estimate plasmaspheric cold electron density. The neural networks are trained using in situ electron density measurements from the Van Allen Probes [2] together with geomagnetic indices. Hybrid models embed key physical processes (such as particle transport, refilling, and loss mechanisms) into the learning framework.

We assess the predictive capability of the hybrid models relative to pure ML and pure physics-based approaches through comparisons with in situ Van Allen Probes observations and global plasmaspheric images from the IMAGE Extreme Ultraviolet instrument [3]. Our results indicate that the hybrid models reproduce both large-scale plasmaspheric structure and smaller-scale features more accurately than either purely data-driven or purely physics-based models across a range of geomagnetic activity levels. Incorporating physical information into the ML framework improves generalizability across different geophysical conditions, including periods of enhanced geomagnetic activity. These results demonstrate the potential of physics-informed machine learning approaches to advance predictive modeling of the near-Earth plasma environment.

References
[1] Aseev, N., Shprits, Y., 2019. Reanalysis of ring current electron phase space densities using Van Allen Probe observations, convection model, and log-normal Kalman filter. Space weather 17, 619–638.
[2] Kletzing, C., Kurth, W., Acuna, M., MacDowall, R., Torbert, R., Averkamp, T., Bodet, D., Bounds, S., Chutter, M., Connerney, J., et al., 2013. The electric and magnetic field instrument suite and integrated science (EMFISIS) on RBSP. Space Science Reviews 179, 127–181.
[3] Sandel, B., Goldstein, J., Gallagher, D., Spasojevic, M., 2003. Extreme ultraviolet imager observations of the structure and dynamics of the plasmasphere. Magnetospheric imaging—The image prime mission , 25–46.
[4] Zhelavskaya, I.S., Shprits, Y.Y., Spasojević, M., 2017. Empirical modeling of the plasmasphere dynamics using neural networks. Journal of Geophysical Research: Space Physics 122, 11–227.

How to cite: Shahsavani, S. and Shprits, Y.: Hybrid Physics–Machine Learning Modeling of Plasmaspheric Cold Electron Density, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3424, https://doi.org/10.5194/egusphere-egu26-3424, 2026.

Reliable modeling of plasmaspheric density during geomagnetically disturbed periods is limited by sparse in-situ observations at high geomagnetic activity. In this study, we extend the PINE (Plasma density in the Inner magnetosphere Neural network-based Empirical) model using a Physics-Informed Neural Network (PINN) framework to improve performance during extreme conditions (Kp > 6). Density predictions from the physics-based VERB-CS model are incorporated to augment training data for high-Kp events, addressing a key limitation of previous empirical approaches. We develop and evaluate two PINN-based models: one trained exclusively on high-Kp data and another trained on a combined data set including electron density measurements from the Van Allen Probes and Arase missions together with VERB-CS density outputs. The performance of these models is directly compared across geomagnetic activity levels, enabling a systematic assessment of the impact of physics-based data integration on plasmaspheric density predictions in terms of accuracy and error variance. Model outputs are also compared with independent IMAGE EUV observations to evaluate each model’s ability to reconstruct global plasmaspheric structures under disturbed conditions.

How to cite: Shilu, L., Shahsavani, S., and Shprits, Y.: Extending PINE for High-Kp Plasmaspheric Density Modeling Using Physics-Informed Neural Networks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18831, https://doi.org/10.5194/egusphere-egu26-18831, 2026.

The subauroral ionosphere is the transition zone between the convecting and corotating plasma and plays an important role in the magnetosphere - ionosphere (MI) interaction. The midlatitude ionospheric trough (MIT), a longitudinally extended depletion in electron density, is an important feature of this region. Various formation mechanisms have been proposed but some of their underlying physics remains unknown. 

The MIT exhibits a strong dependence on magnetospheric activity and magnetic local time (MLT). This dependence has been captured by empirical models describing the location of the MIT (e.g., Deminov and Shubin, 2018; Werner and Prössl 1997).

In this study, we present a new empirical model that describes the location of the MIT electron density minimum and its associated equatorward and poleward walls.  The model is based on empirical observations combined with ionospheric physics. The dataset is derived from the Swarm-PRISM MIT product (https://earth.esa.int/eogateway/activities/swarm-prism)  where MIT features are identified using Langmuir probe measurements from the ESA Swarm mission. The model input parameters are MLT and a time weighted average of the geomagnetic activity represented by the Hp30 index (Yamazakiet et al., 2022).  More than 170 000 of MIT events have been identified which is a large dataset compared to previous models allowing our model to provide a more precise and more featured description of the MIT compared to existing models. Our model can also provide a tool for monitoring magnetospheric processes and can advance the understanding of MIT formation mechanisms.

How to cite: Tomasik, M. and Heilig, B.: An Empirical Model of the Midlatitude Ionospheric Trough Based on Swarm Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21417, https://doi.org/10.5194/egusphere-egu26-21417, 2026.

Accurately estimating three-dimensional wind fields in the mesosphere and lower thermosphere (MLT) is crucial for understanding the dynamics and variability of the middle atmosphere, which exhibits complex behavior driven by a range of atmospheric waves covering spatial scales from kilometers to almost the diameter of the planet and temporal scales reaching from minutes to several days. Vertical winds are of particular interest and determine adiabatic heating/cooling as well as the vertical transport. They are challenging to retrieve due to their relatively weak magnitude compared to the horizontal wind components and instrument limitations. Multistatic meteor radar networks enable sophisticated tomographic wind retrievals, such as the Spherical Volume Velocity Processing (SVVP), or more advanced Bayesian methods like the 3DVAR+DIV algorithm. The current 3DVAR+DIV model is implemented in geographic and Cartesian grid coordinates based on pre-defined grid cells defined by a reference coordinate, which adversely affects the estimation of vertical winds due to the often low statistics and, thus, residual projection errors. The vertical winds are typically an order of magnitude weaker than horizontal winds and highly sensitive to even tiny projection errors.
In this study, we present the 3DVAR+DIV algorithm in spherical coordinates to account for the Earth’s curvature and the latitude-dependent change of the Earth’s radius. This implementation introduces several new unknowns per grid cell and will undergo multiple parameter tests using the Nordic Meteor Radar Cluster (NORDIC). This approach aims to improve the accuracy of wind retrievals, particularly for the vertical wind components. The new algorithm in spherical coordinates will mitigate the residual projection errors caused by the sparsity of the measurements.

How to cite: Poku, L. P., Stober, G., Krochin, W., Kozlovski, A., Lui, A., Janches, D., Tsutsumi, M., Gulbrandsen, N., Nozawa, S., Lester, M., Kero, J., Mitchell, N., and Yi, W.: Implementation of Spherical Coordinates in 3DVAR+DIV Model: An Enhancement of Geophysical Data Assimilation., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5625, https://doi.org/10.5194/egusphere-egu26-5625, 2026.

Stronger solar activity can modulate galactic cosmic rays reaching the Earth, affecting the production of Be-7 in the stratosphere and its subsequent downward transport. Corotating Interaction Regions (CIRs) and High-Speed Solar Wind Streams (HSSWS) significantly perturb the ionosphere, altering electric fields and plasma dynamics in the ionosphere, influencing Es layer formation and behavior. Often causing Es layer formation (higher electron density, stronger critical frequency) during geomagnetic disturbances.

We use radionuclide data (Be-7 in aerosols evaluated by the corresponding activity in aerosols on a weekly basis at the National Radiation Protection Institute Monitoring Section in Prague, Czechia) alongside ionospheric data (Es layers) to understand these interconnected space weather effects and atmospheric dynamics. Es layers, formed by dynamic processes, can influence atmospheric waves and vertical transport, potentially connecting upper atmosphere phenomena with atmospheric radionuclide levels in middle latitudes. The Be-7 concentrations are therefore a very promising indicator of the behavior of all atmospheric layers, including the mesospheric heights where the Es layer is located.

How to cite: Podolská, K., Šindelářová, T., Kozubek, M., Koucká Knížová, P., and Hýža, M.: Be-7 cosmogenic radionuclide concentrations as a tracer of dynamic processes in upper atmosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14769, https://doi.org/10.5194/egusphere-egu26-14769, 2026.

How to cite: Na, G. W., Seon, J., Lee, D.-H., and Park, S. H.: Scenario-Based Surface Charging Guidance for CubeSat-Class Satellites in Low Earth Orbit, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16602, https://doi.org/10.5194/egusphere-egu26-16602, 2026.

ESA’s Sentinel program consists of multiple satellites for Earth observation. The first launches were in 2014; since then, the constellation has continued to grow. In this study, we will utilize Sentinel-1, Sentinel-2, Sentinel-3, and Sentinel-6. They all carry geodetic-type GNSS receivers, which are used for precise orbit determination, but in turn provide highly precise slant TEC observations. The satellites are located in altitudes between 730 km and 1350 km and can measure slant TEC between the receiver and GNSS satellites. This area is also the transition region from the ionosphere to the plasmasphere. Significant efforts have been made over the last few years to reliably connect the ionosphere and plasmasphere. The current IRI-2020 model provides multiple topside and plasmasphere options, recent works adjusted the NeQuick-2 model to better represent the plasmasphere, empirical electron density modeling for a combined ionosphere and plasmasphere, and even neural networks are successfully used. We investigate the performance of selected models by evaluating slant TEC differences between the observations from Sentinel and the models. Investigations are carried out for recent time spans starting in 2021, following the launch of Sentinel-6, including low and high solar activity, quiet and disturbed periods. To our knowledge, this study presents the first analysis of multi-GNSS TEC observations from Sentinel-6.

How to cite: Schreiter, L., Prol, F., Hoque, M. M., Smirnov, A., Milea, I.-A., and Schmidt, M.: Using Sentinel satellites for validation and quality assessment of topside ionosphere and plasmasphere models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18703, https://doi.org/10.5194/egusphere-egu26-18703, 2026.

Solar activity, including variations in solar radiation and transient disturbances in the solar wind, drives a variety of processes in Earth's atmosphere. Solar ultraviolet (UV) radiation provides the primary energy input to the mesosphere and lower thermosphere, while enhanced solar wind plasma and magnetic field variations can indirectly influence atmospheric dynamics through magnetospheric coupling. These processes lead to atmospheric emissions observed as airglow and, at higher latitudes, aurorae.

MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) provides an opportunity to study the mesospheric infrared O₂ A-Band emission, whose variability and excitation mechanisms are not yet fully understood. Using MATS observations from February to May 2023, we extract time series of airglow brightness variations in the mesosphere. To characterize solar activity, we use solar UV flux measurements from NASA's SDO/EVE and TIMED/SEE instruments.

In addition, we examine the occurrence of coronal mass ejections and co-rotating interaction regions during the study period to assess their potential contribution to the observed variability. We present correlations between MATS airglow brightness, solar UV irradiance, and solar wind parameters to quantify the relative roles of radiative and geomagnetic drivers.

How to cite: Rausch, J., Blüthner, G., Temmer, M., Giono, G., Ivchenko, N., and Megner, L.: Solar UV flux in relation to airglow variability as seen by MATS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18805, https://doi.org/10.5194/egusphere-egu26-18805, 2026.

Due to the ionosphere's significant impact on radio signal propagation, accurate modeling and reconstructions of its electron density distribution are crucial for various applications involving trans-ionospheric signals, such as GNSS positioning, GNSS augmentation systems (e.g., EGNOS and WAAS), remote sensing, but also to enhance our understanding of ionospheric processes. Several approaches have been developed for ionospheric reconstruction by combination of actual observations with a physical or an empirical background model. When looking for storage space and runtime saving approaches, algebraic iterative methods have been used to ingest current measurements into background models, e.g. derivatives of the Algebraic Reconstruction Technique (e.g. ART, MART) and column-normalized methods (e.g. SART, SMART). Those methods are working without the modification of the model coefficients but by updating the background in the area surrounding the available current measurements.

We introduce the new 4D electron density reconstruction approach 4DSMART+ as a combination of SMART, the successive correction method and a time propagation model. We apply 4DSMART+ to reconstruct the electron density distribution within the topside ionosphere and plasmasphere on a global grid with altitudes between 430 and 20200 km for a 59-day period of the year 2015 with moderate ionospheric conditions. STEC measurements of eleven LEO satellites (e.g. Swarm, COSMIC-1, MetOp) are used as data base for the reconstructions where the NeQuick model serves as background.

The comparison of the reconstructions to assimilated STEC measurements shows consistency with a median error of 0.1 TECU and a standard deviation of 3.4 TECU.  Furthermore, 4DSMART+ is compared to SMART+ and the NeQuick model with respect to its capability to reproduce independent STEC data from the three LEO satellites GRACE and Swarm A. The results show that 4DSMART+ decreases the median STEC error for GRACE and Swarm A STEC by up to ~84% and ~99%, respectively, compared to SMART+ and the NeQuick model. Validation by means of the COSMIC-1 radio occultation profiles shows that 4DSMART+ reduces the median of the relative residuals by up to 13% in comparison to SMART+ and the NeQuick model.

How to cite: Gerzen, T., Minkwitz, D., Schmidt, M., and Schreiter, L.: 4-D tomography method 4DSMART+ for the reconstruction of topside ionosphere and plasmasphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18373, https://doi.org/10.5194/egusphere-egu26-18373, 2026.

Active experiments in the ionosphere aim to artificially and significantly modify the space and/or ionospheric environment over large spatial scales. A typical goal of such experiment would be to deplete high energy particles from selected orbits, using, for example, physical processes based on wave-particle interactions with artificially emitted electromagnetic waves. In this work, we study electromagnetic waves generated by an electron beam in the ionosphere. We use the Beam Plasma Interaction Experiment (Beam PIE) as reference, with a typical altitude of ~500 km and a ~15 keV electron pulsed beam emitted parallel to the magnetic field. We rely on the heavily parallelized SMILEI code to perform a parametric study with fully kinetic Particle-In-Cell simulations of such beams. Such study is only made possible thanks to simulation cost reduction through a dimension reduction to a 2D problem with cylindrical symmetry. Varying both the main parameters of the beam (beam density, frequency, length, etc.) and of the ambient environment (magnetic field strength and cold plasma density), we investigate the impact of those parameters on the electromagnetic wave generation mechanism and the wave’s properties. We especially look into the dependance of the wave’s energy distribution and power to the initial beam properties.

How to cite: Dargent, J., Ripoll, J.-F., Beck, A., Chust, T., Belmont, G., Le Contel, O., Cerfolli, L., Farge, T., and Retinò, A.: Parametric study of the generation of electromagnetic waves in an active experiment with electron beams, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18083, https://doi.org/10.5194/egusphere-egu26-18083, 2026.