The Low Frequency Array (LOFAR) is one of the most advanced radio telescopes in the world. When radio waves from a distant astronomical source traverse the ionosphere, structures in this plasma affect the signal. The high temporal resolution available (~10 ms), the range of frequencies observed (10-90 MHz & 110-250 MHz) and the large number of receiving stations (currently 52 across Europe) mean that LOFAR can also observe the effects of the midlatitude and sub-auroral ionosphere at an unprecedented level of detail.
Case studies have shown substructure within a sporadic-E layer (Wood et al., 2024), substructure within a Medium Scale Travelling Ionospheric Disturbance (TID) (Dorrian et al., 2023), a Small Scale TID (Boyde et al., 2022) and symmetric quasi-periodic scintillations (Trigg et al., 2024). The small-scale size of many of these features (kilometres to tens of kilometres) implies a local source. A climatology of observations during daylit hours shows that ionospheric waves primarily propagate in the opposite direction to the prevailing wind, suggesting that the structures observed are the ionospheric manifestation of quasi-upward propagating Atmospheric Gravity Waves (AGWs; Boyde et al., under review).
The recent development of a light version of the LOFAR data means that, for the first time, it is possible to undertake a large statistical study spanning all seasons and local times. Approximately 3,000 hours of observations were used to create this first climatology. It is shown that the ionospheric structures occur most frequently on summer evenings, are not primarily driven by geomagnetic activity and that there are striking similarities to a climatology of lighting strikes. This adds to the body of evidence which suggests that these features are the ionospheric manifestation of AGWs. Such waves substantially affect the global atmospheric circulation and the potential use of LOFAR to better determine the effect of AGWs on the global circulation is discussed.
This work is supported by the Leverhulme Trust under Research Project Grant RPG-2020-140.
References
Boyde, B. et al. (2022). Lensing from small-scale travelling ionospheric disturbances observed using LOFAR, J. Space Weather Space Clim., 12, 34. doi:10.1051/swsc/2022030
Dorrian, G. D. et al. (2023). LOFAR observations of substructure within a traveling ionospheric disturbance at mid-latitude, Space Weather, 21, 2022SW003198. doi:10.1029/2022SW003198
Trigg, H. et al. (2024). Observations of high definition symmetric quasi-periodic scintillations in the mid-latitude ionosphere with LOFAR. J. Geophys. Res., 2023JA032336. doi:10.1029/2023JA032336
Wood, A. G. et al. (2024). Quasi-stationary substructure within a sporadic E layer observed by the Low Frequency Array (LOFAR), J. Space Weather Space Clim. 14, 27. doi:10.1051/swsc/2024024
How to cite: Wood, A., Dorrian, G., Boyde, B., Trigg, R., Fallows, R., and Mevius, M.: Driving The Mid-Latitude Ionosphere from Below: Observations Made Using the International LOFAR Telescope, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4241, https://doi.org/10.5194/egusphere-egu25-4241, 2025.
Distinct Ionospheric perturbations such as equatorial plasma bubbles (EPB) and traveling ionospheric disturbances (TID) affect propagation of electromagnetic waves in the ionosphere. Consequently, electromagnetic waves can be used for their investigation. However, the ionospheric perturbations can also be monitored and analysed optically, using airglow emissions of OI red line (630 nm) because the intensity of this emission depends on the electron density and composition of the thermosphere, which changes with height.
Simultaneous observations of EPBs and TIDs over Northern Argentina by airglow imager and Continuous Doppler Sounding (CDS) are presented. The EPBs propagated roughly eastwards as expected, whereas the large scale TIDs detected by both instruments propagated roughly north-westward. The TIDs of shorter periods/wavelengths are mostly observed only by CDS. A likely explanation is that the positive and negative phases of waves with shorter wavelengths are cancelled during integration along the line of sight in a relatively thick OI 630 nm emission layer. Selected examples and their propagation analysis is presented.
How to cite: Chum, J., Mackovjak, Š., Martinis, C., Molina, M. G., and Base, J.: Analysis of ionospheric disturbances using Continuous Doppler Sounding and airglow, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3550, https://doi.org/10.5194/egusphere-egu25-3550, 2025.
Co-seismic ionospheric disturbances (CIDs) are well-documented phenomena typically following medium to large earthquakes. However, several factors influence the detectability of CIDs, and deep-focus earthquakes (depth > 300 km) have long been considered ineffective in generating significant ionospheric disturbances. Consequently, regions like Brazil, which are known for deep-focus seismic activity, have not reported CIDs associated with such events. On January 20, 2024, a deep-focus earthquake of magnitude 6.6 struck near Tarauacá, Brazil, at a depth of 607 km. Although no surface damage was reported, this event marked a significant seismic occurrence in a region influenced by the subducted Nazca Plate. In this study, we used Global Navigation Satellite System (GNSS) Total Electron Content (TEC) data from the Brazilian Network for Continuous Monitoring of GNSS Systems (RBMC) and seismic data from the IRIS network to analyze the earthquake's impact on both the ground surface and the ionosphere. The results revealed clear ionospheric disturbances, or ionoquakes, characterized by "N-wave" patterns in the TEC data, originating from infrasonic-acoustic waves generated by the earthquake’s crustal displacement. These ionoquakes were detected 5.5 - 12.3 minutes after the earthquake, traveling at speeds between 550 m/s and 743 m/s. This is the first report of CIDs associated with a deep-focus earthquake in Brazil. Spectral analysis showed a TEC amplitude peak in the 14–16 mHz frequency range, suggesting high-frequency infrasonic-acoustic wave dynamics.
How to cite: Adebayo, O., Kherani, E. A., and Pimenta, A. A.: First Observation of Co-seismic Ionospheric Disturbances from a Deep-Focus Earthquake in Brazil: Ground Uplift and TEC Analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-86, https://doi.org/10.5194/egusphere-egu25-86, 2025.
In this study, the morphology and climatology of the nighttime periodic disturbances associated with MSTIDs are investigated over the entire China sector from January 2014 to August 2017, using data from global navigation satellite systems (GNSS) receivers. Firstly, a comparative case analysis of propagation characteristics reveals the complexity and day-to-day variations of nighttime MSTID activity. The main statistical findings indicate that these periodic disturbances predominantly occur during the summer months, with a higher occurrence rate during solar minimum. In summer, the disturbances occur more frequently in regions with lower latitudes (20-35°N) and tend to exhibit an extended duration. In the meantime, some disturbances are also detected at much lower latitudes (<20°N), with noticeable longitudinal differences. Additionally, there are two peaks in the geographic distribution of disturbances, located in the sector of 90-100°E and 105-125°E at lower latitudes, respectively. The distinct spatiotemporal evolution patterns of the two peak disturbance regions suggest that their formation mechanisms should be different. The disturbances in the eastern region exhibit similarities with electrified MSTIDs, which are closely related to Perkins instability, whereas the western disturbance region does not display apparent movement, but exhibits a higher occurrence rate and longer durations, which may be attributed to the frequent upward propagation of GWs in the southeastern region of the Qinghai-Tibet Plateau.
How to cite: Li, K. and Zhang, D.: Morphology and Climatology of Nighttime Periodic Ionospheric TEC Disturbances Associated with MSTIDs Over China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1245, https://doi.org/10.5194/egusphere-egu25-1245, 2025.
Solar EUV irradiance ionizes the Earth's dayside atmosphere and, together with the Earth's rotation, forms ionospheric currents called the solar regular (SR) current system. The SR current system consists of two vortices whose turning points deflect the magnetic Y (east-west)-component, forming a systematic daily variation in declination, with maximum in the local morning and a minimum in the afternoon (in the northern hemisphere and oppositely in the south). The daily amplitude (range, rY) of this variation depends on the intensity of ionization and, thereby, on the intensity of solar EUV irradiance. This variation was found by Graham Greene already in 1722, and in 1850s Rudolf Wolf used the yearly rY values to fill in gaps in early sunspot observations when continuing his series of relative sunspot numbers to the 18th century.
Here we use the yearly rY values from six long-running magnetic stations as a long-term proxy of solar EUV irradiance to study the relation between sunspots and solar EUV irradiance during the last 130 years. This period contains one full cycle of the centennial Gleissberg cyclicity (GC) from low cycles at the turn of the 19th and 20th century to a maximum during the highest cycle 19 with a decay to a low cycle 24.
We find that sunspots increase relatively more than EUV irradiance during the GC growth phase (when solar activity is increasing) but also decrease relatively more than EUV irradiance during the GC decay phase (when solar activity is decreasing). Since EUV irradiance mainly originates from solar plages that are chromospheric counterparts of photospheric faculae, this long-term change between sunspots and EUV irradiance implies a variation between sunspots and faculae over the Gleissberg cycle, which gives interesting information about the stellar evolution of the Sun.
How to cite: Mursula, K.: What on Earth can the ionosphere tell about the stellar evolution of the Sun?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15181, https://doi.org/10.5194/egusphere-egu25-15181, 2025.
Very low frequency (VLF, 3-30 kHz) radio waves can propagate large distances around the Earth within the Earth-ionosphere waveguide with relatively low attenuation. As a result, careful measurements of the amplitude, phase, and polarization of subionospherically-propagating VLF waves can be used to remote-sense the D-region ionosphere over large swaths of the Earth. In this paper, we present a new signal processing method for calculating the amplitude, phase, and polarization of subionospherically-propagating VLF waves. The method allows for impulsive sferic rejection as well as local interference rejection, and the integration method mitigates (to some degree) the impact of receiver system noise on the measurement. We apply the new method to a variety of natural VLF events, such as early/fast VLF events and lightning-induced electron precipitation events, and we compare the performance of the method with the performance of other well-known VLF signal processing methods.
How to cite: Moore, R. and Camp, J.: Superior VLF Remote Sensing of the Ionosphere Using Stokes Parameters, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20657, https://doi.org/10.5194/egusphere-egu25-20657, 2025.
Omega bands are a dawn-sector phenomena which appear as wave-like structures in the aurora, which often look like a chain of the Greek letter Ω. Omega bands have recently been shown to be responsible for large variations in dB/dt which can trigger geomagnetically induced currents (GICs), which are a significant space weather hazard. Signatures of an omega band event are visible in the European Incoherent SCATter (EISCAT) data at Tromsø, Norway (69.6 °N, 19.2 °E), alongside observations from multiple instruments situated near Tromsø. The omega band is clearly identifiable in the Tromsø all sky camera data from 00:00 – 03:00 UT as it propagates eastward. This event is of interest for several reasons. During this event, the polar cap and field aligned current systems are expanded, and there are multiple intensifications in the AL index. These features are often misidentified as substorms, however in this case the fluctuations in the westward electrojet result from the omega band. Large ground-based magnetic perturbations are visible, and associated ‘spikes’ in dB/dt are identified in the auroral dawn sector. Data from the EISCAT UHF and VHF radars allow us to see enhancements in the ionospheric electron density which occurred as the upwards field aligned current and luminous aurora passed overhead. Additional electron density enhancements in the D region ionosphere were observed, which correspond to enhancements in cosmic noise absorption measured by nearby riometers. We present an overview of the electrodynamics of this omega band event at Tromsø.
How to cite: Hodnett, R., Milan, S., Nozawa, S., and Raita, T.: Observations and electrodynamics of an omega band aurora at Tromsø, Norway, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6487, https://doi.org/10.5194/egusphere-egu25-6487, 2025.
The SPIDER-2 sounding rocket was launched into a Pulsating Aurora event in February 2020. It was launched from Esrange (67° 53 '22.79 " N, 21° 06' 15.00" E) and it recorded multipoint measurements of the plasma parameters and electromagnetic fields up to an altitude of almost 130 km. The in situ measurements obtained by the rocket and the eight free falling units were complemented by ground based optical instrumentation obtained by the ALIS4D sky imagers and a High Speed Camera. The main instruments carried by the main rocket were four electron probes, two ion probes, a dipole antenna for a wave propagation experiment and a photometer, while the free falling units carried four cylindrical Langmuir probes and four spherical electric field probes each, together with magnetometer sensors.
Previously, plasma parameters such as electron density and temperature or ion thermal flux, collected by some of the instruments onboard the rocket, were presented and compared with ground based measurements. Now, the data collected by the electric field probes and the magnetometers has been despinned and analyzed with the goal to reconstruct the currents in the E region during the pulsating aurora event. Here, we present our study on the multi-point measurements of in situ electric and magnetic fields and their relation to the electrodynamics of the E-region.
How to cite: Pérez-Coll Jiménez, J. and Ivchenko, N.: SPIDER-2 Sounding Rocket: Electromagnetic fields in Pulsating Aurora, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16366, https://doi.org/10.5194/egusphere-egu25-16366, 2025.
Space Weather Ionospheric Network Canada (SWINCan), formerly the Canadian High Arctic Ionospheric Network (CHAIN), has provided continuous, near-real-time monitoring of the high-latitude ionosphere since 2007. Capitalizing on Canada’s geographic expanse and proximity to the northern magnetic pole, SWINCan’s expansive instrument network delivers high-latitude ionospheric data including essential space environment quantities for scientific and operational use. This data enables fundamental understanding of the ionosphere and its role in radio propagation and solar-terrestrial interactions, while also providing critical input for ionosphere nowcast/forecast models that support scientific research and operations of navigation, communication, and radar systems at sub-auroral, auroral, and polar latitudes.
In response to growing demand for enhanced high-latitude observational capacity, the Radio and Space Physics Laboratory (RSPL) at the University of New Brunswick is in the process of substantially expanding and modernizing SWINCan. By 2026, this pan-Canadian network will consist of 128 global navigation satellite system (GNSS) ionospheric scintillation and total electron content monitors (GISTMs) and 20 modernized high-frequency (HF) ionospheric sounders, adding to the 28 GISTMs and 10 HF sounders that are currently deployed. SWINCan GISTMs record raw 50 Hz/100 Hz data enabling study of the multi-spatiotemporal-scale structuring of the ionosphere, including fundamental study of radio wave scintillation in a turbulent ionosphere. As part of SWINCan modernization, RSPL has also developed a state-of-the-art, versatile HF platform to enhance SWINCan ionosonde systems. Updated systems are specifically designed for harsh environments such as the Arctic, are fully and remotely configurable, and are capable of interdependent experiments with other ground and spaceborne radio systems.
How to cite: Watson, C.: The Expansion and Modernization of Space Weather Ionospheric Network Canada, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14080, https://doi.org/10.5194/egusphere-egu25-14080, 2025.
Understanding both the spatial and temporal dynamics of the near-Earth space environment is important for successful forecasting of space weather. One example is the auroral Joule heating which causes thermal expansion of the upper atmosphere, increasing the thermospheric density and causing low Earth orbiting (LEO) satellites to experience more drag. This chain of events often begins when geoeffective solar wind transients such as high-speed stream/stream interaction regions (HSS/SIR) or interplanetary coronal mass ejections (ICME) impact Earth’s space environment. Applying a novel method for determining the Joule heating using AMPERE, SuperMAG and SuperDARN data, we study the northern hemispheric Joule heating and global neutral density enhancements at Swarm and GRACE satellites during 231 geomagnetic storms between 2014 and 2024. It is found that the Joule heating in the ionospheric E-region and neutral density enhancements at the altitude of the Swarm and GRACE satellites (350 – 550 km) show characteristics which depend on the geomagnetic storm driver. The Joule heating has a fast increase at the beginning of the storm main phase when the storm is initiated by a HSS/SIR or by the sheath region of ICMEs. In comparison, a more gradual and longer lasting increase is found in storms driven by magnetic clouds within ICMEs. This is in line with previous results of the total field-aligned and ionospheric currents during storms (Pedersen et al., 2021, 2022). The superposed epoch analysis of the thermospheric density increases gradually during the storm main phase to about 120% of the quiet time density, and the enhancements are typically largest and longest-lasting for storms driven by magnetic clouds. This is likely because of the prolonged interval of increased Joule heating during magnetic cloud-driven storms.
How to cite: Pedersen, M., Vanhamäki, H., Aikio, A., Cai, L., Myllymaa, M., Waters, C., and Gjerloev, J.: Joule heating and neutral density enhancements during geomagnetic storms driven by solar wind high-speed streams and coronal mass ejections, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16944, https://doi.org/10.5194/egusphere-egu25-16944, 2025.
A comprehensive understanding of ionospheric irregularities is crucial for satellite communications and navigation systems. These irregularities are significantly shaped by various external factors, including solar activity, geomagnetic disturbances, and impacts from the lower atmosphere. This study aims to underscore the complex irregularities within the thermosphere-ionosphere system while elucidating the substantial role of solar and geomagnetic drivers, as evidenced by observational data and model simulations. We will analyze key parameters of the thermosphere and ionosphere, including the ratio of atomic oxygen (O) to molecular nitrogen (N2), molecular oxygen (O2), total electron content (TEC), and electron density (Ne). For this analysis, we will utilize data from the Global-Scale Observations of the Limb and Disk (GOLD) ultraviolet imaging spectrograph, the International GNSS Service (IGS), and predictions from the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM).
Furthermore, we investigate the delayed response of TEC to changes in solar flux over a 27-day solar rotation period, taking into account the effects of geomagnetic activity. Our findings reveal that geomagnetic activity plays an important role in influencing the ionospheric delay.
How to cite: Vaishnav, R., Jacobi, C., Schmölter, E., and Dühnen, H.: Influence of Solar and Geomagnetic Activity on the Thermosphere-Ionosphere System, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1490, https://doi.org/10.5194/egusphere-egu25-1490, 2025.
Total Electron Content (TEC) is broadly used in characterizing ionospheric response to solar and geomagnetic activity. Understanding how TEC structures vary over time can help mitigate the risks of space weather events to navigation and communication systems. Global Ionospheric Maps (GIMs) produced by the Jet Propulsion Laboratory (JPL) provide 20 years of GNSS observations at a spatial resolution of 1◦ × 1◦ longitude/latitude and temporal resolution of 15 minutes. We transform each of these maps into geomagnetic coordinates centered about the sub-solar point and isolate the top 1% of TEC values to define High Density Regions (HDRs) of TEC. We demonstrate how this quantile threshold of TEC varies over the 20 year data set. Using image processing tools we have constructed an algorithm that detects and tracks HDRs to identify a population of contiguous, uniquely labelled space-time TEC HDRs. Extracting and following these HDRs over multiple years allows us to explore their statistical dependencies upon geomagnetic activity, latitude and season. We find that HDRs naturally divide into two populations by peak area, separated by an intensification area of 8.0×106km2, which is around the continental scale. These populations are studied for different storm conditions - quiet (Kp < 4), moderate (4 ≤ Kp < 7) and extreme (Kp ≥ 7). Small HDRs form primarily in four magnetic latitude clusters and move approximately along lines of constant magnetic latitude. Continental scale HDRs form around the same latitudes as small HDRs but follow more complex paths. The statistical nature of our results may inform predictive ionospheric models and reveal reproducible trends in the formation and subsequent propagation paths of ionospheric enhancements.
How to cite: Cafolla, M., Chapman, S., Watkins, N., Meng, X., and Verkhoglyadova, O.: Dynamics of Space-Time TEC Enhancements seen in JPL GIMs: Variations with Latitude, Season and Geomagnetic Activity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6212, https://doi.org/10.5194/egusphere-egu25-6212, 2025.
The super-intense geomagnetic storm of May 2024, known as the Mother's Day superstorm, is the largest event of its kind in the past two decades. During this storm, the coupled ionosphere-thermosphere system was significantly impacted, accompanied by strong disturbances. Neutral winds play a crucial role in both electro-dynamic and hydro-dynamic processes in the upper atmosphere. For the first time, we analyze the characteristics of neutral winds in the East Asian sector during this geomagnetic storm, using data observed by Dual-Channel Optical Interferometers (DCOIs) as part of the Chinese Meridian Project (CMP). Total Electron Content (TEC) is derived from measurements taken by 77 Global Navigation Satellite System (GNSS) receivers across China and surrounding regions. By combining data from four high-frequency (HF) radars and all Super Dual Auroral Radar Network (SuperDARN) radars in the northern hemisphere, we can effectively analyze the ionospheric convection pattern and its effects on neutral winds.
The results show that a strong equatorward wind, with a maximum meridional component amplitude of approximately 400 m/s, was observed during the storm main phase. In the East Asian sector, this equatorward wind enhancement was associated with a negative storm on the night of May 10, which was marked by a significant reduction in TEC over China and adjacent areas. Additionally, ionospheric convection extended to 43° MLAT, with eastward ion velocities exceeding 800 m/s near 50° MLAT. This contributed to a strengthening of zonal winds in northern China, resulting in a notable eastward surge of approximately 230 m/s in the dawnside sub-auroral region. Wave-like oscillations in neutral winds, associated with storm-time Traveling Atmospheric Disturbances (TADs), were observed by multiple DCOI stations.
How to cite: Wang, X., Aa, E., Chen, Y., Zhang, J., Zhu, Y., Cai, L., Lu, X., Luo, B., and Liu, S.: Midlatitude Neutral Wind Response during the Mother’s Day Super-Intense Geomagnetic Storm Using Observations from the Chinese Meridian Project, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6186, https://doi.org/10.5194/egusphere-egu25-6186, 2025.
This study reports how the nighttime thermosphere responded to the May 2024 storm at Middle- Low-latitude in Asian and American sectors. The thermospheric wind and temperature data are collected from seven optical instruments of Chinese Meridian Project which include 3 Fabry-Perot Interferometers (FPIs) and 4 Dual-Channel Optical Interferometers (DCOIs), two FPIs at American sector, TIEGCM3.0 simulation and MSIS00 results. During the first period of intense storm on May 10, thermospheric winds turned to more southward and eastward at the geomagnetic latitudes 35N-49N of Asian sector. Remarkable surges occurred in NS wind after Bz continually kept southward for 2 hours, and the maximum speed reached about -395 m/s; meanwhile EW wind reached about 212 m/s. On May 11, the largest speed was -285 m/s in NS wind at Millstone Hill. Observations and TIEGCM3.0 both show large scale TADs at Asian and American sectors. The temperature changes are basically similar between observations and TIEGCM3.0 outputs, but MSIS00 doesn’t capture the temperature disturbances.
How to cite: Jiang, G., Zhu, Y., Lei, J., Xu, J., Liu, W., Wang, T., Liu, S., Yu, T., Jiang, F., Fu, L., Wei, X., and Kerr, R. B.: Nighttime thermosphere responses to the May 2024 storm at Middle- and Low-latitudes: optical observations and model results, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11203, https://doi.org/10.5194/egusphere-egu25-11203, 2025.
The three years of wind observations from the NASA Ionospheric Connection Explorer (ICON) provide millions of wind profiles with altitude resolution between 5 and 30 km (depending on altitude), and 250 or 500 km sampling (depending upon local time). These observations are continuous in daytime with no spatial or temporal gaps outside of observatory resets. Launched during a deep solar minimum, nonetheless ICON observed many geomagnetic disturbances in its mission from 2019 to 2022. Review of the differences between data and numerical models, and how their agreement changes with modification of model parameters, offers a remarkable tool to advance our understanding of the system and to validate the final ICON product, the ICON-TIEGCM. Comparisons of wind disturbance are combined with analyses of ionospheric variability also measured by ICON. The statistics of storm-time winds are carefully considered in context of their drivers, as are the altitude and latitude of the penetration of disturbance winds that generally propagate and expand from the auroral zones. The remarkable features of individual storms show the diversity of storm effects, while the statistical nature of disturbance winds over the three year mission provides a critical reference. We find that globally-propagating atmospheric gravity waves are generated with almost every auroral disturbance, but that disturbance winds are uncommon, with their occurrence related to the persistence of the auroral inputs.
How to cite: Immel, T., Oglesby, L., Harding, B., Maute, A., Wu, Y.-J., Nikoukar, R., Triplett, C., and Heelis, R.: Identifying the Drivers of Thermospheric Disturbance Winds with ICON, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15154, https://doi.org/10.5194/egusphere-egu25-15154, 2025.
Under favorable conditions, the interaction between the interplanetary magnetic field (IMF) and Earth’s magnetic field can produce a dayside aurora at magnetic latitudes above approximately 80 degrees, commonly referred to as the High Latitude Dayside Aurora (HiLDA). This term encompasses various recently identified dayside auroras, including phenomena like space hurricanes and 15 MLT polar cap auroras (15MLT-PCA). These auroras are most frequently observed during the northern hemisphere's summer, particularly when the solar wind exhibits a northward IMF and a positive By component.
This study investigates HiLDA events occurring during northern hemisphere summers, with a specific focus on their ionospheric electrodynamics under two distinct IMF conditions: (1) a dominant positive By IMF combined with a northward Bz component, and (2) a dominant northward Bz IMF with a near-zero By component. Utilizing the Local Mapping of Polar Ionospheric Electrodynamics (Lompe) data assimilation method, the following key insights were identified:
- Under both IMF configurations, the HiLDA spot is positioned at the center of a clockwise lobe convection cell or within the clockwise convection region of the NBZ current system.
- The location of the HiLDA spot is not at the peak but rather at the edge of an intensified upward field-aligned current (FAC) associated with the convection vortex.
- Significant Joule heating occurs in both IMF scenarios, with more pronounced heating observed under the By-dominated condition compared to the Bz-dominated condition.
How to cite: Kebede, F., Laundal, K., Reistad, J., and Hatch, S.: High latitude dayside aurora (HiLDA) ionospheric electrodynamics using data assimilation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6303, https://doi.org/10.5194/egusphere-egu25-6303, 2025.
Large-scale magnetosphere-ionosphere coupling has traditionally been described as a 2D electric circuit, where an electrostatic ionospheric electric field is inferred from prescribed field-aligned currents and ionospheric conductivity. Low-latitude regions are often treated separately, driven primarily by neutral winds. This conventional approach neglects magnetic induction and only accounts for steady states, without addressing how transitions between states occur. We propose an alternative approach in which the ionosphere responds dynamically to an imposed magnetic field, governed by Faraday's law. The imposed magnetic field is derived from prescribed field-aligned currents at high latitudes and constraints on inter-hemispheric symmetries at low latitudes. Simulation results demonstrate that the ionosphere takes several tens of seconds to adapt to variations in the imposed magnetic field, capturing dynamic processes absent in conventional models. Our simulations incorporate neutral winds, realistic magnetic field geometries, and horizontal variations in ionospheric conductivity. The model describes both the dynamic high-latitude magnetosphere-ionosphere coupling and how Sq currents and the so-called penetration electric field are established. To our knowledge, this is the first detailed description of these phenomena in terms of magnetic induction.
How to cite: Laundal, K. M., Skeidsvoll, A., P. Braileanu, B., Hatch, S., Madelaire, M., and T. Kebede, F.: A new model for global inductive magnetosphere-ionosphere-thermosphere coupling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12818, https://doi.org/10.5194/egusphere-egu25-12818, 2025.
The thermospheric composition (O/N2 ratio and NO) condition represents the state of the thermosphere. Significant changes in thermospheric composition and neutral wind are often observed during non-storm time (e.g. a weak substorm on May 29, 2023) due to continous energy and momentum input from solar wind to the geospace. It is challenging to find days when the solar wind impact is minimized and the geospace is at its ground state (super quiet) or undisturbed conditon. After a search of SuperMAG database over two decades (2002-2022), we finally identified a few super quiet intervals with (1) AE or SME < 50 nT, SymH > 0 nT), and (2) low auroral intensities (N2 LBHS (140-150 nm) < 500 R) over 48 consecutive hours or longer. We report one super quiet interval (November 6-7, 2009) with no O/N2 depletion or NO enhancment which represents a “geopace ground state”.
How to cite: Zhang, Y., Wu, Q., Gjerloev, J., Paxton, L., and Schaefer, R.: Ground state of the thermosphere and substorm time thermospheric response, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7438, https://doi.org/10.5194/egusphere-egu25-7438, 2025.
The high latitude ionosphere is highly variable, being driven by multiple processes with their origins in space weather and the neutral atmosphere. The balance between these drivers is still not well understood, though it has been increasingly recognised that the influence of the neutral atmosphere can be significant. In this study we use data from the EISCAT UHF incoherent scatter radar to examine the variability of several ionospheric parameters (e.g. density, temperature, and ion flow) and how they relate to space weather activity and potentially to processes originating in the lower atmosphere, including periods of Joule heating and the passage of Travelling Ionospheric Disturbances (TID). We compare the distribution of the electron density taken from the UHF radar with that calculated from a run from the Whole Atmosphere Community Climate Model (WACCM) to identify times of similarity and deviation.
How to cite: Kavanagh, A. J., Reidy, J., Mandal, S., Grocott, A., and Marsh, D.: Ionospheric variability in the auroral region: sources and impacts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18426, https://doi.org/10.5194/egusphere-egu25-18426, 2025.
The presence of horse-collar auroras (HCAs) during northward interplanetary magnetic field periods offers opportunities to study unique dynamics in the Earth’s high-latitude magnetosphere. Horse-collar auroras have been linked to closure of the polar cap and dual lobe magnetic reconnection, which also results in closure of the dayside terrestrial magnetic field. However, this reconnection event has not been observed in situ. On 14 April 2007, the Defense Meteorological Satellite Program (DMSP) orbiter F17 ultraviolet imager (SSUSI) and spectrometer (SSJ) captured visual and particle flux evidence of an HCA extending from nightside to cusp where an emission spot was present. During this event, the Cluster satellite crossed the high-latitude southern magnetopause, observing bidirectional plasma motion in the magnetosheath and significant plasma populations in the magnetosphere. The former is likely consistent with recently closed dayside magnetic field lines, while the latter is likely consistent with closed magnetotail field lines characteristic of HCAs. Supported by a positive Walén test, we conclude that dual lobe reconnection associated with an HCA may have been detected directly for the first time. Analysis of this event is ongoing and may produce further insights into magnetic flux transport during HCA events.
How to cite: Kaweeyanun, N. and Fear, R.: Potential Detection of Dual Lobe Reconnection Associated with Horse-Collar Auroras via Near-Magnetopause Cluster Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10324, https://doi.org/10.5194/egusphere-egu25-10324, 2025.
Data assimilation is essential for studying ionospheric electrodynamics, as no single data set offers a complete representation of the system. By combining multiple incomplete data sets, data assimilation techniques provide valuable insights into this complex system. However, existing methods typically rely on a steady-state assumption, reducing the ionospheric electric field to a potential electric field.
While this simplification is often useful, it imposes limitations on studying temporal evolution, as the system is modeled independently at each time step. Consequently, interpreting changes between time steps in a physically meaningful way becomes challenging.
We present initial efforts to extend the Lompe data assimilation framework by incorporating the ionospheric induction electric field, thereby introducing time dependence into the model. This is achieved through the implementation of a Kalman filter, enabling the co-estimation of the potential and induction electric fields. By accounting for the temporal dynamics of the system, this approach seeks to provide deeper insights into ionospheric electrodynamics and enhance the interpretation of time-evolving processes.
How to cite: Madelaire, M., Laundal, K., and Hatch, S.: Towards Time-Dependent Data Assimilation of Ionospheric Electrodynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17920, https://doi.org/10.5194/egusphere-egu25-17920, 2025.
How to cite: Araujo, J., Bodin, M., Westman, A., Sergienko, T., Hamrin, M., and Brändström, U.: Interactive framework for the enhanced exploration, interpretation and scientific analysis of spatio-temporal and volumetric ionospheric data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16225, https://doi.org/10.5194/egusphere-egu25-16225, 2025.
Geomagnetic storms cause significant disturbances in the high-latitude ionosphere. Studying these impacts is challenging due to the complex magnetosphere-ionosphere coupling and physical mechanisms involved. Here, we utilized measurements from the Global Navigation Satellite System (GNSS) network to calculate the Total Electron Content (TEC) across GNSS receivers at magnetically conjugate points in Antarctica, Canada, and the United States. We analyzed 25 geomagnetic storms during Solar Cycle 24 (SC24), examining the interhemispheric behavior and differences in TEC under varying seasonal and solar conditions, driven by distinct geomagnetic storm drivers. Our results revealed differences in the interhemispheric velocity of TEC disturbances moving from the poles toward the equator. While comparisons of disturbance velocities with various solar wind and magnetospheric parameters did not show clear relationships, a notable correlation emerges when the rate of decrease in the Dst index is larger than -60 nT/h during storms. This correlation is more pronounced in the Northern Hemisphere than in the Southern Hemisphere. Furthermore, we identified significant variations in the timing of the maximum Vertical TEC (VTEC) occurrence relative to the onset of the storm's main phase. Finally, we studied the relationship between the velocities and seasonal variations, including the different storm drivers, and the results do suggest true hemispherical differences.
How to cite: Castillo-Rivera, C., Stepanova, M., Pinto, V., and Bravo, M.: Evaluation of Interhemispheric Asymmetry using Total Electron Content at High Latitudes During Geomagnetic Storms , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14440, https://doi.org/10.5194/egusphere-egu25-14440, 2025.
Understanding the generation, propagation and attenuation of traveling ionospheric disturbances (TIDs) during strong space weather variations is essential for predicting and mitigating the adverse effects of TIDs on communication, navigation, and other technological systems that rely on the ionosphere. The magnetic storms caused by coronal mass ejections (CME) and corotating interaction regions / high-speed stream (CIR / HSS) are drivers which can affect the ring current and also the course and duration of auroral activity in different ways. Moreover, despite the greater energy output of CME-driven storms, the magnetospheric coupling and total energy input are often more geoeffective for the magnetic storms driven by CIR / HSS events. The objective of the current case study is to investigate thoroughly the TIDs over midlatitude Europe, originated by the CIR / HSS - driven storm on March 30 – April 6, 2023. We employed the data from European dense GNSS receiver network and four ionosondes for joint analysis to detect both large-scale and medium-scale TIDs and estimate their characteristics. We detected several time intervals with intensification of both types of TIDs propagating from the high latitudes towards the equator and associated with an increase in auroral activity. Ionosonde and GNSS based results show the consistency in estimation of characteristics of TIDs, which have the dominant periods of 30 – 80 min, horizontal phase velocities of 200 – 600 m/s and horizontal wavelengths of 400 – 3500 km. We also compared TID occurrence and direction during the comparable magnetically quiet and CIR / HSS - driven storm periods. We noted the significant increase in TID occurrence rate and the prevalence in their southward propagation during the observed magnetic storm. Based on this case study, we spotted that the TIDs at midlatitudes were usually observed several (1 – 4) hours after the increase in the auroral activity characterized by IMAGE IE indices. We continue to analyze other CIR / HSS driven events to establish the validity of such a relationship.
How to cite: Panasenko, S. V., Burešova, D., Skipa, V., and Urbář, J.: Traveling ionospheric disturbances over midlatitude Europe during CIR/HSS driven magnetic storm on March 30 – April 6, 2023, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6512, https://doi.org/10.5194/egusphere-egu25-6512, 2025.
The ionosphere is the ionized region of the atmosphere extending from 50 km to 1000 km. During flares, the Earth’s surrounding space is subjected to high-energy X-ray and EUV radiation, which also impacts the ionosphere. The changes of the ionospheric parameters measured by ionosondes, namely the fmin, foE and foF2 values, were examined during solar flares that occurred in geomagnetically quiet conditions (Dst > -40 nT, Kp < 4). The necessary data were derived from manually evaluated ionograms recorded by a DPS4D ionosonde at Pruhonice station in Czechia (PQ052). The degree of variation was compared to quiet reference days, allowing the determination of the deviations in the required values (dfmin, dfoE, foF2). Time series of the deviations were investigated. Furthermore, the relationship between the deviations and a “geoeffectiveness” parameter of the solar flare defined by some important properties of the event was also examined. The X-ray flux, the solar zenith angle of the station at the time of the event, and the position of the flare on the solar disk were also taken into account for the determination of the "geoeffectiveness" parameter. A positive correlation was observed between dfmin and the "geoeffectiveness" parameter of the flare, which was more significant than the correlation between the dfoF2 and the "geoeffectiveness" parameter.
How to cite: Erdey, J., Buzás, A., and Barta, V.: Impact of Solar Flares on the Ionosphere During Geomagnetically Quiet Periods Based on Ionosonde Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13056, https://doi.org/10.5194/egusphere-egu25-13056, 2025.
The Barium Release Optical Rocket (BROR) mission conducted at Esrange, Sweden, on 23rd March 2023, performed barium releases into the earth’s atmosphere at eight different altitudes between 130 and 245 km to investigate small-scale electromagnetic phenomena in the auroral ionosphere. In the initial three barium releases of the BROR experiment, which were performed at 132 km, 160 km, and 193 km, the motions of both neutral and ionized barium clouds were so clearly and distinctively observed by the ground-based optical camera network that we can reconstruct a three-dimensional tomography-like reconstruction.
In the horizontal plane, all neutral clouds resulting from the initial three releases had a strong westward component in their motion with almost constant velocity. In contrast, the ionized clouds behaved quite differently from each other, which may represent the effect of altitudinal variation of collision frequency between barium ion and neutral particles and the electric field, which may be associated with auroral activity. On the other hand, from the vertical motion of ionized clouds, we found that the first (the lowest) and second (the middle) released ion clouds show significant deviation from the theoretical estimated value, while the third released ion cloud shows a good agreement with the theoretical value. This observed fact implies that there may be a parallel electric field up to a few mV/m at the altitude below about 160 km, and the electric fields at the altitude of the first release and second release are in the opposite sense.
How to cite: Yokoyama, Y. and Tima, S.: Unexpected strong parallel electric field at the lower E region observed during a barium release experiment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13331, https://doi.org/10.5194/egusphere-egu25-13331, 2025.
Equatorial plasma bubbles (EPBs) present significant challenges to trans-ionospheric radio communications, particularly affecting Global Navigation Satellite System (GNSS) signals, which can lead to signal degradation and disruptions in communication and navigation. By reducing the number of usable GNSS satellites for accurate positioning, EPB occurrences underscore the importance of evaluating and predicting them in the development of space systems. One critical factor that remains elusive is the influence of geomagnetic activity on EPBs. This study aims to address this gap by performing a superposed epoch analysis on key parameters: geomagnetic indices, zonal and meridional neutral winds, and the $\sigma$ index, which serves as an indicator of EPB presence. Using data collected by the Ionospheric Connection Explorer (ICON) satellite from 2020 to 2022, between 18:00 and 23:00 SLT, our analysis reveals regional differences in EPB behavior. In South America, EPB occurrences are suppressed during the decline of geomagnetic activity, while over Africa, EPB occurrence increases during periods of heightened geomagnetic activity. Additionally, we observe a shift in zonal winds toward the west near the peak of geomagnetic disturbances. These findings contribute to a deeper understanding of EPB dynamics and highlight the regional variability in their response to geomagnetic disturbed conditions.
How to cite: González, G., Immel, T., Wu, Y.-J. J., Gasque, L. C., Harding, B., and Triplett, C.: Longitudinal Variability of Pre-midnight Equatorial Plasma Bubbles Under Geomagnetic Activity: The role of Thermospheric Winds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-105, https://doi.org/10.5194/egusphere-egu25-105, 2025.
The Earth’s Magnetosphere-Ionosphere-Thermosphere (MIT) system is strongly controlled by the laws of electrodynamics, which include significant contributions from all three components. Today, we face a growing need for a better representation of this MIT system, mostly at low latitudes due to the growing use of GNSS satellites for positioning, which face accuracy and forecasting challenges that are not accessible with current data coverage and processing tools.
The IRAP Plasmasphere-Ionosphere Model (IPIM) is one of the only physical models developed in Europe and validated on observations for its high-latitude version. The IPIM model solves plasma transport equation along magnetic field lines and provides a complete 3D coverage of Earth’s ionosphere and plasmasphere in latitudes, longitudes and altitudes.
The main inputs of the model come from the solar irradiance (FISM model) and the neutral atmosphere (MSIS for neutral densities and temperature and HWM14 for winds). We are extending the IPIM model with a module solving the electrodynamics of the low and mid-latitudes. The specificity of this module is that it is developed using a new orthogonal magnetic coordinate system (called Generalized Eccentric Dipole) which is suited for any analytical representation of the magnetic field, like the International Geomagnetic Reference Field (IGRF). It provides a projection basis and a metric which account for the structures of the Earth's magnetic field, especially near the equatorial region at low altitude and is very similar to a dipolar system at high altitude (or high latitudes).
The final goal of this work is to have a good representation of low-mid latitudes ionosphere-upper atmosphere couplings, mostly in regions with sparse data coverage.
We will present interesting first results of the coupling between IPIM and this new electrodynamical module showing expected low- and mid-latitudes phenomena such as the equatorial ionization anomaly detected on global total electron content and foF2 maps or the presence of the Equatorial ElectroJet and Solar quiet currents during the day.
Finally, we will discuss the results and the perspectives of applications and developments.
How to cite: Resseguier, A., Blelly, P.-L., and Marchaudon, A.: Implementation of a low and mid-latitudes electrodynamical module in the IRAP Plasmasphere-Ionosphere Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2392, https://doi.org/10.5194/egusphere-egu25-2392, 2025.
The interaction between the Earth's conducting ground surface (with varying land cover types) and the ionospheric D-region (60–90 km altitude) forms a waveguide that supports the propagation of Very Low Frequency (VLF) and Low Frequency (LF) radio waves (3–30 kHz and 0.5–470 kHz, respectively). Variations in these VLF signals provide a valuable tool for remotely sensing dynamic changes in the D-region's conductivity under both ambient and disturbed ionospheric conditions. This study employs an innovative approach, combining amplitude and phase deviations from colocated perpendicular antenna measurements, to characterize elliptical polarization parameters during an intense geomagnetic storm. This method outperforms conventional techniques that rely solely on isolated phase or amplitude variations from VLF transmitters to detect ionospheric disturbances. Subsequently, the extracted polarization parameters were analyzed using cross-wavelet analysis in conjunction with a high-resolution SYM-H geomagnetic index. Cross-wavelet analysis was chosen for its ability to evaluate localized correlations between two datasets across both time and frequency domains and to identify the leading or lagging parameter in a periodic context. The results, particularly concerning the delayed response of the D-region, not only confirm existing findings but also offer new insights into the underlying mechanisms. These advancements contribute to a deeper understanding of D-region dynamics, improving ionospheric modeling and enhancing the accuracy of space weather prediction frameworks.
How to cite: Ajakaiye, M. P., Romano, B., and Reuveni, Y.: Ionospheric Diagnostics via VLF Elliptical Polarization and Cross-Wavelet Analysis: Assessing the Impacts of Geomagnetic Storms, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4975, https://doi.org/10.5194/egusphere-egu25-4975, 2025.
The ionosphere consists of various ionised layers in Earth’s upper atmosphere, located roughly between 60 and 1000 km. Space weather events like solar flares cause enhanced absorption of radio waves in the ionosphere most notably in the lowest part of it, the D-region (ca. 60–100 km altitude range) which can weaken radio signals and can pose difficulties to radio communication at certain frequencies. There exist several methods to qualitatively and/or quantitatively assess the absorption in the layers of Earth’s ionosphere. In the present study, one such method is focused on, namely, the so-called ionosounding technique in which an instrument called the ionosonde actively emits radio pulses towards the ionosphere over a selected frequency sweep, typically between 1.5 and 12 MHz, and the passive antenna system of the same instrument receives the reflected echoes. Based on the received amplitudes of the echoes, the D-region absorption in the ionosphere can be quantified.
State-of-the-art DPS-4D ionosondes are installed in Dourbes, Belgium and Sopron, Hungary, respectively, with the two stations being part of the same international network of ionosondes (GIRO network). There have been various research collaborations between the two groups in the past (e.g., participating in the same European project called T-FORS). In a paper by Buzás et al., 2023, we investigated the impact of solar flares on the absorption of radio waves emitted by ionosondes. As a continuation of this study, we looked for other ways to quantify the ionospheric absorption and to compare our results with other methods. One such method is to utilize the upper, higher-frequency part of the spectrum (practically 10–30 MHz) of the ionosonde where usually there are no reflections from the emitted electromagnetic pulses. Basically the instrument “listens” to the background noise (either of terrestrial or extraterrestrial origin) received by the antenna system at these frequencies. In this mode of measurement, it is possible to extract information on the ionospheric absorption.
Here, we aim to show our preliminary results concerning the possibility of the utilization of the above-10 MHz-part of the ionosonde spectrum. To this end, we analysed ionosonde amplitude data recorded at Dourbes and Sopron stations both during quiet periods and periods with M- and X-class solar flare events in 2024. The seasonal and diurnal variation of some selected frequency bands are discussed, as well as the ionospheric response at different frequencies during the flare events.
References:
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. Frontiers in Astronomy and Space Sciences, 10, 1201625.
How to cite: Buzás, A., Verhulst, T., and Barta, V.: Measuring ionospheric absorption based on received ionosonde amplitudes using sounding frequencies above 10 MHz – preliminary results, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11730, https://doi.org/10.5194/egusphere-egu25-11730, 2025.
Using line-of-sight velocity measurements made by SuperDARN (The Super Dual Auroral Radar Network) radars with overlapping fields of view, it is possible to estimate the vorticity of the ionospheric convection flow over a wide range of scales. Here we exploit previous statistical analyses of 6 years of SuperDARN vorticity measurements to study the spatial variation of meso-scale flows in ionospheric convection. By making certain assumptions, we can statistically separate probability density functions (PDFs) of vorticity made at different locations in the ionosphere into two populations: (i) That due to the large-scale two-cell convection flow driven primarily by magnetic reconnection, and (ii) that due to meso-scale flow structures driven by processes such as turbulence. The resulting PDFs are fit by model functions using maximum likelihood estimation, and the spatial variation of the estimators is determined. The spatial variations of the large-scale vorticity estimators are ordered by the average convection flow, which is highly dependent on the IMF direction. The spatial variations of the meso-scale vorticity estimators appear independent of the senses of vorticity and IMF direction, but have a different character in the polar cap, the cusp, the auroral region, and the sub-auroral region.
How to cite: Chisham, G. and Freeman, M.: Using vorticity to characterise meso-scale ionospheric flow variations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10641, https://doi.org/10.5194/egusphere-egu25-10641, 2025.
We employ ground magnetometers in North America, Greenland, and Antarctica and use the Spherical Elementary Current (SEC) technique in order to investigate the Birkeland currents (also known as field-aligned currents) flowing between January 2015 and December 2016. We convert the measurements into altitude-adjusted corrected geomagnetic (AACGM) coordinates, and then average across each day for which we have data to obtain global maps in both the Northern and Southern Hemispheres for the period in question. We examine the systematic asymmetry in the data by focusing on the relationship between the two hemispheres at equinox, and we find that the observed currents are stronger in the Northern Hemisphere, consistent with observations made by AMPERE, Swarm and DMSP.
How to cite: Coxon, J., Weygand, J., and Oliveira, D.: Hemispheric asymmetries in Birkeland currents observed from the ground, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18873, https://doi.org/10.5194/egusphere-egu25-18873, 2025.
Ionospheric parameters, totaling about 72, were measured at ITU-Dynasonde site including F2 region critical frequency and its virtual height from 2012 to 2018. This project utilizes F2 region critical frequency to determine the storm related variations and quantify the storm effects over İstanbul (42N, 29E). Three strong geomagnetic storm events were selected and the differences in foF2 betwen quiet (non-storm) and active (storm) days were identified. It was found that when a geomagnetic storm occurs, the ionospheric electron densities increase at noon times and decrease during the night times around midnight. These variations were seen to occur during the main phase of the storm and continues during the recovery phase. During the following days of the storm main phase, increasing electron densities at noon times subsided and even reversed indicating a deficit of electron density. The noon decrease became even stronger after two days following the storm occurrence while the nighttime variations stayed at the same level. Strong increases in the solar wind dynamic pressure and strong IMF southward variations were detected in L1 data from WIND spacecraft. The maximum positive electron density difference at noon was obtained to be about 10% while the storm associated midnight decrease was found to be about 15 %. While the electron densities in a region can be associated with several physical processes initiated by the magnetic storm in the upper atmosphere, association to neutral atmosphere dynamics were searched by examining the thermospheric neutral density from SWARM satellites at about 500 kms during these storm days in order to bring some understanding on the storm time variations of electron density over Istanbul latitudes. Some of these findings support those in the literature while some others were reported for the first time here in relation to the magnetic storms. It is intended to expand the analysis to more storm cases from 2012 to 2018 in order to obtain a statistical base. The results from the preliminary search based on the statistical analyses and the corresponding SWARM neutral density will be presented in order to address on the ionosphere-thermosphere coupling at these latitudes.
How to cite: Keskin, B. and Kaymaz, Z.: Statistical Analyses of Ionospheric Electron Density Variations resulting from Geomagnetic Storms over Istanbul, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16096, https://doi.org/10.5194/egusphere-egu25-16096, 2025.
Geomagnetic disturbances perturb the ionosphere-thermosphere (IT) dynamics, modify the background densities, compositions, etc. on the global scale. Sudden energy deposition in the auroral region during geomagnetic events can generate wave-like disturbances which further propagate through the IT system under favourable background condition, known as travelling ionospheric disturbances (TIDs). The disturbances can be of different scale sizes, ranging from few kilometres (kms) to thousands of km. Large-scale TIDs (LSTIDs), having typical horizontal scale sizes of several thousands of km and periodicities of a few hours, propagate with a speed of 400-1000 ms-1. In this study, we have investigated a LSTIDs present over Indian longitudes during a geomagnetic storm of 20-21 December 2015. The imprint of the TIDs is seen in the OI 630.0 nm nightglow emissions, height variation of F-layer, heights of ionospheric iso-electron densities, and total electron count (TEC) over low-latitude Indian longitudes. The variation was wave-like with a period of around 2-3 hours. The detailed study carried out using the TEC variation obtained by 12 International GNSS Service (IGS) stations located at Indian and Australian sector. The LSTIDs originated around the onset of the geomagnetic storm on 20 December in the southern hemisphere near Australian sector, propagated northward, crossed the equator, and then dissipated in the low-latitudes of the Indian longitudes. The LSTIDs were found to be propagating with a speed of around 800 ms-1 at the Australian sector, but their speeds are reduced to around 200 ms-1 near the equator. Further, the background changes in the low-latitude IT system are investigated using the measurement of equatorial electrojet, O/N2 variation. These results will be discussed.
How to cite: Saha, S., Pallamraju, D., Kumar, S., Narayanan, V. L., and Sunda, S.: On the dynamics of Travelling Ionospheric Disturbances and Background Ionospheric changes over low-latitude Indian sector during December 2015 Geomagnetic Storm, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-688, https://doi.org/10.5194/egusphere-egu25-688, 2025.
The classic ionospheric dynamo theory suggests the Interhemispheric Field-Aligned Currents (IHFACs) are season and local time dependent that arises from asymmetric ionospheric conductivities and thermospheric winds between the northern and southern hemispheres. Recent studies showed IHFACs have extremely longitudinal variations and show “C”-shaped morphology in Atlantic-American region that beyond previous thought. However, there are less detailed studies about the mechanism for the reversal phenomenon. This study analyzed Pedersen conductivity in the two hemispheres and geomagnetic structure to investigate the reasons for the reversal of IHFACs. The result suggests the geomagnetic declination connects the ionosphere in the two hemispheres at different local times, causing large conductance asymmetry. The conductance asymmetry exceeding 10 S will result in the reversal of IHFACs. This study further discussed the mechanism of the reversal and the impact on the ionosphere to reveal the regional electrodynamic process.
How to cite: Zhang, P., Sun, Y.-Y., and Chen, C.-H.: Unique morphology of Interhemispheric Field-aligned Currents and the Associated Factors and Mechanism, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6423, https://doi.org/10.5194/egusphere-egu25-6423, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 3
EGU25-12948 | Posters virtual | VPS27
Unusually large positive geomagnetic variation (AU) near noon on 11 May, 2024Thu, 01 May, 14:00–15:45 (CEST) | vP3.19
During the May 2024 space weather event, Kiruna magnetometer (KIR) registered historically large positive deviation of the northward geomagnetic disturbance (dX = +1300 nT) at around 12 UT (14 MLT, i.e., postnoon). The large dX is observed entire Scandinavia, giving AU = 1431 nT at 12:11 UT, but not in the Atlantic or North American sectors (although we do not know the disturbance at 15-23 ML because no data at > 55° Mlat is available).
Such large positive dX of dayside stations is not very rare, most of them are observed in the North American continent. Out of total 21 AU peaks of > +1300 nT separated by more than 1 hour (12 magnetic storms) during 1978-2019, 2 events are peaked at 09-15 UT, 8 events at 15-21 UT, 6 events at 21-03 UT, and 5 events at 03-09 UT.
For the European sector, dX value in the May 2024 event is the second largest after the 24 November 2001 event in both AU statistics (1978-2019) and Kiruna magnetometer (1962-2024). The same uncommon nature is even seen in Kp=9 that was registered at 09-12 UT. During 1932-2024, Kp=9 was observed only during 4 events at 09-15 UT, whereas Kp=9 was observed during 10 events at 15-21 UT, 8 events at 21-03 UT, and 5 events at 03-09 UT.
Although these UT anomaly is within the statistical fluctuation, we attribute this to the geomagnetic tilt toward the North American sector. This makes stations at the same geomagnetic latitudes (e.g., AE stations and Kp stations) located at lower geographic latitudes (i.e., under higher ionospheric conductivity) in the North American sector than the other longitudes when the stations are located near noon (09-15 MLT). Accordingly, the dayside dX and local K tends to register higher in the North American sector than the other longitudes. Since extremely large AU (> 1300 nT) tends to occur near noon (this is the case with the 12 storms mentioned above), we expect more frequent large dX when the North America is near noon (15-24 UT). For Kp, large Kp requires K=9 at Kp station even in the dayside where the disturbance is normally smaller than the nightside. Then the North America may easier to register large K even during daytime due to higher conductivity. If the rareness of high AU and Kp during 09-15 UT has such solid reason, the May 2024 space weather event was actually very unusual.
Finally, there is one more peculiar feature of the large dayside AU for the May 2024 event is that it is preceded only by normal substorm (AL ≈ -600 nT) and followed by a strong negative excursion in the Alaska-Pacific sector instead. This is quite different from ordinary dayside positive dX that is normally preceded by substorm of large AL (which is the case for the 24 November 2001 event with AL < -1300 nT).
Acknowledgment: We used provisional AE, SuperMAG, INTERMAGNET and Kp. We thank all contributing observatories and institutions for these datasets.
How to cite: Yamauchi, M., Nanjo, S., Kotani, T., and Matzka, J.: Unusually large positive geomagnetic variation (AU) near noon on 11 May, 2024, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12948, https://doi.org/10.5194/egusphere-egu25-12948, 2025.
EGU25-5836 | ECS | Posters virtual | VPS27
Investigation of the Drivers of Long-Duration Positive Ionospheric Storms During the Geomagnetic Storm on February 26-27, 2023Thu, 01 May, 14:00–15:45 (CEST) | vP3.20
A typical long-duration positive ionospheric storm (LDPS) developed in the midlatitude ionosphere in the European sector in response to a strong geomagnetic storm of February 26-27, 2023 (Kp = 7-, minimum SYM-H = -161 nT). To advance the current understanding of storm-time midlatitude ionosphere, we investigated the drivers of this LDPS using combination of multi-instrument observations and modeling, with focus on magnetically conjugate locations. Simulations with the field line interhemispheric plasma (FLIP) model constrained by the observed F2-layer peak height (hmF2) and density (NmF2) data at Kharkiv (50oN, 36oE) and Grahamstown (33.3oS, 26.5oE) were validated with the O/N2 ratio data from the Global Ultraviolet Imager (GUVI). Our results indicate that neither the F2-layer peak uplift nor the O/N2 ratio increase can be considered exclusive drivers of an LDPS. Each driver can be dominant depending on conditions. An LDPS can develop even when the hmF2 decreases and sometimes, a small hmF2 increase of ~10-20 km can cause a strong LDPS. Similarly, an O/N2 increase is not a primary or necessary condition for an LDPS to develop but a small O/N2 increase of ~20-30% can cause a prominent LDPS. Finally, the formation of a positive or negative storm can be inhibited if the raising/lowering of hmF2 is counterbalanced by a decrease/increase in the O/N2 ratio.
How to cite: Reznychenko, M., Kotov, D., Richards, P. G., Bogomaz, O., Goncharenko, L., Paxton, L. J., Hernandez-Pajares, M., Reznychenko, A., Shkonda, D., Barabash, V., and Domnin, I.: Investigation of the Drivers of Long-Duration Positive Ionospheric Storms During the Geomagnetic Storm on February 26-27, 2023, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5836, https://doi.org/10.5194/egusphere-egu25-5836, 2025.
EGU25-6829 | Posters virtual | VPS27
Magnetic field induced by the ionospheric shell currents.Thu, 01 May, 14:00–15:45 (CEST) | vP3.21
Recently, a model of the vertical profiles of shell currents and the magnetic field in the ionosphere has been developed (Romashets and Vandas, 2024). The distribution was determined for polar and equatorial regions. A global three-dimensional pattern of the shell-currents flow and its interconnections with the field aligned current (FAC) can be reconstructed. The magnetic field induced by the shell currents can produce at some locations a geomagnetic effect comparable to that of the ring current. The Biot-Savart integration over the entire ionosphere to derive the shell-currents induced magnetic field could be a challenging task. Here, we present an alternative method which utilizes spherical harmonics of different types for the inner and outer problems. The magnetic field inside the ionosphere is known, and outside of it is current-free and is represented as a gradient of a scalar potential, a sum of spherical harmonic functions with their coefficients. For the inner problem, only terms with (r/r0)-n-1 are present in the sum, while the outer scalar potential contains only terms with (r/r0)n. Here 0<n<N, N=13, and r0 is the average distance from the Earth’s center to the ionosphere. Both the inner and outer problems for finding the induced magnetic field have only one condition: the magnetic field calculated with the scalar potential must be equal to the known magnetic field in the ionosphere. This research was supported by the NSF 2230363 and AVCR RVO:67985815 grants.
References.
- Romashets, M, Vandas, Determination of Vertical Profiles of Shell
Currents in the Ionosphere, Annales Geophysicae, submitted, 2024.
How to cite: Romashets, E. and Vandas, M.: Magnetic field induced by the ionospheric shell currents., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6829, https://doi.org/10.5194/egusphere-egu25-6829, 2025.
