It is well known that the ionosphere is a highly dynamic medium, and the electron density can vary significantly within a very short period of time at a given location. One of the reasons for the irregular variations are ionospheric signatures of Atmospheric Gravity Waves (AGWs) – Travelling Ionospheric Disturbances (TIDs). TIDs are one of the major and frequent wave-like perturbations of the ionospheric plasma. Medium scale TIDs (MSTIDs) have been described as perturbations characterized by a wavelength, period and phase speed of 50–500 km, 12–60 min and 50–400 m/s, respectively. The wave-like effects of the MSTIDs are one of the main obstacles for accurate interpolation of ionospheric corrections in a medium scale reference of the Global Positioning System (GPS) networks as the ionospheric delay is almost proportional to Total Electron Content (TEC) along the signal path and inversely proportional to the frequency squared. MSTIDs are a common phenomenon from high to low latitudes.

The main objective of the T-FORS project is the development of new validated models able to issue forecasts and alerts for TIDs several hours ahead, exploiting a broad range of observations of the solar corona, the interplanetary medium, the magnetosphere, the ionosphere and lower atmosphere. This paper presents our results on the analysis of dynamic events that trigger MSTIDs. The events identified for the purposes of the analysis were such as geomagnetic disturbances, deep tropospheric convections, earthquakes and volcano eruptions. Based on the T-FORS methodologies all available data (detrended TEC, Continuous Doppler Sounding System -CDSS measurements, Digisonde vertical and oblique soundings and gradients of the electron density, reference meteorological and seismic data) were used for this analysis. The MSTIDs occurrence was recorded and analysed and propagation pattern for these events were extracted and compared with the results of the climatological model. This comparison will support the definition of alerts criteria when the detected disturbances exceed the climatology. Physical conditions that triggered enhanced MSTID activity were also analysed to compile an inventory of parameters that can be considered as early indicators of enhanced MSTIDs.

How to cite: Buresova, D., Chum, J., Mani, S., Mielich, J., Urbar, J., Barta, V., Belehaki, A., Verhulst, T. G. W., Altadill, D., Segara, A., Kouba, D., Guerra, M., Koucka Knizova, P., Mosna, Z., Berényi, K. A., Cesaroni, C., and Spogli, L.: Analysis of MSTIDs triggered by dynamical events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9005, https://doi.org/10.5194/egusphere-egu24-9005, 2024.

I use yearly average noontime foF2 from six ionospheric stations from four continents, Juliusruh, Pruhonice, Roma, Boulder, Kokubunji and Canberra over periods 1976-1995 and 1996-2014, and six solar activity indices F10.7, F30, Mg II, solar H Lyman-α flux, sunspot numbers and He II. The results reveal somewhat and sometimes even substantially different trends of foF2 when the effect of solar cycle is removed/reduced from foF2 data with different solar activity proxies. Only F30 provides for all stations and both periods the trends of the same sign (negative), other indices reveal both positive and negative trends for different stations and periods. Therefore together with results of other criteria F30 is considered to be the most reliable solar activity index for long-term studies of midlatitude foF2.

How to cite: Laštovička, J.: Different long-term trends of foF2 with different solar activity indices, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1288, https://doi.org/10.5194/egusphere-egu24-1288, 2024.

The solar extreme ultraviolet (EUV) radiation drives the major ionization processes in the upper atmosphere. Its variability causes a related response in ionospheric observables. Especially of interest is the delayed response of electron density (Ne), integrated total electron content (TEC), and the density of major neutral and ionized species to the 27-d solar rotation period. But this solar signature is often influenced by underlying trends on shorter and longer time-scales. Therefore, this study examines the ionospheric response to a solar 27-d signature superposed with a long-term increase in solar EUV, showing that complex composition changes in the upper atmosphere influence the expected response significantly. Using high-resolution simulations of the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM), we compare two different 27-d solar rotation periods from the year 2014 with enhanced solar activity. This allows us to compare an almost ideal solar activity input with one that is superposed with an increase in solar activity. The main results show that the accumulation of ionized species O⁺ and O₂⁺ in the lower ionosphere, especially up to the maximum density of ionized oxygen (O⁺) at about 230 km, is significantly affected by the long-term increase in solar activity.  Nevertheless, the 27-d solar rotation period dominates the ionization in both, ideal and complex model run for altitudes above 230 km. Thus, our results are in good agreement with preceding studies and extend the study of the delayed ionospheric response to more complex cases.

How to cite: Dühnen, H., Vaishnav, R., Schmölter, E., and Jacobi, C.: Solar variability and delayed ionospheric response: Insights from complex 27-day solar EUV signatures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1426, https://doi.org/10.5194/egusphere-egu24-1426, 2024.

GDC is a six-satellite constellation, designed to investigate the dynamics of the coupling between the ionosphere and thermosphere. The mission will provide multipoint observations of both the energy inputs and the ionosphere-thermosphere system response with sufficient spatial and temporal resolution to finally unravel the physical processes underlying the observed system-level dynamical responses. A critical component of the measurement requirements are the characteristics of the thermal plasma. TPS is a multi-sensor instrument designed to measure the three components of the ion drift, the ion density and temperature, and the mass fractions of the major constituent ions. We present an overview of the instrument, the methods by which the measurements are made, and the science questions to be addressed.

How to cite: Anderson, P.: The Thermal Plasma Sensor (TPS) for the Geospace Dynamics Constellation (GDC) mission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3589, https://doi.org/10.5194/egusphere-egu24-3589, 2024.

Gravity waves (GWs) are an important class of atmospheric waves that can propagate from the troposphere up to the upper atmosphere, where they can contribute significantly to the dynamical changes in the ionosphere. The aim of the present contribution is to gain a deeper understanding of the coupling between the lower and the middle ionosphere via gravity waves by the concurrent analysis of narrowband VLF measurements (characterizing GWs in the E layer) carried out at the Tihany Geophysical Observatory (TGO), Hungary and the multi-point and multi-frequency continuous Doppler sounding system (characterizing GWs in the F layer) operated by the Institute of Atmospheric Physics, CAS in the Czech Republic. The signal from the German VLF transmitter (call sign: DHO, frequency: 23.4 kHz) detected at the TGO have been considered for the present study, since the Doppler system located in the western part of the Czech Republic is close to the midpoint of the DHO-TGO wave propagation path. The inferred gravity wave activities have also been compared with the lightning locations provided by the World Wide Lightning Location Network (WWLLN) in order to identify the possible source areas of the upward propagating gravity waves. 

The preliminary analysis was carried out for the summer months of 2021. From the narrowband VLF measurements, the day-to-day variation of the average GW activity for each night was determined using the Wavelet transform. In the case of the Doppler system, the estimated Doppler shifts and the spreadF proxy were used to characterize the nighttime GW activity. Our results show low correlation (~0.04) between GW activity inferred from the VLF and Doppler measurements. On the other hand, for both the VLF and Doppler measurements, we could identify certain areas where the large number of lightning strokes was associated with enhanced GW activity in the corresponding ionospheric measurement. However, the areas found for the two measurements do not overlap, which may indicate that the VLF measurement is sensitive to a different area where the Doppler system is located. This work has been supported by the PITHIA-NRF Trans-National Access (TNA) programme.

How to cite: Bozóki, T. and Chum, J.: Comparison of gravity waves detected in the lower ionosphere by narrowband VLF measurements and in the F layer by a continuous Doppler sounding system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3841, https://doi.org/10.5194/egusphere-egu24-3841, 2024.

During geomagnetic storms, a latitudinally narrow band of strong sunward plasma drifts occurs just equatorward of auroral electron precipitation in the afternoon to pre-midnight sector, which is termed subauroral polarization steams (SAPS). SAPS are produced when the downward Region-2 current is closed through the subauroral region of low ionospheric conductivity and a strong poleward electric field is established to ensure current continuity. SAPS are a manifestation of the strong coupling between the magnetosphere and the ionosphere and thermosphere system. In this study, we employ the high-resolution Multiscale Atmosphere-Geospace Environment (MAGE) model that is developed by the NASA DRIVE Science Center for Geospace Storms (CGS) to simulate the SAPS effects on the global thermosphere-ionosphere system during the March 17 2013 geomagnetic storm. We compare two MAGE model runs, one with SAPS in the entire simulation and the other with the SAPS drifts being turned off when the ionospheric electric fields are used to calculate ion frictional heating, neutral Joule heating, ion drag and plasma transport. By comparing the results from these two runs we quantify the effects of SAPS on the thermosphere and ionosphere system. Our results show that with SAPS ionospheric total electron content (TEC) and electron densities are enhanced in the afternoon sector at middle and high latitudes. This provides a strong source of ionization for the high-latitude convection pattern to transport the plasma into the polar cap to form the polar tongue of ionization (TOI) and patches. Therefore, SAPS facilitate the occurrence and strengthening of TOI. The MAGE simulations also show that the phase and speed of storm-time traveling atmospheric disturbances and neutral circulation are modulated by the SAPS, and the SAPS effects are thus transmitted globally to affect the behavior of the entire thermosphere and ionosphere system during the storm.

How to cite: Wang, W., Ling, D., Merkin, S., Wu, Q., and Zhang, Y.: The Thermosphere and Ionosphere System Responses to Subauroral Polarization Streams (SAPS) During the March, 17, 2013 Geomagnetic Storm, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6177, https://doi.org/10.5194/egusphere-egu24-6177, 2024.

The amplitude of GWs increases with height due to the decrease in the density of the atmosphere, but at the same time the attenuation of the waves also increases with height due to the dissipation of energy through friction.

In this study, the propagation of GWs in the ionosphere is observed remotely, using multi-point, multi-frequency continuous HF Doppler sounding system situated in the western Czechia. The configuration of the system allows to determine not only the amplitude, but also the speed and direction of GWs propagation at different heights. An ionosonde located not far away from the Doppler sounding system is used to assign the reflection heights to individual measurements.

The amplitudes of medium-scale atmospheric gravity waves propagating in the ionosphere are measured and statistically processed to investigate the daily and annual variations, and their relation to the speed of the neutral winds and the measurement height. Results from periods of solar maximum and minimum are compared.

How to cite: Rusz, J., Chum, J., and Baše, J.: Amplitudes of medium scale gravity waves (GWs) in the ionosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7983, https://doi.org/10.5194/egusphere-egu24-7983, 2024.

Energetic particle precipitation is the major source of electron production that controls the ionospheric Pedersen and Hall conductances at high latitudes. Typically, the ionospheric conductances are estimated using either theoretical or empirical equations. The former method requires several ionospheric and thermospheric parameters as inputs. By contrast, empirical equations are simple, such as Robinson formulas and Galand formulas that have been widely used. In this study, we evaluate the empirical formulas of ionospheric conductances during four different types of auroral precipitation conditions based on 63 conjugate events observed by DMSP and EISCAT. The conductances calculated from the DMSP data with the empirical formulas are compared with those based on EISCAT measurements with the standard equations. The best correlation between these two is found when the empirical Robinson formulas are used in the presence of diffuse electron precipitation without ions. In the presence of ion precipitation, the correlation coefficients are smaller, but the correlation improves when the Galand formulas are used to estimate the contribution of ion precipitation to the conductances. For the condition of pure ion precipitation, the ionospheric conductances are increased up to 2-7 S for Pedersen and 2.5-10 S for Hall conductances. The increase is larger for a higher geomagnetic AE index. Overall, the empirical formulas applied to the DMSP particle spectra underestimate the ionospheric conductances.

How to cite: Wang, X., Cai, L., Aikio, A., Vanhamäki, H., Virtanen, I., Zhang, Y., Luo, B., and Liu, S.: Ionospheric conductance due to electron and ion precipitations based on the comparison between EISCAT and DMSP estimates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11018, https://doi.org/10.5194/egusphere-egu24-11018, 2024.

High-rate Radio Occultation (RO) measurement using the COSMIC-2 constellation has enabled the observation of the transient changes in the ionosphere's three-dimensional (3D) structure.  This capability enables studying the changes to the 3D ionospheric structure during a geomagnetic storm. So far, the ionospheric storms (positive/negative ionospheric storms) that follow space weather events, have mostly been studied globally using two-dimensional (2D) TEC maps generated using ground-based networks. Ground-based networks also limit the measurements to only over the landmass and islands. High-rate 3D observation from COSMIC-2 can overcome these limitations of the ground-based networks. Such measurements provide 3D ionospheric variations over a large region lying within +/- 40⁰ geographic latitude, with a spatiotemporal resolution significant enough to provide new insights.  This paper presents a 3D perspective of the ionospheric impact of the November 04, 2021, geomagnetic storm. In the present study, electron density has been binned with latitude, longitude, altitude, and time resolution of 6⁰, 30⁰, 25 km, and 2 hours, respectively. It must be noted that the present study excludes electron density variation below 225 km altitude where RO retrievals are not considered reliable. Some of the key observed features of the ionospheric storm under consideration are: (a) Large enhancement in the ionospheric plasma density due to the enhanced ‘fountain effect’ in the main phase is most significant in the topside ionosphere with a maximum variation observed above 450 km, (b) the most significant enhancement in the topside ionospheric plasma density (positive storm effect) was seen during the midnight period, irrespective of the longitude under consideration, (c) enhancement in the electron density also indicated some longitudinal dependence, and (d) most significant impact of the ionospheric storm was observed over the latitudinal belt lying beyond the poleward boundary of the EIA crests.  These and several other interesting observations will be presented. Results will also be discussed in light of the current understanding of ionospheric storms.

How to cite: Joshi, L. M.: Three-dimensional monitoring of Ionospheric storms using COSMIC-2 RO, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12540, https://doi.org/10.5194/egusphere-egu24-12540, 2024.

Travelling Ionospheric Disturbances (TID) and the underlying Atmospheric Gravity Waves (AGW) have long been associated with cases of extreme geomagnetic activity. This is especially true for geomagnetic storms that have been linked to large scale TIDs (LSTID). However, in the case of mid-scale TIDs (MSTID), a clear correlation has yet to be shown with geomagnetic activity, except for isolated cases. Such a correlation has been long suspected and assumed, since the mechanism by which these waves are generated must be linked to particle precipitation and localized heating, which occurs to some extent at all levels of geomagnetic activity due to the solar wind - magnetosphere - ionosphere coupling.

Our study used 7 years of measurements from the Tromso dynasonde, specifically the electron density and ionospheric tilts height profiles. These are generally available at a 2-minute cadence and thus can be used to resolve the bulk of the gravity wave spectrum. The excellent height resolution of the data, as well as the directionality of the two ionospheric tilts allow us to quantify the TID activity using an estimator based on the power spectral density integral. This proxy for overall TID activity accounts for all waves from all sources: auroral, orographic, from tropospheric weather, etc. We then demonstrate the relative importance of auroral waves by showing that TIDs with a north-south propagating direction correlate very well with geomagnetic indices indicative of geomagnetic disturbances at high-latitude (the AE, Kp and Polar Cap Indices), while less so for the SYM-H index, which is more indicative of lower latitudes. Long-term correlations are discussed, with an emphasis on changes to the statistical distribution describing the correlation. Finally, a high-precision analysis was performed to pin-point the time-delay between geomagnetic and TID activity at Tromso. The results show a dominant population of TIDs characterized by a delay of 2-6 hours, with a secondary population with delays larger than 10 hours.

How to cite: Negrea, C., Zabotin, N., Echim, M., and Rietveld, M.: Statistical correlations between geomagnetic activity and high-latitude TIDs investigated with the Tromso Dynasode, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13541, https://doi.org/10.5194/egusphere-egu24-13541, 2024.

Solar eclipses present a unique opportunity to study the effects of a supersonic cooling shadow and its modulation of the structure and energetics of the ionosphere-thermosphere system. Atmospheric Perturbations around Eclipse Path (APEP) is an eclipse rocket campaign that launched 3 sounding rockets from White Sands Missile Range (WSMR) during the Oct 2023 annular eclipse and will launch 3 sounding rockets from the Wallops Flight Facility (WFF) during the April 2024 total solar eclipse. This campaign will be the first simultaneous multipoint spatio-temporal in-situ observations of electrodynamics and neutral dynamics associated with solar eclipses. For each eclipse, the first instrumented rocket will be launched ~35 minutes before peak local eclipse, second at peak local eclipse, third ~35 minutes after peak local eclipse. The launches are supported by ground-based observations from AFRL Digisondes for WSMR launch and by VIPIR Dynasonde and Millstone ISR for WFF launch. Ground based meteor radar observations of neutral winds are also performed for both eclipses. These observations will be used to constrain comprehensive modeling during data analysis. 

How to cite: Barjatya, A., Clayton, R., Debchoudhury, S., Zettergren, M., Valentine, H., Graves, N., Conway, R., Ribbens, P., Milford, J., Obenberger, K., Holmes, J., Chau, J. (., Lynch, K., Mrak, S., and Bullett, T.: APEP: Eclipse Sounding Rocket Campaign, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13772, https://doi.org/10.5194/egusphere-egu24-13772, 2024.

Recent studies have identified a quasi six-year oscillation (QSYO) spanning various Earth system parameters, including the length of day, polar motion, secular variation of the magnetic field, sea level, precipitation, terrestrial water storage, land ice, and winds. This oscillation is linked to fluid dynamics processes in the liquid outer core, yet the mechanism facilitating its transmission from the core to the broader Earth system remains unclear. One of the proposed scenario is the plausible role of the magnetic field as a conduit for transmitting the QSYO from the core to the climatic system

Leveraging data from atmospheric and magnetic models alongside observations from Global Navigation Satellite System (GNSS), our approach employs statistical analysis to explore the presence of the QSYO in the atmosphere. We specifically analyze various parameters in both the charged (e.g., Total Electron Content - TEC) and neutral (e.g., nebulosities) atmospheric layers. This study aims to establish the existence of the QSYO in the atmosphere and link its variations with those from core in the magnetic field. 

How to cite: Chicot, G., Dehant, V., and De Viron, O.: Correlation of Magnetic Field Dynamics and Atmosphere for the study of the quasi six-year oscillation from Earth's core, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18179, https://doi.org/10.5194/egusphere-egu24-18179, 2024.