ST3.1

Recently, citizen scientist photographs led to the discovery of a new auroral form called "the dune aurora" which exhibits parallel stripes of brighter emission in the green diffuse aurora at about 100 km altitude. This discovery raised several questions, such as (i) whether the dunes are associated with particle precipitation, (ii) whether their structure arises from spatial inhomogeneities in the precipitating fluxes or in the underlying neutral atmosphere, and (iii) whether they are the auroral manifestation of an atmospheric wave called a mesospheric bore. This study investigates a large-scale dune aurora event on 20 January 2016 above Northern Europe. The dunes were observed from Finland to Scotland, spanning over 1500 km for at least four hours. Spacecraft observations confirm that the dunes are associated with electron precipitation and reveal the presence of a temperature inversion layer below the mesopause during the event, creating suitable conditions for mesospheric bore formation. The analysis of a time lapse of pictures by a citizen scientist from Scotland leads to the estimate that, during this event, the dunes propagate toward the west-southwest direction at about 200 m/s, presumably indicating strong horizontal winds near the mesopause. These results show that citizen science and dune aurora studies can fill observational gaps and be powerful tools to investigate the least-known region of near-Earth space at altitudes near 100 km.

How to cite: Grandin, M., Palmroth, M., Whipps, G., Kalliokoski, M., Ferrier, M., Paxton, L. J., Mlynczak, M. G., Hilska, J., Holmseth, K., Vinorum, K., and Whenman, B.: Large-scale dune aurora event investigation combining Citizen Scientists' photographs and spacecraft observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5986, https://doi.org/10.5194/egusphere-egu21-5986, 2021.

The mid-latitude ionospheric trough (MIT) is a well-known feature in the topside ionosphere and plasmasphere. In this report, we investigated the plasma irregularities inside the MIT region based on the high-resolution (2 Hz) measurements of electron density and temperature from the Swarm satellite. We developed a method to automatically identify the mid-latitude trough from Swarm in-situ density measurements, and the small-scale irregularities inside MIT region can also be well determined by considering appropriate thresholds of both the relative (∆Ne/Ne) and absolute (∆Ne) density fluctuations. Further statistics has been performed based-on the multi-years database of identified MITs and irregularities from Swarm. Finally, we provided for the first time the seasonal and magnetic local time distributions of irregularities within the MIT region, and the involved plasma instabilities that cause the irregularities at the MIT region have been discussed.

How to cite: Liu, Y., Xiong, C., and Wan, X.: Ionospheric plasma irregularities inside the mid-latitude trough by using Swarm observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7293, https://doi.org/10.5194/egusphere-egu21-7293, 2021.

Mid-latitude trough (MIT) is the distinct structure observed in Earth’s ionosphere at high latitudes especially at the nighttimes. The phenomenon is observed at both hemispheres. As it resides at the topside ionosphere in the sub-auroral region, its behaviour and properties are highly sensitive to the solar and geomagnetic activity. Generally as the geomagnetic activity is more pronounced the MIT is observed at lower latitudes, it also deepens and becomes much more distinct in comparison to the low magnetic activity periods. MIT responds as well to the rapid changes in geomagnetic conditions, as are the geomagnetic storms, mainly caused by the CMEs. 

Based on the observations gathered by DEMETER data between 2005 and 2010 years  we present a set of geomagnetic storm cases and how the MIT properties has been changing as the storm evolves. We also discuss how it corresponds to the current solar activity and their evolutionary history  described by a set of different parameters.

How to cite: Przepiórka, D., Matyjasiak, B., Chuchra, A., and Rothkaehl, H.: Solar activity and its impact on the mid-latitude trough during geomagnetic storms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6457, https://doi.org/10.5194/egusphere-egu21-6457, 2021.

Solar wind and its embedded interplanetary magnetic field (IMF) affects Earth’s upper atmosphere by changing high-latitude ionospheric convection patter, producing auroral precipitation and depositing energy and momentum at high latitudes. These processes are greatly enhanced during geomagnetically active periods.  The geomagnetic activity induced changes at high latitudes are then transmitted to middle and low latitudes. In this work we employ the recently developed Multiscale Atmosphere-Geospace Environment (MAGE) model to simulate the non-linear electrodynamic and dynamic processes by which solar wind and IMF affect low and middle latitude thermosphere and ionosphere during geomagnetically active periods, including the stream interaction region event that happened in September 2020.  We examine the changes in ionospheric electric fields caused by penetration electric fields and neutral wind dynamo, as well as changes in neutral winds, temperature, composition  and ionospheric plasma densities. Model results are compared with  data from recent satellite mission, including COSMIC 2, GOLD and ICON to obtain new insight in the physical processes in the global thermosphere ionosphere responses to disturbed solar wind and IMF driving conditions.

How to cite: Wang, W., Wu, Q., and Ling, D.: Low and middle latitude thermosphere and ionosphere responses to geomagnetic activity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6764, https://doi.org/10.5194/egusphere-egu21-6764, 2021.

The dynamic evolution of the double tongue of ionization (TOI) into a single TOI at 400 km during the geomagnetic storm on September 7, 2015 was studied using the Defense Meteorological Satellite Program observations and Thermosphere Ionosphere Electrodynamic General Circulation model simulations. The double TOIs occurred in the presence of increased southward Bz and weak positive By, while the single TOI occurred in the presence of northward turning of Bz and duskward turning of By. In both double and single TOI events, the plasma at middle latitudes in the afternoon (prenoon) sector was greatly enhanced due to the local upward (upward) and zonal (meridional) E × B. The transition process is due to both the northward and duskward turning of IMF. The northward turning of IMF Bz weakens the SED and the TOI in both afternoon and morning sectors, while the increasing duskward IMF By strengthens the morning TOI.

How to cite: Zhang, K., Wang, H., Liu, J., Zheng, Z., He, Y., Gao, J., Sun, L., and Zheng, Y.: Dynamics of the tongue of ionizations during the geomagnetic storm on September 7, 2015, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-802, https://doi.org/10.5194/egusphere-egu21-802, 2021.

The paper is focused on differences/similarities in regular daily ionospheric variability and in the ionospheric response to CME- and CIR/CHSS-related magnetic disturbances above magnetically conjugated ionospheric stations located at Northern and Southern Hemisphere. We analysed variability of critical frequency foF2 and the F2 layer peak height hmF2 obtained for European-African sector for initial, main and recovery phases of magnetic storms of different intensity, which occurred within the last two solar cycles. We also used exclusively GPS-based detection methods, specifically information on TEC, TEC deviations in space and time from a background reference (dTEC), and the Rate of TEC change in time (ROT), all inferred from GPS receiver networks in Europe and Africa to compare behavior of Large Scale Traveling Ionospheric Disturbances (LSTIDs) at both hemispheres. We conclude that hemispheric conjugacy of LSTID is highly probable during both CME- and CIR/CHSS-related storms while interhemispheric circulation rather unlikely but still occurring during some periods.

How to cite: Buresova, D., Habarulema, J. B., Araujo-Pradere, E., Tshisaphungo, M., Watermann, J., and Lastovicka, J.: Differences in regular and storm time ionospheric variability at magnetically conjugated locations of the Northern and Southern Hemisphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4611, https://doi.org/10.5194/egusphere-egu21-4611, 2021.

Height-integrated ionospheric Pedersen and Hall conductances play a major role in ionospheric electrodynamics and Magnetosphere-Ionosphere coupling. Especially the Pedersen conductance is a crucial parameter in estimating ionospheric energy dissipation via Joule heating. Unfortunately, the conductances are rather difficult to measure directly in extended regions, so statistical models and various proxies are often used.

We discuss a method for estimating the Pedersen Conductance from magnetic and electric field data provided by the Swarm satellites. We need to assume that the height-integrated Pedersen current is identical to the curl-free part of the height integrated ionospheric horizontal current density, which is strictly valid only if the conductance gradients are parallel to the electric field. This may not be a valid assumption in individual cases but could be a good approximation in a statistical sense. Further assuming that the cross-track magnetic disturbance measured by Swarm is mostly produced by field-aligned currents and not affected by ionospheric electrojets, we can use the cross-track ion velocity and the magnetic perturbation to directly estimate the height-integrated Pedersen conductance.

We present initial results of a statistical study utilizing 5 years of data from the Swarm-A and Swarm-B spacecraft, and discuss possible applications of the results and limitations of the method.

How to cite: Vanhamäki, H., Aikio, A., Kauristie, K., Käki, S., and Knudsen, D.: Statistical estimates of auroral Pedersen conductance using electric and magnetic measurements by the Swarm spacecraft, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12569, https://doi.org/10.5194/egusphere-egu21-12569, 2021.

Large thermospheric neutral density enhancements in the cusp region have been examined for many years. The CHAMP satellite for example has enabled many observations of the perturbation, showing that it is mesoscale in size and exists on statistical timescales. Further studies examining the relationship with magnetospheric energy input have shown that fine-scale Poynting fluxes are associated with the density perturbations on a case-by-case basis, whilst others have found that mesoscale downward fluxes also exist in the cusp region statistically.

In this study, we use nearly 8 years of the overlapping SuperDARN and AMPERE datasets to generate global-scale patterns of the high-latitude and height-integrated Poynting flux into the ionosphere, with a time resolution of two minutes. From these, average patterns are generated based on the IMF orientation. We show the cusp is indeed an important feature in the Poynting flux maps, but the magnitude does not correlate well with statistical neutral mass density perturbations observed by the CHAMP satellite on similar spatial scales. Mesoscale height-integrated Poynting fluxes thus cannot fully account for the cusp neutral mass density enhancement, meaning energy deposition in the F-region or on fine-scales, which is not captured by our analysis, could be the primary driver.

How to cite: Billett, D., Perry, G., Clausen, L., Archer, W., McWilliams, K., Haaland, S., and Burchill, J.: Large scale thermospheric density enhancements in relation to downward Poynting fluxes: Statistics from CHAMP, AMPERE and SuperDARN, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1389, https://doi.org/10.5194/egusphere-egu21-1389, 2021.

Energetic electron precipitation (EEP) into the Earth's atmosphere can collide with gases and deposit their energy there. The collisions between electrons and atmospheric gasses initiate several chemical reactions which can reduce the ozone concentration. Ozone is critically important in the middle atmosphere energy budget as changes in the ozone concentration impact temperature and winds. EEP is not fully understood in terms of how much energy is being deposited and what the associated drivers are. An accurate quantification of EEP has limitations due to instrumental challenges and therefore imposes limitations of the associated EEP parameterization into climate models. A solution to this problem is a better understanding of the driver processes of energetic electron acceleration and precipitation, alongside optimized data handling. In this study the bounce loss cone fluxes are inferred from EEP measurements by the Medium Energy Proton and Electron Detector (MEPED) on board the Polar Orbiting Environmental Satellite (POES) and the Meteorological Operational Satellite Program of Europe (METOP) at tens of keV to relativistic energies. It investigates EEP in contexts of different solar wind structures: high-speed solar wind streams (HSSs) and coronal mass ejections (CMEs), during an eleven-year period from 2004 – 2014. While today's chemistry climate models only provide snapshots of EEP, independent of context, this study aims to understand the context EEP is created in, which will allow a more accurate estimate of the EEP to be applied in atmospheric climate models.

How to cite: Salice, J. A., Tyssøy, H. N., Smith-Johnsen, C., and Babu, E. M.: Solar wind structures and their effects on energetic electron precipitation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1084, https://doi.org/10.5194/egusphere-egu21-1084, 2021.

Previous observations and simulations have shown that the low-energy electron precipitation in the cusp plays an important role in ionosphere and thermosphere through particle impact ionization and heating. In this study, we investigate the precipitating particles in the Earth's polar cap region, which is also an open-field line region as the cusp. In many numerical simulations of the upper atmosphere, the polar cap region is described as a uniform area with no spatial and temporal variations of the particle energy and fluxes. We analyze years of the particle observations from DMSP satellites to show the temporal variations of particle characteristics in the region poleward of 80 degree magnetic latitudes in this study. The results show the solar cycle, annual and seasonal variations of particle (electrons, ions) energy, number flux and energy flux in the polar cap. The results will be useful to improve the polar-latitude precipitating particle description in upper atmosphere modeling.

How to cite: Huang, Y. and Liang, S.: Temporal variation of particle precipitation in Erath's polar cap from DMSP observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15738, https://doi.org/10.5194/egusphere-egu21-15738, 2021.

Energetic electron precipitation (EEP) from the plasma sheet and the radiation belts, can collide with gases in the atmosphere and deposit their energy. EEP increase the production of NOx and HOx, which will catalytically destroy stratospheric ozone, an important element of atmospheric dynamics. Therefore, measurement of latitudinal extent of the precipitation boundaries is important in quantifying atmospheric effects of Sun-Earth interaction and threats to spacecrafts and astronauts in the Earth's radiation belt.
This study uses measurements by MEPED detectors of six NOAA/POES and EUMETSAT/METOP satellites from 2004 to 2014 to determine the latitudinal boundaries of EEP and its variability with geomagnetic activity and solar wind drivers. Variation of the boundaries with respect to different particle energies and magnetic local time is studied. Regression analyses are applied to determine the best predictor variable based on solar wind parameters and geomagnetic indices. The result will be a key element for constructing a model of EEP variability to be applied in atmosphere climate models.

How to cite: Babu, E. M., Tyssøy, H. N., Smith-Johnsen, C., Maliniemi, V., Salice, J. A., and Millan, R.: Determining latitudinal extent of energetic electron precipitation  using MEPED on-board NOAA POES, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1240, https://doi.org/10.5194/egusphere-egu21-1240, 2021.

After more than seven years in orbit, the ESA Swarm satellites have provided an already large statistics of measurements of several important physical parameters of the ionosphere. In particular, electron density and temperature are measured by pairs of Langmuir Probes, and the quality of such data is now considered good enough for many studies, either science cases or climatological characterisations. Concerning specifically the electron temperature, a rather elusive parameter which is quite difficult to correctly characterize “in situ”, and for which the past literature is not so abundant with respect to other ionospheric physical quantities, the overall distributions observed by Swarm are qualitatively consistent with expectations from theory and past observations. However, a non-negligible amount of high and very high electron temperature values is regularly observed, whose distributions and properties are not trivial. In this study we aim at characterizing such features statistically as a function of latitude, local time, and season.

How to cite: Coco, I., Consolini, G., De Michelis, P., Giannattasio, F., Pezzopane, M., Pignalberi, A., and Tozzi, R.: Climatology of very high ionospheric electron temperature occurrences as observed by Swarm constellation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10211, https://doi.org/10.5194/egusphere-egu21-10211, 2021.

The IRAP Plasmasphere Ionosphere Model (IPIM) is an ionospheric model which describes the transport equations of ionospheric plasma species along magnetic closed field lines. The previous iteration of IPIM used some basic models to provide estimations of the solar wind conditions and associated motions of plasma and precipitation within the ionosphere as input. In this presentation, we discuss developments to IPIM as part of the EUHFORIA project, to consistently observe space weather conditions from the Sun to the Earth’s surface. The developments of the model include using in-situ solar wind observations from the OMNI data set, ionospheric radar data of plasma motions from the Super Dual Auroral Radar Network (SuperDARN), and the Ovation model of auroral precipitation, as inputs to the model. We compare the new version with the former version and ionospheric observations to explore the differences observed by including these data within the model. We present some new results using this new version of the model to explore the ionosphere’s response to solar wind transient events such as high-speed streams and coronal mass ejections.

How to cite: Thomas, S., Blelly, P.-L., Marchaudon, A., Eisenbeis, J., and Bird, S.: Applying Solar Wind Observations to the IPIM Ionospheric Model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2354, https://doi.org/10.5194/egusphere-egu21-2354, 2021.

The thermospheric winds play an important role in the vertical and horizontal couplings of the upper atmosphere by modulating neutral and plasma dynamics. A large variety of observation techniques and numerical as well as empirical models have been developed to understand the behavior of thermospheric winds. The Fabry-Perot interferometer (FPI) is a widely used ground- and satellite-based optical instrument for the thermospheric winds observations in the upper atmosphere. Due to solar contamination of the fainter airglow emission during the daytime, most of the ground-based interferometric wind measurements are limited to the nighttime period only. Despite these constraints, the Second‐generation, Optimized, Fabry‐Perot Doppler Imager (SOFDI) is designed for both daytime and nighttime measurements of thermospheric winds from OI 630‐nm emission and is currently operating at the Huancayo, Peru, near the geomagnetic equator. In this study, we present a comparative analysis of the observed SOFDI wind climatological data and several other modeled results including, but not limited to, Horizontal Wind Model 2014 (HWM-14), Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model with and without implementing Prompt Penetration Electric Field (PPEF), Whole Atmosphere Model (WAM), SAMI3 model, and Magnetic mEridional NeuTrAl Thermospheric (MENTAT) model. We examine the relative performances of these models in the context of the direct-measured thermospheric winds. The day and nighttime modeled winds show an excellent agreement with the SOFDI wind data at the equatorial latitude, except for the daytime zonal winds. Further, this analysis gives a comprehensive picture of how well the measured winds provided by the SOFDI instrument and various models represent the features of the equatorial thermosphere. We also investigate and give an overview of the sources, drivers, effects, and possible mechanisms of the wind variability in the low-latitude thermosphere.

How to cite: Khadka, S., Gerrard, A., Fedrizzi, M., Dandenault, P., and Meriwether, J.: Comparative Analysis of the Measured and Modeled Equatorial Thermospheric Wind Climatology, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6883, https://doi.org/10.5194/egusphere-egu21-6883, 2021.

We present statistical investigation of the seasonal, geomagnetic activity and interplanetary magnetic field (IMF) dependence of  hemispheric asymmetry in the auroral currents. Magnetic data from the Swarm satellites has been analyzed by applying the spherical elementary current system (SECS) method. Bootstrap resampling has been used to remove the difference in the number of samples as well as activity and IMF conditions between the local seasons and the hemispheres. In general, the currents are larger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Asymmetry is larger during low (Kp<2) than high Kp (Kp≥2) and during local winter and local autumn than local summer and local spring. Averaging over all Kp and IMF conditions, we find larger currents flowing in the NH than in the SH with the NH/SH ratio for FACs: 17­±5%, 14±5%,7±4% and 2±4% in winter, autumn spring and summer, respectively.  When making the statistical analysis for different IMF directions, we find that the orientation of IMF By has strong influence on the hemispheric asymmetry in the auroral currents, but this influence depends on local season. When IMF By is positive in NH (negative in SH), on average FACs as well as ionospheric horizontal currents are stronger in NH than inSH in most local seasons under both signs of IMF Bz. Conversely, when IMF By is negative in NH (positive in SH), the hemispheric differences of auroral currents during most local seasons are small except in local winter. Overall, comparing the hemispheres for opposite signs of IMF By, we find larger hemispheric asymmetry when IMF By is positive in  NH (negative  in SH) than vice versa.

The factors causing the observed hemispheric asymmetries in the auroral currents are not understood at the moment. Background conductances from the IRI model and cross polar cap potential values from SuperDARN dynamic modelsuggest that solar induced ionospheric conductances and convection electric field cannot explain all the observed features of the hemispheric asymmetry in auroral currents. The role of conductance enhancements due to auroral particle precipitation and possible asymmetries in the energy  flux of precipitating particles need to be investigated in future studies.

How to cite: Workayehu, A., Vanhamäki, H., Aikio, A., and Shepherd, S.: Seasonal, Kp and IMF dependence of hemispheric asymmetry in ionospheric horizontal and field-aligned currents, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9697, https://doi.org/10.5194/egusphere-egu21-9697, 2021.

Through advanced statistical investigation and evaluation of solar wind plasma and magnetic field data, we investigate the statistical relation between the magnetic field B_z component, measured at L1, and Earth’s thermospheric neutral density. We will present preliminary results of the time series analyzes using in-situ plasma and magnetic field measurements from different spacecraft in near Earth space (e.g., ACE, Wind, DSCOVR) and relate those to derived thermospheric densities from various satellites (e.g., GRACE, CHAMP). The long and short term variations and dependencies in the solar wind data are related to variations in the neutral density of the thermosphere and geomagnetic indices. Special focus is put on the specific signatures that stem from coronal mass ejections and stream or corotating interaction regions.  The results are used to develop a novel short-term forecasting model called SODA (Satellite Orbit DecAy). This is a joint study between TU Graz and University of Graz funded by the FFG Austria (project “SWEETS”).

How to cite: Kroisz, S., Drescher, L., Temmer, M., Krauss, S., Süsser-Rechberger, B., and Mayer-Gürr, T.: Statistical relations between in-situ measured Bz component and thermospheric density variations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4773, https://doi.org/10.5194/egusphere-egu21-4773, 2021.

Observations of upper mesosphere/lower thermosphere (MLT) wind have been performed at Collm (51°N, 13°E) and Kazan (56°N, 49°E), using two SKiYMET all-sky meteor radars with similar configuration. Daily vertical profiles of mean winds and tidal amplitudes have been constructed from hourly horizontal winds. We analyze the response of mean winds and tidal amplitudes to geomagnetic disturbances. To this end we compare winds and amplitudes for very quiet (Ap ≤ 5) and unsettled/disturbed (Ap ≥ 20) geomagnetic conditions. Zonal winds in both the mesosphere and lower thermosphere are weaker during disturbed conditions for both summer and winter. The summer equatorward meridional wind jet is weaker for disturbed geomagnetic conditions. Tendencies over Collm and Kazan for geomagnetic effects on mean winds qualitatively agree during most of the year. For the diurnal tide, amplitudes in summer are smaller in the mesosphere but greater in the lower thermosphere, but no clear tendency is seen for winter. Semidiurnal tidal amplitudes increase during geomagnetic active days in summer and winter. Terdiurnal amplitudes are slightly reduced in the mesosphere during disturbed days, but no clear effect is visible for the lower thermosphere. Overall, while there is a noticeable effect of geomagnetic variability on the mean wind, the effect on tidal amplitudes, except for the semidiurnal tide, is relatively small and partly different over Collm and Kazan.

How to cite: Jacobi, C., Lilienthal, F., Korotyshkin, D., Merzlyakov, E., and Stober, G.: Influence of geomagnetic disturbances on midlatitude mesosphere/lower thermosphere mean winds and tides, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3163, https://doi.org/10.5194/egusphere-egu21-3163, 2021.

For long-term studies as ionospheric trends investigations we have to use proxies of solar activity, because homogenous and sufficiently long data series of solar ionizing radiation are not available. Here I deal with selection of the optimum solar proxy for yearly average and monthly median values near noon (11-13 LT). Six solar proxies are used, F10.7, F30, Mg II, He II, Fα (solar H Lyman alpha flux) and R (sunspot number), foF2 from European ionosondes Juliusruh, Pruhonice and Rome, and foE from Chilton and Juliusruh over the period 1976-2019. For yearly values Mg II is the optimum proxy (but it is available only since late 1978) for foF2, with F30 being the second best. For foE the optimum proxy appears to be F10.7. For monthly medians of January, April, July and October the general pattern is the same as for yearly values.

How to cite: Laštovička, J.: What is the optimum solar proxy for long-term ionospheric studies?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3017, https://doi.org/10.5194/egusphere-egu21-3017, 2021.

We investigated seasonal variations of relationships between main ionospheric characteristics and solar and geomagnetic indices in longitudinal perspective. We consider statistically significant differences in connections of ionospheric response to the F10.7cm, R, and Kp indices on seasonal time-scales during years 1975 – 2010 covering 21^st – 23^rd Solar Cycles. The periods of 21 days before and after Winter/Summer Solstices and Vernal/Autumnal Equinoces are considered as season. The foF2 time series in our analysis represent measurements of daily observational data which were obtained using mid-latitude (41.4°N – 54°N) ionosondes (Chilton, Slough RL052/SL051, Juliusruh/Rugen JR055, Boulder BC840). We used local time noon 5-hour foF2 averages. For the investigation, we used seasonal differences method of conditional independence graphs (CIG) models. Significant seasonal variations are visible during ascending and descending phases of Solar cycles.

How to cite: Podolská, K., Koucká Knížová, P., and Chum, J.: Seasonal Variability of Relationship between Main Ionospheric Characteristics and Solar/Geomagnetic Indices via Graphical Models of Conditional Independences, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8453, https://doi.org/10.5194/egusphere-egu21-8453, 2021.

Azimuth of medium scale gravity waves (GWs) propagation in the thermosphere/ionosphere fundamentally depends on the daytime and day of year. Previous studies show that the GWs mostly propagate against the predominant direction of neutral winds in the ionosphere. However, several cases of propagation along the wind direction have also been identified, specifically around the equinoxes. The analysis is based on remote observation of the ionosphere using multi–frequency and multipoint continuous Doppler sounding. The network consists of at least three spatially separated sounding paths (transmitter-receiver pairs) at three frequencies, situated in the western part of the Czech Republic. The apparent horizontal velocity and azimuth of GWs are derived from the time shifts observed for different measuring paths. The HWM14 neutral wind model is used for comparison of neutral winds with the observed phase speeds of GWs. Cases of anomalous propagation of GWs along the direction of neutral winds are analyzed. It is shown that the observed GW periods can be substantially shorter than the intrinsic periods in the wind-rest frame owing to Doppler shift.

How to cite: Rusz, J., Chum, J., and Baše, J.: Anomalous propagation of medium scale GWs along neutral winds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4250, https://doi.org/10.5194/egusphere-egu21-4250, 2021.

     Characteristics of gravity waves (GWs) are studied from multi-point and multi-frequency continuous Doppler sounding in the Czech Republic. Three dimensional (3D) phase velocities of GWs are determined from phase shifts between the signals reflecting from the ionosphere at different locations that are separated both vertically and horizontally; the reflection heights are determined by a nearby ionospheric sounder located in Průhonice. Wind-rest frame (intrinsic) velocities are calculated by subtracting the neutral wind velocities, obtained by HWM-14 wind model, from the observed GW velocities. In addition, attenuation of GWs with height was estimated from the amplitudes (Doppler shifts) observed at different altitudes. A statistical analysis was performed over two one-year periods: a) from July 2014 to June 2015 representing solar maximum b) from September 2018 to August 2019 representing solar minimum.   

     The results show that the distribution of elevation angles of wave vectors in the wind–rest frame is significantly narrower than in the Earth frame (observed elevations). Possible differences were also found between the wind–rest frame elevation angles obtained for the solar maximum (mean value (around -24°) and solar minimum (mean value round -37°). However, it is demonstrated that the elevation angles partly depended on the daytime and day of year. As the distribution of the time intervals suitable for the 3D analysis in the daytime–day of year plane was partly different for solar maximum and minimum, no reliable conclusion about the possible dependence of elevation angles on the solar activity can be drawn.

     It is shown that the attenuation of GWs in the ionosphere was in average smaller at the lower heights. This is consistent with the idea that mainly viscous damping and losses due to thermal conductivity are responsible for the attenuation.

How to cite: Chum, J., Podolska, K., Base, J., and Rusz, J.: Elevation angles and attenuation of gravity waves in the ionosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-866, https://doi.org/10.5194/egusphere-egu21-866, 2021.

Formation the feature, in a form of deep trough, in frequency dependence of the wave field strength for single-hop paths with distances near classical limiting distance 3000 km at low level of solar activity was considered. Model calculations within the framework of the extended global ionospheric IRI model show high probability for appearing such a situation in the local daytime with a developed regular E-layer of the ionosphere. Some experimental results in multifrequency radio sounding of the ionosphere with a registration of the deep trough in frequency dependence of signal-to-noise ratio (SNR) were analyzed. It is shown that the IRI model, in principle, makes it possible to reproduce this peculiarity in the wave field energy parameters, but in some cases of experimental data, to a large extent, is able to provide only a qualitative description of this effect. Possible reasons for the quantitative discrepancy between experimental and model results are discussed.

How to cite: Atamaniuk, B., Krasheninnikov, I. V., Popov, A., and Matyjasiak, B.: Problem ot the energy transfer for radio paths near single-hop limiting distance for low solar activity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6351, https://doi.org/10.5194/egusphere-egu21-6351, 2021.

Analysis of the direction of motion of the vector of Sq-variations of the Earth's magnetic field, depending on the time of day and season of the year, shows that the observed Sq-variation is similar to the magnetic field created by a negatively charged spherical body moving in space. Transformations of the Sq-variation vector from the local coordinate system of the magnetic observatory to the ecliptic coordinate system are performed. A possible connection between the origin of the Sq-variation and the electric dipole moment of quartz molecules oriented towards the center of the Earth during the crystallization of the mineral and causing the electric and dipole magnetic fields of the Earth is considered. A scheme for conducting an experiment that allows us to separate the effects of extraterrestrial and extraterrestrial sources of Sq-variations is proposed.

How to cite: Zhumabayev, B. and Vassilyev, I.: On the possibility of an intra-Earth source of Sq-variations of the Earth's magnetic field, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2148, https://doi.org/10.5194/egusphere-egu21-2148, 2021.