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.

We have detected and characterize traveling ionospheric disturbances (TIDs) in the mid‐latitude ionosphere over Europe using data from the Kharkiv incoherent scatter (IS) radar. The study focused on observations near solstices and equinoxes during solar cycle 24 under magnetically quiet conditions. We examined the diurnal, seasonal, and solar activity dependencies of both large‐scale (LS) and medium‐scale (MS) TIDs, evaluating 140 TID events. Key estimated characteristics included energetic (relative amplitudes), temporal (dominant periods, frequency of occurrence), and spatial (heights of maximum relative amplitudes, vertical and horizontal phase velocities, and wavelengths) parameters. Our findings suggest that moving solar terminators are the primary generation mechanism for magnetically quiet‐time LS TIDs, though a contribution from auroral activity cannot be excluded. In contrast, MS TIDs under magnetically quiet conditions are likely initiated from a broader range of sources, including gravity wave dissipation, severe tropospheric convection, coupling processes between the E s ‐layer and F ‐region, polarization electric fields, and Perkins instability. We found a positive correlation between the heights of the maximum relative TID amplitudes and the solar activity for LSTIDs. The TID characteristics obtained during extremely quiet conditions provide a useful context for analyzing the possible TID response to localized energy releases including those of anthropogenic origin. Additionally, they enable improvements in global and regional ionospheric models by clarifying the contribution of wave processes to the overall energy budget of the atmosphere and ionosphere.

We present the results of ground based remote sensing observations of large-scale traveling ionospheric disturbances (LSTIDs) occurring during the moderate magnetic storm evolution (22-24 September 2020) over central and eastern Europe. Three ionosondes located in Juliusruh, Pruhonice and near Kharkiv, and the Kharkiv incoherent scatter radar were employed to study temporal and spatial LSTID signatures in ionospheric F2 peak density and height and electron density variations at the heights of 100-300 km. Two types of LSTIDs are detected, which are originated during enhancement in auroral activity (2 events) and local sunrise terminator passage (3 events) from the ionosonde data. The magnetic storm-related LSTIDs exhibit equatorward propagation with the horizontal phase velocities of 546 m/s and 576 m/s, similar dominant periods of 135-150 min and 165-180 min over all three sites and a longitudinal dependence in fractional (relative) amplitudes of electron density perturbation. The solar terminator induced LSTIDs demonstrate the variety in both relative amplitudes and dominant periods over different locations. They have a westward apparent horizontal phase velocities of 288-345 m/s, which are close to the solar terminator velocity at ionospheric heights. Employment of incoherent scatter data enabled the detection of additional LSTIDs over Ukraine with the periods in a broader range of 41-168 min, an establishment of phase and onset differences for the oscillations in the ionospheric F2 peak electron density and height. (c) 2023 COSPAR. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

The paper presents results of the analysis of the TID activity and changes in the regular ionospheric variability observed over central and eastern Europe during geomagnetically quiet days, and during CME and CIR/HSSS-related storms. We analyzed main ionospheric parameters retrieved from manually scaled ionograms obtained at several central and eastern European locations and incoherent scatter radar data (Kharkiv, Ukraina). Large scale traveling ionospheric disturbance (LSTIDs) are thought to be mostly originated in the auroral zone in consequence of increased geomagnetic activity. Although there have been numerous studies of TIDs, current knowledge is often based on observing only limited set of parameters and two-dimensional characteristics (for example, total electron content by GNSS receivers or airglow brightness by all-sky imagers). Incoherent scatter technique enables simultaneous studies of altitudinal characteristics of TIDs in several parameters like electron density, electron and ion temperature and plasma drift, thus providing important information needed to investigate TIDs, their propagation and consider probable association of TIDs with their sources. This technique also yields all components of wave vector, provided that the radar has the ability to operate in multi-beam mode. In order to obtain quantitative information on the likeliness and morphology of the passage of LSTIDs over Europe at about 40 events were examined lasting between 8 and 24 hours each. In this paper we focused mainly on a couple of geomagnetic disturbances (depending on the incoherent scatter radar data availability). Most of the observed storm-related TIDs had periods of 60-180 min (LSTIDs). During the analyzed storms we also observed extraordinary spreads and plasma bubbles at the F region heights.

Правильний вибір білінгової системи (БС) критичний для прибутковості підприємства сфери обслуговування. На певному етапі зростання компанії білінг перетворюється з надійного і швидкого помічника у зборі та обробці інформації в інструмент для розширення і вдосконалення сервісу на існуючій технічній базі, а значить, для залучення нових клієнтів. Від надійності та швидкості роботи БС залежить якість обслуговування клієнтів і можливості, які отримує фірма-постачальник, що, у кінцевому рахунку, впливає на прибутковість підприємства сфери обслуговування. У роботі наведено результати багатокритеріального синтезу організаційної структури білінгової інформаційної системи (БІС) методом аналізу ієрархій (МАІ). Метод призначений для прийняття багатокритеріальних проектних рішень в умовах слабкої структурованості організаційно-технічних систем і невизначеності вихідної інформації, заданої набором кількісних і якісних залежностей. Обґрунтованість і достовірність прийнятих рішень багато у чому залежать від узгодженості експертних думок, які формалізовано виражаються через властивості зв'язності та транзитивності між експертними оцінками вихідного факторного простору. Закладений в основу МАІ принцип декомпозиції складної проблеми сукупністю більш простих складових, дозволяє здійснити побудову найбільш оптимального варіанту організаційної структури БІС відповідного призначення.

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We present a concept of atmospheric gravity wave (AGW) detector based on the fuzzy logic approach. The random-generated data as well as the data acquired using Kharkiv incoherent scatter (IS) radar are employed to test the expert system under development. We designed and selected input and output variables, types of membership functions and wrote the rules for the operation of the expert system. As input variables, we used two equivalent signal-to-noise ratios and oscillation durations at two adjacent heights as well as differences between phases, onsets and periods of these oscillations. Detection capability and belonging to wave were assigned to the output variables. Testing of the program detector using a number of randomly generated signals showed that it correctly detects the received signal the determines the signatures of wave patterns. We also apply the developed approach to detect traveling ionospheric disturbances caused by AGW propagation near local solar terminator passage times in the altitude-time maps of IS power.

According to the results of joint ionosonde studies of variations in the ionospheric F2 layer critical frequency over Kharkiv and Tromsø during low solar activity for fall equinox on September 22 – 24, 2020, the features of foF2 variations in middle and low latitudes were investigated for magnetically quiet and magnetically disturbed conditions. On the magnetically quiet day of September 22, 2020, the foF2 values over Kharkiv were found to exceed the foF2 values over Tromsø for the entire time interval of joint observations 02:45 - 16:45 UT. Both over Tromsø and over Kharkiv, a rapid increase in foF2 to its local maximum value was observed after the sunrise. Quasi-periodic variations in foF2 were revealed at high latitudes, which had lower amplitude compared to variations in foF2 over Kharkiv. Over both measuring sites, a pre-sunset local maximum in foF2 was observed. During magnetically disturbed conditions over Tromsø and Kharkiv, quasi-periodic fluctuations in foF2 were observed after the sunrise. Oscillations over Tromsø had lower amplitude than over Kharkiv, and were almost completely suppressed after the onset of a strong magnetic disturbance at high latitudes on September 23, 2020. The foF2 values over Tromsø exceeded its values over Kharkiv in a time interval of 10:45 – 12:15 UT. Comparison of the time variation of foF2 over Tromso on a magnetically quiet day, September 22, 2020, and on a magnetically disturbed day, September 23, 2020, showed that the foF2 value for September 23, 2020 from 10:15 to 15:00 UT exceeded the foF2 values for the same period on September 22, 2020. Comparison of the temporal variations in foF2 over Kharkiv on a magnetically quiet day, September 22, 2020, and on a magnetically disturbed day, September 24, 2020, showed that the foF2 value for September 24, 2020 exceeded its value for September 22, 2020 from 03:00 to 04:45 UT and from 07:00 to 13:00 UT. Magnetic disturbances were found to cause a rapid increase in foF2 values both over Kharkiv and Tromsø, which exceeded foF2 values under magnetically quiet conditions, and also led to a significant increase in the relative amplitudes of traveling ionospheric disturbances over Kharkiv.

This paper presents the results of a coordinated measurement campaign with ground based and satellite observations over European and Japanese regions during September 5–6, 2017. Two incoherent scatter radars, two satellite missions, International Reference Ionosphere (IRI-2016) empirical model, and Field Line Interhemispheric Plasma (FLIP) physical model were employed to examine the regular behavior of the F2-layer peak height and density and the topside ionosphere electron density, electron, and ion temperatures as well as traveling ionospheric disturbances (TIDs). The daily ionospheric variations over Kharkiv and Shigaraki exhibited similar behavior qualitatively and quantitatively. The results show that none of the empirical IRI-2016 models of F2-layer peak height, topside electron density, and temperature can be preferred for predicting the key qualitative features of variations in ionospheric plasma parameters over Kharkiv and Shigaraki. The likely reason is rapid day to day changes in solar activity and series of moderate enhancements of magnetic activity occurring in the observation period and preceding days. Compared with IRI-2016 model, the FLIP physical model was shown to provide the best agreement with the observations when constrained to follow the observed diurnal variations of F2-layer peak height both over Europe and Japan. This paper presents the first direct comparison of the mid-latitude electron density measured by the Swarm satellite with incoherent scatter radar data and it confirms the high quality of the space-borne data. For the first time, evidence of the possible need to increase the neutral hydrogen density in NRLMSISE-00 model by at least a factor of 2 was obtained for the Asian longitudinal sector. The TIDs, which have predominant periods of about 50 min over Europe and 80 min over Japan, were detected, likely caused by passage of the solar terminator. Such a difference in the periods could indicate regional features and is the topic for further research.

Based on the results of simultaneous ionosonde observations during low solar and weak magnetic activities, a coupling was found between diurnal and quasi-periodic variations in ionospheric parameters over magnetically conjugated regions, where the Ukrainian Antarctic Station (UAS) and Millstone Hill Observatory are located. A significant impact of the summer hemisphere on the nighttime variations of the F2 layer critical frequency foF2 in the magnetically conjugated region in the winter hemisphere was found. The most characteristic manifestation of this impact is the control of foF2 variations over the UAS not by the local sunset (sunrise), but by the sunset (sunrise) over Millstone Hill. It was found that the sunset over Millstone Hill leads to an increase in foF2 over the UAS, while the sunrise leads to a decrease in foF2 with a subsequent sharp increase. Both phenomena are associated with changes in the photoelectron flux from the northern hemisphere, corresponding changes in the electron temperature in the ionosphere above the UAS and the effect of these changes on the compression or rarefaction of the ionospheric plasma and changes in the plasmaspheric fluxes of H + ions. It was shown that the transition from nighttime to daytime conditions over both observation points was characterized by a significant decrease in the F2 layer peak height, and the difference in the values of this ionospheric parameter over Millstone Hill and UAS at night is due to seasonal differences in the thermospheric circulation and the difference in the behavior of the ionospheric parameters in the Northern and Southern hemispheres. Manifestations of atmospheric gravity waves, caused by the passage of local sunrise terminators, as traveling ionospheric disturbances with periods of about 90 and 75 – 120 mins over Millstone Hill and UAS, respectively, were found. These waves were most likely generated in the region located between the ionospheric F1 and F2 layers, where the sharp gradients in the electron and ion densities occur during changes in the intensity of solar radiation. It is confirmed that wave disturbances in atmospheric and ionospheric parameters can be transferred between magnetically conjugated regions by slow magnetohydrodynamic waves generated both at the heights of the ionospheric dynamo region due to the modulation of atmospheric and ionospheric parameters by atmospheric waves and the occurrence of external currents, and at the top of the plasmaspheric tube, where sharp plasma compression and heating or rarefaction and cooling occur during the passage of the solar terminator. Keywords: the ionosphere, F2 region, ionosonde measurements, geomagnetic field tube, magnetoconjugate region coupling, atmospheric gravity waves, traveling ionospheric disturbances, generation of slow magnetohydrodynamic waves

We proposed a new method aiming to identify the lower ionosphere processes and estimate their parameters. For this purpose, we combined fixed and fully steerable parabolic antennas of Kharkiv incoherent scatter (IS) radar to be directed to zenith and operate simultaneously. The 100-m fixed antenna is used in both transmit and receive mode, while the fully steerable one being 25 m in diameter receives IS signal only. This enables to eliminate a negative effect of the antenna switch on measured characteristics of received signal and eventually on retrieved ionospheric parameters. Such effect is due to a gas-filled arrester tube that needs a definite time to return to a stationary state in the receive mode after the end of sounding signal transmission. The modification of radio receiver system was made by adding new radio elements to a path blanking system of the receiver connected to 25-m antenna and aims to ensure this blanking to be independent on 100-m antenna receiver path and its optimization. A number of experiments was conducted, the results of which evidence the efficiency of the proposed method for measuring characteristics of the signal scattered from the lower ionosphere. In particular, wave-like patterns in received signal power were detected at altitudes of 50-100 km. We detected factors causing a lower limit altitude for which this method can be applied. One of them is a strong interference resulted from transmitted signal reflection from a local object spaced at 41 km away. The source of such interference is found to be the Kharkiv television center tower producing the reflected signal that is received by 25-m antenna side lobe. We suggested this fully steerable antenna to be set in azimuth in such a way to achieve the minimum reflected signal level received by the side lobes.

We present the results of a comprehensive study of traveling ionospheric disturbances (TIDs) occurring over Europe during the total solar eclipse of 20 March 2015. For detection of wave structures and estimation of TID parameters, two remote sensing techniques were combined: incoherent scatter (IS) radars and European and Finnish dense GPS receiver networks. Similar procedures were applied for processing both IS and GPS data. We developed a new method enabling to analyze TEC data separately in the temporal and spatial domain. For the first time, we produced maps of band-pass filtered TEC variations and reported both large- and medium-scale prevailing TIDs observed during this solar eclipse, both having similar periods of about 50 – 60 min. The downward phase progression indicates that TIDs were induced by atmospheric gravity waves generated at lower altitudes. The variations in IS power attained peak relative amplitudes of 0.22 (22%) at 220 km over Tromsø and of 0.17 (17%) at 200 km over Kharkiv. The vertical phase velocity was about 57 m/s over Tromsø. It increased from 25 to 170 m/s over Kharkiv with altitude increasing from 120 to 310 km. Over Western Europe, large-scale TIDs (LSTIDs) had prevailing north-east direction over the region from 45°to 50°N and 2°W to 8°E. Here, their average horizontal phase velocity Vm was 803±281m∕s and the absolute amplitudes of TEC variations usually do not exceed 0.17 TECU. For this region, we found strong differences in LSTID propagation azimuth between the solar eclipse day and the two adjacent days of 19 and 21 March 2015, used as reference. This most likely indicates that these LSTIDs were directly caused by the solar eclipse through local heating/cooling processes occurring during the passing of the Moon penumbra. Over another region, limited by 44°–50°N and 13°–19°E, the LSTIDs had south-east propagation. Over Finland, the LSTIDs also propagated southeastward having Vm=774±202m∕s and TEC amplitudes up to 0.6 TECU. A possible evidence of LSTID generation at high latitudes indirectly by this solar eclipse through an excitation of slow magnetosonic waves was experimentally detected. Medium-scale TIDs (MSTIDs) propagated southeastward over both regions having Vm values of 144±54m∕s over Western Europe and of 104±43m∕s over Finland. Over Northern Europe, the maximum MSTID amplitudes were greater by a factor of 5 compared to those over Western Europe and reached 0.4 TECU. We did not detect a clear difference in MSTID propagation between solar eclipse and reference days. The IS and GPS results are in consistency with each other. The detected TID parameters of predominant periods, relative amplitudes, altitude range and MSTID horizontal propagation direction generally correspond to the results of other studies.

We present the results of comparative analysis of ultrawideband signals observed in TEC variations over Europe during the solar eclipse of 20 March 2015. Wave disturbances over a number of European cities are detected which have periods of 50 - 60 min and durations of 120 - 180 min. Their amplitudes are of 0.8 - 2 TECU and exhibit positive correlation with Hurst exponent values. The fractional bandwidth is of 0.67 - 1.14 for all analyzed signals. Obtained results agree closely with those from incoherent scatter and vertical sounding techniques.

We present the results of comparative study of traveling ionospheric disturbances (TIDs) obtained at middle latitudes of different longitudinal sectors during two coordinated observational campaigns. The joint measurements were conducted near the vernal equinox and summer solstice in 2016 using Kharkiv (49.6 N, 36.3 E) and Millstone Hill (42.6 N, 288.5 E) incoherent scatter radars. The same methods and software were used for analysis of both data sets to ensure consistency. We found that TIDs with periods of 40-80 min are observed during all measurements and concentrated predominantly near the sunrise and sunset terminators over both sites. There is no obvious relationship between the observed wave processes and variations in the auroral electrojet. Absolute and relative amplitudes, time of appearance, durations and phase differences of TIDs show strong height and seasonal variability. Relative amplitudes are substantially greater over Millstone Hill, whereas higher absolute amplitudes are observed over Kharkiv. During the summer solstice, the overall wave activity is smaller than during vernal equinox. Additional joint observations are needed to identify the seasonal and longitudinal dependences of TID characteristics.

We present the results of detection and parameter estimation of ultrawideband signals in the incoherent scatter power, electron density and plasma temperatures occurred over Kharkiv during the solar eclipse of 20 March 2015. The prevailing periods are detected to be of 50 - 60 min in all observed parameters. The durations of wave disturbances were of 70 - 120 min. We detected the increase in Hurst exponent values during solar eclipse period for all analyzed dependences. The whole signal values of fractional bandwidth were close between the incoherent scatter power and the electron density on the one hand, and between the ion and electron temperatures on the other hand. Improved methods for ultrawideband signal detection in a number of observed dependences ensure the reliability of retrieval of wave response on different natural and artificial high energy events, including solar eclipses.

The paper presents methods used for Kharkiv incoherent scatter radar data processing and analysis. These methods formed the basis for the developed software package UPRISE. Noise removing, altitudinal correction, as well as plasma temperature, ion composition, and velocity estimation are described. UPRISE package allowed obtaining a number of qualitatively new unique geophysical results based on data acquired by the Kharkiv incoherent scatter radar.