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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.

Response of middle latitude ionospheric F-region to two sequential geomagnetic storms on 7–8 September 2017 has been studied using the incoherent scatter radar of Institute of Ionosphere $(49.60^{\circ}N, 36.30^{\circ}E)$. The G3-class geomagnetic storm on 7 September and the G4-class geomagnetic storm on 8 September had close intensities. The first geomagnetic storm was accompanied by the positive disturbance during the main phase and the negative disturbance during the recovery phase. Effects of the second geomagnetic storm caused the negative disturbance. The ionosphere was characterized by a largescale variation in critical frequency $fo F2$ (from 6 to 8 MHz and from 6 to 4 MHz), F2-layer peak height $hm F2$ (by 70–80 km) and the vertical plasma drift velocity oscillations (up to 50–80 m/s).

We present the results of observations of variations in the mid-latitude ionospheric parameters and physical processes in the geospace during March 20, 2015 partial solar eclipse over Kharkiv (49.60° N, 36.30° E) where the eclipse magnitude was about 0.54. The Kharkiv incoherent scatter (IS) radar and digital ionosonde were used for ionospheric observations and estimations of the parameters of the thermal and dynamical processes. At the time of the maximum obscuration of the Sun's area, an increase in the ionospheric F2 peak height by about 40 km was observed. At the same time, the electron density at altitudes of 190 and 210 km decreased by approximately 18.5 and 16.5%, respectively. During the eclipse, a decrease in the electron temperature and apparent changes in the vertical plasma drift velocity were observed. The observations and analysis have shown that the solar eclipse led to significant restructuring of the thermal and dynamic state of the ionospheric plasma over Kharkiv.

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.

The equipment and methodical characteristics of determining the vertical component of the ionospheric plasma motion velocity Vz based on an incoherent scatter radar of Institute of Ionosphere, National Academy of Sciences and Ministry of Education and Science of Ukraine (Kharkiv), which is the only radar of such type in Central Europe, are described. Based on the radar data, the patterns of altitude and diurnal variations in Vz near the maximum of solar cycle 24 for the typical geophysical conditions (around the summer and winter solstices, the spring and fall equinoxes) at low geomagnetic activity and the specifics of these changes during ionospheric storms are presented. The results of modeling of the dynamic processes in ionospheric plasma under the conditions of the undisturbed ionosphere, including the determination of altitudetime variations in the thermospheric wind velocity, are presented. It has been established that this velocity can significantly differ from the thermospheric wind velocity calculated by the known empirical global models. This difference is likely related to the regional features of thermospheric wind that are not shown in the global models.

A comprehensive study of the response of the ionosphere-plasmasphere system at mid-latitudes to weak (Dstmin > -50 nT) magnetic storms is presented. For the first time, it is shown that weak magnetic disturbances can lead to significant modulation of ionosphere-plasmasphere H+ ion fluxes. It is found that this modulation is caused by the enhancements/reductions of the topside O+ ion density, which is induced by F2-layer peak height rise and fall during the storms. The F2-layer motion is caused by thermospheric wind changes and by a penetration electric field. Both drivers are closely related to the changes in the Bz component of interplanetary magnetic field. The most prominent manifestation of the H+ ion flux modulation is strong changes in H+ ion fraction in the topside ionosphere. This study also indicates that the NRLMSISE-00 model provides the correct relative changes of neutral H density during weak magnetic storms and also that there is a compelling need to include geomagnetic activity indices, in addition to solar activity (F10.7), as input parameters to empirical topside ionosphere models.

This study investigates the causes of nighttime enhancements in ionospheric density that are observed in winter by the incoherent scatter radar at Kharkiv, Ukraine. Calculations with a comprehensive physical model reveal that large downward ion fluxes from the plasmasphere are the main cause of the enhancements. These large fluxes are enabled by large upward H+ fluxes into the plasmasphere from the conjugate summer hemisphere during the daytime. The nighttime downward H+ flux at Kharkiv is sensitive to the thermosphere model H density, which had to be increased by factors of 2 to 3 to obtain model-data agreement for the topside H+ density. Other studies support the need for increasing the thermosphere model H density for all seasons at solar minimum. It was found that neutral winds are less effective than plasmaspheric fluxes for maintaining the nighttime ionosphere. This is partly because increased equatorward winds simultaneously oppose the downward H+ flux. The model calculations also reveal the need for a modest additional heat flow from the plasmasphere in the afternoon. This source could be the quiet time ring current.

The features of reception and transformation of the incoherent scatter signal as well as digital processing signals extracted at low and intermediate frequencies are considered. The system for recording and processing signal at intermediate frequency is proposed. The justification for the choice of its frequency multiplier unit is adduced for forming ADC reading pulses that rigidly linked to intermediate frequency. The developed system allows employ algorithms that adapted to the altitude range under study and ionospheric plasma conditions.

This research investigates anomalous nighttime ion density behaviour over the Kharkiv, Ukraine incoherent scatter radar (49.6° N, 36.3° E, 45.3° inv) during the equinoxes of 2006–2010. The observations show that the altitude of the transition from O+ to lighter ions was much lower than empirical and physical models predict. The standard physical model produces very good agreement for the O+ densities but underestimates the H+ densities by a factor of 2 in March 2006 and a factor of 3 in March 2009. The anomalously low transition height is a result of similar lowering of the ionospheric peak height and also of significantly increased H+ density. The lower ionospheric peak height may be caused by weaker nighttime neutral winds. The calculations indicate that the higher measured topside ionosphere H+ densities are most likely due to higher neutral hydrogen densities. Both factors could be the result of weaker than usual magnetic activity, which would reduce the energy input to high latitudes. Prolonged low activity periods could cause a global redistribution of hydrogen and also allow more neutral hydrogen to settle down from the exosphere into the mid-latitude ionosphere. The finding of the need for higher H densities agrees well with recent H-alpha airglow measurements and it is important for accurate modelling of plasmasphere refilling rates and night-time NmF2 values.

Characteristics of the wave disturbances of the ionospheric electron number density were measured using the Kharkov incoherent scatter radar. The disturbance generation accompanied the SURA heating of the near-Earth plasma by high-power periodic radiation. The distance between the heater and the radar was about 960 km. The possibility of generating ionospheric wave disturbances with a period of 20 to 30 min in the internal gravity wave range was confirmed. The disturbance propagation velocity was near 320–400 m/s, and the relative amplitude of the electron density variation was 1–10%. The wave disturbances appeared in the altitude range 145–235 km. Aperiodic bursts of the electron number density with a relative amplitude of up to 5–10% were detected after the first switch-ons of periodic radiation in the 30-min heating — 30-min pause regime at altitudes of 145 to 310 km. The observation results generally conform to the synchronous observation data obtained using the Kharkov vertical-sounding Doppler radar and a network of ionosondes.

The paper presents the structure and peculiarities of the developed database used for Kharkiv incoherent scatter radar data storing. The heterogeneity of the raw data, the existence of specific periods of data acquisition, the use of the IS radar data processing program to estimate size and quality of the data, the use of the external server to store the results of data processing, and the ability to fill database with data acquired by different radiophysical instruments are described.

Приведены результаты исследования отклика области F и внешней ионосферы на сильную магнитную бурю 13–14 ноября 2012 г. (Kp max= 6+ ). Наблюдения проведены с помощью радара некогерентного рассеяния, расположенного вблизи г. Харькова. Магнитная буря сопровождалась ионосферной бурей со знакопеременными фазами. Особенностью данной бури является наличие двух положительных и одной отрицательной фаз возмущения. Ключевые слова: геокосмическая буря, фазы ионосферной бури, ионосфера, некогерентное рассеяние Статья поступила в редакцию 14.02.2014 Radio phys. radio astron. 2014, 19(2): 170-180 СПИСОК ЛИТЕРАТУРЫ 1. Черногор Л. Ф., Домнин И. Ф . Физика геокосмических бурь. – Х.: ХНУ имени В. Н. Каразина, 2014. – 408 с. 2. Chernogor L. F., Grigorenko Ye. I., Lysenko V. N., and Taran V. I. Dynamic processes in the ionosphere during magnetic storms from the Kharkov incoherent scatter radar observations // Int. J. Geomagn. Aeron. – 2007. – Vol. 7, No. 3. – id. GI3001. 3. Buonsanto M. J. Ionospheric Storms: A Review // Space Sci. Rev. – 1999. – Vol. 88, No. 3–4. – P. 563–601. 4. Mikhailov A. V. and Foster J. C. Daytime thermosphere above Millstone Hill during severe geomagnetic storms // J. Geophys. Res: Space Phys. – 1997. – Vol. 102, Is. A8. – P. 17275–17282. 5. Danilov A. D. F2 region response to geomagnetic disturbances // J. Atmos. Solar-Terr. Phys. – 2001. – Vol. 63, Is. 5. – P. 441–449. 6. Домнин И. Ф., Емельянов Л. Я., Кацко С. В., Ляшенко М. В., Черногор Л. Ф. Ионосферные эффекты магнитной бури 13–15 ноября 2012 г. // Cб. тез. докл. 13-й украинской конф. по космическим исследованиям. – Евпатория (Украина). – 2013. – С. 52. 7. Кацко С. В. Геокосмическая буря 14 ноября 2012 года: результаты наблюдений на харьковском радаре некогерентного рассеяния // Сб. тез. докл. конф. ИОН-2013 “Дистанционное радиозондирование ионосферы”. – Малый Маяк, Крым (Украина). – 2013. – С. 46. 8. Черногор Л. Ф. Физика Земли, атмосферы и геокосмоса в свете системной парадигмы // Радиофизика и радиоастрономия. – 2003. – Т. 8, № 1. – С. 59–106. 9. Черногор Л. Ф. Земля – атмосфера – ионосфера – магнитосфера как открытая динамическая нелинейная физическая система. 1 // Нелинейный мир. – 2006. – Т. 4, № 12. – С. 655–697. 10. Бархатов Н. А., Бархатова О. М. Выявление классов ионосферной возмущенности по многолетним данным о критической частоте слоя F2 // Геомагнетизм и аэрономия. – 2012. – Т. 52, № 4. – С. 510–518. 11. Mikhailov A. V., Skoblin M. G., and Forster M. Daytime F2-layer positive storm effect at middle and lower latitudes // Ann. Geophys. – 1995. – Vol. 13, No. 5. – P. 532–540. 12. Данилов А. Д., Морозова Л. Д. Ионосферные бури в области F2. Морфология и физика (обзор) // Геомагнетизм и аэрономия. – 1985. – Т. 25, № 5. – С. 705–721. 13. Кринберг И. А., Тащилин А. В. Ионосфера и плазмосфера. – М.: Наука, 1984. – 190 с. 14. Данилов А. Д., Морозова Л. Д., Мирмович Э. Г. О возможной природе положительной фазы ионосферных бурь // Геомагнетизм и аэрономия. – 1985. – Т. 25, № 5. – С. 768–772. 15. Черногор Л. Ф. Земля – атмосфера – ионосфера – магнитосфера как открытая динамическая нелинейная физическая система. 2 // Нелинейный мир. – 2007. – Т. 5, № 4. – С. 225–246. 16. Chernogor L. F. The Earth – atmosphere – geospace system: main properties and processes // Int. J. Remote Sens. – 2011. – Vol. 32, No. 11. – P. 3199–3218.

The observation results of the effects in the geospace plasma during a partially (magnitude ∼0.42) solar eclipse are presented. The experimental data were obtained with an incoherent scatter radar of the Institute of the Ionosphere (near Kharkov). During the eclipse, the density at the F2 layer maximum decreased by 32%, the foF2 critical frequency decreased by 17.5%, and the altitude of the F2 layer maximum increased insignificantly. At altitudes of 290–680 km, the electron density decreased by ∼25%. During the eclipse, the electron and ion temperature decreased by 70–180 and 0–140 K, respectively, at altitudes of 190–490 km. Near the eclipse main phase, the plasma velocity vertical component decreased by 10–45 m/s at altitudes of 200–470 km, respectively. At the time of the eclipse main phase, the hydrogen ion fractional density increased by 50% as compared to the reference day at altitudes of 450–650 km.

We present the results of observations of the wave disturbances in the ionospheric F region over the city of Kharkov, which accompanied the impact on the ionosphere by high-power radio emission of the Sura heating facility located about 960 km from the observation site. Enhancement of the wave activity in the heater operation intervals is detected. A 1.5–4-fold increase in the relative amplitude of the wave disturbance with a period of about 30 min close to the Sura operation mode at altitudes 160–235 km is revealed. The parameters of this disturbance are evaluated. It is shown that this effect can be due to the propagation of internal gravity waves in the atmospheric waveguide having about 200 km in height and 80–100 km in width. The efficiency of comprehensive analysis of the experimental data which we used to reveal and estimate the parameters of the wave disturbances with a small (a few percent) relative amplitude is demonstrated.

We describe the observation results of ionospheric disturbances at altitudes of 100 to 140 km, which occurred at a distance of about 1000 km from the Sura facility. The observations have been made using the incoherent scatter radar located near Kharkov. The electron density increase by 10–70 % had a temporal duration of 10–20 min and accompanied the high-power HF heating. The time of disturbance evolution was about 10 min. The observation effect can be explained by the intensification of the subsystem coupling in the ionosphere–magnetosphere–upper atmosphere– ionosphere system, which leads to a precipitation of energetic electrons from the magnetosphere. Parameters of the precipitating particles and precipitation-produced ionization are estimated.

We describe the results of using the incoherent scatter technique to observe time-altitude variations in regular parameters of the ionospheric plasma and wave disturbances, which accompanied periodic modification of the near-Earth plasma by radio waves emitted by the “Sura” facility. A distinctive feature of the experiments was that the processes in the ionosphere were diagnosed at a distance of about 1000 km from the facility. It was found that the spectrum composition of wave disturbances in the electron density was changing noticeably during the active experiment. Quasi-periodic processes in the ionosphere were observed with a delay of about 40–60 min. The relative amplitude of wave disturbances was equal to 0.02–0.10, and the periods were equal to 30, 60, 120, and 150–180 min. The observed effect can be explained by the generation and/or amplification of traveling ionospheric disturbances. The results of theoretical estimations agree well with the observational data.