Magnetic and Ionospheric Effects of a Meteoroid Plume

This paper is concerned with the study of the possibility of products of a meteoroid explosion in the atmosphere (meteoroid plume) to reach ionospheric altitudes. It has been shown that, in the case of meter-sized or larger space bodies entering the atmosphere, the plume is able to reach the lower ionosphere. The plume can be one of the sources of the formation of nacreous and noctilucent clouds. The aerosols ejected by the plume to lower ionospheric altitudes can lead to the formation of dust plasma, significantly changing the electrodynamic properties of the medium. The motion of the plume with a velocity of ~1 km/s is accompanied by the generation of a ballistic shock with a radius of 1–10 km. The relative excess pressure in the shock front can cause relative disturbances in the electron content at the altitudes of D, E, and F1 layers by ~10–100%. The geomagnetic effect of the plume and ballistic shock can reach ~1–10 nT.     

Ionospheric disturbances during the severe magnetic storm of November 7–10, 2004

Results of the study of the behavior of the F ₂ region and topside ionosphere during the magnetic storm on November 7–10, 2004, which was a superposition of two sequent Severe magnetic disturbances (Kp = 9–) are presented. The observations were conducted by the incoherent scatter radar at Kharkov. Considerable effects of a negative ionospheric disturbance are registered, including a decrease in the electron density in the F ₂-layer maximum by a factor of 6–7 and of the total electron content up to a height of 1000 km by a factor of 2, a lifting up of the ionospheric F ₂ layer by 300 km at night and by 150–180 km in the daytime, unusual nighttime heating of the plasma with an increase of the ion and electron temperatures up to 2000 and 3000 K, respectively, and a decrease in the relative density of hydrogen ions N(H⁺)/N _e by a factor of up to 3.5 because of the emptying of the magnetic flux tube passing over Kharkov. The effects usually observed in the high-latitude ionosphere, including the coherent echoes, are detected during the main phase of the storm. The results obtained manifest a shift of the large-scale structures of the high-latitude ionosphere (the auroral oval, main ionospheric trough, hot zone, etc.) down to latitudes close to the latitude of the Kharkov radar.     

Effects of solar eclipses in the ionosphere: Results of Doppler sounding: 1. Experimental data

The results of experimental studies of variations in the Doppler frequency shift at a vertical radio path caused by partial solar eclipses are presented. Eclipses were observed near Kharkov in 1999?C2008. The eclipse phase varied from 0.24 to 0.78. It is shown that the eclipses caused sign-changing variations in the Doppler frequency shift, deformations of the Doppler spectra, and also quasi-periodic changes in the Doppler frequency shift. This was manifested in changes in the electron concentration, generation of wave processes, and plasma motions caused by the eclipses.     

Effects of solar eclipses in the ionosphere: Doppler sounding results: 2. Spectral analysis

The results of a spectral analysis of time variations in the Doppler frequency shift which accompanied solar eclipses in 1999?C2008 and calculations and estimates of disturbances in signal parameters are presented. Parameters of the ionosphere and its irregular structure are estimated on the basis of observational data. The calculation results correspond to the results of observations.     

Wave processes in the ionosphere over Europe that accompanied the solar eclipse of March 20, 2015

Ionospheric disturbances at an altitude of 300 km that accompanied the solar eclipse of March 20, 2015, have been analyzed based on the ionosondes located in Europe. It has been confirmed that the eclipse was accompanied by the generation of gravity waves in the neutral atmosphere and traveling ionospheric disturbances. The period of the latter was 30–100 min, and the amplitude of relative electron density disturbances was 4–19%. The disturbances continued for not less than 2 h. During the eclipse, the disturbance amplitude more frequently increased. It decreased in one case, since the wave process observed previously was suppressed by the process generated by the eclipse.     

Wave activity in the ionosphere during the geospace storm of November 7–10, 2004

This paper presents the results of studies of wave disturbances in the electron concentration N in the ionosphere during a prominent geospace storm, in the process of which the electron concentration decreased by a factor of 6–7, whereas the temperatures of ions and electrons at night increased up to 2000 and 3000 K, respectively. The height-time variations in the parameters of wave disturbances are also analyzed. It is shown that the geospace storm was accompanied by a substantial change in wave activity in the ionosphere. In the period of negative ionospheric storms, the amplitude Δ _N decreased by a factor of 2–10. At the same time, the relative amplitude δ _N = ΔN/N changed insignificantly and was within the limits 0.05–0.10 during day-time. At night, δ _N reached 0.25–0.30 and sometimes even 0.4–0.5. During both disturbed and undisturbed days, quasi-periodic processes with a period of 40–60 and 80–120 min prevailed. The maximum values of the absolute and relative amplitudes were achieved at a height of 200–270 km. A soliton-like disturbance formed near the main phase of the magnetic storm on November 10, 2004 was detected. Its appearance was related to the oblique coherent reflection of sounding signals.     

Physical processes in the middle ionosphere accompanying the solar eclipse of January 4, 2011, in Kharkov

Aperiodic and quasi-periodic variations in the critical frequency of the F2 layer and Doppler frequency shift of radiowaves at vertical paths on the day of a partial (the magnitude was ～0.78) solar eclipse and on background days are analyzed. According to the experiment, the relative decrease in the electron concentration was 0.41 (0.46 according to calculations) and 0.50 (0.53 according to calculations) in the E region and in the lower part of the F region of the ionosphere. At a height of the main maximum of the electron concentration, the relative decrease in the electron concentration was 0.52 (0.51 according to calculations). It is shown that on the day of the eclipse and on the background day, the characteristics of wave disturbances within the height range 160–240 km were substantially different. Changes in the spectral composition began 30 min after the eclipse occurrence and, depending on the period, lasted from 2 to 4 h. The calculation results of the main parameters of the medium and signal correspond to the observational results.     

Solar eclipse of August 1, 2008, above Kharkov: 2. Observation results of wave disturbances in the ionosphere

Quasi-periodic variations in the power of incoherent scattered signals, caused by wave disturbances of the electron concentration in the ionosphere, are analyzed for the day of a partial solar eclipse and for a background day. The windowed and adaptive Fourier transforms and the wavelet transform are used for spectral analysis. The spectral parameters of the wave disturbances at altitudes of 100–500 km in the 10–120 min period range differed significantly on the day of the solar eclipse and on the background day. Variations in the spectrum began near the onset of the phase of maximum disk occultation and continued no less than 2 h. The amplitude of time variations N was 2 × 10⁹–4 × 10¹⁰ m^?3, and the relative amplitude was 0.10–0.15. Wave disturbances have been compared for five solar eclipses; the comparison shows a noticeable variation in the spectrum of the wave disturbances during these events.     

Wave response of the ionosphere to the partial solar eclipse of August 1, 2008

Quasi-periodic variations in the Doppler shift of the HF range frequency at a vertical path and critical frequency of the F ₂ layer caused by wave disturbances in the ionosphere on the day of the partial (the magnitude was about 0.42) solar eclipse and on background days are analyzed. For the spectral analysis, the window Fourier transform, adaptive Fourier transform, and wavelet analysis were jointly used. It is shown that on the day of the eclipse and the background day, spectral characteristics of wave disturbances within the 150–200 km height range differed substantially. The changes in the spectral composition began approximately 30–35 min after the solar eclipse beginning and lasted more than 1.5 h.     

Effects of the solar eclipse of March 29, 2006, in the ionosphere and atmosphere

The observations of the effects of the partial (about 77%) solar eclipse (SE) of March 29, 2006, in the ionospheric plasma are presented. The experimental data were obtained using the Kharkov incoherent scatter radar. At the moment of the maximum phase of SE, a decrease in the critical frequency of the ionospheric F ₂ layer by 18%, a depletion of the density in the F ₂ layer maximum by 33%, and an increase in the maximum height z _m by 30 km were observed. The solar eclipse caused a decrease in the electron and ion temperatures by 150–300 and 100–200 K, respectively, within the height range 210–490 km. An increase in the relative density of the hydrogen ions during the maximum phase of SE by 20–25% within the height range 900–1200 km is detected. Calculations of the parameters of dynamical processes and thermal regime of the ionospheric plasma during SE are performed.