Latitudinal structure of the longitudinal effect in the nighttime ionosphere during the summer and winter solstice

The paper reports the basic morphological characteristics of the longitudinal variations of the electron density in the nighttime F region of the ionosphere at different latitudes obtained from data collected by the Intercosmos-19 satellite and from the results of calculations within the framework of the Global Self-Consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP). Based on the Intercosmos-19 satellite data for a high solar activity, spatial distributions of the critical frequency foF2 of the F2 layer for near-midnight hours of the local time are plotted. The study revealed the main features of the mechanisms of the formation of longitudinal features of the nighttime ionosphere at various latitudes during the summer and winter solstices, as well as two reasons for their occurrence. In particular, we consider (1) the mechanisms of the formation of the nighttime peaks at the longitudes of the Yakutsk anomaly and Weddell Sea anomaly, (2) manifestations of longitudinal variations of the main ionospheric trough, and (3) the longitudinal dependence of the disappearance of the equatorial anomaly during the June and December solstices.     

Lower polar ionosphere during a solar flare as revealed from radiooccultation data in satellite-to-satellite links

It is shown that there are typical variations in the amplitude and phase of decimetric radio waves in satellite-to-satellite links due to variations in the polar ionosphere structure. The altitude profiles of the electron number density and vertical size of the ionospheric sporadic structures in the nighttime polar regions during the period of intense solar activity in October 25 to November 09, 2003 are estimated. Correlation between the the ionosphere characteristics and the solar-wind parameters is discussed. It is noted that the effect of energetic-particle precipitation due to the influence of shock waves of the solar wind is the main factor responsible for strong variations in the nighttime polar ionosphere. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 3, pp. 181–191, March 2009.     

Mid-latitude anomalies in the diurnal variation of electron density in the ionosphere

The main morphological features of the F region of the mid-latitude ionosphere as obtained from Intercosmos-19 satellite measurements are presented. The causes of the anomalies in the diurnal variation of the electron density in certain longitudinal areas at the June and December solstice in the northern (Yakutsk anomaly) and southern (Weddell Sea anomaly (WSA)) hemispheres are determined. For both anomalies, the nighttime values of the critical frequency of the F2 layer, foF2, are higher than the daytime ones. Based on Intercosmos-19 satellite data, global maps of foF2 distribution for midday and midnight local time under high solar activity are drawn. Both anomalies occupy a large area in latitude and longitude, about 100° and 30°, respectively. The maximum difference between nighttime and daytime values of foF2 in the Yakutsk anomaly area reaches 1.0–1.5 MHz, smaller than that for the WSA (3.5–4.0 MHz). In the present work, these anomalies are reproduced with the help of a global self-consistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP), and the mechanisms of their formation are preliminary investigated.     

Specific features of ionospheric total electron content variations in the periods of preparation of the earthquakes on March 11, 2011 (Japan) and October 23, 2011 (Turkey)

The main morphological features of variations of the total electron content (TEC) of the ionosphere before the earthquakes on March 11, 2011 (Japan) and October 23, 2011 (Turkey) are examined. The revealed features are compared to those of ionospheric TEC disturbances observed prior to several other large seismic events, as well as to those included in a list of the most frequently observed ionospheric TEC disturbances interpreted as possible ionospheric precursors of earthquakes. It is shown that, in the periods of preparation of the earthquakes under consideration, on March 8–11 and October 20–23, abnormal ionospheric TEC disturbances were observed as long-lived structures in a near-epicentral region and in the region magnetically conjugated to it.     

Effect of NO concentration disturbances on the global distribution of ionospheric parameters during geomagnetic storms

The role of nitric oxide (NO) in the ionospheric effects during geomagnetic storm on May 1–3, 2010, is examined. The studies are performed using a global self-consistent model of the thermosphere, ionosphere and protonosphere (GSM TIP). Two versions of calculations are used: (1) based on an analytical approximation of the NO concentration and (2) self-consistent calculation of the global distribution of nitric oxide over the ionosphere. It is shown that, during a geomagnetic disturbance, the NO concentration at high latitudes shows an increase, which under the influence of the horizontal circulation of neutral gas leads to an increase in the concentration of NO at mid-latitudes ～1 day after the start of the perturbation. Simulated values of foF2 are compared to experimental data obtained at a number of Russian mid-latitude stations. It is noted that the self-consistent calculations of the NO concentration better describes the spatial-temporal behavior of ionospheric parameters during geomagnetic storms.     

Results of Determining the Electron Number Density in the Ionospheric E Region from Relaxation Times of Artificial Periodic Irregularities of Different Scales

We present the first results of determining the electron number density in the ionospheric E region by a novel technique based on the creation of artificial periodic irregularities when the ionosphere is affected by powerful radio emission at two frequencies. Using the results of the measurements performed in October 2006 during heating of the ionosphere by the “Sura” facility radiation at frequencies 4.7 and 5.6 MHz, we obtained the electron number density profiles in an altitude range of 100 to 110 km. Features of the procedure of measurement and calculation of the electron number density are described in detail. It is shown that the method can be used for a study of the irregular structure of the lower ionosphere. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 6, pp. 477–484, June 2008.     

Simulation of the electric field in Earth’s ionosphere during a geomagnetic storm

Previously, a global self-consistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP) was used to study the ionospheric effects of geomagnetic storms in 2005, 2006, 2010, and 2011. In these studies, the input parameters of the model were specified using different dependences of variations of the potential difference across the polar caps and of the spatial distribution of Region 2 field-aligned currents during geomagnetic storms on the geomagnetic activity indices, solar wind parameters, and interplanetary magnetic field parameters. In the present work, we have tried to examine how correct was the choice of these relationships and how faithful are the obtained global distributions of the electric field in the ionosphere. For this, we present the results of a comparative analysis of the electric field in the ionosphere during geomagnetic storms of May 2–3, 2010, obtained using two models (GSM TIP and LC06) based on different approaches to solving this problem.     

Transcontinental radio tomographic chain: First results of ionospheric imaging

The results of studying the structure of the ionospheric plasma distribution from data obtained at the transcontinental Russian radio tomographic chain, which is the world’s longest, are presented. The 4000 km long tomographic chain extends from the Svalbard Archipelago to Sochi. The unique feature of this upgraded radio tomographic system is that for the first time observations cover a wide sector of the ionosphere from high latitudes (polar cap and auroral region) to low latitudes. This allows us to study the transfer of perturbations in the system auroral-subauroral-midlatitude-low latitude ionosphere, and to analyze ionospheric electron density distributions in different latitudinal regions as a function of different external factors and solar-geophysical conditions. The first recent results speak for a complex structure of the ionospheric plasma, even in quiet geophysical conditions (K _p < 2.)     

Sounding of the ionosphere disturbed by the “Sura” heating facility radiation using signals of the GPS satellites

We present the results of experimental studies of the properties of the plasma-density disturbances created during heating of the ionospheric F₂ region by high-power HF radio waves radiated by the “Sura” heating facility (Radiophysical Research Institute, Nizhny Novgorod). These experiments are specific in that they were performed in a sunlit (daytime) ionosphere when the generation of ionospheric turbulence has specific features and the turbulence intensity level is low enough. The plasma-density disturbances induced by high-power HF radio emission were sounded by signals of the GPS satellites, the line of sight to which crossed different parts of the disturbed ionosphere region. Threshold powers of the excitation of artificial plasma-density variations as well as spatial, temporal, spectral, and energy characteristics of the generated disturbances are determined.     

Allowance for the solar-magnetospheric connections in a problem of predicting the critical frequency of the subauroral ionosphere

The cause-and-effect relation between variations in the critical frequency of the F ₂ subauroral ionospheric layer and the key solar-magnetospheric parameters is studied. The features of the dependence of the critical frequency of the subauroral ionosphere on the value and components of the interplanetary magnetic field, the solar-wind parameters, the X-ray and ultraviolet radiation intensities, the solar zenith angle, and the intensity of precipitation of low-energy particles are established. Within the framework of this study, codes allowing one to solve the problems of predicting the critical frequency of the ionosphere by the method of artificial neural networks has been developed. The neural-network forecasting experiments reveal the characteristic times of the ionospheric response to magnetospheric disturbancs. The found optimal architecture of the neural network allows us to predict the time series of the critical frequency of the high-latitude ionosphere for the interval 0.5–3 h with an accuracy of up to 93%. The obtained linear and nonlinear dependences of the critical frequency of the ionospheric F ₂ layer on the geophysical parameters can be used for developing ionospheric models required for determining the maximum usable frequency of HF radio communication. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 2, pp. 109–117, February 2009.     

Analyses of electron and proton scattering to low-excitation isoscalar states in 20Ne, 24Mg and 28Si

The excitation of low-lying isoscalar 2⁺ and 4⁺ states in ²⁰Ne, ²⁴Mg and ²⁸Si by electron and proton scattering is studied. Large basis models of nuclear structure are used to determine both the electromagnetic and hadronic transition densities. The analyses of the longitudinal form factors obtained from electron scattering show that little or no effective charges are required with these nuclear structure models. Proton inelastic scattering to these states then is analysed to test effective forces based upon the Paris and Hamada-Johnston interactions. At intermediate energies (155 MeV) density-dependent t-matrices from both potentials were used with fits to data giving a clear preference for that based upon the Paris interaction. For lower energies only the Hamada-Johnston t-matrix is available and comparison of analyses of 24 and 49 MeV data made using this (complex) t-matrix with those in which the (real) Paris G-matrix is used as the effective force show a clear preference for the t-matrix. This is particularly the case with analyses of polarization data and suggests that the use of the G-matrix as an effective force in nuclear reaction calculations is inadequate even at low energies.     

Auger electron emission spectra from foil and gas excited carbon beams

Auger electron emission spectra from 2 MeV C⁺ ion excited by collisions with thin carbon foils and Ne gas are presented. The similarity of qualitative features for the C⁺ → C (foil) and C⁺ → Ne spectra indicates the similarity of ionization mechanisms for beam foil and beam gas excitation. The spectra were normalized to the lowest lying Li-like quartet state (1s 2s 2p)⁴P⁰ in carbon by comparison with time delayed foil excited electron decay-in-flight spectra. Comparison to Hartree-Fock calculated transition energies indicates that transitions in three and four electron carbon ions dominate the prompt spectra.     

Observations of Acoustic Gravity Waves during the Solar Eclipse of March 20, 2015 in Kaliningrad

Results of observations of atmospheric and ionospheric parameters during the solar eclipse of March 20, 2015 have been described. The observations have been conducted by lidar sensing in the lower atmosphere and analysis of the total electron content (TEC) in the ionosphere in Kaliningrad. Observations at the troposphere altitudes have been conducted using an atmospheric lidar. Ionospheric parameter TEC has been determined according to observations of navigation satellite signals. The spectral analysis of the monitored parameters during the solar eclipse has shown that, in the lower atmosphere and the ionosphere in a period range of 2–20 min, internal gravity waves (IGWs) and infrasonic waves are excited. During the main phase of the eclipse, the major contribution to variations in the parameters of the medium comes from infrasonic vibrations. Changes in the variations in the atmospheric and ionospheric parameters with IGW periods are observed only in the initial and final phases of the eclipse.     

Disturbances of the upper atmosphere and ionosphere caused by acoustic-gravity wave sources in the lower atmosphere

The results of observations of acoustic-gravity waves in the troposphere and the ionosphere at middle latitudes during periods of passage of the solar terminator are presented. Tropospheric observations were performed using a lidar. The frequency characteristics of variations of the tropospheric parameters are determined based on observations of the intensity of the scattered lidar signal. The characteristics of variations of the total electron content (TEC) in the atmosphere are determined from data collected by GPS navigation satellites. An analysis of the observational data showed that the spectrum of variations of the atmospheric and ionospheric parameters is indicative of acoustic-gravity waves (AGW) propagating from the lower atmosphere. Modeling studies of the vertical propagation of AGW from the Earth’s surface showed that such waves quickly (within ~15 min) reach altitudes of the upper atmosphere (~300 km). The refraction and dissipation of waves in the upper atmosphere produces perturbations of the background state of the atmosphere and gives rise to the waveguide propagation of infrasonic wave components. The observed manifestations of TEC disturbances caused by AGW propagating from the lower atmosphere can be explained by the diurnal variation of the altitude of the ionosphere and the waveguide propagation of infrasonic waves.     

Effect of Acoustic Gravity Waves on Variations in the Lower-Ionosphere Parameters as Observed using Artificial Periodic Inhomogeneities

We study the effect of acoustic gravity waves on variations in the atmospheric parameters of the lower ionosphere. The observations were carried out by the method of radio-wave scattering on artificial periodic inhomogeneities of the ionospheric plasma, induced by powerful radio-wave heating of the ionosphere. Measuring the altitude profile of the relaxation time of the scattered signal allowed us to determine the atmospheric temperature and density at heights 95 to 120 km, while recording the signal phase made it possible to obtain the vertical velocity of the plasma. The joint analysis of variations in the vertical velocity and the atmospheric temperature and density showed the simultaneous existence of oscillations with the same periods ranging from 5–10 min to a few hours. The amplitudes of these oscillations were, respectively, 1.5 to 4 m s^-1 for the vertical velocity and 6–20% for the temperature and density. We simulate the characteristics of acoustic gravity waves using the linear theory of their free propagation in an unbounded isothermal undisturbed atmosphere. Based on the polarization relations for low-frequency waves, we calculate the corresponding relative amplitudes of variations in the atmospheric temperature and density with periods from 15 min to 4 h using the measured amplitudes of the vertical velocity. Comparison of the calculation results with the measured values shows their good agreement for waves with periods 15–30 min.     

高功率微波在电离层中传播的折射率研究

 高功率微波在电离层中的传播特性主要由其折射率的变化决定，而高功率微波的大气折射率与相应传输层面的电子浓度有关。结合电离层电子浓度分布模型对电子浓度和大气折射率进行了数值模拟，对电离层折射率以及折射率垂直梯度相对于高度的变化特性进行了分析。结合射线描迹法对高功率微波波束传播高度、仰角和距离进行了修正，并在低功率微波下进行实验验证，证实修正值更接近实际值。     

Magnetic zenith effect and some features of the multifractal structure of the small-scale artificial ionospheric turbulence

We present the results of the experiment on studying the multifractal structure (with inhomogeneity sizes from tens to hundreds of meters across the Earth’s magnetic field) of the artificial ionospheric turbulence when the midlatitude ionosphere is affected by high-power HF radio waves. The experimental studies were performed on the basis of the “Sura” heating facility with the help of radio sounding of the disturbed region of the ionospheric plasma by signals from the Earth’s orbital satellites. The influence of the magnetic zenith effect on measured multifractal characteristics of the small-scale artificial turbulence of the midlatitude ionosphere was examined. In the case of vertical radio sounding of the disturbed ionosphere region, the measured multipower and generalized multifractal spectra of turbulence coincide well with similar multifractal characteristics of the ionospheric turbulence under natural conditions. This result is explained by the fact that the scattering of signals by weak quasi-isotropic small-scale inhomogeneities of the electron number density in a thick layer with a typical size of several hundred kilometers above the region of reflection of high-power HF radio waves gives the major contribution to the observed amplitude fluctuations of received signals. In the case of oblique sounding of the disturbance region at small angles between the line of sight to the satellite and the direction of the Earth’s magnetic field, the nonuniform structure of the small-scale turbulence with a relatively narrow multipower spectrum and small variations in the generalized multifractal spectrum of the electron number density was detected. Such a fairly well ordered structure of the turbulence is explained by the influence of the magnetic zenith effect on the generation of anisotropic small-scale artificial turbulence in a thin layer having a typical size of several ten kilometers and located below the pump-wave reflection height in the upper ionosphere.     

Excitation of the quasi-bound state in 4He by electron scattering at medium momentum transfer

The cross sections of inelastic electron scattering on ⁴He leading to the quasi-bound state (0⁺, ε = 20.1 MeV) were measured in the momentum transfer range 0.8 fm^?2 < q² < 2.4 fm^?2. We found it to be a pure longitudinal transition and give the form factor of this C0transition.     

Determination of the permittivity,permeability and conductivity profile for the ionosphere using an inverse scattering approach

A method for reconstructing the conductivity of the ionosphere together with the permittivity and conductivity as a function of altitude is discussed. This method is derived by solving the inverse scattering problem for an inhomogeneous dispersive plasma with a layered structure. Two ionospheric models are considered for this purpose, one at the equator and one at the polar caps. The experimental data required are clearly defined and methods of generating such data are discussed.     

Study of the Ionospheric D Layer using Partial Reflections at the Middle Latitudes and in the Auroral Zone

Using the measuring facilities located in different latitudinal regions: in Vasil'sursk near Nizhny Novgorod (56.1^° N and 46.1^° E) and in Tumanny (Murmansk region, 69.0^° N and 35.7^° E), we study the ionospheric D layer by the partial-reflection technique. Quantitative estimates are obtained for the electron density in the polar and mid-latitude D layer, distinctions of these values are revealed, and the possible reasons for latitudinal variations in the electron density at the D-layer altitudes are discussed.