Results of Russian experiments dealing with the impact of powerful HF radiowaves on the high-latitude ionosphere using the EISCAT facilities

We present the results of complex experiments dealing with the impact of powerful HF radiowaves on the high-latitude ionosphere using the European Incoherent Scatter Scientific Association (EISCAT) facilities. During the ionospheric F-region heating by powerful extraordinary (X-mode) polarized HF radiowaves under the conditions of heating near the critical f _H frequency f _H ≈ f _x F2 of the extraordinary wave of the F2-layer, we were first to detect the excitation of intense artificial small-scale ionospheric irregularities (ASIs), accompanied by electron temperature increases by approximately 50%. The results of coordinated satellite and ground-based observations of the powerful HF radiowave impact on the high-latitude ionosphere are considered. During ionospheric F-region heating by powerful HF radiowaves of ordinary polarization (O-mode) during evening hours, the phenomenon of ion outflow accompanied by electron temperature increases and thermal plasma expansion was revealed. Concurrent DMSP-F15 satellite measurements at a height of about 850 km indicate an O⁺ ion density increase. The CHAMP satellite observations identified ULF emissions at the modulation frequency (3 Hz) of the powerful HF radiowave, generated during modulated emissions of the powerful HF radiowave of O-polarization and accompanied by a substantial increase in the electron temperature and ASI generation.     

The association of the residual error of dual-frequency Global Navigation Satellite Systems with ionospheric turbulence parameters

The effects of ionospheric scintillation on the residual error of the dual-frequency Global Navigation Satellite System are investigated. For the ordinary and extraordinary waves the scalar wave equations are obtained to a high-frequency approximation from the Maxwell equations. The solution for these scalar equations to the second-order Rytov approximation made it possible to determine the residual error up to the third order taking into account the ionospheric anisotropy and diffraction effects appearing when the signal is propagating through a turbulent ionospheric plasma. It is shown that the third-order effects, associated with scintillation, that is, with the propagation of the signal through a randomly inhomogeneous ionosphere, can be dominant and exceed second-order effects associated with the influence of the geomagnetic field. We investigate the association of the residual error with such parameters of ionospheric turbulence as the variance, and the inner and outer scales.     

Plasma wave radiation in the main ionospheric trough in the region of the terminator from the APEX satellite data

The data of measurements of broadband wave radiation in the main ionospheric trough in the subauroral zone of the topside ionosphere in the region of the day-night terminator (APEX satellite experiment) are presented. It is shown that the observed attenuation of electrostatic radiation in a broad frequency band and fluctuations (variations) in the cutoff frequency of the electrostatic mode spectrum at the level of the local plasma or upper hybrid frequency are related to plasma heating by damping electrostatic oscillations in the ionospheric trough. Waveguide channels for propagation of electromagnetic whistler-mode waves observed on the satellite can be generated during the propagation of a gravity-thermal disturbance from the terminator.     

Disturbances of the ionosphere of blast and acoustic waves generated at ionospheric heights by rockets

In this paper we present a model, which describes the propagation of acoustic impulses produced by flight of rockets through a model terrestrial atmosphere, and effect of these impulses onto the ionosphere above a rocket. We show, that experimentally observed ionospheric disturbances with duration about 300 s cannot be explained by effect of acoustic impulses onto the ionosphere. We have calculated parameters of a blast wave produced by launch vehicle on the ionospheric heights. It was shown that the blast wave is intense and this wave can generate great disturbance of electron density. The disturbance of electron density can exceed the ambient electron density in 2.6 times. We supposed that the observed ionospheric disturbances might be produced by propagation of delayed magnetoacoustic wave, which, in turn, was produced by the blast wave.     

Unstable plasma irregular structures in the topside ionosphere and spread-<Emphasis Type="Italic">F</Emphasis>

The results of the Cosmos-900 satellite observ ations of plasma density inhomogeneities in the geomagnetic equator region and the longitudinal distributions of the equatorial spread-F, according to the Intercosmos-19 satellite data are presented. It is show n that the dependence of radiosignal propagation in the ionosphere on geophysical parameters is related to development of the electrostatic instability of the inhomo-geneous ionospheric plasma. The longitudinal dependence of the spread-F, can reflect the influence of the energetic sources, located outside the ionospheric layer that scatters a radio pulse, on the ionosphere. The manifestation of the longitudinal effect in the equatorial spread-F, in the Atlantic region can be explained by the influence of the cone instability on the plasma electrodynamics in the South Atlantic geomagnetic anomaly.     

Ionospheric conductivities according to Doppler radar observations of stimulated turbulence

Results of Doppler radar observations are discussed of HF scattering from heater induced inhomogeneities in an underdense ionospheric plasma. The quasiperiodic variations shown by the Doppler frequency shift are associated with the E×H plasma drift in the electric field of geomagnetic pulsations. Combined with a theoretical model of hydromagnetic wave propagation, with allowance for an arbitrary dip angle of the geomagnetic field and arbitrary angle of incidence, the Doppler shift measurements at several points along the geofield tube permit estimating height-integrated ionospheric conductivities     

Nonlinear dynamics of 3D beams of fast magnetosonic waves propagating in the ionospheric and magnetospheric plasma

On the basis of the model of the three-dimensional (3D) generalized Kadomtsev-Petviashvili equation for magnetic field h = B _~/B the formation, stability, and dynamics of 3D soliton-like structures, such as the beams of fast magnetosonic (FMS) waves generated in ionospheric and magnetospheric plasma at a low-frequency branch of oscillations when β = 4πnT/B ² ? 1 and β > 1, are studied. The study takes into account the highest dispersion correction determined by values of the plasma parameters and the angle θ = (B, k), which plays a key role in the FMS beam propagation at those angles to the magnetic field that are close to π/2. The stability of multidimensional solutions is studied by an investigation of the Hamiltonian boundness under its deformations on the basis of solving of the corresponding variational problem. The evolution and dynamics of the 3D FMS wave beam are studied by the numerical integration of equations with the use of specially developed methods. The results can be interpreted in terms of the self-focusing phenomenon, as the formation of a stationary beam and the scattering and self-focusing of the solitary beam of FMS waves. These cases were studied with a detailed investigation of all evolutionary stages of the 3D FMS wave beams in the ionospheric and magnetospheric plasma.     

Ionospheric response to geomagnetic disturbances in the north-eastern region of Asia during the minimum of 23rd cycle of solar activity

We present the results of studies of the subauroral and mid-latitude ionosphere variations in the north-eastern region of Asia. We used the data from network of vertical and oblique-incidence sounding ionosondes and optical measurements. Long-term experiments on the radio paths Magadan–Irkutsk and Norilsk–Irkutsk were carried out within the period 2005–2007. Vertical sounding stations operated in standard regime. Observation of airglow near Irkutsk was provided by the zenith photometer that measured intensities of 557.7 and 630.0 nm atomic oxygen emissions. The results may be summarized as follows. (1) Large daytime negative disturbances are observed during the main and recovery phases mainly at high latitudes, whereas the positive disturbances observed during the main phase at mid latitudes. The disturbances changed their sign between Yakutsk and Irkutsk. (2) During the main and recovery storm phases the fall of foF2 associated with the equatorward wall of the main ionospheric trough is observed in the afternoon and evening. (3) Fluctuations of the electron density more intensive at mid latitudes during the storm main phase are observed during all considered periods. They are classed as traveling ionospheric disturbances (TID). Such sharp gradients of electron density are responsible for the strong changes in the characteristics of the radio wave propagation, particularity MOF. (4) A large-scale ionospheric disturbance is noted at the meridional chain of ionosonds in December 2006 as the sharp increase of foF2. It appears in the evening in the minimum of D_st at high latitude and propagate to equator. (5) A maximum of 630 nm emission above Irkutsk corresponds to the foF2 increase. (6) The obtained experimental data on the net of vertical and oblique-incidence sounding with high time resolution show that such net is the effective facility to study the conditions of the radio wave propagation and can be used for the diagnostic of the ionosphere.     

Ionospheric Response to the Acoustic Gravity Wave Singularity

An original model of atmospheric wave propagation from ground sources to the ionosphere in the atmosphere with a realistic high-altitude temperature profile is analyzed. Shaping of a narrow domain with elevated pressure in the resonance region where the horizontal phase wave velocity is equal to the sound velocity is examined theoretically within the framework of linearized Eq.s. Numerical simulations for the model profiles of atmospheric temperature and viscosity confirm analytical result for the special feature of wave fields. The formation of the narrow domain with plasma irregularities in the D and low E ionospheric layers caused by the acoustic gravity wave singularity is discussed.     

On the sensitivity of total electron content (TEC) to upper atmospheric/ionospheric parameters

The total electron content (TEC) is a key ionospheric parameter for various space weather applications. Over the last decade an extensive database of TEC measurements has become available from both space- and ground-based observations, and these measurements have established the general morphology of the global TEC distributions. In particular, the TOPEX TEC measurements have shown strong longitudinal variations of TEC in addition to the observed day-to-day variabilities. To better understand the observed TEC variations and to better guide its modeling, we have studied the sensitivity of quiet-time TEC to the following key atmospheric and ionospheric parameters: neutral density, neutral wind, plasma temperatures, plasmaspheric flux, and the O⁺–O collision frequency. These parameters are often only roughly known and can cause large uncertainties in model results. For this study, we have developed a numerical mid-latitude ionospheric model, which solves the momentum and continuity equations for the O⁺ density and a simplified set of equations for the H⁺ density. To obtain TEC, the calculated ion densities have been integrated from the bottom altitude (100 km) to the altitude of the TOPEX satellite (1336 km). Our study shows that during the day the neutral wind and the neutral composition have the most important effect on TEC. In particular, the zonal component of the neutral wind can have a large effect on TEC in the southern hemisphere where the magnetic declination angle is large. During the night, most of the above-mentioned parameters can play a significant role in the TEC morphology, except for the plasma temperature, which has only a small effect on TEC. Finally, the TEC varies roughly linearly with respect to all of the parameters except for the neutral wind.     

Numerical Simulation of the High-Latitude Non-Stationary Ionospheric Alfvén Resonator During an IPDP Event

The ionospheric Alfvén resonator (IAR) was numerically simulated under non-stationary ionospheric and magnetospheric conditions of the IPDP event of December 4, 1986. The full numerical wave method was applied using height profiles of the ionospheric plasma parameters obtained from the Scandinavian EISCAT radar measurements close to the Ivalo latitude. An attempt to model the inverse problem of numerical simulation—prolongation of the electron density profiles at altitudes above the ionospheric F layer—was made on the basis of the IAR simulation in correlation with the IPDP frequency increase. The change of the IAR wave characteristics during the substorm was illustrated by height profiles of the total wave amplitude and various polarization characteristics, taking into consideration the ordinary L-mode and the extraordinary R-mode waves for parallel and non-parallel incidence with respect to the magnetic field line.     

Solar wind contribution to the average population of energetic He+ and He++ ions in the Earth’s magnetosphere

Measurements with the ion charge-energy-mass spectrometer CHEM on the AMPTE/CCE spacecraft were used to investigate the origin of energetic He⁺ and He⁺⁺ ions observed in the equatorial plane at 3\leqL\leq9. Special emphasis was laid on the dependence of long-term average distributions on magnetic local time (MLT) and the geomagnetic activity index K_p. The observations are described in terms of the phase space densities f₁ (for He⁺) and f₂ (for He⁺⁺). They confirm preliminary results from a previous study: f₁ is independent of MLT, whereas f₂ is much larger on the nightside than on the dayside. They show, furthermore, that f₁ increases slightly with K_p on intermediate drift shells, but decreases on high drift shells (L\geq7). f₂ increases with K_p on all drift shells outside the premidnight sector. Within this sector a decrease is observed on high drift shells. A simple ion tracing code was developed to determine how and from where the ions move into the region of observations. It provides ion trajectories as a function of the ion charge, the magnetic moment and K_p. The ion tracing enables a distinction between regions of closed drift orbits (ring current) and open convection trajectories (plasma sheet). It also indicates how the outer part of the observation region is connected to different parts of the more distant plasma sheet. Observations and tracing show that He⁺⁺ ions are effectively transported from the plasma sheet on convection trajectories. Their distribution in the observation region corresponds to the distribution of solar wind ions in the plasma sheet. Thus, energetic He⁺⁺ ions most likely originate in the solar wind. On the other hand, the plasma sheet is not an important source of energetic He⁺ ions. Convection trajectories more likely constitute a sink for He⁺ ions, which may diffuse onto them from closed drift orbits and then get lost through the magnetopause. An ionospheric origin of energetic He⁺ ions is unlikely as well, since the source mechanism should be almost independent of K_p. There is considerable doubt, however, that a plausible mechanism also exists during quiet periods that can accelerate ions to ring current energies, while extracting them from the ionosphere. It is concluded, therefore, that energetic He⁺ ions are mainly produced by charge exchange processes from He⁺⁺ ions. This means that most of the energetic He⁺ ions constituting the average distributions also very likely originate in the solar wind. Additional ionospheric contributions are possible during disturbed periods.     

Global aspects of solar wind–ionosphere interactions

Recent observations have quantified the auroral wind O⁺ outflow in response to magnetospheric inputs to the ionosphere, notably Poynting energy flux and precipitating electron density. For moderate to high activity periods, ionospheric O⁺ is observed to become a significant or dominant component of plasma pressure in the inner plasma sheet and ring current regions. Using a global circulation model of magnetospheric fields and its imposed ionospheric boundary conditions, we evaluate the global ionospheric plasma response to local magnetospheric conditions imposed by the simulation and evaluate magnetospheric circulation of solar wind H⁺, polar wind H⁺, and auroral wind O⁺. We launch and track the motions of millions of test particles in the global fields, launched at randomly distributed positions and times. Each particle is launched with a flux weighting and perpendicular and parallel energies randomly selected from defined thermal ranges appropriate to the launch point. One sequence is driven by a two-hour period of southward interplanetary magnetic field for average solar wind intensity. A second is driven by a 2-h period of enhanced solar wind dynamic pressure for average interplanetary field. We find that the simulated ionospheric O⁺ becomes a significant plasma pressure component in the inner plasma sheet and outer ring current region, particularly when the solar wind is intense or its magnetic field is southward directed. We infer that the reported empirical scalings of auroral wind O⁺ outflows are consistent with a substantial pressure contribution to the inner plasma sheet and plasma source surrounding the ring current. This result violates the common assumption that the ionospheric load is entirely confined to the F layer, and shows that the ionosphere is often an important dynamic element throughout the magnetosphere during moderate to large solar wind disturbances.     

Theory of azimuthally small-scale hydromagnetic waves in the axisymmetric magnetosphere with finite plasma pressure

The structure of monochromatic MHD-waves with large azimuthal wave number m 1 in a two-dimensional model of the magnetosphere has been investigated. A joint action of the field line curvature, finite plasma pressure, and transversal equilibrium current leads to the phenomenon that waves, standing along the field lines, are travelling across the magnetic shells. The wave propagation region, the transparency region, is bounded by the poloidal magnetic surface on one side and by the resonance surface on the other. In their meaning these surfaces correspond to the usual and singular turning points in the WKB-approximation, respectively. The wave is excited near the poloidal surface and propagates toward the resonance surface where it is totally absorbed due to the ionospheric dissipation. There are two transparency regions in a finite-beta magnetosphere, one of them corresponds to the Alfvén mode and the other to the slow magneto-sound mode.     

Incoherent scatter radar observations of AGW/TID events generated by the moving solar terminator

Observations of traveling ionospheric disturbances (TIDs) associated with atmospheric gravity waves (AGWs) generated by the moving solar terminator have been made with the Millstone Hill incoherent scatter radar. Three experiments near 1995 fall equinox measured the AGW/TID velocity and direction of motion. Spectral and cross-correlation analysis of the ionospheric density observations indicates that ST-generated AGWs/TIDs were observed during each experiment, with the more-pronounced effect occurring at sunrise. The strongest oscillations in the ionospheric parameters have periods of 1.5 to 2 hours. The group and phase velocities have been determined and show that the disturbances propagate in the horizontal plane perpendicular to the terminator with the group velocity of 300–400 m s^–1 that corresponds to the ST speed at ionospheric heights. The high horizontal group velocity seems to contradict the accepted theory of AGW/TID propagation and indicates a need for additional investigation.     

Observations of the response time of high-latitude ionospheric convection to variations in the interplanetary magnetic field using EISCAT and IMP-8 data

We have combined ∼300 h of tristatic measurements of the field-perpendicular F region ionospheric flow measured overhead at Tromsø by the EISCAT UHF radar, with simultaneous IMP-8 measurements of the solar wind and interplanetary magnetic field (IMF) upstream of the Earth’s magnetosphere, in order to examine the response time of the ionospheric flow to changes in the north-south component of the IMF (B_z). In calculating the flow response delay, the time taken by field changes observed by the spacecraft to first effect the ionosphere has been carefully estimated and subtracted from the response time. Two analysis methods have been employed. In the first, the flow data were divided into 2 h-intervals of magnetic local time (MLT) and cross-correlated with the “half-wave rectifier” function V²B_s, where V is the solar wind speed, and B_s is equal to IMF B_z if the latter is negative, and is zero otherwise. Response delays, determined from the time lag of the peak value of the cross-correlation coefficient, were computed versus MLT for both the east-west and north-south components of flow. The combined data set suggests minimum delays at ∼1400 MLT, with increased response times on the nightside. For the 12-h sector centred on 1400 MLT, the weighted average response delay was found to be 1.3 ± 0.8 min, while for the 12-h sector centred on 0200 MLT the weighted average delay was found to increase to 8.8 ± 1.7 min. In the second method we first inspected the IMF data for sharp and enduring (at least ∼5 min) changes in polarity of the north-south component, and then examined concurrent EISCAT flow data to determine the onset time of the corresponding enhancement or decay of the flow. For the case in which the flow response was timed from whichever of the flow components responded first, minimum response delays were again found at ∼1400 MLT, with average delays of 4.8 ± 0.5 min for the 12-h sector centred on 1400 MLT, increasing to 9.2 ± 0.8 min on the nightside. The response delay is thus found to be reasonably small at all local times, but typically ∼6 min longer on the nightside compared with the dayside. In order to make an estimate of the ionospheric information propagation speed implied by these results, we have fitted a simple theoretical curve to the delay data which assumes that information concerning the excitation and decay of flow propagates with constant speed away from some point on the equatorward edge of the dayside open-closed field line boundary, taken to lie at 77° magnetic latitude. For the combined cross-correlation results the best-fit epicentre of information propagation was found to be at 1400 MLT, with an information propagation phase speed of 9.0 km s⁻¹. For the combined event analysis, the best-fit epicentre was also found to be located at 1400 MLT, with a phase speed of 6.8 km s⁻¹.     

Modeling of the effect of the“apparent <Emphasis Type="Italic">F</Emphasis>1 layer” observed in the Radar-Progress experiment with the help of the software for automated processing of vertical sounding ionograms

The results of the modeling the anomalous behavior of the F ₁ layer characteristics are presented. The anomaly lies in the jump-like variations in the critical frequency of the layer f ₀ F1 and an abnormally large f ₀ F1 value for the considered season and time. The observed effect is simulated based on the propagation of a large-scale travelling ionospheric disturbance. The quantitative values of the disturbance parameter are obtained and some peculiarities of its propagation are analyzed. The investigation was carried out with the help of the software for automated processing of the vertical sounding ionograms. The experimental data were obtained during the Radar-Progress project.     

Dynamics of the large-scale ULF electromagnetic wave structures in the ionosphere

The present article displays the results of theoretical investigation of the planetary ultra-low-frequency (ULF) electromagnetic wave structure, generation and propagation dynamics in the dissipative ionosphere. These waves are stipulated by a spatial inhomogeneous geomagnetic field. The waves propagate in different ionospheric layers along the parallels to the east as well as to the west and their frequencies vary in the range of (10–10⁻⁶) s⁻¹ with a wavelength of order 10³ km. The fast disturbances are associated with oscillations of the ionospheric electrons frozen in the geomagnetic field. The large-scale waves are weakly damped. They generate the geomagnetic field adding up to several tens of nanotesla (nT) near the Earth's surface. It is prescribed that the planetary ULF electromagnetic waves preceding their nonlinear interaction with the local shear winds can self-localize in the form of nonlinear long-living solitary vortices, moving along the latitude circles westward as well as eastward with a velocity different from the phase velocity of the corresponding linear waves. The vortex structures transfer the trapped particles of medium, as well as energy and heat. That is why such nonlinear vortex structures can be the structural elements of the ionospheric strong macro-turbulences.     

Numerical solution to the problem of ionoshperic filtration of ULF waves in thePc1 range. the total wave field inside the ionospheric transition layer

Summary This article is a continuation of the methodological series of the author's papers[2–4] related to the problem of numerical modelling of ionospheric filtration of signals in the Pc1 range of micropulation frequencies. A matrix method of treating the total wave field within the ionospheric transition layer is presented in connection with the total wave fields determined at both boundaries of the ionospheric transition layer. The computation is based on the method of thin layers (homogeneous) in a finely stratified, inhomogeneous and anisotropic (magneto-active) ionosphere. The results can be used in constructing automated computation algorithms which add considerably to the applications of the method in question[2–4].     

On the gravity wave-driven instability of E layer at mid-latitude

The plasma instability process during internal gravity wave propagation through the ionospheric E region is considered. The growth rate of the instability has been found and it has been shown that it depends on perturbation wavelength, gravity wave parameters and direction of propagation. The conditions for the instability are favorable when the vorticity of the associated neutral motion becomes antiparallel to the geomagnetic field. In the proposed instability mechanism plasma irregularities could seed the large-scale sporadic E layer structuring because they are generated in situ as a part of the same neutral wind structure that serves to initiate the formation of the layer.