Electron Density Disturbances Research Articles

Nonlinear electron oscillations in a warm plasma

A class of nonstationary solutions for the nonlinear electron oscillations of a warm plasma are presented using a Lagrangian fluid description. The solution illustrates the nonlinear steepening of an initial Gaussian electron density disturbance and also shows collapse behavior in time. The obtained solution may indicate a class of nonlinear transient structures in an unmagnetized warm plasma.

Studying of the spatial–temporal structure of wavelike ionospheric disturbances on the base of Irkutsk incoherent scatter radar and Digisonde data

In this paper the spatio-temporal structure of traveling ionospheric disturbances characteristics is studied on the base of the electron density profiles measured by two beams of the Irkutsk incoherent scatter radar and the Irkutsk Digisonde. The technique for determination of spatial–temporal structure of wavelike ionospheric disturbances was developed using cross-correlation and spectrum analysis of electron density. The automated method for extracting ionospheric disturbances including both long-period day-to-day variability and short-period variations has been developed. Full analyses of January 15–February 17, 2011 data, including total velocity vector, was carry out for 1–6h ionospheric disturbances, corresponding to internal gravitational waves. The propagation characteristics agree with those obtained from the known studies of the wavelike ionospheric disturbances. An automated method of ionospheric disturbances analysis was created on the basis of regular continuous measurements with the Irkutsk Digisonde. The statistical analysis of electron density disturbances was carried out for 2004–2009 period.

Modeling the effect of sudden stratospheric warming within the thermosphere–ionosphere system

This paper presents an investigation of thermospheric and ionospheric response to the sudden stratospheric warming (SSW) event, which took place in January 2009. This period was characterized by low solar and geomagnetic activity. Analysis was carried out within the Global Self-consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP). The experimental data of the atmospheric temperatures obtained by Aura satellite above Irkutsk and ionosonde data over Yakutsk and Irkutsk were utilized as well. SSW event was modeled by specifying the temperature and density perturbations at the lower boundary of the GSM TIP model (80km altitude). It was shown that by setting disturbances in the form of a stationary planetary perturbation s=1 at the lower boundary of the thermosphere, one could reproduce the negative electron density disturbances in the F region of ionosphere during SSW events. Our scenario for the 2009 SSW event in the GSM TIP allowed to obtain results which are in a qualitative agreement with the observation data.

Sounding of HF heating‐induced artificial ionospheric disturbances by navigational satellite radio transmissions

During experiments carried out in 2009–2011 the midlatitude ionosphere was modified by powerful HF pulses from the Sura heating facility located near Nizhny Novgorod (Russia) and operated by the Radio Physical Research Institute. GPS/GLONASS and Parus/Tsikada satellite radio transmissions responding to the heating‐induced disturbances in electron density were analyzed. The variations in the total electron content (TEC), which are proportional to the reduced phase of navigational signals, were studied for various schemes of radiation of the heating wave. The variations in TEC (their amplitudes and temporal behavior) caused by HF heating are identified in several examples. The TEC spectra contain frequency components corresponding to the modulation periods of the heating wave. For the first time, the spatial structure of the wave disturbances generated in the ionosphere by high‐power radio waves radiated by the Sura heating facility with a square wave modulation of the effective radiated power at a frequency lower than or of the order of the Brunt‐Vaisala frequency of the neutral atmosphere is imaged using the method of low‐orbital radio tomography and GPS/GLONASS data.

An improved model of the lightning electromagnetic field interaction with the D‐region ionosphere

We present an improved time‐domain model of the lightning electromagnetic pulse (EMP) interaction with the lower ionosphere. This improved model inherently accounts for the Earth's curvature, includes an arbitrary number of ion species, and uses a convolutional Perfectly Matched Layer (PML) boundary. We apply an improved model of electron heating due to the lightning EMP and electrostatic fields, and we include ionization, attachment, and detachment. In addition to modeling lightning, this model can be used for long‐distance VLF wave propagation in the Earth‐ionosphere waveguide, heating of the lower ionosphere by VLF transmitters, and heating in the F‐region ionosphere by lightning. In this paper we present three initial results of this model. First, we compare results of ionospheric heating and electron density disturbances with and without electron detachment taken into account. We find that detachment is important only for the QE effects on time scales longer than 1 ms. Second, we find a simple explanation for the recently‐reported “elve doublets”, which we find are an effect of the rise and fall times of the lightning waveform. In particular, we find that all elves are doublets, and the rise and fall times of the current pulse control the brightness and separation in time of the two successive halves of the elve. Third, we find a similar simple explanation for “ring” sprites, whole columns appear in a circle symmetric around the discharge axis. We find that ring sprites can be initiated for particular current waveforms, where the QE and EMP fields in the mesosphere produce a maximum reduced field away from the discharge axis.

Simulation of mesospheric-composition disturbances under the action of high-altitude discharges (sprites)

Recent measurements show that a mesospheric electric discharge (sprite) can provoke disturbances in the chemical composition of the mesosphere. In this paper, we propose a plasmachemical system of equations which allows one to describe the complex relationship among chemical components during the discharge. Disturbances of the mesospheric ion composition are analyzed under the night-time and daytime conditions at an altitude of 75 km, which is typical of the sprite initiation and at an altitude of 85 km where the diffuse region of discharge is usually observed. The most probable scenarios of development of the electric-field and electron-temperature disturbances, which are characteristic of the diffusive and streamer regions of the sprite, are simulated. The value and characteristic time of disturbances of the main ion components (O2 +, NO+, H3O+, H5O2 +, and N2 +) are evaluated. The obtained values of the electron-density disturbances are in agreement with experimental and theoretical data. It was established that the sprite series, which are recorded over the vast stratified regions of mesoscale convection systems, can lead to generation of comparatively long-lived disturbances in the ion composition of mesospheric plasma.

Some effects in the upper atmosphere during geomagnetic storms

This paper examines the response of the high latitude ionosphere–thermosphere system during two intense geomagnetic storms. For that, data taken by instruments on board Dynamic Explorer 2 taken at heights of the F2-layer are used. These results represent a comparison of simultaneous measurements of storm disturbances in gas composition, electron density and temperature in common local time sectors. Documented are an increase in electron temperature and a decrease in electron density; increases both in electron temperature and electron density; and the correlation between electron density decreases and increases in the ratio N 2/O. It is noticed that the decrease in electron density is sometimes due to an increase in the molecular nitrogen density N 2 and not always is attributed both to the increase in N 2 density and the simultaneous decrease in the atomic oxygen density.

Two‐dimensional frequency domain modeling of lightning EMP‐induced perturbations to VLF transmitter signals

The lightning electromagnetic pulse creates observable modifications to the overlying D region ionosphere, exhibited optically as elves. Recent work, both experimental and theoretical, has shown that elves are accompanied by considerable electron density disturbances of up to a factor of 2 increase in local density. We investigate the possibility that these density disturbances are observed by subionospheric VLF transmitter signals as the so‐called early VLF events. We use a finite difference frequency domain model to simulate the VLF transmitter signal propagating subionospherically to a VLF receiver, under ambient conditions and through a disturbed region. We show that modeled electron density disturbances, consistent with optical observations of elves, yield small but detectable perturbations to the VLF transmitter signal and may explain at least some observed early VLF events. We further show that sequences of in‐cloud lightning pulses, as in spider lightning, may yield considerably higher density disturbances and similarly more prominent VLF transmitter perturbations. In this way, the model herein supports previously reported correlations between sferic bursts and early VLF events.

Method for studying the spatial-temporal structure of wave-like disturbances in the ionosphere

The method for studying the spatial-temporal structure and propagation characteristics of traveling ionospheric disturbances, using the spectral and cross-correlation analysis of electron density disturbances at different altitudes, obtained with the incoherent scatter radar and vertical sounding ionosonde, is considered. Different algorithms for detecting traveling ionospheric disturbances and calculating the total vector of the disturbance propagation velocity are presented. The results of the method application have been considered in detail, using September 11, 2005, as an example.

Spectrum of quasi-wave disturbances in the topside daytime ionosphere according to the data of radiosounding onboard the Intercosmos-19 satellite

Quasi-wave disturbances in the topside daytime ionosphere, related to auroral activity, have been detected using the data of radiosounding onboard the Intercosmos-19 satellite on April 28, 1979. A disturbance was caused by an abrupt enhancement of the eastward electrojet, which was not reflected in the variations in the AE and AU indices. According to the estimates, the period of electron density disturbances was about 0.5 h, the velocity was 350 m/s, and the length along the meridian was several hundreds of kilometers, which corresponds to medium-scale traveling ionospheric disturbances (TIDs). The disturbance amplitude was only 30 km in the hmF2 variations and 0.20–0.25 MHz in the foF2 variations but increased to 0.25–0.30 MHz in the plasma frequency variations at satellite altitudes of 520–580 km with increasing altitude. It is impossible to register so weak short-period variations during ground-based sounding. The method for detecting disturbance spatial characteristics has been proposed. The disturbance spectrum including three quasiperiodic structures has been revealed using this method. The optimal estimates have been made for the trend, described by the polynomial of the third degree, and for the expansion of the residuals in terms of three harmonics.

Parameters of large‐scale TEC disturbances during the strong magnetic storm on 29 October 2003

The total electron content (TEC) data obtained by the GPS network and GPS radio interferometry methods developed by the authors has made it possible to determine the spatial structure and dynamics parameters of large‐scale traveling ionospheric disturbances (LS TID) generated during the strong magnetic storm on 29 October 2003. It was shown that the LS TID registered in the auroral zone after a sudden storm commencement (SSC) represented a large‐scale solitary type wave with an annular front shape whose center was located near the geomagnetic pole. The wave had a period of about 40–60 min and traveled up to 4500 km equatorward. The relative amplitude of the LS TID was 5–10%. Comparison with ionosonde data has shown that this value corresponds to the relative amplitude of electron density disturbance in the F layer maximum of about 45–50%. The velocity and travel direction of the LS TID had a strongly pronounced longitudinal dependence. A “swirling” effect was detected in the LS TID movement, the direction of which was opposite to the Earth's rotation. The westward directed zonal projection of LS TID velocity caused this “swirling” effect. In the morning and evening sectors the zonal projection exceeded the meridional one. The diurnal movement of the ionization maximum may influence the zonal transfer of LS TID.

Large-scale traveling ionospheric disturbances of auroral origin according to the data of the GPS network and ionosondes

The intensity of large-scale traveling ionospheric disturbances (LS TIDs), registered using measurements of total electron content (TEC) during the magnetic storms on October 29–31, 2003, and on November 7–11, 2004, had been compared with that of local electron density disturbances. The data of TEC measurements at ground-based GPS receivers located near the ionospheric stations and the corresponding values of the critical frequency of the ionospheric F region f o F2 were used for this purpose. The variations of TEC and f o F2 were similar for all events mentioned above. The previous assumption that the ionospheric region with vertical extension from 150 to 200 km located near the F-layer maximum mainly contributes to the TEC variations was confirmed for the cases when the electron density disturbance at the F region maximum was not more than 50%. However, this region probably becomes vertically more extended when the electron density disturbance in the ionospheric F region is about 85%.

Comparison of the electron density variations measured with instruments of the ISZF SO RAN radar complex under the conditions of different geomagnetic disturbance

The variations in the electron density measured with the incoherent scatter radar, DPS-4 digisonde, and FMCW ionosonde are compared in this work. The main regularities in differences are explained by the effect of different-scale ionospheric irregularities. Considerable morning gradients of electron density result in that ionosondes give increased values as compared to the incoherent scatter radar data. Electron density disturbances measured with different instruments can be of correlated and uncorrelated character. Uncorrelated disturbances are explained by intense medium-scale ionospheric irregularities. Correlated disturbances are caused by large-scale irregularities. Observation of such disturbances can be used to determine the velocity and direction of a disturbance.

Large-scale disturbances of auroral origin during strong magnetic storms of October 29–31, 2003, and November 7–11, 2004, according to the data of the GPS network and ionosondes

The intensity of large-scale traveling ionospheric disturbances (LS TIDs), registered according to measurements of the total electron content (TEC) during the magnetic storms of October 29–31, 2003, and November 7–11, 2004, has been compared with that of local electron density disturbances. The data of TEC measurements at ground-based GPS receivers located near the ionospheric stations and the corresponding values of the critical frequency of the ionospheric F region (foF2) were used for this purpose. The variations in TEC and foF2 were similar for all events mentioned above. The previous assumption that the region of thickness 150–200 km in the vicinity of the ionospheric F region mainly contributes to TEC modulation was confirmed for the cases when the electron density disturbance at an F region maximum was not more than 50%. However, this region probably becomes more extensive in vertical when the electron density disturbance in the vicinity of the ionospheric F region is about 85%.

Ionosphere disturbances during rocket launches at Baikonur (Kazakhstan)

A review of the ionosphere disturbances created by burning rockets is given. Published materials obtained by different authors are used in the review. Contemporary ionospheric data (f0 E, f0 F1, f0 F2, h'F, fmin, f0 Es) of ionosonde measurements obtained at the Alma-Ata [43.25N, 76.92E] and Novokazalinsk [45.77N, 62.12E] sounding stations taken for the time of rocket launching from Baikonur (Kazakhstan) in the periods of 1975, 1979 and October 2000-November 2001 are also analysed.The main characteristics of such disturbances seem to be the deficiency of electrons and strongly disturbed ionosphere structures (strong wave-like disturbances in electron density) occurring along the trajectory of burning rockets, which modify the propagation of radio waves.

Radio tomography and scintillation studies of ionospheric electron density modification caused by a powerful HF-wave and magnetic zenith effect at mid-latitudes

Observations of the ionospheric electron density modified by a powerful wave of the Sura HF heating facility were carried out in Russia at middle latitudes in August 2002. Amplitude scintillations and variations of the phase of VHF signals from Russian orbiting satellites passing over the heated region along the chain of three satellite receivers have been recorded. The experimental data were converted to electron density maps using a stochastic inversion. Tomographic measurements conducted during a low magnetic activity revealed that HF powerful waves can produce significant electron density disturbances up to heights significantly exceeding altitudes of the F layer peak. Both large-scale plasma enhancements and small-scale density irregularities can be generated by the HF radiation. Wavy density structures were also observed within a sector which is much wider than the area covered by the main lobe of the heating antenna. Small-scale density irregularities are mostly field-aligned although large-scale structures can be detected within a much larger area. A distinctive peculiarity of electron density changes occurred during heating is producing a zone of low density inside the area illuminated by the antenna beam. The results indicate that satellite radio tomography and scintillation measurements are effective diagnostic techniques giving a valuable information to studies of effects induced by HF modification. The complete system of plasma density disturbances describing by the theory of “the magnetic zenith effect” has been for the first time studied in this Letter. A good agreement between the theory and experimental data has been obtained.

Early/fast VLF events produced by electron density changes associated with sprite halos

The magnitudes of scattered fields produced during early/fast very low frequency (VLF) events observed at 13 closely spaced (∼65 km) sites are compared with those expected for sprite halo disturbances using a numerical model of wave propagation within the Earth‐ionosphere waveguide. Three different early/fast events of varying magnitudes are analyzed using three different nighttime ambient lower ionospheric electron density profiles. The electron density disturbances associated with sprite‐halo events are determined using a full‐wave electromagnetic (FWEM) model. Observed scattered field amplitudes of typical (VLF amplitude changes of 0.2 dB < ΔA < 0.8 dB) Early/fast events agree with model calculations within a factor of two when the peak return stroke currents (as recorded by the National Lightning Detection Network, referred to in this work as NLDN) are used to determine the sprite‐halo characteristics. Scattered field amplitudes associated with larger early/fast events (ΔA > 1 dB) are found to be within a factor of seven for peak currents of causative lightning based on NLDN. However, in previous studies, some sprite‐producing lightning flashes have exhibited large slow‐tail components, indicating substantial continuing currents and implying charge removal up to 2–3 times larger than that inferred from the peak current reported by NLDN. For the cases discussed in this paper, scattered field calculations using disturbances caused by 2–3 times larger charge removal are found to be within a factor of two of the measured values. VLF scattering from electron density changes associated with sprite halos thus appear to be the underlying cause of at least some of the VLF perturbations observed as early/fast events.

Theoretical model of possible disturbances in the nighttime mid-latitude ionospheric D region over an area of strong-earthquake preparation

We present a theoretical model of possible electron-density disturbances in the nighttime mid-latitude ionospheric D region, preceding strong earthquakes. It is found that the electron density in the nighttime D region over an earthquake epicentral zone can considerably increase before severe earthquakes. The horizontal size of the area of disturbed electron density is about 300 km. The disturbance effect is expected to be more pronounced if a powerful VLF transmitter operates in the vicinity of an imminent earthquake epicentral zone. In this case, a very dense ionization layer of daytime D-layer type can be formed at the altitudes of the upper nighttime mesosphere and can give rise to the effect of strong absorption of HF radio waves propagating over the earthquake preparation area.

Reducing ionospheric electron density errors in satellite radar interferometry applications

It has been demonstrated that ionospheric electron density disturbances can influence multi-pass satellite radar interferometry (SRI). This has been observed to occur near the magnetic poles, particularly during strong magnetic disturbances. Ionospheric disturbances most clearly appear in interferometric synthetic aperture radar (InSAR) as a kilometre-scale modulation in the azimuth pixel shift needed for optimal registration of the interferometric pair. This modulation (also known as "azimuth streaks") also affects the InSAR phase, and consequently such SRI applications as digital elevation model (DEM) generation and displacement measurement, and may appear as "streaks" in the coherence map. The effect is worse for L-band systems (e.g., Japanese Earth resources satellite 1 (JERS-1) and Phased array type L-band synthetic aperture radar (PALSAR)), but can be significant even at C band (e.g., European remote sensing satellites ERS-1/2 and RADARSAT I and II). The influence of ionospheric effects on interferogram phase can often be predicted, and the magnitude can be estimated, by an inspection of a map of the shift in azimuth position for optimal registration obtained using the "speckle tracking" technique. For DEM generation, the ionospheric phase contribution can be approximated, and removed from the interferogram phase, by the scaled and filtered integral of this azimuth shift map. For displacement-measurement applications, appropriate filtering of the distinct patterns of the azimuth streaks is the only resort.

Electron-Density Distribution in the Upper Ionosphere under Conditions of a Mid-Latitude F-Spread

We present the results of the last experiments aimed at studying the phenomenon of mid-latitude F-spread by radio-raying of the ionosphere using the signal from the SURA facility received onboard the NASA spacecraft WIND. A generalized model of spatio-temporal distribution of the electron density in the mid-latitude ionosphere under F-spread conditions is proposed. Based on this model describing large-scale ionospheric irregularities, we calculate the ray trajectories of HF radio waves. We also discuss the known results of comparative measurements of the variances of relative electron-density fluctuations in large-scale irregularities of the mid-latitude ionosphere, carried out by the OGO-6 spacecraft, and the frequency broadening of the ionograms of ground-based stations for the vertical sounding. It is shown that the proposed model of electron-density disturbances in the mid-latitude ionosphere in the presence of F-spread is able not only to describe well the main qualitative feature of HF radiowave propagation under disturbed geophysical conditions, but also to reproduce quite accurately the quantitative parameters of the frequency broadening of reflected HF signals under conditions of standard and developed F-spread.