Waves In Ionosphere Research Articles

Some Features of the Ionospheric Radio Wave Characteristics Over China Observed During the Solar Eclipse of 21 June 2020

AbstractThe Harbin Engineering University, the People's Republic of China, multifrequency multiple‐path coherent radio system operates continuously and provides data for post analysis. The data collected during the solar eclipse of 21 June 2020 have been chosen for this study with the objectives to interpret the variations in the Doppler spectra, Doppler shift, and in the reflected radio wave amplitudes that are associated with the solar eclipse, establish the magnitude and find physical significance of these variations, determine the reduction in the electron density caused by the solar eclipse, and to estimate an increase in wave activity in the ionosphere. The eclipse was accompanied by Doppler spectrum diffuseness resulting from an increase in the number of rays, the temporal variations in the Doppler shift were observed to be bi‐polar, asymmetrical, and anomalously small, with extreme Doppler shift magnitudes varying from −11 to −40 mHz and from 22 to 56 mHz. The duration of processes with negative Doppler shifts varied from 50 to 80 min, and the duration of processes with positive Doppler shifts changed from 30 to 80 min. The multi‐hop propagation (from two to five hops) took place along all propagation paths, with a 360 to 560‐km one‐hop length, due to the anomalous radio wave propagation via the sporadic‐E layer present about 80% of the time on 21 June 2020. The Doppler shift exhibited 4–18‐min period quasi‐sinusoidal variations with 20–10‐mHz amplitudes.

A Systematic Study of 7 MHz Greyline Propagation Using Amateur Radio Beacon Signals

This paper investigates 7 MHz ionospheric radio wave propagation between pairs of distant countries that simultaneously lie on the terminator. This is known as greyline propagation. Observations of amateur radio beacon transmitters recorded in the Weak Signal Propagation Reporter (WSPR) database are used to investigate the times of day that beacon signals were observed during the year 2017. The WSPR beacon network consists of thousands of automated beacon transmitters and observers distributed over the globe. The WSPR database is a very useful resource for radio science as it offers the date and time at which a propagation path was available between two radio stations, as well as their precise locations. This paper provides the first systematic study of grey-line propagation between New Zealand/Eastern Australia and UK/Europe. The study shows that communications were predominantly made from the United Kingdom (UK) to New Zealand at around both sunset and sunrise times, whereas from New Zealand to the UK, communication links occurred mainly during UK sunrise hours. The lack of observations at the UK sunset time was particularly evident during the UK summer. The same pattern was found in the observations of propagation from Eastern Australia to UK, and from New Zealand and Eastern Australia to Italy and the surrounding regions in Europe. The observed asymmetry in reception pattern could possibly be due to the increase in electromagnetic noise across Europe in the summer afternoon/evening from thunderstorms.

Analysis of Ionospheric Compressional Waves and Electron Density Oscillation During Storm Periods Using Swarm Observations

AbstractUsing Swarm satellite observations, we aimed to examine compressional electromagnetic ion cyclotron (EMIC) waves and concurrent plasma density oscillations during storm periods (2014–2018). Compressional waves were accompanied by precipitated energetic proton fluxes, which can lead to increased electron density in the F‐layer. Approximately one‐third of compressional waves were accompanied by electron density (Ne) oscillations. The Ne oscillation occurred more frequently during stronger magnetic storms and with EMIC wave events of larger power density. The morning sector and South Atlantic Anomaly region revealed high occurrence rates of Ne oscillations. Its peak occurrence region showed a local time drift during the storm evolution. These variations with magnetic local time and storm phases are consistent with those of EMIC waves. Phases of the EMIC compressional waves and Ne oscillations exhibited a strong correlation. The phases of EMIC waves and Ne oscillations were linearly related, apart from a bias of ∼17.5° or 200.5°. The relative amplitude ratio of most Ne oscillations to the compressional EMIC wave showed a strong correlation with the local Alfven velocity. When the Alfven velocity increased, the relative amplitude ratio also increased, and there appeared a saturation of the relative amplitude ratio at large Alfven velocity.

Equatorial plasma bubbles for solar maximum & moderate year of the solar cycle 24

The fluctuations in the electron density of the F-region in the ionosphere as compared to the background electron density are the sign of plasma irregularities which is a well-known phenomenon. They occur during post-sunset hours and degrade ionospheric radio wave communication majorly the navigation signals. To explore the features of equatorial plasma bubbles (EPBs) over the Indian region throughout the solar maximum year 2014 and the solar moderate year 2017, we have examined day and night hours plasma irregularities from Defense Meteorological Satellite Program (DMSP) with spacecraft as F15 with total crossings as 9698. From the total crossings, 1115 crossings were obtained with EPBs degrading the communication and navigation signals. The distribution of EPBs was studied monthly, seasonally, and longitudinally for the solar maximum and moderate years which has given significant results. We have also analyzed the occurrence of EPBs during the geomagnetic storms with Disturbed storm time index (Dst) ≤ -100 nT occurred in the solar maximum and moderate years. We have observed that the regular occurrence of EPBs was there during the initial and main phase but smoothens up in course of the recovery phases of the storm. These results are discussed with those of earlier results and are in good agreement too. The observed inferences will help to improve the telecommunication sector in the Indian region.

Resonant Alfvén Waves in the Lower Auroral Ionosphere: Evidence for the Nonlinear Evolution of the Ionospheric Feedback Instability

AbstractDuring the “Auroral Jets” experiment from Poker Flat, Alaska on 2 March 2017, two NASA sounding rockets were simultaneously launched into the active auroral ionosphere. The rockets were equipped with instrumentation to measure DC and AC electric fields, magnetic fields, energetic electrons, plasma density, and neutral winds and achieved apogees of 190 and 330 km. A prominent feature of the electric and magnetic field observations is the presence of localized large‐amplitude (±40 mV/m and ±100 nT) small‐scale (λ⊥∼ 1 km) Alfvén wave structures at altitudes as low as 150 km in the vicinity of up‐ and down‐ward current regions. We interpret the oscillations as representing standing waves associated with the ionospheric Alfvén resonator formed between the ionosphere and the lower magnetosphere. The electric field components of the Alfvén waves show signatures of wave steepening in correlation with electron precipitation and large variations of the background plasma density. The signatures are discussed in the context of nonlinear evolution of the ionospheric feedback instability.

Electromagnetic wave propagation characteristics of oblique incidence nonlinear ionospheric Langmuir disturbance

Based on the generalized Zakharov model, a numerical model of electromagnetic wave propagating in the ionosphere at different angles is established by combining the finite difference time domain (FDTD) method of obliquely incident plasma with the double hydrodynamics equation and through equivalently transforming the two-dimensional Maxwell equation into one-dimensional Maxwell equation and the plasma hydrodynamics equation. In this paper. the dominant equation of Z-wave in obliquely incident nonlinear ionospheric plasma having been analyzed and deduced, the FDTD algorithm suitable for calculating the propagation characteristics of ionospheric electromagnetic wave is deduced. The simulation results prove the accuracy and effectiveness of this method for the Langmuir disturbance caused by electromagnetic wave heating the ionosphere at a small inclination angle. The results show that under small angle incidence, the high-power high-frequency electromagnetic wave excites the Langmuir wave near the O-wave reflection point in the ionospheric plasma. At the same time, the wave particle interaction causes the O-wave to convert into Z-wave and propagate into the higher region of the ionosphere. In this work, the electromagnetic wave propagation characteristics are further studied based on ionospheric plasma, which is helpful in laying the foundation of numerical algorithm for comprehensively and in depth analyzing the influence of ionospheric Langmuir disturbance on ionospheric radio wave propagation characteristics.

Systematic Detection of Anomalous Ionospheric Perturbations Above LEOs From GNSS POD Data Including Possible Tsunami Signatures

In this paper we show the capability of Global Navigation Satellite System (GNSS) Precise Orbit Determination (POD) Low Earth Orbiter (LEO) data to detect anomalous ionospheric disturbances in the spectral range of the signals associated to earthquakes and tsunamis, applied to two of these events in Papua New Guinea (PNG) and Solomon Islands during 2016. This is achieved thanks to the new PIES approach <i>( POD-GNSS LEO Detrended Ionospheric Electron Content Significant Deviations)</i>. The significance of such ionospheric signals above the Swarm LEOs is confirmed with different types of independent data: in-situ electron density measurements provided by the Langmuir Probe (LP) on board Swarm LEOs, DORIS and ground-based GNSS co-located measurements, as it is described in the paper. In this way we conclude the possible detection of the tsunami related ionospheric gravity wave in PNG 2016 event, consistent with the most-recent theory which shows that a tsunami (which is localized in space and time) excites a spectrum of gravity waves, some of which have faster horizontal phase speeds than the tsunami. We believe that this work shows as well the feasibility of a future potential monitoring system of ionospheric disturbances, to be made possible by hundreds of cubesats with POD GNSS receivers among other appropriate sensors, and supported for real-time or near real-time confirmation and characterization by thousands of worldwide existing ground GNSS receivers.

Single-point positioning of ground-based sources of radio emission during reflection of an ionospheric radio wave from an inclined layer of the ionosphere

Single-point positioning of ground-based sources of radio emission during reflection of an ionospheric radio wave from an inclined layer of the ionosphere

Fine-scale dynamics of fragmented aurora-like emissions

Abstract. Fragmented aurora-like emissions (FAEs) are small (few kilometres) optical structures which have been observed close to the poleward boundary of the aurora from the high-latitude location of Svalbard (magnetic latitude 75.3 ∘N). The FAEs are only visible in certain emissions, and their shape has no magnetic-field-aligned component, suggesting that they are not caused by energetic particle precipitation and are, therefore, not aurora in the normal sense of the word. The FAEs sometimes form wave-like structures parallel to an auroral arc, with regular spacing between each FAE. They drift at a constant speed and exhibit internal dynamics moving at a faster speed than the envelope structure. The formation mechanism of FAEs is currently unknown. We present an analysis of high-resolution optical observations of FAEs made during two separate events. Based on their appearance and dynamics, we make the assumption that the FAEs are a signature of a dispersive wave in the lower E-region ionosphere, co-located with enhanced electron and ion temperatures detected by incoherent scatter radar. Their drift speed (group speed) is found to be 580–700 m s−1, and the speed of their internal dynamics (phase speed) is found to be 2200–2500 m s−1, both for an assumed altitude of 100 km. The speeds are similar for both events which are observed during different auroral conditions. We consider two possible waves which could produce the FAEs, i.e. electrostatic ion cyclotron waves (EIC) and Farley–Buneman waves, and find that the observations could be consistent with either wave under certain assumptions. In the case of EIC waves, the FAEs must be located at an altitude above about 140 km, and our measured speeds scaled accordingly. In the case of Farley–Buneman waves a very strong electric field of about 365 mV m−1 is required to produce the observed speeds of the FAEs; such a strong electric field may be a requirement for FAEs to occur.

Propagation characteristics of very low frequency vortex electromagnetic waves in an anisotropic ionosphere

AbstractWe report very low frequency (VLF) orbital angular momentum (OAM) vortex electromagnetic waves propagation in an anisotropic ionosphere by proposing a Hertizan dipole array antenna. The circular array with linear insulated antennas is designed and demonstrated to generate vortex waves carrying OAM modes. To match the impedance of the ionosphere with high refractive index in the VLF band, electromagnetic characteristics of single linear antenna in the ionosphere is adjusted by selecting proper radii and electrical length. Effects of high and anisotropic refractive index of the time‐ and space‐varying ionosphere on the OAM spectra and phase profiles generated by the array antenna are analyzed. Numerical results show that the propagation features present obvious differences if OAM vortex electromagnetic waves change their topological charges. The VLF vortex waves can provide an efficient avenue to increase the spectrum efficiency, more information will be offered by the OAM VLF waves for wireless communications and information transmissions.

Observation of Ionospheric Gravity Waves Introduced by Thunderstorms in Low Latitudes China by GNSS

The disturbances of the ionosphere caused by thunderstorms or lightning events in the troposphere have an impact on global navigation satellite system (GNSS) signals. Gravity waves (GWs) triggered by thunderstorms are one of the main factors that drive short-period Travelling Ionospheric Disturbances (TIDs). At mid-latitudes, ionospheric GWs can be detected by GNSS signals. However, at low latitudes, the multi-variability of the ionosphere leads to difficulties in identifying GWs induced by thunderstorms through GNSS data. Though disturbances of the ionosphere during low-latitude thunderstorms have been investigated, the explicit GW observation by GNSS and its propagation pattern are still unclear. In this paper, GWs with periods from 6 to 20 min are extracted from band-pass filtered GNSS carrier phase observations without cycle-slips, and 0.2–0.8 Total Electron Content Unit (TECU) magnitude perturbations are observed when the trajectories of ionospheric pierce points fall into the perturbed region. The propagation speed of 102.6–141.3 m/s and the direction of the propagation indicate that the GWs are propagating upward from a certain thunderstorm at lower atmosphere. The composite results of disturbance magnitude, period, and propagation velocity indicate that GWs initiated by thunderstorms and propagated from the troposphere to the ionosphere are observed by GNSS for the first time in the low-latitude region.

Local and conjugate ionospheric total electron content variation during the 21 June 2020 solar eclipse

• Ionospheric TEC showed an asymmetric latitudinal depletion around totality path. • Ionospheric disturbances in both local and conjugate eclipse regions were analyzed. • Eclipse-induced ionospheric bow wave structures and TIDs were identified. This paper studies the ionospheric response to a low-latitude annular solar eclipse event on 21 June 2020 at both eclipse and conjugate regions using a dense network of Global Navigation Satellite Systems receivers, Defense Meteorological Satellite Program and Swarm satellites data, as well as ionosonde measurements over the Asian-Oceania sector. The large scale ionospheric variation and small scale wave-like perturbations during the eclipse were analyzed by using high-resolution Total Electron Content (TEC) maps and in-situ electron density/temperature data. The main results are as follows: (1) A local TEC reduction of 4–7 TEC Unit ( ∼ 30–50%) was identified along the totality path, with larger depletion in the southern edge of totality path than the northern edge. (2) The equatorial ionization anomaly in the Asian sector exhibited a complicated variation pattern with a slightly different longitudinal/local time and altitudinal response, which showed considerable TEC/ Ne depletion in the East Asian sector and at ∼ 850 km close to local afternoon during the eclipse, but a slight TEC/ Ne enhancement around the Indian sector and at ∼ 500 km in the post-eclipse periods. (3) Large ionospheric perturbations were identified that traveled at approximately the same velocity as the supersonic moon shadow, and the ionospheric bow wave features were also triggered by the solar eclipse. (4) The Oceania TEC in the Southern Hemisphere conjugate location experienced a coincident minor reduction and wave-like fluctuations during the eclipse, likely indicating some possible interconnections between the eclipse and the conjugate ionospheres.

Investigating Ionospheric Perturbations Following the 2020 Beirut Explosion Event

AbstractWe assess the detection of the August 4, 2020 chemical explosion in Beirut, Lebanon (33°N, 35°E). We use ionospheric total electron content (TEC) observations from a regional network of ground‐based Global Positioning System (GPS) receivers to study the ionospheric variability and wave perturbations generated by the Beirut explosion. Our analysis reveals that the induced wave structures arrived in the ionosphere 10 ± 2 min after the explosion, which is a strong indication of acoustic gravity wave activity. These wave structures are characterized with ΔTEC of 0.06 TECU moving at ∼750 m/s in south‐east direction away from the explosion epicenter. The continuous wavelet analysis we applied shows a dominant wave periodicity of 1.5–2.5 min (6.78–11 mHz) in the ionosphere. Furthermore, we use measurements from ERA‐interim analysis to establish the ambient neutral atmospheric conditions before the Beirut explosion event. Finally, the observed ionospheric wave perturbations appear to be in good agreement with the expected arrival of acoustic gravity waves generated following the explosion.

GPS L1 signals absorption in high-latitude lower ionosphere during severe geomagnetic storm in June 2015

Based on the results of an analysis of FORMOSAT-3/COSMIC radio occultation measurements, the absorption of DM-radio waves (wavelength ∼19 cm) in the lower high-latitude ionosphere of the Earth was detected. The maximum absorption value is ∼3 dB in the range from ∼60 to ∼90 km and, in some cases, it reaches ∼10 dB at altitudes from ∼90 to ∼95 km. A method for determining the vertical profiles of the absorption coefficient by solving the inverse problem of radiosonding in the Earth’s lower ionosphere is proposed. The absorption layers, caused by powerful bursts of X-ray radiation and strong changes in geomagnetic conditions during the storm, were reliably identified in individual sessions. It was found that, at altitudes from ∼90 to ∼100 km, the value of the absorption coefficient of DM-radio waves reached values (5.69 ± 1.35)·10−3 dB/km.

Detection of the Lunar Surface Soil Permittivity with Megahertz Electromagnetic Wave

In this paper, the detection of the lunar surface soil permittivity with megahertz electromagnetic (EM) waves by spaceborne radar is studied based on the EM scattering theory, the Boltzmann–Shukla equations, and the improved scattering matrix method (ISMM). The reflection characteristics of the lunar surface soil subject to megahertz waves are analyzed through the EM scattering theory and expressed by the lunar surface soil permittivity. Then, the lunar ionosphere is assumed to be composed of dusty plasma, and its EM characteristics are described with the Boltzmann–Shukla equations. Finally, the transmission and reflection characteristics of the propagation of EM waves in the lunar ionosphere are numerically calculated with ISMM. Thus, the complex permittivity of lunar surface soil is obtained. In addition, the effects of detection environment situations, such as the lunar illumination intensity, characteristics of the lunar dust and dust charging process in the lunar ionosphere, on the amplitude and phase of EM waves are also investigated in this study. The simulation results show that an EM wave at a high frequency induces a strong effective wave with a stable phase shift and a significantly small interferential wave. Moreover, the lunar illumination is more effective under EM waves in low frequency bands; the characteristics of the lunar dust have a notable influence on the transmission and absorption coefficients of the effective waves. These conclusions help in real applications involving the detection of the lunar surface soil permittivity by spaceborne radar in various lunar environments.

Local Time Differences in the Ionospheric Electromagnetic Ion Cyclotron Waves during Storm Time

By using high-resolution (50 Hz) magnetic field observations from Swarm constellation, the temporal and spatial characteristics of Electromagnetic Ion Cyclotron (EMIC) waves in different local time sectors at mid-latitudes are investigated during the magnetic storm period of 16—25 March 2015. There are comparable number of EMIC wave events in the dawn and dusk sectors, while there are more EMIC wave events in the pre-noon sector than in the pre-midnight sector. The duskside preference is related to the plasmaspheric plume, while the dawnside preference is related to the enhanced solar wind dynamic pressure and dense cold plasma. The wave frequency in the dawn and pre-noon sectors is higher than that in the dusk and pre-midnight sectors, implying the local time difference in the source location and the ion composition. Most of the duskside events occur in the early recovery phase, while the dawnside events occur in the late recovery phase. The time difference comes from the time required for the westward drift of energetic ions and local time difference in the plasmapause position. H⁺ band waves are mainly found in the 06:00 MLT—10:00 MLT sector, while He⁺ band waves are mainly confined in the 18:00 MLT—22:00 MLT sector. There is no H⁺ band but a two band (He⁺ and O⁺) EMIC wave during the storm main phase, indicating the role of the dense oxygen ion in inhibiting the H⁺ band in the inner magnetosphere.

Mode Coupling From Kinetic Alfvén Waves to Electron Acoustic Waves in the Topside Ionosphere

AbstractThe propagation and energy transfer of kinetic Alfvén waves (KAWs) in the topside ionosphere are investigated based on a drift kinetic model. We examine the dependence of the generation of electron acoustic waves (EAWs) on the perpendicular wavelength and on the hot electron temperature. With decreasing perpendicular wavelength and increasing hot electron temperature, the coupling of KAWs to EAWs becomes increasingly important. The Landau damping of the EAWs is strong except in the transition region, where the nonlinear dissipation can be important. With increasing wave amplitude, the generated electron acoustic mode waves become unsustainable when the depletion of cold electron density is comparable to the initial background cold electron density. These findings indicate that electron acoustic mode waves play an important role at kinetic scales in the topside ionosphere.

Noise temperature of the electromagnetic waves in the mid-latitude ionosphere

In this theoretical study, the noise temperature of the different modes (ordinary, extraordinary, right and left polarized) of the electromagnetic wave travelling vertically in the ionosphere has been investigated for the solstice and the equinox days, 2015. The noise temperature values vary between 10−6 and 10−2 K for all results. There is a slight decrease in the noise temperature values near the 105 km and then a rise again for 4, 5, 6 MHz waves at all modes. As the frequency of the wave increases, the noise temperature values change periodically depending on the electron density.

Local Time and Longitudinal Differences in the Occurrence Frequency of Ionospheric EMIC Waves During Magnetic Storm Periods

AbstractThe spatial and temporal distributions of ionospheric electromagnetic ion cyclotron (EMIC) waves during magnetic storms from 2014 to 2018 were studied using Swarm observations. Ionospheric EMIC waves preferably occurred during storms and their recovery phases at subauroral regions within an average magnetic latitude of 40–55°. There were more wave events during more intense and longer period storms. However, the correlation between event number and storm duration was not good. This might be due to the effect of heavy oxygen ions on EMIC wave generation and the loss of ring current high‐energy ions by the EMIC waves. There are obvious magnetic local time (MLT) differences in the peak occurrence frequency of EMIC waves during storm phases. The enhanced solar wind dynamic pressure was favorable for duskside EMIC waves. With an increased substorm activity, the wave occurrence rate peak shifted from the morning side to the dusk‐premidnight sector. During the recovery phase of a storm, EMIC waves in the 12–24 MLT sector appeared preferably in the earlier part than those in the 00–12 MLT sector. This shift in local time is related to the eastward rotation of the plasmaspheric plume toward morning during the late storm recovery phase and its overlap with the ring current. Highest occurrence frequency of the storm time EMIC waves could be found in the South Atlantic Anomaly region, which might be related to the drift shell splitting and the wave propagation effect in the weak magnetic field region.

Local Time Differences in the Ionospheric Electromagnetic Ion Cyclotron Waves during Storm Timeormalsize

利用Swarm卫星的高精度（50 Hz）磁场观测数据，对2015年3月16—25日磁暴期间中纬度电离层电磁离子回旋（EMIC）波时空分布特征进行了研究.结果表明：晨侧EMIC波事件数与昏侧大致相当，午前时段明显多于子夜前时段.昏侧EMIC波高发生率与等离子体羽状结构有关，晨侧EMIC波高发生率与太阳风动压增强及稠密冷等离子体有关.晨侧-正午前EMIC波频率高于昏侧-子夜前，表明源区位置以及离子成分占比存在地方时差异.昏侧事件大多发生在早期恢复相，晨侧事件大多发生在晚期恢复相，晨-昏两侧的时间差异源于磁暴期间高能离子西向漂移所需时间及等离子体层顶位置的地方时差异.磁暴期间，EMIC波以H⁺波和He⁺为主，其中H⁺波主要分布在06：00 MLT—10：00 MLT（磁地方时）扇区，He⁺波主要分布在18：00 MLT—22：00 MLT扇区.在磁暴主相期间没有出现H⁺带波，但是出现He⁺-O⁺双波段EMIC波，表明磁暴主相期间环电流高浓度氧离子对H⁺带EMIC波具有抑制作用.