Radio Scintillation Research Articles

A model of radio scintillations in the deep Venus atmosphere: Application to the DAVINCI probe

Power fluctuations have been noted on radio signals propagating through the Venus atmosphere since the very first descent probe there (Venera 4) and have been observed as a routine feature in radio occultations, where the grazing ray geometry amplifies the effect of refractive scattering structures. Motivated by DAVINCI and other missions currently in development, a physical model of refraction variations in the Venus atmosphere is developed using the VEGA-2 high-resolution temperature profile down to the surface and other data, which suggest several distinct layers of more intense scattering. The resultant modeled radio scintillations are compared with observed scintillations and assessed for the DAVINCI relay link. High-time-resolution radio signal power measurements on the DAVINCI radio link promise to be an interesting probe of the Venus atmosphere.

Correction to: Observation of the Solar Corona Using Radio Scintillation with the Akatsuki Spacecraft: Difference Between Fast and Slow Wind

Correction to: Observation of the Solar Corona Using Radio Scintillation with the Akatsuki Spacecraft: Difference Between Fast and Slow Wind

Antony Hewish. 11 May 1924—13 September 2021

Antony (Tony) Hewish was a pioneer radio astronomer who will always be remembered as the leader of the team in 1967 that discovered the pulsars, which proved to be rapidly rotating, magnetized neutron stars. The discovery resulted from Tony's programme of systematic all-sky surveys to detect the scintillation, or flickering, of small angular diameter radio sources due to electron density fluctuations in the solar wind flowing out from the Sun. The large low-frequency 4.5-acre array was designed by Tony to find radio quasars, which often display radio scintillations, to estimate the angular sizes of the sources and to study the physics of the interplanetary medium. In the course of commissioning the telescope, his research student, Jocelyn Bell (Jocelyn Bell Burnell, FRS 2003), noted a strange 100% scintillating source unlike anything seen before. Tony and the team soon established that this source was a pulsating radio source, Jocelyn first observing the pulsations with period 1.33 s in November 1967. The discovery paved the way for the rapid development of high energy astrophysics and an appreciation that general relativity plays a key role in the stability of neutron stars. Tony's contributions spanned a very wide range of pioneering studies in the new discipline of radio astronomy, including telescope and electronic design, cosmological studies of distant radio sources and the physics of the ionospheric, interplanetary and interstellar plasmas. He was awarded the 1974 Nobel Prize in physics for ‘his decisive role in the discovery of pulsars’.

Observation of the Solar Corona Using Radio Scintillation with the Akatsuki Spacecraft: Difference Between Fast and Slow Wind

Observation of the Solar Corona Using Radio Scintillation with the Akatsuki Spacecraft: Difference Between Fast and Slow Wind

Antony Hewish

Antony Hewish (1924–2021) Pioneer radio astronomer and leader of the team of researchers who identified the first pulsar, remembered by Malcolm Longair. Antony (Tony) Hewish went up to Cambridge University in 1942 to read natural sciences. After his second year, however, he was sent for war service at the Telecommunications Research Establishment, Malvern, where Martin Ryle was head of the radar counter-measures group. Tony worked on devices to jam the radar systems of hostile night-fighters. Returning to Cambridge in 1946, he completed his physics degree and then joined the newly founded radio astronomy group led by Ryle at the Cavendish Laboratory. Tony specialized in the phenomenon of radio scintillation, the twinkling of radio sources caused by plasma irregularities along the line of sight to the source. In 1951–52, he worked out in detail the theory of radio source scintillation (Hewish 1952) and in 1964 the phenomenon was observed in compact radio sources (Hewish et al. 1964). These sources included the recently discovered quasars, among the most extreme examples of active galactic nuclei.

Global Distribution of Nighttime MSTIDs and Its Association With E Region Irregularities Seen by CHAMP Satellite

AbstractWe investigate the correlation of sporadic E (Es) with the occurrence of medium‐scale traveling ionospheric disturbances (MSTIDs) at night in middle latitudes (25°–40°N and 25°–40°S magnetic latitudes) by examining their occurrence climatology. The occurrence climatology of Es and MSTIDs is derived using the Challenging Minisatellite Payload satellite data acquired in 2001–2008 and 2001–2009, respectively. Electron density irregularities and radio scintillations are used as the detection proxies of MSTIDs and Es, respectively. The occurrence rate of MSTIDs shows a semi‐annual variation with the primary peak during June solstices and the secondary peak during December solstices in both hemispheres. However, the occurrence rate of Es shows a seasonal variation with a pronounced peak in summer in both hemispheres. The occurrence of MSTIDs during local summer and equinoxes is correlated with the occurrence of local Es, but the high occurrence rate of MSTIDs in local winter is not correlated with local winter hemisphere Es. MSTIDs in the winter hemisphere are correlated with magnetically conjugate MSTIDs in the summer hemisphere; these summer hemisphere MSTIDs are correlated with the occurrence of Es in the summer hemisphere. The occurrence rate of MSTIDs clearly shows an increase with decreasing solar activity, but the solar cycle dependence of Es is not obvious from the data. This observation suggests that the generation of MSTIDs is significantly affected by factors other than Es such as the growth rate of the Perkins instability, atmospheric gravity waves, and the F region conductance.

Simulation study on cosmic ray background at large zenith angle based on GRANDProto35 coincidence array experiment

Neutrino detection in the 100 PeV energy region is the ultimate means of studying the origin of ultra-high-energy cosmic rays, in which the large radio detection array giant radio array for neutrino detection (GRAND) project aims to use to decipher this century-old problem. The GRANDProto35 compact array is a microform of 35 radio prototype detectors for the GRAND experiment, which verifies the reliability of GRAND performance through operation, and data analysis of the prototype detectors. As radio detectors are a novel development in recent years, and their indexes need to be verified by traditional detectors, the GRAND Cooperation Group designed and constructed the GRANDProto35 coincidence array composed of radio detectors and scintillation detectors. This study simulated the changes in detection efficiency, effective area, and event rate of cosmic rays with zenith angle based on this coincidence array. The study found that the 1017 eV energy region is sensitive to GRANDProto35 detection. When the energy exceeded 1017 eV, the array detection efficiency could reach more than 95% and the effective area was up to ~ 2 × 106 m2. A simulation study on cosmic ray events with large zenith angles showed that the event rate detected by the array decreased significantly with increasing zenith angle, and the event rate of cosmic rays was approximately 0.1 per day for a zenith angle of 75°. This serves as the background pollution rate for neutrino observation caused by large-angle cosmic-ray events, providing an important reference for further experiments. The study results will be verified after the joint operation of the coincidence array.

Ionospheric irregularities and scintillations: a direct comparison of in situ density observations with ground-based L-band receivers

Ionospheric irregularities can affect satellite communication and navigation by causing scintillations of radio signals. The scintillations are routinely measured using ground-based networks of receivers. This study presents observations of ionospheric irregularities by Langmuir probes on the Swarm satellites. They are compared with amplitude scintillation events recorded by the Global Positioning System-Scintillation Network and Decision Aid (GPS-SCINDA) receiver installed in Mbarara (Lat: 0.6^{circ }hbox {S}, Lon: 30.8^{circ }hbox {E} , Mag. lat: 10.2^{circ }hbox {S}). The study covers the years from 2014 to 2018 when both data sets were available. It was found that the ground-based amplitude scintillations were enhanced when Swarm registered ionospheric irregularities for a large number of passes. The number of matching observations was greater for Swarm A and C which orbited at lower altitudes compared to Swarm B. However, some counterexamples, i.e., cases when in situ electron density fluctuations were not associated with any observed L-band amplitude scintillation and vice versa, were also found. Therefore, mismatches between observed irregularity structures and scintillations can occur just over a few minutes and within distances of a few tens of kilometers. The amplitude scintillation strength, characterized by the S4 index was estimated from the electron density data using the well-known phase screen model for weak scattering. The derived amplitude scintillation was on average lower for Swarm B than for A and C and less in accordance with the observed range. Irregularities at an altitude of about 450 km contribute strongly to scintillations in the L-band, while irregularities at about 510-km altitude contribute significantly less. We infer that in situ density fluctuations observed on passes over or near Mbarara may be used to indicate the risk that ionospheric radio wave scintillations occur at that site.

Radio Propagation Studies of the Solar Wind in the Era of Parker Solar Probe

Abstract The NASA Parker Solar Probe mission is providing unprecedented measurements of solar wind plasma and plasma turbulence at heliocentric distances as small as 0.125 au, or 26.9 solar radii. Radioastronomical remote sensing measurements of the coronal and solar wind plasma have been made since the 1960s over a heliocentric distance range that overlaps with and extends that of Parker Solar Probe. This paper will compare radio scintillation and Parker Solar Probe results on the heliocentric-distance-dependence of the plasma density variance (where there may be an inconsistency between the two techniques), the speed at which turbulence density irregularities move radially with respect to the Sun, and other topics.

A Method for Automatic Detection of Plasma Depletions by Using GNSS Measurements

AbstractEnhanced scintillation activities observed at transionospheric radio signals are often correlated with slant total electron content (STEC) depletions in the equatorial ionosphere. In this study, the data derived from high‐rate Global Navigation Satellite System (GNSS) receivers were used to analyze the observed STEC depletions, commonly associated with plasma bubbles causing radio scintillations in the equatorial ionosphere. We found that the observed STEC depletion can be described by a wedge‐shaped structure. To quantitatively describe the structure of STEC depletions, we developed an effective method to routinely characterize the depth and the width of equatorial plasma depletion in automatized data screening. The developed method has been validated by analyzing data obtained from mostly African GNSS stations in 2014 and 2015. The results confirm current knowledge regarding the seasonal occurrence of radio scintillations and related bubbles. The detection results are compared with those from other published plasma bubble detection techniques.

Correlation between the Orientation of Cross-Field Axes of Small-Scale Anisotropic Irregularities in Midlatitude Ionosphere and Drift Direction in the F Region

Introduction. It was previously reported that small-scale irregularities (SSI) in the polar ionosphere are elongated along the magnetic field and anisotropic in its cross-field direction. At the same time, the largest of the SSI cross-field axes tends to orient along the SSI drift direction. This is also indirectly confirmed for the midlatitude ionosphere, however, direct correlations of the SSI anisotropy and ionospheric drift directions in the middle latitudes are absent.Objective. The main objective of this work is a direct comparison of the experimental data of SSI shape with motion parameters of irregularities, which are measured at the same place (Moscow) at the same time. Previously, experimentally obtained values of the SSI cross-field anisotropy orientation in the midlatitude ionosphere were compared only with the neutral winds model.Materials and methods. A tomographic approach is used to determine the SSI anisotropy parameters by processing radio scintillation signals while overfly of several navigation satellites emitting on frequencies of 150 MHz and 400 MHz. Estimations of ratio between the ellipsoids axes and cross-field anisotropy orientations in the framework of SSI model in a form of magnetic field oriented ellipsoids with three different dimensions along and across the Earth's magnetic field are obtained. Irregularities parameters are obtained by selecting the model parameters when the calculated logarithm dispersion of the satellite signals relative amplitude while they orbiting is the closest to the experimentally obtained curve. Estimations of the velocity and drift direction of medium-scale irregularities (MSI) by using DPS-4 ionosonde data acquired while decameter-wave radar studies of ionosphere from the Earth's surface are obtained. The socalled "sky maps" presenting the energy distribution of scattered radio waves on incident angles are used. Simultaneous measurements of Doppler frequency shifts and incident angles of scattered waves allow obtaining estimations of three components of the medium-scale irregularities drift velocity.Results. A good correlation between the drift direction of medium-scale irregularities and cross-field anisotropy orientation of small-scale irregularities is found.Conclusion. The correlation between the cross-field anisotropy orientation of the elongated irregularities and their drift direction can be useful under conditions of the lack of information on ionospheric irregularities.

Axial Ratio and Gain Enhancement of a Circular-Ring Slot Antenna Using a Pair of Asymmetrical Rectangular Slots and a Parasitic Patch for a Radio Beacon on a Nanosatellite

Radio beacons enable measurements of ionospheric radio scintillations and total electron content (TEC). These beacons transmit unmodulated, phase-coherent waves in S-band frequencies. Many satellite applications require circularly polarized (CP) wideband antennas. Their compact size, lightweight, and simple fabrication method make CP antennas suitable for small satellite systems. The slot antenna has wideband impedance, but the 3 dB axial ratio bandwidth (ARBW) is narrower compared to the impedance bandwidth (IBW). In this paper, a circularly polarized circular-slotted antenna (CSA) is proposed to enhance the ARBW and the antenna gain. A pair of asymmetrical rectangular slots, a simple 50 Ω feedline and a parasitic patch were introduced to a CSA to enhance the 3 dB ARBW and the antenna gain. Rectangular slots were inserted on the diagonal axis of the CSA, the feedline was shifted to the left side of the x-axis, and a parasitic patch was attached to the circular slot. The lengths of the rectangular slots correspond to the resonant frequency, and the parasitic patch width corresponds to the higher frequency of the 3 dB ARBW. The asymmetrical rectangular slots, the shifted feedline, and the parasitic patch successfully improved the measured 3 dB ARBW of the antenna by 787.5 MHz or 35.79%. The measured gain of a CSA with left-hand circular polarization (LHCP) was also improved by shifting the feedline and the rectangular slot, achieving a peak gain of 5 dBic.

Contextual Predictions for the Parker Solar Probe. I. Critical Surfaces and Regions

Abstract The solar corona and young solar wind may be characterized by critical surfaces—the sonic, Alfvén, and first plasma-β unity surfaces—that demarcate regions where the solar wind flow undergoes certain crucial transformations. Global numerical simulations and remote sensing observations offer a natural mode for the study of these surfaces at large scales, thus providing valuable context for the high-resolution in situ measurements expected from the recently launched Parker Solar Probe (PSP). The present study utilizes global three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind to characterize the critical surfaces and investigate the flow in propinquitous regions. Effects of solar activity are incorporated by varying source magnetic dipole tilts and employing magnetogram-based boundary conditions. An MHD turbulence model is self-consistently coupled to the bulk-flow equations, enabling investigation of turbulence properties of the flow in the vicinity of critical regions. The simulation results are compared with a variety of remote sensing observations. A simulated PSP trajectory is used to provide contextual predictions for the spacecraft in terms of the computed critical surfaces. Broad agreement is seen in the interpretation of the present results in comparison with existing remote sensing results, both from heliospheric imaging and from radio scintillation studies. The trajectory analyses show that the period of time that PSP is likely to spend inside the β = 1, sonic, and Alfvén surfaces depends sensitively on the degree of solar activity and the tilt of the solar dipole and location of the heliospheric current sheet.

Adaptive Local Iterative Filtering: A Promising Technique for the Analysis of Nonstationary Signals

AbstractMany real‐life signals and, in particular, in the space physics domain, exhibit variations across different temporal scales. Hence, their statistical momenta may depend on the time scale at which the signal is studied. To identify and quantify such variations, a time‐frequency analysis has to be performed on these signals. The dependence of the statistical properties of a signal fluctuation on the space and time scales is the distinctive character of systems with nonlinear couplings among different modes. Hence, assessing how the statistics of signal fluctuations vary with scale will be of help in understanding the corresponding multiscale statistics of such dynamics. This paper presents a new multiscale data analysis technique, the adaptive local iterative filtering (ALIF), which allows to describe the multiscale nature of the geophysical signal studied better than via Fourier transform, and improves scale resolution with respect to discrete wavelet transform. The example of geophysical signal, to which ALIF has been applied, is ionospheric radio power scintillation on L band. ALIF appears to be a promising technique to study the small‐scale structures of radio scintillation due to ionospheric turbulence.

Extreme Radio-wave Scattering Associated with Hot Stars

Abstract We use data on extreme radio scintillation to demonstrate that this phenomenon is associated with hot stars in the solar neighborhood. The ionized gas responsible for the scattering is found at distances up to from the host star, and on average must comprise ∼105 distinct structures per star. We detect azimuthal velocities of the plasma, relative to the host star, up to , consistent with warm gas expanding at the sound speed. The circumstellar plasma structures that we infer are similar in several respects to the cometary knots seen in the Helix and in other planetary nebulae. There the ionized gas appears as a skin around tiny molecular clumps. Our analysis suggests that molecular clumps are ubiquitous circumstellar features, unrelated to the evolutionary state of the star. The total mass in such clumps is comparable to the stellar mass.

The electrodynamic effects of MOSC‐like plasma clouds

The effects on the plasma/electrodynamic environment in the low-latitude ionosphere produced by the artificial plasma clouds created in the Metal Oxide Space Cloud (MOSC) experiment are studied via simulations. The electric fields and plasma flow in the vicinity of the cloud are calculated using its estimated field-line-integrated conductance; it is found that the “comma-like” flow around the cloud seen in the ALTAIR (Advanced Research Project Agency [ARPA] Long-range Tracking and Identification Radar) observations can be explained by the perturbations to the electric field produced by the conductance gradients around the cloud. Next, the conductance is introduced into a simulation of the development of the Rayleigh-Taylor instability. The simulations suggest that a moderately denser cloud than the MOSC cloud, closer to the bottom edge of the F layer, could indeed suppress the development of the low-density plumes and the shorter-wavelength irregularities associated with radio scintillation that form with the Rayleigh-Taylor instability in the low-latitude ionosphere.

Scintillation measurements at Bahir Dar during the high solar activity phase of solar cycle 24

Abstract. Small-scale ionospheric disturbances may cause severe radio scintillations of signals transmitted from global navigation satellite systems (GNSSs). Consequently, small-scale plasma irregularities may heavily degrade the performance of current GNSSs such as GPS, GLONASS or Galileo. This paper presents analysis results obtained primarily from two high-rate GNSS receiver stations designed and operated by the German Aerospace Center (DLR) in cooperation with Bahir Dar University (BDU) at 11.6° N, 37.4° E. Both receivers collect raw data sampled at up to 50 Hz, from which characteristic scintillation parameters such as the S4 index are deduced. This paper gives a first overview of the measurement set-up and the observed scintillation events over Bahir Dar in 2015. Both stations are located close to one another and aligned in an east–west, direction which allows us to estimate the zonal drift velocity and spatial dimension of equatorial ionospheric plasma irregularities. Therefore, the lag times of moving electron density irregularities and scintillation patterns are derived by applying cross-correlation analysis to high-rate measurements of the slant total electron content (sTEC) along radio links between a GPS satellite and both receivers and to the associated signal power, respectively. Finally, the drift velocity is derived from the estimated lag time, taking into account the geometric constellation of both receiving antennas and the observed GPS satellites.

A comparison of the relative effect of the Earth's quasi‐DC and AC electric field on gradient drift waves in large‐scale plasma structures in the polar regions

AbstractRadio signals traversing polar cap plasma patches and other large‐scale plasma structures in polar regions are prone to scintillation. This implies that irregularities in electron concentration often form within such structures. The current standard theory of the formation of such irregularities is that the primary gradient drift instability drives a cascade from larger to smaller wavelengths that manifest as variations in electron concentration. The electric field can be described as the sum of a quasi‐DC and an AC component. While the effect of the quasi‐DC component has been extensively investigated in theory and by modeling, the contribution of the AC component has been largely neglected. This paper investigates the relative contributions of both components, using data from the Dynamics Explorer 2 satellite. It concludes that the contribution of the AC electric field to irregularity growth cannot be neglected. This has consequences for our understanding of large‐scale plasma structures in polar regions (and any associated radio scintillation) as the AC electric field component varies in all directions. Hence, its effect is not limited to the trailing edge of such structures, as it is for the quasi‐DC component. This raises the need for new experimental and modeling investigations of these phenomena.

A Review of Ionospheric Scintillation Models

This is a general review of the existing climatological models of ionospheric radio scintillation for high and equatorial latitudes. Trans-ionospheric communication of radio waves from transmitter to user is affected by the ionosphere which is highly variable and dynamic in both time and space. Scintillation is the term given to irregular amplitude and phase fluctuations of the received signals and related to the electron density irregularities in the ionosphere. Key sources of ionospheric irregularities are plasma instabilities; every irregularities model is based on the theory of radio wave propagation in random media. It is important to understand scintillation phenomena and the approach of different theories. Therefore, we have briefly discussed the theories that are used to interpret ionospheric scintillation data. The global morphology of ionospheric scintillation is also discussed briefly. The most important (in our opinion) analytical and physical models of scintillation are reviewed here.

The CERTO Beacon on CASSIOPE/e-POP and Experiments Using High-Power HF Ionospheric Heaters

A new Coherent Electromagnetic Radio Tomography (CERTO) beacon is on the CASSIOPE satellite and part of the enhanced-Polar Outflow Probe (e-POP) suite of scientific instruments. CERTO signals can be used to measure ionospheric Total Electron Content (TEC) and radio scintillations along propagation paths between CERTO and receivers. The combination of CERTO and the array of e-POP in-situ diagnostics form a powerful tool for studying ionospheric plasma processes that have not been previously possible. Of note, the combination CERTO and the Radio Receiver Instrument (RRI), a modern digital receiver, which measures between 10 Hz to 18 MHz in selectable bands allows for innovative High Frequency (HF) radio propagation experiments. The use of high-power HF ionospheric heating facilities for such experiments further allows for repeatable studies of a number of important plasma processes. The new CERTO beacon transmits un-modulated, phase-coherent waves at 150, 400, and 1067 MHz with either right-hand-circular or linear polarization and TEC is measured using either differential phase and/or Faraday rotation. With a linear array of CERTO receivers, TEC data can be used for tomographic imaging of the ionosphere yielding two-dimensional maps of the plasma below the satellite orbit. In addition, the three CERTO frequencies cover a wide range for determination of radio scintillation effects caused by diffraction from propagation through ionospheric irregularities. We will describe the CERTO beacon and several potential innovative experiments using HF heating facilities in conjunction with CERTO, the RRI and other e-POP instruments.