Field-aligned Ionospheric Irregularities Research Articles

Design of the New MST Radar in Chinese Meridian Project

With the support of the second phase of the Chinese Meridian Project, a new mesosphere–stratosphere–troposphere observation radar (MST radar), called Qinzhou MST radar, located in Qinzhou City, Guangxi Province, China (22°7′55′′N,108°16′20′′E) is under construction. The Qinzhou MST radar is a large VHF monostatic pulse Doppler radar with an active phased array antenna system, mainly using Doppler beam swinging technique for observation. The capability of multibeam observation, space antenna observation, and frequency- and spatial-domain interferometry are also employed. The main scientific objective of this radar is to explore the atmosphere dynamical processes at low latitudes of China. The observation of ionospheric field-aligned irregularities (FAIs) is also an important function of the radar. The radar applies a circular array composed of 1261 3-element crossed Yagi antennas with a diameter of 153 m and an aperture of near 2×104 m2. Thereinto, 997 elements connect both transmitting and receiving channels and 264 elements distributed near the edge connect only receiving channels. The peak power of the transmitter in each transmitting/receiving (T/R) module is 2 kW. The central frequency and bandwidth of the output signal are 50 and 4 MHz, respectively. The peak power of the whole system will be close to 2 MW. This article presents the initial design of the Qinzhou MST radar, and the construction will be completed at the end of 2022.

Positioning of the Ionospheric Field-Aligned Irregularities With Geomagnetic Field Model

An observation model is introduced for accurate positioning of the ionospheric field-aligned irregularities (FAIs). The model is applied to the Hainan coherent scatter phased array radar (HCOPAR) in the Hainan island of China and constructed based on the International Geomagnetic Reference Field (IGRF) model. Compared with the original centerline method, the model method has higher accuracy at a higher altitude and larger azimuth. In the observation of the E-region irregularities, the model can be used to position the sidelobe echoes under certain conditions. Thus, the zonal observation range of the radar can be extended.

Radar phase offset estimate using ionospheric field-aligned irregularities and aircraft

Radar phase offset estimate using ionospheric field-aligned irregularities and aircraft

Characteristics of convective structures of sodium layer in lower thermosphere (105–120 km) at Haikou (19.99°N, 110.34°E), China

The atmospheric sodium layer normally occurs in the mesopause (80–105 km) region, but rarely in the lower thermosphere region (>105 km) at low latitude. We observed a kind of peculiar sodium layer in lower thermosphere at Haikou (19.99°N, 110.34°E)—the thermospheric convective sodium layer (TCSL) in a lidargram. The TCSL's sodium density unstably developed over time and appeared as several discontinuous convective shapes vertically. It is the first time convective sodium layer observed in the lower thermosphere region (105–120 km). Based on Haikou lidar data, we obtained 14 TCSL events during 180 nights from March 2010 to August 2012. Most of the apogees of the TCSL events are higher than 108 km. A TCSL event lasts several hours and is composed of several convective structures, with each veitical shape lasting ∼5–30 min. All TCSL events occurred during spring and summer, and generally appear near midnight (22:00–00:00 LT). The TCSL has potential regional feature and appears to be related to the thermospheric sporadic E (Es) layers, winds, and field-aligned ionospheric irregularities (FAI).

Observations of field-aligned ionospheric irregularities during quiet and disturbed conditions with EKB radar: first results

This paper presents the first results of statistical analysis of 2-year data series obtained with the first midlatitude decameter coherent radar of Russian segment of SuperDARN network. Based on individual events observed on 13–15 December 2013 and 1–4 January 2014, we also demonstrate the possibility of using the radar data for monitoring of magnetosphere-ionosphere dynamics in quiet and disturbed geomagnetic conditions.

Wuhan Ionospheric Oblique-Incidence Sounding System and Its New Application in Localization of Ionospheric Irregularities

In this paper, a novel oblique-incidence ionosonde (Wuhan Ionospheric Oblique-Incidence Sounding System) and its new application in the localization of the ionospheric irregularities are presented. Due to the usage of the binary-phase-coded waveform, a large signal processing gain, a high Doppler and range resolution, and a large unambiguous detection range can be achieved in this ionosonde. This ionosonde also adopts the peripheral component interconnect extensions for instruments (PXI) bus technology and is designed as a small-sized PXI-based system. Furthermore, a high-performance oven-controlled crystal oscillator that is disciplined by the Global Positioning System is used to achieve a good time and frequency synchronization. With multichannel digital receiver and multiple receiving sites, this ionosonde can be applied in the localization of the ionospheric irregularities. The details of the system configuration, the ambiguity function of the sounding waveforms, the signal processing algorithm, and the time and frequency synchronization method are described. The experimental results show that the virtual height along with the ground position of the ionospheric field-aligned irregularities can be preliminarily localized with this ionosonde.

Consistent quasi-periodic variations of the geomagnetic pulsation level and doppler frequency shift of decametric radio waves aspect-scattered by artificial field-aligned ionospheric irregularities

We present the results of experimental studies of consistent quasi-periodic variations of the geomagnetic-pulsation level and effective Doppler frequency shift of decametric radio waves aspectscattered by artificial field-aligned ionospheric irregularities. For processing of signals, we used a system spectral analysis and a correlation analysis. It is shown that quasi-periodic variations of the effective Doppler frequency shift are caused by geomagnetic-field pulsations with an amplitude of 0.5–1.0 nT and a period of 50–150 s. Estimated amplitudes of the quasi-periodic and aperiodic drift velocities of the ionospheric irregularities appeared close to 5–10 and 15–30 m/s, respectively.

First evidence of anisotropy of GPS phase slips caused by the mid-latitude field-aligned ionospheric irregularities

The mid-latitude field-aligned irregularity (FAI) along the magnetic field line is a common phenomenon in the ionosphere. However, few data reveal the field-aligned ionospheric irregularities. They are insufficient to identify FAIs effects so far, particularly effect on global positioning system (GPS) signals. In this paper, the mid-latitude FAIs by line-of-sight angular scanning relative to the local magnetic field vector are investigated using the denser GPS network observations in Japan. It has been the first found that total GPS L2 phase slips over Japan, during the recovery phase of the 12 Feb 2000 geomagnetic storm were caused by GPS signal scattering on FAIs both for the lines-of-sight aligned to the magnetic field line (the field of aligned scattering, FALS) and across the magnetic field line (the field of across scattering, FACS). The FALS results are also in a good agreement with the data of the magnetic field orientation control of GPS occultation observations of equatorial scintillation during thorough low earth orbit (LEO) satellites measurements, e.g. Challenging Minisatellite Payload (CHAMP) and Satellite de Aplicaciones Cientificas-C (SAC-C). The role of large-angle scattering almost along the normal to the magnetic field line in GPS scintillation is determined by attenuation of the irregularity anisotropy factor as compared with the other factors.

Investigation of Low-Latitude Ionospheric Field-Aligned Irregularities by Oblique Backscatter Sounding

The ionosphere is not homogeneous, hosting many irregularities with different scales from dozens of meters to dozens of kilometers. The observation and formation mechanism of the irregularities is among the most active domains for understanding the influence of irregularities on propagation of radio waves. The characteristics of ionospheric field-aligned irregularity (FAI) at low-latitude regions were investigated in this letter in terms of analyzing the data obtained from ionospheric sounding experiments using the Wuhan University ionospheric oblique backscattering system, in which the scales and drift speeds of FAIs were specified.

Non-great-circle propagation modes on the high-latitude HF radio path

We consider characteristics of the non-great-circle signals on the Murmansk—St. Petersburg oblique sounding path with a distance of 1050 km. The path crosses the main ionospheric trough and is highly influenced by the trough’s polar wall and the boundary of diffuse precipitations. Field-aligned ionospheric irregularities and ionization gradients are often observed in this area. The data analysis was performed for quiet, moderately disturbed, and strongly disturbed conditions and for different local times. The main results are as follows. Non-great-circle signals in the form of scattered waves mostly occur in the nighttime hours. The nighttime non-great-circle signals always appear under both quiet and disturbed conditions, while the signals reflected from the ionization gradients appear at any local time during the disturbed periods (storms, substorms). Non-great-circle signals with intense reflections from the ionization gradients are most often observed during a moderate disturbance, especially in the nighttime hours. The ray-tracing model of non-great-circle propagation shows that the calculated oblique sounding ionograms generally coincide with the experimental ones.

Observations of peculiar sporadic sodium structures and their relation with wind variations

Resonance lidar observations of sodium density in the upper mesosphere region over Gadanki (13.5°N, 79.2°E) rarely show complex structures with rapid enhancements of sodium density, completely different from normal sporadic sodium structures. The hourly averaged meteor radar zonal winds over Trivandrum (8.5°N, 76.5°E) show an eastward shear with altitude during the nights, when these events are formed. As suggested by Kane et al. [2001. Joint observations of sodium enhancements and field-aligned ionospheric irregularities. Geophysical Research Letters 28, 1375–1378], our observations show that the complex structures may be formed due to Kelvin–Helmholtz instability, which can occur in the region of strong wind shear.

Statistical characteristics of low-latitude ionospheric field-aligned irregularities obtained with the Piura VHF radar

Abstract. We present a summary of the statistical characteristics of echoes from ionospheric (E- and F-region) field-aligned irregularities obtained with the Piura VHF radar. This radar is located at ~ 7.0° dip latitude, just outside the equatorial electrojet (EEJ) region. Our results are based on (1) intermittent observations made between 1991 and 1999 just few days a year, and (2) continuous observations made between January 2000 and June 2001. During most of the intermittent observations, simultaneous measurements of EEJ and equatorial spread F (ESF) irregularities were performed with the Jicamarca VHF radar. From the continuous measurements, we have obtained the diurnal and seasonal characteristics of a variety of parameters (percentage of occurrence, signal-to-noise ratio and/or Doppler velocities) from the lower and upper E-region irregularities and also from F-region irregularities over Piura. For example, we have found that (1) the E-region echoes are stronger and occur more frequently during local summer (i.e. between December and March); (2) between May and June, the E-region echoes are weaker and occur less frequently; moreover, during these months, a semidiurnal wave with large amplitudes is observed in the meridional wind (> 100 ms- 1); (3) there is vertical wavelength of about 20 km in the Doppler velocity, particularly after midnight; (4) the lower (upper) E-region Doppler velocities are influenced mainly by meridional winds (equatorial F-region vertical drifts). In addition, we have observed that the seasonal and daily occurrences of Piura F-region irregularities are similar to the occurrence of topside ESF irregularities over Jicamarca. The likelihood of occurrence of F-region irregularities over Piura and, therefore, topside ESF over Jicamarca is greater when there are no E-region irregularities over Piura. On the other hand, there is more probability of observing bottomtype/bottomside ESF irregularities over Jicamarca when E-region irregularities are observed over Piura.Key words. Ionosphere (ionospheric irregularities; equatorial ionosphere; instruments and techniques)

New electron gyroharmonic effects in HF scatter from pump‐excited magnetic field‐aligned ionospheric irregularities

Experimental results of resonant high‐frequency (HF) scattering from small‐scale geomagnetic field‐aligned plasma irregularities excited by electromagnetic HF pumping of the ionospheric F region from the Sura radio facility in Russia are reported. These results include the first observations of a minimum in the scattered signal intensity when the pump frequency was near the fourth electron gyroharmonic and of a significant broadening of the frequency spectrum of the scattered signal for pump frequencies above the gyroharmonic. After pump‐off, the flanks of the broad spectrum decayed rapidly. These new observations link together several previous experimental results of gyroharmonic effects in phenomena attributed to the excitation of small‐scale field‐aligned irregularities and are therefore thought to be significant contributions to our understanding of the self‐organization of the space plasma under the action of an external perturbation.

Nonlinear resonance of plasma waves in the thermal irregularities of ionospheric plasma

We study the effect of striction plasma density disturbances on the generation intensity of longitudional cold and plasma oscillations due to polarization of the magnetic field-aligned ionospheric plasma irregularities with δNo<0 by a powerful radio wave. It is assumed that the plasma density level inside the irregularity intersects the upper-hybrid resonance level, in the vicinity of which the cold oscillations excited directly by a powerful radio wave are transformed to shorter-wave plasma oscillations. We consider the short plasma wave limit to reduce the problem to a system of two coupled equations for the cold wave induction and plasma wave electric field. The first equation is supplemented by a local source equal to the integral of the plasma wave electric field in the resonance region. The second equation involves the cold wave induction at the resonance point and describes the electric field of interacting waves in the resonance vicinity. We use simplifications connected with the small absorption of plasma waves propagating inside the irregularity and weak radiation of these waves outside the irregularity. These conditions correspond to the generation of eigenmodes of plasma oscillations trapped in the irregularity. We have obtained a resonance-type nonlinear equation for the electric field intensity (or energy flux) of eigenmode plasma waves with allowance for striction disturbances of the plasma density profile in the resonance region. It is shown that the striction expulsion of plasma is responsible for the occurrence of coefficients describing the change in the intensity of excitation and radiation of plasma waves at the irregularity boundary. Such an expulsion leads to variations of the efficient generation band of plasma eigenmodes with the total phase increment of the wave in the irregularity. It also leads to a change in the phase shift of the plasma wave reflected from the resonance. These coefficients and the nonlinear phase shift are expressed in terms of real wave functions of the nonlinear Airy equation which describes the electric field of the excited waves in the resonance vicinity when the dissipation is absent.

Response of topside radio sounding signals to small-scale field-aligned ionospheric irregularities

Abstract Small-scale ionospheric irregularities produce numerous observed effects during high-frequency radio wave sounding from a satellite. Scattering of z-mode waves radiated by an ionosonde, which results in the occurrence of characteristic traces on ionograms, are among the most complex of them. In the present paper the factors determining the power characteristics of such signals are considered. These are the size and shape of the surface of orthogonality for a family of z-mode waves radiated from a satellite, features of the radiating and propagating radio waves in a non-uniform magnetized plasma, and the details of the scattering process. Simple but adequate physical models for each of these factors are presented and a numerical calculation algorithm of the power of the z-mode scattered signals received by the satellite sounder receiver has been constructed. Values for this calculated quantity are presented as a function of time delay, sounding frequency, and magnetic latitude. A synthesis of topside ionograms showing z-mode scattered traces has been performed. The results support new diagnostic methods of detecting small-scale ionospheric irregularities using topside-sounder z-mode signal returns and the concept that the sounder radiation can, under certain conditions, stimulate artificial plasma turbulence. In addition, it was shown that z-mode scattering may contribute to the resonance observed at the plasma frequency on topside ionograms.

Riometer absorption events at SANAE, L=4.0

The absorption of cosmic radio noise passing through the ionosphere may be described as a function of radio wave frequencyA(f e ) αf e -n , with n ≈ 2.0 for spatially uniform precipitation of electrons and n < 2.0 for spatially nonuniform precipitation. Using multifrequency riometer recordings at SANAE, the following observations are reviewed: (1) The frequency distribution of the power index, n, obtained from 4 min averaged absorptions during 1983, shows a most probable value around n ≈ 1.5, indicating that mostly energetic electrons are precipitated spatially structured onto the upper atmosphere, as in optical aurora. (2) Multifrequency riometer recordings suggest that field-aligned ionospheric irregularities have scattered additional cosmic radio waves from the central region of the Galaxy into the fields of views of the riometer antennae during an auroral absorption event in the early morning hours of 27 July, 1982. With the power reflectivity by ionospheric irregularities inversely proportional to the fourth power of radio wave frequency, as required by the Bragg condition, an estimated 70% increase in the 20 MHz radio flux at 01:22 UT, at the strong absorption peak, can explain the strongly reduced absorption observed in 20 MHz relative to 30 and 51.4 MHz. (3) Gradual increases in absorptions observed at all three riometer frequencies from onset at 11:50 UT of the largest solar proton ground level enhancement on 29 September, 1989, until 18:00 UT, suggest diffusion of the much more intense low energy protons from the polar cap to the L=4.0 geomagnetic field shell and subsequent precipitation at SANAE due to the South Atlantic Geomagnetic Anomaly. (4) The flux of electron energy deposited per second at SANAE is closely related to geomagnetic activity, but has a lower maximum during the years 1971 and 1980 of solar polar magnetic reversals than in the years 1976 and 1986/87 of minimum solar activity. (5) A significant correlation has been found between the arrival of single-hop whistlers and 30 MHz riometer absorption events, using point statistics. The maximum absorption at 30 MHz was ∼0.04 dB with a delay of 3 ± 2 s relative to the whistler.

HF scattering induced by field-aligned irregularities in the equatorial E-region during total solar eclipses

In this paper, results and analyses of solar eclipse effects on the lower ionosphere are presented. After the first contact of the total eclipse on 16 February 1980, an absorption increment of 12 dB was observed. At the same time, the frequency of amplitude fading increased largely and Doppler frequency shift disturbances appeared. The calculation of signal strength is carried out by means of Booker's scattering theory, supposing an outer scale T o = 1000 m and an inner scale T i = 5 m, of space scale spectrum of field-aligned irregularities in the equatorial E-region. The calculated results agree fairly well with observations. Results showed that, because of the formation of lower ionospheric field-aligned irregularities in the course of the obscuration of solar local ionization source, radio wave scattering was strengthened.

Excitation of upper-hybrid waves by a thermal parametric instability

A purely growing instability characterized by a four-wave interaction has been analysed in a uniform, magnetized plasma. Up-shifted and down-shifted upper-hybrid waves and a non-oscillatory mode can be excited by a pump wave of ordinary rather than extraordinary polarization in the case of ionospheric heating. The differential Ohmic heating force dominates over the ponderomotive force as the wave–wave coupling mechanism. The beating current at zero frequency produces a significant stabilizing effect on the excitation of short-scale modes by counterbalancing the destabilizing effect of the differential Ohmic heating. The effect of ionospheric inhomogeneity is estimated, showing a tendency to raise the thresholds of the instability. When applied to ionospheric heating experiments, the present theory can explain the excitation of field-aligned plasma lines and ionospheric irregularities with a continuous spectrum ranging from metre-scale to hundreds of metre-scale. Further, the proposed mechanism may become a competitive process to the parametric decay instability and be responsible for the overshoot phenomena of the plasma line enhancement at Arecibo.

The effects of field-aligned ionospheric irregularities on satellite scintillations

The effects of field-aligned ionospheric irregularities on satellite scintillations

The effects of field-aligned ionospheric irregularities on satellite scintillations

Observations of scintillations of radio signals from the satellites BEB and BEC made at Adelaide have been analysed to obtain information about the ionospheric irregularities which cause the scintillations. Observations of the radio diffraction pattern over the ground, made with three spaced receivers, indicate ionospheric irregularities aligned with their longer dimension along the Earth's magnetic field, and with axial ratios in the range 2–20. Observations of increases of scintillation depth when the direction of the radio ray is close to that of the magnetic field show effects in qualitative agreement with theory, but much larger in magnitude than would be expected on the basis of the above values of axial ratio. It is suggested that this result may indicate the presence of a new type of weakly ionized irregularities with very large values of axial ratio. However, further theoretical development appears to be necessary before a completely satisfactory model of such irregularities, consistent with all the observations, can be given.