Ionospheric Processes Research Articles

Ionospheric processes observed with the passive oblique-incidence HF Doppler radar

Urgency. The urgency is caused by the need to continuously monitor with radio instrumentation dynamic processes acting in the ionosphere, which arise due to variations in space weather, the impact of high-energy sources of natural and anthropogenic origin. To meet this challenge, V. N. Karazin National University and Harbin Engineering University specialists has developed a coherent multi-frequency multi-path radio system for obliquely probing the ionosphere. Purpose of Work. The paper illustrates the instrument capability for the study of dynamic processes arising in the ionosphere during a solar terminator, a moderate earthquake, a strong ionospheric storm, and in the cource of a partial solar eclipse. Techniques and Methodology. The system design is base on the software-defined radio (SDR) technology. The system is capable of receiving radio waves in the 10 kHz – 30 MHz band. The versatile computer software permits us to adjust the system for solving various problems. The number of the radio propagation paths and their orientation depends on the problem being solved. The premise upon which this radio system operation is based is measurements of the Doppler shift of the frequency. The autoregressive algorithm provides a 0.02 Hz root-mean-square Doppler line error and 7.5-s time resolution. Having the Doppler spectrum time dependencies for various radio paths archived, time series corresponding to various radio-wave modes undergo further processing. Results. As an example of successful instrument performance, dynamic processes operating in the course of a dusk terminator, the moderate (magnitude 5.9) earthquake on July 7, 2018, the strong ionospheric storm on August 26, 2018, and the partial (0.74 magnitude) solar eclipse over China on August 11, 2018 have been investigated. The ionospheric response to the impact of energy sources of various nature has been detected and investigated; it was accompanied by an increase in the number of rays, Doppler spectrum broadening, aperiodic and quasi-periodic variations in the Doppler shift of the frequency, generation of alternating sign variations in the electron density and wave disturbances having atmospheric gravity wave and infrasound parameters. Conclusions. The radio system located at the Harbin Engineering University campus successfully performs continuous radio monitoring of dynamic processes caused by various energy source in the ionosphere.

The history of Andøya Rocket Range

Abstract. Just 5 years after Sputnik, on 18 August 1962, Norway launched the first sounding rocket from Andøya in northern Norway. The establishment of Andøya Rocket Range (ARR), in the Arctic and right in the middle of the night-time auroral zone, gave the scientists unique opportunities for studies of the complex processes in the auroral ionosphere and upper atmosphere. In close cooperation with the users, ARR gradually developed its technical and scientific infrastructure and is now one of the world's leading observatories in this field. ARR has also established a launch site at Svalbard, and sounding rockets from both ranges can reach far into the Arctic to study the cusp region and the daytime aurora. The ground-based instruments comprise sophisticated radars and lidars as well as passive instruments. ARR also plays an active role in space education. In 2014 Andøya Rocket Range changed its name to Andøya Space Center (ASC; https://www.andoyaspace.no, last access: 23 November 2018). This change reflects the fact that the activities now comprise much more than sounding rocket launches. ASC is an important company both nationally and in the local community of Andenes. ASC now has a staff of 95 and an annual turnover of NOK 150 million.

In situ investigation of neutrals involved in the formation of Titan tholins

The Cassini Mission has greatly improved our understanding of the dynamics and chemical processes occurring in Titan's atmosphere. It has also provided us with more insight into the formation of the aerosols in the upper atmospheric layers.However, the chemical composition and mechanisms leading to their formation were out of reach for the instruments onboard Cassini. In this context, it is deemed necessary to apply and exploit laboratory simulations to better understand the chemical reactivity occurring in the gas phase of Titan-like conditions. In the present work, we report gas phase results obtained from a plasma discharge simulating the chemical processes in Titan's ionosphere. We use the PAMPRE cold dusty plasma experiment with an N2CH4 gaseous mixture under controlled pressure and gas influx. An internal cryogenic trap has been developed to accumulate the gas products during their production and facilitate their detection. The cryogenic trap condenses the gas-phase precursors while they are forming, so that aerosols are no longer observed during the 2 h plasma discharge. We focus mainly on neutral products NH3, HCN, C2H2 and C2H4. The latter are identified and quantified by in situ mass spectrometry and infrared spectroscopy. We present here results from this experiment with mixing ratios of 90–10% and 99–1% N2CH4, covering the range of methane concentrations encountered in Titan's ionosphere. We also detect in situ heavy molecules (C7). In particular, we show the role of ethylene and other volatiles as key solid-phase precursors.

A Comparison of Model‐Based Ionospheric and Ocean Tidal Magnetic Signals With Observatory Data

AbstractObserved tidal geomagnetic field variations are due to a combination of electric currents in the ionosphere, ocean, and their induced counterparts. Using these variations to constrain subsurface electrical conductivity in oceanic regions is a promising frontier; however, properly separating the ionospheric and oceanic tidal contributions of the magnetic field is critical for this. We compare semidiurnal lunar tidal magnetic signals (i.e., the signals due to the M2 tidal mode) estimated from 64 global observatories to physics‐based forward models of the ionospheric M2 magnetic field and the oceanic M2 magnetic field. At ground level, predicted ionospheric M2 amplitudes are strongest in the horizontal components, whereas the predicted oceanic amplitudes are strongest in the vertical direction. There is good agreement between the predicted and estimated M2 phases for the Y component; however, the F and X components experience deviations that may be indicative of unmodeled ionospheric processes or unmodeled coastal effects. Overall, we find that the agreement between the physics‐based model predictions and the observations is very encouraging for electromagnetic sensing applications, especially since the predicted ionospheric vertical component is very weak.

Air Plasma Parameters of the Lower Ionosphere under Normal Conditions

Plasma-chemical processes in the lower ionosphere at altitudes of 90–100 km are studied. The background concentrations of the main charged particles and the temperatures of electrons under normal conditions are determined, based on numerical simulation. The plasma composition of air at these altitudes is analyzed.

An investigation of the ionospheric F region near the EIA crest in India using OI 777.4 and 630.0 nm nightglow observations

Abstract. Simultaneous observations of OI 777.4 and OI 630.0 nm nightglow emissions were carried at a low-latitude station, Allahabad (25.5° N, 81.9° E; geomag. lat. ∼ 16.30° N), located near the crest of the Appleton anomaly in India during September–December 2009. This report attempts to study the F region of ionosphere using airglow-derived parameters. Using an empirical approach put forward by Makela et al. (2001), firstly, we propose a novel technique to calibrate OI 777.4 and 630.0 nm emission intensities using Constellation Observing System for Meteorology, Ionosphere, and Climate/Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3) electron density profiles. Next, the electron density maximum (Nm) and its height (hmF2) of the F layer have been derived from the information of two calibrated intensities. Nocturnal variation of Nm showed the signatures of the retreat of the equatorial ionization anomaly (EIA) and the midnight temperature maximum (MTM) phenomenon that are usually observed in the equatorial and low-latitude ionosphere. Signatures of gravity waves with time periods in the range of 0.7–3.0 h were also seen in Nm and hmF2 variations. Sample Nm and hmF2 maps have also been generated to show the usefulness of this technique in studying ionospheric processes.

Complex network description of the ionosphere

Abstract. Complex networks have emerged as an essential approach of geoscience to generate novel insights into the nature of geophysical systems. To investigate the dynamic processes in the ionosphere, a directed complex network is constructed, based on a probabilistic graph of the vertical total electron content (VTEC) from 2012. The results of the power-law hypothesis test show that both the out-degree and in-degree distribution of the ionospheric network are not scale-free. Thus, the distribution of the interactions in the ionosphere is homogenous. None of the geospatial positions play an eminently important role in the propagation of the dynamic ionospheric processes. The spatial analysis of the ionospheric network shows that the interconnections principally exist between adjacent geographical locations, indicating that the propagation of the dynamic processes primarily depends on the geospatial distance in the ionosphere. Moreover, the joint distribution of the edge distances with respect to longitude and latitude directions shows that the dynamic processes travel further along the longitude than along the latitude in the ionosphere. The analysis of “small-world-ness” indicates that the ionospheric network possesses the small-world property, which can make the ionosphere stable and efficient in the propagation of dynamic processes.

Equatorial secondary cosmic ray observatory to study space weather and terrestrial events

Recently, equatorial secondary cosmic ray observatory has been established at Equatorial Geophysical Research Laboratory (EGRL), Tirunelveli, (Geographic Coordinates: 8.71°N, 77.76°E), to study secondary cosmic rays (SCR) produced due to the interaction of primary cosmic rays with the Earth’s atmosphere. EGRL is a regional center of Indian Institute of Geomagnetism (IIG), located near the equator in the Southern part of India. Two NaI(Tl) scintillation detectors are installed inside the temperature controlled environment. One detector is cylindrical in shape of size 7.62 cm × 7.62 cm and another one is rectangular cuboid of 10.16 cm × 10.16 cm × 40.64 cm size. Besides NaI(Tl) detectors, various other research facilities such as the Geomagnetic observatory, Medium Frequency Radar System, Digital Ionosonde, All-sky airglow imager, Atmospheric electricity laboratory to measure the near-Earth atmospheric electric fields are also available at EGRL. With the accessibility of multi- instrument facilities, the objective is set to understand the relationship between SCR and various atmospheric and ionospheric processes, during space weather and terrestrial events.For gamma-ray spectroscopy, it is important to test the performance of the NaI(Tl) scintillation detectors and to calibrate the gamma-ray spectrum in terms of energy. The present article describes the details of the experimental setup installed near the equator to study cosmic rays, along with the performance testing and calibration of the detectors under various conditions. A systematic shift in the gain is observed with varying temperature of the detector system. It is found that the detector’s response to the variations in the temperature is not just linear or non-linear type, but it depends on the history of the variation, indicating temperature hysteresis effects on NaI detector and PMT system. This signifies the importance of isothermal environment while studying SCR flux using NaI(Tl) detectors, especially for the experiments conducted during daytime such as solar eclipses etc.

On the Nocturnal Downward and Westward Equatorial Ionospheric Plasma Drifts During the 17 March 2015 Geomagnetic Storm

AbstractDuring quiet period, the nocturnal equatorial ionospheric plasma drifts eastward in the zonal direction and downward in the vertical direction. This quiet time drift pattern could be understood through dynamo processes in the nighttime equatorial ionosphere. The present case study reports the nocturnal simultaneous occurrence of the vertically downward and zonally westward plasma drifts over the Indian latitudes during the geomagnetic storm of 17 March 2015. After ~17:00 UT (~22:10 local time), the vertical plasma drift became downward and coincided with the westward zonal drift, a rarely observed feature of low latitude plasma drifts. The vertical drift turned upward after ~18:00 UT, while the zonal drift became eastward. We mainly emphasize here the distinct bipolar type variations of vertical and zonal plasma drifts observed around 18:00 UT. We explain the vertical plasma drift in terms of the competing effects between the storm time prompt penetration and disturbance dynamo electric fields. Whereas, the westward drift is attributed to the storm time local electrodynamical changes mainly through the disturbance dynamo field in addition to the vertical Pedersen current arising from the spatial (longitudinal) gradient of the field aligned Pedersen conductivity.

Diurnal, monthly and seasonal variation of mean winds in the MLT region observed over Kolhapur using MF radar

Medium Frequency (MF) radar located at Kolhapur (16.8°N, 74.2°E) has been upgraded in August 2013. Since then continuous measurements of zonal and meridional winds are obtained covering larger altitudes from the Mesosphere and Lower Thermosphere (MLT) region. Diurnal, monthly and seasonal variation of these mean winds is presented in this study using four years (2013–2017) of observations. The percentage occurrence of radar echoes show maximum between 80 and 105 km. The mean meridional wind shows Annual Oscillation (AO) between 80 and 90 km altitudes with pole-ward motion during December solstice and equatorial motion during June solstice. Quasi-biennial oscillation (QBO) with weaker amplitudes are also observed between 90 and 104 km. Zonal winds show semi-annual oscillation (SAO) with westward winds during equinoxes and eastward winds during solstices between 80 and 90 km. AO with eastward winds during December solstice and westward wind in the June solstice is also observed in the mean zonal wind between 100 and 110 km. These results match well with that reported from other latitudes within Indian region between 80 and 90 km. However, above 90 km the results presented here provide true mean background winds for the first time over Indian low latitude region as the present station is away from equatorial electro-jet and are not contaminated by ionospheric processes. Further, the results presented earlier with an old version of this radar are found contaminated due to unknown reasons and are corrected in the present work. This upgraded MF radar together with other MLT radars in the Indian region forms unique network to investigate the vertical and lateral coupling.

Understanding the global dynamics of the equatorial ionosphere in Africa for space weather capabilities: A science case for AfrequaMARN

The equatorial region of the Earth's ionosphere is one of the most complex ionospheric regions due to its interactions, instabilities, and several unresolved questions regarding its dynamics, electrodynamics, and physical processes. The equatorial ionosphere overall spans three continents with the longest region being that over the African continent. Satellite observations have demonstrated that very large differences exist in the formation of ionospheric irregularities over the African sector compared with other longitudinal sectors. This may be a consequence of the symmetric shape of the magnetic equator over the continent and the lack of variability in latitude. In this paper, we propose a science campaign to equip the African sector of the magnetic equator with ground-based instruments, specifically magnetometers and radars. The network of radars proposed is similar in style and technique to the high-latitude SuperDARN radar network, while the magnetometers will form an array along the equatorial belt. These two proposed space physics instruments will be used to study this region of the equatorial ionosphere over a long interval of time, at least one solar cycle. The deployment of an array of magnetometers (AfrequaMA) and a radar network (AfrequaRN) in the African sector of the magnetic equator is jointly called the Africa Equatorial Magnetometer Array and Radar Network (AfrequaMARN), which will provide simultaneous observations of both electric and magnetic variations over the African sector. We also examine the possible science questions such a magnetometer array and radar network would be able to address, both individually and in conjunction with other space-based and ground-based instrumentation. The proposed projects will clearly improve our understanding of the dynamics of the equatorial ionosphere and our understanding of its role in balancing the large-scale ionospheric current system, and will contribute to our ability to adequately model ionospheric and plasmaspheric densities. It will also enhance our understanding of global ionospheric processes, which will improve the space weather capabilities of the African and international space science communities.

Features of High-Latitude Ionospheric Irregularities Development as Revealed by Ground-Based GPS Observations, Satellite-Borne GPS Observations and Satellite In Situ Measurements over the Territory of Russia during the Geomagnetic Storm on March 17–18, 2015

The dynamic picture of the response of the high- and mid-latitude ionosphere to the strong geomagnetic disturbances on March 17–18, 2015, has been studied with ground-based and satellite observations, mainly, by transionospheric measurements of delays of GPS (Global Positioning System) signals. The advantages of the joint use of ground-based GPS measurements and GPS measurements on board of the Swarm Low-Earth-Orbit satellite mission for monitoring of the appearance of ionospheric irregularities over the territory of Russia are shown for the first time. The results of analysis of ground-based and space-borne GPS observations, as well as satellite, in situ measurements, revealed large-scale ionospheric plasma irregularities observed over the territory of Russia in the latitude range of 50°–85° N during the main phase of the geomagnetic storm. The most intense ionospheric irregularities were detected in the auroral zone and in the region of the main ionospheric trough (MIT). It has been found that sharp changes in the phase of the carrier frequency of the navigation signal from all tracked satellites were recorded at all GPS stations located to the North from 55° MLAT. The development of a deep MIT was related to dynamic processes in the subauroral ionosphere, in particular, with electric fields of the intense subauroral polarization stream. Analysis of the electron and ion density values obtained by instruments on board of the Swarm and DMSP satellites showed that the zone of highly structured auroral ionosphere extended at least to heights of 850–900 km.

Algorithms of ionospheric anomalies detection in “Aurora” system of operational data analysis

Algorithms for ionospheric data processing are presented in the paper. The algorithms are implemented in the real-time mode of ionospheric parameter analysis. They are a component of “Aurora” software system for geophysical data analysis. The algorithms allow us to estimate the state of the ionosphere in the region of Kamchatka Peninsula and to detect ionospheric anomalies. Assessment of the algorithms efficiency has shown that it is possible to use them to detect ionospheric anomalies that may occur on the eve of magnetic storms. The research is supported by the Russian Science Foundation Grant (Project No. 14-11-00194).

Ionospheric parameters as the precursors of disturbed geomagnetic conditions

Geomagnetic storms and substorms are the principal elements of the disturbed Space Weather conditions. The aim of the study was to reveal the ionospheric precursors that can be used to forecast geomagnetic disturbance beginning. To study the ionospheric processes before, during and after magnetic storms and substorms data from Sodankylä Geophysical Observatory was used (geomagnetic coordinates: 64.1oN, 119.2oE). In earlier works the Main Effect (ME) was revealed for substorms. It consists of the following steps: (a) the increase of critical frequency foF2 from its quiet median before and during the substorm growth phase, four-five hours before To moment that is the moment of the expansion phase onset, (b) the foF2 decrease to the level lower than its median just after To and until Te that is the moment of the end of the expansion phase, (c) the issue “a” repeated during the recovery phase (d) two bell-shape spikes in the cutoff frequency values foEs: first spike occurs three hours before To, second spike – during the expansion phase within the interval between To and Te. In the present work it is shown that ME manifestations can be used as precursors of magnetic substorms at high-latitudes (geomagnetic latitudes 50oN–65oN). In particular, the foF2 growth some hours before To can be used asa precursor of substorm development. The first foEs bell-shaped spike also can be used for short-term forecasting, two–three hours in advance of a substorm. Furthermore, the storms between 2008 and 2012 were studied. It was revealed that the similar ME also takes place in the case of magnetic storms but within the different time scale. More specifically, the first ME maximum in foF2 values occurs one-two days before the storm beginning and can be used as its precursor. In addition, the foEs spike takes place approximately ten hours before a storm and also can be used for the prediction of the storm beginning.

Height-dependent sunrise and sunset: Effects and implications of the varying times of occurrence for local ionospheric processes and modelling

It is well established that the sunrise and sunset periods are of particular importance to ionospheric research and modelling because of the rapid changes in the ionospheric plasma density, temperature, and dynamics. In particular, the sharp increase in the ionisation following sunrise results in a quick increase in the ionospheric peak density, NmF2, and a decrease in the peak height, hmF2. Changes in plasma temperature, scale height and transport processes add further complexity which makes it difficult to investigate and model the ionospheric behaviour during this transitional period from night to day. One of the aspects contributing to this difficulty is that not all ionospheric altitudes are exposed to the first sunlight of the day at the same time. During sunrise, the upper part of the ionosphere is illuminated prior to the lower part which is still in the dark. The boundary between sunlit and dark regions moves downwards until it reaches the surface of the Earth, which is commonly taken as the moment of sunrise at certain geographical coordinates. This means that the sunrise at surface level does not occur until after the entire ionosphere has been illuminated. During sunset, the same process happens in reverse order. This paper addresses the issue of these altitude-dependent times of sunrise and sunset and reports on our study of some of the effects on the diurnal variations in the ionospheric characteristics.

MONITOR Ionospheric Network: two case studies on scintillation and electron content variability

Abstract. The ESA MONITOR network is composed of high-frequency-sampling global navigation satellite systems (GNSS) receivers deployed mainly at low and high latitudes to study ionosphere variability and jointly with global GNSS data and ionospheric processing software in support of the GNSS and its satellite-based augmentation systems (SBAS) like the European EGNOS. In a recent phase of the project, the network was merged with the CNES/ASECNA network and new receivers were added to complement the latter in the western African sector. This paper summarizes MONITOR, presenting two case studies on scintillations (using almost 2 years of data measurements). The first case occurred during the major St. Patrick's Day geomagnetic storm in 2015. The second case study was performed in the last phase of the project, which was supported by ESA EGNOS Project Office, when we paid special attention to extreme events that might degrade the system performance of the European EGNOS.

A new methodology for the development of high‐latitude ionospheric climatologies and empirical models

AbstractMany empirical models and climatologies of high‐latitude ionospheric processes, such as convection, have been developed over the last 40 years. One common feature in the development of these models is that measurements from different times are combined and averaged on fixed coordinate grids. This methodology ignores the reality that high‐latitude ionospheric features are organized relative to the location of the ionospheric footprint of the boundary between open and closed geomagnetic field lines (OCB). This boundary is in continual motion, and the polar cap that it encloses is continually expanding and contracting in response to changes in the rates of magnetic reconnection at the Earth's magnetopause and in the magnetotail. As a consequence, models that are developed by combining and averaging data in fixed coordinate grids heavily smooth the variations that occur near the boundary location. Here we propose that the development of future models should consider the location of the OCB in order to more accurately model the variations in this region. We present a methodology which involves identifying the OCB from spacecraft auroral images and then organizing measurements in a grid where the bins are placed relative to the OCB location. We demonstrate the plausibility of this methodology using ionospheric vorticity measurements made by the Super Dual Auroral Radar Network radars and OCB measurements from the IMAGE spacecraft FUV auroral imagers. This demonstration shows that this new methodology results in sharpening and clarifying features of climatological maps near the OCB location. We discuss the potential impact of this methodology on space weather applications.

Multi-frequency GNSS robust carrier tracking for ionospheric scintillation mitigation

Ionospheric scintillation is the physical phenomena affecting radio waves propagating from the space through the ionosphere to earth. The signal distortion induced by scintillation can pose a major threat to some GNSS application. Scintillation is one of the more challenging propagation scenarios, particularly affecting high-precision GNSS receivers which require high quality carrier phase measurements; and safety critical applications which have strict accuracy, availability and integrity requirements. Under ionospheric scintillation conditions, GNSS signals are affected by fast amplitude and phase variations, which can compromise the receiver synchronization. To take into account the underlying correlation among different frequency bands, we propose a new multivariate autoregressive model (MAR) for the multi-frequency ionospheric scintillation process. Multi-frequency GNSS observations and the scintillation MAR are modeled in state-space, allowing independent tracking of both line-of-sight phase variations and complex gain scintillation components. The resulting joint synchronization and scintillation mitigation problem is solved using a robust nonlinear Kalman filter, validated using real multi-frequency scintillation data with encouraging results.

Dynamic and Thermal Processes in the Mid-Latitude Ionosphere over Kharkov, Ukraine (49.6° N, 36.3° E), During the 13–15 November 2012 Magnetic Storm: Calculation Results

Calculation results of the variations of dynamic and thermal process parameters in geospace plasma during the 13–15 November 2012, magnetic storm (MS) over Kharkov are presented. The calculations were based on experimental data obtained on the Kharkov incoherent scatter radar, single in the European mid-latitudes. Calculations showed that during the MS there took place an increase, by modulus, of the values of vertical component of transfer velocity, due to ambipolar diffusion, up to a factor of 1.4–2.1. During the MS there took place a decrease of the values of energy input to the electron gas by about 20–35%. During the main phase of MS, the heat flux density transferred by electrons increased up to a factor of 2–2.5. Results of estimates of the zonal component electric field value Ey are presented. During the MS the value of Ey was −9.5 mV/m. The vertical component of plasma velocity due to electromagnetic drift vEB has been calculated.

Identification of the different magnetic field contributions during a geomagnetic storm in magnetospheric and ground observations

Abstract. We used the empirical mode decomposition (EMD) to investigate the time variation of the magnetospheric and ground-based observations of the Earth's magnetic field during both quiet and disturbed periods. We found two timescale variations in magnetospheric data which are associated with different magnetospheric current systems and the characteristic diurnal orbital variation, respectively. On the ground we identified three timescale variations related to the solar-wind–magnetosphere high-frequency interactions, the ionospheric processes, and the internal dynamics of the magnetosphere. This approach is able to identify the different physical processes involved in solar-wind–magnetosphere–ionosphere coupling. In addition, the large-timescale contribution can be used as a local index for the identification of the intensity of a geomagnetic storm on the ground.