Ionospheric Irregularities Research Articles

A Small Peak in the Swarm‐LP Plasma Density Data at the Dayside Dip Equator

AbstractIn this paper, we statistically investigate an artifact in Langmuir Probe (LP) observations of Swarm satellites. A small peak of electron density (Ne) is frequently found in the Swarm data around the dayside dip equator. On the contrary, they appear in neither the Total Electron Content data of the Swarm/Global Positioning System Receivers nor COSMIC‐2 in‐situ measurements at similar altitudes but with low orbit inclination. Arguably, this peak does not represent natural ionospheric irregularities but is likely to result from artifacts. The phenomena are found regardless of the season, solar activity, and the velocity direction of the satellite (ascending and descending). They predominantly occur when the magnetic declination is close to zero, that is, when the Swarm ram direction and the Earth's magnetic field are aligned under sunlight. Hence, we attribute the phenomenon to intensified secondary electrons escape when the geomagnetic field lines are normal to conducting surfaces that emit secondary electrons. Since the magnitude of the artifact is only a few percent of the large‐scale background, it does not have a serious impact on the value of the Swarm/LP data in scientific research. Nevertheless, future efforts to determine the exact cause of the artifacts will contribute to improving the reliability and quality of plasma density and temperature measured by Swarm/LP.

Ionospheric Turbulence: A Challenge for GPS Loss of Lock Understanding

AbstractIonospheric irregularities may affect electromagnetic signals propagating through the ionosphere and consequently contribute to the malfunctioning of the Global Navigation Satellite Systems hindering their accuracy and reliability. In this study, we use data recorded on board two of the three satellites of the Swarm constellation (namely, Swarm A and Swarm B) from 15 July 2014 to 31 December 2021 to assess the possible dependence of the Global Positioning System (GPS) signals loss of lock on the presence of a specific kind of ionospheric irregularities. To accomplish this task we study the scaling features of the electron density fluctuations through the structure function analysis simultaneously to the occurrence of loss of lock events through measurements recorded by the Langmuir probes and the precise orbit determination antennas on board Swarm A and Swarm B satellites. We find that the plasma density irregularities in a turbulent state characterized by intermittent structures and extremely high values of the Rate Of change of electron Density Index can lead to GPS loss of lock events. This is always true at mid and high latitudes, especially inside the auroral oval. In the equatorial belt, this happens in at least 75% of identified GPS loss of lock events that basically coincide with the occurrence of plasma bubbles.

Interferometric Study of Ionospheric Plasma Irregularities in Regions of Phase Scintillations and HF Backscatter.

We investigate the nature of small‐scale irregularities observed in the cusp by the Twin Rockets to Investigate Cusp Electrodynamics‐2 (TRICE‐2) in regions of enhanced phase scintillations and high‐frequency coherent radar backscatter. We take advantage of the fact that the irregularities were detected by spatially separated probes, and present an interferometric analysis of both the observed electron density and electric field fluctuations. We provide evidence that fluctuations spanning a few decameters to about a meter have low phase velocity in the plasma reference frame and are nondispersive, confirming that decameter‐scale irregularities follow the E × B velocity. Furthermore, we show that these “spatial” structures are intermittent and prominent outside of regions with strongest precipitation. The observations are then discussed in the context of possible mechanisms for irregularity creation.

On using a double-thin-shell approach and TEC perturbation component to sound night-time mid-latitude E–F coupling

Observations and theoretical analysis on the night-time mid-latitude ionospheric irregularities support the postulation of frequently coupled E and F regions. In this paper, we attempt at asserting this notion while using total electron content (TEC) measurements. The TECs are from a dense GNSS receiver network over Japan with more than 1200 stations and a mean distance of ~ 25 km between receivers; thus, ideal for analyzing small-scale perturbations in ionospheric electron density. We take an ansatz that mid-latitude night-time plasma instabilities concentrate at E and F layers. Then the integrated three-dimensional density perturbations are parameterized with a double-thin-shell model. At each shell, perturbation components are assumed identical at any point within a given grid block. Two days with events of night-time medium-scale traveling ionospheric disturbances (MSTIDs), but with different amplitudes, were investigated. Results show that the newly developed technique can infer several horizontal characteristics on E–F coupled instabilities; the coexistence of northwest–southeast (NW–SE) aligned irregular structures in E and F regions is evident. Both E- and F-region irregularities share similar propagation parameters, a shred of clear evidence of strong coupling.Graphical

Virtual Height Characteristics of Ionospheric and Ground Scatter Observed by Mid‐Latitude SuperDARN HF Radars

AbstractPropagation of high‐frequency (HF) radio signals is strongly dependent on the ionospheric electron density structure along a communications link. The ground‐based, HF space weather radars of the Super Dual Auroral Radar Network (SuperDARN) utilize the ionospheric refraction of transmitted signals to monitor the global circulation of E‐ and F‐region plasma irregularities. Previous studies have assessed the propagation characteristics of backscatter echoes from ionospheric irregularities in the auroral and polar regions of the Earth's ionosphere. By default, the geographic location of these echoes are found using empirical models which estimate the virtual backscattering height from the measured range along the radar signal path. However, the performance of these virtual height models has not yet been evaluated for mid‐latitude SuperDARN radar observations or for ground scatter (GS) propagation modes. In this study, we derive a virtual height model suitable for mid‐latitude SuperDARN observations using 5 years of data from the Christmas Valley East and West radars. This empirical model can be applied to both ionospheric and GS observations and provides an improved estimate of the ground range to the backscatter location compared to existing high‐latitude virtual height models. We also identify a region of overlapping half‐hop F‐region ionospheric scatter and one‐hop E‐region GS where the measured radar parameters (e.g., velocity, spectral width, elevation angle) are insufficient to discriminate between the two scatter types. Further studies are required to determine whether these backscatter echoes of ambiguous origin are observed by other mid‐latitude SuperDARN radars and their potential impact on scatter classification schemes.

The Occurrence Climatology of Equatorial Plasma Bubbles: A Review

Electron density irregularities in the equatorial ionosphere at night are understood in terms of plasma bubbles, which are produced by the transport of low-density plasma from the bottomside of the F region to the topside. Equatorial plasma bubbles (EPBs) have been detected by various techniques on the ground and from space. One of the distinguishing characteristics of EPBs identified from long-term observations is the systematic seasonal and longitudinal variation of the EPB activity. Several hypotheses have been developed to explain the systematic EPB behavior, and now we have good knowledge about the key factors that determine the behavior. However, gaps in our understanding of the EPB climatology still remain primarily because we do not yet have the capability to observe seed perturbations and their growth simultaneously and globally. This paper reviews the occurrence climatology of EPBs identified from observations and the current understanding of its driving mechanisms.

Interaction Between Equatorial to Low‐Latitude Postmidnight F‐Region Irregularities and LSTIDs in China During Geomagnetic Disturbances Based on Ground‐Based Instruments

AbstractIn this paper, the interaction between equatorial to low‐latitude postmidnight ionospheric irregularities and large‐scale traveling ionospheric disturbances (LSTIDs) on 14 December 2015 during strong geomagnetic disturbances in China is studied by using multiple ground‐based observations. Postmidnight irregularities initiated near the magnetic equator and extended northward to higher latitudes (∼28°N) until the local early morning period (∼05 LT), which is unusual in the Northern Hemisphere winter. Multibeam observations by the very high frequency coherent scatter radar at Fuke (19.5°N, 109.1°E; dip latitude 14.4°N), Hainan Island, China, showed that the meter‐scale field‐aligned irregularities were still in the evolutionary phase during the postmidnight period (∼04 LT) instead of the fossil structures that must already be in their decay phase. Meanwhile, the emergence of the postmidnight ionospheric irregularities was accompanied by the passage of LSTIDs, as revealed by total electron content measurements. Southward and northward LSTIDs, with velocities of ∼550–570 m/s and periods of ∼80–100 min, that originated from opposite hemispheres met at ∼27°–28°N, and the LSTIDs might produce localized perturbation during their passage to initiate the instability for the postmidnight irregularity development. The height of the ionospheric F‐layer measured by the collocated Digisonde at Fuke was suggested to be modulated by the overshielding penetration electric field and storm‐related atmospheric gravity waves (AGWs). This interesting case gives insight into the important role of storm‐related AGWs in providing seeding sources for plasma bubble development and reveals unique characteristics of coupling between LSTIDs and plasma bubbles during the postmidnight sector.

Altitude Distribution of Large and Small‐Scale Equatorial Ionospheric Irregularities Sampled From an Elliptical Low‐Earth Orbit

AbstractWe provide insight into the vertical distribution of multi‐scale scintillation‐inducing irregularities in the low‐latitude ionosphere. In four sets of novel experiments, we sampled altitudes from 330 to 1,280 km in the 18–24 magnetic local time (MLT) sector using the Swarm Echo GPS Attitude, Positioning, and Profiling Experiment occultation receiver (GAP‐O) GPS receiver with its antenna oriented toward zenith. In order to identify multi‐scale irregularities both above and at the satellite's position, we utilize high‐sample‐rate GAP‐O amplitude and phase measurements along with a measurement of net current on the surface of the imaging and rapid‐scanning ion mass spectrometer sensor on board, which serves as a proxy for density variations. By calculating the rate of change of total electron content index using two sets of GPS parameter choices, we are able to sample irregularities as small as 160 m, which is comparable to or smaller than the Fresnel scale responsible for scintillation‐inducing irregularities. During one campaign, we find that amplitude scintillations on the GPS signal coincide with strong in‐situ small‐scale density irregularities in 32% of cases, indicative of a broad irregularity region extending from the satellite's position to hundreds of kilometers above. Also, we show that large‐scale ionospheric disturbances (larger than 80 km) occur predominantly below 500 km, and down to the 330 km perigee of Swarm Echo in the 18–21 MLT sector. In contrast, small‐scale variations of total electron content are detected at all MLTs between 18 MLT and magnetic midnight and at all altitudes sampled in this experiment. However, they are more frequent in the 22–24 MLT range.

Generalized Rayleigh‐Taylor Instability: Ion Inertia, Acceleration Forces, and E Region Drivers

AbstractA linear theory of the generalized Rayleigh‐Taylor instability (GRTI) is derived which includes ion inertia and acceleration forces, as well as E region drivers: the zonal neutral wind and plasma drift. This is in contrast to the F region drivers (aside from gravity): the meridional neutral wind and the meridional/vertical plasma drifts. Both a local theory and a flux‐tube integrated theory are presented with application to the onset of ionosphere irregularities associated with equatorial spread F. Inertia and acceleration forces do not affect the growth rate of the GRTI for nominal ionospheric conditions, but the E region zonal drifts can significantly increase or decrease the growth rate of the GRTI in the equatorial and mid‐latitude ionosphere depending on their direction.

Ionospheric Nighttime F‐Region Irregularities During Geomagnetically Quiet Conditions as Observed With 205 MHz VHF Radar at an Equatorial Trough Station, Cochin

AbstractThe VHF radar operating at 205 MHz frequency installed at the Cochin University of Science and Technology (CUSAT) has been configured to probe the nighttime ionospheric field‐aligned irregularities (FAIs) over the near‐equatorial site at Cochin, India during the solar minimum periods. Even though the study period includes the minimum of the 24th and 25th solar cycles, a total of 40 nighttime irregularity events were observed at F‐region heights (150–500 km). Bottom‐type and bottom‐side irregularities were observed in this period, but no large‐scale topside ones at F‐region heights. The nighttime irregularities were most commonly observed at average heights of 200–250 km, accounting for 50% of the total events, and 27.5% of the irregularities preferentially occurred after sunset between 19 and 20 LT. While long‐duration irregularity events were not prominent during this period, irregularities that lasted for less than 50 min were predominant. To check the capability of the 205 MHz VHF radar in observing FAIs, the radar observations were compared with the European Space Agency's ionospheric observation data from the Swarm B satellite. Several derived parameters from the Swarm data set such as electron density (Ne), background Ne (bNe), electron temperature (Te), rate of electron density (ROD), index of ROD (RODI), median vertical total electron content (mVTEC), absolute VTEC (aVTEC), rate of TEC (ROT), ROTI, Bubble Index, and Bubble Probability were utilized for characterizing the ionospheric irregularities. The observation from the Swarm B satellite agrees well with that obtained from the VHF radar.

Instantaneous amplitude of low-latitude ionospheric irregularities probed by ROCSAT-1, DEMETER, and FORMOSAT-7/COSMIC-2

The occurrence probability of plasma irregularities has long been used to quantify that of ionospheric scintillations. We use the Hilbert-Huang transform to examine the occurrence probability and the instantaneous total amplitude of plasma irregularities in the low-latitude nighttime ionosphere observed by the low-inclination satellites, ROCSAT-1 during 1999–2004 and FORMOSAT-7/COSMIC-2 (F7C2) in 2020, as well as a high-inclination satellite, DEMETER, during 2006–2010. Generally, the longitudinal distribution of the occurrence probability is similar to that of the total amplitude, except that the probability of ion density irregularity observed by F7C2 and DEMETER yields nonphysical anomalous enhancements over the South American sector during May–August of 2007–2010 and 2020, respectively. S4 scintillations observed by F7C2 show that the anomalous enhancement results from the low ambient density in calculating the occurrence probability during the low solar activity year of 2020. We suggest the instantaneous total amplitude as a better indicator for describing ionospheric plasma irregularities.

IGS ROTI Maps: Current Status and Its Extension towards Equatorial Region and Southern Hemisphere

The International GNSS Service (IGS) diurnal ROTI maps ionospheric product was developed to characterize ionospheric irregularities occurrence over the Northern hemisphere and has been available for the community since 2014. Currently, the diurnal ROTI maps database hosted by NASA CDDIS covers the period from 2010 to now. Here, we report the ROTI maps product operational status and important changes in the product availability and access. Apart from actual ROTI maps product production, we work on the extension of ROTI maps to cover not only the Northern hemisphere but also the area of the Southern hemisphere and equatorial/low latitude region. Such extended ROTI maps are important for ionospheric irregularities climatology research and ionospheric responses to space weather. We present recent development toward the new ROTI maps product and the updated data format. To evaluate extended the ROTI maps performance, we analyzed the ability to represent key features of ionospheric irregularity occurrence over the Southern hemisphere and low latitudes. For auroral and midlatitudes, we present the cross-comparison of ROTI-derived irregularities patterns over the Northern and Southern hemispheres. For low latitudes, we examined the sensitivity of the resulted ROTI maps to detect plasma irregularities associated with equatorial plasma bubbles development for low, middle, and high solar activity periods.

Solar Cycle and Seasonal Variability of Martian Ionospheric Irregularities from Mars Atmosphere and Volatile Evolution Observations

Spacecraft observations around Mars show that ionospheric irregularities occur frequently in the Martian ionosphere. In this study, Mars Atmosphere and Volatile Evolution data (the region is below ∼200 km) during 2015 January to 2021 March were used to revisit the statistical characteristics of ionospheric irregularities and the comparison of irregularities in Martian years with higher or lower solar activity phase of solar cycle. Results show that the characteristics of the irregularities with a larger length scale associated with the magnetic field and solar zenith angle are similar to the previous studies. Moreover, our results show that the occurrence rate of irregularities exhibits dawn and dusk asymmetry, and the occurrence rate at dusk is higher than that at dawn. In addition, results demonstrate that the occurrence rate of irregularities is higher in Martian years with higher solar activity than Martian years with lower solar activity, which means that the solar cycle might play an important role in the formation of irregularity events. Further studies show that the solar zenith angle (SZA) and altitude at the maximum occurrence rate depend on the level of solar activity. The SZA and altitude of the maximum occurrence rate are smaller in the Martian year with higher solar activity than the lower. We also found that the rate of events is lower during the day than the terminator in the ionospheric dynamo region. By contrast, in the regions where both electrons and ions are magnetized, events have a higher rate during the day than the terminator. Furthermore, the seasonal variation of the irregularity events was also presented in this study. Results show that the occurrence rate in the dynamo region with 80° < SZA < 150° in MY34 and MY35 show an incremental trend from spring to winter, but this trend is not obvious in MY33.

Ionospheric Signatures During G2, G3 and G4 Storms in Mid‐Latitude

AbstractThis paper presents a wavelet‐based analysis of ionospheric irregularities induced by three different geomagnetic storms of varying strength and interplanetary origin over three mid‐latitudes stations, viz. Moscow, Fairford, and Rome. We observed the highest decrease in ionospheric variables (foF2, total electron content (TEC), and NmF2) during the negative phase of the G4 storm. Interestingly, hmF2 exhibits the opposite trend in terms of variation. The maximum ionization height (hmF2) for the G4 event is 500 km (during the main phase) and 150 km (during the recovery phase). Within 2–3 hr of the G4 event, the value of hmF2 is found to decline by 70%. The largest reduction (80%) in critical frequency (foF2) is observed during the negative phase of this event, which is also confirmed by the continuous wavelet transform results. During the negative phase, we observed noticeable power shifts in the signal of the ionospheric parameters toward the lower Fourier period band. During the G4 storm—Particularly during the negative phase—The lowest power linked with the ionospheric parameter's signal was discovered. Additionally, we used detrended cross‐correlation analysis to investigate the correlation and time lag between geomagnetic indices (Symmetric H‐component (SYM‐H) &amp; auroral electrojet) and ionospheric parameters (foF2, NmF2, hmF2 &amp; TEC). The significant association between SYM‐H and ionospheric parameters suggests that the magnetosphere‐ionosphere interaction produces intense electric field disturbances and winds in the mid‐latitudes, resulting in the perturbation of hmF2, foF2, TEC, and NmF2.

A contribution to real-time space weather monitoring based on scintillation observations and IoT

The ionosphere is a region of plasma in altitudes extending up to 1000 km. Over low latitudes, steep depletions in the ionospheric density, commonly referred to as equatorial plasma bubbles, are generated after sunset as a result of plasma instabilities. Large variations in the index of refraction associated with these plasma bubbles affect the amplitude and phase of trans-ionopsheric radio signals used for communication, remote sensing and navigation, causing the so-called ionospheric scintillation. Therefore, better understanding of the ionospheric conditions is important for various applications. Unfortunately, real-time ionospheric monitoring systems have been limited, in most cases, by the cost and distribution of adequate sensors. In this work, we present and discuss an internet-of-things (IoT) system composed of a mobile application that acquires data from a network of low-cost scintillation monitors (ScintPi) capable of detecting the occurrence of ionospheric irregularities. The system, referred to as Ionik2, provides real-time information about ionospheric scintillation. A mobile app named ScintApp provides time-series of scintillation indices (S4) and spatial distribution of scintillation using Google Maps. ScintApp also has post-processing capability allowing database queries. Finally, ScintApp is based on a native mobile smartphone application for Android operating systems. Here, we present initial results obtained with an interim prototype distribution of ScintPi monitors. We compare the information provided by ScintApp with observations made by independent instrumentation that have been widely used for ionospheric studies but do not provide real-time data. The results proof the concept of a system capable of providing realt-time information about scintillation events associated with equatorial plasma bubbles.

The role of global thermospheric zonal winds on the variability of equatorial ionospheric irregularities

We analyze the role of thermospheric winds on the variability of ionospheric plasma density irregularities for solar maximum periods using ionospheric plasma density profiles from the three Swarm satellites and zonal wind data from the Horizontal Wind Model 14 (HWM14). The results show that the plasma density irregularities are strongest during post-midnight hours compared to pre-midnight hours in the African – American longitude sector and this is associated with an enhancement in eastward zonal wind after midnight. In addition, the occurrence of plasma irregularities are observed to show a westward shift. The zonal wind reversal from westward to eastward during post-sunset hours is found to be very important for the generation and variability of plasma irregularities. In the African – American longitudinal sector, where plasma irregularities are the most intense, the eastward wind is strongest in December solstice than for the other seasons. Moreover, plasma irregularity during the December solstice is comparable to the Rayleigh-Taylor Instability mechanism (RTI) favored equinox seasons. But, plasma irregularities are weakest in the June solstice where the zonal eastward wind over geomagnetic equatorial region is weakest as compared to the other seasons. Zonal wind reversal from westward to eastward around post-sunset hours occurred early for seasons with stronger ionospheric irregularity activity whereas the reversal is delayed for the season with weakest ionospheric irregularity activity in the African – American sector. Our results are confirmations of the theoretical prediction on the role of eastward zonal wind in plasma instability growth rate by Kudeki et al. (2007).

Climatology of ionospheric amplitude scintillation on GNSS signals at south American sector during solar cycle 24

Scintillations are caused by ionospheric irregularities and can affect the propagation of trans-ionospheric radio signals. One way to understand and predict the impact of such irregularities on Global Navigation Satellite System (GNSS) signals is through the spatial/temporal characterization of the scintillation's climatology during different phases of a solar cycle covering different latitudes and longitudes. This characterization is performed using amplitude scintillation index S4, during the full solar cycle 24, in the South American (SA) sector. The investigation considers the diurnal, daily, and seasonal variation of S4 index for climatological purpose, and the goal of this study is to investigate the scintillations covering a large spatial scale during the full solar cycle 24. The characterization shows a latitudinal asymmetry, whereas at the south, the scintillations were more frequent and their peak was more distant from the magnetic equator, which can be attributed by the South Atlantic Magnetic Anomaly (SAMA), and/or by the transequatorial meridional neutral winds. It also shows a longitudinal asymmetry, where the scintillations at the eastern sector occurred between November and February, while at the western sector, they occurred during the months of October, November, February and March, which can be attributed to the difference between the magnetic and geographic equators. The occurrence of scintillations during two distinct geomagnetic storms with similar storm time in the SA sector is also presented.

Ionospheric Plasma IRregularities - IPIR - Data Product Based on Data From the Swarm Satellites.

Ionospheric plasma irregularities can be successfully studied with the Swarm satellites. Parameters derived from the in‐situ plasma measurements and from the topside ionosphere total electron content provide a comprehensive dataset for characterizing plasma structuring along the orbits of the Swarm satellites. The Ionospheric Plasma IRregularities (IPIR) data product summarizes these parameters and allows for systematic studies of ionospheric irregularities. IPIR has already been used in investigations of structuring and variability of ionospheric plasma. This report provides a detailed description of algorithms behind the IPIR data product and demonstrates its use for ionospheric studies.

Ionospheric Response During the Tropical Cyclone Debbie Passing Over Eastern Australia in 2017

AbstractThe ionospheric morphology responses to tropical cyclone passing over eastern Australia, named as Debbie in 2017, is investigated using Global Positioning System (GPS) Slant Total Electron Content (STEC), and ionospheric characteristics by ionosonde. Based on the data analysis in this study, some significant morphological characteristics of ionospheric responses to tropical cyclone Debbie are identified as follows. As the GPS satellites PRN05 and PRN20 observed on Townsville GPS station were passing near to the cyclone Debbie center at landfall time, their STEC values are obviously increased. The stronger enhancement of f0F1 and f0F2 were also observed by ionosonde at Townsville on 28th March, when the distance between Townsville and the center of tropical cyclone Debbie was shorter. Regarding the coupling mechanism between the ionospheric disturbance and the tropical cyclone, it is supposed that the electric field perturbations due to turbulent top movement from tropical cyclones might generate ionospheric irregularity and disturbance.

Design of Meteor and Ionospheric Irregularity Observation System and First Results

AbstractThe Meteor and ionospheric Irregularity Observation System (MIOS), which consists of multi‐station optical subsystem at Ledong (18.4°N, 109°E) and Sanya (18.3°N, 109.6°E), and radar subsystem including a 38.9 MHz all‐sky interferometric radar and a 47.5 MHz coherent phased array radar at Ledong, has been in full operational since December 2021. This paper describes the system design and first results of meteor plasma density irregularities and corresponding meteoroids. The MIOS optical subsystem consists of a few tens of video cameras for observing optical meteor trail and spectrum. The MIOS phased array is composed of 135 Yagi antennas, arranged in sword‐like grid and grouped into 15 identical subarrays, with distances separated by 2–19.5 times the wavelength for unambiguous interferometry measurements. The phased array can form narrow and wide beams, with half power width of 8° and 24° in azimuth, respectively, allowing narrow‐beam pulse‐to‐pulse steering and wide‐beam multi‐baseline imaging observations in the east‐west direction. Observational results show that the MIOS is capable of unambiguously locating various meteor echoes, that is, head, specular and non‐specular echoes, revealing the structural evolution of field‐aligned and non‐field‐aligned irregularity, and of determining the properties of meteoroids producing/not producing irregularities. Cases of bright meteors producing non‐field‐aligned irregularities and not producing field‐aligned irregularities respectively are presented, and possible factors affecting the generation of meteor trail irregularities are discussed based on current understanding. It is expected that the MIOS will provide an important tool to study the generation and evolution of various meteor trail irregularities and the properties of the corresponding meteoroids.