Plasma Irregularities Research Articles

Multi-Instrumental Observations of Midlatitude Plasma Irregularities over Eastern Asia during a Moderate Magnetic Storm on 16 July 2003

This study presents the observations of midlatitude plasma irregularities over Eastern Asia during a moderate magnetic storm on 16 July 2003. Multi-instrumental observations, including the ground-based ionosondes, the GNSS networks, and the CHAMP and ROCSAT-1 satellites, were utilized to investigate the occurrence and characteristics of midlatitude plasma irregularities. The midlatitude strong spread F (SSF) mainly occurred in the midnight–morning sector as observed by ionosondes over Japan during this storm. SSF was related to plasma depletions, which is also recorded by GNSS network in the form of the enhancement of the rate of total electron content (TEC) change index (ROTI). The possible mechanism for the generation of SSF is that the enhanced eastward electric fields, associated with the prompt penetration electric fields and disturbance dynamo electric fields, cause the uplift and latitudinal extension of equatorial plasma bubbles (EPBs) to generate the observed midlatitude SSF further. Meanwhile, plasma density increased significantly under the influence of this storm. In addition, other common type of spread F, frequency spread F (FSF), was observed over Japan on the non-storm day and/or at high latitude station WK545, which seems to be closely related to the coupling of medium-scale traveling ionospheric disturbances (MSTIDs) and sporadic E (Es) layer. The above results indicate that various types of midlatitude spread F can be produced by different physical mechanisms. It is found that SSF can significantly affect the performance of radio wave propagation compared with FSF. Our results show that space weather events have a significant influence on the day-to-day variability of the occurrence and characteristics of ionospheric F-region irregularities at midlatitudes.

An Algorithm to Separate Ionospheric Turbulence Radar Echoes From Those of Meteor Trails in Large Data Sets

AbstractCoherent scatter echoes from disintegrating meteors and from the unstable ionospheric E‐region can overlap considerably between 90 and 110 km altitudes. As the physical origin of plasma irregularities produced by meteor trails differs starkly from that of E‐region auroral irregularities, this has consequences for winds as well as electrodynamic studies, thereby introducing a need to distinguish between the two types of echoes. To that goal, we have developed a novel separation algorithm to automatically sort through arbitrarily large data sets in the region of overlap. This proves very useful when the 3D location of echoes is available. The algorithm uses a definition of crowding, or clustering, in both time and space and has been developed and tested with a comprehensive data set obtained from the recently built Canadian icebear 3D radar. We discuss the characteristics belonging to the two classes of echoes, and present statistical results about the location of each type of echo as a function of conditions. Our proposed algorithm can be applied to any coherent scatter echo data with high resolution 3D location information.

The role of particle precipitation on plasma structuring at different altitudes by in-situ measurements

The plasma in the cusp ionosphere is subject to particle precipitation, which is important for the development of large-scale irregularities in the plasma density. These irregularities can be broken down into smaller scales which have been linked to strong scintillations in the Global Navigation Satellite System (GNSS) signals. We present power spectra for the plasma density irregularities in the cusp ionosphere for regions with and without auroral particle precipitation based on in-situ measurements from the Twin Rockets to Investigate Cusp Electrodynamics-2 (TRICE-2) mission, consisting of two sounding rockets flying simultaneously at different altitudes. The electron density measurements taken from the multi-needle Langmuir probe system (m-NLP) were analyzed for the whole flight duration for both rockets. Due to their high sampling rates, the probes allow for a study of plasma irregularities down to kinetic scales. A steepening of the slope in the power spectra may indicate two regimes, a frequency interval with a shallow slope, where fluid-like processes are dominating, and an interval with a steeper slope which can be addressed with kinetic theory. The steepening occurs at frequencies between 20 Hz and 100 Hz with a median similar to the oxygen gyrofrequency. Additionally, the occurrence of double slopes increases where precipitation starts and throughout the rest of the flight. In addition, strong electron density fluctuations were found in regions poleward of the cusp, thus in regions immediately after precipitation. Furthermore, by investigating the integrated power of the fluctuations within different frequency ranges, we show that at low frequencies (10–100 Hz), the power is pronounced more evenly while the rocket encounters particle precipitation, while at high frequencies (100–1000 Hz) fluctuations essentially coincide with the passing through a flow channel.

Incoherent Scattering of a Bessel Vortex Electromagnetic Beam From a Nonmagnetized Plasma

Starting from the description of plane wave angular spectrum superposition of a Bessel vortex beam, with the aid of Thomson scattering theory of a Bessel vortex electromagnetic beam (BVEB) by a low-velocity election, the incoherent scattering power spectra of a BVEB by a non-magnetized plasma is investigated in this paper. The incoherent scattering power spectrum for a BVEB incidence is defined for the backscattered case, and the expression of the scattered power spectral density function is derived. The proposed method is verified in the physical sense by comparing the profiles of distribution parameter of scattered power and the magnitude of average Poynting vector of the incident beam. The effects of the beam parameters (topological charge and half-cone angle) on the scattered power spectral density function are analyzed for the plasmas with Maxwellian velocity distribution. Furtherly, the expression of the scattered power spectral density function is extended to the case of macroscopic moving plasmas. Taking plasma vortices as an example, the results indicate that the direction of the frequency shift of the scattered power spectral density function due to the rotational Doppler effect of the vortex beam is related to angular velocity of the plasma vortex. Additionally, as the topological charge increases, the magnitude of the frequency shifts also increases. Our proposed method provides a theoretical basis for exploring the feasibility of using vortex beams with single or multi orbital angular momentum (OAM) modes in the identifying and inverting parameters of plasma irregularities in ionospheric plasma or laboratory plasma environments.

Ionospheric scintillation characteristics from GPS observations over Malaysian region after the 2011 Valentine’s day solar flare

Abstract Ionospheric scintillations due to plasma irregularities can severely affect the modern dynamic and technological systems whose operations rely on satellite-based navigation systems. We investigate the occurrence of ionospheric scintillation in the equatorial and low latitude region over Malaysia after the 2011 Valentine’s Day solar flare. A network of three Global Ionospheric Scintillation and Total Electron Content Monitor (GISTM) GSV4004B receivers with increasing latitudes from the magnetic equator were used to monitor ionospheric TEC, rate of change of TEC index (ROTI), and amplitude (S4) as well as phase (σ φ) scintillation indices. The results show a simultaneous sudden rise in S4 and σ φ along with a significant depletion of TEC at all three locations. However, the largest enhancement of scintillation indices accompanying a substantial TEC depletion is observed at the farthest low latitude station (UNIMAS) from the equator with values around 0.5, 0.3 rad, and 1 TECU, respectively. The corresponding values at the near-equatorial station (Langkawi; 0.4, 0.2 rad, and 3 TECU) and intermediate station (UKM; 0.45, 0.3 rad, and 5 TECU) are examined along with ROTI variations, confirming the simultaneous occurrence of kilometer-scale and sub kilometer scale irregularities during 17 and 18 February 2011. The radiation effects of the solar flare on the ionosphere were prominently recognized at the local nighttime hours (around 14:00 to 17:00 UT) coinciding with the equatorial prereversal enhancement (PRE) time to seed the equatorial plasma bubbles (EPBs) enhancement that resulted in ionospheric irregularities over the low latitudes. The significant TEC depletion seen in the signals from selected GPS satellites (PRNs 11, 19, 23, and 32) suggests plausible degradation in the performance of GPS-based services over the Malaysian region. The study provides an effective understanding of the post-flare ionospheric irregularities during an episode of minor geomagnetic storm period and aligns with the efforts for mitigating the scintillation effects in space-based radio services over low latitudes.

Electron density fluctuations from Swarm as a proxy for ground-based scintillation data: A statistical perspective

The Swarm satellite mission has been used for numerous studies of the ionosphere. Here we use a global product, based on electron density measurements from Swarm that characterises ionospheric variability. The IPIR (Ionospheric Plasma IRregularities product) provides characteristics of plasma irregularities in terms of their amplitudes, gradients and spatial scales and assigns them to geomagnetic regions. Ionospheric irregularities and fluctuations are often the cause of errors in position, navigation, and timing (PNT) based on the Global Navigation Satellite Systems (GNSS), in which signals pass through the ionosphere. The IPIR dataset also provides an indication, in the form of a numerical value index (IPIR index), of the severity of irregularities affecting the integrity of trans-ionospheric radio signals and hence, the accuracy of GNSS positioning. We analysed datasets from Swarm A and ground-based scintillation receivers. Time intervals (when Swarm A passes over the field of view of the ground-based GPS receiver) are compared to ground-based scintillation data, collecting an azimuthal selection of the GNSS data relevant to the Swarm satellite overpass. We provide validations of the IPIR product against the ground-based measurements from 23 ground-based receivers, focusing on GPS TEC and scintillation data in low-latitude, auroral and polar regions, and in different longitudinal sectors. We have determined the median, mean, maximum and standard deviation of the parameter values for both datasets and each conjunction point. We found a weak correlation of the intensity of both phase and amplitude scintillation with the IPIR index.

Relationship between geomagnetic storms and occurrence of ionospheric irregularities in the west sector of Africa during the peak of the 24th solar cycle

The study of ionospheric irregularities is important since many technological systems might be influenced by the ionosphere. In this work, we use data from the Global Navigation Satellite Systems (GNSS) receiver installed in Abuja, Nigeria, GPS Scintillation Network Decision Aid (SCINDA) TEC data from the Air Force Research Laboratory (AFRL) data archive, and the geomagnetic data from the World Data Center (WDC) in Kyoto, Japan, to investigate the relationship between geomagnetic storm and ionospheric irregularity occurrences using the rate of change of total electron content (TEC) index (ROTI), with a validation using the S4 indices, during the peak of the 24th solar cycle. The occurrences of irregularities were investigated on day-to-day and seasonal bases. The nighttime ionospheric irregularities, which are attributed to ionospheric plasma irregularities in the equatorial ionospheric F-region, were found to be prevalent. To investigate the relationship between the strength of ionospheric irregularities (ROTI) and the geomagnetic storm (Dst), the periodogram power spectral density (PSD) and regression analysis were used. The results showed that there was no correlation, cc = 0.073, between the Dst and ROTI, implying that the strengths of ionospheric irregularities occurring during geomagnetic storms are not strictly decided by the magnitudes of the storms; this was also confirmed using the S4 index. The impact of geomagnetic storms caused enhanced development or inhibition of ionospheric irregularities. We observed that the bulk of the storms occurring during the period of this study is not associated with ionospheric irregularities. Finally, the investigation showed that the correlation between the ROTI and Dst observed during the coronal mass ejection (CME)-driven geomagnetic storms was higher than that during the corotating interaction region (CIR)-driven geomagnetic storms, during the peak of the 24th solar cycle. The results of this work confirm the findings by other researchers.

Linkage of Equatorial Ionization Anomaly With the Day‐To‐Day Occurrence of Postsunset Irregularities and Scintillation in Low‐Latitude Region Around 110°E

The zonal electric field and meridional wind are two major factors to affect the formation of both equatorial ionization anomaly (EIA) and plasma irregularities in equatorial and low-latitude regions, the correlation between the EIA characteristics and the occurrence of both irregularities and the sequent scintillation is always concerned. In this study, we investigated the relationship between the day-to-day occurrence of scintillation based on ground-based GPS observations at Sanya (18.3°N, 109.6°E; dip lat.: 12.8°N) and Hongkong (22.4°N, 114.2°E; dip lat.: 16.1°N), China, and day-to-day variations of EIA inferred from the Gravity Recovery and Climate Experiment observations in equinoctial months (March-April and September-October) during high solar activities (2012–2014). The results indicated that EIA strength can be linked with the day-to-day occurrence of post-sunset irregularities and scintillation, and post-sunset scintillation would be likely to occur as electron density above the EIA trough is low and EIA is strong. There are other key factors to affect the initiation and evolution of irregularities besides zonal electric field and meridional wind, such as seed perturbations or wave-like structures. The day-to-day variations of electron density in EIA regions, EIA strength and EIA asymmetry were not well correlated quantitatively with the scintillation intensity representing by daily S4 maximum in low-latitude region. These results can help us understand and predict the day-to-day variability of irregularities and scintillation in equatorial and low-latitude regions.

Analysis of the Ionospheric Irregularities and Phase Scintillation at Low and Middle Latitudes Based on Swarm Observations

This study presents a statistical analysis of the ionospheric irregularities and topside ionospheric scintillation at low and middle latitudes by using in situ electron density and upward-looking total electron content data measured by the Swarm constellation during 2014–2021. The main purpose of this study is to determine whether the phase scintillation could present similar seasonal, longitudinal, latitudinal, local time, and solar activity features as the in situ ionospheric irregularities do at low and middle latitudes, and how the irregularities affect the phase scintillation. The results are summarized as follows: (1) At low latitudes, the occurrence rate of equatorial plasma irregularities (EPIs) at the equinoxes and December solstice peaks before midnight, but during the June solstice, the EPIs mainly occur after midnight. The occurrence rate of EPIs has a positive correlation with solar activity. The distribution of topside scintillation occurrence is relatively consistent with EPIs, but during the June solstice, the scintillation occurrence rate remains at a very low level. (2) The midlatitude irregularities mainly occur after midnight, and their occurrence rate is negatively correlated with solar activity. Midlatitude irregularities mainly occur during the solstices, concentrated over the Pacific region during the June solstice and over the Pacific American sector during the December solstice. Especially, the distribution of midlatitude irregularities has hemispheric asymmetry, with a higher occurrence rate in the winter hemisphere. However, the occurrence of midlatitude scintillation is comparable in both hemispheres during the June solstice, and it concentrates in the southern hemisphere during the December solstice. (3) The EPIs concentrate more at the altitudes of Swarm A, while the midlatitude irregularities mainly occur at the altitudes of Swarm B.

Effect of the seed perturbation amplitude on the equatorial spread F initiation during solar minimum

The contribution of gravity wave (GW) to the initiation/development of spread F during a solar minimum year was investigated through the comparison of the observed precursory parameters and characteristics of the corresponding equatorial spread F (ESF) events. The ionospheric parameters were recorded at the magnetic equatorial station Sao Luis (2.3°S, 44°W, dip latitude 2°S) during March and October 2010. These data were used to estimate the influence of the relative gravity wave amplitude and the ambient ionospheric condition on the diurnal variation of the spread F initiation. The vertical velocity drift indicated a clear control and defines the threshold for the seasonal variability of the ESF occurrence. However, it was insufficient to solely determine or predict the day to day variation of ESF occurrence. Thus, few days with contrasting ambient ionospheric condition and magnitude of GW amplitude were analysed in order to investigate the role of the different precursory factors in the observed diurnal variation of the plasma irregularity development. The density scale length and gravity wave amplitude were shown to immensely contribute to the linear instability growth rate, especially during the days with a low post-sunset rise. Thus, the experimental observations have demonstrated the strong inter-dependence between the precursory factors and they have also highlighted the probable control of the ESF morphology.

Resolving the High‐Latitude Ionospheric Irregularity Spectra Using Multi‐Point Incoherent Scatter Radar Measurements

AbstractTo provide new insights into the relationship between geomagnetic conditions and plasma irregularity scale‐sizes, high‐latitude irregularity spectra are computed using a novel Incoherent Scatter Radar (ISR) technique. This new technique leverages: (a) the ability of phased array Advanced Modular ISR (AMISR) technology to collect volumetric measurements of plasma density, (b) the slow F‐region cross‐field plasma diffusion at scales greater than 10 km, and (c) the high dip angle of geomagnetic field lines at high‐latitudes. The resulting irregularity spectra are of a higher spatiotemporal resolution than what has been previously possible with ISRs. Spatial structures as small as 20 km are resolved in less than 2 minutes (depending on the radar mode). In this work, we focus on Resolute Bay ISR‐North (RISR‐N) observations operating in the “imaginglptight” mode. In addition to having an unprecedented view of the size and occurrence of irregularities as they traverse the polar cap, we find that as the F‐region plasma density decreases below approximately 2.5 × 1010 m−3 at 350 km altitude the spectral power shifts to scale‐sizes lower than 50 km. Additionally, near magnetic local noon, the spectral power shifts to scales greater than 50 km, and from 15 to 6 magnetic local time, the spectral power shifts to scales lower than 50 km. This reflects the role of photoionization dominating high‐latitude ionospheric structuring in the polar cap.

An Examination of SuperDARN Backscatter Modes Using Machine Learning Guided by Ray‐Tracing

AbstractThe Super Dual Auroral Radar Network (SuperDARN) is a network of High Frequency (HF) radars that are typically used for monitoring plasma convection in the Earth's ionosphere. A majority of SuperDARN backscatter can broadly be divided into three categories: (a) ionospheric scatter due to reflections from plasma irregularities in the E and F regions of the ionosphere, (b) ground scatter caused by reflections from the ground/sea surface following reflection in the ionosphere, and (c) backscatter from meteor trails left by meteoroids as they enter the Earth's atmosphere. Due to the complex nature of HF propagation and mid‐latitude electrodynamics, it is often not straightforward to distinguish between different modes of backscatter observed by SuperDARN. In this study, we present a new two‐stage machine learning algorithm for identifying different backscatter modes in SuperDARN data. In the first stage, a neural network that “mimics” ray‐tracing is used to predict the probability of ionospheric and ground scatter occurring at a given location along with parameters like the elevation angles, reflection heights etc. The inputs to the network include parameters that control HF propagation, such as signal frequency, season, UT time, and geomagnetic activity levels. In the second stage, the output probabilities from the neural network and actual SuperDARN data are clustered together to determine the category of the backscatter. Our model can distinguish between meteor scatter, 1/2 hop E‐/F‐region ionospheric as well as ground/sea scatter. We validate our model by comparing predicted elevation angles with those measured at a SuperDARN radar.

Study of the Mesosphere and Lower Thermosphere by the Method of Creating Artificial Periodic Irregularities of the Ionospheric Plasma

This article presented a brief review of studies of the Earth’s ionosphere at the heights of the mesosphere and lower thermosphere by a method based on the creation of artificial periodic inhomogeneities (APIs) of the ionospheric plasma by high-frequency radiation from powerful thermal installations. APIs are created by a standing wave due to the interference between upward-propagating radio waves and those reflected from the ionosphere. API studies of the ionosphere were based on Bragg scattering of probing impulse signals from an artificial periodic structure. The method makes it possible to measure the parameters of the neutral and ionized components of the Earth’s atmosphere. Note that, despite the fact that the API method assumes an artificial perturbation of the ionospheric plasma, the parameters of the mesosphere and lower thermosphere are determined at the stage of inhomogeneity relaxation and characterize the undisturbed medium. To date, periodic inhomogeneities have been observed at the heating points of Zimenki and Sura ionospheric heating facility (SURA, Vasilsursk, Russia), Gissar (Tajikistan), Arecibo (Puerto Rico, USA), High Power Auroral Stimulation Observatory (HIPAS) and High Frequency Active Auroral Research Program (HAARP, Gakona, AK, USA), and European Incoherent Scatter (EISCAT, Tromso, Norway). Most of the API studies of the ionosphere were carried out at the SURA mid-latitude heating facility (56.1° N; 46.1° E). The review presented the main results of determining the parameters of the ionosphere and neutral atmosphere at altitudes of 60–120 km and studies of the atmosphere during sunrise and sunset events and solar eclipses. In fact, the review is far from a complete illustration of the possibilities of using the API method to study the mesosphere and lower thermosphere.

Vertical Propagation Speeds of Gravity Waves in the Daytime as a Precursor to the Onset of the Equatorial Spread‐F

AbstractThe equatorial spread‐F (ESF) refers to the spread observed in return echoes of ionograms. Such spread in reflected echoes is found both in range and frequency, which can last for a few hours. These are due to large‐scale plasma irregularities occurring in the ionospheric heights on some nights. Under seemingly identical background conditions, ESF might occur on one night but remain absent on the other. These plasma irregularities adversely affect the trans‐ionospheric radio wave propagation but their occurrence on a given night continues to be one of the missing elements in our understanding of the equatorial ionospheric phenomena. In this work, the vertical propagation of gravity waves in daytime thermosphere has been shown to be a crucial parameter for the generation of ESF during post‐sunset hours. Using electron density profiles obtained from digisonde at Trivandrum, a dip‐equatorial location in India, we found that vertical propagation activity of gravity waves exists on 85% of the ESF days, whereas it is only 50% for the days without the occurrence of ESF during post‐sunset hours. Further, vertical propagation speeds of these gravity waves are higher on the ESF days than on the non‐ESF days. Also, ESF has been found to occur on 100% of the occasions, whenever the vertical speeds of these gravity waves are greater than 80 ms−1. This threshold value of vertical propagation speeds of gravity waves can be used to predict the ESF occurrence around 12–14 LT on that day, which is much in advance of the occurrence of ESF.

An Empirical Model of the Ionospheric Sporadic E Layer Based on GNSS Radio Occultation Data

AbstractThe intense plasma irregularities within the ionospheric sporadic E (Es) layers at 90–130 km altitude have a significant impact on radio communications and navigation systems. As a result, the modeling of the Es layer is very important for the accuracy, reliability, and further applications of modern real‐time global navigation satellite system precise point positioning. In this study, we have constructed an empirical model of the Es layer using the multivariable nonlinear least‐squares‐fitting method, based on the S4max from Constellation Observing System for Meteorology, Ionosphere, and Climate satellite radio occultation measurements in the period 2006–2014. The model can describe the climatology of the intensity of Es layers as a function of altitude, latitude, longitude, universal time, and day of year. To validate the model, the outputs of the model were compared with ionosonde data. The correlation coefficients of the hourly foEs and the daily maximum foEs between the ground‐based ionosonde observations and model outputs at Beijing are 0.52 and 0.68, respectively. The model can give a global climatology of the intensity of Es layers and the seasonal variations of Es layers, although the Es layers during the summer are highly variable and difficult to accurately predict. The outputs of the model can be implemented in comprehensive models for a description of the climatology of Es layers and provide relatively accurate information about the global variation of Es layers.

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

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

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.

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.

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.