Global Positioning System Total Electron Research Articles

Unveiling the combined effects of neutral dynamics and electrodynamic forcing on dayside ionosphere during the 3–4 February 2022 “SpaceX” geomagnetic storms

Geomagnetic storms of G1-class were observed on 3 and 4 February 2022, which caused the loss of 38 out of 49 SpaceX satellites during their launch due to enhanced neutral density. The effects of storm-time neutral dynamics and electrodynamics over the American sector during this minor storm have been investigated using Global Positioning System—total electron content (TEC) and Global‐scale Observations of the Limb and Disk (GOLD) mission measured thermospheric composition and temperature. Results revealed an unexpected feature in terms of increase in O/N2 and depletion in TEC over the American low-latitudes. This feature is in addition to the classic storm time ionospheric variations of enhancement in ionospheric electron density in presence of enhanced O/N2 and an intense equatorial electrojet (EEJ). Further, significant morning-noon electron density reductions were observed over the southern mid-high latitudes along the American longitudes. Results from Multiscale Atmosphere-Geospace Environment (MAGE) model simulations elucidated storm-induced equatorward thermospheric wind which caused the strong morning counter electrojet by generating the disturbance dynamo electric field. This further explains the morning TEC depletion at low-latitudes despite an increase in O/N2. Sub-storm related magnetospheric convection resulted in significant noon-time peak in EEJ on 4 February. Observation and modelling approaches together suggested that combined effects of storm-time neutral dynamic and electrodynamic forcing resulted in significant ionospheric variations over the American sector during minor geomagnetic storms.

Processing and Validation of FORMOSAT‐7/COSMIC‐2 GLONASS Total Electron Content Observations

AbstractThe Formosa Satellite‐7/Constellation Observing System for Meteorology, Ionosphere, and Climate‐2 (FORMOSAT‐7/COSMIC‐2, F7/C2) Tri‐GNSS Radio Occultation System observes both Global Positioning System (GPS) and GLObalnaya NAvigazionnaya Sputnikovaya Sistema (GLONASS) slant total electron content (TEC). Space‐based TEC observations have historically relied on GPS signals, and the processing methodologies and data quality of GLONASS absolute TEC observations are thus less well established. We present a description of the differences in the processing for the F7/C2 GLONASS absolute TEC observations. This primarily entails estimation of a paired receiver‐transmitter differential code bias, which is needed due to the GLONASS usage of frequency‐division multiple access. We additionally perform a validation of the F7/C2 GLONASS absolute TEC observations through comparison with colocated F7/C2 GPS absolute TEC observations. Based on this comparison, we estimate the GLONASS absolute TEC error to be ∼2.6 TEC units (TECU), which is similar to previous estimates of the F7/C2 GPS absolute TEC error (∼2.5 TECU). This demonstrates that the F7/C2 GLONASS absolute TEC observations are generally similar in quality to the F7/C2 GPS absolute TEC observations, and are suitable for use by the operational and scientific communities.

Downward Drifting F‐Region Irregularity Observed Above an Eastward Drifting One Before Midnight on 4 March 2014

AbstractOn the night of 4 March 2014, the Hainan COherent Scatter Phased Array Radar (HCOPAR) observed two irregularities appearing simultaneously in the radar scope at different height ranges. The global positioning system total electron content receivers also recorded two groups of plasma bubbles connecting in the observation scope of the HCOPAR. The topside irregularity moved slowly downward with almost no zonal movement, while the bottomside irregularity drifted eastward. There was not much difference among the h’F, hmF, and foF variations recorded by the Hainan Digisonde on that day and the reference days, except for a rapid descent in hmF between 20:45 and 21:15 LT. The downward moving irregularity was also recorded during this period. The prompt penetration electric fields induced by turnings of the interplanetary magnetic field Bz during weak geomagnetic activities are suggested not to influence the whole F‐layer heights at low latitudes but only to change the drift direction of the topside irregularity.

On Constructing a Realistic Truth Model Using Ionosonde Data for Observation System Simulation Experiments

AbstractThe ionosphere contains many small‐scale electron density variations that are under represented in smooth physics‐based or climatological models. This can negatively impact the results of Observation System Simulation Experiments, which use a truth model to simulate data. This paper addresses this problem by using ionosonde data to study ionospheric variability and build a new truth model with empirically driven variations. The variations are studied for their amplitude, horizontal and vertical size, and temporal extent. Results are presented for different local times, seasons, and at solar minimum and solar maximum. We find that these departures from a smooth background are often as large as 25% and are most prevalent near 250 km in altitude. They have horizontal spatial extents that vary from a few hundred to a few thousand kilometers, and typically have the largest horizontal extent at high altitudes. Their vertical extents follow the same pattern of being larger at high altitudes, but they only vary from 10s of km up to 200 km in vertical size. Temporally, these variations can last for a few hours. A procedure for using these spatial and temporal distributions to add empirically driven variance to a smooth truth model is outlined. This process is used to make a truth model with representative variations, which is compared to ionosonde data as well as Global Positioning System Total Electron Content data that was not used to inform the model. The new model resembles the data much better than the smooth models traditionally used.

Analysis of Ionospheric Perturbations Possibly Related to Yangbi Ms6.4 and Maduo Ms7.4 Earthquakes on 21 May 2021 in China Using GPS TEC and GIM TEC Data

On 21 May 2021 (UT), Yangbi Ms6.4 and Maduo Ms7.4 earthquakes occurred in mainland China. This paper analyzed the ionospheric perturbations possibly related to the earthquake, based on global positioning system (GPS) total electron content (TEC) and global ionosphere map (GIM) TEC data. We identified GPS TEC anomalies by the sliding quartile, based on statistical analysis. After eliminating the days with high solar activity levels and strong geomagnetic disturbances, the time series analysis of GPS TEC data showed that there were significant TEC anomalies from 5 to 10 May. TEC anomalies were mainly positive anomalies. We obtained the spatial and temporal distributions of TEC anomalies using natural neighbor interpolation (NNI). The results showed that the TEC anomalies were distributed in the seismogenic zone and surrounded the epicenters of the Maduo and Yangbi earthquakes, indicating that they may be related to the earthquakes. From the GIM TEC difference map, we found the TEC enhancement in the seismogenic zone and its magnetic conjugate area of the Maduo and Yangbi earthquakes at 10:00–12:00 (UT) on the 5 and 6 May. We discussed our results according to the lithosphere-atmosphere-ionosphere coupling mechanism. Finally, based our results, we suggested that the Yangbi and Maduo earthquakes may affect the ionosphere through seismogenic electric field and thermal anomalies generated during the process of lithosphere-atmosphere-ionosphere coupling.

Case Studies on the Day‐to‐Day Variability in the Occurrence of Post‐Sunset Equatorial Spread F

AbstractThe occurrence of post‐sunset equatorial spread F (ESF) is well understood to be associated with the evening pre‐reversal enhancement (PRE). Earlier studies have shown that when large datasets are examined, there is a significant correlation between the occurrence of post‐sunset ESF and the evening PRE. However, this correlation is much lower when the events are examined on a day‐to‐day basis. This has led to the emergence of suggestions that the PRE may not be a necessary condition for the occurrence of post‐sunset ESF. This study presents the results of the occurrence of post‐sunset ESF using data obtained from the Lowell Digisonde at Ilorin, Nigeria (ILR; 4.68°E, 8.50°N; Dip latitude −1.25°), spanning May–September 2019. In this interval, data was available on 124 days and, of this number, post‐sunset ESF occurred on 99 days (79.8%). Of the 99 days for which post‐sunset ESF was observed, two events for which the evening PRE was absent were investigated in detail. Analysis of Digisonde data for these two selected events showed modulation of the bottomside F‐layer plasma in the evening sector by wave structures. Spectral analysis of Global Positioning System Total Electron Content from multiple ground stations across Nigeria showed the appearance of wave structures, consistent with standing waves, in the ionosphere. The results presented show that standing waves are a possible mechanism for the generation of post‐sunset ESF, even in the absence of the PRE.

On the significant impact of the 17 March 2015 St. Patrick’s Day geomagnetic storm on the ionosphere over Indian region

The response of the ionosphere in the Indian region to the extreme space weather events of 17–19 March 2015 is studied using Global Positioning System (GPS) Total electron Content (TEC) measurements, Thermosphere Ionosphere Electrodynamics-General Circulation Model (TIE-GCM) simulations and High Frequency (HF) Radar observations. The data from Thiruvananthapuram (8.5° N, 77° E geographic, 0.3° N magnetic latitude) and northern hemispheric midlatitude station Hanle (32.80° N, 79° E geographic, 23.9° N magnetic latitude) have been analyzed for the above event. The TEC over Thiruvananthapuram, a dip equatorial location exhibits a decrease during the post sunset hours on 17 March 2015 and is followed by the generation of F region irregularities at an altitude of 600 km, as observed by HF radar as well as TEC scintillations. The TEC over the mid latitude station of Hanle decreased during the storm recovery phase on 18March 2015 in response to negative storm effects. The extent of decrease in TEC as observed during the recovery phase could not be simulated by TIE-GCM over Hanle. This difference is attributed to the enhanced Joule heating taking place in the polar region during St. Patrick’s Day storm and the associated composition changes. An anomalous heating scenario was introduced and the simulated TIE-GCM results were found to match the observations. The present study clearly brings out the impact of 17 March 2015, St. Patrick’s Day geomagnetic storm on the ionization distribution over equatorial as well as mid latitude stations over the Indian region using observations as well as TIE-GCM simulations and the evolutionary features of ionospheric irregularities over equatorial location using TEC and HF radar observations. The role played by thermosphere ionosphere coupling in modulating the ionization variability over equatorial as well as mid latitude region during periods of extreme geomagnetic forcing is highlighted.

Investigation of the Gradient Drift Instability as a Cause of Density Irregularities in Subauroral Polarization Streams

AbstractDensity irregularities have been observed in subauroral polarization streams (SAPS). One hypothesis of the cause of this ionospheric turbulence, based on the background morphology, is the gradient drift instability (GDI). This work models the GDI using a two‐dimensional electrostatic fluid model to determine if it is a viable cause of turbulence generation in SAPS. A statistical study of different velocity profiles, based on SuperDARN radar and Global Positioning System total electron content data, is used to prescribe parameters in the numerical model. The parameter space of different SAPS profiles is explored to study the effect on GDI development. As the velocity shear is initialized closer to the unstable density gradient, the GDI becomes increasingly damped. For these cases, the density and electric potential turbulence cascades obtained from the numerical model follow power laws of about −5/3 or −2, which is in agreement with observational data. If the region of sheared velocity overlaps the density gradient, the GDI becomes stabilized. The latitudinal location of maximum GDI growth depends on the density profile, the velocity profile, and the neutral wind direction. Using velocity profiles with regions of low velocity shear can cause instabilities that grow inside SAPS which have turbulence cascades with different behavior. In all parameter regimes considered, the GDI turbulence is precluded from extending through regions of velocity shear. Turbulence is generated for a variety of SAPS relevant conditions; therefore, the GDI has been shown to be a viable candidate for generating ionospheric irregularities in SAPS.

A Case Study of Polar Cap Sporadic-E Layer Associated with TEC Variations

The Sporadic-E (Es) layer is an often-observed phenomenon at high latitudes; however, our understanding of the polar cap Es layer is severely limited due to the scarce number of measurements. Here, the first comprehensive study of the polar cap Es layer associated with Global Positioning System (GPS) Total Electron Content (TEC) variations and scintillations is presented with multiple measurements at Resolute, Canada (Canadian Advanced Digital Ionosonde (CADI), Northward-looking face of Resolute Incoherent-Scatter Radar (RISR-N), and GPS receiver). According to the joint observations, the polar cap Es layer is a thin patch structure with variously high electron density, which gradually develops into the lower E region (~100 km) and horizontally extends >200 km. Moreover, the TEC variations produced by the polar cap Es layer are pulse-like enhancements with a general amplitude of ~0.5 TECu and are followed by smaller but rapid TEC perturbations. Furthermore, the possible scintillation effects likely associated with the polar cap Es layer are also discussed. As a consequence, the results widely expand our understanding on the polar cap Es layer, in particular on TEC variations.

Estimating foF2 from GPS TEC over Islamabad and Darwin using NeQuick2 during 2011–2014

This paper describes statistical attempts of estimating the critical frequency of the F2 layer (foF2) using Global Positioning System (GPS) Total Electron Content (TEC), with the help of electron density model NeQuick2, for monthly hourly median conditions. The stations under study are Islamabad (geog. lat: 33.66° N, long: 73.23° E, geomag. lat: 25.21° N) and Darwin (geog. lat: 12.46° S, long: 130.85° E, geomag. lat: 21.96° S) for the years 2011 to 2014. As first approximation, a linear regression analysis between ionosonde foF2 values and GPS TEC produced a regression coefficient that lies between 77% to 83% at Darwin and between 81% and 87% at Islamabad. Two methods were used for the same purpose - First, using GPS TEC and NeQuick2 slab thickness, which produced the Root Mean Square Error (RMSE) of less than 1 MHz at Islamabad, but greater than 1 MHz for Darwin. Second, using an iteration process by ingesting GPS TEC in NeQuick2 to improve foF2 such that optimum foF2 obtained by iteration process has corresponding NeQuick2 TEC, which is close to GPS one within ±5%. This provides foF2 estimation with 84% confidence over Islamabad. The results show that the attempts are inspiring for obtaining reliable foF2 from GPS TEC over Islamabad.

Multi-instrument observations of SCIPS: 1. ISR and GPS TEC results

An uninterrupted multi-day (6–8 May 2013) ionospheric F-region event with features indicative of medium-scale traveling ionospheric disturbances (MSTIDs) was detected with the Millstone Hill (MH) incoherent scatter radar (ISR). It was later identified, with the addition of Global Positioning System total electron content (GPS-TEC) imaging, as a novel ionospheric phenomenon. This phenomenon is herein termed semi-coherent ionospheric pulsing structures (SCIPS). The presumptive-MSTIDs in this multi-day event had a ~1 h period and were observed during calm-to-minor geomagnetic conditions using both the vertical-looking (Zenith) and steerable (Millstone Hill Steerable Antenna, or MISA) MH ISR systems. To image the MH MSTID events on a larger horizontal scale than is possible with ISR systems alone, a dense network of GPS TEC receivers was leveraged. The ISR-observed event was located in the GPS-TEC data geographically centered on the MH location with a ~100 km resolution (pixel size). However, keogram analysis of the GPS-TEC data revealed that the event had coherency across the continental United States. The same technique additionally exposed similar events occurring globally throughout the observing period. Our multi-instrument approach allows us to conclude that the event was comprised of large-scale and continuously forced, semi-coherent ionospheric pulsing structures (SCIPS) that masqueraded as MSTIDs when viewed locally. The GPS-TEC images show that the SCIPS were stationary in longitude on a global scale, but appeared to propagate in a southward direction in the Northern Hemisphere. It was not possible to obtain direct imaging in the southern hemisphere due to the smaller number of receivers. The SCIPS appear to originate at high latitudes and, in several instances, were coherent across over 10,000 km. The apparent high latitude source location, ubiquity, and large-scale coherence of the SCIPS suggest unexpected impulsive auroral oval sources containing enough energy to continually force the observed MSTID-like structures even during low geomagnetic activity periods.

3‐D Tomographic Reconstruction of SED Plume During 17 March 2013 Storm

AbstractThe three‐dimensional computerized ionospheric tomography (3DCIT) technique is used to reconstruct the spatial distribution of storm‐enhanced density (SED) based on the global positioning system total electron content measurements over the North American area during the 17 March 2013 storm. The reconstruction results are carefully validated with observations from three ionosonde stations, the constellation observing system for meteorology, ionosphere, and climate (COSMIC) radio occultations, and the Millstone Hill incoherent scatter radar. The electron density profiles from the 3DCIT reconstruction show a good agreement with the ionosonde and COSMIC electron density profiles. The 3DCIT‐derived electron density difference between the storm day of 17 March and the quiet day of 16 March also captures the similar SED plume signature that was observed by the Millstone Hill incoherent scatter radar. The 3DCIT reconstruction allows us for the first time to unveil the 3‐D configuration of the SED plume and its spatiotemporal evolution. It was found that the SED plume first appeared around 400 km and then expanded downward to ~300 km as well as upward to ~500 km over the course of a 3‐hr period from 19 to 22 UT on 17 March. Our study also showed that the density enhancement within the SED plume occurred mostly above the storm time F layer peak height.

Sequential Observations of Flux Transfer Events, Poleward‐Moving Auroral Forms, and Polar Cap Patches

AbstractWe report the observation of solar wind‐magnetosphere‐ionosphere interactions using a series of flux transfer events (FTEs) observed by Magnetospheric MultiScale (MMS) mission located near the dayside magnetopause on 18 December 2017. The FTEs were observed to propagate duskward and either southward or slightly northward, as predicted under duskward and southward interplanetary magnetic field (IMF). The Cooling model also predicted a significant dawnward propagation of northward‐moving FTEs. Near the MMS footprint, a series of poleward‐moving auroral forms (PMAFs) occurred almost simultaneously with those FTEs. They propagated poleward and westward, consistent with the modeled FTE propagation. The intervals between FTEs, relatively consistent with those between PMAFs, strongly suggest a one‐to‐one correspondence between the dayside transients and ionospheric responses. The FTEs embedded in continuous reconnection observed by MMS and corresponding PMAFs individually occurred during persistent auroral activity recorded by an all‐sky imager strongly indicate that those FTEs/PMAFs resulted from the temporal modulation of the reconnection rate during continuous reconnection. With the decay of the PMAFs associated with the FTEs, patch‐like plasma density enhancements were detected to form and propagate poleward and then dawnward. Propagation to the dawn was also suggested by the Super Dual Auroral Radar Network (SuperDARN) convection and Global Positioning System (GPS) total electron content data. We relate the temporal variation of the driving solar‐wind and magnetospheric mechanism to that of the high‐latitude and polar ionospheric responses and estimate the response time.

A comparative study between two percentage of occurrence methodologies for computing ionospheric scintillation statistics

This study presents a detailed comparative analysis of the two widely used percentage of occurrence methodologies used to compute the statistics of ionospheric scintillation activity based on the data of a Global Positioning System (GPS) Ionospheric Scintillation and (TEC) Total Electron Content Monitor (GISTM) receiver located at the northern Equatorial Ionization Anomaly (EIA) crest region Agartala (23.76°N, 91.26°E) of the Indian subcontinent, during 2012–2015 of the rising, peak and declining solar activity periods of solar cycle-24. Both the methodologies, one based on the number of scintillation event days and another based on the number of scintillation events, provide the correct and similar scintillation statistics qualitatively. But a rigorous comparative study shows significant quantitative differences between the statistics obtained by the two methodologies. The variation of scintillation occurrence obtained by the two methodologies with solar and geomagnetic activity shows that the methodology based on the number of scintillation events provides more accurate and physically acceptable results. Though this fact may be familiar to some researchers but still the scientific community has been using both the methodologies in parallel to compute scintillation statistics. So, from this comparative analysis future researchers can get a clear scenario of the advantages and disadvantages of these methodologies over one another before adopting any one of those for computing scintillation statistics. We also want to highlight the issue to the scientific community to come to a common platform by adopting the percentage of occurrence methodology based on the number of scintillation events for future studies.

Relative Contributions of Ion Convection and Particle Precipitation to Exciting Large‐Scale Traveling Atmospheric and Ionospheric Disturbances

AbstractDuring geomagnetically active times, the enhanced ion convection and particle precipitation at high latitudes cause substantial disturbances in the ionosphere and thermosphere. Large‐scale traveling ionospheric disturbances (LSTIDs) were identified from Global Positioning System (GPS) total electron content (TEC) measurements from 06:30 to 08:30 UT on 26 March 2014 as a result of southward turning of the interplanetary magnetic field (IMF) Bz and enhanced particle precipitation during a substorm. The comparison of LSTIDs from the global ionosphere‐thermosphere model (GITM) simulations with GPS TEC measurements shows a general agreement. Further theoretical analyses with GITM were conducted to sperate the influence of ion convection and particle precipitation on the total Joule heating as well as on the resulting large‐scale traveling atmospheric disturbances (LSTADs) and LSTIDs. It was found that ion convection and particle precipitation have comparable contributions to the total Joule heating, although the changes of height‐integrated Joule heating due to these two forcing terms may display different distributions. In addition, the magnitudes of neutral density and TEC perturbations due to these two forcing terms were found to be comparable. Using the total energy flux versus time derived from all‐sky imager measurements for this event to drive GITM improves the data‐model comparison of LSTIDs. However, data‐model discrepancies still exist in the timing of LSTIDs and the magnitude of TEC perturbations, which calls for further investigation and realistic event‐specific specifications.

Effect of moderate geomagnetic storms on equatorial plasma bubbles over eastern Africa in the year 2012: Evolution and electrodynamics

Equatorial plasma bubbles (EPBs) are common features of the equatorial and low-latitude ionosphere and are known to cause radio wave scintillation which leads to the degradation of communication and navigation systems. Although these structures have been studied for decades, a full understanding of their evolution and dynamics remains important for space weather mitigation purposes. In this study, we present cases of EPBs occurrences around April and July 2012 geomagnetic storm periods over the African equatorial sector. The EPBs were observed from the Communications/Navigation Outage Forecasting System (C/NOFS) and generally correlated well to the ionospheric irregularities observed from the Global Positioning System total electron content (GPS-TEC) measurements (rate of TEC change, ROT). This study revealed that the evolution of the EPBs during moderate storms is controlled by the strength of the daytime equatorial electrojet (EEJ) currents regardless of the strength of the equatorial ionization anomaly (EIA), the latter is observed during the July storm case in particular. These effects were more evident during the main and part of the early recovery phases of the geomagnetic storm days considered. However, the evening hours TEC gradients between regions of the magnetic equator and ionization crests also played roles in the existence of ionospheric irregularities.

Generation of Regional Ionospheric TEC Maps With EIA Nowcasting/Forecasting Capability During Geomagnetic Storm Conditions

In this paper, ground based Global Positioning System (GPS) Total Electron Content (TEC) observations collected from the GPS Aided GEO Augmented Navigation (GAGAN) network over low latitude Indian subcontinent are assimilated into the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). Gauss-Markov Kalman filter methodology is utilized and the background model error covariance (BMEC) matrix is framed using solar, geomagnetic, cross tail potential and hemispheric power indices using multivariate principal component analysis (MPCA) method. The model variations through different high latitude electric field models (Weimer and Heelis) are utilized in the data assimilation analysis. The proper attempt is modeled for providing TEC forecasts during geomagnetic storm conditions from 15th to 20th March 2015 days over Indian region. The more concentration is given in understanding the equatorial ionization anomaly (EIA) characteristics during the initial, main and recovery phase of St. Patrick’s Day March 2015 geomagnetic storm. The proposed model forecast outperforms the persistence forecast with maximum forecast score (1.6) and forecast skill (2.2) during recovery phase of storm. TEC forecasts are validated with current time step GPS observations and 93 % correlation is observed on quiet day (10th March 2015) and 82 % correlation is noticed on main phase of storm (17th March 2015). Also proposed TEC model analysis and forecast results are compared with International Global Navigation Satellite Service (IGS) TEC stations datasets. A clear negative storm effect (EIA inhibition) has been forecasted well with the proposed Kalman filter and MPCA methodology aspects.

Seismo-ionospheric precursors of strong sequential earthquakes in Nepal region

Global Navigation Satellite Systems record the total electron content via their receivers, and total electron content measurements have become popular with the requirement for capturing any ionospheric abnormalities prior to earthquake. Based on space weather conditions, the solar activity and geomagnetic activity indices are critical to monitor the total electron contents in the ionosphere. This study aimed to investigate the ionospheric variations induced by six sequential earthquakes in Nepal in 2015 with magnitude higher than 6.0, examine the total electron content data from Global Ionosphere Maps and Global Positioning Systems and analyze the contributing factors to the abnormal total electron content levels affected by space environment and geomagnetic activity status. We performed moving median analysis for 15 days to determine the pre- and post-earthquake abnormalities. With the static and dynamic time analysis, we concluded that there was likelihood for positive or negative anomalies, earthquake-induced ionospheric anomalies occurred on the previous day or up to six days earlier and even had potentiality for successive earthquakes.Furthermore, the data used in the analysis can be divided into two groups: Global Ionosphere Maps Total Electron Content and Global Positioning System Total Electron Content variations. LHAZ International Global Navigation Satellite System Service station from which we obtained these was close to the earthquakes’ epicenter. We studied three indices, such as geomagnetic storm index (K-planetary), geomagnetic activity index, and solar activity index, depending on space climate and discussed what factors can be influential in this disaster. Hence, we suggest that the earthquake may account for a typical variation in Global Ionosphere Maps Total Electron Content data as well as Global Positioning System Total Electron Content as solar activities and geomagnetic storms leading to abnormalities in the ionosphere.

Simulation and Observations of the Polar Tongue of Ionization at Different Heights During the 2015 St. Patrick's Day Storms

AbstractWe present the observational and modeling study focused on the major factors determining the spatiotemporal structure of the high‐latitude ionospheric plasma density enhancement—the tongue of ionization (TOI) structure—during the 2015 St. Patrick's Day geomagnetic storm. We use the Global Self‐consistent Model of the Thermosphere, Ionosphere, Protonosphere (GSM TIP) to reproduce the plasma density distribution, and the results are compared with the observational data as deduced from the ground‐based global positioning system total electron content and in situ plasma probe measurements at different altitudes. Both the simulation and observation results show that a large‐scale TOI‐like structure of enhanced plasma density extends from the dayside midlatitude region toward the central polar cap along the antisunward cross‐polar convection flow. We reveal an important role of the clockwise convection cell rotation for the modification of TOI structure. According to model results during the storm main phase, the neutral thermospheric composition, particularly the “tongue” in n(N2), modifies the spatial structure of TOI in such a way that (1) the near‐pole region of enhanced plasma density is shifted to the duskside and, (2) at F region heights, the TOI is split into the dusk and dawn branches. The signature of TOI in the topside ionosphere considerably differs from that in the F region because of a lesser influence of the neutral composition changes at higher altitudes. Model results revealed that at plasmaspheric heights, the TOI structure appears in both the dawn and dusk convection cells.

A statistical analysis of medium-scale traveling ionospheric disturbances during 2014\u20132017 using the Hong Kong CORS network

We report a statistical study of medium-scale traveling ionospheric disturbances (MSTIDs) during 2014–2017 in the low-latitude China region using the Hong Kong Continuously Operating Reference Stations network with a baseline length of 10–15 km. Polynomial fitting and the multichannel maximum entropy method are utilized to derive MSTID parameters from global positioning system total electron content data. We find that MSTIDs can be sorted into three types in this region. One type is daytime MSTIDs, which are mainly distributed during 1000–1700 local time (LT) in spring, autumn and winter. The second type is nighttime MSTIDs, which mainly occur from 2200 to 0300 LT in spring and summer. The third type is morning MSTIDs, mainly occurring from 0500 to 0700 LT in spring and autumn. No clear difference in the MSTID parameters is distinguishable between the cyclone period and non-cyclone period, which may be due to the distance restriction for cyclone identification and different propagation distances of the primary gravity waves (GWs) and secondary GWs.