Traveling Ionospheric Disturbances Research Articles

Spatial Characteristics on the Occurrence of the Nighttime Midlatitude Medium‐Scale Traveling Ionospheric Disturbance at Topside Ionosphere Revealed by the Swarm Satellite

AbstractUsing 6 years collecting of electron density (Ne) data from the Swarm A satellite, this study portrays comprehensive maps of the occurrence of medium‐scale traveling ionospheric disturbance (MSTID) at middle latitudes, which is characterized by the in situ absolute Ne fluctuations above a certain threshold. Two interesting spatial preferences on the occurrence of MSTID as well as their dependence on local time and solar cycle are captured, that is, (1) regional preference near Weddell Sea Anomaly (WSA) to its west during December solstice, MSTID in this region appears even at very low latitudes (at least to 10°N in magnetic latitude) and (2) preference at middle latitudes with a wide zonal extension, which is similar to the recently disclosed nighttime midlatitude plasma band‐like enhancement (NMPBE) of the background plasma density (Zhong et al., 2019, https://doi.org/10.1029/2018JA026059). The first preference of MSTID occurring near WSA region can be understood as the effects of horizontal neutral wind contribution to the Perkins instability, with the principal requirement of sporadic E occurrence via ionospheric E‐F region coupling. The fundamental mechanism of the second preference of MSTID occurring includes the interhemispheric coupling that the MSTID can also develop in the winter hemisphere where the local growth rate of Perkins instability is low. Besides, the presence of NMPBE during low solar activity years sets up a favorable environment for the appearance of MSTID with considerable fluctuation amplitude.

A mathematical model for the numerical simulations of traveling ionospheric disturbances/atmospheric gravity waves generated by the Joule heating

Traveling ionospheric disturbances (TIDs) and atmospheric gravity waves (AGWs) generated by the Joule heating produced from intensified auroral electrojet and/or intense particle precipitation in the auroral and subauroral regions during geomagnetic storms and which propagate downward toward the lower (neutral) atmosphere are numerically simulated using a simple two-dimensional mathematical model for internal gravity waves propagating in the lower atmosphere. An explicit expression for the Joule heating is obtained, and the characteristics of the simulated TIDs/AGWs (e.g., buoyancy frequency, wavenumbers, cutoff wavelength, speed, structures) are also examined and compared with the results obtained from observations. As may be seen in the observations, small-scale TIDs/AGWs with wavelengths shorter than 100 km, medium-scale TIDs/AGWs with wavelengths of several hundred kilometers, and large-scale TIDs/AGWs with wavelengths longer than 1000 km generated by the Joule heating were modeled and numerically simulated. For example, observations have revealed that the Joule heating can generate TID/AGW pairs. The developed numerical model was used to simulate medium-scale TID/AGW wave packet pairs, and the results (wavelength, speed, structure) are in agreement with SuperDARN observations reported by Sofko and Huang, 2000. TIDs/AGWs with shorter horizontal wavelengths are more trapped than those with longer wavelengths (medium- and large-scale TIDs/AGWs). Their cutoff horizontal wavelength was approximated using the linear stability theory of AGWs. The approximated cutoff horizontal wavelength suggests that not all simulated small-scale disturbances with horizontal wavelengths shorter than 100 km are traveling as may be seen in the observations.

Doppler vertical sounding of the ionosphere at the Akademik Vernadsky station

The paper aims at providing the technical information about Doppler vertical sounding of the ionosphere that started at the Ukrainian Antarctic Akademik Vernadsky station since 2017; developing the technique for processing and visualization of data of vertical sounding of the ionosphere in the form of height-time diagrams of median values of ionospheric parameters; demonstrating the capabilities of this technique using the results obtained during the first year of observations, namely the background variations of ionospheric parameters as well as examples of observations of travelling ionospheric disturbances (TID). The methods used in the paper are the following: the vertical sounding of the ionosphere using the IPS-42 ionosonde operating at Akademik Vernadsky station since 1982; Doppler vertical sounding of the ionosphere by the portable ionosonde developed and manufactured in collaboration between the Abdus Salam International Centre for Theoretical Physics (ICTP) and Institute of Radio Astronomy of the National Academy of Sciences of Ukraine (IRA NASU); calculating the height-time diagrams of ionospheric parameters obtained using the data of both ionosondes; and original technique for estimating the median height-time diagrams as background monthly averaged characteristics of the ionosphere. Seasonal and diurnal variations of plasma frequencies, vertical plasma velocities, as well as the signal-to-noise ratio and the probability of the registration of signals are shown using the median height-time diagrams of the corresponding parameters for the first year of synchronous observations by the two ionosondes. The features and potential areas of application of median ionospheric height-time diagrams are discussed. They can be used to calculate automatically variations of maximum usable frequency for a radio link of the specified length. Examples of TID registrations in variations of virtual heights of reflection and Doppler frequency shifts (DFS) of the signals are presented. It is shown that the comparison of TID manifestations in variations of virtual heights and DFS can be used to select a more appropriate model of TID among the models of perfectly reflecting moving surface or three-dimensional plasma density waves traveling through a real ionospheric layer. It could be concluded that simultaneous operation of two ionosondes at the Akademik Vernadsky station has allowed to significantly expand the amount and quality of objective information about the ionospheric behavior over the Antarctic Peninsula.

Tropical Cyclone‐Induced Gravity Wave Perturbations in the Upper Atmosphere: GITM‐R Simulations

AbstractThe tropical cyclone (TC)‐induced concentric gravity waves (CGWs) are capable of propagating upward from convective sources in the troposphere to the upper atmosphere and creating concentric traveling ionospheric disturbances (CTIDs). To examine the CGWs propagation, we implement tropical cyclone‐induced CGWs into the lower boundary of global ionosphere‐thermosphere model with local‐grid refinement (GITM‐R) and simulate the influence of CGWs on the ionosphere and thermosphere. GITM‐R is a three‐dimensional non‐hydrostatic general circulation model for the upper atmosphere with the local‐grid refinement module to enhance the resolution at the location of interest. In this study, CGWs induced by the typhoon Meranti in 2016 have been simulated. Information of the TC shape and moving trails is obtained from the TC best‐track dataset, and the gravity wave patterns are specified at the lower boundary of GITM‐R (100 km altitude). The horizontal wavelength and phase velocity of wave perturbation at the lower boundary are specified to be consistent with the TEC observations. The simulation reveals a clear evolution of CTIDs, which shows reasonable agreement with the GPS‐TEC observations. This is the first time the typhoon‐driven TEC perturbation has been simulated in a general circulation model. To further examine the dependence of the CTIDs on the wavelength and frequency of the gravity wave perturbation at the lower boundary, different waveforms have been tested as well. The magnitude of CTIDs has a negative correlation with the period but a positive correlation with the wavelength when the horizontal phase velocities are sufficiently fast against the critical‐level absorption.

The Persistent Ionospheric Responses Over Japan After the Impact of the 2011 Tohoku Earthquake

AbstractIn this study, we report the persistent impacts of the 2011 Tohoku earthquake/tsunami on the ionosphere using the ground‐based Global Navigation Satellite System and FORMOSAT‐3/COSMIC total electron content. Multiple unusual ionospheric phenomena, such as ionospheric irregularities, nighttime medium‐scale traveling ionospheric disturbances (MSTIDs), and planar traveling ionospheric disturbances (TIDs), were observed after the emergence of tsunami‐induced concentric gravity waves. The ionospheric irregularities initially developed over the Hokkaido region following the interference of gravity waves at ~8:45 UT. Remarkably, the Perkins‐type nighttime MSTIDs accompanying the planar TIDs were discernible over Japan following the irregularities. By comparing with the tsunami model simulation and ocean buoy observations, it is determined that these planar TIDs, lasting for about 10 hr, were likely related to tsunami ocean waves reflected by seamounts, ridges, islands, and seafloor topography in the Pacific Ocean. Due to the absence of sporadic E layers, we suggest that the coupling between the tsunami‐generated gravity waves and the Perkins instability plays an essential role in initiating the equinoctial nighttime MSTIDs. The long‐lasting tsunami can continuously impact the ionosphere, affecting the nighttime ionospheric electrodynamics and making the conditions conducive for the development of midlatitude nighttime ionospheric irregularities and instabilities.

Simulated high frequency ray paths considering traveling ionospheric disturbances

This study presents a modified version of a classical 3-D numerical ray tracing code [originally by Jones and Stephenson (A versatile three-dimensional ray tracing computer program for radio waves in the ionosphere. Office of Telecommunications Report 75–76, US Government Printing Office, Washington, DC, 1975)], now linked to ionosphere, neutral atmosphere, Earth’s magnetic field, and traveling ionospheric disturbances (TIDs) models. This method is applied to study the effect of TIDs on radio waves by simulating the waves’ propagation in a disturbed ionosphere. A 3-D cubic interpolation method is implemented in the ray tracing code to solve discontinuities and guarantee the ray tracing validity and accuracy under all conditions. Changes of the ground range distance (R) and the bearing angle (σ) are assessed for various simulated ray paths. A Pedersen ray case is also shown, for which small changes of signal frequency lead to enhanced variations. The study of HF ray path variations in terms of various TIDs characteristics and under different background ionospheric conditions and transmitter locations and radiation pattern can contribute to the mitigation of TIDs effects, either helping to improve existing methods or to develop new ones. The 3-D ray tracing code described and implemented in this work may well work for this purpose.

Ionospheric Tilt Measurements: Application to Traveling Ionospheric Disturbances Climatology Study

AbstractIonospheric tilt is a concept used to characterize local horizontal electron density gradients in the ionosphere using a mirror reflection model. Experimental results are presented that illustrate the validity and accuracy of such approach. Analysis of the tilt measurements collected in 2012–2014 with a digisonde at Ebro observatory (40.8°N, 0.5°E) is presented. Digisonde systems allow measuring angles of arrival of ionospherically reflected radio signals, from which the ionospheric tilts are derived. The tilts are represented in terms of North‐South and East‐West components. Using several years of observations, a climatological distribution of wavelike variations in the tilt records presumed to be associated with traveling ionospheric disturbances (TIDs) is established. Most of the observed TIDs have their main periods of 30 min to 1.5 hr which is rather typical for medium‐scale TIDs. Summertime appears to have the most frequent occurrence of TIDs. There is a good agreement between the presence of TIDs and sporadic E layer occurrence, suggesting that some TIDs can be driven by instability in the electric field which is initiated via an interhemispheric link between the E and F regions of the ionosphere. Direction of disturbance propagation is also analyzed and compared to the modeled neutral wind. There are indications that during the daytime TIDs tend to propagate in the direction opposite to the background neutral wind. This suggests that daytime TIDs are produced by atmospheric gravity waves originating in the lower atmosphere and experiencing background wind filtering effect on their upward propagation.

When Plasma Streams Tie up Equatorial Plasma Irregularities with Auroral Ones

AbstractWe present a new pattern of storm‐induced ionospheric irregularities behavior at midlatitudes—poleward‐streaming plasma density depletions. Under disturbed conditions, they appear at North America low latitudes as a part of extended postsunset equatorial plasma bubbles, and further, they are streaming from low latitudes in a northwestward, poleward direction toward the main ionospheric trough and auroral irregularities zone. The poleward‐streaming plasma depletions represent a new phenomenon with the similar northwestward transportation path across the continental United States as storm‐enhanced density (SED) plumes. The channels of poleward‐streaming plasma depletions were stretched from low‐latitude base toward higher latitudes—they are found to occur for geomagnetic storms under specific combination of steady southward interplanetary magnetic field, subauroral polarization streams (SAPS) electric fields, and enhanced westward drifts at midlatitudes, resulting in northwestward plasma transportation equatorward of the SAPS region. The poleward‐streaming plasma depletions form an illusion of traveling ionospheric disturbances (TIDs) moving in a poleward, northwestward direction—this propagation direction is opposite to typical equatorward propagation of storm‐induced large‐scale TIDs generated in the auroral zone and propagated toward the equator. This phenomenon is accompanied by strong ionospheric irregularities that occurred over both edges of plasma depletion channel at midlatitudes. For two comparable geomagnetic storms, these poleward‐streaming plasma depletions persisted for several hours, posing a localized threat for GPS‐based positioning applications. Even moderate‐to‐intense storms (Dst minimum−145 nT) can promote such effects at midlatitudes.

Understanding Inter-Hemispheric Traveling Ionospheric Disturbances and Their Mechanisms

Traveling ionospheric disturbances (TIDs) are wave-like disturbances in ionospheric plasma density. They are often observed during both quiet (medium-scale TID) and geomagnetically disturbed (large-scale TID) conditions. Their amplitudes can reach double-digit percentages of the background plasma density, and their existence presents a challenge for accurate ionosphere specification. In this study, we examine TID properties using observations obtained during two geomagnetically disturbed periods using multiple ground and space-borne instruments, such as magnetometers, Global Navigation Satellite System (GNSS) receivers, and the SWARM satellite. Reference quiet time observations are also provided for both storms. We use a thermosphere–ionosphere–electrodynamics general circulation model (TIEGCM) results to properly interpret TID features and their drivers. This combination of observations and modeling allows the investigation of variations of TID generation mechanisms and subsequent wave propagation, particularly as a function of different plasma background densities during various geophysical conditions. The trans-equatorial coupling of TIDs in the northern and southern hemispheres is also investigated with respect to attenuation and propagation characteristics. We show that TID properties during trans-equatorial events may be substantially affected by storm time background neutral wind perturbation.

Залежність просторового періоду рухомих іоносферних збурень від їхньої відносної амплітуди

The relationship between the horizontal spatial period L and the relative amplitude Ad of traveling ionospheric disturbances (TID) at various levels of solar (SA) and geomagnetic (GA) activity is experimentally studied. In the vast majority of cases, the TIDs observed during our study were generated by high-latitude sources. It was found that the period L and amplitude Ad of the medium-scale (MS) TIDs (L = 100 – 800 km) are related by a linear dependence, which does not depend upon the SA level. For large-scale (LS) TID with L = 1000 – 4000 km, the linear approximation of the function L(Ad) at low and high SA levels are increasing or decreasing functions, respectively. For global-scale (GM) TIDs with L = 5000 – 35000 km at low SA levels, the linear approximation L(Ad) is an increasing function. The function L(Ad) for TIDs of all spatial scales does not depend upon the GA level. The data were collected at the radio-physical observatory of V. N. Karazin Kharkiv National University (j = 49.63°N, l = 36.32°E) in 1999—2010 with the ionosphere radio sounding by using coherent radio waves at frequencies of about 150 and 400 MHz radiated by low-orbit navigation satellites Parus and Cicada orbiting at circular near-polar orbit with a height of about 1000 km. The experimental dependence of the horizontal period L of TID upon their relative amplitude Ad is explained based on the global prognostic semi-empirical model of the generation and propagation of acoustic-gravitational waves and traveling ionospheric disturbances.

Identification of potential precursors for the occurrence of Large-Scale Traveling Ionospheric Disturbances in a case study during September 2017

Traveling Ionospheric Disturbances (TIDs) reflect changes in the ionospheric electron density which are caused by atmospheric gravity waves. These changes in the electron density impact the functionality of different applications such as precise navigation and high-frequency geolocation. The Horizon 2020 project TechTIDE establishes a warning system for the occurrence of TIDs with the motivation to mitigate their impact on communication and navigation applications. This requires the identification of appropriate indicators for the generation of TIDs and for this purpose we investigate potential precursors for the TID occurrence. This paper presents a case study of the double main phase geomagnetic storm, starting from the night of 7th September and lasting until the end of 8th September 2017. Detrended Total Electron Content (TEC) derived from Global Navigation Satellite System (GNSS) measurements from more than 880 ground stations in Europe was used to identify the occurrence of different types of large scale traveling ionospheric disturbances (LSTIDs) propagating over the European sector. In this case study, LSTIDs were observed more frequently and with higher amplitude during periods of enhanced auroral activity, as indicated by increased electrojet index (IE) from the International Monitor for Auroral Geomagnetic Effects (IMAGE). Our investigation suggests that Joule heating due to the dissipation of Pedersen currents is the main contributor to the excitation of the observed LSTIDs. We observe that the LSTIDs are excited predominantly after strong ionospheric perturbations at high-latitudes. Ionospheric parameters including TEC gradients, the Along Arc TEC Rate (AATR) index and the Rate Of change of TEC index (ROTI) have been analysed for their suitability to serve as a precursor for LSTID occurrence in mid-latitude Europe, aiming for near real-time indication and warning of LSTID activity. The results of the presented case study suggest that the AATR index and TEC gradients are promising candidates for near real-time indication and warning of the LSTIDs occurrence in mid-latitude Europe since they have a close relation to the source mechanisms of LSTIDs during periods of increased auroral activity.

An overview of methodologies for real-time detection, characterisation and tracking of traveling ionospheric disturbances developed in the TechTIDE project

The main objective of the TechTIDE project (warning and mitigation technologies for travelling ionospheric disturbances effects) is the development of an identification and tracking system for travelling ionospheric disturbances (TIDs) which will issue warnings of electron density perturbations over large world regions. The TechTIDE project has put in operation a real-time warning system that provides the results of complementary TID detection methodologies and many potential drivers to help users assess the risks and develop mitigation techniques tailored to their applications. The TechTIDE methodologies are able to detect in real time activity caused by both large-scale and medium-scale TIDs and characterize background conditions and external drivers, as an additional information required by the users to assess the criticality of the ongoing disturbances in real time. TechTIDE methodologies are based on the exploitation of data collected in real time from Digisondes, Global Navigation Satellite System (GNSS) receivers and Continuous Doppler Sounding System (CDSS) networks. The results are obtained and provided to users in real time. The paper presents the achievements of the project and discusses the challenges faced in the development of the final TechTIDE warning system.

A method for real-time identification and tracking of traveling ionospheric disturbances using ionosonde data: first results

Traveling Ionospheric Disturbances (TIDs) are wave-like propagating irregularities that alter the electron density environment and play an important role spreading radio signals propagating through the ionosphere. A method combining spectral analysis and cross-correlation is applied to time series of ionospheric characteristics (i.e., MUF(3000)F2 or foF2) using data of the networks of ionosondes in Europe and South Africa to estimate the period, amplitude, velocity and direction of propagation of TIDs. The method is verified using synthetic data and is validated through comparison of TID detection results made with independent observational techniques. The method provides near real time capability of detection and tracking of Large-Scale TIDs (LSTIDs), usually associated with auroral activity.

A LOFAR observation of ionospheric scintillation from two simultaneous travelling ionospheric disturbances

This paper presents the results from one of the first observations of ionospheric scintillation taken using the Low-Frequency Array (LOFAR). The observation was of the strong natural radio source Cassiopeia A, taken overnight on 18–19 August 2013, and exhibited moderately strong scattering effects in dynamic spectra of intensity received across an observing bandwidth of 10–80 MHz. Delay-Doppler spectra (the 2-D FFT of the dynamic spectrum) from the first hour of observation showed two discrete parabolic arcs, one with a steep curvature and the other shallow, which can be used to provide estimates of the distance to, and velocity of, the scattering plasma. A cross-correlation analysis of data received by the dense array of stations in the LOFAR “core” reveals two different velocities in the scintillation pattern: a primary velocity of ~20–40 ms−1 with a north-west to south-east direction, associated with the steep parabolic arc and a scattering altitude in the F-region or higher, and a secondary velocity of ~110 ms−1 with a north-east to south-west direction, associated with the shallow arc and a scattering altitude in the D-region. Geomagnetic activity was low in the mid-latitudes at the time, but a weak sub-storm at high latitudes reached its peak at the start of the observation. An analysis of Global Navigation Satellite Systems (GNSS) and ionosonde data from the time reveals a larger-scale travelling ionospheric disturbance (TID), possibly the result of the high-latitude activity, travelling in the north-west to south-east direction, and, simultaneously, a smaller-scale TID travelling in a north-east to south-west direction, which could be associated with atmospheric gravity wave activity. The LOFAR observation shows scattering from both TIDs, at different altitudes and propagating in different directions. To the best of our knowledge this is the first time that such a phenomenon has been reported.

The petitSat mission – Science goals and instrumentation

The mid- and low-latitude ionosphere is home to a variety of plasma density irregularities, including depletions (bubbles), enhancements (blobs), and small-scale scintillation. Previous studies of plasma density enhancements observed using ROCSAT data have posited that these structures are the direct result of the formation of bubbles near the geomagnetic equator. However, more recent observations from the C/NOFS satellite suggest that multiple mechanisms are responsible for forming plasma enhancements, with wave action in the ionosphere and thermosphere as a significant driver of the enhanced densities. Indeed, statistical analysis of enhancements observed from satellites resembles the statistics of Medium-Scale Traveling Ionosphere Disturbances (MSTIDs) with respect to seasonal variability and solar activity.petitSat is a CubeSat mission designed to examine the link between MSTIDs and plasma enhancements. The mission will provide in situ measurements of the plasma density, 3D ion drift, as well as ion and neutral composition. The instrument suite includes a combined retarding potential analyzer and cross-track drift meter and an ion-neutral mass spectrometer. This instrument suite will provide comprehensive information about the fluctuations in plasma, as well as changes in the neutral profile. petitSat will launch into a 51 deg inclination orbit at 400 km (consistent with an International Space Station deployment), allowing for numerous conjunctions with the Boston University All-Sky Imager network over the mission lifetime.

Multi-scale ionosphere responses to the May 2017 magnetic storm over the Asian sector

We investigate multi-scale ionospheric responses to the May 27, 2017, geomagnetic storm over the Asian sector by using multi-instrumental observations, including ground-based global navigation satellite systems (GNSS) network, constellation observing system for meteorology, ionosphere and climate radio occultation, the FengYun-3C (FY-3C) GNSS occultation sounder electron density profiles and in situ plasma density observations provided by both Swarm and defense meteorological satellite program missions. This geomagnetic storm was an intense storm with the minimum symmetric horizontal component reaching − 150 nT and was caused by a coronal mass ejection released on May 23. The main observations are summarized below: (1) two ionospheric positive storm periods were observed. The first one was observed in the noon–afternoon sector during the main phase of the storm on May 28, with nearly 120% TEC enhancement. The second one was of a smaller scale and occurred on the nightside during the recovery phase of the storm on May 29. The first dayside positive storm was initiated by the interplanetary magnetic field (IMF) Bz southward turning and eastward penetration electric field, while the second nightside one was terminated by a later southward turning of the IMF Bz since the Asian sector was on the nightside and the penetration electric field changed westward. (2) A negative storm occurred from 00:00 to 12:00 UT on May 30 over the Asian sector, nearly 2 days after the main phase, which was due to the thermospheric composition change, i.e., decrease in the O/N2 ratio, as shown in the TIMED/GUVI measurements. (3) A band-like TEC enhancement was observed aligning in the northwest–southeast direction and propagated slowly southwestward from 15:00 to 20:00 UT (23:00–04:00 LT, near midnight) on May 28 during the recovery phase of the storm. In situ density observations from the Swarm B and DMSP F15&16 satellites confirmed the density enhancement at 510 km and 850 km, respectively, and revealed that this band-like TEC enhancement structure resembles the so-called plasma blob. The similarities of the observed plasma blob characteristics in terms of spatial structure, propagation trend and temporal evolution with the nighttime traveling ionospheric disturbance (TID) are consistent with the TID-blob theory.

Subauroral and Polar Traveling Ionospheric Disturbances During the 7–9 September 2017 Storms

AbstractThis study provides new scenarios for storm time traveling ionospheric disturbance excitation and subsequent propagation at subauroral and polar latitudes. We used ground‐based total electron content observations from Global Navigation Satellite System receivers combined with wide field, subauroral ionospheric plasma parameters measured with the Millstone Hill Incoherent Scatter Radar during strong September 2017 geospace storms. Observations provide the first evidence of significant influences on traveling ionospheric disturbance (TID) propagation and excitation caused by the presence of large subauroral polarization stream flow channels. Simultaneous large‐ and medium‐scale TIDs evolved during the event in a broad subauroral and midlatitude area near dusk. Similar concurrent TIDs occurred near dawn sectors as well during a period of sustained southward Bz. Medium‐scale TIDs at subauroral and midlatitudes had wave fronts aligned northwest‐southeast near dusk, and northeast‐southwest near dawn. These wave fronts were highly correlated with the direction of storm time large zonal plasma drift enhancements at these latitudes. At high latitudes, unexpected, predominant, and persistent storm time TIDs were identified with 2000+ km zonal wave fronts and 15% total electron content perturbation amplitudes, moving in transpolar propagation pathways from the dayside into the nightside. This propagation direction in the polar region was opposite to the normal assumption that TIDs originated in the nightside auroral region. Results suggest that significant dayside sources, such as cusp regions, can be efficient in generating transpolar TIDs during geospace storm intervals.

Short‐ and Long‐Wavelength TIDs Generated by the Great American Eclipse of 21 August 2017

AbstractOn the 21 August 2017 the eclipse shadow drastically changed the state of the ionosphere over the United States. This effect on the ionosphere is visible in the total electron content measured by Global Navigation Satellite Systems (GNSS). The shadow moved with the supersonic speed of ~1,000 m/s over Oregon to ~650 m/s over South Carolina. In order to exhaustively explore the ionospheric signature of the eclipse, we use data of total electron content from ~3,000 GNSS stations seeing multiple Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS) satellites to visualize the phenomena. This tremendous dataset allows high‐resolution characterization of the frequency content and wavelengths—using an omega‐k analysis based on 3‐D fast Fourier transform—of the eclipse signature in the ionosphere in order to fully identify traveling ionospheric disturbances (TIDs). We confirm the generation of TIDs associated with the eclipse including TIDs interpreted as bow waves in previous studies. Additionally, we reveal, for the first time, short (50–100 km) and long (500–600 km) wavelength TIDs with periods between 30 and 65 min. The sources of the revealed short wavelength TIDs are co‐located with the regions of stronger gradient of the EUV related to sunspots. Our work confirms and describes physical properties of the waves observable in the ionosphere during the Great American Eclipse.

Numerical study of traveling ionosphere disturbances with vertical incidence data

High frequency ionosphere vertical sounding, as an important and representative application for detecting the ionosphere and studying the characteristics of radio propagation, can be utilized to monitor the ionosphere continuously variation and to acquire the ionosphere asymmetrical features of diverse scale above the ionosphere vertical sounding stations. This is a first article on real time application of numerical methods to obtain the parameters of traveling ionosphere disturbances (TIDs) using vertical incident ionograms. In this paper, the distribution of ionosphere electron density with TIDs is constructed using a background ionosphere model superimposed a perturbation theory model. The background ionosphere electron density is modelled by the inversion of vertical incident ionograms which are observed before the appearance of the disturbance. Based on the fourth order Adams-Bashforth-Moulton (the so-called ABM) predictor corrector method, instead of Runge-Kutta method, the fast digital ray tracing method is established. According to process of the disturbed trace simulation and parameters inversion, the characteristic parameters of ionosphere disturbance at different detection time can be obtained in real time. The numerical analysis of TIDs is then captured completely.

ADDTID: An Alternative Tool for Studying Earthquake/Tsunami Signatures in the Ionosphere. Case of the 2011 Tohoku Earthquake

In this work, we characterized the ionospheric disturbances generated during the Japan Tohoku earthquake of 11 March 2011, by means of the Atomic Decomposition Detector of Traveling Ionospheric Disturbances (ADDTID) algorithm. This algorithm automatically detects and characterizes Traveling Ionospheric Disturbances (TIDs) from Global Navigation Satellite System (GNSS) measurements. Applying the high-precision estimates of ADDTID, the propagation parameters would make it easier to distinguish TIDs from different origins, in particular the characteristics conforming the acoustic gravity waves driven by the earthquake/tsunami. This method does not assume that disturbances follow a circular pattern of propagation, and can estimate the location by the propagation pattern of tsunami wavefronts and related TIDs. In this work, we present in a single framework a description of phenomena observed by different researchers. By means of the ADDTID algorithm, we detect: (a) simultaneous TIDs of different characteristics, where the detection was robust against the curvature of the wave fronts of the perturbations and the accuracy of the estimated parameters. The results were double-checked by visual inspection from detrended Vertical Total Electron Content (VTEC) maps and keogram plots, and the parameters of the slow-speed TIDs were consistent with the tsunami waveform measurements; (b) different wavefronts between the west and east TIDs around the epicenter, consistent in time and space with the post-earthquake tsunami; (c) complete evolution of the circular TIDs driven by the tsunami during the GNSS observable area; (d) fast and short circular TIDs related to the acoustic waves of earthquake; (e) the pre-seismic activity consisting of a set of fast westward TIDs, and the comparison with neighboring days; (f) the location estimation of the tsunami wavefront along the coast and the possible use as early warning. Finally, we report disturbances that had not been previously published with a possible application to local and real-time detection of tsunamis.