The International GNSS Service (IGS) Working Group on Ionosphere was created in 1998. Since then, the Scientific community behind IGS, in particular CODE, ESA, JPL and UPC, have been continuosly ...contributing to reliable IGS combined vertical total electron content (VTEC) maps in both rapid and final schedules. The details on how these products are being generated, performance numbers, proposed improvement as far as VTEC evolution trends during near one Solar Cycle, are summarized in this paper. The confirmation of (1) the good performance of the IGS combined VTEC maps, and (2) the characteristic VTEC variability periods, are two main results of this work.
Numerical models of ionospheric coupling with the neutral atmosphere are used to investigate perturbations of plasma density, vertically integrated total electron content (TEC), neutral velocity, and ...neutral temperature associated with large‐amplitude acoustic waves generated by the initial ocean surface displacements from strong undersea earthquakes. A simplified source model for the 2011 Tohoku earthquake is constructed from estimates of initial ocean surface responses to approximate the vertical motions over realistic spatial and temporal scales. Resulting TEC perturbations from modeling case studies appear consistent with observational data, reproducing pronounced TEC depletions which are shown to be a consequence of the impacts of nonlinear, dissipating acoustic waves. Thermospheric acoustic compressional velocities are ∼±250–300 m/s, superposed with downward flows of similar amplitudes, and temperature perturbations are ∼300 K, while the dominant wave periodicity in the thermosphere is ∼3–4 min. Results capture acoustic wave processes including reflection, onset of resonance, and nonlinear steepening and dissipation—ultimately leading to the formation of ionospheric TEC depletions “holes”—that are consistent with reported observations. Three additional simulations illustrate the dependence of atmospheric acoustic wave and subsequent ionospheric responses on the surface displacement amplitude, which is varied from the Tohoku case study by factors of 1/100, 1/10, and 2. Collectively, results suggest that TEC depletions may only accompany very‐large amplitude thermospheric acoustic waves necessary to induce a nonlinear response, here with saturated compressional velocities ∼200–250 m/s generated by sea surface displacements exceeding ∼1 m occurring over a 3 min time period.
Key Points
Large undersea earthquakes generate large‐amplitude acoustic waves with compressional velocities exceeding 200 m/s
Modeled ionospheric responses to the 2011 Tohoku earthquake, including TEC depletions, are consistent with the data
TEC depletions are shown to be a result of an initial acoustic shock followed by nonlinear, dissipating acoustic waves in the thermosphere.
Recent advances in GPS data processing have demonstrated that ground-based GPS receivers are capable of detecting ionospheric TEC perturbations caused by surface-generated Rayleigh, acoustic and ...gravity waves. There have been a number of publications discussing TEC perturbations immediately following the
M
9.0 Tohoku earthquake in Japan on March 11, 2011. Most investigators have focused on the ionospheric responses up to a few hours following the earthquake and tsunami. In our research, in addition to March 11, 2011 we investigate global ionospheric TEC perturbations a day before and after the event. We also compare indices of geomagnetic activity on all three days with perturbations in TEC, revealing strong geomagnetic storm conditions that are also apparent in processed GEONET TEC observations. In addition to the traveling ionospheric disturbances (TIDs) produced by the earthquake and tsunami, we also detect “regular” TIDs across Japan about 5 hours following the Tohoku event, concluding these are likely due to geomagnetic activity. The variety of observed TEC perturbations are consistent with tsunami-generated gravity waves, auroral activity, regular TIDs and equatorial fluctuations induced by increased geomagnetic activity. We demonstrate our capabilities to monitor TEC fluctuations using JPL’s real-time Global Assimilative Ionospheric Model (GAIM) system. We show that a real-time global TEC monitoring network is able to detect the acoustic and gravity waves generated by the earthquake and tsunami. With additional real-time stations deployed, this new capability has the potential to provide real-time monitoring of TEC perturbations that could potentially serve as a plug-in to enhance existing early warning systems.
To numerically simulate earthquake‐induced ionospheric disturbances, we extend the Wave Perturbation‐Global Ionosphere‐Thermosphere Model, which was originally developed for tsunami‐ionosphere ...coupling via gravity waves, to the case of earthquake‐ionosphere coupling via acoustic‐gravity waves. The new Wave Perturbation‐Global Ionosphere‐Thermosphere Model represents epicentral crustal movements by a point source specified with the ground motion data from seismic measurements. The model then solves for the neutral atmospheric perturbations generated by spherical acoustic‐gravity waves and the resulting ionospheric plasma perturbations over the epicentral area. We apply the model to simulate the near‐field ionospheric disturbances during two major earthquake events: the 2011 Tohoku‐Oki, Japan, and the 2015 Illapel, Chile, events. To validate the results, we extract receiver‐to‐satellite total electron content perturbations from the simulations and compare them to the corresponding slant total electron content perturbations from Global Positioning System observations. We find good agreement on magnitudes and arrival times between the simulations and observations.
Key Points
We have developed a novel earthquake‐ionosphere coupling model based on a state‐of‐the‐art upper atmospheric model
The model is capable of simulating ionospheric signatures induced by epicentral crustal movements
Model validation with two earthquake events shows reasonable agreement with observations
We demonstrate extreme ionospheric response to the large interplanetary electric fields during the "Halloween" storms that occurred on October 29 and 30, 2003. Within a few (2 - 5) hours of the time ...when the enhanced interplanetary electric field impinged on the magnetopause, dayside total electron content increases of approx.40% and approx.250% are observed for the October 29 and 30 events, respectively. During the Oct 30 event, approx.900% increases in electron content above the CHAMP satellite (approx.400 km altitude) were observed at mid-latitudes (+/-30 degrees geomagnetic). The geomagnetic storm-time phenomenon of prompt penetration electric fields is a possible contributing cause of these electron content increases, producing dayside ionospheric uplift combined with equatorial plasma diffusion along magnetic field lines to higher latitudes, creating a "daytime super-fountain" effect.
We identify interplanetary plasma regions associated with three intense interplanetary coronal mass ejections (ICMEs)‐driven geomagnetic storm intervals which occurred around the same time of the ...year: day of year 74–79 (March) of 2012, 2013, and 2015. We show that differences in solar wind drivers lead to different dynamical ionosphere‐thermosphere (IT) responses and to different preconditioning of the IT system. We introduce a new hourly based global metric for average low‐latitude and northern middle‐latitude vertical total electron content responses in the morning, afternoon, and evening local time ranges, derived from measurements from globally distributed Global Navigation Satellite System ground stations. Our novel technique of estimating nitric oxide (NO) cooling radiation in 11° latitudinal zones is based on Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED)/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) measurements. The thermospheric cooling throughout the storm phases is studied with this high latitudinal resolution for the first time. Additionally, TIMED/Global Ultraviolet Imager (GUVI) observations of the dynamical response of the thermospheric composition (O/N2 ratio) are utilized to study negative ionospheric storm effects. Based on these data sets, we describe and quantify distinct IT responses to driving by ICME sheaths, magnetic clouds, coronal loop remnants, plasma discontinuities, and high‐speed streams following ICMEs. Our analysis of coupling functions indicates strong connection between coupling with the solar wind and IT system response in ICME‐type storms and also some differences. Knowledge of interplanetary features is crucial for understanding IT storm dynamics.
Key Points
We identify interplanetary plasma regions and analyze ICME intervals on DOY 74‐79 March of 2012, 2013, and 2015
We introduce new metrics for average low‐latitude and northern middle‐latitude VTEC and NO thermospheric emission
Our analysis of coupling functions indicates connection and also differences between coupling with the solar wind and IT system response
We revisit three complex superstorms of 19–20 November 2003, 7–8 November 2004, and 9–11 November 2004 to analyze ionosphere‐thermosphere (IT) effects driven by different solar wind structures ...associated with complex interplanetary coronal mass ejections (ICMEs) and their upstream sheaths. The efficiency of the solar wind‐magnetosphere connection throughout the storms is estimated by coupling functions. The daytime IT responses to the complex driving are characterized by combining and collocating (where possible) measurements of several physical parameters (total electron content or TEC, thermospheric infrared nitric oxide emission, and composition ratio) from multiple satellite platforms and ground‐based measurements. A variety of metrics are utilized to examine global IT phenomena at ~1 h timescales. The role of direct driving of IT dynamics by solar wind structures and the role of IT preconditioning in these storms, which feature complex unusual TEC responses, are examined and contrasted. Furthermore, IT responses to ICME magnetic clouds and upstream sheaths are separately characterized. We identify IT feedback effects that can be important for long‐lasting strong storms. The role of the interplanetary magnetic field By component on ionospheric convection may not be well captured by existing coupling functions. Mechanisms of thermospheric overdamping and consequential ionospheric feedback need to be further studied.
Key Points
IT driving by solar wind structures in November 2003 and 2004 storm intervals is analyzed
External driving effects on the IT system can be altered during strong and/or prolonged storms because of thermospheric feedback
We suggest that solar wind‐magnetospheric coupling functions could be significantly improved as predictors of IT responses
Tsunamis can generate gravity waves propagating upward through the atmosphere, inducing total electron content (TEC) disturbances in the ionosphere. To capture this process, we have implemented ...tsunami‐generated gravity waves into the Global Ionosphere‐Thermosphere Model (GITM) to construct a three‐dimensional physics‐based model WP (Wave Perturbation)‐GITM. WP‐GITM takes tsunami wave properties, including the wave height, wave period, wavelength, and propagation direction, as inputs and time‐dependently characterizes the responses of the upper atmosphere between 100 km and 600 km altitudes. We apply WP‐GITM to simulate the ionosphere above the West Coast of the United States around the time when the tsunami associated with the March 2011 Tohuku‐Oki earthquke arrived. The simulated TEC perturbations agree with Global Positioning System observations reasonably well. For the first time, a fully self‐consistent and physics‐based model has reproduced the GPS‐observed traveling ionospheric signatures of an actual tsunami event.
Key Points
We have developed a 3‐D tsunami‐ionosphere coupling model WP‐GITM
WP‐GITM combines an analytical model and a fully physics‐based ionospheric model
WP‐GITM reproduces traveling ionospheric signatures of a real tsunami
Abstract
Near‐ and far‐field ionospheric responses to atmospheric acoustic and gravity waves (AGWs) generated by surface displacements during the 2015 Nepal
7.8 Gorkha earthquake are simulated. ...Realistic surface displacements driven by the earthquake are calculated in three‐dimensional forward seismic waves propagation simulation, based on kinematic slip model. They are used to excite AGWs at ground level in the direct numerical simulation of three‐dimensional nonlinear compressible Navier‐Stokes equations with neutral atmosphere model, which is coupled with a two‐dimensional nonlinear multifluid electrodynamic ionospheric model. The importance of incorporating earthquake rupture kinematics for the simulation of realistic coseismic ionospheric disturbances (CIDs) is demonstrated and the possibility of describing faulting mechanisms and surface deformations based on ionospheric observations is discussed in details. Simulation results at the near‐epicentral region are comparable with total electron content (TEC) observations in periods (
3.3 and
6‐10 min for acoustic and gravity waves, respectively), propagation velocities (
0.92 km/s for acoustic waves) and amplitudes (up to
2 TECu). Simulated far‐field CIDs correspond to long‐period (
4 mHz) Rayleigh waves (RWs), propagating with the same phase velocity of
4 km/s. The characteristics of modeled RW‐related ionospheric disturbances differ from previously‐reported observations based on TEC data; possible reasons for these differences are discussed.
Key Points
Seismically generated AGW dynamics from ground to exobase are simulated based on realistic spatial and temporal surface displacements
Simulation results of near‐epicentral ionospheric responses to AGWs are consistent with observations in amplitudes, periods, and speeds
Results identify challenges and opportunities for faulting mechanism characterization based on ionospheric observations
We investigate the possibility to constrain the evolution of the 2016 M7.8 Kaikoura earthquake evolution based on Global Positioning System signal‐derived ionospheric total electron content (TEC) ...perturbations, that represent plasma responses to infrasonic acoustic waves (IAWs) generated by surface motion. This earthquake exhibited unusual complexity and some first‐order aspects of its evolution remain unclear; for example, how and when the Papatea fault (PF) and the corresponding large surface deformation occurred. For various earthquake models, a seismic wave propagation code is used to simulate time‐dependent surface deformations, which then excite IAWs in a 3D compressible nonlinear atmospheric model, coupled with a 2D nonlinear multispecies ionospheric plasma dynamic model. Our preferred finite‐fault model reproduces the amplitudes, shapes, and time epochs of appearance of detected TEC perturbations well. Additionally, the incorporation of the PF, ruptured during the earthquake, results in the closest agreement between simulated and observed near‐zenith vertical TEC perturbations, whereas its absence shows significant discrepancy. This supports the hypothesis that the PF was ruptured during the Kaikoura earthquake. Furthermore, the IAWs and resulting ionospheric plasma disturbances contain additional information on the PF rupture progression, including the timing of initiation and propagation direction, indicating new opportunities to further constrain the PF rupture with low elevation angle “slant” TEC data. The results confirm the ability for TEC measurements to constrain evolutions of large crustal earthquakes to provide new insight beyond traditional seismic and geodetic data sets.
Plain Language Summary
Earthquakes launch low‐frequency infrasonic acoustic waves (IAWs) into the Earth's atmosphere. As they reach the ionosphere (∼80–1,000 km altitude), IAWs may cause plasma disturbances detectable in the total electron content (TEC), which are routinely measured via fluctuations in Global Positioning System (GPS) signals. However, robust interpretations of coseismic ionospheric disturbances (CIDs) in TEC remain challenging due to the complexity of the coupled dynamics between the Earth's interior, atmosphere and ionosphere. We analyze the evolution of the 2016 New Zealand earthquake by comparing simulated and detected TEC perturbations. Novel model simulations, accounting for full physics of seismic waves, IAWs, and CIDs, show that the incorporation of the Papatea fault (PF) rupture during the earthquake results in the closest agreement between simulated and observed TEC. This supports the hypothesis that the PF was ruptured during the Kaikoura earthquake, which could not be constrained from available seismometer data. Our results suggest that IAWs and resulting CIDs are both sensitive to earthquake rupture progression. We conclude that the evolution of large earthquakes can be further investigated based on GPS TEC measurements combined with numerical physics‐based simulations.
Key Points
Numerical simulations of acoustic waves and ionospheric plasma disturbances driven by the M7.8 Kaikoura earthquake are performed
Comparisons of simulations with TEC observations strongly suggest that the Papatea fault was ruptured during the Kaikoura earthquake
TEC observations can supplement seismological studies of large crustal earthquake evolutions beyond traditional datasets
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