\u3cem\u3eIonoSeis\u3c/em\u3e: A Package to Model Coseismic Ionospheric Disturbances

We present the framework of the modeling package IonoSeis. This software models Global Navigation Satellite System (GNSS) derived slant total electron content (sTEC) perturbations in the ionosphere due to the interaction of the neutral atmosphere and charged particles in the ionosphere. We use a simplified model to couple the neutral particle momentum into the ionosphere and reconstruct time series of sTEC perturbations that match observed data in both arrival time and perturbation shape. We propagate neutral atmosphere disturbances to ionospheric heights using a three-dimensional ray-tracing code in spherical coordinates called Windy Atmospheric Sonic Propagation (WASP3D), which works for a stationary or non-stationary atmospheric models. The source of the atmosphere perturbation can be an earthquake or volcanic eruption; both couple significant amounts of energy into the atmosphere in the frequency range of a few Millihertz. We demonstrate the output of the code by comparing modeled sTEC perturbation data to the observed perturbation recorded at GNSS station BTNG (Bitung, Indonesia) immediately following the 28 September 2018, Sulawesi-Palu earthquake. With this framework, we provide a software to couple the lithosphere, atmosphere, and ionosphere that can be used to study post-seismic ionospherically-derived signals

Real-Time Monitoring of Ionospheric Irregularities and TEC Perturbations

The ionosphere is a part of the upper atmosphere that is a threat to GNSS and satellite telecommunication systems. In this chapter, we will dive into the GNSS real-time monitoring of ionospheric irregularities and TEC perturbations, with a focus on the detection of small- and medium-scale traveling ionospheric disturbances (TIDs) for natural hazard applications. We will describe the Variometric Approach for Real-Time Ionosphere Observation (VARION) algorithm, which is capable of estimating TEC variations in real time, and it was used to detect tsunami-induced TIDs. In particular, the analytical and physical implications of applying the VARION algorithm both to GNSS dual-frequency MEO (medium Earth orbit) and GEO (geostationary orbit) satellites will be provided, thus highlighting its relevance for natural hazard early warning systems and real-time monitoring of ionospheric irregularities

New applications and challenges of GNSS variometric approach

Global Navigation Satellite Systems (GNSS) are nowadays widely used in several technical and scientific activities. Since the early stages of development (mid 1980 s), given the high level of accuracy achieved in determining the coordinates of the receiver, it became clear that the extensive deployment of GPS stations all over the world would have improved many tasks in geodesy and geodynamics. The use of GNSS signals is now not only limited to the estimation of the receiver's position, but it has eventually become a key instrument for ionospheric and tropospheric remote sensing studies, and for soil features (GNSS reflectometry). In particular, GNSS can be used to monitor the ionosphere at different time and space scales. On a global scale, GNSS signals are used to generate Global Ionosphere Maps (GIM) by measuring the total electron content from stations located around the world. On a regional scale, the same signals can be used to detect fast ionospheric disturbances, including those generated by natural hazards, such as tsunami and earthquakes. %For these reasons, real-time GNSS applications became particularly relevant in a number of different scientific fields. The Variometric Approach is a processing algorithm for GNSS observations which allow a GNSS receiver to provide valuable real-time information in a stand-alone operative mode. This approach is based on single time differences of suitable linear combinations of GNSS carrier-phase measurements, using a stand-alone GNSS receiver and standard GNSS broadcast products (orbits and clocks corrections) that are available in real-time. This thesis investigates the possibility to apply the Variometric Approach to the monitoring of the ionosphere, in order to detect in real-time ionospheric disturbances generated by tsunami. The first chapter of this thesis will serve as a preface to define fundamental concepts that we will refer to throughout the rest of this work. The rest of this thesis is divided into two main parts. In the first part (chapter~\ref{sec:VADASE}), we present some advances and applications of the VADASE (Variometric Approach for Displacements Analysis Standalone Engine) algorithm to estimate in real time ground velocities and displacements using stand-alone GNSS receivers. This algorithm was eventually appointed as an effective strategy to contribute to GNSS seismology. In this section we used the 2016 Meinong earthquake occurred in Taiwan as a case study and we estimated coseismic displacements and propagation properties of the surface waves in a real-time scenario using low-cost GNSS receivers. The second part of this work (chapters \ref{sec:VARION}, \ref{sec:rtscenario}, and \ref{sec:VARIONimpementation}) is devoted to a new GNSS processing algorithm, VARION (Variometric Approach for Real-Time Ionosphere Observation), which is capable of estimating changes in the ionosphere's Total Electron Content (TEC) using stand-alone GNSS receivers in real time. In chapter~\ref{sec:rtscenario}, the effectiveness of VARION was proven on the following study cases: 2012 Haida Gwaii earthquake and tsunami event, 2015 Chile earthquake and tsunami event, 2013 U.S. East Coast meteotsunami event, and 2017 Mexico tsunami and geomagnetic storm events. Finally, some conclusions and relevant prospects for future VARION developments are outlined. VARION may represent a significant contribution to science because the ionosphere is strongly coupled to the dynamics of the Earth's surface, neutral atmosphere, and geomagnetic field. In particular, these ionospheric perturbations can be used to detect in real time detection atmospheric gravity waves due to tsunamis. During the NASA funded GNSS Tsunami Early Warning System 2017 workshop held in Sendai, Japan, July 25-27 2017, the VARION algorithm was appointed as the first real-time GNSS tsunami tracking and warning system based upon NASA's Global Differential GPS system

On the detection of ionospheric waves, relationship with earthquakes and tsunamis

The research of this thesis addresses the detection and characterization of ionospheric waves and its application to traveling ionospheric disturbances (TIDs) induced by the natural events, such as earthquakes and tsunamis. The characterization is done from regional detrended Vertical Total Electron Content (VTEC) maps which are obtained from a set of Global Navigation Satellite System (GNSS) satellites. Note that from the mathematical and signal-processing point of view, the problem presents two key difficulties that are (a) the fact that ionospheric sampling is nonuniform, with different density of samples that somehow reflect the distribution of stations over the earth surface, and (b), that the estimation method can not introduce any constraints in the number of disturbances and their propagation parameters. In the first contribution of the thesis, we propose a method for detecting the number of simultaneous TIDs from a time series of high-pass-filtered VTEC maps and their parameters. The method, which we refer to as the Atomic Decomposition Detector of TIDs (ADDTID), is tested on the detrended VTEC map corresponding to a simulated realistic scenario from the dense GNSS network, Global Positioning System Earth Observation Network (GEONET) in Japan. The contribution consists of the detection of the exact number of independent TIDs from a nonuniform sampling of the ionospheric pierce points. The solution to the problem is set as the estimation of the representative perturbations from a dictionary of atoms that span a linear space of possible TIDs by means of a variation of the LASSO algorithm. These atoms consist of plane waves characterized by a wavelength, direction, and phase on a surface defined, the part of the ionosphere sounded by the GNSS observation. As the second contribution, we apply ADDTID on actual VTEC data to the GEONET network. We have studied the Medium Scale TIDs (MSTIDs) during the Spring Equinox day of 21 March 2011. The geophysical contribution is: (a) detection of circular MSTID waves compatible by time and center with a specific earthquake; (b) simultaneous superposition of two distinct MSTIDs, with almost the same azimuth; and (c) the presence of nighttime MSTIDs with velocities in the range 400-600 m/s. In the third contribution we provide a detailed characterization of the TIDs originated from the total solar eclipse of 21 August 2017, the shadow of which crossed the United States from the Pacific to the Atlantic ocean. This can be modeled in part as if the umbra and penumbra were moving cylinders that intersects with variable elevation angle a curved surface. The result of this is reflected in the time evolution of the TID wavelengths produced by the eclipse, which depend on the vertical angle of the sun with the surface of the earth, and also a double bow wave phenomenon, where the bow waves are generated in advance to the umbra. Finally, we detected a clear pattern of MSTIDs, which appeared in advance of the penumbra, which we could hypothesize as soliton waves associated with the bow wave. In the fourth contribution we characterized the MSTIDs generated during the Japan Tohoku earthquake of 11 March 2011. We found: (a) a confirmation of the performance of the algorithm in face of simultaneous multi-TID, the robustness to the curvature of the wave fronts of the perturbations and the accuracy of the estimated parameters. The results were double checked by the additional visual inspection from VTEC maps and keogram plots; (b) The detection of different wave fronts between the west and east MSTIDs around the epicenter, consistent in time and space with the post-earthquake tsunami; (c) The complete evolution of the circular MSTIDs driven by the tsunami during the GNSS observable area; (d) The detection of the fast and short circular TIDs related to the acoustic waves of earthquake.Esta tesis aborda la detección y caracterización de las ondas ionosféricas y su aplicación a las perturbaciones ionosféricas itinerantes (TID traveling ionospheric disturbances) inducidas por eventos naturales. La caracterización se realiza a partir de mapas regionales de Contenido Total Vertical de Electrones (VTEC) que se obtienen a partir de medidas de un conjunto de satélites del Sistema Navegación GNSS (Global Navigation Satellite System). Obsérvese que, desde el punto de vista matemático y de procesamiento de señales, el problema presenta dos dificultades: a) el hecho de que el muestreo ionosférico no es uniforme, con una densidad de muestras diferente que refleja de alguna manera la distribución de las estaciones sobre la superficie terrestre, y b) el hecho de que el método de estimación no puede introducir ninguna limitación en el número de perturbaciones y sus parámetros de propagación a detectar. En la primera contribución de la tesis, proponemos un método para detectar el número de TIDs simultáneas de una serie temporal de mapas VTEC filtrados por paso alto y sus parámetros. El método, al que denominamos como el Detector de Descomposición Atómica de TIDs (ADDTID), lo probamos con mapas VTEC, que corresponden a un escenario realista simulado en la red GEONET en Japón. La contribución consiste en la detección del número exacto de TIDs independientes a partir de un muestreo no uniforme de los IPPs de la ionosférica. La solución al problema se establece como la estimación de las perturbaciones representativas a partir de un diccionario de átomos que abarcan un espacio lineal de posibles TIDs mediante una variación del algoritmo LASSO. Estos átomos consisten en ondas planas caracterizadas por una longitud de onda, dirección y fase en una superficie definida. Como segunda contribución, aplicamos ADDTID a los datos VTEC a la red GEONET. Para probar el método, hemos estudiado los MSTIDs durante el día del Equinoccio de Primavera del 21 de marzo de 2011. La contribución geofísica es: (a) la detección de ondas circulares MSTID compatibles por tiempo y centro con un terremoto específico; (b) la superposición simultánea de dos MSTID distintos, con casi el mismo acimut; y (c) la presencia durante la noche de MSTID con velocidades en el rango de 400-600 m/s. En la tercera contribución presentamos una caracterización detallada de los TIDs originados por el eclipse solar total del 21 de agosto de 2017, cuya sombra atravesó los Estados Unidos desde el Pacífico hasta el Océano Atlántico. La evolución temporal de las TID producidas por el eclipse, que dependen del ángulo vertical del sol con la superficie de la tierra, y también aparece en un fenómeno de doble onda de choque. Finalmente, detectamos un patrón claro de MSTIDs, que aparecieron antes de la llegada de la penumbra, lo que podríamos hipotetizar como ondas de solitón asociadas con la onda de choque. En la cuarta contribución caracterizamos los MSTIDs generados durante el terremoto de Tohoku en Japón el 11 de marzo de 2011. Lo encontramos: a) una confirmación de la prestación del algoritmo frente al multi-TID simultáneas, la robustez frente a la curvatura de los frentes de onda de las perturbaciones y la precisión en la estimación de los parámetros. Los resultados se verificaron por duplicado mediante la inspección visual adicional de los mapas de VTEC y de los diagramas de keogramas; b) la detección de diferentes frentes de onda entre los MSTID del oeste y del este en torno al epicentro, coherentes en el tiempo y en el espacio con el maremoto posterior al terremoto; c) la evolución completa de las MSTID circulares que impulsó el maremoto durante el período observable en la zona de observación de los GNSS; y d) la detección de las MSTID circulares cortas y rápidas en el espacio en relación con las ondas acústicas asociadas con el terremoto.Postprint (published version

ADDTID: An alternative tool for studying earthquake/tsunami signatures in the ionosphere. Case of the 2011 Tohoku earthquake

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.Peer ReviewedPostprint (published version

Modeling of Ionospheric Responses to Atmospheric Acoustic and Gravity Waves Driven by the 2015 Nepal M w 7.8 Gorkha Earthquake

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

Mesopause Airglow Disturbances Driven by Nonlinear Infrasonic Acoustic Waves Generated by Large Earthquakes

Near-epicentral mesopause airglow perturbations, driven by infrasonic acoustic waves (AWs) during a nighttime analog of the 2011 M9.1 Tohoku-Oki earthquake, are simulated through the direct numerical computation of the 3D nonlinear Navier-Stokes equations. Surface dynamics from a forward seismic wave propagation simulation, initialized with a kinematic slip model and performed with the SPECFEM3D_GLOBE model, are used to excite AWs into the atmosphere from ground level. Simulated mesopause airglow perturbations include steep oscillations and persistent nonlinear depletions up to 50% and 70% from the background state, respectively, for the hydroxyl OH(3,1) and oxygen O(1S) 557.7-nm emissions. Results suggest that AWs excited near a large earthquake\u27s epicenter may be strong enough to drive fluctuations in mesopause airglow, some which may persist after the AWs have passed, that could be readily detectable with ground- and/or satellite-based imagers. Synthetic data demonstrate that future airglow observations may be used for the characterization of earthquake mechanisms and surface seismic waves propagation, potentially complementing tsunami early-warning systems based on total electron content (TEC) observations

CubeSat GPS Observation of Traveling Ionospheric Disturbances After the 2022 Hunga-Tonga Hunga-Ha'apai Volcanic Eruption and Its Potential Use for Tsunami Warning

publishedVersio

Characterizing Coseismic Ionospheric Disturbance for Surface-Rupturing Earthquakes

Coseismic ionospheric disturbances (CID) are commonly identified using global navigation space system (GNSS) satellites. Little research, however, has focused on using total electron content (TEC) observations to characterize acoustic sources on Earth\u27s surface. For this thesis, I investigate the applicability of an analytical method to invert the TEC for the acoustic wave. The inversion is based on the modeling of a transfer function. Deconvolving the TEC by the transfer function gives the acoustic wave. Inverting for the acoustic wave in this way would remove phase differences in the TEC created by atmospheric-ionospheric coupling. I test the assumption in the model of a 1D, vertically varying ionosphere by comparing numerical models of the TEC using 1D and 3D electron density divergences. I find the results are complex and recommend obtaining a transfer function that includes a 3D ionosphere. Regardless, even with the phase shift introduced by ionospheric coupling, we are able to apply seismic methods to the TEC. I show an example of applying seismic methods to the TEC of the 2016 Kaikoura earthquake. In this chapter, I highlight the ionospheric response to the rupture. I use numerical modeling and find the TEC response to be more consistent with an acoustic source located northeast of the initial rupture. I also apply backprojection to the TEC for the first time and obtain a source just northwest of the rupture area. The errors in the backprojection are consistent with expected errors from local winds, which were not included in the model. Besides accounting for local winds in future work, inversion of the acoustic wave should also improve backprojection results by removing phase differences in the TEC

The geospace response to variable inputs from the lower atmosphere:a review of the progress made by Task Group 4 of CAWSES-II

The advent of new satellite missions, ground-based instrumentation networks, and the development of whole atmosphere models over the past decade resulted in a paradigm shift in understanding the variability of geospace, that is, the region of the atmosphere between the stratosphere and several thousand kilometers above ground where atmosphere-ionosphere-magnetosphere interactions occur. It has now been realized that conditions in geospace are linked strongly to terrestrial weather and climate below, contradicting previous textbook knowledge that the space weather of Earth's near space environment is driven by energy injections at high latitudes connected with magnetosphere-ionosphere coupling and solar radiation variation at extreme ultraviolet wavelengths alone. The primary mechanism through which energy and momentum are transferred from the lower atmosphere is through the generation, propagation, and dissipation of atmospheric waves over a wide range of spatial and temporal scales including electrodynamic coupling through dynamo processes and plasma bubble seeding. The main task of Task Group 4 of SCOSTEP's CAWSES-II program, 2009 to 2013, was to study the geospace response to waves generated by meteorological events, their interaction with the mean flow, and their impact on the ionosphere and their relation to competing thermospheric disturbances generated by energy inputs from above, such as auroral processes at high latitudes. This paper reviews the progress made during the CAWSES-II time period, emphasizing the role of gravity waves, planetary waves and tides, and their ionospheric impacts. Specific campaign contributions from Task Group 4 are highlighted, and future research directions are discussed