Detection and description of the different ionospheric disturbances that appeared during the solar eclipse of 21 August 2017

This work will provide a detailed characterization of the travelling ionospheric disturbances (TIDs) created by the solar eclipse of 21 August 2017, the shadow of which crossed the United States from the Pacific to the Atlantic ocean. The analysis is done by means of the Atomic Decomposition Detector of Traveling Ionospheric Disturbances (ADDTID) algorithm. This method automatically detects and characterizes multiple TIDs from the global navigation satellite system (GNSS) observation. The set of disturbances generated by the eclipse has a richer and more varied behavior than that associated with the shock wave directly produced by cooling effects of the moon shadow. This can be modeled in part as if the umbra and penumbra of the eclipse were moving cylinders that intersects with variable elevation angle a curved surface. This projection gives rise to regions of equal penumbra with shapes similar to ellipses, with different centers and foci. 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. We show that the delay in the appearance of the disturbances with the transit of the eclipse are compatible with the physical explanations, linked to the different origins of the disturbances and the wavelengths. Finally, we detected a consistent pattern, in location and time of disturbances in advance to the penumbra as a set of medium scale TIDs, which could be hypothesized as soliton waves of the bow wave. In all cases, the detected disturbances were checked visually on the detrended vertical total electron content (TEC) maps.Peer ReviewedPostprint (published version

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

Ionosphere Monitoring with Remote Sensing

This book focuses on the characterization of the physical properties of the Earth’s ionosphere, contributing to unveiling the nature of several processes responsible for a plethora of space weather-related phenomena taking place in a wide range of spatial and temporal scales. This is made possible by the exploitation of a huge amount of high-quality data derived from both remote sensing and in situ facilities such as ionosondes, radars, satellites and Global Navigation Satellite Systems receivers

Traveling Ionospheric Disturbances in the Vicinity of Storm-Enhanced Density at Midlatitudes

This study provides first storm time observations of the westward-propagating medium-scale traveling ionospheric disturbances (MSTIDs), particularly, associated with characteristic subauroral storm time features, storm-enhanced density (SED), subauroral polarization stream (SAPS), and enhanced thermospheric westward winds over the continental US. In the four recent (2017–2019) geomagnetic storm cases examined in this study (i.e., 2018-08-25/26, 2017-09-07/08, 2017-05-27/28, and 2016-02-02/03 with minimum SYM-H index −206, −146, −142, and −58 nT, respectively), MSTIDs were observed from dusk-to-midnight local times predominately during the intervals of interplanetary magnetic field (IMF) Bz stably southward. Multiple wavefronts of the TIDs were elongated NW-SE, 2°–3° longitude apart, and southwestward propagated at a range of zonal phase speeds between 100 and 300 m/s. These TIDs initiated in the northeastern US and intensified or developed in the central US with either the coincident SED structure (especially the SED basis region) or concurrent small electron density patches adjacent to the SED. Observations also indicate coincident intense storm time electric fields associated with the magnetosphere–ionosphere–thermosphere coupling electrodynamics at subauroral latitudes (such as SAPS) as well as enhanced thermospheric westward winds. We speculate that these electric fields trigger plasma instability (with large growth rates) and MSTIDs. These electrified MSTIDs propagated westward along with the background westward ion flow which resulted from the disturbance westward wind dynamo and/or SAPS

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

Ionosonde and GPS total electron content observations during the 26 December 2019 annular solar eclipse over Indonesia

We report the investigation of the ionospheric response to the passage of an annular solar eclipse over Southeast Asia on 26 December 2019 using multiple sets of observations. Two ionosondes (one at Kototabang and another at Pontianak) were used to measure dynamical changes in the ionospheric layer during the event. A network of ground-based GPS receiver stations in Indonesia was used to derive the distribution of total electron content (TEC) over the region. In addition, extreme ultraviolet (EUV) images of the Sun from the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory (SDO) satellite were also analyzed to determine possible impacts of solar-active regions on the changes that occurred in the ionosphere during the eclipse. We found −1.62 and −1.90 MHz reductions (24.0 % and 27.5 % relative reduction) in foF2 during the solar eclipse over Kototabang and Pontianak, respectively. The respective TEC reductions over Kototabang and Pontianak during the eclipse were −4.34 and −5.45 TECU (24.9 % and 27.9 % relative reduction). Data from both ionosondes indicate a consistent 34–36 min delay between maximum eclipse and minimum foF2. The corresponding time delays for eclipse-related TEC reduction at these two locations were 40 and 16 min, respectively. The ionospheric F layer was found to descend with a speed of 9–19 m s−1 during the first half of the eclipse period. We also found an apparent rise in the ionospheric F-layer height near the end of the solar eclipse period, equivalent to a vertical drift velocity of 44–47 m s−1. The GPS TEC data mapping along a set of cross-sectional cuts indicates that the greatest TEC reduction actually occurred to the north of the solar-eclipse path, opposite of the direction from which the lunar shadow fell. As the central path of the solar eclipse was located just to the north of the southern equatorial ionization anomaly (EIA) crest, it is suspected that such a peculiar TEC reduction pattern was caused by plasma flow associated with the equatorial fountain effect. Net perturbations of TEC were also computed and analyzed, which revealed the presence of some wavelike fluctuations associated with the solar-eclipse event. Some of the observed TEC perturbation patterns that propagated with a velocity matching the lunar shadow may be explained in terms of nonuniform EUV illumination that arose as various active regions on the Sun went obstructed and unobstructed during the eclipse. The remaining wavelike features are likely to be traveling ionospheric disturbances (TIDs) generated by the passage of the solar eclipse on top of other diurnal factors.</p

Ionospheric TEC from the Turkish Permanent GNSS Network (TPGN) and comparison with ARMA and IRI models

Abstract: The present study investigates the ionospheric Total Electron Content (TEC) variations in the lower mid-latitude Turkish region from the Turkish permanent GNSS network (TPGN) and International GNSS Services (IGS) observations during the year 2016. The corresponding vertical TEC (VTEC) predicted by Auto Regressive Moving Average (ARMA) and International Reference Ionosphere 2016 (IRI-2016) models are evaluated to realize their effectiveness over the region. The spatial, diurnal and seasonal behavior of VTEC and the relative VTEC variations are modeled with Ordinary Least Square Estimator (OLSE). The spatial behavior of modeled result during March equinox and June solstice indicates an inverse relationship of VTEC with the longitude across the region. On the other hand, the VTEC variation during September equinox and December solstice including March equinox and June solstice are decreasing with increase in latitude. The GNSS observed and modeled diurnal variation of the VTEC show that the VTEC slowly increases with dawn, attains a broader duration of peak around 09.00 to 12.00 UT, and thereafter decreases gradually reaching minimum around 21.00 UT..

Global ionospheric maps : estimation and assessment in post-processing and real-time

The research of this paper-based dissertation is focused on Global Ionospheric Maps (GIM) generation and assessment. In summary, the novelty and thematic unity in this works relies on four different but complementary topics: 1. Defining a systematic procedure to validate and quantify the quality of GIMs based on independent data sources or techniques. 2. Applying this methodology to not only the GIMs computed at UPC, but also to most of the currently open accessible GIMs inside the scientific community. 3.Including newly available Global Navigation Satellite Systems (GNSS) data to the processing of UPC's GIMs. 4. Assessment and distribution also of real-time GIMs. More in detail, my first contribution has been to the definition of a complete GIM validation procedure. This procedure is based on two methods: direct VTEC (Vertical Total Electron Content) altimeter and GNSS difference of slant TEC (Total Electron Content), both of them giving complementary information of the GIM performance. The main advantage of using satellite altimeter data is the fact that we are using a truly independent information source with regard to the input data used for GIM generation. This allows assessing the TEC from a entirely different point-of-view, fully different and independent to any error that may affect GNSS systems and its processing. The second technique, relies on using the same type of input data but in this case from permanent GNSS stations not participating in the GIM generation. The main advantages of this second technique is twofold: first, it allows to asses the GIMs on land; and second its a low latency direct assessment of the GIM, given a more direct information about the processing and interpolation done with the GNSS input data. Afterwards, a second contribution has been to use the previously defined methodology to validate all the GIMs generated by the International GNSS Service (IGS) Associated Analysis Centers (IAAC), and some other candidates to join them, for a more than a full solar cycle (starting from end of 2001 to beginning of 2017). As a side result, it is also demonstrated that while the time interval of the GIM has little influence on its overall quality, the interpolation technique used by the IAACs has an important role. Finally, this work also lead to the acceptance of the previously mentioned IAAC candidates since it demonstrated the good quality of their GIMs. Another contribution has been, as part of the European GRC project, improving the currently in production UPC's TOMION (TOMographic IONospheric) software used to generate the UQRG (UPC's rapid GIM) map. The software input source data was restricted to GPS L1 and L2. Now it allows processing all current frequencies available for GPS, Galileo and Beidou. This software has been internally tested for some specific days with the previously explained altimeter method giving results with improved quality for specific combinations of GNSS systems and frequencies. Using this work flow but focused on single frequency processing, a last article was published analysing the ionospheric footprint of the solar eclipse over North America during 2017. Finally, another contribution has been to improve the data acquisition and distribution system for the real-time GIM generation processing chain. Furthermore, as part of UPC contribution to the Real Time Ionospheric Monitoring Working Group (RTIM-WG) of the International Association of Geodesy (IAG) and following the previously explained methodology, an assessment of the GIMs generated by the members of this sub-commission have been performed. As a result of all these efforts, UPC has been leading inside the IGS frame, and made a first implementation, of a new real-time combined map.La recerca realitzada en aquesta tesis en format compendi d’articles esta enfocada en la generació i validació de mapes ionosfèrics globals (GIM, del angles Global Ionospheric Maps). En resum, la novetat i unitat temàtica d’aquesta tesis esta basada en quatre temes diferents però complementaris: • Definició d’un procediment sistemàtic per validar i quantificar la qualitat dels GIMs basada en fonts de dades o tècniques independents. • Aplicar aquesta metodologia no nomes als GIMs generats a UPC, sinó també a la resta de GIMs d’accés obert actualment existent dintre la comunitat científica internacional. • Incloure en el processat per generar els GIMs de UPC dades de les noves constel·lacions GNSS (del angles Global Navigation Satellite Systems) disponibles. • Validació i distribució també dels GIMs en temps real. Com a conseqüència, també s’ha aconseguit generar un primer GIM combinat en temps real. Mes en detall, la meva primera contribució va ser definir un procediment complet de validació de GIM. Aquest procediment esta basat en dos mètodes: obtenció directa del contingut vertical total d’electrons (VTEC, del angles, Vertical Total Electron Content) a partir de dades d’altimetria i per diferencies del contingut total d’electrons (TEC, del angles Total Electron Content) inclinat de dades GNSS. Els dos donen informació complementaria de la qualitat dels GIM. L’avantatge principal d’utilitzar dades de satèl·lits altimètrics es que es una font de dades completament diferent de les que s’utilitzen per la generació dels GIMs. Aquest fet ens permet verificar el TEC des d’una perspectiva diferent, plenament independent de qualsevol font d’error que pugui afectar al propi sistema GNSS o el seu processat. El segon mètode, es basa en la mateix tipus de dades que s’utilitzen pel càlcul dels GIM però en aquest cas amb dades d’estacions permanent GNSS no involucrades en la generació dels GIMs a avaluar. L’avantatge principal d’aquest segon mètodes es doble: primer, permet avaluar el GIM sobre els continents; i segon, permet fer la anàlisis directa de baixa latència del GIM, a mes a mes donant informació directa sobre el processat i la interpolació aplicada sobre les dades GNSS. Seguidament, la meva segona contribució va ser utilitzar la metodologia prèviament definida per validar tots els GIM generats per part dels centres d’anàlisis associats al Servei Internacional de GNSS (IGS, del angles International GNSS Service) i altres centres candidats a unir-se a IGS, per mes d’un cicle solar (des de finals del 2001 fins al inici del 2017). Com a resultat secundari, també va permetre demostrar que per una banda l’interval temporal dels GIM te poca influencia sobre la seva qualitat global, però per altra banda la tècnica d’interpolació emprada per part dels centres te un impacte molt important. Finalment, aquest article va portar a l’admissió d’aquests candidats prèviament mencionats a centres d’anàlisis associats a IGS donat que es va demostrar la bona qualitat dels seus GIMs. Una altra contribució important va ser, com a part del projecte europeu GRC, millorar el software TOMION (TOMographic IONospheric) de UPC, actualment en producció generant el GIM UQRG (GIM ràpid de UPC). Aquest software nomes permetia utilitzar dades de GPS L1 i L2. Les millores realitzades durant aquesta tesis permeten processar totes les freqüències actualment existent de GPS, Galileo i Beidou. El software ha estat internament validat per certs dies específics amb el mètode explicat prèviament d’altimetria millorant els resultats en comparació a la versió anterior per certes combinacions de constel·lacions GNSS i freqüències. Utilitzant aquesta nova metodologia de processat aplicada a una sola freqüència, un últim article va ser publicat analitzant l’empremta ionosfèrica de l’eclipsi solar sobre Amèrica del nord durant el 2017. Finalment, una altre contribució va ser millorar el mètode d’adquisició i distribució del sistema de processat del GIM en temps real. Es mes, com a part de la contribució de la UPC, es va realitzar una validació dels GIMs generats pels participants del grup de treball de monitorització en temps real de la ionosfera (RTIM-WG, del angles Real Time Ionospheric Monitoring Working Group) de l’Associació Internacional de Geodèsia (IAG, del angles International Association of Geodesy) seguint la metodologia anteriorment citada. Com a resultat d’aquestes tasques la UPC ha liderat i mplementat un nou mapa combinat en temps real, en el marc de IGS.Postprint (published version

Anthropogenic Space Weather

Anthropogenic effects on the space environment started in the late 19th century and reached their peak in the 1960s when high-altitude nuclear explosions were carried out by the USA and the Soviet Union. These explosions created artificial radiation belts near Earth that resulted in major damages to several satellites. Another, unexpected impact of the high-altitude nuclear tests was the electromagnetic pulse (EMP) that can have devastating effects over a large geographic area (as large as the continental United States). Other anthropogenic impacts on the space environment include chemical release ex- periments, high-frequency wave heating of the ionosphere and the interaction of VLF waves with the radiation belts. This paper reviews the fundamental physical process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure