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Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14623号 / 工博第3091号 / 新制||工||1460(附属図書館) / 26975 / UT51-2009-D335 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 大村 善治, 准教授 松尾 哲司, 准教授 酒井 道 / 学位規則第4条第1項該当

Les résultats basés sur les mesures d’ondes électromagnétiques effectuées par le satellite DEMETER sont présentés. Nous nous concentrons sur deux phénomènes différents : 1) les effets liés à l’activité sismique 2) les émissions avec des structures fréquentielles linéaires. 1) Nous présentons une étude statistique de l’intensité des ondes électromagnétiques observées à proximité des tremblements de terre. Nous montrons que pendant la nuit il y a une diminution statistiquement significative de l’intensité des ondes peu avant le choc principal. 2) Nous présentons une étude systématique des événements ayant des structures fréquentielles linéaires. Un ensemble d’événements statistiquement significatif a été obtenu en utilisant une procédure automatique ainsi qu’une inspection visuelle des données. Tous les événements sont entièrement analysés et classifiés. Dans la gamme EBF (ou toutes les six composantes électromagnétiques sont mesurées pendant le mode Burst), une analyse détaillée des ondes a été faite. / Results based on wave measurements performed by the DEMETER spacecraft are presented. We focus on two different phenomena : 1) effects possibly connected with seismic activity 2) emissions with a line structure. 1) We present a statistical study of intensity of electromagnetic waves observed in the vicinity of earthquakes. It is shown that during the night there is a statistically significant decrease of wave intensity shortly before the time of the main shock. 2)We present a survey of the events with a line structure. A statistically significant set of events has been obtained both by using an automatic identification procedure and visual inspection of the data. All the events are thoroughly analyzed and classified. Moreover, in the ELF range (where all the six electromagnetic field components are measured during the Burst mode), a detailed wave analysis has been performed.

A novel electrostatic analyzer (ESA) simulation method that differs significantly from traditional methods is presented in this study, the "reverse-fly" simulation method. The simulation process and its applications are discussed in detail. This method is tested by comparing its results to the published test data of three experimental instruments; The Proton Electrostatic Analyzer-High Geometric Factor (PESA-H) instrument on the Wind mission [Lin, et al. 1995], the 2π-Toroidal Analyzer (2πTA) of Young, et al., [1988], and the Hot Plasma Composition Analyzer (HPCA) to be used in the upcoming Magnetospheric Multi-scale (MMS) mission. The strong agreement between simulation and experimental results verifies the accuracy of this technique. Our results reveal detailed properties of ESA response that are not practical to assess using laboratory data. This simulation method then is used to compare the transmission characteristics of five published ESA geometries to efficiently determine the optimal ESA geometry for use in future space missions. We show that the simulation methods described here are an important contribution to instrument design and development techniques and are critical to efficient and accurate verification of instrument performance.

Traditionally, Retarding Potential Analyzers (RPAs) operate exclusively on large satellites due to the size, power, and mass constraints posed by nano-satellites like CubeSats. These sensors take in-situ measurements of Earth's atmospheric ion current during a range of time-varied ``retarding" voltage steps. Curve-fitting the retarding voltage versus collected current data provides derived measurements of ion density, ram velocity, and temperature. In order to successfully miniaturize these instruments and validate their performance prior to launch, thorough calibration and comprehensive end-to-end testing must be performed. This paper discusses the difficulties of performing complete system validation in ground-based vacuum chamber testing for RPAs. A procedure for RPA instrument calibration will be presented along with the calibration results for the Lower Atmosphere/Ionosphere Coupling Experiment (LAICE) CubeSat RPA. This paper presents a user-friendly and robust software control suite developed to read, parse, and interpret the data from the LAICE RPA. Electronics noise testing and analysis defines the performance boundaries of the instrument electronics. End-to-end testing of the LAICE RPA with a hot-filament ion source simulating the space plasma verifies the function of the LAICE RPA sensor and electronics, as well as the software control, thus qualifying the instrument for on-orbit use. / Master of Science

Measurements with satellite and sounding rocket borne instruments contain important information on remote and local processes in regions containing matter in the plasma state. The characteristic features of the particle distributions can be used to explain the morphology and dynamics of the different plasma populations. Charged particles are lost from a region due to precipitation into the atmosphere, charge exchange processes, or convection to open magnetic field lines. The sources of the Earth’s magnetospheric plasma are mainly ionization and extraction of upper atmosphere constituents, and entry of solar wind plasma. The intensity and distribution of auroral precipitation is controlled in part by the conditions of the interplanetary magnetic field causing different levels of auroral activity. Acceleration of electrons and positive ions along auroral field lines play an important role in magnetospheric physics. Electric fields that are quasi-steady during particle transit times, as well as fluctuating fields, are important for our understanding of the behaviour of the plasma in the auroral region. High-resolution data from the Swedish Viking and the Swedish/German Freja satellites have increased our knowledge considerably about the interaction processes between different particle populations and between particles and wave fields. This thesis describes acceleration processes influencing both ions and electrons and is based on in-situ measurements in the auroral acceleration/heating region, with special emphasis on; processes at very high latitudes, the role of fluctuating electric fields in producing so called electron conics, and positive ion heating transverse to the geomagnetic field lines. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1994, härtill 6 uppsatser.</p> / digitalisering@umu.se

David PÍŠA Study of electromagnetic emissions recorded by the DEMETER satellite Abstract : This thesis presents results based on wave measurements performed by the DEMETER space- craft. This French spacecraft was operating between 2004 and 2010 at the altitude of ∼660 km. We focus on measurements of the electromagnetic waves and plasma density in the vicinity of imminent earthquakes. In the first part, we present a study of plasma density variations in the vicinity of a very powerful earthquake in Chile (Mw 8.8) which occurred on February 27, 2010. Data recorded before the main shock along orbits close to the future epicenter showed increasing plasma den- sities. A statistical analysis using 4 years of data to monitor density variations under similar conditions has been performed. This study shows that a large increase of the plasma density is very uncommon at this location. In the second part, a statistical study (∼6.5 years) of variations of VLF wave intensity is shown. We have analyzed all available data measured close (in time and space) to large earth- quakes (M≥5). Data related to more than 12000 earthquakes have been compared with an unperturbed background distribution. We confirm the previously reported results of a statis- tically significant decrease of the wave intensity at frequencies of about...

Incoherent scatter radar (ISR) measurements were used in conjunction with plasma simulations to study two micro-scale plasma processes that commonly occur in the auroral ionosphere. These are 1) ion acoustic turbulence and 2) Langmuir turbulence. Through an ISR experiment we investigated the dependence of ion acoustic turbulence on magnetic aspect angle. The results showed a very strong aspect angle sensitivity which could be utilized to classify the turbulence according to allowable generation mechanisms and sources of free energy. In addition, this work presents results that led to the discovery of a new type of ISR echo, explained as a signature of cavitating Langmuir turbulence. A number of incoherent scatter radar experiments, exploiting a variety of beam and pulse patterns, were designed or revisited to investigate the Langmuir turbulence underlying the radar echoes. The experimental results revealed that Langmuir turbulence is a common feature of the auroral ionosphere. The experimental efforts also led to uncovering a relationship between Langmuir turbulence and one type of natural electromagnetic emission that is sometimes detected on the ground, so-called “medium frequency burst”, providing an explanation for the generation mechanism of these emissions. In an attempt to gain insights into the source mechanism underlying Langmuir turbulence, 1-dimensional Zakharov simulations were employed to study the interactions of ionospheric electron beams with a broad range of parameters with the background plasma at the F region peak. A variety of processes were observed, ranging from a cascade of parametric decays, to formation of stationary wave packets and density cavities in the condensate region, and to direct nucleation and collapse at the initial stage of the turbulence. The simulation results were then compared with the ISR measurements where inconsistencies were found in the spectral details and intensity of the simulated and measured Langmuir turbulence echoes, suggesting the possibility that the direct energy for the turbulence was provided by unstable low-energy (5 − 20 eV) electron populations produced locally in the F region of the ionosphere rather than by electron beams originating from the magnetosphere.

Cette thèse présente des résultats basés sur les mesures d'ondes réalisées par le satellite DEMETER. Ce satellite français a été exploité entre les années 2004 et 2010 à l'altitude de ~660 km. Nous nous sommes concentrés sur les mesures des ondes électromagnétiques et de la densité du plasma au voisinage des tremblements de terre imminents .Dans la première partie, nous présentons une étude des variations de la densité du plasma dans le voisinage d'un tremblement de terre très puissant au Chili ( Mω 8.8) qui a eu lieu le 27 Février 2010. Les données enregistrées avant le choc principal le long des orbites proches de l'épicentre ont montré des augmentations de densité du plasma. Dans une deuxième étape, une analyse statistique a été effectuée en utilisant 4 ans de données pour suivre les variations saisonnières de densité. Cette étude montre qu'une augmentation forte de la densité du plasma est très rare dans cette région à l'époque du séisme. Dans la deuxième partie, une étude statistique (~6,5 ans) des variations de l'intensité des ondes TBF est montrée. Nous avons analysé toutes les données mesurées disponibles à proximité (en temps et en distance) de grands séismes (M> ou = 5). Les données relatives à plus de 12000 tremblements de terre ont été comparées avec une distribution de référence non perturbée. Nous confirmons les résultats déjà rapportés de la diminution statistiquement significative de l'intensité des ondes à des fréquences de l'ordre de ~1,7 kHz. Cet effet semble être lié à une diminution de la limite inférieure de l'ionosphére qui affecte les ondes TBF qui se propagent dans le guide Terre-ionosphère. / This thesis presents results based on wave measurements performed by the DEMETER spacecraft. This French spacecraft was operating between 2004 and 2010 at the altitude of ~660 km. We focus on measurements of the electromagnetic waves and plasma density in the vicinity of imminent earthquakes. In a first part, we present a study of plasma density variations in the vicinity of a very powerful earthquake in Chile ( Mω 8.8) which occurred on February 27, 2010. Data recorded before the main shock along orbits close to the future epicenter showed increasing plasma densities. In a second step, a statistical analysis using 4 years of data to monitor density variations under similar conditions has been performed. This study shows that a large increase of the plasma density is very uncommon at this location and at this time. In a second part, a statistical study (~6.5 years) of variations of VLF wave intensity is shown. We have analyzed all available data measured close (in time and in distance) to large earthquakes (M> ou = 5). Data related to more than 12000 earthquakes have been compared with an unperturbed background distribution. We confirm the previously reported results of a statistically significant decrease of the wave intensity at frequencies of about ~1.7kHz. This effect seems to be related to a decrease of the lower ionospheric boundary which affects the VLF waves propagating in the Earth-ionosphere waveguide.

The aim of the project is to investigate the characteristics and causes of two different types of bow shocks at Mars. We define Type 1 as an undefined, drawn out ramp, and Type 2 as a shorter duration ramp that has clearer characteristics and behaves more like a step increase in the magnetic field. A total of forty five events of the two different types were investigated using data from 2014-2015 from NASA’s MAVEN spacecraft. The Power Spectral Density of the magnetic field is calculated for downstream/ramp/upstream intervals. The normal is calculated with a mixed-mode coplanarity model. Proton, alpha particle and atomic oxygen density are also calculated. Results show higher frequencies for nose events of Type 1, and lower for flank events of Type 1. No such pattern can be seen in Type 2 events. Proton and alpha-particles are shown to be shocked, and their densities are slightly higher at the flanks as compared to the nose of the bow shock. Atomic oxygen density stays constant before and after the bow shock, likely due to the fact that the oxygen originates mostly from the exosphere rather than from the solar wind. Ion densities seem not to be affected by whether the event is Type 1 or 2.