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Liléo, Sónia. "Auroral electrodynamics of plasma boundary regions." Doctoral thesis, KTH, Rymd- och plasmafysik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10446.
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The electrodynamic coupling between the auroral ionosphere and the magnetosphere is the main subject of this thesis. Satellite measurements of electric and magnetic fields and of charged particles are used to explore three distinct plasma boundaries, magnetically linked to the nightside auroral ionosphere. These boundaries are the inner edge of the plasma sheet (PS), and the inner and the outer edges of the plasma sheet boundary layer (PSBL). Strong ionospheric electric fields with amplitudes up to 400 mV/m may be observed in the subauroral ionosphere, in the vicinity of the ionospheric projection of the PS inner edge. Intense and dynamic auroral electric fields with local magnitudes up to 150 mV/m associated with upward ion beams and field-aligned currents are observed for the events treated here, at the inner and outer boundaries of the PSBL at an altitude of about 4-5 Earth radii, well above the acceleration region. Subauroral and auroral electric fields are the two main subjects of this thesis. Subauroral ion drifts (SAID) are associated with poleward electric fields, occurring predominantly in the premidnight region during the substorm recovery phase. The recently revealed abnormal subauroral ion drifts (ASAID) are associated with equatorward electric fields, occurring during extended periods of low auroral activity. The results indicate that the generation mechanism of SAID can neither be regarded as a pure voltage generator nor a pure current generator, but having certain characteristics of both generator types. Ionospheric feedback appears to play a major role for the development and maintenance of the SAID electric fields. The formation of ASAID is proposed to result from the proximity and interaction between different plasma boundaries of the innermost magnetosphere during extended periods of low auroral activity. The auroral electric fields observed in the upward current region at the PSBL inner and outer edges are associated with upward parallel electric fields, which partially decouple the high-altitude electric fields from the ionosphere. This is in contrast to the subauroral electric fields which are coupled. Multi-point measurements provided by the Cluster mission show that the observed electric fields are highly variable in space and time, revealing various types of acceleration processes. However, they appear to be tied to the boundary where they are originally formed. A case is presented where they are associated with large electromagnetic energy fluxes directed upward away from the ionosphere. The interaction between the magnetosphere and ionosphere, being more pronounced at plasma boundary regions, is important for the understanding of the formation and regulation of the highly structured auroral electric fields observed in the upward current region.QC 20100727
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Schlatter, Nicola. "Radar Signatures of Auroral Plasma Instability." Doctoral thesis, KTH, Rymd- och plasmafysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160894.
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Incoherent scatter radars are powerful ground based instruments for ionospheric measurements. By analysis of the Doppler shifted backscatter spectrum, containing the signature of electrostatic plasma waves, plasma bulk properties are estimated. At high latitudes the backscattered radar power is occasionally enhanced several orders of magnitude above the thermal backscatter level. These enhancements occur during geomagnetic disturbed conditions and are referred to as naturally enhanced ion acoustic echoes (NEIALs). NEIALs are linked to auroral activity with optical auroral emission observed in the vicinity of the radar measurement volume simultaneously to NEIALs. The backscatter enhancements are thought to be caused by wave activity above thermal level due to instability. A number of theories have been put forward including streaming instabilities and Langmuir turbulence to explain NEIAL observations. NEIALs occur in two classes distinct by their Doppler features. Observations of the first type, which has been studied more extensively, are generally modelled well by the Langmuir turbulence model. The difficulty in trying to understand the driving mechanism of the instability is the limited spatial resolution of the radar measurements. Observations of the second type, reported on more recently, have been interpreted as evidence for naturally occurring strong Langmuir turbulence by means of their Doppler features. Aperture synthesis is a technique to increase the spatial resolution of the radar measurements to below beam width of the single receiver antennas. The technique is employed to investigate the structure of NEIALs in the plane perpendicular to the magnetic field at sub-degree scale corresponding to hundreds of meters to a few kilometres at ionospheric altitudes. Calibration of the radar interferometer is necessary and a calibration technique is presented in paper I. Interferometry observations of a NEIAL event with receivers deployed at the EISCAT incoherent scatter radar on Svalbard are presented in paper II. The size of the enhanced backscatter region is found to be limited to 900 x 500m in the plane perpendicular to the geomagnetic field. These observations constitute the first unambiguous measurements giving evidence for the limited size of the enhanced backscatter region. In paper III observations of strong Langmuir turbulence signatures are presented. The apparent turbulent region in these observations is limited to two narrow altitude regions, 2km extent, and electron density irregularities caused by the turbulence are thought to reach down to decimeter scale length. The turbulence observations were obtained during energetic electron precipitation thereby differing from other observations during which a low energy component in the electron precipitation is reported. In paper IV a statistical study of strong Langmuir turbulence radar signatures is presented. The study reveals differing local time distributions for these signatures from type I NEIALs indicating di_ering driving conditions for the two types of NEIALs. It is found that strong Langmuir turbulence signatures are predominantly observed in the pre-midnight sector where auroral break-up aurora prevails.QC 20150303
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Liléo, Sónia. "Auroral electrodynamics of plasma boundary regions /." Stockholm : Skolan för elektro- och systemteknik, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10446.
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Dreyer, Joshua. "A detailed study of auroral fragments." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388546.
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Aurora occurs in various shapes, one of which is the hitherto unreported phenomenon of auroral fragments. For three periods of occurrence of these fragments their properties were studied in detail during this master’s thesis, using mainly ground-based instrumentation located near Longyearbyen on Svalbard, Norway. A base dataset was constructed from 103 all-sky camera images, manually marking 305 fragments for further analysis. This thesis reports and describes the fragment observations during the observed events, including the auroral and geomagnetic context. Fragments generally seem to fall into two categories, the first being singular, apparently randomly distributed fragments, and the second being periodic fragments that occur in groups with a regular spacing close to auroral arcs. A typical fragment has a small horizontal size below 20 km, a short lifetime of less than a minute and shows no field-aligned extent in the emission. The fragments appear mainly west of zenith (73%) during the three observation nights, whereas their north-south distribution is symmetric around the zenith. Almost all of them exhibit westward drift, the estimated speed for one of the fragments passing the field of view of ASK is ∼1 km/s. A spectral signature can be seen in the green auroral wavelength of O at 557.7 nm and red emission line of N2 at 673.0 nm, but no emission enhancement was observed in the blue wavelengths. One fragment passing the EISCAT Svalbard radar’s field of view shows a local ion temperature increase in a small altitude range of ∼15 km, whereas there is no visible increase in electron density. This could be explained by fragment generation due to locally strong horizontal electric fields. A potential mechanism for this might be electric fields of atmospheric waves superposing with the converging electric fields of auroral arcs created by particle precipitation and the corresponding field-aligned currents. The resulting field would be perpendicular to the magnetic field and the auroral arcs, leading to wave-like density variations of excited plasma close to the arcs. Further study is required to verify this hypothesis and improve the understanding of fragment properties determined from the limited dataset used for this thesis.
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Vedin, Jörgen. "Numerical modeling of auroral processes." Doctoral thesis, Umeå University, Physics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1117.
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One of the most conspicuous problems in space physics for the last decades has been to theoretically describe how the large parallel electric fields on auroral field lines can be generated. There is strong observational evidence of such electric fields, and stationary theory supports the need for electric fields accelerating electrons to the ionosphere where they generate auroras. However, dynamic models have not been able to reproduce these electric fields. This thesis sheds some light on this incompatibility and shows that the missing ingredient in previous dynamic models is a correct description of the electron temperature. As the electrons accelerate towards the ionosphere, their velocity along the magnetic field line will increase. In the converging magnetic field lines, the mirror force will convert much of the parallel velocity into perpendicular velocity. The result of the acceleration and mirroring will be a velocity distribution with a significantly higher temperature in the auroral acceleration region than above. The enhanced temperature corresponds to strong electron pressure gradients that balance the parallel electric fields. Thus, in regions with electron acceleration along converging magnetic field lines, the electron temperature increase is a fundamental process and must be included in any model that aims to describe the build up of parallel electric fields. The development of such a model has been hampered by the difficulty to describe the temperature variation. This thesis shows that a local equation of state cannot be used, but the electron temperature variations must be descibed as a nonlocal response to the state of the auroral flux tube. The nonlocal response can be accomplished by the particle-fluid model presented in this thesis. This new dynamic model is a combination of a fluid model and a Particle-In-Cell (PIC) model and results in large parallel electric fields consistent with in-situ observations.
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Schroeder, James William Ryan. "Exploring the Alfvén-wave acceleration of auroral electrons in the laboratory." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5846.
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Inertial Alfvén waves occur in plasmas where the Alfvén speed is greater than the electron thermal speed and the scale of wave field structure across the background magnetic field is comparable to the electron skin depth. Such waves have an electric field aligned with the background magnetic field that can accelerate electrons. It is likely that electrons are accelerated by inertial Alfvén waves in the auroral magnetosphere and contribute to the generation of auroras. While rocket and satellite measurements show a high level of coincidence between inertial Alfvén waves and auroral activity, definitive measurements of electrons being accelerated by inertial Alfvén waves are lacking. Continued uncertainty stems from the difficulty of making a conclusive interpretation of measurements from spacecraft flying through a complex and transient process. A laboratory experiment can avoid some of the ambiguity contained in spacecraft measurements.
Experiments have been performed in the Large Plasma Device (LAPD) at UCLA. Inertial Alfvén waves were produced while simultaneously measuring the suprathermal tails of the electron distribution function. Measurements of the distribution function use resonant absorption of whistler mode waves. During a burst of inertial Alfvén waves, the measured portion of the distribution function oscillates at the Alfvén wave frequency. The phase space response of the electrons is well-described by a linear solution to the Boltzmann equation. Experiments have been repeated using electrostatic and inductive Alfvén wave antennas. The oscillation of the distribution function is described by a purely Alfvénic model when the Alfvén wave is produced by the inductive antenna. However, when the electrostatic antenna is used, measured oscillations of the distribution function are described by a model combining Alfvénic and non-Alfvénic effects. Indications of a nonlinear interaction between electrons and inertial Alfvén waves are present in recent data.
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Eliasson, Lars. "Satellite observations of auroral acceleration processes." Doctoral thesis, Umeå universitet, Rymdfysik, 1994. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-102339.
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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.Diss. (sammanfattning) Umeå : Umeå universitet, 1994, härtill 6 uppsatser.
digitalisering@umu.se
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Fillingim, Matthew Owen. "Kinetic processes in the plasma sheet observed during auroral activity /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/6824.
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Kalmoni, N. M. E. "The role of magnetospheric plasma instabilities in auroral and substorm dynamics." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1546163/.
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The auroral substorm is the manifestation of explosive energy release from the rapid and global reconfiguration of the magnetotail. The auroral substorm is marked by a sudden brightening and poleward expansion of the most equatorward auroral arc in the midnight sector of the ionosphere. The temporal sequence of magnetospheric processes which lead to the dynamic auroral substorm display remain disputed to this day. This thesis contains original research on the development and exploitation of novel data analysis techniques in order to analyse ground-based all sky imager data of the aurora, enabling the study of substorm processes in remarkable detail. Fourier analysis techniques are used to find the spatial scales of wave-like signatures (otherwise known as auroral beads/rays), which form along substorm onset arcs. Growth rates of ∼0.05 s−1 are found from the exponential growth of the power spectral density of individual spatial scales. By analysing the dataset in this way, comparisons are made between observations and theoretical predictions of plasma instabilities at the near-Earth edge of the plasma-sheet which have been proposed to play a critical part in the substorm onset process. Auroral arc tracking techniques are developed to automate and increase the size of the database of events analysed. The vast majority of independently identified substorm onsets are preceded by azimuthal structuring along the onset arc with median wavelengths of ∼80 km. These beads grow and develop into a magnetospheric instability around 2 minutes prior to auroral substorm onset. Showing that beads are a common feature along the substorm onset arc provides unprecedented quantitative evidence that a near-Earth instability is a fundamental component of the substorm onset process. Finally, analysis techniques are extended to state-of-the-art high resolution multi-spectral auroral data to investigate the processes driving auroral beads. Beads can be resolved in the green-, blue- and red-line aurora with spatial scales as small as 30 km, which later develop into larger structures of ∼80 km. These observations are consistent with Alfvén wave accelerated auroral particle precipitation and therefore imply that the substorm onset arc and auroral beads are driven unstable by waves.
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Kopf, Andrew James. "A multi-instrument study of auroral hiss at Saturn." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/692.
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Over the last fifty years, a multitude of spacecraft and rocket experiments have studied plasma wave emissions from Earth's auroral regions. One such emission is auroral hiss, a low-frequency whistler-mode wave that is produced in the auroral zone. Observations from Earth-orbiting spacecraft show that auroral hiss is generated by field-aligned electron beams, with the resulting plasma wave emission propagating along the resonance cone. This propagation results in auroral hiss appearing as a V-shaped funnel when observed on a frequency-time spectrogram. This thesis presents the first comprehensive study of auroral hiss at a planet other than Earth, using the Cassini spacecraft to study auroral hiss at Saturn.
NASA's Cassini spacecraft, currently in orbit around Saturn, has allowed for the first opportunity to study this emission in detail at another planet. Since 2006, the Cassini spacecraft has twice been in a series of high inclination orbits, allowing investigation and measurements of Saturnian auroral phenomena. During this time, the Radio and Plasma Wave Science (RPWS) Investigation on Cassini detected low frequency whistler mode emissions propagating upward along the auroral field lines, much like terrestrial auroral hiss. Comparisons of RPWS data with observations from several other Cassini instruments, including the Dual-Technique Magnetometer (MAG), Magnetospheric Imaging Instrument (MIMI), and the Cassini Plasma Spectrometer (CAPS), have revealed a complete picture of this emission at Saturn.
Observations from these instruments have been used to make a variety of determinations about auroral hiss at Saturn. RPWS has only observed this emission when Cassini was at high-latitudes, although these observations have shown no preference for local time. Tracking the times this emission has been observed revealed a clear periodicity in the emission. Further study later revealed not one but two rotational modulations, one in each hemisphere, rotating at rates of 813.9 and 800.7 degrees per day in the northern and southern hemispheres, respectively. These rates match with observations of the clock-like Saturn Kilometric Radiation. Study of the field-aligned current structures in the auroral regions revealed a strong upward-directed current in both hemispheres on the lower-latitude side of the auroral hiss emission. Along with correlating particle densities, these observations were used to infer the presence of a high-density plasmasphere at low latitudes, with the series of field-aligned current structures lining up with the outer boundary at L-shell values of around 12-15.
Analysis of electron beams observed in conjunction with auroral hiss shows that these beams produce large growth rates for whistler-mode waves propagating along the resonance cone, similar to terrestrial auroral hiss. Analytical calculation of the normalized growth rates of ten electron beam events on Day 291, 2008, yielded a wide range of growth rates, from 0.004 to over 6.85 times the real frequency. The latter, a non-physical result, came from a violation of the weak growth approximation, suggesting there was so much growth that the analytical calculation was not valid in this instance. Numerical calculation using a plasma dispersion-solving code called WHAMP produced a growth rate of about 0.3, a still very large number, suggesting the detected beams may be the source of the observed auroral hiss plasma wave emission.
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Main, Daniel S. "Multi-ion plasma processes in the low altitude auroral upward current region." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3207758.
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Del, Pozo Carlos F. (Carlos Federico). "440 MHz radar observations of plasma turbulence in the auroral lower ionosphere." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/17235.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989.Includes bibliographical references (p. 274-287).
by Carlos F. del Pozo.
Ph.D.
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Mottez, Fabrice. "Effets des ondes cyclotroniques ioniques sur le plasma auroral : striation du plasma et production de doubles couches faibles." Paris 11, 1991. http://www.theses.fr/1991PA112123.
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Des mesures effectuees in situ, a partir de satellites, entre 5000 et 10000 km d'altitude dans la zone aurorale de la terre montrent que des electrons sont acceleres le long du champ magnetique. Dans ce plasma non collisionnel, la conductivite le long du champ magnetique tend vers l'infini. Seules des structures coherentes issues de la turbulence peuvent engendrer un champ electrique parallele. Les observations mettent en evidence des champs electriques paralleles tres localises engendres par des structures coherentes. Des travaux theoriques recents ont montre que de telles structures, du type doubles couches, peuvent apparaitre dans un plasma soumis a des instabilites de type acoustique ionique. Neanmoins: (i) le plasma de la zone aurorale de haute altitude n'est pas instable vis-a-vis des ondes acoustiques ioniques, mais vis-a-vis des ondes cyclotroniques ioniques, (ii) les doubles couches simulees a partir de l'instabilite acoustique ionique se deplacent dans le sens oppose a celui des structures observees par les sondes. On propose dans ce memoire, a partir de resultats de simulation numerique (avec un code de simulation bi-dimensionnel developpe au cours de la these), un mecanisme de declenchement de doubles couches a partir de la turbulence cyclotronique ionique en champ magnetique fort. Une derive des electrons par rapport aux ions provoque une instabilite cyclotronique ionique, mais cette instabilite se sature sans donner lieu a des structures coherentes. La turbulence engendree par un faisceau d'ions rapides comme par un faisceau d'ions lents permet, dans un premier temps, de forcer la vitesse moyenne des electrons a se situer entre la vitesse du faisceau ionique excitateur et celles des ions thermiques. On constate ensuite une filamentation du plasma. Lorsque la vitesse moyenne des electrons devient suffisamment positive, des structures coherentes de potentiel, analogues aux doubles couches obser
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Brändström, Urban. "The Auroral Large Imaging System : design, operation and scientific results." Doctoral thesis, Umeå University, Space Science, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-36.
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The Auroral Large Imaging System (ALIS) was proposed in 1989 by Åke Steen as a joint Scandinavian ground-based nework of automated auroral imaging stations. The primary scientic objective was in the field of auroral physics, but it was soon realised that ALIS could be used in other fields, for example, studies of Polar Stratospheric Clouds (PSC), meteors, as well as other atmospheric phenomena.
This report describes the design, operation and scientic results from a Swedish prototype of ALIS consisting of six unmanned remote-controlled stations located in a grid of about 50 km in northern Sweden. Each station is equipped with a sensitive high-resolution (1024 x 1024 pixels) unintensified monochromatic CCDimager. A six-position filter-wheel for narrow-band interference filters facilitates absolute spectroscopic measurements of, for example, auroral and airglow emissions. Overlapping fields-of-view resulting from the station baseline of about 50 km combined with the station field-of-view of 50° to 60°, enable triangulation as well as tomographic methods to be employed for obtaining altitude information of the observed phenomena.
ALIS was probably one of the first instruments to take advantage of unintensi- fied (i.e. no image-intensifier) scientific-grade CCDs as detectors for spectroscopic imaging studies with multiple stations of faint phenomena such as aurora, airglow, etc. This makes absolute calibration a task that is as important as it is dificult.
Although ALIS was primarily designed for auroral studies, the majority of the scientific results so far have, quite unexpectedly, been obtained from observations of HF pump-enhanced airglow (recently renamed Radio-Induced Aurora). ALIS made the first unambiguous observation of this phenomena at high-latitudes and the first tomography-like inversion of height profiles of the airglow regions. The scientific results so far include tomographic estimates of the auroral electron spectra, coordinated observations with satellite and radar, as well as studies of polar stratospheric clouds. An ALIS imager also participated in a joint project that produced the first ground-based daytime auroral images. Recently ALIS made spectroscopic observations of a Leonid meteor-trail and preliminary analysis indicates the possible detection of water in the Leonid.
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Sullivan, Joanna Mary. "Spectral studies of small-scale auroral structure and plasma instability in the high-latitude ionosphere." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/65694/.
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Optical measurements of small-scale auroral structures are here combined with spectrographic data in order to study the relationship between auroral morphology and the energy characteristics of the precipitating population. It is shown that rayed auroral structures are associated with precipitating electrons with a broad range in energy, including a significant population at energies of around 100 eV. In comparison, observations of fast-moving auroral arc elements are shown to result from precipitation energy distributions peaking at several keV with a very small low-energy component. This spectrographic information feeds directly into the study of naturally enhanced ion-acoustic lines, or NEIALs, which have been observed by incoherent-scatter radars at high-latitudes. It has been proposed that these radar enhancements result from natural plasma instability, causing the generation of ion-acoustic waves through the decay of unstable Langmuir waves, themselves driven by low-energy electron streams. Using multi-spectral imaging in combination with radar observations, a direct link is shown between ion-acoustic wave enhancements and precipitating electrons at 100 eV energies. Wave enhancements at the radar wavevector which are three orders of magnitude above the thermal level, are successfully modelled using the Langmuir decay interpretation for the time of observation. Electron populations with a broad energy range are thought to result from Alfv´enic acceleration mechanisms, which play an important role in the generation of smallscale auroral structure. With the recent advancements in multi-spectral imaging, it is now possible to resolve auroral filaments of a few hundred meters width. An interferometric imaging capability is under development for the EISCAT Svalbard Radar system, in order to resolve scattering wave structures on similar spatial scales within the radar beam. A technique is demonstrated by which to calibrate the position of coherent echoes detected by the interferometer. This will be of great use in clarifying the role of precipitating electron beams in turbulent plasma processes on small scales.
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Sewell, Stephen. "Efficient particle-in-cell simulation of auroral plasma phenomena using a CUDA enabled graphics processing unit." Thesis, The University of Alabama in Huntsville, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1559557.
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This thesis introduces a software framework that effectively utilizes low-cost commercially available Graphic Processing Units (GPUs) to simulate complex scientific plasma phenomena that are modeled using the Particle-In-Cell (PIC) paradigm. The software framework that was developed conforms to the Compute Unified Device Architecture (CUDA), a standard for general purpose graphic processing that was introduced by NVIDIA Corporation. This framework has been verified for correctness and applied to advance the state of understanding of the electromagnetic aspects of the development of the Aurora Borealis and Aurora Australis.
For each phase of the PIC methodology, this research has identified one or more methods to exploit the problem's natural parallelism and effectively map it for execution on the graphic processing unit and its host processor. The sources of overhead that can reduce the effectiveness of parallelization for each of these methods have also been identified. One of the novel aspects of this research was the utilization of particle sorting during the grid interpolation phase. The final representation resulted in simulations that executed about 38 times faster than simulations that were run on a single-core general-purpose processing system. The scalability of this framework to larger problem sizes and future generation systems has also been investigated.
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Stenberg, Gabriella. "The importance of waves in space plasmas : Examples from the auroral region and the magnetopause." Doctoral thesis, Umeå University, Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-538.
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This thesis discusses the reasons for space exploration and space science. Space plasma physics is identified as an essential building block to understand the space environment and it is argued that observation and analysis of space plasma waves is an important approach.
Space plasma waves are the main actors in many important processes. So-called broadband waves are found responsible for much of the ion heating in the auroral region. We investigate the wave properties of broadband waves and show that they can be described as a mixture of electrostatic wave modes. In small regions void of cold electrons the broadband activity is found to be ion acoustic waves and these regions are also identified as acceleration regions. The identification of the wave modes includes reconstructions of the wave distribution function. The reconstruction technique allow us to determine the wave vector spectrum, which cannot be measured directly. The method is applied to other wave events and it is compared in some detail with a similar method.
Space plasma wave are also sensitive tools for investigations of both the fine-structure and the dynamics of space plasmas. Studies of whistler mode waves observed in the boundary layer on the magnetospheric side of the magnetopause reveal that the plasma is organized in tube-like structures moving with the plasma drift velocity. The perpendicular dimension of these tubes is of the order of the electron inertial length. We present evidence that each tube is linked to a reconnection site and argue that the high density of tube-like structures indicates patchy reconnection.
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Backrud, Marie. "Cluster Observations and Theoretical Explanations of Broadband Waves in the Auroral Region." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5809.
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Yajima, Akira. "Electrostatic particle simulations of the weak double layer in the auroral plasma including the effects of up-flowing ions." 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150836.
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Cavalcanti, Claudio Jose de Holanda. "Emissão, propagação e amplificação da radiação quilométrica das auroras nas subcavidades aurorais." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2001. http://hdl.handle.net/10183/31458.
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O presente trabalho investiga a propagação e amplificação de ondas eletromagnéticas no plasma localizado nas proximidades dos pólos geomagnéticos, a altitudes não muito superiores a três vezes o raio da Terra. O fenômeno estudado é conhecido como Radiação Quilométrica das Auroras (AKR - Auroral Kilometric Radiation), a mais intensa das várias emissões que podem surgir em decorrência da interação entre o vento solar e a magnetosfera terrestre. Inicialmente são abordadas algumas das principais características conhecidas dessa emissão, através de uma revisão observacional do fenômeno. O maser de elétron-ciclotron é então discutido como um possível mecanismo gerador da AKR. Faz-se uso deste mecanismo para o estudo da propagação e amplificação da Radiação Quilométrica das Auroras, sendo os parãmetros físicos necessários para esse estudo obtidos de um modelo físico baseado no trabalho de Chiu & Shulz (1978) [1] que reproduz aproximadamente as condições do plasma na região fonte. Inclui-se no modelo os gradientes perpendiculares ao campo magnético ambiente, com variações em curta escala para a densidade, chamadas de subcavidades aurorais. As componentes do tensor dielétrico do plasma são calculadas para uma distribuição que consiste em uma soma de uma Maxwelliana, que descreve os elétrons frios, e uma cone-de-perda do tipo DGH relativística para os elétrons energéticos, sendo utilizada a aproximação localmente homogênea. É feito um estudo de traçado de raios por meio das equações da ótica geométrica e em cada ponto da trajetória da onda é calculada a emissividade espectral. Através da equação de transferência, obtém-se o fator de amplificação da onda enquanto ela se propaga pela região fonte. Se constata que a inclusão da emissividade do meio no estudo de traçado de raios aumenta o fator de amplificação. Porém, esse aumento não é suficiente para explicar os níveis de amplificação normalmente observados. Em contraponto, conclui-se que a inclusão de variações de curta escala (na direção perpendicular ao campo magnético) na densidade e demais parãmetros do plasma da região fonte, pode ser um fator muito importante na explicação desses níveis de amplificação.The present work investigates the propagation and amplification of electromagnetic waves in a plasma localized in the vicinity of the geomagnetic poles, at heights not much greater than three times the Earth's radius. The phenomena studied is known as the Aurorai Kilometric Radiation (AKR), the strongest of the various types of emission that can occur as a consequence of the interaction of the solar wind and the terrestrial magnetosphere. Initially some of the main known characteristics of this emission are discussed, including a review of the literature on the observational features of the phenomena. The electron cyclotron maser mechanism is then discussed as a possible generator mechanism for the AKR. This mechanism is then utilized in order to study the propagation and amplification of the Aurorai Kilometric Radiation, the physical parameters necessary for this study being obtained from a physical model based in the work of Chiu & Schultz (1978), which approximately reproduces the plasma conditions in the source region. The model includes the gradients perpendicular to the ambient magnetic field, with small scale variations of the density, called auroral subcavities. The componente of the plasma dielectric tensor are calculated for one distribution which consists in a summation of a Maxwellian, which describes cold electrons, and a relativistic DGH distribution for the energetic loss-cone electrons, being used the locally homogeneous approximation. A ray-tracing study is done using the geometrical optics equations, and at each point along the wave trajectory the spectral emissivity is calculated. By means of the transfer equation, the wave amplification factor is obtained for as long as the wave propagates in the source region. It is verified that the inclusion of the emissivity of the medium in the ray tracing calculation enhances the amplification factor. However, the increase obtained is not sufficient to expiam the amplification leveis currently observed. On the other hand, it is concluded that the inclusion of small scale variations (in the direction perpendicular to the magnetic field) in the density and other plasma parameters in the source region, may be an important factor in the explanation of the observed amplification leveis.
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Lamy, Laurent. "Etude des émissions radio aurorales de Saturne, modélisation et aurores UV." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00328763.
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Cette thèse porte sur l'étude du rayonnement radio auroral kilométrique de Saturne (SKR pour Saturn Kilo- metric Radiation) observé de façon quasi-continue par les antennes radio de la sonde Cassini depuis son entrée en orbite autour de Saturne en juillet 2004. Comme les rayonnements radio auroraux des autres planètes magnétisées, le SKR est généré sur des lignes de champ magnétique de haute latitude près des pôles magnétiques. Tirant parti de plusieurs années d'observations, les propriétés macroscopiques du SKR (spectre, polarisation, conjuguaison des sources de chaque hémisphère, mode d'émission) sont déduites par une analyse statistique. Elles montrent en particulier que les caractéristiques de l'émission dépendent fortement de la position de l'observateur. Ceci est une conséquence directe de l'anisotropie du SKR qui engendre de forts effets de visibilité, visibles dans les cartes d'intensité temps-fréquence (arcs, régions d'invisibilité de l'émission). La simulation de ces effets de visibilité apporte de nouvelles contraintes sur les propriétés microscopiques des sources (énergie et distribution des électrons auroraux). Le SKR est connu pour être modulé à une période variable. Une analyse de la variation de cette période radio sur plusieurs années révèle des oscillations à court terme de l'ordre de 20-30 jours dont l'origine est attribuée à la variation de la vitesse caractéristique du vent solaire au niveau de Saturne. Une étude parallèle du rayonnement auroral kilométrique terrestre (AKR), observé lors du survol de la Terre par Cassini en août 1999, met en évidence la découverte d'une modulation diurne semblable à celle du SKR. Enfin, la technique de goniopolarimétrie permet de faire de l'imagerie radio des sources du SKR. L'étude de leur distribution moyenne montre pour la première fois l'existence d'un ovale radio. La comparaison des images des sources du SKR avec celles des ovales auroraux (observés dans l'ultraviolet lointain par le télescope Hubble), ainsi que de leur puissance respective, montre une association étroite entre ces deux processus d'émission.
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Engwall, Erik. "Low-Energy Ion Escape from the Terrestrial Polar Regions." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-100650.
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The contemporary terrestrial atmosphere loses matter at a rate of around 100,000 tons per year. A major fraction of the net mass loss is constituted by ions, mainly H+ and O+, which escape from the Earth’s ionosphere in the polar regions. Previously, the outflow has only been measured at low altitudes, but to understand what fraction actually escapes and does not return, the measurements should be conducted far from the Earth. However, at large geocentric distances the outflowing ions are difficult to detect with conventional ion instruments on spacecraft, since the spacecraft electrostatic potential normally exceeds the equivalent energy of the ions. This also means that little is known about the ion outflow properties and distribution in space far from the Earth. In this thesis, we present a new method to measure the outflowing low-energy ions in those regions where they previously have been invisible. The method is based on the detection by electric field instruments of the large wake created behind a spacecraft in a flowing, low-energy plasma. Since ions with low energy will create a larger wake, the method is more sensitive to light ions, and our measured outflow is essentially the proton outflow. Applying this new method on data from the Cluster spacecraft, we have been able to make an extensive statistical study of ion outflows from 5 to 19 Earth radii in the magnetotail lobes. We show that cold proton outflows dominate in these large regions of the magnetosphere in both flux and density. Our outflow values of low-energy protons are close to those measured at low altitudes, which confirms that the ionospheric outflows continue far back in the tail and contribute significantly to the magnetospheric content. We also conclude that most of the ions are escaping and not returning, which improves previous estimates of the global outflow. The total loss of protons due to high-latitude escape is found to be on the order of 1026 protons/s.
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Palmer, Jonathan Richard. "Plasma density variations in the aurora." Thesis, University of Southampton, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262167.
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Dahlgren, Hanna. "Multi-spectral analysis of fine scale aurora." Doctoral thesis, KTH, Rymd- och plasmafysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-24907.
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The Aurora Borealis is the visible manifestation of the complex plasma interaction between the solar wind and the Earth's magnetosphere and ionosphere. Ground based and in situ measurements demonstrate a prevalence of dynamic fine structure within auroral displays, with spatial scales down to tens of metres and time variations occurring on a fraction of a second.The fine-scale morphology is related to structuring of auroral currents and electric fields and detailed spatial, spectral and temporal observations of the aurora are crucial in understanding the electrodynamic processes taking place in the ionosphere and in its coupling to the magnetosphere. In this thesis, the low-light optical instrument ASK (Auroral Structure and Kinetics) is used to image small-scale structures in the aurora at very high spatial and temporal resolution. ASK is a multi-spectral instrument, imaging the aurora in three selected emissions simultaneously. This provides information on the energy of the precipitating electrons. The SIF (Spectrographic Imaging Facility) instrument has been used in conjunction with ASK, to give a more complete picture of the spectral characteristics of the aurora, and to determine the degree of contaminating emissions present in the same spectral interval as the emission lines observed by ASK. Data from ASK and SIF are used to study the relation between the morphology and dynamics of small-scale structures in the aurora and the energy of the precipitating electrons. By comparing electron density profiles provided by EISCAT (European Incoherent SCATter) radar measurements with modeling results, information on the characteristic energy and the energy flux of the precipitating electrons can be obtained. One of the ASK channels is imaging a metastable O+ emission, which has a lifetime of about 5 s. By tracing the afterglow in this channel optically a direct measure of the E x B drift is obtained from which the local ionospheric electric field can be calculated. ASK data has also been used to analyse the properties of a distorted auroral arc, in which auroral structuring was found to take place simultaneously at different spatial scales. The smallest features, 'ruffs', are undulations found to develop on the edge of an auroral curl, fold or shear. Detailed optical studies of black aurora, including both the type which is associated with plasma shear motions and no or weak shear motions were conducted from ASK data, to investigate the spectral properties and fine scale morphology of the black structures and to shed light on the processes behind this phenomenon.QC 20101001
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Wanzambi, Ellinor, and Maja Gustafsson. "Parallel currents in the magnetotail and their connection to aurora." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-355621.
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We present an analysis from MMS satellites where we detected the strongest parallel currents from their data during the months May till November 2017. The strongest parallel current in July happened 2017-07-16 at 6 o’clock. At this event we found a change in the magnetic flow density at the locations: A. Svalbard, which would have resulted in an aurora borealis if it was not for the summer light. B. Antarctic, which visibly did result in an aurora australis. By examine the source of the parallel current, we looked near the Lagrange point L1 between Earth and the Sun and could observe how the flow pressure and magnetic field changed. This motivated the investigation by looking at the sun pictures by helioviewer, where we could observe an outburst the 2017-07-14, which turned out to be the requested source of this event.
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Pavan, Joel. "Efeitos de gradientes perpendiculares na amplificação da radiação quilométrica das auroras." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/11022.
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A in uência do caráter inomogêneo da região-fonte na ampli cação da Radiação Quilom étrica das Auroras é investigada. Inicialmente é feita uma revisão de trabalhos relevantes publicados a respeito do mesmo tema geral, tanto os que concernem aos dados observacionais como os que concernem aos modelos teóricos e simulações numéricas. Esta revisão é precedida pelo estabelecimento de conceitos e de nições pertinentes ao tema. São consideradas duas abordagens distintas na determinação da ampli cação da radiação na região-fonte. A primeira considera o plasma localmente homogêneo, enquanto a segunda toma em conta, explicitamente, a contribuição dos gradientes dos parâmetros do plasma. A ampli cação da radiação é determinada pela avaliação do tensor dielétrico do plasma e pela evolução da radia ção através do estudo de traçado de raios. Os parâmetros do plasma são obtidos através de uma formulação autoconsistente que toma em conta uma queda de potencial elétrico ao longo das linhas de campo geomagnético. Utiliza-se um modelo de lâmina auroral em que o campo magnético ambiente é considerado localmente homogêneo. O modelo teórico subjacente adotado é o do maser de elétron-cíclotron. O principal resultado obtido revela uma diminuição na ampli cação nal por um fator em torno de três, quando os gradientes dos parâmetros do plasma são considerados explicitamente. Este resultado pode ter implicações na capacidade do maser de elétron-cíclotron em explicar os níveis de radiação mais elevados observados.The in uence from source region inhomogeneous character on ampli cation of Auroral Kilometric Radiation is investigated. Firstly, a review over relevant works published about the same general theme is made, concerning about observational data as well theoretical models and numerical simulations. This review is preceded by the establishment of de nitions and concepts related to the theme. Two distinct approaches are considered in determining the ampli cation of radiation across the source region. First approach takes the plasma as locally homogeneous, while second approach account, explicitly, for gradients on plasma parameters. The ampli cation is obtained through evaluation of the dielectric tensor and the evolution of radiation through ray tracing. Plasma parameters are obtained using a self-consistent formulation which account for an electric potential drop along geomagnetic eld lines. An auroral slab model is used where the ambient magnetic eld is taken as locally homogeneous. The subjacent theoretical model adopted is the electron-cyclotron maser. The main result obtained reveals a reduction on nal ampli cation by a factor about three, when plasma parameters gradients are explicitly accounted. This nding may have implications on capability of electron-cyclotron maser for explanation the most intense levels of radiation observed.
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Hess, Sébastien. "Processus d'accélération et émissions radio dans le circuit Io-Jupiter." Paris 6, 2008. http://www.theses.fr/2008PA066051.
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Gaelzer, Rudi. "O maser de elétron-cíclotron como mecanismo gerador da radiação quilométrica das auroras." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 1991. http://hdl.handle.net/10183/132968.
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Investigamos a possibilidade de amplificação de ondas eletromagnéticas no plasma situado nas proximidades dos pólos geomagnéticos a uma altitude de até cerca de cinco raios terrestres. Nesta região ocorre o fenômeno conhecido como "Radiação Quilométrica das Auroras", o qual é uma conseqüência da interação entre o vento solar e a magnetosfera. É feita inicialmente uma ampla revisão das características observacionais conhecidas do fenômeno. Em seguida, é discutido o maser de elétron-cíclotron como possível mecanismo gerador para o fenômeno. Neste sentido, é feita inicialmente uma revisão dos principais trabalhos teóricos, os quais utilizaram o mecanismo de maser na sua formulação de freqüência complexa. Por fim, principia-se um estudo da Radiação Quilométrica das Auroras fazendo uso do maser na formulação de vetor de onda complexo. Os parâmetros físicos necessários para os cálculos de amplificação foram obtidos a partir de um modelo especialmente criado, o qual reproduz de forma aproximada as condições existentes na região aurora!, supondo inclusive um particular gradiente de densidade na direção perpendicular ao campo geomagnético. Os elementos do tensor dielétrico são calculados na aproximação de plasma localmente homogêneo e a função de distribuição considerada consiste na soma de uma maxwelliana de baixa temperatura mais uma cone-de-perda do tipo Dory-Guest-Harris relativística. A relação de dispersão é resolvida exatamente, mantendo-se todos os harmônicos e ordens de raio de Larmor necessários para garantir a convergência da solução. Foram reali zados também cálculos de traçados de raios na aproximação da óptica geométrica através do método de Poeverlein. Constatou-se que quando a razão ent re as freqüências de pla.sma e de cíclotron elet rônicas é Wpe/De < O, 1, as ondas que se propagam no modo ('X t raordinário rápido são amplificadas em freqüências muito próximas à freqüência. de cíclo t ron eletrônica e em ângulos próximos à perpendicular ao campo geomagnético. No caso oposto, Wpe/De > O, 1, são necessários valores cada vez maiores da componente do vetor de onda paralela ao campo magnético para. ocorrer amplificação, a qual é progressivamente menor. Os cálculos ele traçados ele raios mostraram que a escala espacial de variação de parâmetros, perpendicularmente ao campo magnético, é um fator muito importante na amplificação, e que a distância. necessária para uma dada amplificação pode se reduzir substancialmente quando aumenta o gradiente de densidade.We investigate the possibility of electromagnetic wave amplification in the plasma situated over the geomagnetic peles up to a height around five earth radii. In this region occurs the most intense wave emission phenomenon in the terrestrial magnetosphere, known as "Aurora! Kilometric Radiation", which is a consequence of the solar wind-magnetosphere interaction. Initially, we make a comprehensive review on the known observational characteristics of the phenomenon. Next, the electron-cyclotron maser is discussed as a possible generation mechanism for the phenomenon, anel a review is made on the most important theoretical works, which applied the maser in the complex frequency formulation. We then begin a study on the Auroral Kilometric Radiation applying the maser mechanism in its complex wave frequency formulation . The physical parameters needed for the calculations were obtained from a particular model, especially created to approximately reproduce the real conditions in the aurora! zone, taking into account even a particular density gradient, perpendicular to the geomagnetic field. The components of the dielectric tensor are calculated in the locally homogeneous plasma approximation and the electron distribution function is taken as the sum of a cold maxwellian plus a relativistic Dory-Guest-Harris distribuition. The dispersion relation is exactly solved with all harmonics and powers of Larmor radius needed for the convergency of the solutions. We have also clone ray-tracing studies in the geometrical opti cs approximation, using the Poeverlein's method. We have found Ll1at , wh en Lhe electronic plasma to cyclotron frequencies ratio is Wpe/De < 0.1, the waves t hat propagatc in the fast extraordinary mode are amplified at frequencies very near to Lhe c.\·c lot ron frequency anel in the quasi-perpendi cular direction of the geomagnetic field. On t.hc olhcr hand , c.v·PE/De > 0.1 , the component of the wave vector parallel to the magnet i c fi eld musL have larger values for the amplification to occur, progressively smaller in valu e. The ray-L racing st udies have shown that the spatial scale of the inhomogeneity, perp endi cular to the magnetic field , is a very important factor in the amplification, anel that the cli stance to obtain a given amplification can be substantially reduced when the clensity gra.client is increasecl.
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Eilers, Bischoff Jens, and Sebastian Jovancic. "Variability of Io’s Aurora and the Moon’s Footprint on Jupiter." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-293888.
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We study the variability of intensity of Io’s aurora asa function of Jupiter’s rotation measured in system III longitude.The far-ultraviolet intensity of Io’s aurora was measured by theHubble Space Telescope (HST) using the FUV-MAMA photondetector of the STIS. The data was processed using Matlab tofilter background and reflection, and account for the detector’soptical systems. Target regions of the detector were isolated forthe measurement of the OI(1356 ̊A) and SI(1479 ̊A) emissionsrespectively. By sampling photon detections within each emissionregion, we compute intensity reconstructions that we map tosystem III longitude. Curves were then fitted to the reconstruc-tions using a sinus fit. The results show two intensity peaks atsystem III longitudes (140±5)◦and (284±2)◦for both OIandSI. The difference in amplitude between the peaks are (38±6)%and (28±6)% for OIand SIrespectively. The asymmetriespeak intensities is possibly caused by the probability of excitingsulphur being higher than the probability of exciting sulphur.For a full explanation measurement of the oxygen to sulphurproportion in Ios atmosphere would be needed. We compare theresults to peaks of Io’s footprint on Jupiter measured by JUNOand other HST data sets. We find it likely that we confirm furthervariance in peak angle than reported in other research. This isespecially clear in the first intensity peak as it has a significantlylarger angle. Variability in Jupiter’s magnetic field and densityof the Jovian plasma torus is likely to explain peak angle andintensity variability, but further research is necessary to explainthe mechanisms in detail.Vi studerar hur intensiteten av Ios aurora varierar i relation till Jupiters rotation mätt i system III longitud. Ios aurora mättes inom UVC området av Hubble Space Telescope (HST) med FUV-MAMA fotondetektorn. Matlab användes för att filtrera bort oönskade signaler som reflektion och bakgrund samt ta hänsyn till sensorns optiska system. Observationsområderna på sensorn konstruerades för mätningen av syre OI (1356Å ) och svavel SI (1479Å ) emissionerna. Genom att sampla fo- tondetektioner inom varje observationsområde så rekonstruerar vi en intensitetskurva som vi mappar till system III longitud. En kurva var sedan anpassad till rekonstruktionen med hjälp av en sinusanpassning. Resultaten visar två intensitetstoppar vid system III longituderna (140 ± 5)◦ och (284 ± 2)◦ för både OI och SI . Kvoten mellan topparna var (38 ± 6)% för OI och (28 ± 6)% för SI . Skillnaden i topparna kan förklaras av att sannolikheten att excitera svavel är större än att excitera syre. För fullständig beskrivning av skillnaden i topparna skulle mätningar av syre till svavel proportionen i Ios atmosfär behövas. Vi jämför våra reslutat med mätningar av Ios avtryck på Jupiter från JUNO och andra HST mätningar. Vi finner det sannolikt att vi bekräftar ytterligare varians i topparnas vinkel, främst för den första toppen vars vinkel är signifikant större. Variationer i Jupiters magnetfält och plasmadensitet av Jupiters plasmatorid kan sannolikt förklara positionen av topparna och intensitetsvariationerna. Vidare forskning behövs för att utförligt förklara dessa mekanismer.
Kandidatexjobb i elektroteknik 2020, KTH, Stockholm
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Modin, Emelie. "Estimating Charging on a Sounding Rocket Experiment Using Plasma Simulation." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-293892.
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The aim of this project is to model current volt-age characteristic curves for different plasma conditions (i.eelectron density, electron temperature, ion temperature andplasma potential) that can be found in active auroras. This isdone by simulating the charging of a FFU with a connectedLangmuir probe in the software SPIS. These I-V curves wereused to determine the plasma properties of the auroras in whichthe sounding rockets SPIDER-1 and SPIDER-2 were launched.Through the simulations it was also studied how the differentparameters effects the I-V curves.The results showed that the plasma SPIDER-1 was launchedin most likely had properties close to nominal conditions and forSPIDER-2 there was colder electrons in the plasma. A conclusionthat only the electron temperature affects the shape of the I-Vcurves for the values simulated in this project can be drawnas well as the conclusion that the geometry of the probe doesnot affect the shape of the I-V curves. Another result showsthat electron temperature also affect how the hull of the FFUcharges. A higher electron temperature gives the hull a morenegative charge.Syftet med detta projekt är att modellera ström-pänningskaraktäristisk kurvor för olika plasmatillstånd som finns i aktiva auroror. Detta görs genom att simulera laddning på en FFU med en ansluten Langmuir-prob i SPIS. Dessa I-V-kurvor används för att bestämma plasma egenskaperna för aurororna sondraketerna SPIDER-1 och SPIDER- 2 skjöts upp i. I-V kurvorna används också för att bestämma hur plasma parametrarna elektron temperatur, jon temperatur och elektrondensitet samt hur probens geometri påverkar I-V- kurvornas utseende. Resultaten visade att den plasma SPIDER-1 blev uppskjuten i troligen hade nominella förhållanden och att den SPIDER-2 blev uppskjuten i troligtvis hade kallare elektroner. En slutsats om att endast elektron temperaturen påverkar formen på IV- kurvorna kan dras, såväl som slutsatsen att probens geometri inte påverkar formen på IV-kurvorna. Ett annat resultat visar att elektron temperaturen också påverkar ytpotentialen på FFUn. En högre elektron temperatur ger FFUn en mer negativ laddning.
Kandidatexjobb i elektroteknik 2020, KTH, Stockholm
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Hammarsten, Michael. "A statistical study of incoherent scatter plasma line enhancements during the International Polar Year ’07-’08 in Svalbard." Thesis, Luleå tekniska universitet, Rymdteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60158.
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There was a large radar campaign during 2007 and 2008, the International Polar Year (IPY),and at that time the EISCAT Svalbard Radar was operated and measured the ionosphere continuouslyat most times. This report presents statistical results from an electron enhancementpoint of view. Until now there has been some research into the field and results based on theions in the ionosphere, and the enhancements we refer to as Naturally enhanced ion acousticlines (NEIALs). Plasma line data from May 2007 to February 2008 has been analysed inorder to find and classify enhancements as NEIALs have been classified but with respect tothe electron distribution instead of the ion distribution. A method of detection was developedin order to differentiate the enhancements from the background with a relation between theminimum and maximum power of each measured dump. Results show that there is a largedifference between the downshifted plasma lines and the upshifted plasma lines, both has arange distribution peak at 180 km and the upshifted plasma line has another peak at 230 kmwhich the downshifted plasma line does not. The occurrence rate of the enhancements was1.64 % for the downshifted plasma line and 4.69 % for the upshifted plasma line. Threedifferent types of enhancements are classified using the variance distribution for the peakfrequency of that detected dump, Single, Profile, and Diffuse. The Single enhancements havea bit different spectral, range, and time of day distributions than of the Profile and Diffusedistributions. The Diffuse classifications are mostly wrong classifications and aliasing and itis very similar to Profile enhancements as seen by its distribution.
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Bouhram, Mehdi. "Étude des échappements d'ions ionosphériques du côté jour des zones aurorales." Paris 6, 2002. http://www.theses.fr/2002PA066048.
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Génot, V. "Étude des phénomènes d'accélération de particules dans les régions aurorales des magnétosphères." Phd thesis, Université de Versailles-Saint Quentin en Yvelines, 1999. http://tel.archives-ouvertes.fr/tel-00010474.
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L'accélération de particules est une thématique d'astrophysique générale qui peut être étudiée dans un laboratoire naturel : les régions aurorales de la
Terre, et plus globalement, celles des planètes magnétisées. Ces régions sont
en effet le siège de nombreux processus qui donnent, entre autres, naissance
aux aurores boréales et australes, phénomènes spectaculaires mais dont de
nombreux aspects restent incompris. En particulier, de multiples mesures de
satellites ont montré l'existence de populations de particules énergétiques
précipitant vers la Terre, nécessitant le maintien d'une différence de
potentiel électrique élevée que la plupart des modèles proposés sont incapables
de reproduire. D'une manière générale, comprendre l'accélération, c'est
comprendre une partie du couplage dynamique entre la magnétosphère, où
l'énergie est libérée lors des sous-orages, et l'ionosphère où l'énergie est
dissipée. L'étude de cette dissipation, qui opère sur de courtes échelles
spatiales et temporelles, constitue le thème principal de ce travail. Dans
ce but, nous considérons une perturbation électromagnétique, sous forme d'onde
d'Alfvén, se propageant le long des lignes de champ magnétique. Son
interaction, en région aurorale, avec les cavités de plasma, structures
fortement inhomogènes, conduit à l'apparition de champs électriques parallèles
susceptibles d'accélérer les particules, ainsi qu'à un transfert d'énergie
significatif des ondes vers les électrons. Finalement, cette étude permet de
dégager un nouveau scénario de formation des arcs auroraux. Ce travail a été
mené de façon analytique avant d'être traité numériquement grâce à un code
particulaire.
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El-Alaoui, Mostafa. "Etude des faisceaux d'ions détectés en région aurorale par le satellite AUREOL-3 : synthèse des observations et apport de la modélisation numérique." Toulouse 3, 1994. http://www.theses.fr/1994TOU30037.
Full textAbstract:
Les resultats amasses pendant plus d'un millier de passages du satellite franco-sovietique aureol-3 au-dessus des regions des hautes latitudes ont ete analyses afin de determiner les proprietes de la precipitation des particules chargees. Cette recherche a permis la decouverte de nombreux faisceaux d'ions energetiques et, pour la premiere fois, leurs proprietes sont decrites en detail. Ces faisceaux sont localises au voisinage de la separatrice entre l'ovale des precipitations aurorales et la calotte polaire; leur caracteristique fondamentale est l'accroissement de leur energie avec la latitude. On demontre en particulier que ces faisceaux, confines en latitude dans une region de moins de 1 degre d'etendue, sont la signature aurorale a basse altitude des faisceaux deja observes par le passe dans les couches limites du feuillet de plasma. A ces faisceaux peut etre associee une region nouvelle qui est aussi mise en evidence et decrite dans ce travail pour la premiere fois: autour de minuit local un minimum prononce de precipitation ionique separe la region aurorale diffuse de la region des faisceaux d'ions et ce minimum correspond partiellement a la region des arcs d'electrons. A partir de l'analyse des equations du mouvement des ions, il est montre que ces faisceaux proviennent des regions tres lointaines de la magnetosphere et transportent des informations fondamentales sur les mecanismes d'accel2ration agissant dans la queue geomagnetique. Au voisinage d'un feuillet neutre les particules executent differentes familles de trajectoires dans l'espace; la physique complexe qui gouverne ce mouvement en presence d'un champ electrostatique de convection et du champ geomagnetique sera discutee puis confirmee et etendue au moyen des simulations numeriques
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Payan, Alexia Paule Marie-Renee. "Uncovering local magnetospheric processes governing the morphology and periodicity of Ganymede’s aurora using three-dimensional multifluid simulations of Ganymede’s magnetosphere." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51756.
Full textAbstract:
The electrodynamic interaction of Ganymede’s mini-magnetosphere with Jupiter’s corotating magnetospheric plasma has been shown to give rise to strong current systems closing through the moon and its ionosphere as well as through its magnetopause and magnetotail current sheet. This interaction is strongly evidenced by the presence of aurorae at Ganymede and of a bright Ganymede footprint on Jupiter’s ionosphere. This footprint is located equatorward of the main auroral emissions, at the magnetic longitude of the field line threading Ganymede. The brightness of Ganymede’s auroral footprint at Jupiter along with its latitudinal position have been shown to depend on the position of Ganymede relative to the center of the Jovian plasma sheet. Additionally, observations using the Hubble Space Telescope showed that Ganymede’s auroral footprint brightness is characterized by variations of three different timescales: 5 hours, 10-40 minutes, and ~100 seconds. The goal of the present study is to examine the relationship between the longest and the shortest timescale periodicities of Ganymede’s auroral footprint brightness and the local processes occurring at Ganymede. This is done by coupling a specifically developed brightness model to a three-dimensional multifluid model which tracks the energies and fluxes of the various sources of charged particles that precipitate into Ganymede’s ionosphere to generate the aurora. It is shown that the predicted auroral brightnesses and morphologies agree well with observations of Ganymede’s aurora from the Hubble Space Telescope. Our results also suggest the presence of short- and long-period variabilities in the auroral emissions at Ganymede due to magnetic reconnections on the magnetopause and in the magnetotail, and support the hypothesis of a correlation between the variability of Ganymede’s auroral footprint on Jupiter’s ionosphere and the variability in the brightness and morphology of the aurora at Ganymede. Finally, the modeled aurora at Ganymede reveals that the periodicities in the morphology and brightness of the auroral emissions are produced by two different dynamic reconnection mechanisms. The Jovian flow facing side aurora is generated by electrons sourced in the Jovian plasma and penetrating into Ganymede’s ionosphere through the cusps above the separatrix region. In this case, the reconnection processes responsible for the auroral emissions occur on Ganymede’s magnetopause between the Jovian magnetic field lines and the open magnetic field lines threading Ganymede’s Polar Regions. As for the magnetotail side aurora, it is generated by electrons originating from Ganymede’s magnetospheric flow. These electrons are accelerated along closed magnetic field lines created by magnetic reconnection in Ganymede’s magnetotail, and precipitate into Ganymede’s ionosphere at much lower latitudes, below the separatrix region.
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Garcia, Geraldine. "Etude de la dynamique des electrons en presence de fortes densites de courant." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://tel.archives-ouvertes.fr/tel-00250116.
Full textAbstract:
L'objet de notre étude est la dynamique des plasmas collisionnels soumis à un champ électrique aligné au champ magnétique en bordure d'aurore. De fortes densités de courant aligné ont été mises en évidence à la fois par des modèles électrodynamiques et des mesures satellites ou radars. Différents auteurs et différents types de travaux (expérimentaux ou de modélisation) montrent que les densités de courant peuvent atteindre des centaines de μA.m−2 en bordure des arcs auroraux. Ces densités de courant sont à l'origine de multiples phénomènes tels que : le chauffage du plasma ionosphérique, l'échappement des ions et le développement d'instabilités. Ces fortes densités de courant impliquent la présence d'un champ électrique parallèle qui peut entraîner des effets cinétiques tels que la création d'électrons runaway. L'étude des électrons runaway n'est pas nouvelle et intervient dans différents domaines tels que la fusion nucléaire, le chauffage de la couronne solaire ou les phénomènes lumineux transitoires tels que les sprites. Dans notre cas, nous nous intéressons à l'ionosphère terrestre où l'étude des électrons runaway est un sujet très novateur. Ainsi, nous allons étudier la dynamique des électrons portant ces courants très intenses. Pour cela, nous considérons un ensemble d'électrons se déplaçant à travers un gaz ionosphérique d'ions et de neutres et soumis à un champ électrique aligné au champ magnétique. Nous avons développé un modèle cinétique de collisions, incluant les collisions électrons/électrons, électrons/ions et électrons/neutres. Nous utilisons une approche Fokker-Planck afin de décrire les collisions binaires entre les particules chargées (interactions à longue portée). L'opérateur de collisions comporte deux parties : l'équation de Langevin pour les collisions électrons/électrons et électrons/ions et la méthode de Monte-Carlo avec une approche "collision nulle" pour les collisions électrons/neutres. Nous donnons un exemple de retour à l'équilibre afin de tester ces opérateurs de collisions et d'étudier l'impact des différents termes (les collisions électrons/électrons et électrons/ions d'une part et les collisions électrons/neutres d'autre part).
Tout d'abord, nous considérons un champ électrique constant au cours du temps. Dans ce test, les électrons sont déplacés uniquement selon z, la direction parallèle au champ electrique et au champ magnétique. Nous constatons alors que les fonctions de distribution ne sont plus maxwelliennes et que des électrons runaway sont créés. Ces électrons représentent 20% de la densité totale et ce sont eux qui portent le courant. Cependant, nous remarquons que nous ne conservons pas la divergence du courant nulle.
Nous introduisons alors des modifications majeures telles qu'une rétroaction sur le champ électrique ou la résolution des équations fluides afin de tenir compte de l'évolution des moments de la fonction de distribution des ions. Nous observons que les fonctions de distribution des électrons restent non maxwelliennes. Des électrons suprathermiques sont créés et portent le courant. En effet, la population correspondant au coeur de la distribution reste au repos. Comme ces électrons subissent moins de collisions, ils augmentent la conductivité du plasma.
Enfin, nous avons réalisé une étude paramétrique afin d'étudier l'influence des divers paramètres d'entrée (densité de courant, densité électronique, temps de montée du courant...) sur les fonctions de distribution. Pour cela, nous ajustons deux maxwelliennes qui correspondent au coeur de la distribution et à la population suprathermique. Nous mettons en avant le fait que le temps de montée du courant, c'est-à-dire le temps nécessaire pour atteindre la valeur maximale du courant, est un paramètre clef. En effet, augmenter ce temps influe essentiellement sur les températures : la température moyenne des électrons, mais aussi celle des électrons de la population représentant le coeur de la distribution et de la population suprathermique. La densité de courant joue également un rôle primordial.Augmenter la densité de courant augmente l'ensemble des paramètres : la densité et la vitesse moyenne des électrons runaway et les températures électroniques des deux populations. L'étude sur la densité a révélé que, plus la densité électronique totale augmente, plus la température et la vitesse moyenne des électrons suprathermiques diminuent.
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Teste, Alexandra. "Aurores et échappements de particules au-dessus des calottes polaires terrestres : observations à haute altitude par la mission Cluster." Paris 6, 2007. https://tel.archives-ouvertes.fr/tel-00803178.
Full textAbstract:
Lorsque le champ magnétique interplanétaire est dirigé vers le Nord, les régions polaires de la magnétosphère terrestre, situées à haute altitude, sont peuplées d'électrons accélérés. L'ionosphère polaire voit quant à elle l'apparition d'aurores. Grâce aux observations magnétosphériques de la mission multi-satellites Cluster et à notre modélisation du transport de particules le long des lignes de force du champ magnétique terrestre B, nous avons montré, au cours de cette thèse, que les électrons à l'origine de ces aurores proviennent de la couche frontière de la magnétosphère. Localisée à très haute altitude, cette couche sépare les milieux terrestre et interplanétaire. Accélérés par des champs électriques parallèles à B, situés à des altitudes aussi bien inférieures que supérieures à celles des satellites, ces électrons précipitent dans l'ionosphère avec des énergies de l'ordre du keV. Ils sont accompagnés par des échappements d'ions ionosphériques et l'ensemble des particules transporte des courants alignés le long de B et dirigés vers la magnétosphère, équivalents à quelques µA/m² aux altitudes ionosphériques. Le système de courant se referme par des courants alignés dirigés vers la Terre, d'intensité comparable, portés par des faisceaux d'électrons étroits et variables. Très alignés le long de B, ces électrons s'échappent de l'ionosphère avec des énergies de ~ 50 eV et déclenchent des instabilités faisceau-plasma à l'origine d'ondes électrostatiques large bande observées par Cluster et reproduites par les modèles.
38
Dandouras, Jean. "Etude de la dynamique de la queue de la magnetosphere terrestre et des conditions de declenchement des sous-orages magnetospheriques." Toulouse 3, 1988. http://www.theses.fr/1988TOU30191.
Full textAbstract:
Les differentes signatures des sous-orages causes par des populations variees de plasma qui constituent la magnetosphere sont etudiees statistiquement. Les decroissances transitoires des flux de particules associes a ces sous-orages sont interpretees en terme d'amincissement de la couche de plasma. Des correlations avec le phenomene d'injection de particules energetiques dans la partie interne de la magnetosphere cote nuit sont mises en evidence. Ceci permet de developper un modele decrivant le processus physique responsable a la fois des amincissements et des injections
39
Teste, Alexandra. "AURORES ET ECHAPPEMENTS DE PARTICULES AU-DESSUS DES CALOTTES POLAIRES TERRESTRES Observations à haute altitude par la mission Cluster." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://tel.archives-ouvertes.fr/tel-00803178.
Full textAbstract:
Lorsque le champ magnétique interplanétaire est dirigé vers le Nord, les régions polaires de la magnétosphère terrestre, situées à haute altitude, sont peuplées d'électrons accélérés. L'ionosphère polaire voit quant à elle l'apparition d'aurores. Grâce aux observations magnétosphériques de la mission multi-satellites Cluster et à notre modélisation du transport de particules le long des lignes de force du champ magnétique terrestre B, nous avons montré, au cours de cette thèse, que les électrons à l'origine de ces aurores proviennent de la couche frontière de la magnétosphère. Localisée à très haute altitude, cette couche sépare les milieux terrestre et interplanétaire. Accélérés par des champs électriques parallèles à B, situés à des altitudes aussi bien inférieures que supérieures à celles des satellites, ces électrons précipitent dans l'ionosphère avec des énergies de l'ordre du keV. Ils sont accompagnés par des échappements d'ions ionosphériques et l'ensemble des particules transporte des courants alignés le long de B et dirigés vers la magnétosphère, équivalents à quelques µA/m² aux altitudes ionosphériques. Le système de courant se referme par des courants alignés dirigés vers la Terre, d'intensité comparable, portés par des faisceaux d'électrons étroits et variables. Très alignés le long de B, ces électrons s'échappent de l'ionosphère avec des énergies de ~ 50 eV et déclenchent des instabilités faisceau-plasma à l'origine d'ondes électrostatiques large bande observées par Cluster et reproduites par les modèles.
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Parham, Jonathan Brent. "Satellite swarms for auroral plasma science." Thesis, 2019. https://hdl.handle.net/2144/34921.
Full textAbstract:
With the growing accessibility of space, this thesis work sets out to explore space-based swarms to do multipoint magnetometer measurements of current systems embedded within the Aurora Borealis as an initial foray into concepts for space physics applications using swarms of small spacecraft.
As a pathfinder, ANDESITE---a 6U CubeSat with eight deployable picosatellites---was built as part of this research. The mission will fly a local network of magnetometers above the Northern Lights. With the spacecraft due to launch on an upcoming ELaNa mission, here we discuss the details of the science motivation, the mathematical framework for current field reconstruction, the particular hardware implementation selected, the calibration procedures, and the pragmatic management needed to realize the spacecraft.
After describing ANDESITE and defining its capability, we also propose a follow-on that uses propulsive nodes in a swarm, allowing measurements that can adaptively change to capture the physical phenomena of interest. To do this a flock of satellites needs to fall into the desired formation and maintain it for the duration of the science mission. A simple optimal controller is developed to model the deployment of the satellites. Using a Monte Carlo approach for the uncertain initial conditions, we bound the fuel cost of the mission and test the feasibility of the concept.
To illustrate the system analysis needed to effectively design such swarms, this thesis also develops a framework that characterizes the spatial frequency response of the kilometer-scale filter created by the swarm as it flies through various current density structures in the ionospheric plasma. We then subjugate a nominal ANDESITE formation and the controlled swarm specified to the same analysis framework. The choice of sampling scheme and rigorous basic mathematical analysis are essential in the development of a multipoint-measurement mission.
We then turn to a novel capability exploiting current trends in the commercial industry. Magnetometers deployed on the largest constellation to date are leveraged as a space-based magnetometer network. The constellation, operated by Planet Labs Inc., consists of nearly 200 satellites in two polar sun-synchronous orbits, with median spacecraft separations on the order of 375 km, and some occasions of opportunity providing much closer spacing. Each spacecraft contains a magneto-inductive magnetometer, able to sample the ambient magnetic field at 0.1 Hz to 10 Hz with <200 nT sensitivity. A feasibility study is presented wherein seven satellites from the Planet constellation were used to investigate space-time patterns in the current systems overlying an active auroral arc over a 10-minute interval.
Throughout the this work advantages, limitations, and caveats in exploiting networks of lower quality magnetometers are discussed, pointing out the path forward to creating a global network that can monitor the space environment.
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Akbari, Hassanali. "Beam-plasma interactions and Langmuir turbulence in the auroral ionosphere." Thesis, 2015. https://hdl.handle.net/2144/16310.
Full textAbstract:
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.
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Lambour, Richard Lee. "A comparison of the magnetospheric specification model, the Hardy et al. model, and satellite observations for precipitating auroral electron energy fluxes." Thesis, 1992. http://hdl.handle.net/1911/13677.
Full textAbstract:
A semi-quantitative comparison has been made of the observed and calculated precipitating electron energy fluxes for the April 1988 magnetic storm. Electron energy fluxes were calculated by the Rice Magnetospheric Specification Model (MSM), a comprehensive model of the inner magnetospheric environment, and by the Hardy et al. model, a statistical model of electron precipitation in the auroral zone.
The MSM correlates better with the observed fluxes than does the Hardy et al. model in terms of auroral boundaries, latitudinal profile and extent, and the actual magnitude of the energy flux. The sources of error in the MSM are probably: (1) Artificial flux dropouts created near the ionospheric projection of the model outer boundary, (2) an overestimate of the convection electric field, and (3) errors in locating the polar cap boundary.
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"Dynamical coupling of plasma motions and neutral winds in the presence of short time-scale(10-90 min)wavelike structures in the auroral ionosphere." Thesis, 2001. http://hdl.handle.net/2237/11221.
Full text
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大山, 伸一郎, and Shin-ichiro Oyama. "Dynamical coupling of plasma motions and neutral winds in the presence of short time-scale(10-90 min)wavelike structures in the auroral ionosphere." Thesis, 2001. http://hdl.handle.net/2237/11221.
Full text
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Beever, Zachary. "Quantifying loss of current sheet scattered electrons during the substorm growth phase." Thesis, 2021. https://hdl.handle.net/2144/42586.
Full textAbstract:
Particles trapped in the magnetosphere are naturally accelerated by the exchange of electromagnetic and kinetic energy, resulting in relativistic plasma populations. Through a number of processes, these particles can be scattered into the atmosphere and lost to interactions. Such precipitating particles can affect radio communications, ozone chemistry, and thermal structures. For these reasons, it is important to characterize loss mechanisms and quantify precipitation rates. This thesis examines one particular loss mechanism known as current sheet scattering (CSS).
If interactions are negligible, charged particles in a magnetic field have approximately conserved quantities that characterize their motion provided the background field changes sufficiently slowly over space and time. The first of these ‘adiabatic invariants,’ the magnetic moment, is related to the particle’s mirror point along its bounce trajectory—the location at which the particle reverses direction in its journey from weaker to stronger B. In the equatorial region of the near-Earth magnetotail, where the radius of field line curvature of the magnetic field can become comparable to the gyroradius of ≈ 100 keV electrons, the homogeneity conditions needed for conservation of the magnetic moment of this population are broken. Upon passing through this location, known as the current sheet, these particles experience a chaotic change in their magnetic moment, and thus an alteration of their mirror point. This is the phenomenon of CSS. If the resulting mirror point lies within the atmosphere, the particle will most likely be lost through interactions.
CSS is often investigated for highly relativistic electrons. However, recent observations suggest that this mechanism may account for a significant proportion of precipitating electrons between 100 and 300 keV during the substorm growth phase, a common space weather event wherein magnetic field lines in the near-Earth magnetotail become highly stretched. In this thesis, we test the efficacy of CSS as a loss mechanism for < 300 keV electrons by developing a relativistic charged particle tracer capable of solving complex trajectories in realistic magnetospheric magnetic field models. We then find distributional characteristics through Monte Carlo methods, comparing simulated ratios of loss- to total-flux with observations of the same quantities for a single substorm event. These observations are obtained by comparison of in situ measurements made by THEMIS (Time History of Events and Macroscale Interactions during Substorms) with ionospheric energy flux remotely sensed by PFISR (Poker Flat Incoherent Scatter Radar).
Given an input distribution from THEMIS satellite measurements, we find agreement between observed and simulated loss- to total-flux ratios within an order of magnitude, with closer agreement for electrons between 100 and 300 keV. This implies CSS can explain a significant proportion of observed precipitation for the event studied and demonstrates its role as a prominent radiation belt loss mechanism. In particular, these findings suggest that the measured loss flux of < 300 keV electrons during such events can be immediately related to the geometry of the near-Earth magnetotail. This is further supported by a parametric study of initially field aligned distributions spawned at various nightside locations, showing a low-energy peak in the loss- to total-flux ratio at the boundary between the outermost radiation belt and the magnetotail. Measurements of particle orientation taken from THEMIS are low resolution, and agreement between simulated and observed loss- to total-flux ratios can be increased by assuming a more field aligned distribution for electrons below 100 keV. This suggests the presence of other physical processes besides CSS that may preferentially structure the pitch angle distributions of low energy electrons to be field aligned. Additional analysis is needed to identify these possible mechanisms.
In summary, findings from this work support the role of CSS as an important contributor to < 300 keV electron loss during the substorm growth phase. Though there is an underestimation of loss for < 100 keV electrons, it is known that the empirical magnetic field models employed overestimate the radius of curvature in the current sheet. Furthermore, the dawn-dusk electric field has been neglected, though it has the possibility to produce field aligned electrons through current sheet acceleration. The inclusion of these effects in future studies may further improve agreement between simulation and observations.
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"Large scale plasma density perturbations in the polar F-region ionosphere." Thesis, 2015. http://hdl.handle.net/10388/ETD-2015-02-1947.
Full textAbstract:
The most compelling evidence of the complex interaction between the geomagnetic field of the Earth and the magnetic field of the Sun is found in the polar ionosphere. Large scale F-region plasma density perturbations result from the coupling between the two fields. Plasma density enhancements known as ionization patches, and depletions can have lifetimes of several hours in the F region and are almost always present everywhere throughout the nighttime polar ionosphere. The perturbations can seed ionospheric irregularities that severely hamper communication and navigational networks, even during times of subdued geomagnetic activity. Up until recently, it has been difficult to study the perturbations due to the remoteness of their location. In the past decade an array of optical and radio instruments have been deployed to the Canadian sector of the Arctic, enabling a more thorough sampling of the polar ionosphere and the large scale perturbations therein.
In this work, common volume measurements from the Rankin Inlet Super Dual Auroral Radar Network (SuperDARN), Resolute Bay Incoherent Scatter Radar - North (RISR-N) and Optical Mesosphere and Thermosphere Imagers (OMTI) system at Resolute Bay are employed to investigate the generation mechanisms, transport properties, and optical and radio signatures of the large scale perturbations. A model connecting the optical signatures of patches to their velocity profile through the ionosphere is introduced and applied to OMTI data. In addition, an algorithm is developed to detect the presence of patches using RISR-N. Using the algorithm, a survey of patches sampled over several days is conducted, providing a comprehensive account of the variable polar ionosphere in terms of its plasma state parameters. Furthermore, the algorithm is used to diagnose patches as a primary source of coherent backscatter for the Rankin Inlet SuperDARN radar. Lastly, the generation of a deep plasma density depletion is analyzed using the three aforementioned instruments. Using a model, it is shown that such perturbations can be forged by intense frictional heating events in the polar ionosphere on a time scale of 15 minutes, and can subsequently be transported through the region.
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Moore, Christopher Hudson. "Monte Carlo simulation of the Jovian plasma torus interaction with Io’s atmosphere and the resultant aurora during eclipse." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-08-4245.
Full textAbstract:
Io, the innermost Galilean satellite of Jupiter, exhibits a wide variety of complex phenomena such as interaction with Jupiter’s magnetosphere, volcanic activity, and a rarefied multi-species sublimating and condensing atmosphere with an ionosphere. Io’s orbital resonance with Jupiter and the other Galilean satellites produces intense tidal heating. This makes Io the most volcanically active body in the solar system with plumes that rise hundreds of kilometers above the surface. In the present work, the interaction of Io’s atmosphere with the Jovian plasma torus is simulated via the Direct Simulation Monte Carlo (DSMC) method and the aurora produced via electron-neutral excitation collisions is examined using electron transport Monte Carlo simulation.
The electron-transport Monte Carlo simulation models the electron collisions with the neutral atmosphere and their transport along field lines as they sweep past Io, using a pre-computed steady atmosphere and magnetic field. As input to the Monte Carlo simulation, the neutral atmosphere was first modeled using prior 2D sunlit continuum simulations of Io’s atmosphere produced by others. In order to justify the use of a sunlit atmosphere for eclipse, 1D two-species (SO2 and a non-condensable) DSMC simulations of Io’s atmospheric dynamics during and immediately after eclipse were performed. It was found that the inclusion of a non-condensable species (SO or O2) leads to the formation of a diffusion layer which prevents rapid collapse. The degree to which the diffusion layer slowed the atmospheric collapse was found to be extremely sensitive to both the initial non-condensable mole fraction and the reaction (or sticking) probability on the surface of the “non-condensable”. Furthermore, upon egress, vertical stratification of the atmosphere occurred with the non-condensable species being lifted to higher altitudes by the rapid sublimation of SO2 as the surface warms.
Simulated aurorae (specifically the [OI] 6300 Å and the S2, SO, and SO2 molecular band emission in the middle ultraviolet) show good agreement with observations of Io in eclipse and an attempt was made to use the simulations to constrain the upstream torus electron temperature and Io’s atmospheric composition, structure, and volcanic activity. It is found that the position of the bright [OI] 6300 Å wake spot relative to Io’s equator depends on the position of Io relative to the plasma torus’ equator and the asymmetric electron number flux that results. Using HST/STIS UV-Vis spectra, the upstream electron temperature is weakly constrained to be between 3 eV and 8 eV depending on the flux of a low energy (35 eV), non-thermal component of the plasma (more non-thermal flux requires lower thermal plasma temperatures to fit the spectrum). Furthermore, an upper limit of 5% of the thermal torus density (or 180 cm−3 based on the Galileo J0 plasma density at Io) is obtained for the low energy non-thermal component of the plasma. These limits are consistent with Galileo observations of the upstream torus temperature and estimates for the the non-thermal component. Finally, plume activity and S2 content during eclipse observations with HST/STIS were constrained by examining the emission intensity along the spatial axis of the aperture. During the August 1999 UV-Vis observations, the auroral simulations indicate that the large volcanoes Pele and Surt were inactive whereas Tvashtar was active and that Dazhbog and possibly Loki were also actively venting gas. The S2 content inferred for the large Pele-type plumes was between 5% (Tvashtar) and 30% (Loki, if active), consistent with prior observations (Spencer et al., 2000; Jessup et al., 2007).
A 3D DSMC simulation of Io’s sublimation and sputtered atmosphere including photo- and plasma-chemistry was developed. In future work these atmospheric simulations will replace the continuum target atmosphere in the auroral model and thus enable a better match to the observed high altitude auroral emission. In the present work, the plasma interaction is modeled by a flux of ions and electrons which flow around and through Io’s atmosphere along pre-computed fields and interact with the neutral gas. A 3D DSMC simulation of Io’s atmosphere assuming a simple thermal model for the surface just prior to ingress into eclipse and uniform frost coverage has been performed in order to understand how Io’s general atmospheric dynamics are affected by the new plasma model with chemistry and sputtering. Sputtering was found to supply most of the nightside atmosphere (producing an SO2 column of ~5×1013 cm−2); however, the dense dayside sublimation atmosphere was found to block sputtering of the surface. The influence of the dynamic plasma pressure on the day-to-night circumplanetary flow was found to be quite substantial causing the day-to-night wind across the dawn terminator to flow slightly towards the equator. This results in a region of high density near the equator that extends far (~2000 km for the condensable species) onto the nightside across the dawn terminator. Thus, even without thermal lag due to rotation or variable surface frost, highly asymmetric equatorial column densities relative to the subsolar point are obtained. The non-condensable O2, which is a trace species on the dayside, is the dominant species on the nightside despite increased SO2 sputtering because the loss rate of O2 is slow. Finally, a very intriguing O2 flow feature was observed near the dusk terminator where the flow from the leading hemisphere (pushed by the plasma) meets the flow from the dayside trailing hemisphere. Since the O2 does not condense on the surface, it slowly convects towards the poles and then back onto the nightside, eventually to be dissociated or stripped away by the plasma.text