Zugl.: Braunschweig, Techn. Univ., Diss., 2008

A recently proposed set of demagnetization diagnostics [Scudder et al., submitted to Physics of Plasmas, 2015] is related to the preconditions of Guiding Center Theory (GCT) and benchmarked in kinetic particle-in-cell simulations. Specifically, GCT requires that the time and length scales of the field are long compared to the Larmor motion of the particles. When this condition is violated, the particles become demagnetized and the assumptions of magnetohydrodynamics are no longer valid. In this thesis, these diagnostics are applied to different space plasma layers of different length scales. In the past, proxy diagnostics that are not based on fundamental GCT conditions have been used to search for, and provide evidence of, demagnetization in different space plasma layers. The problem with these proxy diagnostics is that they are not invertible to demagnetization. The diagnostics presented in this thesis are not only unique to demagnetization, but also have the additional advantages of being dimensionless, scalar, and independent of coordinate system. These diagnostics are applied to three space plasma layers of different length scales, resulting in new insights and methods for detecting particle demagnetization. First, the evidence for wave heating in the solar wind is reexamined through its fundamental assumptions of demagnetization. The proxy diagnostic commonly used for demagnetization is non-conservation of the Chew-Goldberger-Low conserved quantity. This diagnostic is a good proxy for the first adiabatic invariant in the supersonic regime. To test this and compare it to the assumptions of the Helios analysis [Marsch et al., Journal of Geophysical Research: Space Physics, 88(A4), 1983], the solar wind is modeled through a self-consistent Vlasov mapping. In addition, other experimental assumptions in that same Helios analysis are also examined. Second, a new method for estimating local length scales is demonstrated across a known bow shock crossing. This new method, based on one of the demagnetization diagnostics, is different from current methods in that it can be performed with single spacecraft data and does not require a special coordinate system. Third, a new set of invertible signatures of the electron diffusion region (EDR) is introduced and applied to five magnetopause events to search for layers of collisionless magnetic reconnection. Four of these magnetopause events have not been identified before in the literature. The five EDR diagnostics are large electron pressure anisotropy, non-perturbative GCT expansion parameters, order one electron pressure agyrotropy, and order one electron thermal mach number. These EDR diagnostics are compared to a wide range of degenerate diagnostics that are commonly used in reconnection studies. The results of this analysis show that, compared to these degenerate diagnostics, the EDR diagnostics are much more surgical in their identification of electron-scale current layers.

The magnetopause is an important feature in near-Earth space, where the continuously emitted solar wind from the sun meets the magnetic field of the Earth. This boundary region between the so-called magnetosheath on the outside and magnetosphere on the inside is a constantly back-and-forth moving discontinuity upheld by a pressure balance on both sides, upon which an important process in mass and energy transportation through the universe called magnetic reconnection occurs. To gain further understanding about the magnetopause, this study aimed to produce additional statistical scientific material concerning the discontinuity, including the total pressure difference across it, pressure values and total pressure contributions in the magnetosheath and magnetosphere bordering it, and velocity of the magnetopause related to pressure difference. This was done by analysing data from the MMS-project during crossings of the magnetopause in late 2017 and throughout 2018 at the subsolar point and dawn-/dusk flanks. While the results show in general good agreement with previous studies, some intriguing features were noted, including a pressure difference bias towards higher mean total pressures in the magnetosheath in all regions, as well as shift in dominating pressure in the magnetosphere from magnetic pressure at the subsolar point to thermal pressure on the flanks. Further study to confirm these features ought to be conducted. Finally, no clear connection was revealed between magnetopause velocity and pressure imbalance. / Magnetopausen är en viktig struktur i den jordnära rymden, där den ständigt utskickade solvinden från solen möter jordens magnetfält. Detta gränsområde mellan det så kallade magnetosheath på utsidan och magnetosfären på insidan är en diskontinuitet i ständig rörelse fram och tillbaka, upprätthållen av en tryckbalans på båda sidor, på vars yta en mycket viktig process för mass- och energitransport i universum sker kallad magnetisk rekonnektion. För att öka förståelsen för magnetopausen, har denna studie haft som mål att skapa ytterligare statistiskt material gällande diskontinuiteten. Detta inkluderar den totala tryckskillnaden över den, tryckvärden och deras bidrag till det totala trycket i magnetosheath och magnetosfären som gränsar den, samt magnetosfärens hastighet kopplat till tryckskillnaden över den. Detta gjordes genom analys av data från MMS-projektet, specifikt korsningar av magnetopausen i slutet av 2017 och under 2018 vid subsolar point och morgon- /kvällsflankerna. Om än resultaten visar på generellt sätt god överensstämmelse med tidigare studier, noterades en del intressanta resultat. Främst av dessa var en tydlig tendens för högre totalt tryck i magnetosheath jämfört med magnetosfären i alla undersökta regioner, samt ett oväntat skifte av dominerande tryck i magnetosfären från magnetiskt tryck vid subsolar point till termiskt tryck vid flankerna. Fortsatta studier för att bekräfta dessa resultat bör genomföras. Gällande magnetopaushastighet kopplat till tryckskillnad kunde ingen klar koppling ses från resultaten.

This thesis is focused on the role of Alfvén waves in the energy transformation and transport in the magnetosphere. Different aspects of Alfvén wave generation, propagation and dissipation are considered. The study involves analysis of experimental data from the Freja, Polar and Cluster spacecraft, as well as theoretical development. An overview of the linear theory of Alfvén waves is presented, including the effects of fnite parallel electron inertia and fnite ion gyroradius, and nonlinear theory is developed for large amplitude Alfvén solitons and structures. The methodology is presented for experimental identification of dispersive Alfvén waves in a frame moving with respect to the plasma, which facilitates the resolution of the space-time ambiguity in such measurements. Dispersive Alfvén waves are identified on field lines from the topside ionosphere up to the magnetopause and it is suggested they play an important role in magnetospheric physics. One of the processes where Alfvén waves are important is the establishment of the field aligned current system, which transports the energy from the reconnection regions at the magnetopause to the ionosphere, where a part of the energy is dissipated. The main mechanism for the dissipation in the top-side ionosphere is related to wave-particle interactions leading to particle energization/heating. An observed signature of such a process is the presence of parallel energetic electron bursts associated with dispersive Alfvén waves. The accelerated electrons (electron beams) are unstable with respect to the generation of high frequency plasma wave modes. Therefore this thesis also demonstrates an indirect coupling between low frequency Alfvén wave and high frequency oscillations.

L'interaction entre le vent solaire (VS) et la magnétosphère (MSP) terrestre se fait par l'intermédiaire de la magnétopause (MP). Le VS éjecté du Soleil, voyage transportant avec lui le champ magnétique interplanétaire (CMI). Ce dernier interagit avec le champ géomagnétique provoquant le phénomène de reconnexion magnétique (RM). La RM permet l'entrée d'une grande quantité de particules du VS dans la MSP. Si le CMI est dirigé vers le nord, la RM peut avoir lieu à haute latitude, mais n'est pas assez efficace pour justifier la quantité de plasma typique du VS, observée par les satellites à l'intérieur de la MSP. En outre, dans les cas où le CMI est dirigé vers le nord, la formation d'une couche de mélange est observée à basse latitude. Les tourbillons de Kelvin-Hemholtz (KH) fournissent un mécanisme efficace pour la formation d'une couche de mélange à la MP. Les simulations numériques montrent que l'évolution temporelle de l'instabilité de KH dépend fortement des profils initiales à grande échelle. La comparaison des données spatiales et des simulations numériques est donc d'une importance fondamentale dans ce contexte. Les principaux résultats obtenus au cours de ce travail sont la caractérisation de la turbulence à l'intérieur des tourbillons de KH, ainsi que des événements de RM à petite échelle; la sélection d'un événement où nous avons une combinaison des données des satellites avant et après KHI se développe; l'observation d'un décalage entre les profils de densité et de vitesse et constat que ce décalage initial entraîne une évolution différente de la simulations numériques qui est en accord avec les observations satellites. / Solar Wind (SW) and the Earth's magnetosphere interaction is mediated by the magnetopause. The SW carries with it the Interplanetary Magnetic Field (IMF) which interacts with northwards geomagnetic field lines causing magnetic reconnection (MR) events that make SW particles to be tranferred into the Earth's magnetosphere. If the IMF is directed northward, MR takes place at high latitude, but it is not efficient enough to justify the amount of SW plasma observed by satellites inside the magnetosphere. During northwards conditions one observe the formation of a wide boundary layer (BL) at the low latitude. This BL is thought to be driven by the the Kelvin-Helmholtz instability (KHI) , originating from the velocity shear between SW and the almost static near-Earth plasma. Numerical simulations (NS) have shown that the long time evolution of the KHI depends strongly on the initial large scale field profiles used as initial conditions. In order to make a further step towards the comprehension of this complex system, it is imperative to combine satellite data and NS. The idea here is to initialize NS by using in-situ observations of the main field profiles since only a correct initialization can reproduce the correct dynamics. The main results achieved in this work are: characterize the turbulence inside KH vortices and the small scale MR; select one event where there is a combination of a satellite measurements before and after KH develops, find that density and velocity profiles are shifted by a distance comparable to their shear lengths and that this initial shift cause a different evolution of the KHI leading to a final state in agreement with satellites observations.

When the solar wind encounters a planet’s magnetic field, they interact and the different plasma and magnetic field behaviours divides the magnetosphere into different regions. Two important region boundaries to the outer magnetosphere, called the magnetosheath, are the bow shock and magnetopause. A good deal of knowledge about the planet’s magnetic field can be obtained by studing these boundaries. Moreover, the strength of Jupiter’s magnetic field makes its magnetosheath boundaries an interesting case study. The aim of this study was to compile data covering the crossings of the Jovian bow shock and magnetopause from NASA’s Juno probe and use this data to investigate their shape and location. In doing so, we hoped to be able to assess the validity of previous models and the stability of Jupiter’s magnetic field over time. Both a parabolic curve model and a location distribution function were created as part of this objective. The distribution of boundary crossings prevented fine details in the shape and location of the bow shock and magnetopause from being determined. By analysing the density of occurring boundary crossings it was found that the bow shock and magnetopause are generally positioned closer to Jupiter than determined by previous studies. / Nar solvinden färdas nära en planet växelverkar de. Detta ger upphov till magnetosfären som består av olika områden med varierande plasmabeteenden. Två viktiga gränser till magnetosfärens yttre del, kallad magnetosheath, är bogchocken och magnetopausen. De är intressanta då man vid undersökning kan lära sig mycket om planets magnetfält överlag. Dessutom utgör gränserna av Jupiters magnetosheath en intressant fallstudie på grund av planetens starka magnetfält. Målet med denna studie var att sammanställa data över korsningar av Jupiters bogchock och magnetopause av NASA:s rymdsond Juno for att undersöka deras form och position. Med detta hoppades vi på att kunna bedöma validiteten hos tidigare modeller och bedöma stabiliteten av Jupiters magnetfält över tid. Både en parabolisk modellkurva och en fördelningsfunktion över gränsernas position skapades som en del av detta mål. Fördelningen av gränskorsningar förhindrade bestämmandet av mindre detaljer av form och position hos bogchocken och magnetopausen. Genom att analysera tätheten av förekommande korsningar upptäcktes det att bogchocken och magnetopausen befinner sig i allmänhet närmare Jupiter än vad som bestämts i tidigare studier / Kandidatexjobb i elektroteknik 2022, KTH, Stockholm

viii Title: Dynamics of the bow shock and magnetopause Author: Karel Jelínek Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Zdeněk Němeček, DrSc. Department of Surface and Plasma Science e-mail address: zdenek.nemecek@mff.cuni.cz Abstract: The interplanetary space is a unique laboratory which allows us to dis- cover (i) a behavior of the plasma under different conditions, (ii) origin of its insta- bilities, and (iii) its interaction with obstacles such as the Earth's magnetosphere. The present thesis analyzes the outer Earth's magnetosphere. The results are based on the in situ sensing by a variety of the spacecraft (e.g., IMP-8, INTERBALL-1, MAGION-4, Geotail, Cluster-II and Themis). The solar wind curently monitored by the WIND and ACE spacecraft near the La- grange point L1 affects by its dynamic pressure the Earth's magnetic field which acts as a counter-pressure and the boundary where these pressures are balanced is the magnetopause. Due to supersonic solar wind speed, the bow shock forms in front of the magnetopause and a region in between, where plasma flows around an obstacle is named the magnetosheath. The thesis contributes to a deaper understanding of the dependence of magnetopause and bow shock shapes and positions, especially, (1) on the orientation of the inter-...

<p>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.</p><p>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.</p><p>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.</p>

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.

Une nouvelle approche, en utilisant un 3D code électromagnétique (PIC), est présentée pour étudier la sensibilité de la magnétosphère de la terre à la variabilité du vent solaire. Commençant par un vent solaire empiétant sur une terre magnétisée, le temps a été laissé au système ainsi une structure d'état d'équilibre de la magnétosphère a été atteinte. Une perturbation impulsive a été appliquée au système par changeant la vitesse du vent solaire pour simuler une dépression en sa pression dynamique, pour zéro, au sud et du nord du champ magnétique interplanétaire(IMF). La perturbation appliquée, un effet de trou d'air qui pourrait être décrit comme espace ~15Re est formé pour tous les cas d'état de IMF. Dès que le trou d'air a frappé le choc d'arc initial de la magnétosphère régulière, une reconnexion entre le champ magnétique de la terre et le IMF sud a été notée à la coté jour magnétopause(MP). Pendant la phase d'expansion du système, la frontière externe de la coté jour du MP a enfoncé quand IMF=0, et pourtant elle sa forme de balle quand un IMF au sud et nordique étaient inclus. La relaxation de temps du MP pour les trois cas de IMF a été étudiée. Le code est alors appliqué pour étudier l'événement d'Halloween de l'octobre 2003. Notre simulation a produit un nouveau genre de trou d'air, un espace raréfié qui a été produit après un gradient fort en IMF d'empiétement. Un tel dispositif est tout à fait semblable aux anomalies chaudes observées d'écoulement et peut avoir la même origine