The Rosetta spacecraft orbited around comet 67P/Churyumov-Gerasimenko from 2014 to 2016. During this time, several thousands of cometary jets occurred and were photographed by the onboard cameras. Since the spacecraft slowly orbited around the comet nucleus and assuming an angular spread of 20º for the jets, it can be assumed that sometimes Rosetta flew through some of them. The dust particles ejected from the jet travel radially outward virtually unaffected by gravity, but as the jet is ongoing for several hours and as the comet nucleus rotates, the dust trace forms a spiral-like trajectory shape in space. Tracking the spacecraft's position around the times the jets were photographed, and checking whether it was within the dust cone, we found that Rosetta travelled across 181 out of the 3946 listed jets. Then, we looked into the plasma density and spacecraft potential data for every jet, finding some interesting events that could give rise to a further study into plasma interactions between jets and surrounding plasma in the cometary coma.

Earth-space traversing electromagnetic waves become attenuated as they propagate through the atmosphere. The sources of attenuation are weather phenomena in the Troposphere, and scintillation and absorption in the Ionosphere. On behalf of Arctic Space Technologies AB, an empirical model based on data from the last decade was built in Python, in order to estimate the level of attenuation and provide a better picture of the frequency environment at the site in Piteå. By utilizing recommendations from the International Telecommunication Union Radiocommunication Sector, and constraining the project to only consider the case where the satellite is at an 5° apparent elevation in Piteå, and a range of weather phenomena a nuanced picture can be obtained. It was found that the attenuation from the Ionosphere in typical satellite frequency bands is not of significance, and therefore only the Tropospheric sources were considered. The results showed that the S-band is the most reliable band to utilize, since little to no changes were observed for a range of weather scenarios. For the X-band, larger changes in the level of attenuation were observed for higher levels of precipitation, yet not as severe as for the Ku- and Ka- bands. However, for the Ku- and Ka-bands, large fluctuations in the attenuation were observed for different cases. In conclusion, the attenuation at Arctic space's site in Piteå for the S- and X-bands are the lowest and least effected by changes in weather. On the other hand, the Ku- and Ka-bands should be used predominantly under good weather circumstances.

High speed plasma flows (jets) are ubiquitous phenomena in the universe. For example, they carry energy from the most powerful sources (e.g active galactic nucleï AGN) to the medium at rest surrounding them. When the plasma at rest encounters the front of the fast flow, it gains energy via conversion from magnetic field energy to particle heating and acceleration. High speed plasma flows are also common in planetary magnetospheres including the Earth's magnetotail. In particular the fast Earthward magnetic reconnection outflows in the Earth's magnetotail provide a laboratory to address some of the open questions related to plasma jet fronts and the associated energy conversion. In this thesis, we use the four Magnetospheric Multiscale (MMS) spacecraft to investigate current sheet flapping, particle heating and particle acceleration associated with the fast magnetotail flows. In paper I, we investigate a short-period kink-like flapping motion of an ion scale current sheet in the wake of a plasma jet front. We show that the kink-like motion propagates along the current direction toward the flank of the magnetosphere, and that the prediction of the wavelength of the drift-kink instability of a thin current sheet agrees with our estimation of the wavelength of the observed kink-like current sheet. In paper II, we investigate particle acceleration at turbulent Earthward jet fronts during a moderately active substorm. We show that a proton with a gyroradius smaller than the scale of the Earthward convected structures gain energy from the bulk flow. On the other hand, we show that, depending on the time scale of the electromagnetic fluctuations with respect to the proton scale, protons with larger gyroradius get accelerated via resonant interaction with the jet front or via direct acceleration by the dawn-dusk electric field in a spatially limited electric field pulse.

Collisionless shocks are one of the most peculiar phenomena in space where non-linear collective phenomena in the plasma dominate the dynamics. They are believed to be one of the most efficient particle accelerators in the universe, and have internal dynamics that are yet to be fully explored. In this project we aim to understand the interplay between the electrostatic turbulence in the shock ramp and the electron dynamics leading to thermalization across the shock. To do so we first use a machine learning technique to compile a database of shocks crossings observed by magnetospheric multiscale (MMS), which will facilitate both case studies and statistical studies of shocks using MMS. The database contains 2803 shock crossings spanning a period from October 2015 to December 2020. For each crossing we provide key parameters necessary for understanding shock dynamics such as Alfv\'nic Mach number and the angle  between the upstream magnetic field and the vector normal to the shock $\theta_$. We then study whistler waves upstream of 11 quasiperpendicular supercritical shocks. We first apply four spacecraft timing method to magnetic field data from MMS to properly characterize the observed whistler waves. We determine their frequency in the plasma rest frame to range from 0.3 to 1.2 the lower hybrid frequency,their wavelength to range from 0.7 to 1.7 ion inertial length and $\theta_$ to range between $20^\circ$ and $42^\circ$. We then use particle data provided by MMS to show that a reflected beam component in the ion velocity distribution function is in resonance with the observed waves indicating that a kinetic cross field streaming instability (KCFSI) is behind the generation of such waves. Finally a kinetic solver is used to model to observed distribution and reinforce the previous conclusion that the KCFSI is behind the generation of the observed whistlers. We end this thesis by discussing the ongoing projects pertaining to the interaction of electrostatic wave mode determination in the shock ramp and the correlation between whistler waves and electrostatic waves around quasi-perpendicular shocks.

The results of past studies indicate that there is an influence of the presence of a nonzero dusk-dawn i.e. y component of the interplanetary magnetic field(IMF By) on the near-Earth magnetotail. Specifically, on the dusk-dawn component (By) of the magnetic field and plasma ion convection, resulting in interhemispheric asymmetries. This project aimed to investigate whether the same is true for mid-tail distances (around 60 RE downtail, at around the moon distance) by investigating data from the ARTEMIS P1 satellite and the OMNI IMF database. This was done by first filtering the data to only include plasma sheet data using criteria on ion temperature and density, and then constructing averages of both tail By and the ion velocity perpendicular to the magnetic field. These average were constructed separately for clearly positive IMF By (> 3 nT) and clearly negative IMF By (< -3 nT), and separately for the northern and southern plasma sheet. It was found that there is a clear effect of the sign of IMF By on both tail By and ion flows, leading to asymmetries similar to those reported at near-Earth distances. Thus it can be concluded that the presence of clearly nonzero IMF By affects the mid-tail region as well, and potentially the entire magnetotail. While these results are consistent with near-Earth studies, this is the first time the asymmetries due to nonzero IMF By are reported in the mid-tail.

Data fusion is the methodology of efficiently combining the relevant information from different sources. The goal is to achieve estimates and inferences with better confidence than those achievable by relying on a single source. Initial data fusion applications were predominantly in defense: target tracking, threat assessment and land mine detection. Nowadays, data fusion is applied to robotics (e.g., environment identification for navigation), medicine (e.g., medical diagnosis), geoscience (e.g., data integration from different sources) and industrial engineering (e.g., fault detection). This thesis focuses on data fusion for distributed multisensor tracking systems. In these systems, each sensor can provide the information as measurements or local estimates, i.e., tracks. The purpose of this thesis is to advance the research in the fusion of local estimates for multisensor multitarget tracking systems, namely, track fusion. This study also proposes new methods for track-to-track association, which is an implicit subproblem of track fusion. The first contribution is for the case where local sensors perform tracking using particle filters (Monte Carlo based methods). A method of associating tracks estimated through labeled particle clouds is developed and demonstrated with subsequent fusion. The cloud-to-cloud association cost is devised together with computation methods for the general and specialized cases. The cost introduced is proved to converge (with increasing clouds cardinality) toward the corresponding distance between the underlying distributions. In order to simulate the method introduced, a particle filter labeled at particle level was developed, based on the Probability Hypothesis Density (PHD) particle filter. The second contribution is for the case where local sensors produce tracks using Kalman filter-type estimators, in the form of track state estimate and track state covariance matrix. For this case the association and fusion is improved in both terms of accuracy and identity, by introducing at each fusion time the prior information (both estimate and identity) from the previous fusion time. The third contribution is for the case where local sensors produce track estimates under the form of MHT, therefore where each local sensor produces several hypotheses of estimates. A method to use the information from other sensors in propagating each sensor's internal hypotheses over time is developed. A practical fusion method for real world local tracking sensors, i.e., asynchronous and with incomplete information available, is also developed in this thesis. / Thesis / Doctor of Philosophy (PhD)

Plasma physics emerged in the early 20th century and became a focal point for research after the Second World War due to the potential uses of nuclear fusion.The reasons for this varied from the creation of hydrogen bombs to fusion for energy production. Moreover, with recent developments in semiconductors and nanoscale objects, where quantum effects are non-negligible, a theory of quantum plasma wasrequired. Plasmas can be split into two main regimes, Classical and Quantum, each requiring a separate theory. In this thesis, we introduce the kinetic theory of plasmas. We study the two regimes separately and obtain a description of the plasmas in terms of a phase-space distribution function; a distribution 𝑓 in the classical case, and the quantum analogue in the Wigner function 𝑊. These are governed by the classical Vlasov equation and the quantum analogue in the Wigner equation. The introduction of the Wigner function in Wigner’s article [5] in 1932, made it easier to connect the two theories since theyboth reside within the phase space. To show that the quantum theory is equivalent to the classical theory with the addition of quantum effects, we used perturbation theory, with a perturbation in the form of an electrostatic linear wave. This results in two dispersion relations, one for each regime. These are equal except for a single term, which can be interpreted as quantum effects. This confirms that the two theories are equivalent in the classical limit. Moreover, we introduce the density matrix, a way to describe systems with statistical mixtures of quantum states. This enables us to derive the set of equations known as the BBGKY-hierarchy. In turn, this hierarchy allows us to reduce the number of particles we need to consider, something that comes in handy when dealing with many-particle systems, which otherwise can be close to impossible.

The Earth’s magnetosheath is a space plasma region consisting of solar wind plasma which is heated and compressed due to interaction with the Earth’s magnetic field. This turbulent region contains coherent structures and various plasma waves which affect the particle dynamics and collisionless energy transfer. In this licentiate thesis, we investigate such processes and where they occur. Through in-situ measurements from NASA’s Magnetospheric Multiscale (MMS) mission, we study whistler waves – electromagnetic, right-hand polarized waves known to heat electrons – and how they interact with electrons. We show how whistler waves are generated by electrons in the turbulent magnetosheath. We also investigate which plasma conditions are favorable for whistler waves to form.

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