We use particle and magnetic field data from the Ion and Neutral Camera (INCA) and the magnetometer (MAG) onboard Cassini to detect and examine an energetic particle event that occurred upstream from the Saturnian bow shock during DOY 229/2007. The energetic (>100 keV) O+ ions are observed only when the Interplanetary Magnetic Field (IMF) connects the spacecraft with the planetary bow shock. We provide strong evidence showing the magnetospheric origin of the observed ions: (1) We detect singly ionized oxygen (O+) which is not resident of the solar wind, (2) the particle pitch angle distribution indicates that the ions travel along the field line connecting the spacecraft to the bow shock and (3) the ion intensity increases are observed only during the periods of magnetic connection to the bow shock. Our results show that the Saturnian dayside magnetosphere is not as sealed as thought to be, but can -under certain circumstances- allow high energy magnetospheric plasma to leak into the nearby solar wind and further in space.

As the solar wind reaches Mercury it interacts with the planet’s magnetic field slowing down, forming a bow shock in front of the planet and diverting the flow around it. Along with the solar wind comes the interplanetary magnetic field, an extension of the sun’s magnetic field. The interaction between the bow shock and the interplanetary magnetic field impacts the behaviour of the plasma both up- and downstream of the bow shock. An important factor is the angle between the normal to the bow shock surface and the interplanetary magnetic field, θBN. The angle can be divided into two categories: quasi-parallel for when θBN < 45° and quasi-perpendicular for θBN > 45°. It is expected for a quasi-parallel configuration to have stronger fluctuations in both the solar wind upstream of the bow shock and in the magnetosheath downstream caused by reflected particles backstreaming into the solar wind. Quasi-perpendicular configurations are expected to have less fluctuations in both regions due to fewer solar wind particles being reflected back. In this thesis this connection is investigated at the bow shock at Mercury using magnetic field data from the MESSENGER mission. By looking at the data when the spacecraft travels through the thin bow shock the local θBN angle can be calculated. The fluctuation level is then calculated as the standard deviation of the magnetic field in a 30 second period upstream and downstream of the crossing. The results found are unexpected as the correlation between θBN and the fluctuation levels are weaker and more uniformly distributed than expected compared to similar studies conducted at Earth using the Cluster satellites. This is most likely due to the smaller spatial scale of the Hermean system: the structures perpendicular to the interplanetary magnetic field of upstream activity, such as SLAMS, cover a greater proportion of the bow shock than at Earth allowing them to extend over into neighbouring regions of different θBN values, giving a more uniform distribution of the fluctuation levels. / När solvinden når Merkurius växelverkar den med planetens magnetfält och solvinden saktas ned och avledes till att flöda kring planeten. Då solvinden decelereras formas en chock framför planeten, bogchocken. Tillsammans med solvinden kommer det interplanetära magnetfältet, som är en förlängning av solens magnetfält. Växelverkan mellan bogchocken och det interplanetära magnetfältet påverkar plasmat både upp- och nedströms från bogchocken. En viktigt faktor är vinkeln mellan normalen till bogchocken och det interplanetära magnetfältet, θBN . Bogchocken kan delas in i två kategorier: kvasi-parallell då θBN < 45° och kvasi-vinkelrät då θBN > 45°. Vid kvasi-parallella förhållanden förväntas starkare fluktuationer i magnetfältet både uppströms i solvinden och nedströms i magnetskiktet, orsakat av reflekterade partiklar som färdas in i den inkommande solvinden. Kvasi-vinkelräta förhållanden förväntas ha mindre fluktuationer då färre partiklar reflekteras. I den här uppsatsen undersöks kopplingen vid Merkurius bogchock med data från rymdsonden MESSENGER. Genom att använda data då rymdsonden färdas igenom den tunna bogchocken kan det lokala värdet på θBN uträknas. Fluktuationsnivåerna räknas ut som standardavvikelsen av magnetfältet under en 30 sekundersperiod uppströms och nedströms från korsningen. Resultaten är ej som förväntade då kopplingen mellan θBN och fluktuationsnivån är mycket svagare och jämnt fördelade än förväntat, baserat på resultat från jorden från Cluster-satelliterna. Den mest troliga förklaringen är att Merkurius och dess bogchock är mindre än jordens: de strukturerna som är vinkelräta till det interplanetära magnetfältet hos uppströmsfenomen, t.ex SLAMS, täcker då en större proportion av bogchocken än vid jorden vilket tillåter dem att sträcka sig in i närliggande regioner med annorlunda θBN värden, vilket ger en mer jämn utbredning av fluktuationsnivåerna.

Since Venus is an unmagnetized planet, it doesn’t interact with the solar wind in the same way as planets with an intrinsic magnetic field do. Due to its conductive ionosphere, however, it still possesses an induced magnetosphere. Venus’s magnetosphere contains different boundaries, identified by changes in the plasma or magnetic field characteristics. The boundaries we studied in this project are the bow shock and the Ion Composition Boundary (ICB). Previous studies identified the boundaries’ locations and compared them with plasma measurements outside of the magnetosphere, finding how the boundaries react to varying solar wind upstream conditions. What has been more rarely done, instead, is to find the analytical dependency of the bow shock and ICB on the upstream conditions. This was the purpose of this project. Developing this comprehensive analytical model allows us to determine the location of the boundaries, once the upstream conditions are defined. We used a database of boundary crossings and upstream conditions measurements deriving from the Venus EXpress (VEX). The procedure we followed was first to divide the boundaries crossings into bins, analyzing one upstream condition at a time. Then, we fitted the crossings using analytical equations depending on geometrical parameters. For the bow shock we used a conic section with semi-latus rectum L and eccentricity ε as geometrical parameters, for the dayside ICB we used a circumference with the radius R as geometrical parameter. We fitted these geometrical parameters with the upstream conditions in each bin and found the final model. The final equation for the bow shock depends on the Interplanetary Magnetic Field (IMF) magnitude, the solar wind mass flux, and the angle between the IMF direction and the local shock normal. For the ICB the final equation depends on the solar wind energy flux and the solar Extreme UltraViolet (EUV) flux. Given these solar wind and IMF properties, the geometrical parameters of the boundaries are uniquely identified. Then, we were able to determine the boundaries’ locations and shapes with higher accuracy than the general fitting models that don’t consider upstream conditions. For the bow shock we improved the accuracy by 17%, for the ICB by 8%. / Eftersom Venus är en omagnetisk planet växelverkar den inte med solvinden på samma sätt som planeter med ett inneboende magnetfält. På grund av sin ledande jonosfär har den dock fortfarande en inducerad magnetosfär. Venus magnetosfär innehåller olika gränser, identifierade av förändringar i plasma- eller magnetfältets egenskaper. Gränserna vi studerade i det här projektet är bogshocken och Ion Composition Boundary (ICB). Tidigare studier identifierade gränsernas lägen och jämförde dem med plasmamätningar utanför magnetosfären, och hittade hur gränserna ändras med varierande solvind uppströms. Vad som har gjorts mer sällan är att hitta det analytiska beroendet av bogchocken och ICB på uppströmsförhållandena. Det var syftet med det här projektet. Genom att utveckla de här analytiska modellerna kan vi bestämma placering för gränserna när uppströmsförhållandena har definierats. Vi använde en databas med gränsövergångar och mätningar av uppströmsförhållanden härrörande från Venus EXpress (VEX). Proceduren vi följde var först att dela upp gränsövergångarna i dataintervall och analysera ett uppströmsläge i taget. Sedan anpassade korsningarna med hjälp av analytiska ekvationer beroende på geometriska parametrar. För bogshocken använde vi en konisk sektion med semi-latus rektum L och excentricitet ε som geometriska parametrar, för dagsida ICB använde vi en omkrets med radien R som geometrisk parameter. Vi anpassade de här geometriska parametrarna för olika uppströmsförhållanden och tog fram en modell. Den slutliga ekvationen för bogshocken beror på det interplanetära magnetfältets (IMF) magnitud, solvindens rörelsemängd och vinkeln mellan IMF och den lokala shocknormalen. För ICB beror den slutliga ekvationen på solvindenergiflödet och extrem ultraviolett (EUV) flöde. Med avseende på de här solvinds- och IMF-egenskaperna är de geometriska parametrarna för gränserna identifierade. Sedan kunde vi bestämma gränsernas placeringar och former med högre noggrannhet än de allmänna modellerna som inte tar hänsyn till uppströmsförhållanden. För bogchocken förbättrade vi noggrannheten med 17% och för ICB med 8%.

A comprehensive understanding of high-speed liquid jets is required for their introduction into engine and combustion applications. Their transient nature, short lifetime, unique characteristics and the inability to take many experimental readings, has inhibited this need. This study investigates the outflow of a high-speed liquid jet into quiescent atmospheric air. The key characteristics present are, a bow shock wave preceding the jet head, an enhanced mixing layer and the transient deformation of the liquid jet core. The outflow regime is studied in an experimental and numerical manner. In the experimental investigation, a high-speed liquid water jet is generated using the momentum exchange by impact method. The jet velocity is supersonic with respect to the impinged gaseous medium. The resulting jet speed is Mach 1.8. The jet is visualised with the use of shadowgraph apparatus. Visualisation takes place over a variety of time steps in the liquid jet???s life span and illustrates the four major development stages. The stages progress from initial rapid core jet expansion to jet stabilisation and characteristic uniform gradient formation. The visualisation shows that at all stages of the jet???s life it is axi-symmetric. One dimensional nozzle analysis and a clean bow shock wave indicate that the pulsing jet phenomenon can be ignored. In the numerical investigation, a time marching finite volume scheme is employed. The bow shock wave characteristics are studied with the use of a blunt body analogy. The jet at a specific time frame is considered a solid body. The jet shape is found to have an important influence on the shock position and shape. Analysis of the results indicates a shock stand-off similar to that seen in experimental observations and the prediction of shock data. The jet life span is modelled using a species dependent density model. The transient calculations reproduce the key jet shape characteristics shown in experimental visualisation. The mushrooming effect and large mixing layer are shown to develop. These effects are strongest when the shock wave transience has yet to stabilise. Quantitative analysis of the mixing layer at varying time steps is presented.

A comprehensive understanding of high-speed liquid jets is required for their introduction into engine and combustion applications. Their transient nature, short lifetime, unique characteristics and the inability to take many experimental readings, has inhibited this need. This study investigates the outflow of a high-speed liquid jet into quiescent atmospheric air. The key characteristics present are, a bow shock wave preceding the jet head, an enhanced mixing layer and the transient deformation of the liquid jet core. The outflow regime is studied in an experimental and numerical manner. In the experimental investigation, a high-speed liquid water jet is generated using the momentum exchange by impact method. The jet velocity is supersonic with respect to the impinged gaseous medium. The resulting jet speed is Mach 1.8. The jet is visualised with the use of shadowgraph apparatus. Visualisation takes place over a variety of time steps in the liquid jet???s life span and illustrates the four major development stages. The stages progress from initial rapid core jet expansion to jet stabilisation and characteristic uniform gradient formation. The visualisation shows that at all stages of the jet???s life it is axi-symmetric. One dimensional nozzle analysis and a clean bow shock wave indicate that the pulsing jet phenomenon can be ignored. In the numerical investigation, a time marching finite volume scheme is employed. The bow shock wave characteristics are studied with the use of a blunt body analogy. The jet at a specific time frame is considered a solid body. The jet shape is found to have an important influence on the shock position and shape. Analysis of the results indicates a shock stand-off similar to that seen in experimental observations and the prediction of shock data. The jet life span is modelled using a species dependent density model. The transient calculations reproduce the key jet shape characteristics shown in experimental visualisation. The mushrooming effect and large mixing layer are shown to develop. These effects are strongest when the shock wave transience has yet to stabilise. Quantitative analysis of the mixing layer at varying time steps is presented.

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

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

Electrons accelerating in shock events occur oftenin outer space, for example in supernovas and the poles of blackholes, and are of high interest to physicists and other researchers.The technology to take a closer look at events that far awaydoes not exist yet, but luckily we can observe similar events inplaces where the Earth’s magnetic fields and particle streamsfrom the Sun meet. Using data from NASA’s MMS mission thispaper aims to gather information about what variables affect theacceleration, under what conditions the most energetic eventsoccur and create a ranked list of several hundreds of theseevents. It did this by calculating the expected value of the electrondistribution function at different times to create a dimensionlessranking. The study showed that these events are highly complexand that it is difficult to assign a few variables which would affectthe acceleration. However it also showed that most accelerationoccurs after the most abrupt shock crossing and not exactly atthe location where the expected value is maximal, and that thereare some correlations with angle relative to the solar magneticfield and electron number density. / Elektroner som accelereras i shockar skerofta i yttre rymden, till exmepel i supernovor och vid polernahos svarta hål, och är därför av högt intresse hos fysikeroch andra forskare. Teknologin för att titta närmre på dessafjärran fenomen existerar inte ännu, men som tur är så kan viobservera liknande händelser på platser där Jordens magnetfältmöter partikelvindar från Solen. Med hjälp av data från NASAsMMS uppdrag har detta projekt önskat att samla informationom vilka variabler som påverkar accelerationen, under vilkaomständigheter de mest energirika händelserna sker och skapa enrankad lista av flera hundra av dessa händelser. Det gjorde dettagenom att beräkna det förväntade värdet på elektronernas distributionsfunktionvid flera tillfällen för att skapa en dimensionslösrank. Studien visade att dessa händelser är mycket komplexaoch att det är svårt att tilldela ett fåtal variabler som skullepåverka accelerationen. Dock så visade projektet att den störstaaccelerationen sker efter den mest abrubta shockkorsningen ochinte exakt vid det tillfälle då det förväntansvärdet är som högst,och att det finns någon korrelation med vinkeln relativt solensmagnetfält och elektronernas nummerdensitet. / Kandidatexjobb i elektroteknik 2021, KTH, Stockholm

A stator cascade was developed to simulate the flow conditions within a close-stage-spacing transonic axial compressor. Experiments were conducted in a linear transonic blowdown cascade wind tunnel with an inlet Mach number of 0.65. The bow shock from the downstream rotor was simulated by a single moving normal shock generated with a shock tube. First, steady pressure data were gathered to ensure that the stator cascade operated properly without the presence of the shock. Next, the effects of the passing shock on the stator flow field were investigated using shadowgraph photography and Digital Particle Image Velocimetry (DPIV). Measurements were taken for three different shock strengths. In every case studied, a vortex formed near the stator trailing edge as the shock impacted the blade. The size of this vortex was shown to be directly related to the shock strength, and the vortex remained present in the trailing edge flow field throughout the cycle duration. Analysis of the DPIV data showed that the vortex acts as a flow blockage, with the extent of this blockage ranging from 2.9% of the passage for the weakest shock, to 14.3% of the passage for the strongest shock. The vortex was also shown to cause flow deviation up to 75° for the case with the strongest shock. Further analysis estimated that the total pressure losses due to shock-induced vorticity ranged from 46% to 113% of the steady wake losses. Finally, the total pressure loss purely due to the upstream-propagating normal shock was estimated to be roughly 0.22%. / Master of Science

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-...