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-...

The purpose of this project is to investigate the spectral properties of turbulence in the magnetosheath of Saturn, using in-situ magnetic field measurements from the Cassini spacecraft. According to models of incompressible, turbulent fluids, the energy spectrum in the inertial range scales as the frequency to the power of -5/3, which has been observed in the near-Earth Solar wind but not in the Terrestrial magnetosheath unless close to the magnetopause. 120 time intervals for when Cassini is inside the magnetosheath are identified — 40 in each category of behind quasi-perpendicular bow shocks, behind quasi-parallel bow shocks, and inside the middle of the magnetosheath. The power spectral density is thereafter calculated for each interval, with logarithmic regressions performed at the MHD and sub-ion scales separated by the ion gyrofrequency. The results seem to indicate similar behaviour as in the magnetosheath of Earth, without significant difference between quasi-perpendicular and quasi-parallel cases except somewhat steeper exponents at the MHD scale for the former. These observations confirm the role of the bow shock in destroying the fully developed turbulence of the Solar wind, thus explaining the absence of the inertial range. / Syftet med detta projekt är att undersöka de spektrala egenskaperna hos turbulens i Saturnus magnetoskikt, med in-situ-mätningar av magnetfältet från Cassini-rymdsonden. Enligt modeller av inkompressibla, turbulenta fluider, är energispektrumet i det intertiala omfånget proportionellt mot frekvensen upphöjd i -5/3, vilket har observerats i den jordnära Solvinden men inte i det jordiska magnetoskiktet förutom nära magnetopausen. 120 tidsintervall för när Cassini befinner sig inuti magnetoskiktet identifieras — 40 styck i kategorierna bakom kvasi-vinkelräta bogchockar, bakom kvasi-parallella bogchockar, och inuti mellersta delen av magnetoskiktet. Effektspektraltätheten beräknas därefter för varje intervall, med logaritmiska regressioner på MHD- och subjon-skalorna som separeras av jongyrofrekvensen. Resultaten verkar tyda på liknande beteende som i Jordens magnetoskikt, utan märkvärdig skillnad mellan kvasi-vinkelräta och kvasi-parallella fall förutom något brantare exponenter på MHD-skalan för de förnämnda. Dessa observationer bekräftar bogchokens roll i förstörandet av den fullt utvecklade turbulensen i Solvinden, därmed förklarande avsaknaden av det inertiala omfånget.

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.

Title: Evolution of Interplanetary Coronal Mass Ejections Author: Andrii Lynnyk Department: Department of Surface and Plasma Science Supervisor: RNDr. Marek Vandas, DrSc. e-mail address: vandas@ig.cas.cz Abstract: This thesis deals with deformation of the Interplanetary Coronal Mass Ejections (ICMEs) and their sub-class Magnetic Clouds (MCs) during their propagation in the Solar Wind (SW). The statistical study of the expanded MCs has shown that expansion greatly affects the MC internal magnetic field. We had shown that this influence is more clear for the MCs observed close to their axes. The study of the stand-off shock distance in front of the supersonic ICME confirms a smooth deformation of the ICMEs along their path from the Sun into interplanetary space. We observed that this deformation is increasing with the velocity of the ICME. This study also confirmed the difference in sheaths that are created in front of expanding and non-expanding ICMEs. We found that velocity distribution inside the MC is not uniform and it has large fluctuations. We found that the MC cross-section is usually strongly deformed. Keywords: interplanetary coronal mass ejection, magnetic cloud, magnetosheath, flux rope, magnetic field, shock, fitting

Title: Correlation properties of magnetosheath fluctuations Author: Olga Gutynska Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Jana Šafránková, DrSc. e-mail address: Jana.Safrankova@mff.cuni.cz Abstract: This thesis deals with fluctuations of the magnetic field (MF) and plasma density in different magnetosheath locations. The statistical study of the correlation length of these quantities has shown that these lengths are surprisingly low for both the ion flux and MF (approx. 1 RE). However, the correlation length increases with an increasing correlation between the magnetosheath and interplanetary magnetic fields (IMF). Further, we have found that the correlation length of MF fluctuations depends on the solar wind speed, on a correlation between IMF and magnetosheath MF fluctua- tions, and on the amplitude of fluctuations. The statistical study of radial profiles of cross-correlations between MF and plasma density at the subsolar and flank regions based on Cluster and THEMIS magnetosheath observa- tions revealed better correlations toward the magnetopause. A study of the modification of the IMF direction in the magnetosheath has shown that a reliable prediction of the magnetosheath BZ sign requires |IMF BZ| > 2 nT and that this prediction is more precise during solar minimum....

In July 2031, a new chapter in the exploration of the Jovian system will begin with the arrival of the Jupiter Icy Moons Explorer (Juice) at Jupiter. Launched on April 14 2024 as part of ESA’s Cosmic Vision programme, the mission aims to study Jupiter and its icy Galilean moons Callisto, Europa, and Ganymede. Juice carries a whole suite of instruments for in-situ and remote ground observations, one of which is the Jovian plasma Dynamics and Composition analyser (JDC). As a part of the Particle Environment Package (PEP), the particle detector will measure the energy, mass, charge and arrival direction of ions and electrons in the Jovian magnetosphere. Spacecraft charging caused by interactions between the spacecraft and its surrounding plasma environment poses a significant problem for JDC because the electrostatic potential of the spacecraft accelerates/decelerates charged particles, resulting in distorted measurements, particularly for the lowest energy particles.  In this report, we show the results of spacecraft charging and instrument simulations performed in the Spacecraft Plasma Interaction System (SPIS) for the solar wind and Earth’s magnetosheath—two environments that Juice will encounter at the start of the cruise phase. We found that the conductive surfaces that cover the majority of the spacecraft become positively charged as a result of a large photoelectron current in both the solar wind and magnetosheath environments. We show that these surfaces are expected to reach potentials of 9 V in the solar wind and 4 V in the magnetosheath. The four radiators on Juice that are covered with dielectric paint and shaded by the sun shield become negatively charged in both simulated environments. The radiator potentials can be as low as -40 V in the solar wind and -100 V in the magnetosheath. We also conclude that due to blocking by the spacecraft main body, the ion population cannot be sampled in the solar wind unless a spacecraft roll is performed. Furthermore, due to the high ion f low energy, spacecraft charging will not influence JDC measurements in this environment.  In the magnetosheath, the ion population can be sampled by JDC, and we identified three distortion mechanisms: (1) repulsion by the main body, (2) attraction by two of the radiators, and (3) repulsion by the MAG boom. Of all the distortion modes, the one originating from a negatively charged (-67.8 V) radiator close to JDC is the strongest, affecting ions with energies above 80 eV. The least powerful but most prevalent mode is the repulsion of ions by the main body. Our results can be compared with future in-situ measurements to identify distortion mechanisms well ahead of the science phase in which the scientifically important measurements will be carried out.