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Turbulence at MHD and sub-ion scales in the magnetosheath of Saturn: a comparative study between quasi-perpendicular and quasi-parallel bow shocks using in-situ Cassini data
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
2018 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

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.

Abstract [sv]

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.

Place, publisher, year, edition, pages
2018. , p. 38
Series
FYSAST ; FYSKAND1080
Keywords [en]
Saturn, magnetosheath, bow shock, turbulence, Cassini
Keywords [sv]
Saturnus, magnetoskikt, bogchock, turbulens, Cassini
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-354775OAI: oai:DiVA.org:uu-354775DiVA, id: diva2:1222629
Educational program
Bachelor Programme in Physics
Supervisors
Examiners
Available from: 2018-07-02 Created: 2018-06-21 Last updated: 2018-07-02Bibliographically approved

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Department of Physics and AstronomySwedish Institute of Space Physics, Uppsala Division
Fusion, Plasma and Space Physics

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