Graduation Semester and Year
Spring 2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Physics and Applied Physics
Department
Physics
First Advisor
Dr. Victoria D. Wilder
Second Advisor
Dr. Ramon E. Lopez
Third Advisor
Dr. Nevin N. Weinberg
Fourth Advisor
Dr. Yue Deng
Fifth Advisor
Dr. Zdzislaw E. Musielak
Abstract
Earth’s magnetosheath is a region of shocked plasma that mediates energy and momentum transfer from the solar wind to the magnetosphere. The dynamics and thus the plasma structures of this region are highly dependent on upstream solar wind conditions. As such, the region is often characterized as a turbulent environment, with the most intense periods of turbulence occurring often under quasi-parallel bow shock conditions. This magnetosheath turbulence displays as variable and large-scale fluctuations with in-situ measurements. Given that turbulence is a characteristic feature of the magnetosheath, this dissertation asks two questions: (1) How are plasma structures inside the sheath affected by turbulence? (2) How do plasma structures behave in a turbulent environment? Aspects of these questions were addressed with two studies conducted throughout this thesis project: (1) Using multiple years of observations from NASA’s Magnetospheric Multiscale (MMS) mission, we created statistical maps of electric current to test the hypothesis of magnetohydrodynamic (MHD) simulations of bow shock current closure across the magnetosheath. Under low (< 5) magnetosonic Mach number conditions, observations agreed with current closure predictions for northward and southward IMF orientations. However, under typical (5-7) magnetosonic Mach number conditions, all IMF orientations had a high degree of variability in the direction of current in the magnetosheath. This suggest that when the sheath is not magnetically dominated, the region is characterized by turbulence and filamented currents. (2) Secondly, we investigated the properties of whistler waves inside magnetic holes, dubbed “Lion Roars”, during a MMS traversal of the magnetosheath under quasi-parallel bow shock conditions. Unlike their counterparts under quasi-perpendicular bow shock conditions, we observed from a collection of Lion Roar events that: whistlers with high order harmonics were prevalent in the sheath; the magnetic holes for each Lion Roar event were shallow in depth; and that each event featured an electron beam moving near the electron Alfvén speed. Additionally, there were observational differences between the
nonharmonic and High Order Harmonic LR (HOHLR) events. The HOHLRs exhibited strong antiparallel Poynting flux and high counts of solitary wave activity surrounding their corresponding magnetic holes. The nonharmonic LRs observed a strong presence of solitary waves inside their magnetic hole, leading to a population of trapped electrons with a parallel/antiparallel temperature anisotropy, strong parallel electric field fluctuations, and an oblique Poynting flux with respect to the background magnetic field.
Keywords
bow shock, bow shock current closure, Earth's magnetosheath, lion roar, magnetic holes, quasi-parallel bow shock, harmonic whistlers
Disciplines
Atmospheric Sciences | Other Earth Sciences | Other Physical Sciences and Mathematics | Physical Processes | Plasma and Beam Physics
License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Salinas, Hector A., "Characterizing the Earth's Magnetosheath with In Situ Measurements" (2025). Physics Dissertations. 177.
https://mavmatrix.uta.edu/physics_dissertations/177
Included in
Atmospheric Sciences Commons, Other Earth Sciences Commons, Other Physical Sciences and Mathematics Commons, Physical Processes Commons, Plasma and Beam Physics Commons