Browsing by Author "Chhiber, Rohit"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Studies in multi-scale turbulent dynamics of the solar wind(University of Delaware, 2018) Chhiber, RohitThe solar wind is the continuous outflow of plasma from the Sun, driven by the pressure difference between the hot corona and the interstellar medium. This complex, dynamically evolving flow permeates all of interplanetary space, and its behavior and properties have significant implications for near-Earth space weather, the health of space travelers, and the proper functioning of both terrestrial and space-faring elec- tronic systems. As the only astrophysical plasma where direct spacecraft measurements are possible, the solar wind provides an archetype of a strongly turbulent magnetized system. ☐ This dissertation examines several problems within the context of multi-scale turbulent dynamics of the solar wind, employing a “model heliosphere” produced by a well-tested global two-fluid magnetohydrodynamic (MHD) code. The three- dimensional simulations are based on a Reynolds-averaging approach, in which resolved large-scale flow is self-consistently coupled to smaller-scale fluctuations by means of a dynamical turbulence transport model. The focus is on the inner heliosphere (coronal surface to 3 astronomical units); effects of solar variability are incorporated through changing source magnetic dipole tilts and magnetogram-derived boundary data from different solar-activity epochs. ☐ The simulations are used to study the collisional history of the solar wind; full integral calculations of the collisional age are compared with simpler one-point estimates commonly employed in observational work, the relationship between the collisional age and the Knudsen number is clarified, and the collisional age is contrasted with the turbulent age of the solar wind. ☐ The diffusion tensor that describes scattering of energetic particles by magnetic fluctuations is evaluated throughout the inner-heliosphere, with the heliospheric current sheet emerging as a region of strong diffusion perpendicular to the magnetic field. The rigidity-dependence of the parallel diffusion coefficient is shown to evolve with heliocentric distance. ☐ Critical (sonic, Alfvénic, and plasma-beta unity) surfaces that mark the transi- tion of the magnetically-structured corona into the predominantly hydrodynamic solar wind are localized. The flow in regions propinquitous to these surfaces is investigated, and simulation results are compared with a variety of remote sensing observations. The often-overlooked concept of a “range of influence” that limits the length scales at which fluctuations may interact in the expanding solar wind is discussed. ☐ With the importance of the critical surfaces established, contextual predictions for the soon-to-be-launched Parker Solar Probe (PSP ) mission are provided by com- bining the simulations with the spacecraft’s planned trajectory. PSP crossings of the critical surfaces are simulated, and the turbulence environment likely to be observed during early orbits is discussed. ☐ In an ancillary observational study, comparative statistical analyses of multi- scale intermittent turbulence in the Earth’s magnetosheath and the solar wind are performed, employing high-resolution multi-spacecraft data provided by the Magneto- spheric Multiscale mission. Strong signatures of intermittent turbulent structures at electron and ion scales in the magnetosheath are observed. These signatures appear to be absent at sub-ion scales in the solar wind, which does, nevertheless, exhibit inter- mittency in the inertial range. The findings also include different power-law spectral behavior in the two regions. Comparisons of a multi-spacecraft technique with single- spacecraft estimates permits a verification of the accuracy of the Taylor “frozen-in” hypothesis.Item The Trans-Heliospheric Survey(Astronomy & Astrophysics, 2023-07-24) Maruca, Bennett A.; Qudsi, Ramiz A.; Alterman, B. L.; Walsh, Brian M.; Korreck, Kelly E.; Verscharen, Daniel; Bandyopadhyay, Riddhi; Chhiber, Rohit; Chasapis, Alexandros; Parashar, Tulasi N.; Matthaeus, William H.; Goldstein, Melvyn L.Context. Though the solar wind is characterized by spatial and temporal variability across a wide range of scales, long-term averages of in situ measurements have revealed clear radial trends: changes in average values of basic plasma parameters (e.g., density, temperature, and speed) and a magnetic field with a distance from the Sun. Aims. To establish our current understanding of the solar wind's average expansion through the heliosphere, data from multiple spacecraft needed to be combined and standardized into a single dataset. Methods. In this study, data from twelve heliospheric and planetary spacecraft - Parker Solar Probe (PSP), Helios 1 and 2, Mariner 2 and 10, Ulysses, Cassini, Pioneer 10 and 11, New Horizons, and Voyager 1 and 2 - were compiled into a dataset spanning over three orders of magnitude in heliocentric distance. To avoid introducing artifacts into this composite dataset, special attention was given to the solar cycle, spacecraft heliocentric elevation, and instrument calibration. Results. The radial trend in each parameter was found to be generally well described by a power-law fit, though up to two break points were identified in each fit. Conclusions. These radial trends are publicly released here to benefit research groups in the validation of global heliospheric simulations and in the development of new deep-space missions such as Interstellar Probe.