Author

Tae K. Kim

Date of Award

2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Committee Chair

Nikolai V. Pogorelov

Committee Member

Vladimir Florinski

Committee Member

Jacob Heerikhuisen

Committee Member

Jakobus le Roux

Committee Member

Gary P. Zank

Subject(s)

Solar wind., Heliosphere., Interstellar matter., Galactic cosmic rays., Solar activity.

Abstract

The Sun is the source of charged particles called the solar wind that escape the Sun's gravity and transport the solar magnetic field and energy outward. Far beyond the solar system, the solar wind pushes against the interstellar plasma and forms a huge cavity called the heliosphere. Modeling the solar wind outflow to the distant boundary regions with the local interstellar medium (LISM) requires computational resources capable of handling the complex physical processes taking place in the outer heliosphere, particularly near the solar wind-LISM boundary, and a set of time-dependent boundary conditions that closely replicate the cyclical and day-to-day variations in the solar wind parameters. We utilize interplanetary scintillation (IPS) observations from the Solar-Terrestrial Environment Laboratory to construct such boundary conditions for Multi-Scale Fluid-Kinetic Simulations Suite (MS-FLUKSS), which is a set of numerical codes consisting of several modules suitable for simulating the interactions between ions and neutral atoms that characterize the region of our interest. However, since IPS observations contain a line-of-sight integration effect, they must be deconvolved through a tomographic procedure to provide a more accurate, three-dimensional map of the solar wind parameters. At first, we use the MHD-IPS tomography to generate the boundary conditions at 5 AU for an extended period of time to simulate the time-dependent solar wind-LISM interaction. Comparisons of the simulation results with Voyager measurements across the termination shock suggest that the MHD-IPS tomography, which is not capable of reproducing transient structures, needs significant improvements to accurately reproduce the long-term fluctuations in the global solar wind dynamic pressure. Next, we turn to the time-dependent IPS tomography to obtain the inner boundary conditions for our heliospheric MHD model since it boasts remarkable accuracy in its solar wind speed (and density) reconstruction at Earth despite the use of an oversimplified solar wind model to iteratively fit the IPS data (and near-Earth spacecraft measurements). We find considerable differences between the MHD simulation results and spacecraft data (radial velocity in particular) and conclude that a MHD model should be iteratively fit to IPS data in a truly time-dependent fashion to improve the three-dimensional reconstruction of the global heliosphere.

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