UCLA

Parker Solar Probe (PSP) was launched in late 2018, and since then it has been providing in situ measurements of the inner heliosphere and upper solar corona. The journey of PSP to the Sun is continuously pushing the frontiers of heliophysics. In this dissertation, by combining in situ observations and computer simulations, we aimed to bring new insights from PSP to our current understanding of Alfvén waves, turbulence, and solar wind structures. The primary results of this dissertation are the following: (1) Through 1D MHD simulation, we show that the total wave action is conserved in the linear mode conversion of magnetosonic waves at the equipartition layer (where the sound speed equals the Alfvén speed); (2) Close to the Sun, contrary to standard solar wind turbulence models, the energy-containing 1/f range disappears in solar wind turbulence. Instead, the low-frequency turbulence spectrum is characterized by a shallow-inertial double power law, where the low-frequency part scales like f^{-0.5}; (3) The in situ observed magnetic field magnitude B shows a surprisingly sensitive response to Gaussianity tests, which leads to a scale- and location-dependent Gaussianity scalogram, unveiling coherent structures spanning seven orders of magnitude in time. Notably, combined with Potential Field Source Surface (PFSS) modeling, we confirmed that the radially normalized B follows a near-perfect Gaussian distribution when PSP is immersed in magnetic field lines that are connected back to coronal holes. Additionally, computer simulations show that Gaussian distribution is the natural relaxation state for Alfvénic turbulence. (4) The shallow-inertial double power law indicates a concentration of fluctuation energy around the 'bend' in spectral slopes. Based on statistics from the first 17 PSP encounters, we found a systematic trend that the primary fluctuation frequency decreases with solar wind advection time and eventually saturates at around 3 minutes for the most pristine solar wind. This is consistent with remote sensing observations of the chromosphere, and indicates that the Alfvén waves in the solar wind could ultimately be driven by p-mode oscillations in the photosphere. Our results have two primary implications: (1) Gaussianity of B serves as a good parameter for identifying structures in the solar wind, especially the time intervals that are magnetically connected to coronal holes; (2) Alfvén waves in the solar wind are likely originating from the solar convection zone resonance chamber. Therefore, this dissertation can serve as a preliminary study to provide constraints on the formation of 1/f energy containing range and coronal heating mechanisms.