On the Structure of Streamer-stalk Solar Wind: In-situ Observations, Theory and Simulation

The major purpose of this thesis is to understand the structure of the streamer-stalk solar wind, from in-situ observation, theory and simulation views. First, we analyze the in-situ observations from Advanced Composition Explorer (ACE) during 1998--2009 and ULYSSES during 1991--2009. We divide the solar wind into three categories by their different electron temperature derived from the O7+/O6+ ratio: solar wind from streamer stalk region, solar wind from outside of streamer stalk region, that can be associated, in part, with coronal holes, and solar wind associated with interplanetary coronal mass ejections (ICMEs). We find during the solar cycle 22/23 minimum, the streamer-stalk wind originates from a band about 40° in width about the heliospheric current sheet; however at the cycle 23/24 minimum, it is from a much narrower band of < 20° around the current sheet. In addition, during this solar minimum, the open magnetic flux of the Sun is lower compared to the previous minimum. We find the increase in area outside the stalk region is equal and opposite to the decrease in open magnetic flux, suggesting that the total amount of the open magnetic flux in the region outside the streamer stalk region remains constant in each solar minimum. The implications of the conservation of open magnetic flux for models of the behavior of the solar magnetic field are then discussed. We also analyze the observations of ULYSSES and ACE at the solar cycle 23/24 minimum and find the previous solar wind acceleration theory still holds. In the last part of this thesis, we investigate numerically a new model for the magnetic helicity transport process by using the Adaptively Refined Magnetohydrodynamic Solver (ARMS). We perform a series of numerical experiments to study the evolution of magnetic helicity injected into the solar corona by photospheric motions. We then analyze the kinetic energy, magnetic energy in the simulation system. The evolution of the magnetic helicity is also discussed.