The Solar Wind and Its Magnetic Sources at Sunspot Maximum

Abstract

We use in situ measurements from the Advanced Composition Explorer and magnetograph data from the National Solar Observatory to relate the properties of the solar wind during 1998-2002 to its source region magnetic fields. The great bulk of the solar maximum wind is characterized by low proton speeds (vp ~ 420 km s-1) and high oxygen charge state ratios (nO7+/nO6+ ~ 0.3). This slow wind originates from small, sheared open-field regions located near active regions and characterized by very large flux tube expansion factors (fexp 10) and high footpoint field strengths (B0 ~ 30 G). In contrast, the occasional high-speed streams emanate from weak-field regions (B0 ~ 5 G) with small expansion factors (fexp ~ 4) and show relatively low charge state ratios (nO7+/nO6+ ~ 0.1); their proton velocities (vp ~ 550 km s-1) are substantially reduced by interactions with the surrounding sea of low-speed wind. We attribute the high freeze-in temperatures of the slow wind to enhanced heating taking place in the low corona in the presence of the very strong, rapidly diverging source fields, which are found to be correlated with high mass and energy flux densities at the coronal base.