The Magnetic Nature of Coronal Holes

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Abstract
Solar wind streams originate from low-density, magnetically open regions of the sun's corona, known as coronal holes. The locations, areal sizes, rotation, and solar-cycle evolution of these regions can be reproduced and understood by applying simple extrapolation models to measurements of the photospheric magnetic field. The surprisingly rigid rotation displayed by many coronal holes suggests that field-line reconnection occurs continually in the corona, despite the high electrical conductivity of the coronal plasma. The magnetic field strengths and field-line divergence rates in coronal holes can be related empirically to the bulk speed and the mass and energy flux densities of the solar wind plasma. Such relations may help to illuminate the physical processes responsible for heating the corona and driving the solar wind.