Pickup Ion Acceleration in the Heliosphere: Consequences of Organized Footpoint Motion on the Sun

Abstract

Suprathermal and pickup ion tails exist ubiquitously in slow solar wind. What is the intrinsic property of slow solar wind that causes ubiquitous particle acceleration? Observations from Ulysses have shown that statistical acceleration through transit time damping of fluctuations in field strength is the vehicle by which pickup ion tails are produced. But the source of compressive fluctuations in slow solar wind has not been established. We show that shearing of magnetic fields by small‐scale fluctuations in the solar wind speed provides a strong and continuous source of compressive fluctuations. This effect occurs naturally if slow solar wind is generated from material stored in coronal loops and released due to organized drifts of open magnetic field footpoints on the Sun. Another consequence of these organized footpoint drifts is the creation of large‐scale magnetic field structures that connect fast and slow solar wind — located for example in the outer heliosphere at the latitudinal boundaries betwee...