A Correlation Between the Solar Wind's Alfvén Point and the Coronal Heating Boundary

Abstract:

As the solar wind travels outwards through the corona, it continues to be strongly and preferentially heated, but the location at which this heating primarily occurs is unknown. Some theories attribute the non-thermal plasma properties observed at 1AU to a continuous heating, while others see it as a relic of heating that occurred closer to the solar surface. A recent study by Kasper et al. has provided new insights, using an analysis of collisional age to construct a model of the solar wind in which the outflowing plasma is energized only up to a boundary point, and after which it ceases to be preferentially heated. This boundary is found to exist in the 30 and 50 solar radii range, varying with changing solar wind conditions, and the model shows very good agreement with measurements taken by the Wind spacecraft at 1AU. In the study presented here, a relationship between the Kasper et al. heating boundary and the solar wind’s Alfvén point is investigated. A model of the Alfvén point location is constructed and calculated using Wind spacecraft observations, and the Wind data is subsequently split into bins based on Alfvén point height. Recalculating the height of the preferential heating boundary for each of these bins reveals a very strong linear correlation between the heating boundary and the Alfvén point. This suggests that the Alfvén point may play an important role in determining how and where the preferential heating of the solar wind occurs.