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Abstract

One of the key findings of the Parker Solar Probe mission has been that patches of steep Alfvén waves, or "switchbacks," pervade both the fast and the slow solar wind in the inner heliosphere. This finding has inspired a boom of creative and thoughtful work towards explaining the origin and the fate of the switchback. Perhaps overlooked is the relevance of the phenomenon in solar wind heating and acceleration on a global scale. As solar activity approaches maximum and Parker approaches its final orbit, the Parker SWEAP and Fields experiments are increasingly able to sample solar wind streams that originate at low heliographic latitudes. The super- and sub-corotation phases of the Parker orbit, along with advantageous multi-spacecraft conjunctions near perihelion, have created opportunities in 2022-23 to observe these streams from both above and below the Alfvén critical point. In this presentation, we will review the most recent such observations, focusing on ion and electron distribution functions obtained by the SWEAP experiment. In particular, we will present examples where the power supplied by the influx of magnetic switchbacks near or below the Alfvén critical point was found to be comparable, within measurement uncertainties, to the excess in kinetic energy flux measured downstream. We thereby quantify the contribution to solar wind heating and acceleration by switchback dissipation. We will also briefly summarize the future prospects for Parker and the SWEAP experiment as it enters the second half of the mission.