Coronal Mass Ejection–Induced Sub-Alfvénic Solar Wind: Key Insights from Parker Solar Probe

Abstract Since its eighth encounter, starting on 2022 April 28, Parker Solar Probe has consistently sampled the elusive sub-Alfvénic solar wind during each perihelion pass, offering unprecedented insights into these critical regions of the solar atmosphere. Here, we analyze sub-Alfvénic solar wind intervals longer than 10 minutes during the 10th encounter. The plasma sampled during these intervals shares some common features: considerable density drop relative to the surrounding plasma, very low plasma beta ( β p ), significantly reduced levels of magnetic field fluctuations, and high magnetic field variance anisotropy (transverse to the mean field). Interestingly, no switchbacks are observed in the analyzed sub-Alfvénic regions. We explore the potential role of coronal mass ejections (CMEs) in generating sub-Alfvénic wind regions. Remarkably, we find that every extended sub-Alfvénic wind interval during encounter 10 is linked to a CME. While all the observed sub-Alfvénic intervals are associated with CME wakes, the latter also has periods that are super-Alfvénic.