The Parker Solar Probe (PSP) entered a region of subAlfvénic solar wind during encounter 8, and we present the first detailed analysis of lowfrequency turbulence properties in this novel region. The magnetic field and flow velocity vectors were highly aligned during this interval. By constructing spectrograms of the normalized magnetic helicity, crosshelicity, and residual energy, we find that PSP observed primarily Alfvénic fluctuations, a consequence of the highly fieldaligned flow that renders quasi2D fluctuations unobservable to PSP. We extend Taylor’s hypothesis to sub and superAlfvénic flows. Spectra for the fluctuating forward and backward Elsässer variables (
Parker Solar Probe (PSP) observed subAlfvénic solar wind intervals during encounters 8–14, and lowfrequency magnetohydrodynamic (MHD) turbulence in these regions may differ from that in superAlfvénic wind. We apply a new mode decomposition analysis to the subAlfvénic flow observed by PSP on 2021 April 28, identifying and characterizing entropy, magnetic islands, forward and backward Alfvén waves, including weakly/nonpropagating Alfvén vortices, forward and backward fast and slow magnetosonic (MS) modes. Density fluctuations are primarily and almost equally entropy and backwardpropagating slow MS modes. The mode decomposition provides phase information (frequency and wavenumber
 NSFPAR ID:
 10502660
 Publisher / Repository:
 DOI PREFIX: 10.3847
 Date Published:
 Journal Name:
 The Astrophysical Journal
 Volume:
 966
 Issue:
 1
 ISSN:
 0004637X
 Format(s):
 Medium: X Size: Article No. 75
 Size(s):
 Article No. 75
 Sponsoring Org:
 National Science Foundation
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