Direct Measurement of Polar Coronal Hole-like Solar Wind in Its Acceleration Phase

@article{badman2026direct,
  title = {{Direct Measurement of Polar Coronal Hole-like Solar Wind in Its Acceleration Phase}},
  author = {Samuel T. Badman and Yeimy J. Rivera and Michael Louis Stevens and Mari Paz Miralles and Steven R. Cranmer and Andrea Verdini and Lynn B. Wilson and Xiangyu Wu and Georgios Nicolaou and Jean-Baptiste Dakeyo and Kai Jaffarove and Tamar Ervin and Dominic S. Payne and Michael Terres and Kristopher G. Klein and Jasper S. Halekas and Sujan Prasad Gautam and William H Matthaeus and Riddhi Bandyopadhyay and Srijan Bharati Das and Tatiana Niembro and Christopher J. Owen and Rungployphan Kieokaew and Ali Rahmati and Orlando M. Romeo and Federico Fraschetti and Marco Velli and Lorenzo Matteini and Kristoff W. Paulson and Lidiya Ahmed and Stuart D. Bale and Phyllis Whittlesey and Marc Pulupa and Nour E. Raouafi and Timothy S. Horbury and Jean Morris and Helen O’Brien and Roberto Livi and Davin E. Larson and Adam J. Finley and Philippe Louarn},
  journal = {The Astrophysical Journal Letters},
  year = {2026},
  month = nov,
  doi = {10.3847/2041-8213/aeb371},
  url = {https://iopscience.iop.org/article/10.3847/2041-8213/aeb371},
  note = {CC BY 4.0},
}

TY  - JOUR
TI  - Direct Measurement of Polar Coronal Hole-like Solar Wind in Its Acceleration Phase
AU  - Samuel T. Badman
AU  - Yeimy J. Rivera
AU  - Michael Louis Stevens
AU  - Mari Paz Miralles
AU  - Steven R. Cranmer
AU  - Andrea Verdini
AU  - Lynn B. Wilson
AU  - Xiangyu Wu
AU  - Georgios Nicolaou
AU  - Jean-Baptiste Dakeyo
AU  - Kai Jaffarove
AU  - Tamar Ervin
AU  - Dominic S. Payne
AU  - Michael Terres
AU  - Kristopher G. Klein
AU  - Jasper S. Halekas
AU  - Sujan Prasad Gautam
AU  - William H Matthaeus
AU  - Riddhi Bandyopadhyay
AU  - Srijan Bharati Das
AU  - Tatiana Niembro
AU  - Christopher J. Owen
AU  - Rungployphan Kieokaew
AU  - Ali Rahmati
AU  - Orlando M. Romeo
AU  - Federico Fraschetti
AU  - Marco Velli
AU  - Lorenzo Matteini
AU  - Kristoff W. Paulson
AU  - Lidiya Ahmed
AU  - Stuart D. Bale
AU  - Phyllis Whittlesey
AU  - Marc Pulupa
AU  - Nour E. Raouafi
AU  - Timothy S. Horbury
AU  - Jean Morris
AU  - Helen O’Brien
AU  - Roberto Livi
AU  - Davin E. Larson
AU  - Adam J. Finley
AU  - Philippe Louarn
PY  - 2026
DA  - 2026/11/05
JO  - The Astrophysical Journal Letters
DO  - 10.3847/2041-8213/aeb371
UR  - https://iopscience.iop.org/article/10.3847/2041-8213/aeb371
AB  - The early evolution of fast polar coronal hole (PCH) solar wind remains largely unconstrained by in situ measurements. In 2025 March, Parker Solar Probe (Parker) at its closest approach of 9.86 solar radii ( R ⊙ ) measured outflow from a large equatorial coronal hole (ECH), which was also measured at 1 au and at intermediate distances by Solar Orbiter (also near its perihelion). At 1 au the stream properties are consistent with PCH properties established by Ulysses. The stream was measured by Parker substantially below the Alfvén surface, with proton temperatures in excess of 2 MK and a speed at ∼10 R ⊙ which was only ∼60% of its asymptotic value. The Solar Orbiter data indicate that the acceleration is largely complete by 60 R ⊙ . Spherically polarized fluctuations in the stream are observed to develop from near-transverse and small-angle at Parker to full reversal “switchbacks” at Solar Orbiter. Comparison of the implied acceleration profile to historical Doppler-dimming measurements suggests that the stream’s low coronal acceleration is similar to that of PCH flows. Consistent with previous work, this acceleration requires significantly more energy than can be provided by the observed thermal pressure gradients, with a significant contribution likely from the abundant Alfvénic fluctuation energy observed at Parker. These observations provide unique constraints on models of the radial evolution of the fastest solar wind, and indicate that these wind streams experience gradual, steady acceleration over their first few tens of solar radii of evolution.
SN  - 2041-8213
SN  - 2041-8205
ER  -