Alpha-proton differential flow of the young solar wind: Parker solar probe observations. Mostafavi, P., Allen, R. C., McManus, M. D., Ho, G. C., Raouafi, N. E., Larson, D. E., Kasper, J. C., & Bale, S. D. Astrophysical Journal Letters, 2022. Publisher: Iop Publishing Ltd Type: Article tex.date-modified: 2022-04-12 11:34:54 +0100![Alpha-proton differential flow of the young solar wind: Parker solar probe observations [link]](https://bibbase.org/img/filetypes/link.svg "link")
Paper doi abstract bibtex The velocity of alpha particles relative to protons can vary depending on the solar wind type and distance from the Sun. Measurements from the previous spacecraft provided the alpha-proton differential velocities down to 0.3 au. The Parker Solar Probe (PSP) now enables insights into differential flows of the newly accelerated solar wind closer to the Sun for the first time. Here we study the difference between proton and alpha bulk velocities near PSP perihelia of encounters 3-7 when the core solar wind is in the field of view of the Solar Probe Analyzer for Ions instrument. As previously reported at larger heliospheric distances, the alpha-proton differential speed observed by PSP is greater for fast wind than the slow solar wind. We compare PSP observations with various spacecraft measurements and present the radial and temporal evolution of the alpha-proton differential speed. The differential flow decreases as the solar wind propagates from the Sun, consistent with previous observations. While Helios showed a small radial dependence of differential flow for the slow solar wind, PSP clearly showed this dependency for the young slow solar wind down to 0.09 au. Our analysis shows that the alpha-proton differential speed's magnitude is mainly below the local Alfven speed. Moreover, alpha particles usually move faster than protons close to the Sun. The PSP crossed the Alfven surface during its eighth encounter and may cross it in future encounters, enabling us to investigate the differential flow very close to the solar wind acceleration source region for the first time.
@article{Mostafavi2022,
title = {Alpha-proton differential flow of the young solar wind: {Parker} solar probe observations},
volume = {926},
issn = {2041-8205},
url = {https://doi.org/10.3847/2041-8213/ac51e1},
doi = {10.3847/2041-8213/ac51e1},
abstract = {The velocity of alpha particles relative to protons can vary depending on the solar wind type and distance from the Sun. Measurements from the previous spacecraft provided the alpha-proton differential velocities down to 0.3 au. The Parker Solar Probe (PSP) now enables insights into differential flows of the newly accelerated solar wind closer to the Sun for the first time. Here we study the difference between proton and alpha bulk velocities near PSP perihelia of encounters 3-7 when the core solar wind is in the field of view of the Solar Probe Analyzer for Ions instrument. As previously reported at larger heliospheric distances, the alpha-proton differential speed observed by PSP is greater for fast wind than the slow solar wind. We compare PSP observations with various spacecraft measurements and present the radial and temporal evolution of the alpha-proton differential speed. The differential flow decreases as the solar wind propagates from the Sun, consistent with previous observations. While Helios showed a small radial dependence of differential flow for the slow solar wind, PSP clearly showed this dependency for the young slow solar wind down to 0.09 au. Our analysis shows that the alpha-proton differential speed's magnitude is mainly below the local Alfven speed. Moreover, alpha particles usually move faster than protons close to the Sun. The PSP crossed the Alfven surface during its eighth encounter and may cross it in future encounters, enabling us to investigate the differential flow very close to the solar wind acceleration source region for the first time.},
number = {2},
journal = {Astrophysical Journal Letters},
author = {Mostafavi, P. and Allen, R. C. and McManus, M. D. and Ho, G. C. and Raouafi, N. E. and Larson, D. E. and Kasper, J. C. and Bale, S. D.},
year = {2022},
note = {Publisher: Iop Publishing Ltd
Type: Article
tex.date-modified: 2022-04-12 11:34:54 +0100},
}
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Here we study the difference between proton and alpha bulk velocities near PSP perihelia of encounters 3-7 when the core solar wind is in the field of view of the Solar Probe Analyzer for Ions instrument. As previously reported at larger heliospheric distances, the alpha-proton differential speed observed by PSP is greater for fast wind than the slow solar wind. We compare PSP observations with various spacecraft measurements and present the radial and temporal evolution of the alpha-proton differential speed. The differential flow decreases as the solar wind propagates from the Sun, consistent with previous observations. While Helios showed a small radial dependence of differential flow for the slow solar wind, PSP clearly showed this dependency for the young slow solar wind down to 0.09 au. Our analysis shows that the alpha-proton differential speed's magnitude is mainly below the local Alfven speed. Moreover, alpha particles usually move faster than protons close to the Sun. 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Measurements from the previous spacecraft provided the alpha-proton differential velocities down to 0.3 au. The Parker Solar Probe (PSP) now enables insights into differential flows of the newly accelerated solar wind closer to the Sun for the first time. Here we study the difference between proton and alpha bulk velocities near PSP perihelia of encounters 3-7 when the core solar wind is in the field of view of the Solar Probe Analyzer for Ions instrument. As previously reported at larger heliospheric distances, the alpha-proton differential speed observed by PSP is greater for fast wind than the slow solar wind. We compare PSP observations with various spacecraft measurements and present the radial and temporal evolution of the alpha-proton differential speed. The differential flow decreases as the solar wind propagates from the Sun, consistent with previous observations. 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