Effects of Alpha-Proton Differential Flow on Proton Temperature Anisotropy Instabilities in the Solar Wind: Wind Observations

• Published in: The Astrophysical journal Vol. 884; no. 1; pp. 60 - 65
• Main Authors: Zhao, G. Q., Li, H., Feng, H. Q., Wu, D. J., Li, H. B., Zhao, A.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 10.10.2019; IOP Publishing
• Subjects: Alpha particles; Alpha rays; Anisotropy; Astrophysics; Cyclotron frequency; Cyclotrons; instabilities; interplanetary medium; Kinetic energy; Polarization; Protons; Solar wind; waves; Wind observation
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab3d35

Plasma kinetic waves and alpha-proton differential flow are two important subjects on the topic of solar wind evolution. Based on the Wind data during 2005-2015, this paper reports that the occurrence of electromagnetic cyclotron waves (ECWs) near the proton cyclotron frequency significantly depends on the direction of alpha-proton differential flow . As rotates from the anti-Sunward direction to the Sunward direction, the occurrence rate of ECWs as well as the percentage of left-handed (LH) polarized ECWs decreases considerably. In particular, it is shown that the dominant polarization changes from LH polarization to right-handed polarization during the rotation. The investigation on proton and alpha particle parameters ordered by the direction of further illustrates that large kinetic energies of alpha-proton differential flow correspond to high occurrence rates of ECWs. These results are consistent with theoretical predictions for effects of alpha-proton differential flow on proton temperature anisotropy instabilities.