2018/12/13 by G. Q. Zhao, Zhao, G. Q., H. Q. Feng +7
Earth and Planetary Sciences · Physics and Astronomy · #Earthquake Detection and Analysis #FOS: Physical sciences #Ionosphere and magnetosphere dynamics #Solar and Space Plasma Dynamics #Space Physics (physics.space-ph)
paper · pdf · doi:10.48550/arxiv.1812.05323
openalex publication_date 2018/12/13 · openalex created_date 2019/06/27 · openalex updated_date 2026/07/28
Electromagnetic cyclotron waves (ECWs) near the proton cyclotron frequency are frequently observed in the solar wind, yet their generation mechanism is still an open question. Based on the Wind data during the years 2005-2015, this paper carries out a statistical study on plasma characteristics associated with the occurrence of ECWs. The probability density distributions (PDDs) of proton temperature anisotropy (T_⊥/T_∥) and proton parallel beta (β_∥) are investigated, where ⊥ and ∥ refer to perpendicular and parallel to the background magnetic field, respectively. The PDDs depend on solar wind types as well as wave polarizations, and those for ECWs with left-handed (LH) polarization exhibit considerable differences from the PDDs for ambient solar winds. The distributions of occurrence rates of LH ECWs in (β_∥, T_⊥/T_∥) space show a tendency that the occurrence rates increase with proton temperature anisotropies. The β_∥ with maximum of occurrence rates is near 0.1 when T_⊥/T_∥ > 1 while it is around 1 when T_⊥/T_∥ < 1. The presence of alpha-proton differential flow with large kinetic energy corresponds to a much high occurrence rate as well as the domination of LH polarization of ECWs. Based on these observations and existing theories, we propose that the proton cyclotron and parallel firehose instabilities with effects of alpha-proton differential flow are likely responsible for the local generation of LH ECWs in the solar wind. The generation mechanism of right-handed ECWs seems to be complicated and more discussions are needed in future researches.