Dynamics of Large-Scale Solar-Wind Streams Obtained by the Double Superposed Epoch Analysis: 4. Helium Abundance

摘要

This work is a continuation of our previous articles (Yermolaev et al., 2015, https://doi.org/ 10.1002/2015JA021274; 2017, https://doi.org/10.1007/s11207-017-1205-1; 2018, https://doi.org/10.1007/ s11207-018-1310-9), which describe the average temporal profiles of interplanetary plasma and field parameters in large-scale solar-wind (SW) streams: corotating interaction regions (CIRs), interplanetary coronal mass ejections (ICMEs including both magnetic clouds (MCs), and ejecta), and sheaths as well as interplanetary shocks (ISs). In this work, we analyze the average profile of helium abundance, N_α/N_p, for 1976-2016. Our results confirm the main results that were obtained in earlier studies: N_α/N_p is higher in quasi-stationary fast streams than in slow ones; it slowly changes in compression regions CIRs and sheaths from values in undisturbed SW to values in the corresponding fast stream type pushing like a piston, in high-speed stream (HSS) flow for CIRs, or in ICME for sheaths; in ejecta, it is close to the abundance observed in undisturbed streams, and it is maximal in MCs. For the first time, the results show that N_α/N_p correlates with the proton β-parameter in compression regions CIRs and sheath and anticorrelates in ICMEs. The N_α/N_p versus β dependence is stronger in MCs than in ejecta and may be used as an indicator of conditions at the place on the Sun where CMEs are formed.