In Situ Observation of Alfvén Waves in an ICME Shock-Sheath Indicating the Existence of Alfvénic Turbulence

The dynamic evolution of a coronal mass ejection (CME) in the interplanetary space generates a highly turbulent, compressed, and heated shock-sheath. This region provides an exceptional setting for investigating the intricate fluctuations occurring at small scales and offers a valuable opportunity to unravel the underlying physical processes responsible for turbulence dissipation and plasma heating. Understanding the role of turbulence in controlling the energy transport process in a magnetized plasma, within space and astrophysics, remains an enticing challenge of the twenty-first century. In this article, we study sheath regions observed by the Wind spacecraft from 1995 to 2021. We find 80 sheath events out of the studied 384 events that show a significant Alfvenic nature (approximate to 21%). These fluctuations are interpreted as Alfvenic wave packets propagating either parallel or antiparallel to the background magnetic field, quantified by the normalized crosshelicity (sigma C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{C}$\end{document}). We find 47 sheath events with outward-propagating Alfvenic fluctuations and 33 events with inward Alfvenic characteristics. The Alfvenic sheaths had a mean value of sigma C=0.46 +/- 0.03\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{C} = 0.46 \pm 0.03 $\end{document} and -0.43 +/- 0.02\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$-0.43 \pm 0.02$\end{document} for outward- and inward-directed Alfvenic sheaths, respectively. Furthermore, we compare the average interplanetary parameter values of both the Alfvenic sheaths and the ambient solar wind. The study has strong implications in the domain of interplanetary space plasmas, its interaction with planetary plasmas, and astrophysical plasmas.