First Analysis of In Situ Observation of Surface Alfvén Waves in an ICME Flux Rope

Abstract

Alfvén waves (AWs) are ubiquitous in space and astrophysical plasma. Their crucial role in various physical processes has triggered intense research in solar–terrestrial physics. Simulation studies have proposed the generation of AWs along the surface of a cylindrical flux rope, referred to as surface AWs (SAWs); however, the observational verification of this distinct wave has been elusive to date. We report the first in situ observation of SAWs in a flux rope of an interplanetary coronal mass ejection. We apply the Walén test to identify them. We have used Elsässer variables to estimate the characteristics of SAWs. They may be excited by the movement of the flux rope’s footpoints or by instabilities along the boundaries of the plasma magnetic cloud. Here, the change in plasma density or field strength in the surface-aligned magnetic field may trigger SAWs.

Observation of Kinetic Alfvén Waves inside an Interplanetary Coronal Mass Ejection Magnetic Cloud at 1 au

“…The magnetic and kinetic forces within ICMEs are no longer in perfect equilibrium, leading to the excitation of both MHD and kinetic-scale waves (Jacques 1977). While previous studies have delved into MHD-scale waves within magnetic clouds (Raghav & Kule 2018a, 2018bRaghav et al 2018Raghav et al , 2019Raghav et al , 2023aDhamane et al 2023bDhamane et al , 2024, the understanding of kinetic-scale mode waves remains a challenge. In a recent study, Dhamane et al (2023a) observed one aspect of kineticscale waves, specifically those aligned with the background magnetic field, by studying Alfvén ion cyclotron waves.…”

Observation of Alfvén Ion Cyclotron Waves in ICME Magnetic Clouds at 1 au

“…(see, e.g., Siu-Tapia et al 2015). The various in situ observations suggest the existence of Alfvén waves in ICME substructures, i.e., sheath and MC during CME-CME/CMEhigh-speed stream interactions (Raghav & Kule 2018a, 2018bRaghav et al 2018Raghav et al , 2019Shaikh et al 2019a;Dhamane et al 2023a;Raghav et al 2022Raghav et al , 2023Dhamane et al 2023b). However, how these waves dissipated in a flux rope structure remains an open question.…”