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.
