Abstract. A train of likely Kelvin–Helmholtz (K–H) vortices with plasma
transport across the magnetopause has been observed by the Time History of
Events and Macroscale Interactions during Substorms (THEMIS) at the duskside
of the magnetopause. This unique event occurs when the interplanetary magnetic
field (IMF) abruptly turns northward, which is the immediate change to
facilitate the K–H instability. Two THEMIS spacecraft, TH-A and TH-E,
separated by 3 RE, periodically encountered the duskside magnetopause and
the low-latitude boundary layer (LLBL) with a period of 2 min and
tailward propagation of 212 km s−1. Despite surface waves also
explaining some of the observations, the rotations in the bulk velocity
observation, a distorted magnetopause with plasma parameter fluctuations and
the magnetic field perturbations, as well as a high-velocity low-density
feature indicate the possible formation of rolled-up K–H vortices at the
duskside of the magnetopause. The coexistence of magnetosheath ions with
magnetospheric ions and enhanced energy flux of hot electrons is identified
in the K–H vortices. These transport regions appear more periodic at the
upstream spacecraft and more dispersive at the downstream location,
indicating significant transport can occur and evolve during the tailward
propagation of the K–H waves. There is still much work to do to fully
understand the Kelvin–Helmholtz mechanism. The observations of the direct
response to the northward turning of the IMF, the possible evidence of
plasma transport within the vortices, involving both ion and electron fluxes,
can provide additional clues as to the K–H mechanism.