Abstract
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.
Highlights
Kelvin–Helmholtz (K–H) instability can be activated at the interface between different plasma regimes with different velocities, and the perturbations propagate along the direction of the velocity shear as a form of surface wave developing into nonlinear vortices
The K–H instability is thought to be facilitated by a denser boundary layer formed by the dayside magnetic reconnections (Grygorov et al, 2016), by the plasma plume (Walsh et al, 2015), or by the pre-existing denser boundary layer formed by the high-latitude reconnections under the northward interplanetary magnetic field (IMF) (Hasegawa et al, 2009; Nakamura et al, 2017)
It is worth noting that the magnetopause oscillations started as soon as the IMF turned northward at 22:22 UT, which can facilitate the K–H instability, or else, the surface waves were amplified by the K–H instability
Summary
Kelvin–Helmholtz (K–H) instability can be activated at the interface between different plasma regimes with different velocities, and the perturbations propagate along the direction of the velocity shear as a form of surface wave developing into nonlinear vortices. The K–H instability is thought to be facilitated by a denser boundary layer formed by the dayside magnetic reconnections (Grygorov et al, 2016), by the plasma plume (Walsh et al, 2015), or by the pre-existing denser boundary layer formed by the high-latitude reconnections under the northward IMF (Hasegawa et al, 2009; Nakamura et al, 2017). Both northward and southward IMF can favor the K–H instability at the low-latitude magnetopause. We show a solar wind transport into the magnetosphere occurs and evolves within the vortices
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