Prolonged Kelvin–Helmholtz Waves at Dawn and Dusk Flank Magnetopause: Simultaneous Observations by MMS and THEMIS

S W Lu,H U Auster,C T Russell,R B Torbert,V Angelopoulos,J P Mcfadden,W Y Li,B B Tang,C Wang,J L Burch,B L Giles

doi:10.3847/1538-4357/ab0e76

Abstract

Abstract The Kelvin–Helmholtz (K-H) waves predominantly excited at the Earth’s low-latitude magnetopause were suggested to be dawn–dusk asymmetric. We report a prolonged simultaneous observations of the K-H waves on the dawn and dusk magnetopause by Magnetospheric Multiscale (MMS) and THEMIS-A (THA) spacecraft, respectively. The quasi-periodic K-H waves on both flanks have unambiguous low-density and high-speed patterns. The wave periods vary gradually on both flanks, with similar average periods (303 ± 107 s for MMS and 266 ± 102 s for THA). The lag time between the variations of the wave periods is close to the wave propagation time from THA to MMS, which suggests that the K-H waves generate and propagate quasi-symmetrically on both flanks. Larger local magnetic shear angles are observed on the trailing edges by MMS than by THA, which is probably due to the strong magnetic field distortion during the tailward propagation. The increased magnetic shear may excite magnetic reconnection, thus contributing to the formation of the low-latitude boundary layer.

Highlights

The Kelvin–Helmholtz (K-H) instability could be excited at a plasma boundary where large velocity shear exists
We report the first simultaneous observations of the Kelvin– Helmholtz waves by Magnetospheric Multiscale (MMS) and THA on the dawn and dusk flank magnetopause on 2017 May 29
The dawnside K-H waves are observed by MMS at [−15.0, −16.3, 3.5] RE, while the duskside K-H waves are observed by THEMIS-A at [3.9, 11.7, −3.7] RE

Summary

Introduction

The Kelvin–Helmholtz (K-H) instability could be excited at a plasma boundary where large velocity shear exists. The K-H instability is considered to be an important mechanism for the transport of solar wind particles and energy into the Earth’s magnetosphere (Hasegawa et al 2004, 2009; Fairfield et al 2007). Both numerical simulations (Nykyri & Otto 2001; Nakamura & Fujimoto 2005; Nakamura et al 2013, 2017) and in situ observations (Hasegawa et al 2009; Eriksson et al 2016; Li et al 2016) have shown that the magnetic reconnection induced by the K-H waves breaks the frozen-in condition of plasma during the large-scale evolution of the waves, allowing plasma transport from the solar wind into the magnetosphere. The symmetry and correlations of the K-H waves on both flanks are analyzed in detail

Instruments

K-H Waves Observed by MMS and THA

Magnetosphere–Magnetosheath Boundary Conditions of the K-H Waves

Properties of K-H Waves

Findings

Summary