Kelvin‐Helmholtz vortices observed by THEMIS at the duskside of the magnetopause under southward interplanetary magnetic field

Abstract

The Time History of Events and Macroscale Interactions during Substorms (THEMIS) observed several magnetopause crossings periodically at the duskside of magnetopause under southward interplanetary magnetic field (IMF), with significant sunward returning flows inside the magnetopause. The vortex features of the flows and the periodic enhancements in the calculated vorticity normal to the spacecraft plane could be found in the observation. The distortion of the magnetopause, the periodic features of vortex flows, the tailward propagation, and the evaluation of Kelvin-Helmholtz instability (KHI) condition support the evidence of the Kelvin-Helmholtz vortices produced by the velocity shear at the duskside of magnetopause. Based on three-point simultaneous observations of the flow, the vorticity was calculated to be about 0.15 s À1 , similar to previous results. The tailward propagation of the vortices along the flank magnetopause was estimated to be about 292 km/s. The circular-induced electric field of several mV/m was deduced perpendicular to the magnetic field when the magnetic field compression occurred at the edges of the vortices.

The Earth: Plasma Sources, Losses, and Transport Processes

“…The statistics of and show observations usually at low latitudes, and not only tailward but also sunward of the terminator (suggesting that at least sometimes they may develop very rapidly). Events have also been reported on the dusk flank during sourthward IMF conditions (Yan et al 2014), as previously predicted.…”

IMF Control of Alfvénic Energy Transport and Deposition at High Latitudes

“…The occurrence of the K‐H instability is favorable under conditions of northward B z (Hasegawa et al, , ) or high solar wind speed (Rae et al, ), or both (Kavosi & Raeder, ). The instability nevertheless operates under every solar wind speed in the typically observed range, 200–600 km/s, and under virtually every IMF configuration (Farrugia et al, ; Hwang et al, ; Kavosi & Raeder, ; Yan et al, ), which could explain the persistence of the prenoon and postnoon enhanced broadband number flux for every ϕ IMF orientation in Figure . However, this explanation offers no obvious clues as to the apparent preferential generation of prenoon IAW power.…”

On the Dawn‐Dusk Asymmetry of the Kelvin‐Helmholtz Instability Between 2007 and 2013

“…The KH waves have been frequently observed at the magnetopause of Earth's low-latitude boundary layer during northward (Eriksson et al, 2016;Fairfield et al, 2000;Hasegawa et al, 2004;Lin et al, 2014), PS (Moore, 2012;Moore et al, 2016;Nykyri et al, 2006), southward IMF (Hwang et al, 2011;Yan et al, 2014), and also at the boundary layers of other planets (Boardsen et al, 2010;Delamere & Bagenal, 2010;Ma et al, 2015;Masters et al, 2010;McComas & Bagenal, 2008;Pope et al, 2009;Ruhunusiri et al, 2016;Sundberg et al, 2012).…”