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

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(-1), 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.