Dawn-dusk Asymmetry Distribution of Kelvin-Helmholtz Instability at the Magnetopause of the Mid-magnetotail

The Kelvin-Helmholtz (K-H) instability is an unstable phenomenon that occurs in the boundary layer between two different fluids with velocity shear, and plays an important role in particle, momentum, and energy transport from the solar wind to the magnetosphere. At the Earth’s magnetopause, the magnetosheath plasma flows rapidly along the magnetopause and creates a velocity shear with the stationary magnetospheric plasma, providing favorable conditions for the occurrence of the K-H instability. Our investigation selects the magnetopause crossings at the mid-magnetotail region (X ≈ –60 R_e) from 2015 to 2020 using the observation data from the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) satellite and, in conjunction with the 51 K-H instability events that also take place in the mid-magnetotail, conducts a statistical analysis of the dawn-dusk asymmetric distribution of K-H instability at the mid-magnetotail magnetopause. The findings suggest that the occurrence rate of K-H instability is relatively high on the dawn side of the magnetopause in the mid-magnetotail region. Under northward Interplanetary Magnetic Field (IMF) condition, the occurrence rate of the K-H instability events on the dawn side significantly surpasses that on the evening side; when the Parker-spiral IMF dominates, there are more K-H instability events on the duskside. The varying parameters of the solar wind also significantly influence the distribution of K-H vortices at dawnside and duskside of the mid-magnetotail magnetopause. Under conditions of low magnetoacoustic Mach number, the occurrence rate is higher on the dawnside. For slow solar winds, K-H vortices are significantly more frequent on the dawnside compared to the duskside. And the occurrence rate peak on the dawnside is pronounced under low dynamic pressure, while the occurrence rate at duskside is slightly higher than at dawnside for increased dynamic pressure. The K-H waves in the magnetotail region may contribute to the asymmetrical distribution of plasma in the magnetotail plasma sheet.