Study on the instability in Mars' induced magnetospheric boundary: Kelvin-Helmholtz waves and associated magnetic flux ropes

The plasma instabilities in Mars' induced magnetospheric boundary such as the Kelvin- Helmholtz (K-H) instability induced by velocity shear, significantly affect the structure of Mars' induced magnetosphere and the transport of ions within the Martian magnetosphere. In this study, using the magnetic field and plasma data provided by the Magnetometer (MAG) and Super Thermal and Thermal Ion Composition (STATIC) instruments onboard the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, we analyze the K-H instability events observed at the induced magnetospheric boundary on May 21, 2018. We identify five consecutive quasi- periodic variations in the magnetic field, heavy ion flux, ion composition and density, and ion. velocity. The estimated period of the K-H waves is approximately 100 seconds. Furthermore, we observe magnetic flux rope structures within two of the K-H vortices. The axial direction of the magnetic flux rope is nearly perpendicular to the normal of the boundary layer, and its ion composition is similar to that of the ionospheric plasma within the vortices. This indicates that the magnetic flux rope in this region is likely formed during the development of Kelvin-Helmholtz waves. The overall velocity of the magnetic flux rope is much greater than the ion escape velocity in this region, which could result in the rapid escape of heavy ions O+ and Of from the Martian atmosphere.