Kelvin-Helmholtz Instability Observations on Mercury’s magnetopause: MESSENGER Study

Kelvin-Helmholtz (K-H) instability plays an important role in transporting mass, momentum and energy at the magnetopause of planetary magnetospheres. Previous studies have shown that the K-H waves on Mercury’s magnetosphere exhibit clear dawn-dusk asymmetry, i.e., they are frequently observed on the duskside magnetopause but rarely on the dawnside. In this presentation, we first present a case study of K-H waves on the dawnside of Mercury’s magnetosphere and a  statistical study of K-H waves from 2014 to 2015 based on MSEEENGER’s observations.

In the case study, the K-H waveforms on the dawnside side were divided into linear waves and nonlinear waves by modeling the magnetopause as Harris current sheet. The 30mHz compressional ultra-low-frequency waves and ion-Bernstein modes were observed in the magnetosphere adjacent to these K-H waves, which are interpreted as the evidence of energy and mass transport by K-H waves. However, only a few magnetopause oscillations were observed on the duskside during the same MESSENGER’s orbit under similar interplanetary magnetic field conditions. No compressional waves or ion-Berstein modes were observed associated with these oscillations. 

Our statistical study found that K-H waves were equably prevalent on both the dawnside and duskside, which are different from the previously reported dawn-dusk asymmetry. We categorized our cases into linear and nonlinear stages and analyzed their interplanetary magnetic field conditions. Our results provide  insights into the study of K-H instability at Mercury, especially the mechanism of asymmetry and transport of plasma and energy.