Observations of Kelvin‐Helmholtz Waves on Mercury's Pre‐Dawnside Magnetopause: MESSENGER Case Study

Kelvin‐Helmholtz (K‐H) waves are important in transporting mass, momentum, and energy across magnetic boundaries in space plasma. This study presents the observations of K‐H waves on Mercury's pre‐dawnside magnetopause, where more than 10 linear and non‐linear K‐H waveforms were identified. Adjacent to these waves, compressional ultra‐low frequency waves and ion‐Bernstein modes along with a proton distribution exhibiting a positive phase space density gradient were observed. These observations suggest that energy and mass are transported by the K‐H waves. However, during the same MESSENGER's orbit on the pre‐duskside magnetopause, only a few magnetopause oscillations were observed and there is no accompanied compressional waves and ion‐Bernstein modes. The differences might be attributed to that MESSENGER crossed the dusk magnetopause on the dayside, where K‐H waves may not have fully developed. Another possible reason might be due to the direction of the interplanetary magnetic field. When the quasi‐parallel bow shock is located on the dawnside, it generates a smaller tangential magnetic field in the magnetosheath, which allows K‐H waves to be more easily excited. Our findings provide new insights into occurrences and energy transport of K‐H waves in Mercury's magnetosphere.