Electrostatic Waves and Turbulent Plasma Mixing in the Kelvin-Helmholtz Instability at Earth
Abstract
The Kelvin-Helmholtz Instability (KHI) forms in response to flow shear at the flank magnetopause and is thought to be an important driver of mass and momentum transfer from the solar wind to the Earth's magnetosphere. Recent studies have suggested that magnetic reconnection and turbulence may play an important role in facilitating this mass and momentum transfer. We present observations from NASA's magnetospheric multi-scale mission of ion acoustic-like waves associated with these processes during the KHI interval on 8 September 2015. These parallel electrostatic waves are non-linear, can have amplitudes in excess of 100 mV/m, and may be associated with a field-aligned potential drop. We present detailed analysis of an example of these waves that suggests their growth might be due to a drift in the cold magnetospheric electron population. We show several examples of these waves, and demonstrate that they tend to occur in regions where hot magnetospheric ions are injected from below the spacecraft, which then mix with the magnetosheath plasma. We perform a survey of all vortices in the 8 September 2015 event, investigating the occurrence of electrostatic waves below the ion plasma frequency. We find that they tend to occur in the turbulent region in the middle of the KHI vortices, as opposed to on the compressed current sheets where reconnection is typically observed. They do not appear to associated with current sheets in the turbulent region either, which suggests they may be due to plasma mixing associated with distant reconnection events. These results are indicative that plasma mixing on multiple scales occurs throughout the equatorial KHI region. In addition - we show other KHI events observed by MMS at different positions along the magnetospheric flank, and discuss what is different about those events where the large amplitude parallel electrostatic waves are not observed.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1101W