MMS Observations of the Kelvin-Helmholtz Instability and Associated Ion Scale Waves

Author

Rachel C. RiceFollow

Date of Award

Spring 2022

Access Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Engineering Physics

Department

Physical Sciences

Committee Chair

Katariina Nykyri

First Committee Member

Peter Delamere

Second Committee Member

Kshitija Desphande

Third Committee Member

Xuanye Ma

Fourth Committee Member

Matthew Zettergren

Abstract

The detailed mechanisms coupling the solar wind to Earth's magnetosphere are not yet fully understood. Solar wind plasma is heated non-adiabatically as it penetrates the magnetosphere, and this process must span scale sizes. Reconnection alone is not able to account for the observed heating; other mechanisms must be at work. One potential process is the Kelvin-Helmholtz instability (KHI). The KHI is a convective instability which operates at the fluid scale in plasmas, but is capable of driving secondary process at smaller scales. Previous work has shown evidence of magnetic reconnection, various ion scale wave modes, mode conversion, and turbulence associated with the KHI, all of which can contribute to heating and/or plasma transport across the magnetopause boundary.

The launch of the Magnetosphere Multiscale (MMS) mission in 2015 offered a new opportunity to study secondary processes associated with the KHI down to the electron scale. The MMS mission's goal was to study the microphysics of magnetic reconnection at the dayside magnetopause and in the magnetotail. It comprises 4 identical spacecraft, which fly in formation and are equipped with the highest resolution instrumentation available. MMS is the first mission capable of resolving electron scale processes due to its combination of high temporal resolution instrumentation and its record breaking spacecraft separation. The work presented in this dissertation focuses on the fluid and ion scale behavior of the KHI as a proof of concept for the techniques used. Future work will apply these methods to smaller scales to fully take advantage of MMS's capabilities.

This work uses MMS observations of 45 KHI events between September 2015 and March 2020 to determine the influence of the KHI on magnetosphere dynamics and solar wind-magnetosphere coupling. The observed events are well distributed along the magnetopause, and occur for the full range of solar wind conditions and IMF orientations. The KHI growth rates and the percent of the solid angle unstable to the development of the KHI (which we term the unstable solid angle) are not effected by the solar wind conditions or IMF strength. The observed KHI grow more quickly and in more unstable regions the farther downtail they occur.

Ion scale wave intervals observed within the KHI are consistent with the ion cyclotron, kinetic Alfvén, and kinetic magnetosonic wave modes, all of which can contribute to enhanced ion heating across the magnetopause. These ion scale wave intervals are compared with observations made when the KHI is not active. The KHI is associated with strong increases in quasi-perpendicular (quasi-parallel) ion scale wave activity in the magnetosphere (magnetosheath), consistent with previous studies of data from the Cluster spacecraft. Observations show electron beta is decreased and ion temperature anisotropy is increased in the magnetosheath when the KHI is present, which can help explain a KHI associated increase in quasi-parallel wave activity in the sheath. Additionally, parallel velocity shears are increased when the KHI is active, which may further drive wave activity in all regions.

Ion scale wave intervals show enhanced Poynting flux in all regions and at all wave angles when the KHI is active, suggesting more energy is available to drive ion heating during the KHI. Increased Poynting flux is also well correlated with larger changes in energy during KH associated ion scale waves. The rate of heating, described by the characteristic heating frequency, also increases for ion scale waves associated with the KHI. These findings suggest that plasma heating is both increased and more efficient in the presence of the KHI.

Scholarly Commons Citation

Rice, Rachel C., "MMS Observations of the Kelvin-Helmholtz Instability and Associated Ion Scale Waves" (2022). Doctoral Dissertations and Master's Theses. 651.
https://commons.erau.edu/edt/651