Characteristics of Kelvin-Helmholtz Waves as Observed by the MMS from
September 2015 to March 2020
Abstract
The Magnetospheric Multiscale (MMS) mission has presented a new
opportunity to study the fine scale structures and phenomena of the
Earth’s magnetosphere, including cross scale processes associated with
the Kelvin-Helmholtz Instability (KHI), but such studies of the KHI and
its secondary processes will require a database of MMS encounters with
Kelvin-Helmholtz (KH) waves. Here we present an overview of 45 MMS
observations of the KHI from September 2015 to March 2020. Growth rates
and unstable solid angles for each of the 45 events were calculated
using a new technique to automatically detect plasma regions on either
side of the magnetopause boundary. There was no apparent correlation
between solar wind conditions during the KHI and its growth rate and
unstable solid angle, which is not surprising as KH waves were observed
downstream of their source region. We note all KHI were observed for
solar wind flow speeds between 295 km/s and 610 km/s, likely due to a
filtering effect of the instability onset criteria and plasma
compressibility. Two-dimensional Magnetohydrodynamic (2D MHD)
simulations were compared with two of the observed MMS events.
Comparison of the observations with the 2D MHD simulations indicates
that the new region sorting method is reliable and robust. The ability
to automatically detect separate plasma regions on either side of a
moving boundary and determine the KHI growth rate may prove useful for
future work identifying and studying secondary processes associated with
the KHI.