Abstract
Using Magnetospheric Multiscale (MMS) data, we find, classify and
analyze transient dynamic pressure enhancements in the magnetosheath
(jets) from May 2015 until May 2019. A classification algorithm is
presented, using in-situ MMS data to classify jets (n = 8499) into
different categories according to their associated angle between IMF and
the bow shock normal vector ( θ ). Jets appearing for θ < 45°
are referred to as quasi-parallel, while jets appearing for θ
> 45° as quasi-perpendicular jets. Furthermore, we define
those jets that occur at the boundaries between quasi-parallel and
quasi-perpendicular magnetosheath as boundary jets. Finally,
encapsulated jets are jet-like structures with similar characteristics
to quasi-parallel jets while the surrounding plasma is of
quasi-perpendicular nature. We present the first statistical results of
such a classification and provide comparative statistics for each class.
Furthermore, we investigate correlations between jet quantities.
Quasi-parallel jets have the highest dynamic pressure while occurring
more often than quasi-perpendicular jets. The infrequent
quasi-perpendicular jets, have a much smaller duration, velocity, and
density and are therefore relatively weaker. We conclude that
quasi-parallel and boundary jets have similar properties and are
unlikely to originate from different generation mechanisms. Regarding
the encapsulated jets, we suggest that they are a special subset of
quasi-parallel jets originating from the flanks of the bow shock, for
large IMF cone angles although a relation to FTEs and magnetospheric
plasma is also possible. Our results support existing generation
theories, such as the bow shock ripple and SLAMS-associated mechanisms
while indicating that other factors may contribute as well.