We present a comprehensive statistical analysis of 106 sheath regions driven
by coronal mass ejections (CMEs) and measured near 1 AU. Using data from the
STEREO probes, this extended analysis focuses on two discrete categorizations.
In the first categorization, we investigate how the generic features of sheaths
change with their potential formation mechanisms (propagation and expansion
sheaths), namely, their associations with magnetic ejectas (MEs) which are
primarily expanding or propagating in the solar wind. We find propagation
sheaths to be denser and driven by stronger MEs, whereas expansion sheaths are
faster. Exploring the temporal profiles of these sheaths with a superposed
epoch technique, we observe that most of the magnetic field and plasma
signatures are more elevated in propagation sheaths relative to expansion
sheaths. The second categorization is based on speed variations across sheaths.
Employing linear least squares regression, we categorize four distinct speed
profiles of the sheath plasma. We find that the associated shock properties and
solar cycle phase do not impact the occurrence of such variations. Our results
also highlight that the properties of the driving MEs are a major source of
variability in the sheath properties. Through logistic regression, we conclude
that the magnetic field strength and the ME speed in the frame of the solar
wind are likely drivers of these speed variations.
