Exploring He II 304 Å Spicules and Macrospicules at the Solar Limb

Abstract:

We present results from a study of He II 304 Ang spicules and macrospicules
observed at the limb of the Sun in 304 Ang channel image sequences from the
Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). These
data have both high spatial (0.6 arcsec pixels) and temporal (12 s) resolution.
All of the observed events occurred in quiet or coronal hole regions near the solar
pole. He II 304 Ang spicules and macrospicules are both transient jet-like
features, with the macrospicules being wider and having taller maximum heights than
the spicules. We looked for characteristics of the populations of these two
phenomena that might indicate whether they have the same initiation mechanisms. We
examine the maximum heights, time-averaged rise velocities, and lifetimes of about
30 spicules and about five macrospicules. For the spicules, these quantities are,
respectively, ~10,000----40,000 km, 20---100 km/s, and a few 100--- ~600 sec. For
the macrospicules the corresponding properties are >~60,000 km, >~55 km/s, and
lifetimes of >~1800 sec. Therefore the macrospicules have velocities comparable to
those of the fastest spicules and live longer than the spicules. The leading-edge
trajectories of both the spicules and the macrospicules match well a second-order
(``parabolic'') profile, although the acceleration in the fitted profiles is
generally weaker than that of solar gravity. The macrospicules also have obvious
brightenings at their bases at their birth, while such brightenings are not
apparent for most of the spicules. Our findings are suggestive of the two
phenomena possibly having different initiation mechanisms, but this is not yet
conclusive. A.C.S. and R.L.M. were supported by funding from the Heliophysics
Division of NASA's Science Mission Directorate through the Living With a Star
Targeted Research and Technology Program, and the Hinode Project. I.R.S. was
supported by NSF's Research Experience for Undergraduates Program.