Author name code: sekse
ADS astronomy entries on 2022-09-14
author:"Sekse, Dan Henrik"
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Title: Interplay of Three Kinds of Motion in the Disk Counterpart
of Type II Spicules: Upflow, Transversal, and Torsional Motions
Authors: Sekse, D. H.; Rouppe van der Voort, L.; De Pontieu, B.;
Scullion, E.
Bibcode: 2013ApJ...769...44S
Altcode: 2013arXiv1304.2304S
Recently, it was shown that the complex dynamical behavior of spicules
has to be interpreted as the result of simultaneous action of three
kinds of motion: (1) field aligned flows, (2) swaying motions, and
(3) torsional motions. We use high-quality observations from the
CRisp Imaging SpectroPolarimeter at the Swedish 1-m Solar Telescope
to investigate signs of these different kinetic modes in spicules on
the disk. Earlier, rapid blue-shifted excursions (RBEs), short-lived
absorption features in the blue wing of chromospheric spectral lines,
were identified as the disk counterpart of type II spicules. Here we
report the existence of similar absorption features in the red wing of
the Ca II 8542 and Hα lines: rapid redshifted excursions (RREs). RREs
are found over the whole solar disk and are located in the same regions
as RBEs: in the vicinity of magnetic field concentrations. RREs have
similar characteristics as RBEs: they have similar lengths, widths,
lifetimes, and average Doppler velocity. The striking similarity
of RREs to RBEs implies that RREs are a manifestation of the same
physical phenomenon and that spicules harbor motions that can result
in a net redshift when observed on-disk. We find that RREs are less
abundant than RBEs: the RRE/RBE detection count ratio is about 0.52
at disk center and 0.74 near the limb. We interpret the higher number
of RBEs and the decreased imbalance toward the limb as an indication
that field-aligned upflows have a significant contribution to the
net Dopplershift of the structure. Most RREs and RBEs are observed in
isolation, but we find many examples of parallel and touching RRE/RBE
pairs which appear to be part of the same spicule. We interpret the
existence of these RRE/RBE pairs and the observation that many RREs
and RBEs have varying Dopplershift along their width as signs that
torsional motion is an important characteristic of spicules. The fact
that most RBEs and RREs are observed in isolation agrees with the idea
that transversal swaying motion is another important kinetic mode. We
find examples of transitions from RRE to RBE and vice versa. These
transitions sometimes appear to propagate along the structure with
speeds between 18 and 108 km s-1 and can be interpreted as
the sign of a transverse (Alfvénic) wave.
Title: On the Temporal Evolution of the Disk Counterpart of Type II
Spicules in the Quiet Sun
Authors: Sekse, D. H.; Rouppe van der Voort, L.; De Pontieu, B.
Bibcode: 2013ApJ...764..164S
Altcode: 2012arXiv1212.4988S
The newly established type II spicule has been speculated to provide
enough hot plasma to play an important role in the mass loading
and heating of the solar corona. With the identification of rapid
blueshifted excursions (RBEs) as the on-disk counterpart of type II
spicules we have analyzed three different high-quality timeseries
with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish
Solar Telescope on La Palma and subjected to an automated detection
routine to detect a large number of RBEs for statistical purposes. Our
observations are of a quiet-Sun region at disk center and we find
lower Doppler velocities, 15-40 km s-1, and Doppler widths,
2-15 km s-1, of RBEs than in earlier coronal hole studies,
30-50 km s-1 and 7-23 km s-1, respectively. In
addition, we examine the spatial dependence of Doppler velocities and
widths along the RBE axis and conclude that there is no clear trend to
this over the field of view or in individual RBEs in the quiet Sun at
disk center. These differences with previous coronal hole studies are
attributed to the more varying magnetic field configuration in quiet-Sun
conditions. Using an extremely high-cadence data set has allowed us
to improve greatly on the determination of lifetimes of RBEs, which we
find to range from 5 to 60 s with an average lifetime of 30 s, as well
as the transverse motions in RBEs, with transverse velocities up to
55 km s-1 and averaging 12 km s-1. Furthermore,
our measurements of the recurrence rates of RBEs provide important
new constraints on coronal heating by spicules. We also see many
examples of a sinusoidal wave pattern in the transverse motion of
RBEs with periods averaging 54 s and amplitudes from 21.5 to 129 km
which agrees well with previous studies of wave motion in spicules at
the limb. We interpret the appearance of RBEs over their full length
within a few seconds as the result of a combination of three kinds
of motions as is earlier reported for spicules. Finally, we look at
the temporal connection between Hα and Ca II 8542 RBEs and find that
Ca II 8542 RBEs in addition to being located closer to the footpoint
also appear before the Hα RBEs. This connection between Ca II 8542
and Hα supports the idea that heating is occurring in spicules and
contributes more weight to the prominence of spicules as a source for
heating and mass loading of the corona.
Title: An in-depth study of the on-disc counterpart to type II
spicules
Authors: Sekse, Dan Henrik
Bibcode: 2013PhDT.......717S
Altcode:
No abstract at ADS
Title: Statistical Properties of the Disk Counterparts of Type
II Spicules from Simultaneous Observations of Rapid Blueshifted
Excursions in Ca II 8542 and Hα
Authors: Sekse, D. H.; Rouppe van der Voort, L.; De Pontieu, B.
Bibcode: 2012ApJ...752..108S
Altcode: 2012arXiv1204.2943S
Spicules were recently found to exist as two different types when a new
class of so-called type II spicules was discovered at the solar limb
with the Solar Optical Telescope on board the Hinode spacecraft. These
type II spicules have been linked with on-disk observations of rapid
blueshifted excursions (RBEs) in the Hα and Ca II 8542 lines. Here
we analyze observations optimized for the detection of RBEs in both
Hα and Ca II 8542 lines simultaneously at a high temporal cadence
taken with the Crisp Imaging Spectropolarimeter at the Swedish Solar
Telescope on La Palma. In this study, we used a high-quality time
sequence for RBEs at different blueshifts and employed an automated
detection routine to detect a large number of RBEs in order to expand
on the statistics of RBEs. We find that the number of detected RBEs
is strongly dependent on the associated Doppler velocity of the images
on which the search is performed. Automatic detection of RBEs at lower
velocities increases the estimated number of RBEs to the same order of
magnitude expected from limb spicules. This shows that RBEs and type
II spicules are indeed exponents of the same phenomenon. Furthermore,
we provide solid evidence that Ca II 8542 RBEs are connected to Hα
RBEs and are located closer to the network regions with the Hα RBEs
being a continuation of the Ca II 8542 RBEs. Our results show that
RBEs have an average lifetime of 83.9 s when observed in both spectral
lines and that the Doppler velocities of RBEs range from 10 to 25 km
s-1 in Ca II 8542 and 30 to 50 km s-1 in Hα. In
addition, we automatically determine the transverse motion of a much
larger sample of RBEs than previous studies, and find that, just like
type II spicules, RBEs undergo significant transverse motions of the
order of 5-10 km s-1. Finally, we find that the intergranular
jets discovered at Big Bear Solar Observatory are a subset of RBEs.