Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spicules and downflows in the solar chromosphere   High-speed downflows have been observed in the solar transition region (TR)
and lower corona for many decades. Despite their abundance, it has been hard to
find signatures of such downflows in the solar chromosphere. In this work, we
target an enhanced network region that shows ample occurrences of rapid
spicular downflows in the \halpha\ spectral line that could potentially be
linked to high-speed TR downflowing counterparts. We used the $k$-means
algorithm to classify the spectral profiles of on-disk spicules in \halpha{}
and \cak{} data observed from the Swedish 1-m Solar Telescope (SST) and
employed an automated detection method based on advanced morphological image
processing operations to detect such downflowing features, in conjunction with
rapid blue-shifted and red-shifted excursions (RBEs and RREs). We report the
existence of a new category of RREs (termed as downflowing RRE) for the first
time that, contrary to earlier interpretation, are associated with
chromospheric field-aligned downflows moving towards the strong magnetic field
regions. Statistical analysis performed on nearly 20,000 RBEs and 15,000 RREs
(including the downflowing counterparts), detected in our 97~min long dataset,
shows that the downflowing RREs are very similar to RBEs and RREs except for
their oppositely directed plane-of-sky motion. Furthermore, we also find that
RBEs, RREs and downflowing RREs can be represented by a wide range of spectral
profiles with varying Doppler offsets, and \halpha{} line core widths, both
along and perpendicular to the spicule axis, that causes them to be associated
with multiple substructures that evolve together. We speculate that these rapid
plasma downflows could well be the chromospheric counterparts of the commonly
observed TR downflows.

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The categories of this paper are: adap-org
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The categories of this paper are: funct-an
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The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: physics
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The categories of this paper are: math-ph
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The categories of this paper are: cs
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: mtrl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat