Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Supersonic Downflows at the Umbra-Penumbra Boundary of Sunspots   High resolution spectropolarimetric observations of 3 sunspots taken with
Hinode demonstrate the existence of supersonic downflows at or close to the
umbra-penumbra boundary which have not been reported before. These downflows
are confined to large patches, usually encompassing bright penumbral filaments,
and have lifetimes of more than 14 hr. The presence of strong downflows in the
center-side penumbra near the umbra rules out an association with the Evershed
flow. Chromospheric filtergrams acquired close to the time of the
spectropolarimetric measurements show large, strong, and long-lived
brightenings in the neighborhood of the downflows. The photospheric intensity
also exhibit persistent brightenings comparable to the quiet Sun.
Interestingly, the orientation of the penumbral filaments at the site of the
downflows is similar to that resulting from the reconnection process described
by Ryutova et al. The existence of such downflows in the inner penumbra
represents a challenge for numerical models of sunspots because they have to
explain them in terms of physical processes likely affecting the chromosphere.

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The categories of this paper are: hep-ex
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The categories of this paper are: cs
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The categories of this paper are: solv-int
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The categories of this paper are: quant-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: math
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The categories of this paper are: hep-th
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The categories of this paper are: gr-qc
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
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The categories of this paper are: funct-an
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The categories of this paper are: econ
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The categories of this paper are: ao-sci
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin
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The categories of this paper are: supr-con