Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evolution of the flow field in decaying active regions, Transition from
  a moat flow to a supergranular flow   We investigate the evolution of the horizontal flow field around sunspots
during their decay by analysing its extension and horizontal velocity around
eight spots using SDO/HMI Doppler maps. By assuming a radially symmetrical flow
field, the applied analysis method determines the radial dependence of the
azimuthally averaged flow field. For comparison, we studied the flow in
supergranules using the same technique. All investigated, fully fledged
sunspots are surrounded by a flow field whose horizontal velocity profile
decreases continuously from 881 m s$^{-1}$ at 1.1 Mm off the spot boundary,
down to 199 m s$^{-1}$ at a mean distance of 11.9 Mm to that boundary. Once the
penumbra is fully dissolved, however, the velocity profile of the flow changes:
The horizontal velocity increases with increasing distance to the spot boundary
until a maximum value of about 398 m s$^{-1}$ is reached. Then, the horizontal
velocity decreases for farther distances to the spot boundary. In
supergranules, the horizontal velocity increases with increasing distance to
their centre up to a mean maximum velocity of 355 m s$^{-1}$. For larger
distances, the horizontal velocity decreases. We thus find that the velocity
profile of naked sunspots resembles that of supergranular flows. The evolution
of the flow field around individual sunspots is influenced by the way the
sunspot decays and by the interplay with the surrounding flow areas.
Observations of the flow around eight decaying sunspots suggest that as long as
penumbrae are present, sunspots with their moat cell are embedded in network
cells. The disappearance of the penumbra (and consequently the moat flow) and
the competing surrounding supergranular cells, both have a significant role in
the evolution of the flow field: The moat cell transforms into a supergranule,
which hosts the remaining naked spot.

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The categories of this paper are: hep-lat
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The categories of this paper are: cs
30
The categories of this paper are: q-alg
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: q-fin
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess
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The categories of this paper are: math-ph
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The categories of this paper are: econ
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The categories of this paper are: comp-gas
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The categories of this paper are: gr-qc
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The categories of this paper are: chao-dyn
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The categories of this paper are: quant-ph