Recent insights on the penumbra formation process. (arXiv:1901.05207v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Murabito_M/0/1/0/all/0/1">M. Murabito</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Romano_P/0/1/0/all/0/1">P.Romano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zuccarello_F/0/1/0/all/0/1">F. Zuccarello</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Guglielmino_S/0/1/0/all/0/1">S.L.Guglielmino</a>
Using high-resolution spectropolarimetric data acquired by textit{IBIS}, as
well as textit{SDO}/HMI observations, we studied the penumbra formation in AR
NOAA 11490 and in a sample of twelve ARs appeared on the solar disk on 2011 and
2012, which were characterized by $beta$-type magnetic field configuration.
The results show that the onset of the classical Evershed flow occurs in a very
short time scale, 1-3 hours. Studying the formation of the first penumbral
sector around the following proto-spot, we found that a stable penumbra forms
in the area facing the opposite polarity, which appears to be co-spatial with
an AFS, i.e. in a flux emergence region, in contrast with the results of
cite{Schlichenmaier2010} concerning the leading polarity of AR NOAA 11490.
Conversely, analyzing the sample of twelve ARs, we noticed that there is not a
preferred location for the formation of the first penumbral sector. We also
observed before the penumbra formation an inverse Evershed flow, which changes
its sign when the penumbra appears. This confirms the observational evidence
that the appearance of the penumbral filaments is correlated with the
transition from the inverse Evershed to the classical Evershed flow.
Furthermore, the analysis suggests that the time needed to form the penumbra
may be related to the location where the penumbra first appears. New
high-resolution observations, like those that will be provided by the European
Solar Telescope, are expected to increase our understanding of the penumbra
formation process.
Using high-resolution spectropolarimetric data acquired by textit{IBIS}, as
well as textit{SDO}/HMI observations, we studied the penumbra formation in AR
NOAA 11490 and in a sample of twelve ARs appeared on the solar disk on 2011 and
2012, which were characterized by $beta$-type magnetic field configuration.
The results show that the onset of the classical Evershed flow occurs in a very
short time scale, 1-3 hours. Studying the formation of the first penumbral
sector around the following proto-spot, we found that a stable penumbra forms
in the area facing the opposite polarity, which appears to be co-spatial with
an AFS, i.e. in a flux emergence region, in contrast with the results of
cite{Schlichenmaier2010} concerning the leading polarity of AR NOAA 11490.
Conversely, analyzing the sample of twelve ARs, we noticed that there is not a
preferred location for the formation of the first penumbral sector. We also
observed before the penumbra formation an inverse Evershed flow, which changes
its sign when the penumbra appears. This confirms the observational evidence
that the appearance of the penumbral filaments is correlated with the
transition from the inverse Evershed to the classical Evershed flow.
Furthermore, the analysis suggests that the time needed to form the penumbra
may be related to the location where the penumbra first appears. New
high-resolution observations, like those that will be provided by the European
Solar Telescope, are expected to increase our understanding of the penumbra
formation process.
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