552 research outputs found
Satellite observations of reconnection between emerging and pre-existing small-scale magnetic fields
We report multi-wavelength ultraviolet observations taken with the IRIS
satellite, concerning the emergence phase in the upper chromosphere and
transition region of an emerging flux region (EFR) embedded in the unipolar
plage of active region NOAA 12529. The photospheric configuration of the EFR is
analyzed in detail benefitting from measurements taken with the
spectropolarimeter aboard the Hinode satellite, when the EFR was fully
developed. In addition, these data are complemented by full-disk, simultaneous
observations of the SDO satellite, relevant to the photosphere and the corona.
In the photosphere, magnetic flux emergence signatures are recognized in the
fuzzy granulation, with dark alignments between the emerging polarities,
cospatial with highly inclined fields. In the upper atmospheric layers, we
identify recurrent brightenings that resemble UV bursts, with counterparts in
all coronal passbands. These occur at the edges of the EFR and in the region of
the arch filament system (AFS) cospatial to the EFR. Jet activity is also found
at chromospheric and coronal levels, near the AFS and the observed brightness
enhancement sites. The analysis of the IRIS line profiles reveals the heating
of dense plasma in the low solar atmosphere and the driving of bi-directional
high-velocity flows with speeds up to 100 km/s at the same locations.
Furthermore, we detect a correlation between the Doppler velocity and line
width of the Si IV 1394 and 1402 \AA{} line profiles in the UV burst pixels and
their skewness. Comparing these findings with previous observations and
numerical models, we suggest evidence of several long-lasting, small-scale
magnetic reconnection episodes between the emerging bipole and the ambient
field. This process leads to the cancellation of a pre-existing photospheric
flux concentration of the plage with the opposite polarity flux patch of the
EFR. [...]Comment: 4 pages, 2 figures, to be published in "Nuovo Cimento C" as
proceeding of the Third Meeting of the Italian Solar and Heliospheric
Communit
Height dependence of the penumbral fine-scale structure in the inner solar atmosphere
We studied the physical parameters of the penumbra in a large and
fully-developed sunspot, one of the largest over the last two solar cycles, by
using full-Stokes measurements taken at the photospheric Fe I 617.3 nm and
chromospheric Ca II 854.2 nm lines with the Interferometric Bidimensional
Spectrometer. Inverting measurements with the NICOLE code, we obtained the
three-dimensional structure of the magnetic field in the penumbra from the
bottom of the photosphere up to the middle chromosphere. We analyzed the
azimuthal and vertical gradient of the magnetic field strength and inclination.
Our results provide new insights on the properties of the penumbral magnetic
fields in the chromosphere at atmospheric heights unexplored in previous
studies. We found signatures of the small-scale spine and intra-spine structure
of both the magnetic field strength and inclination at all investigated
atmospheric heights. In particular, we report typical peak-to-peak variations
of the field strength and inclination of G and , respectively, in the photosphere, and of G and
in the chromosphere. Besides, we estimated the vertical
gradient of the magnetic field strength in the studied penumbra: we find a
value of G km between the photosphere and the middle
chromosphere. Interestingly, the photospheric magnetic field gradient changes
sign from negative in the inner to positive in the outer penumbra.Comment: 14 page, 9 figures, accepted for Ap
Recent insights on 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 -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.Comment: 3 pages, 2 figures, to be published in "Nuovo Cimento C" as
proceeding of the Third Meeting of the Italian Solar and Heliospheric
Communit
Restoring process of sunspot penumbra
We describe the disappearance of a sector of sunspot penumbra and its
restoring process observed in the preceding sunspot of active region NOAA
12348. The evolution of the magnetic field and the plasma flows support the
idea that the penumbra forms due to a change of inclination of the magnetic
field of the canopy. Moving magnetic features have been observed during the
disintegration phase of that sector of sunspot penumbra. During the restoring
phase we have not observed any magnetic flux emergence around the sunspot. The
restoring process of the penumbra sector completed in about 72 hours and it was
accompanied by the transition from the counter-Evershed flow to the classical
Evershed flow. The inversion of photospheric spectropolarimetric measurements
taken by IBIS allowed us to reconstruct how the uncombed configuration of the
magnetic field forms during the new settlement of the penumbra, i.e., the
vertical component of the magnetic field seems to be progressively replaced by
some horizontal field lines, corresponding to the intra-spines.Comment: 34 pages, 11 figures, accepted for Ap
Re-identification of objects from aerial photos with hybrid siamese neural networks
In this paper, we consider the task of re-identifying the same object in different photos taken from separate positions and angles during aerial reconnaissance, which is a crucial task for the maintenance and surveillance of critical large-scale infrastructure. To effectively hybridize deep neural networks with available domain expertise for a given scenario, we propose a customized pipeline, wherein a domain-dependent object detector is trained to extract the assets (i.e., sub-components) present on the objects, and a siamese neural network learns to re-identify the objects, exploiting both visual features (i.e., the image crops corresponding to the assets) and the graphs describing the relations among their constituting assets. We describe a real-world application concerning the re-identification of electric poles in the Italian energy grid, showing our pipeline to significantly outperform siamese networks trained from visual information alone. We also provide a series of ablation studies of our framework to underline the effect of including topological asset information in the pipeline, learnable positional embeddings in the graphs, and the effect of different types of graph neural networks on the final accuracy
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