5,124 research outputs found
Evolution of small-scale magnetic elements in the vicinity of granular-size swirl convective motions
Advances in solar instrumentation have led to a widespread usage of time
series to study the dynamics of solar features, specially at small spatial
scales and at very fast cadences. Physical processes at such scales are
determinant as building blocks for many others occurring from the lower to the
upper layers of the solar atmosphere and beyond, ultimately for understanding
the bigger picture of solar activity. Ground-based (SST) and space-borne
(Hinode) high-resolution solar data are analyzed in a quiet Sun region
displaying negative polarity small-scale magnetic concentrations and a cluster
of bright points observed in G-band and Ca II H images. The studied region is
characterized by the presence of two small-scale convective vortex-type plasma
motions, one of which appears to be affecting the dynamics of both, magnetic
features and bright points in its vicinity and therefore the main target of our
investigations. We followed the evolution of bright points, intensity
variations at different atmospheric heights and magnetic evolution for a set of
interesting selected regions. A description of the evolution of the
photospheric plasma motions in the region nearby the convective vortex is
shown, as well as some plausible cases for convective collapse detected in
Stokes profiles.Comment: 9 figure
Granular-Scale Elementary Flux Emergence Episodes in a Solar Active Region
We analyze data from Hinode spacecraft taken over two 54-minute periods
during the emergence of AR 11024. We focus on small-scale portions within the
observed solar active region and discover the appearance of very distinctive
small-scale and short-lived dark features in Ca II H chromospheric filtergrams
and Stokes I images. The features appear in regions with close-to-zero
longitudinal magnetic field, and are observed to increase in length before they
eventually disappear. Energy release in the low chromospheric line is detected
while the dark features are fading. In time series of magnetograms a diverging
bipolar configuration is observed accompanying the appearance of the dark
features and the brightenings. The observed phenomena are explained as
evidencing elementary flux emergence in the solar atmosphere, i.e small-scale
arch filament systems rising up from the photosphere to the lower chromosphere
with a length scale of a few solar granules. Brightenings are explained as
being the signatures of chromospheric heating triggered by reconnection of the
rising loops (once they reached chromospheric heights) with pre-existing
magnetic fields as well as to reconnection/cancellation events in U-loop
segments of emerging serpentine fields. We study the temporal evolution and
dynamics of the events and compare them with the emergence of magnetic loops
detected in quiet sun regions and serpentine flux emergence signatures in
active regions. Incorporating the novel features of granular-scale flux
emergence presented in this study we advance the scenario for serpentine flux
emergence.Comment: 24 pages, 9 figures. Accepted for publication in Solar Physic
Photospheric plasma and magnetic field dynamics during the formation of solar AR 11190
The Sun features on its surface typical flow patterns called the granulation,
mesogranulation, and supergranulation. These patterns arise due to convective
flows transporting energy from the interior of the Sun to its surface. In this
paper we will shed light on the interaction between the convective flows in
large-scale cells as well as the large-scale magnetic fields in active regions,
and investigate in detail the statistical distribution of flow velocities
during the evolution and formation of National Oceanic and Atmospheric
Administration (NOAA) active region 11190. To do so, we employed local
correlation tracking methods on data obtained by the Solar Dynamics Observatory
(SDO) spacecraft in the continuum as well as on processed line-of-sight (LOS)
magnetograms. We find that the flow fields in an active region can be modelled
by a two-component distribution. One component is very stable, follows a
Rayleigh distribution, and can be assigned to the background flows, whilst the
other component is variable in strength and velocity range and can be
attributed to the flux emergence visible both in the continuum maps as well as
magnetograms. Generally, the plasma flows, as seen by the distribution of the
magnitude of the velocity, follow a Rayleigh distribution even through the time
of formation of active regions. However, at certain moments of large-scale fast
flux emergence, a second component featuring higher velocities is formed in the
velocity magnitudes distribution. The plasma flows are generally highly
correlated to the motion of magnetic elements and vice versa except during the
times of fast magnetic flux emergence as observed by rising magnetic elements.
At these times, the magnetic fields are found to move faster than the
corresponding plasma.Comment: 15 pages, 11 figures, 5 equations. Accepted for publication in
Astronomy and Astrophysics (A&A
Twisting solar coronal jet launched at the boundary of an active region
A broad jet was observed in a weak magnetic field area at the edge of active
region NOAA 11106. The peculiar shape and magnetic environment of the broad jet
raised the question of whether it was created by the same physical processes of
previously studied jets with reconnection occurring high in the corona. We
carried out a multi-wavelength analysis using the EUV images from the
Atmospheric Imaging Assembly (AIA) and magnetic fields from the Helioseismic
and Magnetic Imager (HMI) both on-board the SDO satellite. The jet consisted of
many different threads that expanded in around 10 minutes to about 100 Mm in
length, with the bright features in later threads moving faster than in the
early ones, reaching a maximum speed of about 200 km s^{-1}. Time-slice
analysis revealed a striped pattern of dark and bright strands propagating
along the jet, along with apparent damped oscillations across the jet. This is
suggestive of a (un)twisting motion in the jet, possibly an Alfven wave. A
topological analysis of an extrapolated field was performed. Bald patches in
field lines, low-altitude flux ropes, diverging flow patterns, and a null point
were identified at the basis of the jet. Unlike classical lambda or
Eiffel-tower shaped jets that appear to be caused by reconnection in current
sheets containing null points, reconnection in regions containing bald patches
seems to be crucial in triggering the present jet. There is no observational
evidence that the flux ropes detected in the topological analysis were actually
being ejected themselves, as occurs in the violent phase of blowout jets;
instead, the jet itself may have gained the twist of the flux rope(s) through
reconnection. This event may represent a class of jets different from the
classical quiescent or blowout jets, but to reach that conclusion, more
observational and theoretical work is necessary.Comment: 12 pages, 9 figures, accepted for publication in A&
Flare Energy Release in the Lower Solar Atmosphere Near the Magnetic Field Polarity Inversion Line
We study flare processes in the solar atmosphere using observational data for
a M1-class flare of June 12, 2014, obtained by New Solar Telescope (NST/BBSO)
and Helioseismic Magnetic Imager (HMI/SDO). The main goal is to understand
triggers and manifestations of the flare energy release in the photosphere and
chromosphere using high-resolution optical observations and magnetic field
measurements. We analyze optical images, HMI Dopplergrams and vector
magnetograms, and use Non-Linear Force-Free Field (NLFFF) extrapolations for
reconstruction of the magnetic topology and electric currents. The NLFFF
modelling reveals interaction of two magnetic flux ropes with oppositely
directed magnetic field in the PIL. These flux ropes are observed as a compact
sheared arcade along the PIL in the high-resolution broad-band continuum images
from NST. In the vicinity of PIL, the NST H alpha observations reveal formation
of a thin three-ribbon structure corresponding to a small-scale photospheric
magnetic arcade. The observational results evidence in favor of location of the
primary energy release site in the chromospheric plasma with strong electric
currents concentrated near the polarity inversion line. In this case, magnetic
reconnection is triggered by the interacting magnetic flux ropes forming a
current sheet elongated along the PIL.Comment: arXiv admin note: substantial text overlap with arXiv:1604.0538
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