8,507 research outputs found
RADYN simulations of non-thermal and thermal models of Ellerman bombs
Ellerman bombs (EBs) are brightenings in the H line wings that are
believed to be caused by magnetic reconnection in the lower atmosphere. To
study the response and evolution of the chromospheric line profiles, we perform
radiative hydrodynamic simulations of EBs using both non-thermal and thermal
models. Overall, these models can generate line profiles that are similar to
observations. However, in non-thermal models we find dimming in the H
line wings and continuum when the heating begins, while for the thermal models
dimming occurs only in the H line core, and with a longer lifetime.
This difference in line profiles can be used to determine whether an EB is
dominated by non-thermal heating or thermal heating. In our simulations, if a
higher heating rate is applied, the H line will be unrealistically
strong, while there are still no clear UV burst signatures.Comment: 20 pages, 9 figures, accepted for publication in Ap
Parallel Mapper
The construction of Mapper has emerged in the last decade as a powerful and
effective topological data analysis tool that approximates and generalizes
other topological summaries, such as the Reeb graph, the contour tree, split,
and joint trees. In this paper, we study the parallel analysis of the
construction of Mapper. We give a provably correct parallel algorithm to
execute Mapper on multiple processors and discuss the performance results that
compare our approach to a reference sequential Mapper implementation. We report
the performance experiments that demonstrate the efficiency of our method
The Theory of the Interleaving Distance on Multidimensional Persistence Modules
In 2009, Chazal et al. introduced -interleavings of persistence
modules. -interleavings induce a pseudometric on (isomorphism
classes of) persistence modules, the interleaving distance. The definitions of
-interleavings and generalize readily to multidimensional
persistence modules. In this paper, we develop the theory of multidimensional
interleavings, with a view towards applications to topological data analysis.
We present four main results. First, we show that on 1-D persistence modules,
is equal to the bottleneck distance . This result, which first
appeared in an earlier preprint of this paper, has since appeared in several
other places, and is now known as the isometry theorem. Second, we present a
characterization of the -interleaving relation on multidimensional
persistence modules. This expresses transparently the sense in which two
-interleaved modules are algebraically similar. Third, using this
characterization, we show that when we define our persistence modules over a
prime field, satisfies a universality property. This universality result
is the central result of the paper. It says that satisfies a stability
property generalizing one which is known to satisfy, and that in
addition, if is any other pseudometric on multidimensional persistence
modules satisfying the same stability property, then . We also show
that a variant of this universality result holds for , over arbitrary
fields. Finally, we show that restricts to a metric on isomorphism
classes of finitely presented multidimensional persistence modules.Comment: Major revision; exposition improved throughout. To appear in
Foundations of Computational Mathematics. 36 page
The Effects of Spatio-temporal Resolution on Deduced Spicule Properties
Spicules have been observed on the sun for more than a century, typically in
chromospheric lines such as H-alpha and Ca II H. Recent work has shown that
so-called 'type II' spicules may have a role in providing mass to the corona
and the solar wind. In chromospheric filtergrams these spicules are not seen to
fall back down, and they are shorter-lived and more dynamic than the spicules
that have been classically reported in ground-based observations. Observations
of type II spicules with Hinode show fundamentally different properties from
what was previously measured. In earlier work we showed that these dynamic type
II spicules are the most common type, a view that was not properly identified
by early observations.The aim of this work is to investigate the effects of
spatio-temporal resolution in the classical spicule measurements. Making use of
Hinode data degraded to match the observing conditions of older ground-based
studies, we measure the properties of spicules with a semi-automated algorithm.
These results are then compared to measurements using the original Hinode data.
We find that degrading the data has a significant effect on the measured
properties of spicules. Most importantly, the results from the degraded data
agree well with older studies (e.g. mean spicule duration more than 5 minutes,
and upward apparent velocities of about 25 km/s). These results illustrate how
the combination of spicule superposition, low spatial resolution and cadence
affect the measured properties of spicules, and that previous measurements can
be misleading.Comment: Accepted for publication in ApJ. 5 pages, 3 figures. Movies of
figures 1 and 3 available via Data Conservanc
Non-LTE Calculations of the Fe I 6173 {\AA} Line in a Flaring Atmosphere
The Fe I 6173 {\AA} line is widely used in the measurements of vector
magnetic fields by instruments including the Helioseismic and Magnetic Imager
(HMI). We perform non-local thermodynamic equilibrium calculations of this line
based on radiative hydrodynamic simulations in a flaring atmosphere. We employ
both a quiet-Sun atmosphere and a penumbral atmosphere as the initial one in
our simulations. We find that, in the quiet-Sun atmosphere, the line center is
obviously enhanced during an intermediate flare. The enhanced emission is
contributed from both radiative backwarming in the photosphere and particle
beam heating in the lower chromosphere. A blue asymmetry of the line profile
also appears due to an upward mass motion in the lower chromosphere. If we take
a penumbral atmosphere as the initial atmosphere, the line has a more
significant response to the flare heating, showing a central emission and an
obvious asymmetry. The low spectral resolution of HMI would indicate some loss
of information but the enhancement and line asymmetry are still kept. By
calculating polarized line profiles, we find that the Stokes I and V profiles
can be altered as a result of flare heating. Thus the distortion of this line
has a crucial influence on the magnetic field measured from this line, and one
should be cautious in interpreting the magnetic transients observed frequently
in solar flares.Comment: 12 pages, 5 figures, accepted by ApJ
The Formation of IRIS diagnostics. IV. The Mg II triplet lines as a new diagnostic for lower chromospheric heating
A triplet of subordinate lines of Mg II exists in the region around the h&k
lines. In solar spectra these lines are seen mostly in absorption, but in some
cases can become emission lines. The aim of this work is to study the formation
of this triplet, and investigate any diagnostic value they can bring. Using 3D
radiative magnetohydrodynamic simulations of quiet Sun and flaring flux
emergence, we synthesize spectra and investigate how spectral features respond
to the underlying atmosphere. We find that emission in the lines is rare and is
typically caused by a steep temperature increase in the lower chromosphere
(above 1500 K, with electron densities above 10 m). In both
simulations the lines are sensitive to temperature increases taking place at
column masses >= 5e-4 g cm. Additional information can also be inferred
from the peak-to-wing ratio and shape of the line profiles. Using observations
from NASA's Interface Region Imaging Spectrograph we find both absorption and
emission line profiles with similar shapes to the synthetic spectra, which
suggests that these lines represent a useful diagnostic that complements the
MgII h&k lines.Comment: 8 pages, 7 figures. Accepted for publication in Ap
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