2,125 research outputs found
Magnetic field variations associated with umbral flashes and penumbral waves
Umbral flashes (UF) and running penumbral waves (RPWs) in sunspot
chromospheres leave a dramatic imprint in the intensity profile of the Ca II
854.2 nm line. Recent studies have focussed on also explaining the observed
polarization profiles, that show even more dramatic variations during the
passage of these shock fronts. While most of these variations can be explained
with an almost constant magnetic field as a function of time, several studies
have reported changes in the inferred magnetic field strength during UF phases.
In this study we investigate the origin of these periodic variations of the
magnetic field strength by analyzing a time-series of high temporal cadence
observations acquired in the Ca II line with the CRISP instrument at the
Swedish 1-m Solar Telescope. In particular, we analyze how the inferred
geometrical height scale changes between quiescent and UF phases, and whether
those changes are enough to explain the observed changes in . We have
performed non-LTE data inversions with the NICOLE code of a time-series of very
high spatio-temporal resolution observations in the Ca II and Fe I
630.15\630.25 nm lines. Our results indicate that the Ca II line in sunspots is
greatly sensitive to magnetic fields at during UFs and
quiescence. However, this optical depth value does not correspond to the same
geometrical height during the two phases. Our results indicate that during UFs
and RPWs the is located at a higher geometrical height than
during quiescence. Additionally, the inferred magnetic field values are higher
in UFs (~270 G) and in RPWs (~100 G). Our results suggest that opacity changes
caused by UFs and RPWs cannot explain the observed temporal variations in the
magnetic field, as the line seems to form at higher geometrical heights where
the field is expected to be lower.Comment: Accepted in A&
The chromosphere above a -sunspot in the presence of fan-shaped jets
-sunspots are known to be favourable locations for fast and energetic
events like flares and CMEs. The photosphere of this type of sunspots has been
thoroughly investigated in the past three decades. The atmospheric conditions
in the chromosphere are not so well known, however. his study is focused on the
chromosphere of a -sunspot that harbours a series of fan-shaped jets in
its penumbra . The aim of this study is to establish the magnetic field
topology and the temperature distribution in the presence of jets in the
photosphere and the chromosphere. We use data from the Swedish 1-m Solar
Telescope (SST) and the Solar Dynamics Observatory. We invert the
spectropolarimetric FeI 6302~\AA\ and CaII ~8542~\AA\ data from the SST using
the the non-LTE inversion code NICOLE to estimate the magnetic field
configuration, temperature and velocity structure in the chromosphere. A
loop-like magnetic structure is observed to emerge in the penumbra of the
sunspot. The jets are launched from the loop-like structure. Magnetic
reconnection between this emerging field and the pre-existing vertical field is
suggested by hot plasma patches on the interface between the two fields. The
height at which the reconnection takes place is located between and . The magnetic field vector and the
atmospheric temperature maps show a stationary configuration during the whole
observation.Comment: 12 pages, 15 figures. Recommended for publication in A&
The effect of isotopic splitting on the bisector and inversions of the solar Ca II 854.2 nm line
The Ca II 854.2 nm spectral line is a common diagnostic of the solar
chromosphere. The average line profile shows an asymmetric core, and its
bisector shows a characteristic inverse-C shape. The line actually consists of
six components with slightly different wavelengths depending on the isotope of
calcium. This isotopic splitting of the line has been taken into account in
studies of non-solar stars, but never for the Sun. We performed non-LTE
radiative transfer computations from three models of the solar atmosphere and
show that the asymmetric line-core and inverse C-shape of the bisector of the
854.2 nm line can be explained by isotopic splitting. We confirm this finding
by analysing observations and showing that the line asymmetry is present
irrespective of conditions in the solar atmosphere. Finally, we show that
inversions based on the Ca II 854.2 nm line should take the isotopic splitting
into account, otherwise the inferred atmospheres will contain erroneous
velocity gradients and temperatures.Comment: Accepted for ApJ
Recovering Thermodynamics from Spectral Profiles observed by IRIS: A Machine and Deep Learning Approach
Inversion codes allow reconstructing a model atmosphere from observations.
With the inclusion of optically thick lines that form in the solar
chromosphere, such modelling is computationally very expensive because a
non-LTE evaluation of the radiation field is required. In this study, we
combine the results provided by these traditional methods with machine and deep
learning techniques to obtain similar-quality results in an easy-touse, much
faster way. We have applied these new methods to Mg II h&k lines observed by
IRIS. As a result, we are able to reconstruct the thermodynamic state
(temperature, line-of-sight velocity, non-thermal velocities, electron density,
etc.) in the chromosphere and upper photosphere of an area equivalent to an
active region in a few CPU minutes, speeding up the process by a factor of
-. The open-source code accompanying this paper will allow the
community to use IRIS observations to open a new window to a host of solar
phenomena.Comment: 8 pages, 5 figure
Emergence of granular-sized magnetic bubbles through the solar atmosphere. II. Non-LTE chromospheric diagnostics and inversions
Magnetic flux emergence into the outer layers of the Sun is a fundamental
mechanism for releasing energy into the chromosphere and the corona. In this
paper, we study the emergence of granular-sized flux concentrations and the
structuring of the corresponding physical parameters and atmospheric
diagnostics in the upper photo- sphere and in the chromosphere. We make use of
a realistic 3D MHD simulation of the outer layers of the Sun to study the
formation of the Ca II 8542 line. We also derive semi-empirical 3D models from
non-LTE inversions of our observations. These models contain depth-dependent
information of the temperature and line-of-sight stratification. Our analysis
explains the peculiar Ca II 8542 profiles observed in the flux-emerging region.
In addition, we derive detailed temperature and velocity maps describing the
ascent of magnetic bubbles from the photosphere to the chromosphere. The
inversions suggest that, in active regions, granular-sized bubbles emerge up to
the lower chromosphere where the existing large-scale field hinders their
ascent. We report hints of heating when the field reaches the chromosphere.Comment: Submitted to ApJ, 10 Figure
On chromospheric heating during flux emergence in the solar atmosphere
Context. The radiative losses in the solar chromosphere vary from
4~kW~m in the quiet Sun, to 20~kW~m in active regions. The
mechanisms that transport non-thermal energy to and deposit it in the
chromosphere are still not understood. Aims. We aim to investigate the
atmospheric structure and heating of the solar chromosphere in an emerging flux
region. Methods. We use observations taken with the CHROMIS and CRISP
instruments on the Swedish 1-m Solar Telescope in the Ca II K, Ca II 854.2 nm,
H, and Fe I 630.1 nm and 630.2 nm lines. We analyse the various line
profiles and in addition perform multi-line, multi-species, non-Local
Thermodynamic Equilibrium (non-LTE) inversions to estimate the spatial and
temporal variation of the chromospheric structure. Results. We investigate
which spectral features of Ca II K contribute to the frequency-integrated Ca II
K brightness, which we use as a tracer of chromospheric radiative losses. The
majority of the radiative losses are not associated with localized high-Ca II
K-brightness events, but instead with a more gentle, spatially extended, and
persistent heating. The frequency-integrated Ca II K brightness correlates
strongly with the total linear polarization in the Ca II 854.2 nm line, while
the Ca II K profile shapes indicate that the bulk of the radiative losses occur
in the lower chromosphere.
Non-LTE inversions indicate a transition from heating concentrated around
photospheric magnetic elements below to a more
space-filling and time-persistent heating above . The
inferred gas temperature at correlates strongly with
the total linear polarization in the Ca II 854.2 nm line, suggesting that that
the heating rate correlates with the strength of the horizontal magnetic field
in the low chromosphere.Comment: Accepted for publication by A&
Observations of Ellerman bomb emission features in He I D3 and He I 10830 {\AA}
Context. Ellerman bombs (EBs) are short-lived emission features,
characterized by extended wing emission in hydrogen Balmer lines. Until now, no
distinct signature of EBs has been found in the He I 10830 {\AA} line, and
conclusive observations of EBs in He I D 3 have never been reported. Aims. We
aim to study the signature of EBs in neutral helium triplet lines. Methods. The
observations consist of 10 consecutive SST/TRIPPEL raster scans close to the
limb, featuring the H, He I D3 and He I 10830 {\AA} spectral regions. We
also obtained raster scans with IRIS and make use of the SDO/AIA 1700 {\AA}
channel. We use Hazel to invert the neutral helium triplet lines. Results.
Three EBs in our data show distinct emission signatures in neutral helium
triplet lines, most prominently visible in the He I D3 line. The helium lines
have two components: a broad and blue-shifted emission component associated
with the EB, and a narrower absorption component formed in the overlying
chromosphere. One of the EBs in our data shows evidence of strong velocity
gradients in its emission component. The emission component of the other two
EBs could be fitted using a constant slab. Our analysis hints towards thermal
Doppler motions having a large contribution to the broadening for helium and
IRIS lines. We conclude that the EBs must have high temperatures to exhibit
emission signals in neutral helium triplet lines. An order of magnitude
estimate places our observed EBs in the range of K.Comment: 15 pages, 14 figure
Modeling of the hydrogen Lyman lines in solar flares
The hydrogen Lyman lines (91.2 nm < λ < 121.6 nm) are significant contributors to the radiative losses of the solar chromosphere, and they are enhanced during flares. We have shown previously that the Lyman lines observed by the Extreme Ultraviolet Variability instrument onboard the Solar Dynamics Observatory exhibit Doppler motions equivalent to speeds on the order of 30 km s−1. However, contrary to expectations, both redshifts and blueshifts were present and no dominant flow direction was observed. To understand the formation of the Lyman lines, particularly their Doppler motions, we have used the radiative hydrodynamic code, RADYN, along with the radiative transfer code, RH, to simulate the evolution of the flaring chromosphere and the response of the Lyman lines during solar flares. We find that upflows in the simulated atmospheres lead to blueshifts in the line cores, which exhibit central reversals. We then model the effects of the instrument on the profiles, using the Extreme Ultraviolet Variability Experiment (EVE) instrument's properties. What may be interpreted as downflows (redshifted emission) in the lines, after they have been convolved with the instrumental line profile, may not necessarily correspond to actual downflows. Dynamic features in the atmosphere can introduce complex features in the line profiles that will not be detected by instruments with the spectral resolution of EVE, but which leave more of a signature at the resolution of the Spectral Investigation of the Coronal Environment instrument onboard the Solar Orbiter
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