1,116 research outputs found
Dissecting bombs and bursts: non-LTE inversions of low-atmosphere reconnection in SST and IRIS observations
Ellerman bombs and UV bursts are transient brightenings that are ubiquitously
observed in the lower atmospheres of active and emerging flux regions. Here we
present inversion results of SST/CRISP and CHROMIS, as well as IRIS data of
such transient events. Combining information from the Mg II h & k, Si IV and Ca
II 8542A and Ca II H & K lines, we aim to characterise their temperature and
velocity stratification, as well as their magnetic field configuration. We find
average temperature enhancements of a few thousand kelvin close to the
classical temperature minimum, but localised peak temperatures of up to
10,000-15,000 K from Ca II inversions. Including Mg II generally dampens these
temperature enhancements to below 8000 K, while Si IV requires temperatures in
excess of 10,000 K at low heights, but may also be reproduced with secondary
temperature enhancements of 35,000-60,000 K higher up. However, reproducing Si
IV comes at the expense of overestimating the Mg II emission. The line-of-sight
velocity maps show clear bi-directional jet signatures and strong correlation
with substructure in the intensity images, with slightly larger velocities
towards the observer than away. The magnetic field parameters show an
enhancement of the horizontal field co-located with the brightenings at similar
heights as the temperature increase. We are thus able to largely reproduce the
observational properties of Ellerman bombs with UV burst signature with
temperature stratifications peaking close to the classical temperature minimum.
Correctly modelling the Si IV emission in agreement with all other diagnostics
is, however, an outstanding issue. Accounting for resolution differences,
fitting localised temperature enhancements and/or performing spatially-coupled
inversions is likely necessary to obtain better agreement between all
considered diagnostics.Comment: Accepted for publication in Astronomy & Astrophysics. 24 pages, 17
figure
Stratification of canopy magnetic fields in a plage region. Constraints from a spatially-regularized weak-field approximation method
The role of magnetic fields in the chromospheric heating problem remains
greatly unconstrained. Most theoretical predictions from numerical models rely
on a magnetic configuration, field strength and connectivity whose details have
not been well established with observational studies. High-resolution studies
of chromospheric magnetic fields in plage are very scarce or non-existent in
general. Our aim is to study the stratification of the magnetic field vector in
plage regions. We use high-spatial resolution full-Stokes observations acquired
with CRISP instrument at the Swedish 1-m Solar Telescope in the Mg I
5173, Na I 5896 and Ca II 8542 lines. We have
developed a spatially-regularized weak-field approximation (WFA) method based
on the idea of spatial regularization. This method allows for a fast
computation of magnetic field maps for an extended field of view. The fidelity
of this new technique has been assessed using a snapshot from a realistic 3D
magnetohydrodynamics simulation. We have derived the depth-stratification of
the line-of-sight component of the magnetic field from the photosphere to the
chromosphere in a plage region. The magnetic fields are concentrated in the
intergranular lanes in the photosphere and expand horizontally toward the
chromosphere, filling all the space and forming a canopy. Our results suggest
that the lower boundary of this canopy must be located around 400-600 km from
the photosphere. The mean canopy total magnetic field strength in the lower
chromosphere ( km) is 658 G. At km we estimate
G. We propose a modification to the WFA that
improves its applicability to data with worse signal-to-noise ratio. These
methods provide a quick and reliable way of studying multi-layer magnetic field
observations without the many difficulties inherent to other inversion methods.Comment: Accepted for publication on 2020-08-2
Modelling Contamination of Raw Milk with Butyric Acid Bacteria Spores
Raw milk contains low concentrations of bacterial endospores, originating from the farm environment (e.g. soil, feeds, faeces). Spores of Clostridium tyrobutyricum, also called butyric acid bacterium (BAB), are of great interest to the dairy industry. They survive milk pasteurisation and cause off-flavours and texture defects in various cheese types. The contamination pathway of BAB spores is well known. Their primary origin is soil. In silage the number of spores will increase if conditions permit BAB growth. The spores are excreted in the cows faeces and are transferred to milk by contaminated teat surfaces. Many factors are involved in the contamination of milk with BAB spores. In this study, the contamination pathway was described using a combination of predictive models. The objective of the study was to quantitatively assess the importance of the different steps of the contamination pathway and to identify the most effective control points
Intermittent reconnection and plasmoids in UV bursts in the low solar atmosphere
Magnetic reconnection is thought to drive a wide variety of dynamic phenomena
in the solar atmosphere. Yet the detailed physical mechanisms driving
reconnection are difficult to discern in the remote sensing observations that
are used to study the solar atmosphere. In this paper we exploit the
high-resolution instruments Interface Region Imaging Spectrograph (IRIS) and
the new CHROMIS Fabry-Perot instrument at the Swedish 1-m Solar Telescope (SST)
to identify the intermittency of magnetic reconnection and its association with
the formation of plasmoids in so-called UV bursts in the low solar atmosphere.
The Si IV 1403A UV burst spectra from the transition region show evidence of
highly broadened line profiles with often non-Gaussian and triangular shapes,
in addition to signatures of bidirectional flows. Such profiles had previously
been linked, in idealized numerical simulations, to magnetic reconnection
driven by the plasmoid instability. Simultaneous CHROMIS images in the
chromospheric Ca II K 3934A line now provide compelling evidence for the
presence of plasmoids, by revealing highly dynamic and rapidly moving
brightenings that are smaller than 0.2 arcsec and that evolve on timescales of
order seconds. Our interpretation of the observations is supported by detailed
comparisons with synthetic observables from advanced numerical simulations of
magnetic reconnection and associated plasmoids in the chromosphere. Our results
highlight how subarcsecond imaging spectroscopy sensitive to a wide range of
temperatures combined with advanced numerical simulations that are realistic
enough to compare with observations can directly reveal the small-scale
physical processes that drive the wide range of phenomena in the solar
atmosphere.Comment: Accepted for publication in Astrophysical Journal Letters. Movies are
available at http://folk.uio.no/rouppe/plasmoids_chromis
ALMA observations of transient heating in a solar active region
We aim to investigate the temperature enhancements and formation heights of
impulsive heating phenomena in solar active-regions such as Ellerman bombs
(EBs), ultraviolet bursts (UVBs), and flaring active-region fibrils (FAFs)
using interferometric observations in the millimeter (mm) continuum provided by
the Atacama Large Millimeter/submillimeter Array (ALMA). We examined 3 mm
signatures of heating events identified in Solar Dynamics Observatory (SDO)
observations of an active region and compared the results with synthetic
spectra from a 3D radiative magnetohydrodynamic simulation. We estimated the
contribution from the corona to the mm brightness using differential emission
measure analysis. We report the null detection of EBs in the 3 mm continuum at
" spatial resolution, which is evidence that they are sub-canopy
events that do not significantly contribute to heating the upper chromosphere.
In contrast, we find the active region to be populated with multiple compact,
bright, flickering mm bursts -- reminiscent of UVBs. The high brightness
temperatures of up to K in some events have a significant
contribution (up to 7%) from the corona. We also detect FAF-like events
in the 3 mm continuum that show rapid motions of K plasma launched
with high plane-of-sky velocities () from bright
kernels. The mm FAFs are the brightest class of warm canopy fibrils that
connect magnetic regions of opposite polarities. The simulation confirms that
ALMA should be able to detect the mm counterparts of UVBs and small flares and
thus provide a complementary diagnostic for localized heating in the solar
chromosphere.Comment: revised; accepted in Astronomy & Astrophysic
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