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Author name code: madjarska
ADS astronomy entries on 2022-09-14
author:"Madjarska, Maria"
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Title: Mini-filament eruption, QSL reconnection, and
reconnection-driven outflows: IRIS and AIA/HMI/SDO observations
and modelling
Authors: Madjarska, Maria S.; Mackay, Duncan H.; Galsgaard, Klaus;
Xie, Haixia; Wiegelmann, Thomas
2022cosp...44.2533M Altcode:
We will present unique observations of a mini-filament eruption
associated with cancelling magnetic fluxes of a small-scale loop system
known as a coronal bright point. The event is uniquely recorded in
both the imaging and spectroscopic data taken with the Interface
Region Imaging Spectrograph (IRIS). The study aims at providing
a better understanding of the physical processes driving these
ubiquitous small-scale eruptions. We also analysed images taken in the
extreme-ultraviolet channels of the Atmospheric Imaging Assembly (AIA)
and line-of-sight magnetic-field data from the Helioseismic Magnetic
Imager (HMI) onboard the Solar Dynamics Observatory. As the observations
can only give an inkling about the possible physical processes at play,
we also employed a non-linear force-free field (NLFFF) relaxation
approach based on the HMI magnetogram time series. Furthermore, we
computed the squashing factor, Q, in different horizontal planes of
the NLFFF model. This allowed us to further investigate the evolution
of the magnetic-field structures involved in the eruption process.
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Title: Eruptions from coronal bright points: A spectroscopic
view by IRIS of a mini-filament eruption, QSL reconnection, and
reconnection-driven outflows
Authors: Madjarska, Maria S.; Mackay, Duncan H.; Galsgaard, Klaus;
Wiegelmann, Thomas; Xie, Haixia
2022A&A...660A..45M Altcode: 2022arXiv220200370M
Context. Our study investigates a mini-filament eruption associated with
cancelling magnetic fluxes. The eruption originates from a small-scale
loop complex commonly known as a coronal bright point (CBP). The
event is uniquely recorded in both the imaging and spectroscopic data
taken with the Interface Region Imaging Spectrograph (IRIS). <BR />
Aims: The investigation aims to gain a better understanding of the
physical processes driving these ubiquitous small-scale eruptions. <BR
/> Methods: We analysed IRIS spectroscopic and slit-jaw imaging
observations as well as images taken in the extreme-ultraviolet
channels of the Atmospheric Imaging Assembly (AIA) and line-of-sight
magnetic-field data from the Helioseismic Magnetic Imager (HMI) on
board the Solar Dynamics Observatory. As the observations can only
indicate the possible physical processes at play, we also employed a
non-linear force-free field (NLFFF) relaxation approach based on the
HMI magnetogram time series. This allowed us to further investigate
the evolution of the magnetic-field structures involved in the eruption
process. <BR /> Results: We identified a strong small-scale brightening
as a micro-flare in a CBP, recorded in emission from chromospheric to
flaring plasmas. The mini-eruption is manifested via the ejection of hot
(CBP loops) and cool (mini-filament) plasma recorded in both the imaging
and spectroscopic data. The micro-flare is preceded by the appearance
of an elongated bright feature in the IRIS slit-jaw 1400 Å images,
located above the polarity inversion line. The micro-flare starts
with an IRIS pixel size brightening and propagates bi-directionally
along the elongated feature. We detected, in both the spectral and
imaging IRIS data and AIA data, strong flows along and at the edges of
the elongated feature; we believe that these represent reconnection
outflows. Both edges of the elongated feature that wrap around the
edges of the erupting MF evolve into a J-type shape, creating a
sigmoid appearance. A quasi-separatrix layer (QSL) is identified in
the vicinity of the polarity inversion line by computing the squashing
factor, Q, in different horizontal planes of the NLFFF model. <BR />
Conclusions: This CBP spectro-imaging study provides further evidence
that CBPs represent downscaled active regions and, as such, they may
make a significant contribution to the mass and energy balance of
the solar atmosphere. They are the sources of all range of typical
active-region features, including magnetic reconnection along QSLs,
(mini-)filament eruptions, (micro-)flaring, reconnection outflows,
etc. The QSL reconnection site has the same spectral appearance
as the so-called explosive events identified by strong blue- and
red-shifted emission, thus providing an answer to an outstanding
question regarding the true nature of this spectral phenomenon. <P
/>Movies associated to Figs. A.1 and A.2 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142439/olm">https://www.aanda.org</A>
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Title: Investigation of the subsurface structure of a sunspot based
on the spatial distribution of oscillation centers inferred from
umbral flashes
Authors: Cho, Kyuhyoun; Chae, Jongchul; Madjarska, Maria S.
2021A&A...656A..86C Altcode: 2021arXiv210911185C
The subsurface structure of a solar sunspot is important for the
stability of the sunspot and the energy transport therein. Two
subsurface structure models have been proposed, the monolithic
and cluster models, but no clear observational evidence supporting
a particular model has been found to date. To obtain clues about
the subsurface structure of sunspots, we analyzed umbral flashes
in merging sunspots registered by IRIS Mg II 2796 Å slit-jaw
images. Umbral flashes are regarded as an observational manifestation
of magnetohydrodynamic shock waves originating from convection cells
below the photosphere. By tracking the motion of individual umbral
flashes, we determined the position of the convection cells that
are the oscillation centers located below the umbra. We found that
the oscillation centers are preferentially located at dark nuclei
in the umbral cores rather than in bright regions such as light
bridges or umbral dots. Moreover, the oscillation centers tend to
deviate from the convergent interface of the merging sunspots where
vigorous convection is expected to occur. We also found that the
inferred depths of the convection cells have no noticeable regional
dependence. These results suggest that the subsurface of the umbra
is an environment where convection can occur more easily than the
convergent interface, and hence support the cluster model. For more
concrete results, further studies based on umbral velocity oscillations
in the lower atmosphere are required. <P />Movie is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141500/olm">https://www.aanda.org</A>
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Title: Coronal Hole Detection and Open Magnetic Flux
Authors: Linker, Jon A.; Heinemann, Stephan G.; Temmer, Manuela;
Owens, Mathew J.; Caplan, Ronald M.; Arge, Charles N.; Asvestari,
Eleanna; Delouille, Veronique; Downs, Cooper; Hofmeister, Stefan J.;
Jebaraj, Immanuel C.; Madjarska, Maria S.; Pinto, Rui F.; Pomoell,
Jens; Samara, Evangelia; Scolini, Camilla; Vršnak, Bojan
2021ApJ...918...21L Altcode: 2021arXiv210305837L
Many scientists use coronal hole (CH) detections to infer open
magnetic flux. Detection techniques differ in the areas that they
assign as open, and may obtain different values for the open magnetic
flux. We characterize the uncertainties of these methods, by applying
six different detection methods to deduce the area and open flux of
a near-disk center CH observed on 2010 September 19, and applying
a single method to five different EUV filtergrams for this CH. Open
flux was calculated using five different magnetic maps. The standard
deviation (interpreted as the uncertainty) in the open flux estimate
for this CH ≍ 26%. However, including the variability of different
magnetic data sources, this uncertainty almost doubles to 45%. We
use two of the methods to characterize the area and open flux for
all CHs in this time period. We find that the open flux is greatly
underestimated compared to values inferred from in situ measurements
(by 2.2-4 times). We also test our detection techniques on simulated
emission images from a thermodynamic MHD model of the solar corona. We
find that the methods overestimate the area and open flux in the
simulated CH, but the average error in the flux is only about 7%. The
full-Sun detections on the simulated corona underestimate the model
open flux, but by factors well below what is needed to account for
the missing flux in the observations. Under-detection of open flux in
coronal holes likely contributes to the recognized deficit in solar
open flux, but is unlikely to resolve it.
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Title: On the Nature of Propagating Intensity Disturbances in Polar
Plumes during the 2017 Total Solar Eclipse
Authors: Cho, Kyung-Suk; Cho, Il-Hyun; Madjarska, Maria S.; Nakariakov,
Valery M.; Yang, Heesu; Choi, Seonghwan; Lim, Eun-Kyung; Lee,
Kyung-Sun; Seough, Jung-Jun; Lee, Jaeok; Kim, Yeon-Han
2021ApJ...909..202C Altcode: 2021arXiv210202085C
The propagating intensity disturbances (PIDs) in plumes are still
poorly understood, and their identity (magnetoacoustic waves or flows)
remains an open question. We investigate PIDs in five plumes located
in the northern polar coronal hole observed during the 2017 total solar
eclipse. Three plumes are associated with coronal bright points, jets,
and macrospicules at their base (active plumes), and the other two
plumes are not (quiet plumes). The electron temperature at the base of
the plumes is obtained from the filter ratio of images taken with the
X-ray Telescope on board Hinode and the passband ratio around 400 nm
from an eclipse instrument, the Diagnostic Coronagraph Experiment. The
phase speed (v<SUB>r</SUB>), frequency (ω), and wavenumber (k) of the
PIDs in the plumes are obtained by applying a Fourier transformation to
the spacetime (r - t plane) plots in images taken with the Atmospheric
Imaging Assembly (AIA) in three different wavelength channels (171,
193, and 211 Å). We found that the PIDs in the higher-temperature AIA
channels, 193 and 211 Å, are faster than that of the cooler AIA 171
Å channel. This tendency is more significant for the active plumes
than the quiet ones. The observed speed ratio (∼1.3) between the
AIA 171 and 193 Å channels is similar to the theoretical value (1.25)
of a slow magnetoacoustic wave. Our results support the idea that PIDs
in plumes represent a superposition of slow magnetoacoustic waves and
plasma outflows that consist of dense cool flows and hot coronal jets.
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Title: The chromospheric component of coronal bright points. Coronal
and chromospheric responses to magnetic-flux emergence
Authors: Madjarska, Maria S.; Chae, Jongchul; Moreno-Insertis,
Fernando; Hou, Zhenyong; Nóbrega-Siverio, Daniel; Kwak, Hannah;
Galsgaard, Klaus; Cho, Kyuhyoun
2021A&A...646A.107M Altcode: 2020arXiv201209426M
Context. We investigate the chromospheric counterpart of small-scale
coronal loops constituting a coronal bright point (CBP) and its
response to a photospheric magnetic-flux increase accompanied by
co-temporal CBP heating. <BR /> Aims: The aim of this study is
to simultaneously investigate the chromospheric and coronal layers
associated with a CBP, and in so doing, provide further understanding on
the heating of plasmas confined in small-scale loops. <BR /> Methods:
We used co-observations from the Atmospheric Imaging Assembly and
Helioseismic Magnetic Imager on board the Solar Dynamics Observatory,
together with data from the Fast Imaging Solar Spectrograph taken
in the Hα and Ca II 8542.1 Å lines. We also employed both linear
force-free and potential field extrapolation models to investigate
the magnetic topology of the CBP loops and the overlying corona,
respectively. We used a new multi-layer spectral inversion technique
to derive the temporal variations of the temperature of the Hα loops
(HLs). <BR /> Results: We find that the counterpart of the CBP, as
seen at chromospheric temperatures, is composed of a bundle of dark
elongated features named in this work Hα loops, which constitute an
integral part of the CBP loop magnetic structure. An increase in the
photospheric magnetic flux due to flux emergence is accompanied by
a rise of the coronal emission of the CBP loops, that is a heating
episode. We also observe enhanced chromospheric activity associated
with the occurrence of new HLs and mottles. While the coronal emission
and magnetic flux increases appear to be co-temporal, the response of
the Hα counterpart of the CBP occurs with a small delay of less than
3 min. A sharp temperature increase is found in one of the HLs and
in one of the CBP footpoints estimated at 46% and 55% with respect
to the pre-event values, also starting with a delay of less than 3
min following the coronal heating episode. The low-lying CBP loop
structure remains non-potential for the entire observing period. The
magnetic topological analysis of the overlying corona reveals the
presence of a coronal null point at the beginning and towards the end
of the heating episode. <BR /> Conclusions: The delay in the response
of the chromospheric counterpart of the CBP suggests that the heating
may have occurred at coronal heights. <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202039329/olm">https://www.aanda.org</A>
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Title: Detection of Opposite Magnetic Polarity in a Light Bridge:
Its Emergence and Cancellation in Association with LB Fan-shaped Jets
Authors: Lim, Eun-Kyung; Yang, Heesu; Yurchyshyn, Vasyl; Chae,
Jongchul; Song, Donguk; Madjarska, Maria S.
2020ApJ...904...84L Altcode: 2020arXiv201010713L
Light bridges (LBs) are relatively bright structures that divide
sunspot umbrae into two or more parts. Chromospheric LBs are known to
be associated with various activities including fan-shaped jet-like
ejections and brightenings. Although magnetic reconnection is
frequently suggested to be responsible for such activities, not many
studies present firm evidence to support the scenario. We carry out
magnetic field measurements and imaging spectroscopy of an LB where
fan-shaped jet-like ejections occur with co-spatial brightenings
at their footpoints. We study LB fine structure and magnetic field
changes using TiO images, Near-InfraRed Imaging Spectropolarimeter,
and Hα data taken by the 1.6 m Goode Solar Telescope. We detect
magnetic flux emergence in the LB that is of opposite polarity to that
of the sunspot. The new magnetic flux cancels with the pre-existing
flux at a rate of 5.6 × 10<SUP>18</SUP> Mx hr<SUP>-1</SUP>. Both
the recurrent jet-like ejections and their base brightenings are
initiated at the vicinity of the magnetic flux cancellation, and show
apparent horizontal extension along the LB at a projected speed of up
to $18.4$ km s<SUP>-1</SUP> to form a fan-shaped appearance. Based on
these observations, we suggest that the fan-shaped ejections may have
resulted from slipping reconnection between the new flux emerging in
the LB and the ambient sunspot field.
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Title: Eruptions from coronal hole bright points: Observations and
non-potential modelling
Authors: Madjarska, Maria S.; Galsgaard, Klaus; Mackay, Duncan H.;
Koleva, Kostadinka; Dechev, Momchil
2020A&A...643A..19M Altcode: 2020arXiv200904628M
Context. We report on the third part of a series of studies on eruptions
associated with small-scale loop complexes named coronal bright points
(CBPs). <BR /> Aims: A single case study of a CBP in an equatorial
coronal hole with an exceptionally large size is investigated to
expand on our understanding of the formation of mini-filaments, their
destabilisation, and the origin of the eruption triggering the formation
of jet-like features recorded in extreme ultraviolet (EUV) and X-ray
emission. We aim to explore the nature of the so-called micro-flares
in CBPs associated with jets in coronal holes and mini coronal mass
ejections in the quiet Sun. <BR /> Methods: Co-observations from the
Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager
(HMI) on board the Solar Dynamics Observatory as well as GONG Hα
images are used together with a non-linear force free field (NLFFF)
relaxation approach, where the latter is based on a time series of
HMI line-of-sight magnetograms. <BR /> Results: A mini-filament (MF)
that formed beneath the CBP arcade about 3-4 h before the eruption is
seen in the Hα and EUV AIA images to lift up and erupt triggering the
formation of an X-ray jet. No significant photospheric magnetic flux
concentration displacement (convergence) is observed and neither is
magnetic flux cancellation between the two main magnetic polarities
forming the CBP in the time period leading to MF lift-off. The
CBP micro-flare is associated with three flare kernels that formed
shortly after the MF lift-off. No observational signature is found
for magnetic reconnection beneath the erupting MF. The applied NLFFF
modelling successfully reproduces both the CBP loop complex as well
as the magnetic flux rope that hosts the MF during the build-up to
the eruption. <BR /> Conclusions: The applied NLFFF modelling is
able to clearly show that an initial potential field can be evolved
into a non-potential magnetic field configuration that contains
free magnetic energy in the region that observationally hosts the
eruption. The comparison of the magnetic field structure shows that the
magnetic NLFFF model contains many of the features that can explain
the different observational signatures found in the evolution and
eruption of the CBP. In the future, it may eventually indicate the
location of destabilisation that results in the eruptions of flux
ropes. <P />Movies associated to Figs. 9 and B.2 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038287/olm">https://www.aanda.org</A>
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Title: Impulsive wave excitation by rapidly changing granules
Authors: Kwak, Hannah; Chae, Jongchul; Madjarska, Maria S.; Cho,
Kyuhyoun; Song, Donguk
2020A&A...642A.154K Altcode: 2020arXiv200812779K
It is not yet fully understood how magnetohydrodynamic waves in
the interior and atmosphere of the Sun are excited. Traditionally,
turbulent convection in the interior is considered to be the source of
wave excitation in the quiet Sun. Over the last few decades, acoustic
events observed in the intergranular lanes in the photosphere have
emerged as a strong candidate for a wave excitation source. Here we
report our observations of wave excitation by a new type of event:
rapidly changing granules. Our observations were carried out with the
Fast Imaging Solar Spectrograph in the Hα and Ca II 8542 Å lines
and the TiO 7057 Å broadband filter imager of the 1.6 m Goode Solar
Telescope at the Big Bear Solar Observatory. We identify granules in
the internetwork region that undergo rapid dynamic changes such as
collapse (event 1), fragmentation (event 2), or submergence (event
3). In the photospheric images, these granules become significantly
darker than neighboring granules. Following the granules' rapid
changes, transient oscillations are detected in the photospheric and
chromospheric layers. In the case of event 1, the dominant period of
the oscillations is close to 4.2 min in the photosphere and 3.8 min
in the chromosphere. Moreover, in the Ca II-0.5 Å raster image, we
observe repetitive brightenings in the location of the rapidly changing
granules that are considered the manifestation of shock waves. Based on
our results, we suggest that dynamic changes of granules can generate
upward-propagating acoustic waves in the quiet Sun that ultimately
develop into shocks. <P />Movie attached to Fig. A.1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038288/olm">https://www.aanda.org</A>
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Title: Inference of chromospheric plasma parameters on the
Sun. Multilayer spectral inversion of strong absorption lines
Authors: Chae, Jongchul; Madjarska, Maria S.; Kwak, Hannah; Cho,
Kyuhyoun
2020A&A...640A..45C Altcode:
The solar chromosphere can be observed well through strong absorption
lines. We infer the physical parameters of chromospheric plasmas
from these lines using a multilayer spectral inversion. This is a
new technique of spectral inversion. We assume that the atmosphere
consists of a finite number of layers. In each layer the absorption
profile is constant and the source function varies with optical depth
with a constant gradient. Specifically, we consider a three-layer
model of radiative transfer where the lowest layer is identified
with the photosphere and the two upper layers are identified with
the chromosphere. The absorption profile in the photosphere is
described by a Voigt function, and the profile in the chromosphere
by a Gaussian function. This three-layer model is fully specified
by 13 parameters. Four parameters can be fixed to prescribed values,
and one parameter can be determined from the analysis of a satellite
photospheric line. The remaining 8 parameters are determined from a
constrained least-squares fitting. We applied the multilayer spectral
inversion to the spectral data of the Hα and the Ca II 854.21 nm
lines taken in a quiet region by the Fast Imaging Solar Spectrograph
(FISS) of the Goode Solar Telescope (GST). We find that our model
successfully fits most of the observed profiles and produces regular
maps of the model parameters. The combination of the inferred Doppler
widths of the two lines yields reasonable estimates of temperature and
nonthermal speed in the chromosphere. We conclude that our multilayer
inversion is useful to infer chromospheric plasma parameters on the Sun.
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Title: Inference of chromospheric plasma parameters on the Sun
Authors: Chae, Jongchul; Madjarska, Maria S.; Kwak, Hannah; Cho,
Kyuhyoun
2020arXiv200611981C Altcode:
The solar chromosphere can be observed well through strong absorption
lines. We infer the physical parameters of chromospheric plasmas
from these lines using a multilayer spectral inversion. This is a
new technique of spectral inversion. We assume that the atmosphere
consists of a finite number of layers. In each layer the absorption
profile is constant and the source function varies with optical depth
with a constant gradient. Specifically, we consider a three-layer
model of radiative transfer where the lowest layer is identified
with the photosphere and the two upper layers are identified with
the chromosphere. The absorption profile in the photosphere is
described by a Voigt function, and the profile in the chromosphere
by a Gaussian function. This three-layer model is fully specified
by 13 parameters. Four parameters can be fixed to prescribed values,
and one parameter can be determined from the analysis of a satellite
photospheric line. The remaining 8 parameters are determined from a
constrained least-squares fitting. We applied the multilayer spectral
inversion to the spectral data of the H$\alpha$ and the Ca II 854.21 nm
lines taken in a quiet region by the Fast Imaging Solar Spectrograph
(FISS) of the Goode Solar Telescope (GST). We find that our model
successfully fits most of the observed profiles and produces regular
maps of the model parameters. The combination of the inferred Doppler
widths of the two lines yields reasonable estimates of temperature and
nonthermal speed in the chromosphere. We conclude that our multilayer
inversion is useful to infer chromospheric plasma parameters on the Sun.
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Title: Helium abundance and speed difference between helium ions
and protons in the solar wind from coronal holes, active regions,
and quiet Sun
Authors: Fu, Hui; Madjarska, Maria S.; Li, Bo; Xia, Lidong; Huang,
Zhenghua
2019EGUGA..21.3666F Altcode:
Two main models have been developed to explain the mechanisms of
release, heating, and acceleration of the nascent solar wind, the
wave-turbulence-driven (WTD) models and reconnection-loop-opening
(RLO) models, in which the plasma release processes are fundamentally
different. Given that the statistical observational properties of
helium ions produced in magnetically diverse solar regions could
provide valuable information for the solar wind modelling, we examine
the statistical properties of the helium abundance (A_He) and the
speed difference between helium ions and protons (v_αp) for coronal
holes (CHs), active regions (ARs), and the quiet Sun (QS). We find
bimodal distributions in the space of A_He and v_αp/v<SUB>A</SUB>
(where v<SUB>A</SUB> is the local Alfven speed) for the solar wind as
a whole. The CH windmeasurements are concentrated at higher A_He and
v_αp/v<SUB>A</SUB> values with a smaller A_He distribution range,
while the AR and QS wind is associated with lower A_He and v_αp/v_A,
and a larger A_He distribution range. The magnetic diversity of the
source regions and the physical processes related to it are possibly
responsible for the different properties of A_He and v_αp/v_A. The
statistical results suggest that the two solar wind generation
mechanisms, WTD and RLO, work in parallel in all solar wind source
regions. In CH regions WTD plays a major role, whereas the RLO mechanism
is more important in AR and QS.
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Title: Coronal bright points
Authors: Madjarska, Maria S.
2019LRSP...16....2M Altcode:
Coronal bright points (CBPs) are a fundamental class of solar
activity. They represent a set of low-corona small-scale loops with
enhanced emission in the extreme-ultraviolet and X-ray spectrum that
connect magnetic flux concentrations of opposite polarities. CBPs
are one of the main building blocks of the solar atmosphere outside
active regions uniformly populating the solar atmosphere including
active region latitudes and coronal holes. Their plasma properties
classify them as downscaled active regions. Most importantly, their
simple structure and short lifetimes of less than 20 h that allow to
follow their full lifetime evolution present a unique opportunity
to investigate outstanding questions in solar physics including
coronal heating. The present Living Review is the first review of
this essential class of solar phenomena and aims to give an overview
of the current knowledge about the CBP general, plasma and magnetic
properties. Several transient dynamic phenomena associated with CBPs
are also briefly introduced. The observationally derived energetics
and the theoretical modelling that aims at explaining the CBP formation
and eruptive behaviour are reviewed.
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Title: Eruptions from quiet Sun coronal bright
points. II. Non-potential modelling
Authors: Galsgaard, Klaus; Madjarska, Maria S.; Mackay, Duncan H.;
Mou, Chaozhou
2019A&A...623A..78G Altcode: 2019arXiv190109875G
Context. Our recent observational study shows that the majority
of coronal bright points (CBPs) in the quiet Sun are sources of
one or more eruptions during their lifetime. <BR /> Aims: Here, we
investigate the non-potential time-dependent structure of the magnetic
field of the CBP regions with special emphasis on the time-evolving
magnetic structure at the spatial locations where the eruptions are
initiated. <BR /> Methods: The magnetic structure is evolved in time
using a non-linear force-free field (NLFFF) relaxation approach based
on a time series of helioseismic and magnetic imager (HMI) longitudinal
magnetograms. This results in a continuous time series of NLFFFs. The
time series is initiated with a potential field extrapolation based
on a magnetogram taken well before the time of the eruptions. This
initial field is then evolved in time in response to the observed
changes in the magnetic field distribution at the photosphere. The
local and global magnetic field structures from the time series of NLFFF
field solutions are analysed in the vicinity of the eruption sites at
the approximate times of the eruptions. <BR /> Results: The analysis
shows that many of the CBP eruptions reported in a recent publication
contain a twisted flux tube located at the sites of eruptions. The
presence of flux ropes at these locations provides in many cases a
direct link between the magnetic field structure, their eruption,
and the observation of mini coronal mass ejections (mini-CMEs). It is
found that all repetitive eruptions are homologous. <BR /> Conclusions:
The NLFFF simulations show that twisted magnetic field structures are
created at the locations hosting eruptions in CBPs. These twisted
structures are produced by footpoint motions imposed by changes in
the photospheric magnetic field observations. The true nature of the
micro-flares remains unknown. Further 3D data-driven magnetohydrodynamic
modelling is required to show how these twisted regions become unstable
and erupt. <P />Movies associated to Figs. 1-5 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201834329/olm">https://www.aanda.org</A>
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Title: Solar Ultraviolet Bursts
Authors: Young, Peter R.; Tian, Hui; Peter, Hardi; Rutten, Robert J.;
Nelson, Chris J.; Huang, Zhenghua; Schmieder, Brigitte; Vissers, Gregal
J. M.; Toriumi, Shin; Rouppe van der Voort, Luc H. M.; Madjarska, Maria
S.; Danilovic, Sanja; Berlicki, Arkadiusz; Chitta, L. P.; Cheung, Mark
C. M.; Madsen, Chad; Reardon, Kevin P.; Katsukawa, Yukio; Heinzel, Petr
2018SSRv..214..120Y Altcode: 2018arXiv180505850Y
The term "ultraviolet (UV) burst" is introduced to describe small,
intense, transient brightenings in ultraviolet images of solar active
regions. We inventorize their properties and provide a definition
based on image sequences in transition-region lines. Coronal signatures
are rare, and most bursts are associated with small-scale, canceling
opposite-polarity fields in the photosphere that occur in emerging flux
regions, moving magnetic features in sunspot moats, and sunspot light
bridges. We also compare UV bursts with similar transition-region
phenomena found previously in solar ultraviolet spectrometry and
with similar phenomena at optical wavelengths, in particular Ellerman
bombs. Akin to the latter, UV bursts are probably small-scale magnetic
reconnection events occurring in the low atmosphere, at photospheric
and/or chromospheric heights. Their intense emission in lines with
optically thin formation gives unique diagnostic opportunities
for studying the physics of magnetic reconnection in the low solar
atmosphere. This paper is a review report from an International Space
Science Institute team that met in 2016-2017.
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Title: Eruptions from quiet Sun coronal bright points: Observations
& Modeling
Authors: Madjarska, Maria S.; Galsgaard, Klaus; Mou, Chauzhou
2018csc..confE.122M Altcode:
We present a two part study that aims first to observationally explore
in full detail the morphological and dynamical evolution of eruptions
from coronal bright points (CBPs) in the context of the full lifetime
evolution of 11 CBPs. Next, we employ data-driven modelling based on a
relaxation code to reproduce the time evolution of the magnetic field
of these eruptive CBPs, and provide an insight on the possible causes
for destabilisation and eruption. Observations of the full lifetime
of CBPs in data taken with the Atmospheric Imaging Assembly (AIA) on
board the Solar Dynamics Observatory in four passbands He II 304 Å,
Fe IX/X 171 Å, Fe XII 193 Å, and Fe XVIII 94 Å are investigated
for the occurrence of plasma ejections, micro-flaring, mini-filament
eruptions and mini coronal mass ejections (mini-CMEs). Data from the
Helioseismic and Magnetic Imager are analysed to study the longitudinal
photospheric magnetic field evolution associated with the CBPs and
related eruptions. The magnetic structure of each CBP is then evolved
in time using the relaxation approach, based on a time series of
HMI magnetograms. This results in a series of Non-Linear Force Free
Field Extrapolations (NLFFF). The time series is initiated with a
potential field extrapolation based on a HMI magnetogram well before
the eruptions, and evolved in time as a response to the changes in the
magnetic field distribution in the photosphere. This time series of
NLFFF field solutions is analysed for the local and global magnetic
field structure in the vicinity of the eruption sites.
---------------------------------------------------------
Title: Eruptions from quiet Sun coronal bright points. I. Observations
Authors: Mou, Chauzhou; Madjarska, Maria S.; Galsgaard, Klaus;
Xia, Lidong
2018A&A...619A..55M Altcode: 2018arXiv180804541M
Context. Eruptions from coronal bright points (CBPs) are investigated
in a two-part study. <BR /> Aims: The present study aims to explore in
full detail the morphological and dynamical evolution of these eruptions
in the context of the full lifetime evolution of CBPs. A follow-up
study employs data-driven modelling based on a relaxation code to
reproduce the time evolution of the magnetic field of these eruptive
CBPs, and provide insight into the possible causes for destabilisation
and eruption. <BR /> Methods: Observations of the full lifetime of
CBPs in data taken with the Atmospheric Imaging Assembly (AIA) on
board the Solar Dynamics Observatory in four passbands, He II 304 Å,
Fe IX/X 171 Å, Fe XII 193 Å, and Fe XVIII 94 Å are investigated
for the occurrence of plasma ejections, micro-flaring, mini-filament
eruptions, and mini coronal-mass ejections (mini-CMEs). Data from
the Helioseismic and Magnetic Imager are analysed to study the
longitudinal photospheric magnetic field evolution associated with
the CBPs and related eruptions. <BR /> Results: First and foremost,
our study shows that the majority (76%) of quiet Sun CBPs (31 out of
42 CBPs) produce at least one eruption during their lifetime. From 21
eruptions in 11 CBPs, 18 of them occur, on average, ∼17 h after the
CBP formation. The average lifetime of the CBPs in AIA 193 Å is ∼21
h. The time delay in the eruption occurrence coincides in each CBP with
the convergence and cancellation phase of the CBP bipole evolution
during which the CBPs become smaller until they fully disappear. The
remaining three eruptions happen 4-6 h after the CBP formation. In
16 out of the 21 eruptions, the magnetic convergence and cancellation
involve the CBP main bipoles, while in three eruptions, one of the BP
magnetic fragments and a pre-existing fragment of opposite polarity
converge and cancel. In one BP with two eruptions, cancellation was
not observed. The CBP eruptions involve in most cases the expulsion of
chromospheric material either as an elongated filamentary structure
(mini-filament, MF) or a volume of cool material (cool plasma cloud,
CPC), together with the CBP or higher overlying hot loops. Coronal waves
were identified during three eruptions. A micro-flaring is observed
beneath all erupting MFs/CPCs. Whether the destabilised MF causes
the micro-flaring or the destabilisation and eruption of the MF is
triggered by reconnection beneath the filament remains uncertain. In
most eruptions, the cool erupting plasma either partially or fully
obscures the micro-flare until the erupting material moves away from the
CBP. From 21 eruptions, 11 are found to produce mini-CMEs. The dimming
regions associated with the CMEs are found to be occupied by both the
"dark" cool plasma and areas of weakened coronal emission caused by
the depleted plasma density. <BR /> Conclusions: The present study
demonstrates that the small-scale loop structures in the quiet Sun,
the evolution of which is determined by their magnetic footpoint
motions and/or ambient field topology, evolve into an eruptive phase
that triggers the ejection of cool and hot plasma in the corona. <P
/>The movies associated to Figs 1, 3, 4, 6 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833243/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Helium abundance and speed difference between helium ions
and protons in the solar wind from coronal holes, active regions,
and quiet Sun
Authors: Fu, Hui; Madjarska, Maria S.; Li, Bo; Xia, Lidong; Huang,
Zhenghua
2018MNRAS.478.1884F Altcode: 2018arXiv180502880F; 2018MNRAS.tmp.1157F
Two main models have been developed to explain the mechanisms of
release, heating, and acceleration of the nascent solar wind, the
wave-turbulence-driven (WTD) models and reconnection-loop-opening
(RLO) models, in which the plasma release processes are fundamentally
different. Given that the statistical observational properties
of helium ions produced in magnetically diverse solar regions
could provide valuable information for the solar wind modelling,
we examine the statistical properties of the helium abundance
(A<SUB>He</SUB>) and the speed difference between helium ions and
protons (v<SUB>αp</SUB>) for coronal holes (CHs), active regions (ARs),
and the quiet Sun (QS). We find bimodal distributions in the space of
A<SUB>He</SUB> and v<SUB>αp</SUB>/v<SUB>A</SUB> (where v<SUB>A</SUB>
is the local Alfvén speed) for the solar wind as a whole. The CH
wind measurements are concentrated at higher A<SUB>He</SUB> and
v<SUB>αp</SUB>/v<SUB>A</SUB> values with a smaller A<SUB>He</SUB>
distribution range, while the AR and QS wind is associated with
lower A<SUB>He</SUB> and v<SUB>αp</SUB>/v<SUB>A</SUB>, and a
larger A<SUB>He</SUB> distribution range. The magnetic diversity
of the source regions and the physical processes related to it are
possibly responsible for the different properties of A<SUB>He</SUB>
and v<SUB>αp</SUB>/v<SUB>A</SUB>. The statistical results suggest
that the two solar wind generation mechanisms, WTD and RLO, work in
parallel in all solar wind source regions. In CH regions WTD plays a
major role, whereas the RLO mechanism is more important in AR and QS.
---------------------------------------------------------
Title: Energetics of Hi-C EUV brightenings
Authors: Subramanian, Srividya; Kashyap, Vinay L.; Tripathi, Durgesh;
Madjarska, Maria S.; Doyle, John G.
2018A&A...615A..47S Altcode: 2018arXiv180309505S
We study the thermal structure and energetics of the point-like extreme
ultraviolet (EUV) brightenings within a system of fan loops observed
in the active region AR 11520. These brightenings were simultaneously
observed on 2012 July 11 by the High-resolution Coronal (Hi-C) imager
and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory (SDO). We identified 27 brightenings by automatically
determining intensity enhancements in both Hi-C and AIA 193 Å light
curves. The energetics of these brightenings were studied using the
Differential Emission Measure (DEM) diagnostics. The DEM weighted
temperatures of these transients are in the range log T(K) = 6.2-6.6
with radiative energies ≈10<SUP>24-25</SUP> ergs and densities
approximately equal to a few times 10<SUP>9</SUP> cm<SUP>-3</SUP>. To
the best of our knowledge, these are the smallest brightenings in
EUV ever detected. We used these results to determine the mechanism
of energy loss in these brightenings. Our analysis reveals that the
dominant mechanism of energy loss for all the identified brightenings
is conduction rather than radiation.
---------------------------------------------------------
Title: Magnetic topological analysis of coronal bright points
Authors: Galsgaard, K.; Madjarska, M. S.; Moreno-Insertis, F.; Huang,
Z.; Wiegelmann, T.
2017A&A...606A..46G Altcode: 2017arXiv170704174G
Context. We report on the first of a series of studies on coronal
bright points which investigate the physical mechanism that generates
these phenomena. <BR /> Aims: The aim of this paper is to understand
the magnetic-field structure that hosts the bright points. <BR />
Methods: We use longitudinal magnetograms taken by the Solar Optical
Telescope with the Narrowband Filter Imager. For a single case,
magnetograms from the Helioseismic and Magnetic Imager were added
to the analysis. The longitudinal magnetic field component is used
to derive the potential magnetic fields of the large regions around
the bright points. A magneto-static field extrapolation method is
tested to verify the accuracy of the potential field modelling. The
three dimensional magnetic fields are investigated for the presence
of magnetic null points and their influence on the local magnetic
domain. <BR /> Results: In nine out of ten cases the bright point
resides in areas where the coronal magnetic field contains an opposite
polarity intrusion defining a magnetic null point above it. We find that
X-ray bright points reside, in these nine cases, in a limited part of
the projected fan-dome area, either fully inside the dome or expanding
over a limited area below which typically a dominant flux concentration
resides. The tenth bright point is located in a bipolar loop system
without an overlying null point. <BR /> Conclusions: All bright points
in coronal holes and two out of three bright points in quiet Sun regions
are seen to reside in regions containing a magnetic null point. An as
yet unidentified process(es) generates the brigh points in specific
regions of the fan-dome structure. <P />The movies are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201731041/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: The Plasma Parameters and Geometry of Cool and Warm Active
Region Loops
Authors: Xie, Haixia; Madjarska, Maria S.; Li, Bo; Huang, Zhenghua;
Xia, Lidong; Wiegelmann, Thomas; Fu, Hui; Mou, Chaozhou
2017ApJ...842...38X Altcode: 2017arXiv170502564X
How the solar corona is heated to high temperatures remains an unsolved
mystery in solar physics. In the present study we analyze observations
of 50 whole active region loops taken with the Extreme-ultraviolet
Imaging Spectrometer on board the Hinode satellite. Eleven loops were
classified as cool loops (<1 MK) and 39 as warm loops (1-2 MK). We
study their plasma parameters, such as densities, temperatures,
filling factors, nonthermal velocities, and Doppler velocities. We
combine spectroscopic analysis with linear force-free magnetic field
extrapolation to derive the 3D structure and positioning of the loops,
their lengths and heights, and the magnetic field strength along
the loops. We use density-sensitive line pairs from Fe xii, Fe xiii,
Si x, and Mg vii ions to obtain electron densities by taking special
care of intensity background subtraction. The emission measure loci
method is used to obtain the loop temperatures. We find that the loops
are nearly isothermal along the line of sight. Their filling factors
are between 8% and 89%. We also compare the observed parameters with
the theoretical Rosner-Tucker-Vaiana (RTV) scaling law. We find that
most of the loops are in an overpressure state relative to the RTV
predictions. In a follow-up study, we will report a heating model of a
parallel-cascade-based mechanism and will compare the model parameters
with the loop plasma and structural parameters derived here.
---------------------------------------------------------
Title: Charge States and FIP Bias of the Solar Wind from Coronal
Holes, Active Regions, and Quiet Sun
Authors: Fu, Hui; Madjarska, Maria S.; Xia, LiDong; Li, Bo; Huang,
ZhengHua; Wangguan, Zhipeng
2017ApJ...836..169F Altcode: 2017arXiv170107610F
Connecting in situ measured solar-wind plasma properties with typical
regions on the Sun can provide an effective constraint and test to
various solar wind models. We examine the statistical characteristics of
the solar wind with an origin in different types of source regions. We
find that the speed distribution of coronal-hole (CH) wind is bimodal
with the slow wind peaking at ∼400 km s<SUP>-1</SUP> and the fast at
∼600 km s<SUP>-1</SUP>. An anti-correlation between the solar wind
speeds and the O<SUP>7+</SUP>/O<SUP>6+</SUP> ion ratio remains valid in
all three types of solar wind as well during the three studied solar
cycle activity phases, I.e., solar maximum, decline, and minimum. The
{N}<SUB>{Fe</SUB>}/{N}<SUB>{{O</SUB>}} range and its average values
all decrease with the increasing solar wind speed in different types of
solar wind. The {N}<SUB>{Fe</SUB>}/{N}<SUB>{{O</SUB>}} range (0.06-0.40,
first ionization potential (FIP) bias range 1-7) for active region
wind is wider than for CH wind (0.06-0.20, FIP bias range 1-3),
while the minimum value of {N}<SUB>{Fe</SUB>}/{N}<SUB>{{O</SUB>}}
(∼ 0.06) does not change with the variation of speed, and it
is similar for all source regions. The two-peak distribution
of CH wind and the anti-correlation between the speed and
O<SUP>7+</SUP>/O<SUP>6+</SUP> in all three types of solar wind can
be explained qualitatively by both the wave-turbulence-driven and
reconnection-loop-opening (RLO) models, whereas the distribution
features of {N}<SUB>{Fe</SUB>}/{N}<SUB>{{O</SUB>}} in different
source regions of solar wind can be explained more reasonably by the
RLO models.
---------------------------------------------------------
Title: Explosive events in active region observed by IRIS and
SST/CRISP
Authors: Huang, Z.; Madjarska, M. S.; Scullion, E. M.; Xia, L. -D.;
Doyle, J. G.; Ray, T.
2017MNRAS.464.1753H Altcode: 2016arXiv160907698H
Transition-region explosive events (EEs) are characterized by
non-Gaussian line profiles with enhanced wings at Doppler velocities
of 50-150 km s<SUP>-1</SUP>. They are believed to be the signature
of solar phenomena that are one of the main contributors to coronal
heating. The aim of this study is to investigate the link of EEs to
dynamic phenomena in the transition region and chromosphere in an active
region. We analyse observations simultaneously taken by the Interface
Region Imaging Spectrograph (IRIS) in the Si IV 1394 Å line and the
slit-jaw (SJ) 1400 Å images, and the Swedish 1-m Solar Telescope
in the Hα line. In total 24 events were found. They are associated
with small-scale loop brightenings in SJ 1400 Å images. Only four
events show a counterpart in the Hα-35 km s<SUP>-1</SUP> and Hα+35
km s<SUP>-1</SUP> images. Two of them represent brightenings in the
conjunction region of several loops that are also related to a bright
region (granular lane) in the Hα-35 km s<SUP>-1</SUP> and Hα+35
km s<SUP>-1</SUP> images. 16 are general loop brightenings that do
not show any discernible response in the Hα images. Six EEs appear
as propagating loop brightenings, from which two are associated with
dark jet-like features clearly seen in the Hα-35 km s<SUP>-1</SUP>
images. We found that chromospheric events with jet-like appearance
seen in the wings of the Hα line can trigger EEs in the transition
region and in this case the IRIS Si IV 1394 Å line profiles are
seeded with absorption components resulting from Fe II and Ni II. Our
study indicates that EEs occurring in active regions have mostly
upper-chromosphere/transition-region origin. We suggest that magnetic
reconnection resulting from the braidings of small-scale transition
region loops is one of the possible mechanisms of energy release that
are responsible for the EEs reported in this paper.
---------------------------------------------------------
Title: Sources of the Slow Solar Wind During the Solar Cycle 23/24
Minimum
Authors: Kilpua, E. K. J.; Madjarska, M. S.; Karna, N.; Wiegelmann,
T.; Farrugia, C.; Yu, W.; Andreeova, K.
2016SoPh..291.2441K Altcode: 2016arXiv160605142K; 2016SoPh..tmp..149K
We investigate the characteristics and the sources of the slow
(<450 kms−<SUP>1</SUP>) solar wind during the four years (2006 -
2009) of low solar activity between Solar Cycles 23 and 24. We used a
comprehensive set of in-situ observations in the near-Earth solar wind
(Wind and ACE) and removed the periods when large-scale interplanetary
coronal mass ejections were present. The investigated period features
significant variations in the global coronal structure, including
the frequent presence of low-latitude active regions in 2006 - 2007,
long-lived low- and mid-latitude coronal holes in 2006 - mid-2008
and mostly the quiet Sun in 2009. We examined Carrington rotation
averages of selected solar plasma, charge state, and compositional
parameters and distributions of these parameters related to the quiet
Sun, active region Sun, and the coronal hole Sun. While some of the
investigated parameters (e.g. speed, the C<SUP>+6</SUP>/C<SUP>+4</SUP>
and He/H ratios) show clear variations over our study period and with
solar wind source type, some (Fe/O) exhibit very little changes. Our
results highlight the difficulty of distinguishing between the slow
solar wind sources based on the inspection of solar wind conditions.
---------------------------------------------------------
Title: Narrow-line-width UV Bursts in the Transition Region above
Sunspots Observed by IRIS
Authors: Hou, Zhenyong; Huang, Zhenghua; Xia, Lidong; Li, Bo;
Madjarska, Maria S.; Fu, Hui; Mou, Chaozhou; Xie, Haixia
2016ApJ...829L..30H Altcode: 2016arXiv160804892H
Various small-scale structures abound in the solar atmosphere above
active regions, playing an important role in the dynamics and evolution
therein. We report on a new class of small-scale transition region
structures in active regions, characterized by strong emissions but
extremely narrow Si IV line profiles as found in observations taken
with the Interface Region Imaging Spectrograph (IRIS). Tentatively
named as narrow-line-width UV bursts (NUBs), these structures are
located above sunspots and comprise one or multiple compact bright
cores at sub-arcsecond scales. We found six NUBs in two data sets
(a raster and a sit-and-stare data set). Among these, four events
are short-lived with a duration of ∼10 minutes, while two last
for more than 36 minutes. All NUBs have Doppler shifts of 15-18 km
s<SUP>-1</SUP>, while the NUB found in sit-and-stare data possesses
an additional component at ∼50 km s<SUP>-1</SUP> found only in the
C II and Mg II lines. Given that these events are found to play a
role in the local dynamics, it is important to further investigate
the physical mechanisms that generate these phenomena and their role
in the mass transport in sunspots.
---------------------------------------------------------
Title: Homologous prominence non-radial eruptions: A case study
Authors: Duchlev, P.; Koleva, K.; Madjarska, M. S.; Dechev, M.
2016NewA...48...66D Altcode: 2016arXiv160502299D
The present study provides important details on homologous eruptions
of a solar prominence that occurred in active region NOAA 10904 on
2006 August 22. We report on the pre-eruptive phase of the homologous
feature as well as the kinematics and the morphology of a forth from
a series of prominence eruptions that is critical in defining the
nature of the previous consecutive eruptions. The evolution of the
overlying coronal field during homologous eruptions is discussed and a
new observational criterion for homologous eruptions is provided. We
find a distinctive sequence of three activation periods each of them
containing pre-eruptive precursors such as a brightening and enlarging
of the prominence body followed by small surge-like ejections from its
southern end observed in the radio 17 GHz. We analyse a fourth eruption
that clearly indicates a full reformation of the prominence after the
third eruption. The fourth eruption although occurring 11 h later has
an identical morphology, the same angle of propagation with respect
to the radial direction, as well as similar kinematic evolution as the
previous three eruptions. We find an important feature of the homologous
eruptive prominence sequence that is the maximum height increase of each
consecutive eruption. The present analysis establishes that all four
eruptions observed in Hα are of confined type with the third eruption
undergoing a thermal disappearance during its eruptive phase. We suggest
that the observation of the same direction of the magnetic flux rope
(MFR) ejections can be consider as an additional observational criterion
for MFR homology. This observational indication for homologous eruptions
is important, especially in the case of events of typical or poorly
distinguishable morphology of eruptive solar phenomena.
---------------------------------------------------------
Title: Oscillatory Response of the Solar Chromosphere to a Strong
Downflow Event above a Sunspot
Authors: Kwak, Hannah; Chae, Jongchul; Song, Donguk; Kim, Yeon-Han;
Lim, Eun-Kyung; Madjarska, Maria S.
2016ApJ...821L..30K Altcode: 2016arXiv160402252K
We report three-minute oscillations in the solar chromosphere
driven by a strong downflow event in a sunspot. We used the Fast
Imaging Solar Spectrograph of the 1.6 m New Solar Telescope and the
Interface Region Imaging Spectrograph (IRIS). The strong downflow
event is identified in the chromospheric and transition region lines
above the sunspot umbra. After the event, oscillations occur at the
same region. The amplitude of the Doppler velocity oscillations is
2 km s<SUP>-1</SUP> and gradually decreases with time. In addition,
the period of the oscillations gradually increases from 2.7 to 3.3
minutes. In the IRIS 1330 Å slit-jaw images, we identify a transient
brightening near the footpoint of the downflow detected in the Hα+0.5
Å image. The characteristics of the downflowing material are consistent
with those of sunspot plumes. Based on our findings, we suggest that
the gravitationally stratified atmosphere came to oscillate with a
three-minute period in response to the impulsive downflow event as
was theoretically investigated by Chae & Goode.
---------------------------------------------------------
Title: Transition region bright dots in active regions observed by
the interface region imaging spectrograph
Authors: Hou, Zhenyong; Huang, Zhenghua; Xia, Lidong; Li, Bo;
Madjarska, Maria S.; Fu, Hui
2016AIPC.1720b0001H Altcode: 2018arXiv180308294H
The Interface Region Imaging Spectrograph (IRIS) reveals numerous
small-scale (sub-arcsecond) brightenings that appear as bright dots
sparkling the solar transition region in active regions. Here,
we report a statistical study on these transition-region bright
dots. We use an automatic approach to identify 2742 dots in a Si IV
raster image. We find that the average spatial size of the dots is
0.8 arcsec<SUP>2</SUP> and most of them are located in the faculae
area. Their Doppler velocities obtained from the Si IV 1394 Å line
range from -20 to 20 km s<SUP>-1</SUP>. Among these 2742 dots, 1224 are
predominantly blue-shifted and 1518 are red-shifted. Their non-thermal
velocities range from 4 to 50 km s<SUP>-1</SUP> with an average of
24 km s<SUP>-1</SUP>. We speculate that the bright dots studied here
are small-scale impulsive energetic events that can heat the active
region corona.
---------------------------------------------------------
Title: Magnetic Flux Supplement to Coronal Bright Points
Authors: Mou, Chaozhou; Huang, Zhenghua; Xia, Lidong; Madjarska,
Maria S.; Li, Bo; Fu, Hui; Jiao, Fangran; Hou, Zhenyong
2016ApJ...818....9M Altcode: 2015arXiv151109215M
Coronal bright points (BPs) are associated with magnetic bipolar
features (MBFs) and magnetic cancellation. Here we investigate how
BP-associated MBFs form and how the consequent magnetic cancellation
occurs. We analyze longitudinal magnetograms from the Helioseismic and
Magnetic Imager to investigate the photospheric magnetic flux evolution
of 70 BPs. From images taken in the 193 Å passband of the Atmospheric
Imaging Assembly (AIA) we dermine that the BPs’ lifetimes vary from
2.7 to 58.8 hr. The formation of the BP MBFs is found to involve three
processes, namely, emergence, convergence, and local coalescence of
the magnetic fluxes. The formation of an MBF can involve more than one
of these processes. Out of the 70 cases, flux emergence is the main
process of an MBF buildup of 52 BPs, mainly convergence is seen in 28,
and 14 cases are associated with local coalescence. For MBFs formed by
bipolar emergence, the time difference between the flux emergence and
the BP appearance in the AIA 193 Å passband varies from 0.1 to 3.2 hr
with an average of 1.3 hr. While magnetic cancellation is found in all
70 BPs, it can occur in three different ways: (I) between an MBF and
small weak magnetic features (in 33 BPs); (II) within an MBF with the
two polarities moving toward each other from a large distance (34 BPs);
(III) within an MBF whose two main polarities emerge in the same place
simultaneously (3 BPs). While an MBF builds up the skeleton of a BP,
we find that the magnetic activities responsible for the BP heating
may involve small weak fields.
---------------------------------------------------------
Title: Cool transition region loops observed by the Interface Region
Imaging Spectrograph
Authors: Huang, Z.; Xia, L.; Li, B.; Madjarska, M. S.
2015AGUFMSH31D..09H Altcode:
An important class of loops in the solar atmosphere, cool transition
region loops, have received little attention mainly due to instrumental
limitations. We analyze a cluster of these loops in the on-disk active
region NOAA 11934 recorded in a Si IV 1402.8 Å spectral raster and
1400Å slit-jaw (SJ) images taken by the Interface Region Imaging
Spectrograph. We divide these loops into three groups and study
their dynamics, evolution and interaction.The first group comprises
geometrically relatively stable loops, which are finely scaled with
382~626 km cross-sections. Siphon flows in these loops are suggested by
the Doppler velocities gradually changing from -10 km/s (blue-shifts)
in one end to 20 km/s (red-shifts) in the other. Nonthermal velocities
from 15 to 25 km/s were determined. The obtained physical properties
suggest that these loops are impulsively heated by magnetic reconnection
occurring at the blue-shifted footpoints where magnetic cancellation
with a rate of 1015 Mx/s is found. The released magnetic energy is
redistributed by the siphon flows. The second group corresponds to two
active footpoints rooted in mixed-magnetic-polarity regions. Magnetic
reconnection in both footpoints is suggested by explosive-event line
profiles with enhanced wings up to 200 km/s and magnetic cancellation
with a rate of ~1015 Mx/s. In the third group, an interaction between
two cool loop systems is observed. Mixed-magnetic polarities are seen
in their conjunction area where explosive-event line profiles and
magnetic cancellation with a rate of 3×1015 Mx/s are found. This is
a clear indication that magnetic reconnection occurs between these two
loop systems. Our observations suggest that the cool transition region
loops are heated impulsively most likely by sequences of magnetic
reconnection events.
---------------------------------------------------------
Title: Active region upflows. I. Multi-instrument observations
Authors: Vanninathan, K.; Madjarska, M. S.; Galsgaard, K.; Huang,
Z.; Doyle, J. G.
2015A&A...584A..38V Altcode: 2015arXiv150905624V
Context. We study upflows at the edges of active regions, called AR
outflows, using multi-instrument observations. <BR /> Aims: This study
intends to provide the first direct observational evidence of whether
chromospheric jets play an important role in furnishing mass that could
sustain coronal upflows. The evolution of the photospheric magnetic
field, associated with the footpoints of the upflow region and the
plasma properties of active region upflows is investigated with the
aim of providing information for benchmarking data-driven modelling of
this solar feature. <BR /> Methods: We spatially and temporally combine
multi-instrument observations obtained with the Extreme-ultraviolet
Imaging Spectrometer on board the Hinode, the Atmospheric Imaging
Assembly and the Helioseismic Magnetic Imager instruments on board
the Solar Dynamics Observatory and the Interferometric BI-dimensional
Spectro-polarimeter installed at the National Solar Observatory, Sac
Peak, to study the plasma parameters of the upflows and the impact of
the chromosphere on active region upflows. <BR /> Results: Our analysis
shows that the studied active region upflow presents similarly to
those studied previously, i.e. it displays blueshifted emission of 5-20
kms<SUP>-1</SUP> in Fe xii and Fe xiii and its average electron density
is 1.8 × 10<SUP>9</SUP> cm<SUP>-3</SUP> at 1 MK. The time variation
of the density is obtained showing no significant change (in a 3σ
error). The plasma density along a single loop is calculated revealing
a drop of 50% over a distance of ~20 000 km along the loop. We find a
second velocity component in the blue wing of the Fe xii and Fe xiii
lines at 105 kms<SUP>-1</SUP> reported only once before. For the first
time we study the time evolution of this component at high cadence and
find that it is persistent during the whole observing period of 3.5 h
with variations of only ±15 kms<SUP>-1</SUP>. We also, for the first
time, study the evolution of the photospheric magnetic field at high
cadence and find that magnetic flux diffusion is responsible for the
formation of the upflow region. High cadence Hα observations are used
to study the chromosphere at the footpoints of the upflow region. We
find no significant jet-like (spicule/rapid blue excursion) activity
to account for several hours/days of plasma upflow. The jet-like
activity in this region is not continuous and blueward asymmetries
are a bare minimum. Using an image enhancement technique for imaging
and spectral data, we show that the coronal structures seen in the
AIA 193 Å channel are comparable to the EIS Fe xii images, while
images in the AIA 171 Å channel reveal additional loops that are a
result of contribution from cooler emission to this channel. <BR />
Conclusions: Our results suggest that at chromospheric heights there
are no signatures that support the possible contribution of spicules
to active region upflows. We suggest that magnetic flux diffusion is
responsible for the formation of the coronal upflows. The existence of
two velocity components possibly indicates the presence of two different
flows, which are produced by two different physical mechanisms,
e.g. magnetic reconnection and pressure-driven jets. <P />Movies
associated to Figs. A.1-A.3 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201526340/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Active region upflows. II. Data driven magnetohydrodynamic
modelling
Authors: Galsgaard, K.; Madjarska, M. S.; Vanninathan, K.; Huang,
Z.; Presmann, M.
2015A&A...584A..39G Altcode: 2015arXiv150905639G
Context. Observations of many active regions show a slow systematic
outflow/upflow from their edges lasting from hours to days. At present
no physical explanation has been proven, while several suggestions have
been put forward. <BR /> Aims: This paper investigates one possible
method for maintaining these upflows assuming, that convective
motions drive the magnetic field to initiate them through magnetic
reconnection. <BR /> Methods: We use Helioseismic and Magnetic Imager
(HMI) data to provide an initial potential 3D magnetic field of the
active region NOAA 11123 on 2010 November 13 where the characteristic
upflow velocities are observed. A simple 1D hydrostatic atmospheric
model covering the region from the photosphere to the corona is
derived. Local correlation tracking of the magnetic features in the
HMI data is used to derive a proxy for the time dependent velocity
field. The time dependent evolution of the system is solved using a
resistive 3D magnetohydrodynamic code. <BR /> Results: The magnetic
field contains several null points located well above the photosphere,
with their fan planes dividing the magnetic field into independent
open and closed flux domains. The stressing of the interfaces between
the different flux domains is expected to provide locations where
magnetic reconnection can take place and drive systematic flows. In
this case, the region between the closed and open flux is identified
as the region where observations find the systematic upflows. <BR />
Conclusions: In the present experiment, the driving only initiates
magneto-acoustic waves without driving any systematic upflows at any of
the flux interfaces. <P />Movie is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201526339/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: ADAHELI: exploring the fast, dynamic Sun in the x-ray, optical,
and near-infrared
Authors: Berrilli, Francesco; Soffitta, Paolo; Velli, Marco; Sabatini,
Paolo; Bigazzi, Alberto; Bellazzini, Ronaldo; Bellot Rubio, Luis
Ramon; Brez, Alessandro; Carbone, Vincenzo; Cauzzi, Gianna; Cavallini,
Fabio; Consolini, Giuseppe; Curti, Fabio; Del Moro, Dario; Di Giorgio,
Anna Maria; Ermolli, Ilaria; Fabiani, Sergio; Faurobert, Marianne;
Feller, Alex; Galsgaard, Klaus; Gburek, Szymon; Giannattasio, Fabio;
Giovannelli, Luca; Hirzberger, Johann; Jefferies, Stuart M.; Madjarska,
Maria S.; Manni, Fabio; Mazzoni, Alessandro; Muleri, Fabio; Penza,
Valentina; Peres, Giovanni; Piazzesi, Roberto; Pieralli, Francesca;
Pietropaolo, Ermanno; Martinez Pillet, Valentin; Pinchera, Michele;
Reale, Fabio; Romano, Paolo; Romoli, Andrea; Romoli, Marco; Rubini,
Alda; Rudawy, Pawel; Sandri, Paolo; Scardigli, Stefano; Spandre,
Gloria; Solanki, Sami K.; Stangalini, Marco; Vecchio, Antonio;
Zuccarello, Francesca
2015JATIS...1d4006B Altcode:
Advanced Astronomy for Heliophysics Plus (ADAHELI) is a project concept
for a small solar and space weather mission with a budget compatible
with an European Space Agency (ESA) S-class mission, including launch,
and a fast development cycle. ADAHELI was submitted to the European
Space Agency by a European-wide consortium of solar physics research
institutes in response to the "Call for a small mission opportunity
for a launch in 2017," of March 9, 2012. The ADAHELI project builds
on the heritage of the former ADAHELI mission, which had successfully
completed its phase-A study under the Italian Space Agency 2007 Small
Mission Programme, thus proving the soundness and feasibility of
its innovative low-budget design. ADAHELI is a solar space mission
with two main instruments: ISODY: an imager, based on Fabry-Pérot
interferometers, whose design is optimized to the acquisition of
highest cadence, long-duration, multiline spectropolarimetric images
in the visible/near-infrared region of the solar spectrum. XSPO: an
x-ray polarimeter for solar flares in x-rays with energies in the 15
to 35 keV range. ADAHELI is capable of performing observations that
cannot be addressed by other currently planned solar space missions,
due to their limited telemetry, or by ground-based facilities, due to
the problematic effect of the terrestrial atmosphere.
---------------------------------------------------------
Title: Coronal Response to an EUV Wave from DEM Analysis
Authors: Vanninathan, K.; Veronig, A. M.; Dissauer, K.; Madjarska,
M. S.; Hannah, I. G.; Kontar, E. P.
2015ApJ...812..173V Altcode: 2015arXiv150905269V
Extreme-Ultraviolet (EUV) waves are globally propagating disturbances
that have been observed since the era of the Solar and Heliospheric
Observatory/Exteme-ultraviolet Imaging Telescope instrument. Although
the kinematics of the wave front and secondary wave components have been
widely studied, there is not much known about the generation and plasma
properties of the wave. In this paper we discuss the effect of an EUV
wave on the local plasma as it passes through the corona. We studied the
EUV wave, generated during the 2011 February 15 X-class flare/coronal
mass ejection event, using Differential Emission Measure diagnostics. We
analyzed regions on the path of the EUV wave and investigated the local
density and temperature changes. From our study we have quantitatively
confirmed previous results that during wave passage the plasma visible
in the Atmospheric Imaging Assembly (AIA) 171 Å channel is getting
heated to higher temperatures corresponding to AIA 193 and 211 Å
channels. We have calculated an increase of 6%-9% in density and 5%-6%
in temperature during the passage of the EUV wave. We have compared
the variation in temperature with the adiabatic relationship and
have quantitatively demonstrated the phenomenon of heating due to
adiabatic compression at the wave front. However, the cooling phase
does not follow adiabatic relaxation but shows slow decay indicating
slow energy release being triggered by the wave passage. We have also
identified that heating is taking place at the front of the wave pulse
rather than at the rear. Our results provide support for the case that
the event under study here is a compressive fast-mode wave or a shock.
---------------------------------------------------------
Title: Cool Transition Region Loops Observed by the Interface Region
Imaging Spectrograph
Authors: Huang, Zhenghua; Xia, Lidong; Li, Bo; Madjarska, Maria S.
2015ApJ...810...46H Altcode: 2015arXiv150707594H
We report on the first Interface Region Imaging Spectrograph (IRIS)
study of cool transition region loops, a class of loops that has
received little attention in the literature. A cluster of such loops
was observed on the solar disk in active region NOAA11934, in the
Si iv 1402.8 Å spectral raster and 1400 Å slit-jaw images. We
divide the loops into three groups and study their dynamics. The
first group comprises relatively stable loops, with 382-626 km
cross-sections. Observed Doppler velocities are suggestive of siphon
flows, gradually changing from -10 km s<SUP>-1</SUP> at one end to 20
km s<SUP>-1</SUP> at the other end of the loops. Nonthermal velocities
of 15 ∼ 25 km s<SUP>-1</SUP> were determined. Magnetic cancellation
with a rate of 10<SUP>15</SUP> Mx s<SUP>-1</SUP> is found at the
blueshifted footpoints. These physical properties suggest that these
loops are impulsively heated by magnetic reconnection, and the siphon
flows play an important role in the energy redistribution. The second
group corresponds to two footpoints rooted in mixed-magnetic-polarity
regions, where magnetic cancellation with a rate of 10<SUP>15</SUP> Mx
s<SUP>-1</SUP> and explosive-event line profiles with enhanced wings
of up to 200 km s<SUP>-1</SUP> were observed. In the third group,
interaction between two cool loop systems is observed. Evidence for
magnetic reconnection between the two loop systems is reflected in the
explosive-event line profiles and magnetic cancellation with a rate of
3× {10}<SUP>15</SUP> Mx s<SUP>-1</SUP> observed in the corresponding
area. The IRIS has provided opportunity for in-depth investigations
of cool transition region loops. Further numerical experiments are
crucial for understanding their physics and their roles in the coronal
heating processes.
---------------------------------------------------------
Title: A coronal wave and an asymmetric eruptive filament in SUMER,
CDS, EIT, and TRACE co-observations
Authors: Madjarska, M. S.; Doyle, J. G.; Shetye, J.
2015A&A...575A..39M Altcode: 2014arXiv1412.1984M
Context. The investigation covers the complex subject of coronal waves
and the phenomena contributing to and/or causing their formation. <BR
/> Aims: The objectives of the present study is to provide a better
physical understanding of the complex inter-relation and evolution
of several solar coronal features comprising a double-peak flare,
a coronal dimming caused by a coronal mass ejection (CME), a
CME-driven compression, and a fast-mode wave. For the first time,
the evolution of an asymmetric eruptive filament is analysed in
simultaneous Solar Ultraviolet Measurement of Emitted Radiation
(SUMER) spectroscopic and Transition Region and Coronal Explorer
(TRACE) and Extreme-ultraviolet Imaging Telescope (EIT) imaging
data. <BR /> Methods: We use imaging observations from EIT and
TRACE in the 195 Å channel and spectroscopic observations from the
Coronal Diagnostic Spectrometer (CDS) in a rastering and SUMER in a
sit-and-stare observing mode. The SUMER spectra cover spectral lines
with formation temperatures from log T(K) ~ 4.0 to 6.1. <BR /> Results:
Although the event was already analysed in two previous studies,
our analysis brings a wealth of new information on the dynamics and
physical properties of the observed phenomena. We found that the dynamic
event is related to a complex flare with two distinct impulsive peaks,
one according to the Geostationary Operational Environmental Satellite
(GOES) classification as C1.1 and the second - C1.9. The first energy
release triggers a fast-mode wave and a CME with a clear CME driven
compression ahead of it. This activity is related to, or possibly
caused, by an asymmetric filament eruption. The filament is observed to
rise with its leading edge moving at a speed of ~300 kms<SUP>-1</SUP>
detected both in the SUMER and CDS data. The rest of the filament body
moves at only ~150 kms<SUP>-1</SUP> while untwisting. No signature is
found of the fast-mode wave in the SUMER data, suggesting that the
plasma disturbed by the wave had temperatures above 600 000 K. The
erupting filament material is found to emit only in spectral lines at
transition region temperatures. Earlier identification of a coronal
response detected in the Mg x 609.79 Å line is found to be caused by
a blend from the O iv 609.83 Å line. <BR /> Conclusions: We present a
unique analysis of the complex phenomenon called "EIT/coronal wave",
confirming its bimodal nature. We suggest that the disintegration of
the dimming/CME and the CME-driven compression are either caused by
a CME-CME interaction taking place in the low solar atmosphere or by
an impulsive CME cavity overexpansion in the low solar atmosphere. <P
/>A movie associated to Fig. A.1 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424754/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Erratum: Erratum to: Off-limb (Spicule) DEM Distribution from
SoHO/SUMER Observations
Authors: Vanninathan, K.; Madjarska, M. S.; Scullion, E.; Doyle, J. G.
2014SoPh..289.4749V Altcode: 2014SoPh..tmp..127V
No abstract at ADS
---------------------------------------------------------
Title: Explosive Events on a Subarcsecond Scale in IRIS Observations:
A Case Study
Authors: Huang, Zhenghua; Madjarska, Maria S.; Xia, Lidong; Doyle,
J. G.; Galsgaard, Klaus; Fu, Hui
2014ApJ...797...88H Altcode: 2014arXiv1409.6425H
We present a study of a typical explosive event (EE) at subarcsecond
scale witnessed by strong non-Gaussian profiles with blue- and
redshifted emission of up to 150 km s<SUP>-1</SUP> seen in the
transition region Si IV 1402.8 Å, and the chromospheric Mg II
k 2796.4 Å and C II 1334.5 Å observed by the Interface Region
Imaging Spectrograph (IRIS) at unprecedented spatial and spectral
resolution. For the first time an EE is found to be associated with
very small-scale (~120 km wide) plasma ejection followed by retraction
in the chromosphere. These small-scale jets originate from a compact
bright-point-like structure of ~1.”5 size as seen in the IRIS 1330
Å images. SDO/AIA and SDO/HMI co-observations show that the EE lies
in the footpoint of a complex loop-like brightening system. The EE is
detected in the higher temperature channels of AIA 171 Å, 193 Å,
and 131 Å, suggesting that it reaches a higher temperature of log
T = 5.36 ± 0.06 (K). Brightenings observed in the AIA channels with
durations 90-120 s are probably caused by the plasma ejections seen
in the chromosphere. The wings of the C II line behave in a similar
manner to the Si IV'S, indicating close formation temperatures, while
the Mg II k wings show additional Doppler-shifted emission. Magnetic
convergence or emergence followed by cancellation at a rate of 5 ×
10<SUP>14</SUP> Mx s<SUP>-1</SUP> is associated with the EE region. The
combined changes of the locations and the flux of different magnetic
patches suggest that magnetic reconnection must have taken place. Our
results challenge several theories put forward in the past to explain
non-Gaussian line profiles, i.e., EEs. Our case study on its own,
however, cannot reject these theories; thus, further in-depth studies
on the phenomena producing EEs are required.
---------------------------------------------------------
Title: Hα spectroscopy and multiwavelength imaging of a solar flare
caused by filament eruption
Authors: Huang, Z.; Madjarska, M. S.; Koleva, K.; Doyle, J. G.;
Duchlev, P.; Dechev, M.; Reardon, K.
2014A&A...566A.148H Altcode: 2014arXiv1405.2194H
Context. We study a sequence of eruptive events including filament
eruption, a GOES C4.3 flare, and a coronal mass ejection. <BR /> Aims:
We aim to identify the possible trigger(s) and precursor(s) of the
filament destabilisation, investigate flare kernel characteristics,
flare ribbons/kernels formation and evolution, study the interrelation
of the filament-eruption/flare/coronal-mass-ejection phenomena as
part of the integral active-region magnetic field configuration, and
determine Hα line profile evolution during the eruptive phenomena. <BR
/> Methods: Multi-instrument observations are analysed including Hα
line profiles, speckle images at Hα - 0.8 Å and Hα + 0.8 Å from
IBIS at DST/NSO, EUV images and magnetograms from the SDO, coronagraph
images from STEREO, and the X-ray flux observations from Fermi and
GOES. <BR /> Results: We establish that the filament destabilisation
and eruption are the main triggers for the flaring activity. A
surge-like event with a circular ribbon in one of the filament
footpoints is determined as the possible trigger of the filament
destabilisation. Plasma draining in this footpoint is identified as
the precursor for the filament eruption. A magnetic flux emergence
prior to the filament destabilisation followed by a high rate of flux
cancellation of 1.34 × 10<SUP>16</SUP> Mx s<SUP>-1</SUP> is found
during the flare activity. The flare X-ray lightcurves reveal three
phases that are found to be associated with three different ribbons
occurring consecutively. A kernel from each ribbon is selected and
analysed. The kernel lightcurves and Hα line profiles reveal that the
emission increase in the line centre is stronger than that in the line
wings. A delay of around 5-6 min is found between the increase in the
line centre and the occurrence of red asymmetry. Only red asymmetry is
observed in the ribbons during the impulsive phases. Blue asymmetry
is only associated with the dynamic filament. <P />Appendix A and
movie associated to Fig. A.4 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201323097/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Intensity Enhancement of O VI Ultraviolet Emission Lines in
Solar Spectra due to Opacity
Authors: Keenan, F. P.; Doyle, J. G.; Madjarska, M. S.; Rose, S. J.;
Bowler, L. A.; Britton, J.; McCrink, L.; Mathioudakis, M.
2014ApJ...784L..39K Altcode: 2014arXiv1403.1470K
Opacity is a property of many plasmas. It is normally expected that if
an emission line in a plasma becomes optically thick, then its intensity
ratio to that of another transition that remains optically thin
should decrease. However, radiative transfer calculations undertaken
both by ourselves and others predict that under certain conditions the
intensity ratio of an optically thick to an optically thin line can show
an increase over the optically thin value, indicating an enhancement
in the former. These conditions include the geometry of the emitting
plasma and its orientation to the observer. A similar effect can
take place between lines of differing optical depths. While previous
observational studies have focused on stellar point sources, here we
investigate the spatially resolved solar atmosphere using measurements
of the I(1032 Å)/I(1038 Å) intensity ratio of O VI in several regions
obtained with the Solar Ultraviolet Measurements of Emitted Radiation
instrument on board the Solar and Heliospheric Observatory satellite. We
find several I(1032 Å)/I(1038 Å) ratios observed on the disk to be
significantly larger than the optically thin value of 2.0, providing
the first detection (to our knowledge) of intensity enhancement in
the ratio arising from opacity effects in the solar atmosphere. The
agreement between observation and theory is excellent and confirms
that the O VI emission originates from a slab-like geometry in the
solar atmosphere, rather than from cylindrical structures.
---------------------------------------------------------
Title: Ellerman Bombs—Evidence for Magnetic Reconnection in the
Lower Solar Atmosphere
Authors: Nelson, C. J.; Shelyag, S.; Mathioudakis, M.; Doyle, J. G.;
Madjarska, M. S.; Uitenbroek, H.; Erdélyi, R.
2013ApJ...779..125N Altcode: 2013arXiv1310.7756N
The presence of photospheric magnetic reconnection has long been thought
to give rise to short and impulsive events, such as Ellerman bombs (EBs)
and Type II spicules. In this article, we combine high-resolution,
high-cadence observations from the Interferometric BIdimensional
Spectrometer and Rapid Oscillations in the Solar Atmosphere instruments
at the Dunn Solar Telescope, National Solar Observatory, New Mexico,
with co-aligned Solar Dynamics Observatory Atmospheric Imaging Assembly
and Hinode Solar Optical Telescope (SOT) data to observe small-scale
events situated within an active region. These data are then compared
with state-of-the-art numerical simulations of the lower atmosphere
made using the MURaM code. It is found that brightenings, in both the
observations and the simulations, of the wings of the Hα line profile,
interpreted as EBs, are often spatially correlated with increases in
the intensity of the Fe I λ6302.5 line core. Bipolar regions inferred
from Hinode/SOT magnetic field data show evidence of flux cancellation
associated, co-spatially, with these EBs, suggesting that magnetic
reconnection could be a driver of these high-energy events. Through
the analysis of similar events in the simulated lower atmosphere,
we are able to infer that line profiles analogous to the observations
occur co-spatially with regions of strong opposite-polarity magnetic
flux. These observed events and their simulated counterparts are
interpreted as evidence of photospheric magnetic reconnection at scales
observable using current observational instrumentation.
---------------------------------------------------------
Title: Diagnosing transient ionization in dynamic events
Authors: Doyle, J. G.; Giunta, A.; Madjarska, M. S.; Summers, H.;
O'Mullane, M.; Singh, A.
2013A&A...557L...9D Altcode: 2013arXiv1307.8251D
<BR /> Aims: The present study aims to provide a diagnostic line ratio
that will enable the observer to determine whether a plasma is in
a state of transient ionization. <BR /> Methods: We use the Atomic
Data and Analysis Structure (ADAS) to calculate line contribution
functions for two lines, Si iv 1394 Å and O iv 1401 Å, formed in
the solar transition region. The generalized collisional-radiative
theory is used. It includes all radiative and electron collisional
processes, except for photon-induced processes. State-resolved direct
ionization and recombination to and from the next ionization stage
are also taken into account. <BR /> Results: For dynamic bursts
with a decay time of a few seconds, the Si iv 1394 Å line can be
enhanced by a factor of 2-4 in the first fraction of a second with
the peak in the line contribution function occurring initially at a
higher electron temperature due to transient ionization compared to
ionization equilibrium conditions. On the other hand, the O iv 1401 Å
does not show such any enhancement. Thus the ratio of these two lines,
which can be observed with the Interface Region Imaging Spectrograph,
can be used as a diagnostic of transient ionization. <BR /> Conclusions:
We show that simultaneous high-cadence observations of two lines formed
in the solar transition region may be used as a direct diagnostic of
whether the observed plasma is in transient ionization. The ratio of
these two lines can change by a factor of four in a few seconds owing
to transient ionization alone.
---------------------------------------------------------
Title: Evolution of magnetic field corresponding to X-ray brightening
events in coronal holes and quiet Sun
Authors: Huang, Zhenghua; Madjarska, Maria; Doyle, Gerry; Lamb, Derek
2013IAUS..294..155H Altcode:
We study the magnetic field structure and evolution for 26 X-ray
brightening events in coronal holes and quiet Sun regions, including
bright points and jets. We found that all brightening events are
associated with bipolar regions and caused by magnetic flux emergence
followed by cancellation. The emission fluctuations seen in the X-ray
bright points are associated with reoccurring magnetic cancellation
in the footpoints. An X-ray jet presents similar magnetic behaviour in
the footpoints but its magnetic flux cancellation rate is much higher
than in the bright point. Comparing coronal holes and the quiet Sun, we
do not find differences in their corresponding magnetic field behavior.
---------------------------------------------------------
Title: Jets from coronal holes - possible source of the slow
solar wind
Authors: Madjarska, Maria; Huang, Zhenghua; Subramanian, Srividya;
Doyle, Gerry
2013EGUGA..15.2455M Altcode:
We will report on statistical studies on the occurrence rate, plasma
properties, dynamics and structural evolution, including the magnetic
field evolution, of small-scale transients in and along the boundaries
of equatorial coronal holes. A comparison is made with quiet-Sun
transients. We use multi-instrument observations from the photosphere
to the corona comprising imaging, magnetogram and imaging spectroscopy
data from EIS, XRT and SOT on board Hinode and SUMER onboard SoHO. The
visual analysis of these transients reveals that around 70% of them
in equatorial, polar and transient coronal holes and their boundaries
show expanding loop structures and/or collimated outflows, i.e. jets. In
the quiet Sun only 30% of the brightenings show flows with most of them
appearing to be contained in the solar corona by closed magnetic field
lines. This strongly suggests that magnetic reconnection of co-spatial
open and closed magnetic field lines creates the necessary conditions
for plasma outflows to large distances. The ejected plasma always
originates from preexisting or newly emerging (at X-ray temperatures)
bright points. We will discuss in detail the evolution of individual
jets and the possibility whether these phenomena could be one of the
sources of the slow solar wind.
---------------------------------------------------------
Title: Statistical Analysis of Small Ellerman Bomb Events
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Huang, Z.;
Madjarska, M. S.; Mathioudakis, M.; Mumford, S. J.; Reardon, K.
2013SoPh..283..307N Altcode: 2013arXiv1301.1351N
The properties of Ellerman bombs (EBs), small-scale brightenings in
the Hα line wings, have proved difficult to establish because their
size is close to the spatial resolution of even the most advanced
telescopes. Here, we aim to infer the size and lifetime of EBs using
high-resolution data of an emerging active region collected using
the Interferometric BIdimensional Spectrometer (IBIS) and Rapid
Oscillations of the Solar Atmosphere (ROSA) instruments as well as
the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO). We develop an algorithm to track EBs through their
evolution, finding that EBs can often be much smaller (around 0.3″)
and shorter-lived (less than one minute) than previous estimates. A
correlation between G-band magnetic bright points and EBs is also
found. Combining SDO/HMI and G-band data gives a good proxy of the
polarity for the vertical magnetic field. It is found that EBs often
occur both over regions of opposite polarity flux and strong unipolar
fields, possibly hinting at magnetic reconnection as a driver of these
events.The energetics of EB events is found to follow a power-law
distribution in the range of a nanoflare (10<SUP>22−25</SUP> ergs).
---------------------------------------------------------
Title: Ellerman bombs: small-scale brightenings in the photosphere
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Madjarska, M.;
Mumford, S. J.
2013MmSAI..84..436N Altcode:
Observations of small-scale events in the solar atmosphere are
limited by the spatial and temporal resolutions of the current crop
of observational instruments. Both high-cadence and high-resolution
observations of the photosphere have shown the continued dynamics to
extremely small-scales. Ellerman bombs, brightening events in the
wings of the Halpha line profile, are one example of small-scale,
short-lived events which have been widely studied due to their fast
dynamics in recent years. By combining the Interferometric BIdimensional
Spectrometer (IBIS) instrument with the Helioseismic and Magnetic Imager
(HMI/SDO), we show the small-scale nature of these events, as well as
their link to the background magnetic field. It is found that EBs can
be much smaller and shorter-lived than previous estimates have stated,
implying the continued dynamics of the solar atmosphere below current
observational limits.
---------------------------------------------------------
Title: Nature of Quiet Sun Oscillations Using Data from the Hinode,
TRACE, and SOHO Spacecraft
Authors: Gupta, G. R.; Subramanian, S.; Banerjee, D.; Madjarska,
M. S.; Doyle, J. G.
2013SoPh..282...67G Altcode: 2012arXiv1209.5252G; 2012SoPh..tmp..247G
We study the nature of quiet-Sun oscillations using multi-wavelength
observations from TRACE, Hinode, and SOHO. The aim is to investigate
the existence of propagating waves in the solar chromosphere and
the transition region by analyzing the statistical distribution of
power in different locations, e.g. in bright magnetic (network),
bright non-magnetic and dark non-magnetic (inter-network) regions,
separately. We use Fourier power and phase-difference techniques
combined with a wavelet analysis. Two-dimensional Fourier power maps
were constructed in the period bands 2 - 4 minutes, 4 - 6 minutes, 6 -
15 minutes, and beyond 15 minutes. We detect the presence of long-period
oscillations with periods between 15 and 30 minutes in bright magnetic
regions. These oscillations were detected from the chromosphere to the
transition region. The Fourier power maps show that short-period powers
are mainly concentrated in dark regions whereas long-period powers are
concentrated in bright magnetic regions. This is the first report of
long-period waves in quiet-Sun network regions. We suggest that the
observed propagating oscillations are due to magnetoacoustic waves,
which can be important for the heating of the solar atmosphere.
---------------------------------------------------------
Title: Coronal hole boundaries at small scales. IV. SOT view. Magnetic
field properties of small-scale transient brightenings in coronal
holes
Authors: Huang, Z.; Madjarska, M. S.; Doyle, J. G.; Lamb, D. A.
2012A&A...548A..62H Altcode: 2012arXiv1210.2009H
Context. We study the magnetic properties of small-scale transients
in coronal holes and a few in the quiet Sun identified in X-ray
observations and spectroscopic data in two previous papers. <BR />
Aims: We aim to investigate the role of small-scale transients in the
evolution of the magnetic field in an equatorial coronal hole. <BR />
Methods: Two sets of observations of an equatorial coronal hole and
another two in quiet-Sun regions were analysed using longitudinal
magnetograms taken by the Solar Optical Telescope. An automatic
feature tracking program, SWAMIS, was used to identify and track
the magnetic features. Each event was then visually analysed in
detail. <BR /> Results: In both coronal holes and quiet-Sun regions,
all brightening events are associated with bipolar regions and are
caused by magnetic flux emergence followed by cancellation with the
pre-existing and/or newly emerging magnetic flux. In the coronal
hole, 19 of 22 events have a single stable polarity which does not
change its position in time. In eleven cases this is the dominant
polarity. In the coronal hole, the magnetic features with the largest
flux are those of the dominant polarity, while the opposite polarity is
distributed in weaker features. The number of magnetic features of the
dominant polarity is four times grater than the opposite polarity. The
supergranulation configuration appears to preserve its general shape
during approximately nine hours of observations although the large
concentrations (the dominant polarity) in the network did evolve
and/or were slightly displaced, and their strength either increased or
decreased. The emission fluctuations/radiance oscillations seen in the
X-ray bright points are associated with recurring magnetic cancellation
in the footpoints. Unique observations of an X-ray jet reveal similar
magnetic behaviour in the footpoints, i.e. cancellation of the opposite
polarity magnetic flux. We find that the magnetic flux cancellation rate
during the jet is much higher than in bright points. Not all magnetic
cancellations result in an X-ray enhancement, suggesting that there is
a threshold of the amount of magnetic flux involved in a cancellation
above which brightening would occur at X-ray temperatures. <BR />
Conclusions: Our study demonstrates that the magnetic flux in coronal
holes is continuously processed through magnetic reconnection which
is responsible for the formation of numerous small-scale transient
events. The open magnetic flux forming the coronal-hole phenomenon
is largely involved in these transient features. The question of
whether this open flux is transported as a result of the formation and
evolution of these transient events, however, still remains open. <P
/>Three movies and Appendix A are available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Off-limb (Spicule) DEM Distribution from SoHO/SUMER
Observations
Authors: Vanninathan, K.; Madjarska, M. S.; Scullion, E.; Doyle, J. G.
2012SoPh..280..425V Altcode: 2012SoPh..tmp...88V; 2012arXiv1203.2073V
In the present work we derive a Differential Emission Measure (DEM)
distribution from a region dominated by spicules. We use spectral
data from the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on-board the Solar Heliospheric Observatory
(SoHO) covering the entire SUMER wavelength range taken off-limb in
the Northern polar coronal hole to construct this DEM distribution
using the CHIANTI atomic database. This distribution is then used to
study the thermal properties of the emission contributing to the 171 Å
channel in the Atmospheric Imaging Assembly (AIA) on-board the Solar
Dynamics Observatory (SDO). From our off-limb DEM we found that the
radiance in the AIA 171 Å channel is dominated by emission from the
Fe IX 171.07 Å line and has sparingly little contribution from other
lines. The product of the Fe IX 171.07 Å line contribution function
with the off-limb DEM was found to have a maximum at logT<SUB>max</SUB>
(K)=5.8 indicating that during spicule observations the emission in
this line comes from plasma at transition region temperatures rather
than coronal. For comparison, the same product with a quiet Sun and
prominence DEM were found to have a maximum at logT<SUB>max</SUB>
(K)=5.9 and logT<SUB>max</SUB> (K)=5.7, respectively. We point out
that the interpretation of data obtained from the AIA 171 Å filter
should be done with foreknowledge of the thermal nature of the observed
phenomenon. For example, with an off-limb DEM we find that only 3.6 %
of the plasma is above a million degrees, whereas using a quiet Sun DEM,
this contribution rises to 15 %.
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Title: Coronal hole boundaries evolution at small scales. III. EIS
and SUMER views
Authors: Madjarska, M. S.; Huang, Z.; Doyle, J. G.; Subramanian, S.
2012A&A...545A..67M Altcode: 2012arXiv1207.1281M
Context. We report on the plasma properties of small-scale
transient events identified in the quiet Sun, coronal holes and their
boundaries. <BR /> Aims: We aim at deriving the physical characteristics
of events that were identified as small-scale transient brightenings
in XRT images. <BR /> Methods: We used spectroscopic co-observations
from SUMER/SoHO and EIS/Hinode combined with high-cadence imaging
data from XRT/Hinode. We measured Doppler shifts using single and
multiple Gaussian fits of the transition region and coronal lines as
well as electron densities and temperatures. We combined co-temporal
imaging and spectroscopy to separate brightening expansions from
plasma flows. <BR /> Results: The transient brightening events in
coronal holes and their boundaries were found to be very dynamical,
producing high-density outflows at high speeds. Most of these events
represent X-ray jets from pre-existing or newly emerging coronal
bright points at X-ray temperatures. The average electron density of
the jets is log<SUB>10</SUB> N<SUB>e</SUB> ≈ 8.76 cm<SUP>-3</SUP>
while in the flaring site it is log<SUB>10</SUB> N<SUB>e</SUB> ≈ 9.51
cm<SUP>-3</SUP>. The jet temperatures reach a maximum of 2.5 MK but in
the majority of the cases the temperatures do not exceed 1.6 MK. The
footpoints of jets have maximum temperatures of 2.5 MK, though in a
single event scanned a minute after the flaring the measured temperature
was 12 MK. The jets are produced by multiple microflaring in the
transition region and corona. Chromospheric emission was only detected
in their footpoints and was only associated with downflows. The Doppler
shift measurements in the quiet Sun transient brightenings confirmed
that these events do not produce jet-like phenomena. The plasma flows
in these phenomena remain trapped in closed loops. <BR /> Conclusions:
We can conclude that the dynamic day-by-day and even hour-by-hour
small-scale evolution of coronal hole boundaries reported in Paper
I is indeed related to coronal bright points. The XRT observations
reported in Paper II revealed that these changes are associated with
the dynamic evolution of coronal bright points producing multiple jets
during their lifetime until their full disappearance. We demonstrate
here through spectroscopic EIS and SUMER co-observations combined
with high-cadence imaging information that the co-existence of open
and closed magnetic fields results in multiple energy depositions,
which propel high-density plasma along open magnetic field lines. We
conclude from the physical characteristics obtained in this study that
X-ray jets are important candidates for the source of the slow solar
wind. This, however, does not exclude the possibility that these jets
are also the microstreams observed in the fast solar wind, as recently
suggested. <P />Figures A.1, A.2, and movies are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Solar Fine-Scale Structures. I. Spicules and Other Small-Scale,
Jet-Like Events at the Chromospheric Level: Observations and Physical
Parameters
Authors: Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I.; Madjarska,
M. S.; Doyle, J. G.; Suematsu, Y.
2012SSRv..169..181T Altcode: 2012SSRv..tmp...65T; 2012arXiv1207.3956T
Over the last two decades the uninterrupted, high resolution
observations of the Sun, from the excellent range of telescopes aboard
many spacecraft complemented with observations from sophisticated
ground-based telescopes have opened up a new world producing
significantly more complete information on the physical conditions of
the solar atmosphere than before. The interface between the lower solar
atmosphere where energy is generated by subsurface convection and the
corona comprises the chromosphere, which is dominated by jet-like,
dynamic structures, called mottles when found in quiet regions,
fibrils when found in active regions and spicules when observed at
the solar limb. Recently, space observations with Hinode have led to
the suggestion that there should exist two different types of spicules
called Type I and Type II which have different properties. Ground-based
observations in the Ca ii H and K filtergrams reveal the existence of
long, thin emission features called straws in observations close to
the limb, and a class of short-lived events called rapid blue-shifted
excursions characterized by large Doppler shifts that appear only
in the blue wing of the Ca ii infrared line. It has been suggested
that the key to understanding how the solar plasma is accelerated
and heated may well be found in the studies of these jet-like,
dynamic events. However, while these structures are observed and
studied for more than 130 years in the visible, but also in the UV
and EUV emission lines and continua, there are still many questions
to be answered. Thus, despite their importance and a multitude of
observations performed and theoretical models proposed, questions
regarding their origin, how they are formed, their physical parameters,
their association with the underlying photospheric magnetic field, how
they appear in the different spectral lines, and the interrelationship
between structures observed in quiet and active regions on the disk
and at the limb, as well as their role in global processes has not
yet received definitive answers. In addition, how they affect the
coronal heating and solar wind need to be further explored. In this
review we present observations and physical properties of small-scale
jet-like chromospheric events observed in active and quiet regions,
on the disk and at the limb and discuss their interrelationship.
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Title: The Diagnostic Potential of Transition Region Lines Undergoing
Transient Ionization in Dynamic Events
Authors: Doyle, J. G.; Giunta, A.; Singh, A.; Madjarska, M. S.;
Summers, H.; Kellett, B. J.; O'Mullane, M.
2012SoPh..280..111D Altcode: 2012SoPh..tmp..118D; 2012arXiv1204.6598D
We discuss the diagnostic potential of high cadence UV spectral
data when transient ionization is considered. For this we use high
cadence UV spectra taken during the impulsive phase of a solar flare
(observed with instruments on-board the Solar Maximum Mission) which
showed excellent correspondence with hard X-ray pulses. The ionization
fraction of the transition region ion O V and, in particular, the
contribution function for the O V 1371 Å line are computed within
the Atomic Data and Analysis Structure, which is a collection of
fundamental and derived atomic data and codes to manipulate them. Due
to transient ionization, the O V 1371 Å line is enhanced in the
first fraction of a second with the peak in the line contribution
function occurring initially at a higher electron temperature than in
ionization equilibrium. The rise time and enhancement factor depend
mostly on the electron density. The fractional increase in the O V
1371 Å emissivity due to transient ionization can reach a factor
of two-four and can explain the fast response in the line flux of
transition regions ions during the impulsive phase of flares solely
as a result of transient ionization. This technique can be used to
diagnose the electron temperature and density of solar flares observed
with the forthcoming Interface Region Imaging Spectrograph.
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Title: Kinematics and helicity evolution of a loop-like eruptive
prominence
Authors: Koleva, K.; Madjarska, M. S.; Duchlev, P.; Schrijver, C. J.;
Vial, J. -C.; Buchlin, E.; Dechev, M.
2012A&A...540A.127K Altcode: 2012arXiv1202.4541K
<BR /> Aims: We aim at investigating the morphology as well as
kinematic and helicity evolution of a loop-like prominence during its
eruption. <BR /> Methods: We used multi-instrument observations from
AIA/SDO, EUVI/STEREO and LASCO/SoHO. The kinematic, morphological,
geometrical, and helicity evolution of a loop-like eruptive
prominence were studied in the context of the magnetic flux rope
model of solar prominences. <BR /> Results: The prominence eruption
evolved as a height-expanding twisted loop with both legs anchored
in the chromosphere of a plage area. The eruption process consisted
of a prominence activation, acceleration, and a phase of constant
velocity. The prominence body was composed of counter-clockwise twisted
threads around the main prominence axis. The twist during the eruption
was estimated at 6π (3 turns). The prominence reached a maximum height
of 526 Mm before contracting to its primary location and was partially
reformed in the same place two days after the eruption. This ejection,
however, triggered a coronal mass ejection (CME) observed in LASCO
C2. The prominence was located in the northern periphery of the CME
magnetic field configuration and, therefore, the background magnetic
field was asymmetric with respect to the filament position. The physical
conditions of the falling plasma blobs were analysed with respect to
the prominence kinematics. <BR /> Conclusions: The same sign of the
prominence body twist and writhe, as well as the amount of twisting
above the critical value of 2π after the activation phase indicate that
possibly conditions for kink instability were present. No signature
of magnetic reconnection was observed anywhere in the prominence body
and its surroundings. The filament/prominence descent following the
eruption and its partial reformation at the same place two days later
suggest a confined type of eruption. The asymmetric background magnetic
field possibly played an important role in the failed eruption. <P
/>Movies showing the temporal evolution are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Multi-instrument study of chromospheric jets
Authors: Vanninathan, Kamalam; Madjarska, Maria; Doyle, Gerry
2012decs.confE..21V Altcode:
The contribution to coronal heating by jets of various kinds like
spicules, mottles, surges etc. originating in the solar chromosphere
is an issue which is being currently largely explored. We analyse
multi-instrument data taken in the plage area of active regions
during dedicated observing runs with ROSA, IBIS at Sac Peak, USA,
SOT, EIS/XRT/Hinode and AIA/SDO. The high-resolution and high-cadence
data allow us to track chromospheric jets through the solar atmosphere
and thus helps us to understand the dynamics and plasma properties of
these features. The study is a forward step towards the exploration
of the forthcoming state-of-art IRIS observations.
---------------------------------------------------------
Title: Coronal hole boundaries and the slow solar wind from
Hinode/EIS/XRT/SOT and SUMER/SoHO
Authors: Madjarska, M. S.; Huang, Zh.; Doyle, J. G.; Subramanian, S.
2012decs.confE..16M Altcode:
We present a statistical study on outflows at coronal hole boundaries
and inside coronal holes and discuss their role in the slow solar
wind formation in the low solar corona. The outflows are studied in
XRT/Hinode image data taken with the Al_poly filter using an automatic
identification method. A spectroscopic analysis is made using EIS and
SUMER data of spectral lines with formation temperatures in the range
from 10 000 K to 12 MK. The derived plasma parameters of about 60
phenomena will be reported. The longitudinal magnetic field data for
each feature falling in the SOT/Hinode field-of-view (more than 25)
are studied using a magnetic feature tracking procedure and a visual
inspection. The mechanism of the outflow formation and acceleration
will be discussed.
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Title: What is the true nature of blinkers?
Authors: Subramanian, S.; Madjarska, M. S.; Doyle, J. G.; Bewsher, D.
2012A&A...538A..50S Altcode: 2011arXiv1111.2149S
<BR /> Aims: The aim of this work is to identify the true nature of the
transient EUV brightenings, called blinkers. <BR /> Methods: Co-spatial
and co-temporal multi-instrument data, including imaging (EUVI/STEREO,
XRT and SOT/Hinode), spectroscopic (CDS/SoHO and EIS/Hinode) and
magnetogram (SOT/Hinode) data, of an isolated equatorial coronal hole
were used. An automatic program for identifying transient brightenings
in CDS O v 629 Å, EUVI 171 Å and XRT was applied. <BR /> Results: We
identified 28 blinker groups in the CDS O v 629 Å raster images. All
CDS O v 629 Å blinkers showed counterparts in EUVI 171 Å and 304 Å
images. We classified these blinkers into two categories, one associated
with coronal counterparts and other with no coronal counterparts as seen
in XRT images and EIS Fe xii 195.12 Å raster images. Around two-thirds
of the blinkers show coronal counterparts and correspond to various
events like EUV/X-ray jets, brightenings in coronal bright points
or foot-point brightenings of larger loops. These brightenings occur
repetitively and have a lifetime of around 40 min at transition region
temperatures. The remaining blinker groups with no coronal counterpart
in XRT and EIS Fe xii 195.12 Å appear as point-like brightenings and
have chromospheric/transition region origin. They take place only once
and have a lifetime of around 20 min. In general, lifetimes of blinkers
are different at different wavelengths, i.e. different temperatures,
decreasing from the chromosphere to the corona. <BR /> Conclusions: This
work shows that the term blinker covers a range of phenomena. Blinkers
are the EUV response of various transient events originating at coronal,
transition region and chromospheric heights. Hence, events associated
with blinkers contribute to the formation and maintenance of the
temperature gradient in the transition region and the corona.
---------------------------------------------------------
Title: Magnetic reconnection resulting from flux emergence:
implications for jet formation in the lower solar atmosphere?
Authors: Ding, J. Y.; Madjarska, M. S.; Doyle, J. G.; Lu, Q. M.;
Vanninathan, K.; Huang, Z.
2011A&A...535A..95D Altcode: 2011arXiv1109.5606D
<BR /> Aims: We aim at investigating the formation of jet-like features
in the lower solar atmosphere, e.g. chromosphere and transition
region, as a result of magnetic reconnection. <BR /> Methods: Magnetic
reconnection as occurring at chromospheric and transition regions
densities and triggered by magnetic flux emergence is studied using a
2.5D MHD code. The initial atmosphere is static and isothermal, with
a temperature of 2 × 10<SUP>4</SUP> K. The initial magnetic field
is uniform and vertical. Two physical environments with different
magnetic field strength (25 G and 50 G) are presented. In each case,
two sub-cases are discussed, where the environments have different
initial mass density. <BR /> Results: In the case where we have a
weaker magnetic field (25 G) and higher plasma density (N<SUB>e</SUB> =
2 × 10<SUP>11</SUP> cm<SUP>-3</SUP>), valid for the typical quiet Sun
chromosphere, a plasma jet would be observed with a temperature of 2-3
× 10<SUP>4</SUP> K and a velocity as high as 40 kms<SUP>-1</SUP>. The
opposite case of a medium with a lower electron density (N<SUB>e</SUB>
= 2 × 10<SUP>10</SUP> cm<SUP>-3</SUP>), i.e. more typical for the
transition region, and a stronger magnetic field of 50 G, up-flows
with line-of-sight velocities as high as ~90 kms<SUP>-1</SUP> and
temperatures of 6 × 10<SUP>5</SUP> K, i.e. upper transition region -
low coronal temperatures, are produced. Only in the latter case, the low
corona Fe ix 171 Å shows a response in the jet which is comparable to
the O v increase. <BR /> Conclusions: The results show that magnetic
reconnection can be an efficient mechanism to drive plasma outflows
in the chromosphere and transition region. The model can reproduce
characteristics, such as temperature and velocity for a range of jet
features like a fibril, a spicule, a hot X-ray jet or a transition
region jet by changing either the magnetic field strength or the
electron density, i.e. where in the atmosphere the reconnection occurs.
---------------------------------------------------------
Title: Can coronal hole spicules reach coronal temperatures?
Authors: Madjarska, M. S.; Vanninathan, K.; Doyle, J. G.
2011A&A...532L...1M Altcode: 2011arXiv1105.1296M
<BR /> Aims: The present study aims to provide observational evidence
of whether coronal hole spicules reach coronal temperatures. <BR />
Methods: We combine multi-instrument co-observations obtained with
the SUMER/SoHO and with the EIS/SOT/XRT/Hinode. <BR /> Results:
The analysed three large spicules were found to be comprised of
numerous thin spicules that rise, rotate, and descend simultaneously
forming a bush-like feature. Their rotation resembles the untwisting
of a large flux rope. They show velocities ranging from 50 to 250
kms<SUP>-1</SUP>. We clearly associated the red- and blue-shifted
emissions in transition region lines not only with rotating but
also with rising and descending plasmas. Our main result is that
these spicules although very large and dynamic, are not present in
the spectral lines formed at temperatures above 300 000 K. <BR />
Conclusions: In this paper we present the analysis of three Ca ii H
large spicules that are composed of numerous dynamic thin spicules
but appear as macrospicules in lower resolution EUV images. We found
no coronal counterpart of these and smaller spicules. We believe that
the identification of phenomena that have very different origins as
macrospicules is due to the interpretation of the transition region
emission, and especially the He ii emission, wherein both chromospheric
large spicules and coronal X-ray jets are present. We suggest that
the recent observation of spicules in the coronal AIA/SDO 171 Å
and 211 Å channels probably comes from the existence of transition
region emission there. <P />Movie is available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Dynamics and plasma properties of an X-ray jet from SUMER,
EIS, XRT, and EUVI A & B simultaneous observations
Authors: Madjarska, M. S.
2011A&A...526A..19M Altcode: 2010arXiv1008.3983M
Context. Small-scale transient phenomena in the quiet Sun are
believed to play an important role in coronal heating and solar wind
generation. One of them, called “X-ray jet”, is the subject of our
study. <BR /> Aims: We intend to investigate the dynamics, evolution,
and physical properties of this phenomenon. <BR /> Methods: We combine
multi-instrument observations obtained simultaneously with the SUMER
spectrometer onboard SoHO, with EIS and XRT onboard Hinode, and with
EUVI/SECCHI onboard the Ahead and Behind STEREO spacecrafts. We derive
plasma parameters such as temperatures and densities as well as dynamics
by using spectral lines formed in the temperature range from 10 000 K
to 12 MK. We also use an image difference technique to investigate the
evolution of the complex structure of the studied phenomenon. <BR />
Results: With the available unique combination of data we were able
to establish that the formation of a jet-like event is triggered by
not one, but several energy depositions, which are most probably
originating from magnetic reconnection. Each energy deposition
is followed by the expulsion of pre-existing or newly reconnected
loops and/or collimated flow along open magnetic field lines. We
derived in great detail the dynamic process of X-ray jet formation
and evolution. For the first time we also found spectroscopically
a temperature of 12 MK (Fe xxiii 263.76 Å) and density of 4 ×
10<SUP>10</SUP> cm<SUP>-3</SUP> in the quiet Sun, obtained from a
pair of Fe xii lines with a maximum formation temperature of 1.3
× 10<SUP>6</SUP> K, in an energy deposition region. We point out
a problem concerning an uncertainty in using the SUMER Mg x 624.9
Å line for coronal diagnostics. We clearly identified two types of
up-flow: one collimated up-flow along open magnetic field lines and
a plasma cloud formed from the expelled BP loops. We also report
a cooler down-flow along closed magnetic field lines. A comparison
is made with a model developed by Moreno-Insertis et al. (2008). <P
/>Figures 10-16 and movie are only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Coronal hole boundaries evolution at small scales. II. XRT
view. Can small-scale outflows at CHBs be a source of the slow
solar wind
Authors: Subramanian, S.; Madjarska, M. S.; Doyle, J. G.
2010A&A...516A..50S Altcode: 2010arXiv1002.1675S
<BR /> Aims: We aim to further explore the small-scale evolution of
coronal hole boundaries using X-ray high-resolution and high-cadence
images. We intend to determine the fine structure and dynamics of the
events causing changes of coronal hole boundaries and to explore the
possibility that these events are the source of the slow solar wind. <BR
/> Methods: We developed an automated procedure for the identification
of transient brightenings in images from the X-ray telescope on-board
Hinode taken with an Al Poly filter in the equatorial coronal holes,
polar coronal holes, and the quiet Sun with and without transient
coronal holes. <BR /> Results: We found that in comparison to the quiet
Sun, the boundaries of coronal holes are abundant with brightening
events including areas inside the coronal holes where closed magnetic
field structures are present. The visual analysis of these brightenings
revealed that around 70% of them in equatorial, polar and transient
coronal holes and their boundaries show expanding loop structures and/or
collimated outflows. In the quiet Sun only 30% of the brightenings show
flows with most of them appearing to be contained in the solar corona
by closed magnetic field lines. This strongly suggests that magnetic
reconnection of co-spatial open and closed magnetic field lines creates
the necessary conditions for plasma outflows to large distances. The
ejected plasma always originates from pre-existing or newly emerging
(at X-ray temperatures) bright points. <BR /> Conclusions: The present
study confirms our findings that the evolution of loop structures known
as coronal bright points is associated with the small-scale changes
of coronal hole boundaries. The loop structures show an expansion
and eruption with the trapped plasma consequently escaping along the
“quasi” open magnetic field lines. These ejections appear to be
triggered by magnetic reconnection, e.g. the so-called interchange
reconnection between the closed magnetic field lines (BPs) and the
open magnetic field lines of the coronal holes. We suggest that
these plasma outflows are possibly one of the sources of the slow
solar wind. <P />4 movies are only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Chromospheric magnetic reconnection caused by photospheric
flux emergence: implications for jet-like events formation
Authors: Ding, J. Y.; Madjarska, M. S.; Doyle, J. G.; Lu, Q. M.
2010A&A...510A.111D Altcode: 2009arXiv0912.4449D
Magnetic reconnection in the low atmosphere, e.g. chromosphere, is
investigated in various physical environments. Its implications for
the origination of explosive events (small-scale jets) are discussed. A
2.5-dimensional resistive magnetohydrodynamic (MHD) model in Cartesian
coordinates is used. It is found that the temperature and velocity of
the outflow jets as a result of magnetic reconnection are strongly
dependent on the physical environments, e.g. the magnitude of the
magnetic field strength and the plasma density. If the magnetic
field strength is weak and the density is high, the temperature of
the jets is very low (~10<SUP>4</SUP> K) as well as its velocity (~40
km s<SUP>-1</SUP>). However, if environments with stronger magnetic
field strength (40 G) and smaller density (electron density N_e=2×
10<SUP>10</SUP> cm<SUP>-3</SUP>) are considered, the outflow jets
reach higher temperatures of up to 6× 10^5 K and a line-of-sight
velocity of up to 130 km s<SUP>-1</SUP> which is comparable with the
observational values of jet-like events.
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Title: Fine Structure of a Coronal Bright Point as Seen with SoHO,
TRACE, and Hinode
Authors: Pérez-Suárez, D.; Maclean, R. C.; Doyle, J. G.; Madjarska,
M. S.
2009ASPC..415..140P Altcode:
We present a study of a Coronal Bright Point (BPs) where data from
Hinode, SoHO and TRACE are analyzed. Covering a large temperature
range, we study the variation of the BP from the surface to the
corona investigating both the morphology and variation in physical
parameters, such as electron density, Doppler-shift and magnetic field
variability. We obtain excellent correlation between the X-ray light
curve with the positive magnetic flux; also a good agreement is found
between a potential extrapolated magnetic field and the loops seen in
the X-ray images.
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Title: Coronal hole boundaries evolution at small scales. I. EIT
195 Å and TRACE 171 Å view
Authors: Madjarska, M. S.; Wiegelmann, T.
2009A&A...503..991M Altcode: 2009arXiv0906.2556M
Aims: We aim to study the small-scale evolution at the boundaries of an
equatorial coronal hole connected with a channel of open magnetic flux
to the polar region and an “isolated” one in the extreme-ultraviolet
spectral range. We determine the spatial and temporal scale of these
changes. <BR />Methods: Imager data from TRACE in the Fe ix/x 171
Å passband and EIT on-board Solar and Heliospheric Observatory in
the Fe xii 195 Å passband were analysed. <BR />Results: We found
that small-scale loops known as bright points play an essential role
in coronal hole boundary evolution at small scales. Their emergence
and disappearance continuously expand or contract coronal holes. The
changes appear to be random on a time scale comparable to the lifetime
of the loops seen at these temperatures. No signature was found
for a major energy release during the evolution of the loops. <BR
/>Conclusions: Although coronal holes seem to maintain their general
shape during a few solar rotations, a closer look at their day-by-day
and even hour-by-hour evolution demonstrates significant dynamics. The
small-scale loops (10´´-40´´ and smaller) which are abundant along
coronal hole boundaries contribute to the small-scale evolution of
coronal holes. Continuous magnetic reconnection of the open magnetic
field lines of the coronal hole and the closed field lines of the
loops in the quiet Sun is more likely to take place. <P />Movies are
only available in electronic form at http://www.aanda.org
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Title: Explosive Events Associated with a Surge
Authors: Madjarska, M. S.; Doyle, J. G.; de Pontieu, B.
2009ApJ...701..253M Altcode: 2009arXiv0906.2544M
The solar atmosphere contains a wide variety of small-scale transient
features. Here, we explore the interrelation between some of them such
as surges, explosive events, and blinkers via simultaneous spectral
and imaging data taken with the TRACE imager, the SUMER and Coronal
Diagnostics Spectrometer (CDS) on board SOHO, and Swedish Vacuum Solar
Telescope La Palma. The features were observed in spectral lines with
formation temperatures from 10,000 K to 1 MK and with the TRACE Fe
IX/X 171 Å filter. The Hα filtergrams were taken in the wings of
the Hα 6365 Å line at ±700 mÅ and ±350 mÅ. The alignment of all
data in both time and solar XY shows that SUMER line profiles, which
are attributed to explosive events, are due to a surge phenomenon. The
surge's up- and downflows, which often appear simultaneously, correspond
to the blue- and redshifted emission of the transition region N V
1238.82 Å and O V 629.77 Å lines as well as radiance increases of
the C I, S I, and S II and Si II chromospheric lines. Some parts of
the surge are also visible in the TRACE 171 Å images which could
suggest heating to coronal temperatures. The surge is triggered,
most probably, by one or more Elerman bombs which are best visible
in Hα ± 350 Å but were also registered by TRACE Fe IX/X 171 Å
and correspond to a strong radiance increase in the CDS Mg IX 368.07
Å line. With the present study, we demonstrate that the division of
small-scale transient events into a number of different subgroups,
for instance explosive events, blinkers, spicules, surges or just
brightenings, is ambiguous, implying that the definition of a feature
based only on either spectroscopic or imaging characteristics as well
as insufficient spectral and spatial resolution can be incomplete.
---------------------------------------------------------
Title: The structure and dynamics of a bright point as seen with
Hinode, SoHO and TRACE
Authors: Pérez-Suárez, D.; Maclean, R. C.; Doyle, J. G.; Madjarska,
M. S.
2008A&A...492..575P Altcode: 2008arXiv0810.1020P
Context: Solar coronal bright points have been studied for more than
three decades, but some fundamental questions about their formation and
evolution still remain unanswered. <BR />Aims: Our aim is to determine
the plasma properties of a coronal bright point and compare its magnetic
topology extrapolated from magnetogram data with its appearance in
X-ray images. <BR />Methods: We analyse spectroscopic data obtained with
EIS/Hinode, Ca ii H and G-band images from SOT/Hinode, UV images from
TRACE, X-ray images from XRT/Hinode and high-resolution/high-cadence
magnetogram data from MDI/SoHO. <BR />Results: The BP comprises several
coronal loops as seen in the X-ray images, while the chromospheric
structure consists of tens of small bright points as seen in Ca ii
H. An excellent correlation exists between the Ca ii H bright points
and increases in the magnetic field strength, implying that the Ca
ii H passband is a good indicator for the concentration of magnetic
flux. Furthermore, some of the Ca ii H bright points are the locations
of the loop foot-points as determined from a comparison between the
extrapolated magnetic field configuration and the X-ray images. Doppler
velocities between 6 and 15 km s<SUP>-1</SUP> are derived from the Fe
xii and Fe xiii lines for the bright point region, while for Fe xiv
and Si vii they are in the range from -15 to +15 km s<SUP>-1</SUP>. The
coronal electron density is 3.7 × 10<SUP>9</SUP> cm<SUP>-3</SUP>. An
excellent correlation is found between the positive magnetic flux and
the X-ray light-curves. <BR />Conclusions: The remarkable agreement
between the extrapolated magnetic field configuration and some of the
loops composing the bright point as seen in the X-ray images suggests
that a large fraction of the magnetic field in the bright point is close
to potential. However, some loops in the X-ray images do not have a
counterpart in the extrapolated magnetic field configuration implying
a non-potential component. The close correlation between the positive
magnetic flux and the X-ray emission suggests that energy released by
magnetic reconnection is stimulated by flux emergence or cancellation.
---------------------------------------------------------
Title: EIS/ Hinode Observations of Doppler Flow Seen through the
40-Arcsec Wide-Slit
Authors: Innes, D. E.; Attie, R.; Hara, H.; Madjarska, M. S.
2008SoPh..252..283I Altcode: 2008SoPh..tmp..174I; 2008arXiv0807.1185I
The Extreme ultraviolet Imaging Spectrometer (EIS) onboard Hinode
is the first solar telescope to obtain wide-slit spectral images
that can be used for detecting Doppler flows in transition region
and coronal lines on the Sun and to relate them to their surrounding
small-scale dynamics. We select EIS lines covering the temperature
range 6×10<SUP>4</SUP> to 2×10<SUP>6</SUP> K that give spectrally
pure images of the Sun with the 40-arcsec slit. In these images Doppler
shifts are seen as horizontal brightenings. Inside the image it is
difficult to distinguish shifts from horizontal structures but emission
beyond the image edge can be unambiguously identified as a line shift
in several lines separated from others on their blue or red side by
more than the width of the spectrometer slit (40 pixels). In the blue
wing of He II, we find a large number of events with properties (size
and lifetime) similar to the well-studied explosive events seen in
the ultraviolet spectral range. Comparison with X-Ray Telescope (XRT)
images shows many Doppler shift events at the footpoints of small X-ray
loops. The most spectacular event observed showed a strong blue shift
in the transition region and lower corona lines from a small X-ray
spot that lasted less than 7 min. The emission appears to be near
a cool coronal loop connecting an X-ray bright point to an adjacent
region of quiet Sun. The width of the emission implies a line-of-sight
velocity of 220 km s<SUP>−1</SUP>. In addition, we show an example
of an Fe XV shift with a velocity of about 120 km s<SUP>−1</SUP>,
coming from what looks like a narrow loop leg connecting a small X-ray
brightening to a larger region of X-ray emission.
---------------------------------------------------------
Title: On the relation between DC current locations and an EUV bright
point: A case study
Authors: Santos, J. C.; Büchner, J.; Madjarska, M. S.; Alves, M. V.
2008A&A...490..345S Altcode:
Context: Motion of the photospheric plasma forces the footpoints of
magnetic flux tubes to move. This can give rise to electric currents in
the solar atmosphere. The dissipation of these electric currents and
the consequent heating of the solar plasma may be responsible for the
formation of Extreme-UltraViolet (EUV) and X-ray bright points. Earlier
bright point models usually consider either the emergence or the
canceling of photospheric magnetic features as being responsible for
reconnection causing the bright point. <BR />Aims: We investigate the
consequences of different patterns of horizontal photospheric plasma
motion for the generation of electric currents in the solar atmosphere
and locate them with respect to an observed EUV bright point. The goal
is to find out whether these currents might be responsible for the
heating of bright points. <BR />Methods: To perform this study we use
a “data driven” three dimensional magnetohydrodynamic model. The
model solves an appropriate set of magnetohydrodynamic equations and
uses, as initial condition, the magnetic field extrapolated from the
line-of-sight component of the photospheric magnetic field observed by
MDI/SoHO and the height-stratified, equilibrium density and temperature
of the solar corona. We apply different patterns of horizontal
photospheric plasma motion, derived from the temporal evolution of the
photospheric magnetic structures in the course of the bright point
lifetime, as boundary conditions of the model. <BR />Results: All
applied patterns of horizontal photospheric plasma motion (shearing,
convergence and fragmentation) lead to the formation of electric
currents in the chromosphere, transition region and corona. Currents
do not develop everywhere in the region where the motion is applied
but in specific places where the magnetic field connectivity changes
significantly. An important result is that the position where the
electric currents develop is independent of the motion pattern used
as boundary condition of the model. A comparison with data obtained
by TRACE in the 1550 Å channel and by the EIT in the 195 Å channel
shows that the region where the strongest current concentrations are
formed coincides with the region where the EUV bright point appears.
---------------------------------------------------------
Title: Explosive Events in the Quiet Sun as Seen by EIS and SUMER
Authors: Madjarska, M. S.; Boutry, C.; Bewsher, D.
2008ASPC..397..180M Altcode:
We present preliminary results on the capabilities of EIS to register
explosive events in the quiet Sun. The events were registered with
EIS/Hinode and SUMER/SoHO during the Hinode/SoHO observing campaign
in April 2007. First results on the coronal response of these events
are shown. Both SUMER and EIS were observing spectral lines from the
widest possible temperature range from a few thousand to a few million
degrees Kelvin.
---------------------------------------------------------
Title: Study of Transition Region Transient Events with Hinode
Authors: Subramanian, S.; Madjarska, M.; Doyle, J. G.
2008ASPC..397..194S Altcode:
We present preliminary results of a study of transient events in the
solar transition region (TR), using observations taken at disk centre
on 9 April, 2007 with SOT, XRT and EIS on-board Hinode; CDS and MDI
on-board SoHO, plus TRACE covering the photosphere to corona.
---------------------------------------------------------
Title: Magnetic topology of blinkers
Authors: Subramanian, S.; Madjarska, M. S.; Maclean, R. C.; Doyle,
J. G.; Bewsher, D.
2008A&A...488..323S Altcode:
Context: Co-spatial and co-temporal spectroscopic, imaging and
magnetogram data enable us to better understand various solar transient
phenomena. Here, we study brightening events in the transition region
of the quiet Sun, also called “blinkers”. <BR />Aims: We aim
to investigate the physical mechanism responsible for blinkers. <BR
/>Methods: An automated blinker identification procedure (BLIP) is
used to identify blinker events in SoHO/CDS data. The 3D magnetic
topology of the magnetic field in the blinker region is reconstructed
based on SoHO/MDI magnetogram data. <BR />Results: During 3 h of
SoHO/CDS observations on 2006 January 18, 66 blinkers were identified
in the O v 629 Å emission line. Out of them, a group comprising of
16 events were modelled here. They were found to be associated with
the emergence of magnetic flux which gave rise to the appearance of,
and multiple magnetic reconnection events across, an upper atmosphere
(coronal) magnetic null point, along with a loop structure as observed
with TRACE. <BR />Conclusions: This blinker group results from the
release of energy that was accumulated during flux emergence, although
whether all blinkers follow the same formation scenario requires
further investigation using additional multi-instrument/multi-mission
studies. <P />2 movies are only available in electronic form at
http://star.arm.ac.uk/preprints/ and http://www.aanda.org
---------------------------------------------------------
Title: Small-scale flows in SUMER and TRACE high-cadence
co-observations
Authors: Madjarska, M. S.; Doyle, J. G.
2008A&A...482..273M Altcode: 2008arXiv0802.2477M
Context: We report on the physical properties of small-scale
transient flows observed simultaneously at high cadence with
the SUMER spectrometer and the TRACE imager in the plage area of
an active region. <BR />Aims: Our major objective is to provide a
better understanding of the nature of transient phenomena in the solar
atmosphere by using high-cadence imager and spectrometer co-observations
at similar spatial and temporal resolution. <BR />Methods: A sequence
of TRACE Fe IX/X λ171 Å and high-resolution MDI images were analysed
together with simultaneously obtained SUMER observations in spectral
lines covering a temperature range from 10 000 K to 1 MK. <BR />Results:
We reveal the existence of numerous transient flows in small-scale loops
(up to 30 Mm) observed in the plage area of an active region. These
flows have temperatures from 10 000 K (the low temperature limit
of our observations) to 250 000 K. The coronal response of these
features is uncertain due to a blending of the observed coronal line
Mg x λ624.85 Å. The duration of the events ranges from 60 s to 19
min depending on the loop size. Some of the flows reach supersonic
velocities. <BR />Conclusions: The Doppler shifts often associated with
explosive events or bi-directional jets can actually be identified with
flows (some of them reaching supersonic velocities) in small-scale
loops. Additionally, we demonstrate how a line-of-sight effect can
give misleading information on the nature of the observed phenomena
if only either an imager or a spectrometer is used. <P />An animation
of the TRACE λ171 Å images is only available in electronic form
at http://www.aanda.org
---------------------------------------------------------
Title: Jets or High-Velocity Flows Revealed in High-Cadence
Spectrometer and Imager Co-observations?
Authors: Madjarska, M. S.; Doyle, J. G.; Innes, D. E.; Curdt, W.
2007ApJ...670L..57M Altcode: 2007arXiv0710.2199M
We report on active region EUV dynamic events observed simultaneously
at high cadence with SOHO SUMER and TRACE. Although the features
appear in the TRACE Fe IX/X 171 Å images as jets seen in projection
on the solar disk, the SUMER spectral line profiles suggest that the
plasma has been driven along a curved large-scale magnetic structure,
a preexisting loop. The SUMER observations were carried out in
spectral lines covering a large temperature range from 10<SUP>4</SUP>
to 10<SUP>6</SUP> K. The spectral analysis revealed that a sudden
heating from an energy deposition is followed by a high-velocity
plasma flow. The Doppler velocities were found to be in the range
from 90 to 160 km s<SUP>-1</SUP>. The heating process has a duration
which is below the SUMER exposure time of 25 s while the lifetime of
the events is from 5 to 15 minutes. The additional check on soft X-ray
Yohkoh images shows that the features most probably reach 3 MK (X-ray)
temperatures. The spectroscopic analysis showed no existence of cold
material during the events.
---------------------------------------------------------
Title: Evolution of coronal hole boundaries seen in EIT 195 Å and
TRACE 171 Å images
Authors: Madjarska, M. S.; Wiegelmann, T.
2007msfa.conf..249M Altcode:
We aim at studying the spatial and temporal scales of the small-scale
evolution of coronal hole boundaries using EUV observations from TRACE
(171 Å) and EIT (195 Å) on-board SoHO with a spatial resolution of
1" and 5.5", respectively, and various time cadences. We found that
small-scale loops known as bright points may play an essential role in
coronal hole boundaries evolution. Their emergence and disappearance
continuously expand or contract coronal holes. The changes appear to
be random on a time scale comparable with the lifetime of the loops
seen at these temperatures. No signature was found for a major energy
release during the evolution of the loops.
---------------------------------------------------------
Title: Dynamic features in the solar atmosphere with unusual spectral
line enhancements and Doppler-shifts
Authors: Doyle, J. G.; Ishak, B.; Madjarska, M. S.; O'Shea, E.;
Dzifćáková, E.
2006A&A...451L..35D Altcode:
Context.The solar atmosphere contains a wide variety of transient
features, here, we discuss data relating to one such feature. <BR
/>Aims.To explore via simultaneous spectral and imaging data the
nature of high-velocity flow events in the solar transition region. <BR
/>Methods.High spectral and temporal resolution data from SUMER/SoHO
plus high resolution images from TRACE are used. <BR />Results.In the
transient feature discussed, we see a factor of two enhancement in N
v 1238, coupled with a factor of two decrease in O v 629 visible over
3”-4” along the slit. Furthermore, the O v line shows a secondary
component with a down-flow of ≈75 km s<SUP>-1</SUP>, while the
N v line shows only a small additional broadening of the line. <BR
/>Conclusions.Inclusion of an electron density dependent ionization
calculation will increase the N v radiance over that of O v at large
electron densities. We suggest this feature can be explained via a
highly focused jet at the O v/Ovi formation temperature resulting from
reconnection. Also, we believe that this event is not unique but that
their detection depends on the availability of simultaneous spectral
and imaging data of comparable spatial and temporal resolution.
---------------------------------------------------------
Title: Study of a transient siphon flow in a cold loop
Authors: Doyle, J. G.; Taroyan, Y.; Ishak, B.; Madjarska, M. S.;
Bradshaw, S. J.
2006A&A...452.1075D Altcode:
Context: .The nature of loops is still a matter of debate with several
explanations having been put forward. Simultaneous spectral and imaging
data have the capacity to provide a new insight into mass motions,
dynamics and energetics of loops.<BR /> Aims: .We report on spectral
data taken with the Solar Ultraviolet Measurements of Emitted Radiation
spectrograph (SUMER) and imaging data from the Transition Region and
Coronal Explorer (TRACE) of a transient event which occurred in a cold
loop, lasting a few minutes.<BR /> Methods: .A sequence of TRACE images
in the 1550 Å and 171 Å filters show a disturbance which originated
at one foot-point and propagates along the loop. The SUMER slit was
placed at the other foot-point of the loop. In order to interpret the
results, numerical simulations were performed with the results then
converted into observable quantities and compared with the data.<BR />
Results: .During the event a radiance increase and a relative red shift
of ≈ 20~km s<SUP>-1</SUP> was detected in the N v 1238.82 Å line. 1D
numerical simulations are performed and observable quantities derived
from the results of the simulations. The observed dynamic behaviour of
the N v 1238.82 Å line profiles was recovered.<BR /> Conclusions: .The
results suggest that the observations could be interpreted in terms of
a short-lived siphon flow reaching a speed of 120~km s<SUP>-1</SUP>
and driven by a nonlinear heating pulse. The energies required to
drive the observed red-shifts are estimated to be about 10<SUP>25</SUP>
erg. The absence of a significant blue-shift caused by the return flow
is explained.
---------------------------------------------------------
Title: Macrospicules and blinkers as seen in Shutterless EIT 304 Å
Authors: Madjarska, M. S.; Doyle, J. G.; Hochedez, J. -F.; Theissen, A.
2006A&A...452L..11M Altcode:
Aims.Small-scale transient phenomena in the solar atmosphere are
believed to play a crucial role in the coronal heating and solar
wind generation. This study aims at providing new observational
evidence on blinkers and macrospicules appearance in imager data and
in doing so, establish the long disputed relationship between these
phenomena.<BR /> Methods: .We analyse unique high-cadence images in
the transition region He ii 304 Å line obtained in a shutterless mode
of the Extreme-ultraviolet Imaging Telescope on board the Solar and
Heliospheric Observatory. The data have a cadence of approximately 68
s and a pixel size of 2.62 arcsec. The events are identified through
an automatic brightenings identification procedure. Features showing
a jet-like structure seen in projection on the disk were selected
and their light-curve further analysed.<BR /> Results: .The temporal
evolution of the intensity in three events is shown, two of them seen
on-disk as jet-like features and one above the limb. The flux increase,
size and duration derived from the light-curve of the on-disk events
show an identity with the blinker phenomenon.<BR /> Conclusions: .The
light curves of these events suggest that the off-limb and on-disk
features are in fact one and the same phenomenon and therefore that
some blinkers are the on-disk counterparts of macrospicules.
---------------------------------------------------------
Title: Study of a Transient Siphon Flow in a Cold Loop
Authors: Taroyan, Y.; Doyle, J. G.; Ishak, B.; Madjarska, M. S.;
Bradshaw, S. J.
2005ESASP.600E..25T Altcode: 2005ESPM...11...25T; 2005dysu.confE..25T
No abstract at ADS
---------------------------------------------------------
Title: Optical and EUV observations of solar flare kernels
Authors: García-Alvarez, D.; Johns-Krull, C. M.; Doyle, J. G.;
Ugarte-Urra, I.; Madjarska, M. S.; Butler, C. J.
2005A&A...444..593G Altcode:
We present high-resolution spectral observations, covering the entire
optical region (3800-9000 Å), of a solar flare observed during
a multi-wavelength campaign. The flare, recorded on 2002 January
11, was a medium solar flare event (GOES class C7.5). The spectral
observations were carried out using the Hamilton echelle spectrograph on
the coudé auxiliary telescope at Lick Observatory and with the Coronal
Diagnostic Spectrometer (CDS) on board SoHO. The high signal-to-noise
optical spectra are analysed using the same techniques as we applied to
stellar flare data. Hα images obtained at Big Bear Solar Observatory
(BBSO), plus magnetograms obtained with the Michelson Doppler Imager
(MDI) on board SoHO and Transition Region And Coronal Explorer (TRACE)
1600 Å were used in the flare analysis. We observe stellar-like
behaviour in the main solar chromospheric activity indicators, which
show either filling-in or emission during the flare. We find that the
Balmer and Ca II lines show asymmetric profiles, with red-shifted
wings and blue-shifted cores. This behaviour could be explained by
material expanding. During the flare, the Mg i and Fe i lines show
a filling-in of the line profile indicating that the flare affected
the lower atmosphere. There is some evidence for pre-flare heating
as seen in Fe xix 592 Å. Furthermore, O v 629 Å shows an increase
in flux some 10 min. before the coronal lines, perhaps indicating
particle beam heating in the initial stages of the flare. We have
also determined the main physical parameters at flare maximum. The
electron densities and electron temperatures found for the flare imply
that the Balmer emitting plasma originates in the chromosphere. The
physical parameters obtained for the modelled flare are consistent
with previously derived values for solar flares.
---------------------------------------------------------
Title: Spicules and Blinkers as Seen in Shutterless EIT 304 Å
Authors: Madjarska, M. S.; Doyle, J. G.; Hochedez, J. F.; Theissen, A.
2005ESASP.596E..73M Altcode: 2005ccmf.confE..73M
No abstract at ADS
---------------------------------------------------------
Title: Electron density along a coronal loop observed with CDS/SOHO
Authors: Ugarte-Urra, I.; Doyle, J. G.; Walsh, R. W.; Madjarska, M. S.
2005A&A...439..351U Altcode:
The analysis of a coronal loop observed by CDS and EIT on board SOHO
is presented. The loop was situated above the North-East limb at
a latitude of ~48°, being clearly visible in the hottest lines of
the dataset, Fe xvi 360.76 Å, i.e. greater than 2 000 000 K. The
cooler lines in the sample (i.e. O v 629.73 Å and He i 584.35 Å)
showed only a brightening at the footpoints location. Based on
the Fe xiv 353.84/334.17 line ratio, the electron density along
the loop was determined following three different approaches for
the background subtraction. No differences, within the error bars,
can be found between the three methods. At the apex, the density is
0.9×10<SUP>9</SUP> cm<SUP>-3</SUP>, while at the footpoint it is
50% greater, i.e. 1.4×10<SUP>9</SUP> cm<SUP>-3</SUP>. The inferred
filling factor values along the loop, at the formation temperature
of the lines, are in the range 0.2-0.9. One dimensional hydrodynamic
modelling of the loop along a given field line, gravity neglected,
was performed. A minimum χ<SUP>2</SUP> analysis results in a best fit
case where the total energy input is directed preferentially to the loop
footpoint (the heating rate is three times larger at the base than at
the apex). An isochoric solution can not be ruled out completely. The
exercise illustrates the necessity of accurate spectral diagnostics
in order to derive definite conclusions from theoretical models and
suggests the need for simultaneous density and temperature diagnostics.
---------------------------------------------------------
Title: Line broadening of EUV lines across the Solar limb: A spicule
contribution?
Authors: Doyle, J. G.; Giannikakis, J.; Xia, L. D.; Madjarska, M. S.
2005A&A...431L..17D Altcode:
Spectral lines formed in the solar transition region show an increase
in the line width, peaking at ≈10 000 km above the limb. Looking at
a region off-limb with no obvious spicules, the non-spicule region has
a significantly smaller line width above 6000 km compared those taken
in a spicule region. We suggest that this increase in line broadening
is not due to small scale random motions but rather to unresolved line
shifts due to spicules and/or macro-spicules activity.
---------------------------------------------------------
Title: Transition region small-scale dynamics as seen by SUMER on SOHO
Authors: Teriaca, L.; Banerjee, D.; Falchi, A.; Doyle, J. G.;
Madjarska, M. S.
2004A&A...427.1065T Altcode:
High spectral, spatial and temporal resolution UV observations
of the quiet Sun transition region show a highly structured and
dynamical environment where transient supersonic flows are commonly
observed. Strongly non-Gaussian line profiles are the spectral
signatures of these flows and are known in the literature as explosive
events. In this paper we present a high spatial resolution (≈ 1”)
spectroheliogram of a 273”× 291” area of the quiet Sun acquired with
SUMER/SOHO in the O VI spectral line at λ103.193 nm. The extremely high
quality of these observations allows us to identify tens of explosive
events from which we estimate an average size of 1800 km and a birthrate
of 2500 s<SUP>-1</SUP> over the entire Sun. Estimates of the kinetic and
enthalpy fluxes associated with these events show that explosive events
are not important as far as solar coronal heating is concerned. The
relationship with the underlying photospheric magnetic field is also
studied, revealing that explosive events generally occur in regions
with weak (and, very likely, mixed polarity) magnetic flux. By studying
the structure of upward and downward flows exceeding those associated
to average quiet Sun profiles, we find a clear correlation between
the “excess” flows and the magnetic network. However, although
explosive events are always associated with flow patterns often
covering areas larger than the explosive event itself, the contrary is
not true. In particular, almost all flows associated with the stronger
concentrations of photospheric magnetic flux do not show non-Gaussian
line profiles. In some cases, non-Gaussian line profiles are associated
with supersonic flows in small magnetic loops. The case of a small
loop showing a supersonic siphon-like flow of ≈130 km s<SUP>-1</SUP>
is studied in detail. This is, to our knowledge, the first detection
of a supersonic siphon-like flow in a quiet Sun loop. In other cases,
the flow patterns associated with explosive events may suggest a
relation with UV spicules.
---------------------------------------------------------
Title: Coronal response of Bi-directional Jets
Authors: Doyle, J. G.; Madjarska, M. S.; DzifČÁkovÁ, E.; Dammasch,
I. E.
2004SoPh..221...51D Altcode:
EUV bi-directional jets are a prominent class of phenomena
characterizing the solar transition region. Using simultaneously
obtained SUMER observations in the chromospheric Si ii 1251.16 Å
and C i 1251.17 Å, transition region N v 1238.8 Å and coronal Mg x
625 Å lines we show an example of a bi-directional jet observed in
the chromospheric and the transition region lines but not showing
any detectable signature in the coronal line. The phenomenon,
however, was also clearly detected by the TRACE imager with the 171
Å filter. This discrepancy is explained here with a non-Maxwellian
electron distribution which makes a significant fraction of the plasma
in the TRACE 171 Å pass-band to be derived from temperatures around ≈
300 000 K, as opposed to ≈ 800 000 K. This could have implications
for other phenomena observed in the TRACE pass-bands, including the
transition region `moss' and the 3- and 5-min oscillations.
---------------------------------------------------------
Title: New insight into the blinker phenomenon and the dynamics of
the solar transition region
Authors: Doyle, J. G.; Roussev, I. I.; Madjarska, M. S.
2004A&A...418L...9D Altcode:
We present, for the first time, blinker phenomena being associated
with brightenings in pre-existing coronal loops registered by the
Extreme-ultraviolet Imaging Telescope (EIT) in Fe XII 195 Å. The
brightenings occur during the emergence of new magnetic flux as
registered by the Big Bear Solar Observatory (BBSO) magnetograph. The
blinkers were identified using simultaneous observations obtained
with the Coronal Diagnostic Spectrometer (CDS) and Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrograph. In light of
the new observational results, we present one possible theoretical
interpretation of the blinker phenomenon. We suggest that the
blinker activity we observe is triggered by interchange reconnection,
serving to provide topological connectivity between newly emerging
flux and pre-existing flux. The EIT images show the existence of loop
structures prior to the onset of the blinker activity. Based on the
available spatial resolution the blinker occurs within, or nearby,
an existing coronal loop. The temperature interfaces created in the
reconnection process between the cool plasma of the newly emerging
loop and the hot plasma of the existing loop are what we suggest to
causes the observed activity seen in both the SUMER and CDS data. As
the temperature interfaces propagate with the characteristic speed of a
conduction front, they heat up the cool chromospheric plasma to coronal
temperatures, an increasing volume of which brightens at transition
region temperatures. We believe this new interpretation gives further
qualitative understanding about the evolution of newly emerging flux
on the Sun. This also provides new insight into the dynamic nature of
the solar transition region.
---------------------------------------------------------
Title: Signature of oscillations in coronal bright points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.; O'Shea, E.
2004A&A...418..313U Altcode:
A detailed study of two consecutive bright points observed
simultaneously with the Coronal Diagnostic Spectrometer (CDS),
the Extreme ultraviolet Imaging Telescope (EIT) and the Michelson
Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory
(SOHO) is presented. The analysis of the evolution of the photospheric
magnetic features and their coronal counterpart shows that there is
a linear dependence between the EIT Fe XII 195 Å flux and the total
magnetic flux of the photospheric bipolarity. The appearance of the
coronal emission is associated with the emergence of new magnetic
flux and the disappearance of coronal emission is associated with
the cancellation of one of the polarities. In one of the cases the
disappearance takes place ∼3-4 h before the full cancellation of
the weakest polarity. <P />The spectral data obtained with CDS show
that one of the bright points experienced short time variations in
the flux on a time scale of 420-650 s, correlated in the transition
region lines (O V 629.73 Å and O III 599.60 Å) and also the He I
584.34 Å line. The coronal line (Mg IX 368.07 Å) undergoes changes
as well, but on a longer scale. The wavelet analysis of the temporal
series reveals that many of these events appear in a random fashion and
sometimes after periods of quietness. However, we have found two cases
of an oscillatory behaviour. A sub-section of the O V temporal series
of the second bright point shows a damped oscillation of five cycles
peaking in the wavelet spectrum at 546 s, but showing in the latter few
cycles a lengthening of that period. The period compares well with that
detected in the S VI 933.40 Å oscillations seen in another bright point
observed with the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer, which has a period of 491 s. The derived electron
density in the transition region was 3×10<SUP>10</SUP> cm<SUP>-3</SUP>
with some small variability, while the coronal electron density was
5×10<SUP>8</SUP> cm<SUP>-3</SUP>.
---------------------------------------------------------
Title: Evidence of Magnetic Reconnection along Coronal Hole Boundaries
Authors: Madjarska, M. S.; Doyle, J. G.; van Driel-Gesztelyi, L.
2004ApJ...603L..57M Altcode:
The present study reveals for the first time the existence of
bidirectional jets, which are a signature of magnetic reconnection,
occurring along coronal hole boundaries. The Solar Ultraviolet
Measurement of Emitted Radiation spectrometer observations obtained
in the N IV 765.15 Å (1.3×10<SUP>5</SUP> K) and Ne VIII 770.42
Å (6×10<SUP>5</SUP> K) emission lines in an equatorial extension
of a polar coronal hole, known as the “Elephant's Trunk” coronal
hole, show small regions of a few arcseconds size with strong blue-
and redshifted emission reaching Doppler shifts of up to 150 km
s<SUP>-1</SUP>, i.e., bidirectional jets. The jets' number density
along coronal hole boundaries was found to be about 4-5 times higher
with respect to the quiet Sun.
---------------------------------------------------------
Title: Bi-Directional Jets at Coronal Hole Boundaries
Authors: Madjarska, M. S.; Doyle, J. G.; van Driel-Gesztelyi, L.
2004ESASP.547..397M Altcode: 2004soho...13..397M
Our study reveals, for the first time, the presence of bi-directional
jets which are considered to be signatures of magnetic reconnection
occurring along coronal hole boundaries. The SUMER observations obtained
in Ne VIII 770.42 Å (6 10 K) and N IV 765.15 Å (1.3 10 K) show small
regions of a few arcsec size with strong blueand red-shifted emission
reaching Doppler shifts up to 150 km s which appear along the coronal
hole boundaries where evolving loop systems are present.
---------------------------------------------------------
Title: Oscillations in Coronal Bright Points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.; O'Shea, E.
2004ESASP.547..329U Altcode: 2004soho...13..329U
No abstract at ADS
---------------------------------------------------------
Title: Coronal Oscillations above Sunspots?
Authors: Doyle, J. G.; Dzifćáková, E.; Madjarska, M. S.
2003SoPh..218...79D Altcode:
Observational data clearly indicate the presence of 3-min oscillations
in sunspots in spectral lines covering a vast temperature range
from the low chromosphere to those lines normally associated with
coronal temperatures. We show that after folding in the sunspot
plume emission measure distribution, the contribution functions for
lines normally formed just below 1×10<SUP>6</SUP> K are shifted to
lower temperatures. For example, the Fe ix 171 Å line is shifted to
6×10<SUP>5</SUP> K for a Maxwellian distribution and to less than
5×10<SUP>5</SUP> K with a non-Maxwellian distribution. Other lines
such as Mg ix 368 Å will also be affected. This then questions some
previous work regarding the suggested detection of 3-min oscillations
in the corona above sunspots.
---------------------------------------------------------
Title: Line Shift Variations in Solar Transition Region Lines
Authors: Doyle, J. G.; Madjarska, M.; Giamikakis, J.; Teriaca, L.;
Roussev, I.
2003csss...12..619D Altcode:
Two high time cadence datasets, taken in C III 977Å and O VI 1032Å
were analysed in an effort to establish the extent of the variability
in the Doppler-shift of typical mid-transition region lines. In C
III, the shortest time-scale variability seems to occur in the network
boundary regions where the line-shift can vary by 7-8 km s<SUP>-1</SUP>
in less than 1 min. The internetwork region also shows variability
although this tends to be longer lived, ∼2-3 mins. The average C III
line-shift in all regions is for a red-shift of ∼ 8 km s<SUP>-1</SUP>
in very good agreement with that derived by others. Furthermore, there
does not seem to be any obvious difference in the average line-shift
in network and internetwork regions. On a few rare occasions, the C
III line was blue-shifted. The O VI line was also red-shifted with the
network region showing evidence for a periodicity. These observations
were compared to model line profiles based on the response of a 2D MHD
environment representing the solar transition region to micro-scale
energy depositions. A variety of temperatures at which the energy
deposition takes place as well as the amount of energy deposited
was examined.
---------------------------------------------------------
Title: Sunspot plume observations in the EUV. The gas pressure
differential between the umbra and surrounding region
Authors: Doyle, J. G.; Madjarska, M. S.
2003A&A...407L..29D Altcode:
The electron density over a bright sunspot plume region was evaluated
using lines within the O V 760 Å multiplet. The plume showed an
intensity enhancement factor of ~9 in the O V lines compared to regions
outside the sunspot umbra. Internal agreement between the various
ratios is excellent which would suggest that the O V lines do not
suffer from blending problems. The derived mean electron densities for
the sunspot plume is log N<SUB>e</SUB>/cm<SUP>-3</SUP> ~ 9.9 compared
to log N<SUB>e</SUB>/cm<SUP>-3</SUP> ~ 10.20-10.45 in the surrounding
area. The derived gas pressure in the plume compared to that outside
leads weight to the suggestion that it is plasma flowing from outside
the spot into the umbra at transition region temperatures that is the
main cause of the down-flows. The plume non-thermal velocities are 5 to
10 km ; s<SUP>-1</SUP> smaller than those measured in regions external
to the spot, suggesting significantly less turbulence within the umbra.
---------------------------------------------------------
Title: Simultaneous observations of solar transition region blinkers
and explosive events by SUMER, CDS and BBSO. Are blinkers, explosive
events and spicules the same phenomenon?
Authors: Madjarska, M. S.; Doyle, J. G.
2003A&A...403..731M Altcode:
The SoHO discovery of the new “blinker” phenomena focused our study on
the search of its relation to already known phenomena such as explosive
events and spicules. The study was performed using a specially planned
joint observing program involving the Coronal Diagnostic Spectrometer
(CDS), Solar Ultraviolet Measurements of Emitted Radiation spectrograph
(SUMER) and Big Bear Solar Observatory (BBSO) magnetograph. Within
each blinker, the SUMER data reveal the presence of small-scale (3
arcsec-5 arcsec), short-lived (2-3 min) bright features not seen in
the CDS data which has sometimes being interpreted as oscillations in
SUMER data. With this data we have clearly identified UV explosive
events in CDS data. The explosive events show a size close to the
small-scale brightenings forming the blinker core. However, they appear
in the SUMER data with their typical strong blue and red wings while
the blinker shows at best only a small increase in the emission of
the blue and red wings and in most instances the typical transition
region red-shift in the center of the line. In all cases the explosive
events cover one pixel in CDS corresponding to a size of 4arcsec x
4arcsec -6arcsec . All identified explosive events were located at
the border of the bright network i.e. the blinker, in the network or
even in the internetwork. From this data, we believe that blinkers and
explosive events are two separate phenomena not directly related or
triggering each other. In this study, the Doppler shift was derived in
a blinker phenomenon for the first time. It ranges from -5 to 25 km ;
s<SUP>-1</SUP> and is predominantly red-shifted. The observed magnetic
flux increase during the blinker phenomena seems to play a crucial
role in the development of this event. We suggest that “blinkers”
maybe the on-disk signature of spicules.
---------------------------------------------------------
Title: An EUV Bright Point as seen by SUMER, CDS, MDI and EIT
on-board SoHO
Authors: Madjarska, M. S.; Doyle, J. G.; Teriaca, L.; Banerjee, D.
2003A&A...398..775M Altcode:
This paper presents the formation, evolution and decay of a coronal
bright point via a spectroscopic analysis of its transition region
counterpart and the evolution of the underlying magnetic bipole during
3 days of almost continuous observations. The data were obtained with
various instruments on-board SoHO, including the SUMER spectrograph
in the transition region line S VI 933.40 Å, CDS in the He I 584.33,
O V 629.73 and Mg IX 368.06 Å lines, plus MDI and EIT. The existence
of the coronal feature is strongly correlated with the evolution of
the underlying bipolar region. The lifetime of the bright point from
the moment when it was first visible in the EIT images until its
complete disappearance was ~ 18 hrs. Furthermore, the bright point
only became visible at coronal temperatures when the two converging
opposite magnetic polarities were ~ 7000 km apart. As far as the
temporal coverage of the data permits, we found that the bright point
disappeared at coronal temperatures after a full cancellation of one of
the magnetic polarities. The spectroscopic analysis reveals the presence
of small-scale ( ~ 6 arcsec) transient brightenings within the bright
point with a periodicity of ~ 6 min. The Doppler shift in the bright
point was found to be in the range of -10 to 10 km ; s<SUP>-1</SUP>
although it is dominated by a red-shifted emission which is associated
with regions characterized by stronger “quiet” Sun photospheric
magnetic flux. Small-scale brightenings within the bright point show
velocity variations in the range 3-6 km ; s<SUP>-1</SUP>. In general
the bright point has a radiance ~ 4 times higher than that of the
network. No relation was found between the bright point and the UV
explosive event phenomena.
---------------------------------------------------------
Title: Transition region small-scale dynamics: UV explosive events
Authors: Teriaca, L.; Falchi, A.; Doyle, J. G.; Madjarska, M. S.;
Banerjee, D.
2002ESASP.506..777T Altcode: 2002ESPM...10..777T; 2002svco.conf..777T
High spectral, spatial and temporal resolution UV observations of the
quiet Sun transition region show a highly structured and dynamical
environment where transient events such as brightenings, blinkers
and explosive events occur continuously. In particular explosive
events are characterized by strongly non-Gaussian line profiles
witnessing velocities up to 200 km s<SUP>-1</SUP>. The high kinetic
and enthalpy fluxes associated with these events could be important
in the energy balance of the transition region and, perhaps, of the
whole corona. In this paper we present a high spatial resolution (~1")
spectroheliogram of a 270×290 arcsec<SUP>2</SUP> wide area of the
quiet Sun acquired with SUMER/SoHO in the O VI 1032 spectral line. The
extremely high quality of these observations allows us to identify
tens of explosive events and to study their relationship with the
underlying photospheric magnetic field. Moreover, the behaviour of lines
emitted by plasma at chromospheric (2×10<SUP>4</SUP>K) and coronal
(10<SUP>6</SUP>K) temperatures during transition region explosive
events is investigated. We conclude that those events do not contribute
significantly to the energy balance of the corona and seems typical
of structure not obviously connected to the T≥10<SUP>6</SUP>K corona.
---------------------------------------------------------
Title: Temporal variability in the Doppler-shift of solar transition
region lines
Authors: Doyle, J. G.; Madjarska, M. S.; Roussev, I.; Teriaca, L.;
Giannikakis, J.
2002A&A...396..255D Altcode:
High cadence datasets taken in C III 977 Å, O VI 1032 Å and Ne
VIII 720 Å were analysed in an effort to establish the extent
of the variability in the Doppler-shift of typical mid-transition
region lines. The shortest time-scale variability seems to occur
in the network boundary regions where the line-shift can vary by
7-8 km s<SUP>-1</SUP> in less than 1 min. The internetwork region
also shows variability although this tends to be longer lived, ~
2-3 min. The average line-shift in C III is a red-shift which ranges
from ~ 2 km s<SUP>-1</SUP> to ~ 20 km s<SUP>-1</SUP> with an average
value for all regions selected being around 10 km s<SUP>-1</SUP>
in very good agreement with that derived by others. The red-shift
values indicate a clear difference between network and internetwork
regions, with the largest red-shift being present at the network
boundary. For O VI, this gives an average red-shift ranging from 5 to
10 km s<SUP>-1</SUP>. For Ne VIII, there is a 13 km s<SUP>-1</SUP>
difference between internetwork and bright network plasma with the
bright network being more red-shifted. This could imply that the
bright network regions are dominated by spicule down-flow.\ In the
second part we present results from 2-dimensional (2D) dissipative
magnetohydrodynamic (MHD) simulations of the response of the solar
transition region to micro-scale energy depositions. A variety of
temperatures at which the energy deposition takes place as well as the
amount of energy deposited are examined. This work is a continuation
of previous related simulations where small-scale energy depositions
were modelled in 1D hydrodynamics. The observable consequences of
such transient events are then computed for three transition region
lines, namely C IV 1548 Å, O VI 1032 Å, and Ne VIII 770 Å, under
the consideration of non-equilibrium ionization.
---------------------------------------------------------
Title: The OIV and SIV intercombination lines in the ultraviolet
spectra of astrophysical sources
Authors: Keenan, F. P.; Ahmed, S.; Brage, T.; Doyle, J. G.; Espey,
B. R.; Exter, K. M.; Hibbert, A.; Keenan, M. T. C.; Madjarska, M. S.;
Mathioudakis, M.; Pollacco, D. L.
2002MNRAS.337..901K Altcode:
New electron density diagnostic line ratios are presented for
the OIV 2s<SUP>2</SUP>2p <SUP>2</SUP>P-2s2p<SUP>24</SUP>P and SIV
3s<SUP>2</SUP>3p <SUP>2</SUP>P-3s3p<SUP>24</SUP>P intercombination
lines around 1400Å. A comparison of these with observational data
for the symbiotic star RR Telescopii (RR Tel), obtained with the
Space Telescope Imaging Spectrograph (STIS), reveals generally
very good agreement between theory and observation. However the
SIV<SUP>2</SUP>P<SUB>3/2</SUB>-<SUP>4</SUP>P<SUB>1/2</SUB> transition
at 1423.824Å is found to be blended with an unknown feature at
1423.774Å. The linewidth for the latter indicates that the feature
arises from a species with a large ionization potential. In addition,
the SIV<SUP>2</SUP>P<SUB>1/2</SUB>-<SUP>4</SUP>P<SUB>3/2</SUB>
transition at 1398.044Å is identified for the first time (to
our knowledge) in an astrophysical source other than the Sun,
and an improved wavelength of 1397.166 Å is measured for the
OIV<SUP>2</SUP>P<SUB>1/2</SUB>-<SUP>4</SUP>P<SUB>3/2</SUB> line. The
OIV and SIV line ratios in a sunspot plume spectrum, obtained with
the Solar Ultraviolet Measurements of the Emitted Radiation (SUMER)
instrument on the Solar and Heliospheric Observatory, are found to be
consistent, and remove discrepancies noted in previous comparisons of
these two ions.
---------------------------------------------------------
Title: Magnetic properties of ultraviolet transient phenomena. Are
blinkers and explosive events the same phenomenon?
Authors: Madjarska, M. S.; Doyle, J. G.
2002ESASP.505..489M Altcode: 2002solm.conf..489M; 2002IAUCo.188..489M
Simultaneous 'quiet' Sun observations were performed on 2001 October 23
with the SUMER and CDS spectrometers on-board SoHO together with the Big
Bear Solar Observatory magnetograph. The aim was to study the magnetic
properties and distinct nature of the transition region phenomena
such as explosive events and blinkers. The different appearance of the
two phenomena in both spectrometer observations was analysed. Blinker
phenomena were clearly associated with bipolar magnetic regions with
always one polarity stronger than the other one. Higher resolution
observations are needed in order to associate explosive events with
any particular magnetic field changes.
---------------------------------------------------------
Title: Electron density variation in off-limb solar corona structures
Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.
2002ESASP.505..595U Altcode: 2002IAUCo.188..595U; 2002solm.conf..595U
We present a study of the electron density variation for off
limb observations with the Coronal Diagnostic Spectrometer (CDS)
on board SoHO using the density sensitive coronal line ratio Si X
(356.0/347.4). The analysis is divided into three parts: the latitudinal
variation from 1.01 < r/R<SUB>solar</SUB> < 1.09, the temporal
variation in successive rasters, and the electron density along a hot
coronal loop found in one of the rasters.
---------------------------------------------------------
Title: Transition region explosive events: Do they have a coronal
counterpart?
Authors: Teriaca, L.; Madjarska, M. S.; Doyle, J. G.
2002A&A...392..309T Altcode:
EUV explosive events are a prominent class of phenomena characterizing
the solar transition region. Their correct location in the wider
frame-work of the outer solar atmosphere can provide important insight
on the nature of the transition region itself and its relationship
with the hotter corona and the cooler chromosphere. In this paper
we present new high-cadence SUMER observations of the “quiet”
Sun obtained simultaneously in the mid-transition region N V 1238.8
Å line (1.8x 10<SUP>5</SUP> K) and in the coronal Mg X 625 Å line
(1.1x 10<SUP>6</SUP> K). These observations are aimed at providing
information on the behaviour of the coronal plasma during EUV
transition region explosive events detected in N V 1238.8 Å. None of
the events observed in N V shows any detectable signature in the Mg
X line profile or in its integrated intensity. The analysis of 1996
observations obtained simultaneously in N V 1238.8 Å and S II 1253.8
Å (3.5x 10<SUP>4</SUP> K) shows, instead, a weak but clear presence
of enhanced wings in the S II line profile during a series of events
observed in N V. These results suggest that EUV explosive events are
not directly relevant in heating the corona and are characteristic of
structures not obviously connected with the upper corona. The evidence
of a chromospheric response suggests that, contrary to some previous
suggestions, explosive events have a chromospheric origin.
---------------------------------------------------------
Title: Transition region counterpart of X-ray/EUV coronal bright
points registered by SUMER, CDS, EIT and MDI/SOHO
Authors: Madjarska, M. S.; Doyle, J. G.
2002ESASP.508..311M Altcode: 2002soho...11..311M
We present a spectroscopic analysis of the transition region counterpart
of Coronal Bright Points (BPs). Simultaneous observations obtained
with the SUMER spectrometer in the S VI 933.38 Å and Ly 6 930.75
&Aring lines, CDS in the He I 584.33, O V 629.73 and Mg IX 368.06
Å MDI and EIT Fe XII 195 Å on-board SoHO were analysed. The dataset
obtained on 1996 October 16, 17 & 18 reveals a complete picture
of the formation, temporal evolution and decay of a bright point. The
nature of the intensity variations in a BP, its Doppler velocities
and its relation to transient phenomena such as explosive events and
blinkers are discussed.
---------------------------------------------------------
Title: Dynamics and Diagnostics of Explosive Events and Blinkers
Authors: Madjarska, M. S.; Doyle, J. G.; Teriaca, L.
2002mwoc.conf...69M Altcode:
The knowledge of the main physical parameters of UV explosive events
and blinkers, such as density and temperature, is of great importance
for the better understanding of the true nature of these transient
events. In this context, density and temperature diagnostics based on
lines belonging to O iv 1400Å and O iii multiplets is presented for
both kind of events. The dynamics of the solar transient phenomena
is revealed through their temporal and spatial evolution as observed
in spectral lines covering a wide temperature range. The results
are obtained using SUMER, CDS, MDI and EIT aboard SoHO, TRACE and
Big Bear Solar Observatory observations and are aimed to give more
information about the main properties of these phenomena. The events
are also studied in connection with the evolution of the underlying
magnetic field, searching for observational evidences of their further
propagation higher in the solar corona.
---------------------------------------------------------
Title: Temporal evolution of different temperature plasma during
explosive events
Authors: Madjarska, M. S.; Doyle, J. G.
2002A&A...382..319M Altcode:
High cadence observations (10 s exposure time) obtained with the SUMER
spectrometer on-board SoHO in the Ly 6 (20 000 K) and S VI (200 000 K)
lines reveal new insight on the nature of explosive events. A time
delay in the response of the S VI line with respect to the Ly 6 line
has been observed, with the Ly 6 line responding with about 20-40
s earlier. A temporal series obtained with 30 s exposure time and
covering the entire Lyman series plus O I, C II and S VI (temperature
range from 15 000 to 200 000 K) has also been explored showing the
response of all these lines during transient phenomena. New common
features linking explosive events and blinkers were found. During
explosive events, the central intensity increases between 1.6 and 2.0
times the pre-event value while the same range of intensity increase
was already reported during blinker phenomena. On the other hand the
maximum intensity increase in Ly 6 was only 13%.
---------------------------------------------------------
Title: Temporal evolution of explosive events as observed in Lyman
and S VI lines
Authors: Madjarska, M. S.; Doyle, J. G.
2001ESASP.493..279M Altcode: 2001sefs.work..279M
No abstract at ADS
---------------------------------------------------------
Title: Temporal Variability in Transition Region Line .
Authors: Giannikakis, I.; Doyle, J. G.; Antonopoulou, E.; Madjarska, M.
2001hell.confE..41G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electron density variations during ultraviolet transient events
Authors: Teriaca, L.; Madjarska, M. S.; Doyle, J. G.
2001SoPh..200...91T Altcode:
% High-resolution temporal observations performed with the SUMER
spectrometer on SOHO provide an opportunity to investigate the electron
density variations in the `quiet-Sun' solar transition region due to
UV transient events. Two datasets obtained in the density sensitive
lines belonging to the O iv 1400 Å multiplet were searched for such
events, leading to the identification of two explosive events, on 10
July 1996 and 31 May 1997. In both cases, the O iv 1401.16/1404.81
density-sensitive line intensity ratio shows a clear variation,
corresponding to enhancements in the electron density by factors of
∼3. This is fully consistent with recent 2.5D MHD simulations. The
10 July 1996 dataset also provided us with the opportunity to monitor
the behavior of the electron density through an UV blinker. Despite
an increase of a factor of two in the line intensities, no variation
of the electron density was found. This suggests that the intensity
enhancement is due to an increase in the filling factor.
---------------------------------------------------------
Title: Electron Density Enhancement During an UV Explosive Event
Authors: Madjarska, M. S.; Doyle, J. G.; Teriaca, L.
2001IAUS..203..407M Altcode:
High resolution temporal observations performed with the SUMER
spectrometer on SOHO provide us the opportunity to investigate the
electron density variations in the solar mid transition region due
to explosive event-like phenomena. The O IV 1401.16/1404.81 density
sensitive line intensity ratio shows a clear increase during a strong
explosive event, corresponding to an electron density enhancement of
a factor of ~ 3.5 respect to pre-event values. This is consistent
with recent MHD simulations (2.5 D) carried out by Karpen et
al. (1998). Karpen J. T., Antiochos S. K., DeVore C. R. and Golub L.,
1998, ApJ 495, 491.
---------------------------------------------------------
Title: Plasma Parameters of a Prominence Observed on October 16/17
1999 by SUMER and CDS/SOHO
Authors: Madjarska, M. S.; Vial, J. -C.; Boccialini, K.; Dermendijiev,
V. N.
2001IAUS..203..410M Altcode:
The aim of our study was to confirm and enrich the results obtained
so far on dynamics and diagnostics of solar prominences. A prominence
observed on October 16/17, 1999 during MEDOC campaign # 4 in the frame
of the updated joint observing programme 09 was studied. The main
prominence plasma parameters like temperature and density were derived
as well as their changes during 8 hours of observations. The relative
line-of-sight velocities were obtained in the cool plasma material
(SUMER, Si IV, 8 10<SUP>4</SUP> K) and prominence-corona transition
region (SUMER, O IV, 2 10<SUP>5</SUP> K). Velocity and line width maps
in both CDS He I 584 Å and O V 629.73 Å were derived. A study of the
blend of O IV 1404.81 Å by Si IV 1404.77 Å and the second order line
O III 702.31 Å was made.
---------------------------------------------------------
Title: Multi-wavelength study of the slow “disparition brusque"
of a filament observed with SOHO
Authors: Schmieder, B.; Delannée, C.; Yong, Deng Yuan; Vial, J. C.;
Madjarska, M.
2000A&A...358..728S Altcode:
A mid-latitude filament was observed before and after its eruption with
SOHO (EIT, SUMER, CDS and LASCO) and with ground based observatories
(Meudon and Pic du Midi) in the context of a coordinated MEDOC
campaign in Orsay. The eruption was followed by a large Coronal
Mass Ejection well observed by LASCO. Few hours before its eruption,
the filament is partially heated (as seen in 195 Ä with EIT). The
physical conditions of the filament before its eruption have been
investigated by spectroscopic analysis of SUMER (the Lyman series L4 to
L9) and of CDS combined with the Multi-channel Subtractive Double Pass
Spectrograph (MSDP) spectra of Hα . Five hours before the eruption,
large broadenings of chromospheric and transition region lines (CDS)
were observed in the main body of the filament suggesting strong
turbulence as well as opposite Dopplershifts on each side of the
filament (Hα and He I) which could be interpreted as twist motions. The
optical thickness of the filament is rather large. During the eruption
the twist is largely developed as observed in 304 Ä. The Doppler
shifts of the filament estimated from Lyman lines are in good agreement
with the velocity of the front edge of the CME bright loop. We notice
that both, the filament and the bright loop, are deviated towards the
equator. This implies that they belong to the same global expansion
event constrained to remain in the equatorial streamer. An X-ray bright
point observed close to a filament footpoint could be the signature of
reconnection process linked to the destabilization of the filament. It
is interpreted in the framework of new MHD modeling of lateral filament
footpoints (Aulanier & Démoulin 1998).
---------------------------------------------------------
Title: Plasma Diagnostics Of A Solar Prominence Observed On 12 June
1997 by EIT, Sumer And CDS
Authors: Madjarska, M. S.; Vial, J. -C.; Bocchialini, K.; Dermendjiev,
V. N.
1999ESASP.446..467M Altcode: 1999soho....8..467M
The plasma diagnostics of a quiescent prominence observed on June 12,
1997 with SUMER, CDS and EIT instruments aboard SOHO in the frame
of Joint Observing Programme 9 has been made. Two sets of SUMER
observations were taken in the four spectral lines Si IV 1393.755,
1402.770 (6-8 10<SUP>4</SUP> K) and O IV 1401.156, 1404.812 (1.7-2.0
10<SUP>5</SUP> K) at two different slit positions on the prominence
body. The relative line-of-sight velocities using both Si IV 1393.755
and 1402.770 lines are derived. The electron density (derived
from the intensity ratio of O IV 1401.156 to 1404.812 lines) in the
prominence-corona interface is determined for both slit positions. CDS
obtained 10 rasters in Si X 347.40, He I 584.33, Si X 356.04, Fe XVI
360.76, Mg IX 368.06, O V 629.73 lines covering a temperature range
from 10<SUP>4</SUP> to 10<SUP>6</SUP> K. By analysing the CDS spectra
in He I and O V ions the relative line-of-sight velocity maps with
regards to the quiet sun are derived.
---------------------------------------------------------
Title: Behaviour of H-alpha and H CA II Emission Lines in a Prominence
Before and During its Dynamic "Disparition Brusque"
Authors: Madjarska, M. S.; Dermendjiev, V. N.; Mouradian, Z.; Kotrc, P.
1998ASPC..150..326M Altcode: 1998npsp.conf..326M; 1998IAUCo.167..326M
No abstract at ADS
---------------------------------------------------------
Title: Small-Scale Structure in Loops and Prominence Threads
Authors: Rudawy, P.; Madjarska, M. S.
1998ASPC..150...63R Altcode: 1998IAUCo.167...63R; 1998npsp.conf...63R
No abstract at ADS
---------------------------------------------------------
Title: On a Possible Mechanism of Quiescent Prominence Destabilization
Authors: Nenovski, P.; Dermendjiev, V. N.; Madjarska, M. S.; Vial,
J. -C.
1998ASPC..150..354N Altcode: 1998IAUCo.167..354N; 1998npsp.conf..354N
No abstract at ADS
---------------------------------------------------------
Title: Observation of the 1961 Total Solar Eclipse in Bulgaria
Authors: Madjarska, M.; Dermendjiev, V. N.
1996RoAJ....6...13M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sudden Disappearance of a Quiescent Prominence on April 23,
1989. Morphology, Dynamics and MHD Interpretation
Authors: Madjarska, M. S.; Dermendjiev, V. N.; Mouradian, Z.;
Nenovski, P.
1996ApL&C..34..113M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Possible preflare phase of the white light flares.
Authors: Dermendjiev, V. N.; Dechev, M.; Madjarska, M. S.
1996joso.proc..152D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Small-scale clusters of photospheric network bright points
and their dependence on the solar cycle phase
Authors: Dermendjev, V. N.; Muller, R.; Madjarska, M. S.
1994SoPh..155...45D Altcode:
The tendency of network bright points (NBPs) to form in their surface
distribution non-random, small-scale clusters is studied by a 2-D
nearest-neighbours test, based on observational data for the distance
between separate NBPs. High-resolution photographs taken from long time
series obtained atλ4308 å with the 50-cm refractor of Pic du Midi
Observatory are used. Three different epochs of the solar cycle were
chosen. The results obtained suggest that the degree of clustering
depends on the solar cycle phase. Supposing that the NBPs are good
tracers of the kilogauss small-scale magnetic field, we use them to
obtain information about the subphotospheric small-scale magnetic
field organisation and its dependence on the solar cycle phase.
---------------------------------------------------------
Title: On the Dynamics of Surge Plasma Knots
Authors: Dermendjiev, V. N.; Okten, A.; Madjarska, M. S.
1994scs..conf..369D Altcode: 1994IAUCo.144..369D
Plasma knots of a high latitude surge, consisting of only one thin
and very long jet are studied over long series of Hα filtergrams. An
attempt to evaluate the influence of magnetic flux tube oscillation
on the surge plasma was made.
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Title: Small-scale clusters of photospheric network bright points.
Authors: Dermendjiev, V. N.; Muller, R.; Madjarska, M. S.
1993sova.conf...68D Altcode:
The authors report the basic results of their study on the problem
of NBP surface distribution obtained on the basis of Pic-du-Midi
observations and using the processing and computer facilities of
NAO-Rozhen.
