72 research outputs found
Observational Signatures of Simulated Reconnection Events in the Solar Chromosphere and Transition Region
We present the results of numerical simulations of wave-induced magnetic
reconnection in a model of the solar atmosphere. In the magnetic field geometry
we study in this article, the waves, driven by a monochromatic piston and a
driver taken from Hinode observations, induce periodic reconnection of the
magnetic field, and this reconnection appears to help drive long-period
chromospheric jets. By synthesizing observations for a variety of wavelengths
that are sensitive to a wide range of temperatures, we shed light on the often
confusing relationship between the plethora of jet-like phenomena in the solar
atmosphere, e.g., explosive events, spicules, blinkers, and other phenomena
thought to be caused by reconnection.Comment: 13 pages, 22 figures. Submitted to The Astrophysical Journa
Wave Propagation and Jet Formation in the Chromosphere
We present the results of numerical simulations of wave propagation and jet
formation in solar atmosphere models with different magnetic field
configurations. The presence in the chromosphere of waves with periods longer
than the acoustic cutoff period has been ascribed to either strong inclined
magnetic fields, or changes in the radiative relaxation time. Our simulations
include a sophisticated treatment of radiative losses, as well as fields with
different strengths and inclinations. Using Fourier and wavelet analysis
techniques, we investigate the periodicity of the waves that travel through the
chromosphere. We find that the velocity signal is dominated by waves with
periods around 5 minutes in regions of strong, inclined field, including at the
edges of strong flux tubes where the field expands, whereas 3-minute waves
dominate in regions of weak or vertically oriented fields. Our results show
that the field inclination is very important for long-period wave propagation,
whereas variations in the radiative relaxation time have little effect.
Furthermore, we find that atmospheric conditions can vary significantly on
timescales of a few minutes, meaning that a Fourier analysis of wave
propagation can be misleading. Wavelet techniques take variations with time
into account and are more suitable analysis tools. Finally, we investigate the
properties of jets formed by the propagating waves once they reach the
transition region, and find systematic differences between the jets in inclined
field regions and those in vertical field regions, in agreement with
observations of dynamic fibrils.Comment: 27 pages, 29 figures; accepted for publication in Astrophysical
Journa
Numerical Simulations of Shock Wave-Driven Jets
We present the results of numerical simulations of shock wave-driven jets in
the solar atmosphere. The dependence of observable quantities like maximum
velocity and deceleration on parameters such as the period and amplitude of
initial disturbances and the inclination of the magnetic field is investigated.
Our simulations show excellent agreement with observations, and shed new light
on the correlation between velocity and deceleration and on the regional
differences found in observations.Comment: 7 pages, 11 figures, submitted to Ap
On-disk counterparts of type II spicules in the Ca II 854.2 nm and Halpha lines
Recently a second type of spicules was discovered at the solar limb with the
Solar Optical Telescope (SOT) onboard the Japanese Hinode spacecraft. These
previously unrecognized type II spicules are thin chromospheric jets that are
shorter-lived (10-60 s) and that show much higher apparent upward velocities
(of order 50-100 km/s) than the classical spicules. Since they have been
implicated in providing hot plasma to coronal loops, their formation, evolution
and properties are important ingredients for a better understanding of the mass
and energy balance of the low solar atmosphere. Here we report on the discovery
of the disk counterparts of type II spicules using spectral imaging data in the
Ca II 854.2 nm and Halpha lines with the CRisp Imaging SpectroPolarimeter
(CRISP) at the Swedish Solar Telescope (SST) in La Palma. We find rapid
blueward excursions in the line profiles of both chromospheric lines that
correspond to thin, jet-like features that show apparent velocities of order 50
km/s. These blueward excursions seem to form a separate absorbing component
with Doppler shifts of order 20 and 50 km/s for the Ca II 854.2 nm and Halpha
line respectively. We show that the appearance, lifetimes, longitudinal and
transverse velocities and occurrence rate of these rapid blue excursions on the
disk are very similar to those of the type II spicules at the limb. A detailed
study of the spectral line profiles in these events suggests that plasma is
accelerated along the jet, and plasma is being heated throughout the short
lifetime of the event.Comment: Accepted for publication in Astrophysical Journal. See
http://www.astro.uio.no/~rouppe/rbe/ for better resolution figures and movie
Non-homogeneous Behaviour of the Spatial Distribution of Macrospicules
In this paper the longitudinal and latitudinal spatial
distribution of macrospicules is examined. We found a statistical
relationship between the active longitude determined by
sunspot groups and the longitudinal distribution of macrospicules.
This distribution of macrospicules shows an inhomogeneity and
non-axysimmetrical behaviour in the time interval from June
2010 until December 2012 covered by observations of the Solar
Dynamic Observatory (SDO) satellite. The enhanced positions
of the activity and its time variation has been calculated. The
migration of the longitudinal distribution of macrospicules shows
a similar behaviour as that of the sunspot groups
Oscillations and waves in solar spicules
Since their discovery, spicules have attracted increased attention as energy/mass bridges between the dense and dynamic photosphere and the tenuous hot solar corona. Mechanical energy of photospheric random and coherent motions can be guided by magnetic field lines, spanning from the interior to the upper parts of the solar atmosphere, in the form of waves and oscillations. Since spicules are one of the most pronounced features of the chromosphere, the energy transport they participate in can be traced by the observations of their oscillatory motions. Oscillations in spicules have been observed for a long time. However the recent high-resolutions and high-cadence space and ground based facilities with superb spatial, temporal and spectral capacities brought new aspects in the research of spicule dynamics. Here we review the progress made in imaging and spectroscopic observations of waves and oscillations in spicules. The observations are accompanied by a discussion on theoretical modelling and interpretations of these oscillations. Finally, we embark on the recent developments made on the presence and role of Alfven and kink waves in spicules. We also address the extensive debate made on the Alfven versus kink waves in the context of the explanation of the observed transverse oscillations of spicule axes
Harmonising and linking biomedical and clinical data across disparate data archives to enable integrative cross-biobank research
A wealth of biospecimen samples are stored in modern globally distributed biobanks. Biomedical researchers worldwide need to be able to combine the available resources to improve the power of large-scale studies. A prerequisite for this effort is to be able to search and access phenotypic, clinical and other information about samples that are currently stored at biobanks in an integrated manner. However, privacy issues together with heterogeneous information systems and the lack of agreed-upon vocabularies have made specimen searching across multiple biobanks extremely challenging. We describe three case studies where we have linked samples and sample descriptions in order to facilitate global searching of available samples for research. The use cases include the ENGAGE (European Network for Genetic and Genomic Epidemiology) consortium comprising at least 39 cohorts, the SUMMIT (surrogate markers for micro- and macro-vascular hard endpoints for innovative diabetes tools) consortium and a pilot for data integration between a Swedish clinical health registry and a biobank. We used the Sample avAILability (SAIL) method for data linking: first, created harmonised variables and then annotated and made searchable information on the number of specimens available in individual biobanks for various phenotypic categories. By operating on this categorised availability data we sidestep many obstacles related to privacy that arise when handling real values and show that harmonised and annotated records about data availability across disparate biomedical archives provide a key methodological advance in pre-analysis exchange of information between biobanks, that is, during the project planning phase
Fine-scale Explosive Energy Release at Sites of Prospective Magnetic Flux Cancellation in the Core of the Solar Active Region Observed by Hi-C 2.1, IRIS, and SDO
The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial and temporal resolution (~250 km, 4.4 s) coronal EUV images of Fe ix/x emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21–19:01:56 UT. Three morphologically different types (I: dot-like; II: loop-like; III: surge/jet-like) of fine-scale sudden-brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. Although type Is (not reported before) resemble IRIS bombs (in size, and brightness with respect to surroundings), our dot-like events are apparently much hotter and shorter in span (70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying likely flux cancellation at the microflare's polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. In types I and II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow. The light curves from Hi-C, AIA, and IRIS peak nearly simultaneously for many of these events, and none of the events display a systematic cooling sequence as seen in typical coronal flares, suggesting that these tiny brightening events have chromospheric/transition region origin
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Toward a global and reproducible science for brain imaging in neurotrauma: the ENIGMA adult moderate/severe traumatic brain injury working group
Abstract: The global burden of mortality and morbidity caused by traumatic brain injury (TBI) is significant, and the heterogeneity of TBI patients and the relatively small sample sizes of most current neuroimaging studies is a major challenge for scientific advances and clinical translation. The ENIGMA (Enhancing NeuroImaging Genetics through Meta-Analysis) Adult moderate/severe TBI (AMS-TBI) working group aims to be a driving force for new discoveries in AMS-TBI by providing researchers world-wide with an effective framework and platform for large-scale cross-border collaboration and data sharing. Based on the principles of transparency, rigor, reproducibility and collaboration, we will facilitate the development and dissemination of multiscale and big data analysis pipelines for harmonized analyses in AMS-TBI using structural and functional neuroimaging in combination with non-imaging biomarkers, genetics, as well as clinical and behavioral measures. Ultimately, we will offer investigators an unprecedented opportunity to test important hypotheses about recovery and morbidity in AMS-TBI by taking advantage of our robust methods for large-scale neuroimaging data analysis. In this consensus statement we outline the working group’s short-term, intermediate, and long-term goals
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