scholarly journals Temporal evolution of arch filaments as seen in He I 10 830 Å

2018 ◽  
Vol 617 ◽  
pp. A55 ◽  
Author(s):  
S. J. González Manrique ◽  
C. Kuckein ◽  
M. Collados ◽  
C. Denker ◽  
S. K. Solanki ◽  
...  
Keyword(s):  
Spectral Range ◽  
Analytic Functions ◽  
Temporal Evolution ◽  
Peak Velocity ◽  
Line Of Sight ◽  
Doppler Velocity ◽  
Solar Telescope ◽  
Supersonic Velocities ◽  
Resolution Element ◽  
High Cadence

Aims. We study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them. Methods. We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10 830 Å spectral range. The He I triplet profiles were fitted with analytic functions to infer line-of-sight (LOS) velocities to follow plasma motions within the AFS. Results. We tracked the temporal evolution of an individual arch filament over its entire lifetime, as seen in the He I 10 830 Å triplet. The arch filament expanded in height and extended in length from 13″ to 21″. The lifetime of this arch filament is about 30 min. About 11 min after the arch filament is seen in He I, the loop top starts to rise with an average Doppler velocity of 6 km s−1. Only two minutes later, plasma drains down with supersonic velocities towards the footpoints reaching a peak velocity of up to 40 km s−1 in the chromosphere. The temporal evolution of He I 10 830 Å profiles near the leading pore showed almost ubiquitous dual red components of the He I triplet, indicating strong downflows, along with material nearly at rest within the same resolution element during the whole observing time. Conclusions. We followed the arch filament as it carried plasma during its rise from the photosphere to the corona. The material then drained toward the photosphere, reaching supersonic velocities, along the legs of the arch filament. Our observational results support theoretical AFS models and aids in improving future models.

scholarly journals Evolving Features of Hβ Doppler Velocity Fields at Sites of Flares

1993 ◽  
Vol 141 ◽  
pp. 267-270
Author(s):  
Wei Li ◽  
Guoxiang Ai ◽  
Hongqi Zhang
Keyword(s):  
Velocity Field ◽  
Active Regions ◽  
Velocity Fields ◽  
Time Sequence ◽  
Line Of Sight ◽  
Doppler Velocity

AbstractWe analyzed eight active regions with more than 600 flare kernels and ribbons, and relevant time sequence Hβ chromospheric Dopplergrams. These data showed that during several hours prior to the flares, the velocity field evolves so that the sites of the flare kernels and ribbons become close to the inversion line of the velocity field. This result holds regardless of whether or not the flare sites are wholly located in blue-shifted areas, or are far from the the inversion line of the line-of-sight velocity field, or are partly within red-shifted areas.

scholarly journals Capabilities of bisector analysis of the Si I 10 827 Å line for estimating line-of-sight velocities in the quiet Sun

2020 ◽  
Vol 634 ◽  
pp. A19 ◽  
Author(s):  
S. J. González Manrique ◽  
C. Quintero Noda ◽  
C. Kuckein ◽  
B. Ruiz Cobo ◽  
M. Carlsson
Keyword(s):  
Spectral Line ◽  
Line Profile ◽  
Line Of Sight ◽  
Solar Telescope ◽  
Simple Method ◽  
Quiet Sun ◽  
Line Intensities ◽  
Line Core ◽  
Reference Images ◽  
Non Local

We examine the capabilities of a fast and simple method to infer line-of-sight (LOS) velocities from observations of the photospheric Si I 10 827 Å line. This spectral line is routinely observed together with the chromospheric He I 10 830 Å triplet as it helps to constrain the atmospheric parameters. We study the accuracy of bisector analysis and a line core fit of Si I 10 827 Å. We employ synthetic profiles starting from the Bifrost enhanced network simulation. The profiles are computed solving the radiative transfer equation, including non-local thermodynamic equilibrium effects on the determination of the atomic level populations of Si I. We found a good correlation between the inferred velocities from bisectors taken at different line profile intensities and the original simulation velocity at given optical depths. This good correlation means that we can associate bisectors taken at different line-profile percentages with atmospheric layers that linearly increase as we scan lower spectral line intensities. We also determined that a fit to the line-core intensity is robust and reliable, providing information about atmospheric layers that are above those accessible through bisectors. Therefore, by combining both methods on the Si I 10 827 Å line, we can seamlessly trace the quiet-Sun LOS velocity stratification from the deep photosphere to higher layers until around logτ = −3.5 in a fast and straightforward way. This method is ideal for generating quick-look reference images for future missions like the Daniel K. Inoue Solar Telescope and the European Solar Telescope, for example.

scholarly journals Why should we correct reported pulsation frequencies for stellar line-of-sight Doppler velocity shifts?

2014 ◽  
Vol 445 (1) ◽  
pp. L94-L98 ◽  
Author(s):  
G. R. Davies ◽  
R. Handberg ◽  
A. Miglio ◽  
T. L. Campante ◽  
W. J. Chaplin ◽  
...  
Keyword(s):  
Line Of Sight ◽  
Doppler Velocity

scholarly journals Observation of High Doppler Velocity Wings in the Nascent Wind of R Doradus

2020 ◽  
Vol 30 (1) ◽  
pp. 85
Author(s):  
Hoai Thi Do ◽  
Nhung Tuyet Pham ◽  
Tuan-Anh Pham ◽  
Pierre Darriulat ◽  
Diep Ngoc Pham ◽  
...  
Keyword(s):  
Current Knowledge ◽  
Line Emission ◽  
Terminal Velocity ◽  
Spectral Lines ◽  
Line Of Sight ◽  
Doppler Velocity ◽  
Agb Stars ◽  
Gas Streams ◽  
Stellar Pulsations ◽  
Molecular Lines

We study the morpho-kinematics in the nascent wind of AGB star R Doradus in the light of high Doppler velocity wings observed in the spectral lines of several species. We probe distances from the star between ∼10 and ∼100 au using ALMA observations of the emission of five different molecular lines. High Doppler velocity enhancements of the line emission are observed in the vicinity of the line of sight crossing the star, reminiscent of those recently interpreted as gas streams in the nascent wind of a similar AGB star, EP Aqr. They are present in both blue-shifted and red- shifted hemispheres but are not exactly back-to-back. They are accelerated at a typical rate of 0.7 km s\(^{−1}\) au\(^{−1}\) up to some 20 km s\(^{−1}\). Important differences are observed between the emissions of different molecules. We exclude an effect of improper continuum subtraction. However, in contrast to EP Aqr, the line of sight plays no particular role in the R Dor morpho-kinematics, shedding doubt on the validity of a gas stream interpretation. We discuss possible interpretations in terms of stellar pulsations or of rotation of the gas in the environment of the star. We conclude that, in the state of current knowledge, no fully convincing picture of the physics governing the production of such high velocities, typically twice as large as the terminal velocity, can be reliably drawn. New high resolution analyses of observations of the nascent wind of oxygen-rich AGB stars are needed to clarify the issue.

scholarly journals The ESA GOME-Evolution "Climate" water vapor product: A homogenized time-series of H<sub>2</sub>O columns from GOME/SCIAMACHY/GOME-2

2017 ◽  
Author(s):  
Steffen Beirle ◽  
Johannes Lampel ◽  
Yang Wang ◽  
Kornelia Mies ◽  
Margherita Grossi ◽  
...  
Keyword(s):  
Time Series ◽  
Water Vapor ◽  
Spatial Resolution ◽  
Spectral Range ◽  
Temporal Evolution ◽  
Global Scale ◽  
Global Distribution ◽  
Pixel Size ◽  
Systematic Effects ◽  
Consistent Treatment

Abstract. We present time-series of the global distribution of water vapor columns over more than two decades based on measurements from the satellite instruments GOME, SCIAMACHY, and GOME-2 in the red spectral range. Particular focus is the consistency amongst the different sensors to avoid jumps from one instrument to another. This is reached by applying robust and simple retrieval settings consistently. Potentially systematic effects due to differences in ground pixel size are avoided by merging SCIAMACHY and GOME-2 observations to GOME spatial resolution, which also allows for a consistent treatment of cloud effects. In addition, the GOME-2 swath is reduced to that of GOME and SCIAMACHY to have consistent viewing geometries. Remaining systematic differences between the different sensors are investigated during overlap periods and are corrected for in the homogenized time series. The resulting "Climate" product (https://doi.org/10.1594/WDCC/GOME-EVL_water_vapor_climate) allows to study the temporal evolution of water vapor over the last 20 years on global scale.

scholarly journals Spectroscopic detection of coronal plasma flows in loops undergoing thermal non-equilibrium cycles

2020 ◽  
Vol 634 ◽  
pp. A54 ◽  
Author(s):  
Gabriel Pelouze ◽  
Frédéric Auchère ◽  
Karine Bocchialini ◽  
Clara Froment ◽  
Susanna Parenti ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Line Of Sight ◽  
Doppler Velocity ◽  
Temperature Plasma ◽  
Imaging Spectrometer ◽  
Periodic Flows ◽  
Evaporation And Condensation ◽  
Spatially Resolved ◽  
Euv Imaging ◽  
Non Equilibrium

Context. Long-period intensity pulsations were recently detected in the EUV emission of coronal loops and attributed to cycles of plasma evaporation and condensation driven by thermal non-equilibrium (TNE). Numerical simulations that reproduce this phenomenon also predict the formation of periodic flows of plasma at coronal temperatures along some of the pulsating loops. Aims. We aim to detect these predicted flows of coronal-temperature plasma in pulsating loops. Methods. We used time series of spatially resolved spectra from the EUV imaging spectrometer (EIS) onboard Hinode and tracked the evolution of the Doppler velocity in loops in which intensity pulsations have previously been detected in images of SDO/AIA. Results. We measured signatures of flows that are compatible with the simulations but only for a fraction of the observed events. We demonstrate that this low detection rate can be explained by line of sight ambiguities combined with instrumental limitations, such as low signal-to-noise ratio or insufficient cadence.

scholarly journals Fast downflows in a chromospheric filament

2019 ◽  
Vol 15 (S354) ◽  
pp. 454-457
Author(s):  
K. Sowmya ◽  
A. Lagg ◽  
S. K. Solanki ◽  
J. S. Castellanos Durán
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Fields ◽  
Velocity Component ◽  
Field Vector ◽  
Line Of Sight ◽  
Plasma Velocity ◽  
Supersonic Velocities ◽  
Slow Velocity ◽  
The Magnetic Field

AbstractAn active region filament in the upper chromosphere is studied using spectropolarimetric data in He i 10830 Å from the GREGOR telescope. A Milne-Eddingon based inversion of the Unno-Rachkovsky equations is used to retrieve the velocity and the magnetic field vector of the region. The plasma velocity reaches supersonic values closer to the feet of the filament barbs and coexist with a slow velocity component. Such supersonic velocities result from the acceleration of the plasma as it drains from the filament spine through the barbs. The line-of-sight magnetic fields have strengths below 200 G in the filament spine and in the filament barbs where fast downflows are located, their strengths range between 100 - 700 G.

scholarly journals 2D non-LTE modelling of a filament observed in the Hα line with the DST/IBIS spectropolarimeter

2019 ◽  
Vol 631 ◽  
pp. A146 ◽  
Author(s):  
P. Schwartz ◽  
S. Gunár ◽  
J. M. Jenkins ◽  
D. M. Long ◽  
P. Heinzel ◽  
...  
Keyword(s):  
Local Thermodynamic Equilibrium ◽  
Line Of Sight ◽  
Solar Telescope ◽  
Line Profiles ◽  
Forward Modelling ◽  
Dynamic Nature ◽  
Synthetic Spectra ◽  
Quiescent Stage ◽  
2D Model ◽  
Quiescent Filament

Context. We study a fragment of a large quiescent filament observed on May 29, 2017 by the Interferometric BIdimensional Spectropolarimeter (IBIS) mounted at the Dunn Solar Telescope. We focus on its quiescent stage prior to its eruption. Aims. We analyse the spectral observations obtained in the Hα line to derive the thermodynamic properties of the plasma of the observed fragment of the filament. Methods. We used a 2D filament model employing radiative transfer computations under conditions that depart from the local thermodynamic equilibrium. We employed a forward modelling technique in which we used the 2D model to produce synthetic Hα line profiles that we compared with the observations. We then found the set of model input parameters, which produces synthetic spectra with the best agreement with observations. Results. Our analysis shows that one part of the observed fragment of the filament is cooler, denser, and more dynamic than its other part that is hotter, less dense, and more quiescent. The derived temperatures in the first part range from 6000 K to 10 000 K and in the latter part from 11 000 K to 14 000 K. The gas pressure is 0.2–0.4 dyn cm−2 in the first part and around 0.15 dyn cm−2 in the latter part. The more dynamic nature of the first part is characterised by the line-of-sight velocities with absolute values of 6–7 km s−1 and microturbulent velocities of 8–9 km s−1. On the other hand, the latter part exhibits line-of-sight velocities with absolute values 0–2.5 km s−1 and microturbulent velocities of 4–6 km s−1.

Repaired aortic coarctation in adults—magnetic resonance imaging with velocity mapping shows distortions of anatomy and flow

1996 ◽  
Vol 6 (1) ◽  
pp. 20-27 ◽  
Author(s):  
Philip J. Kilner ◽  
Tokuko Shinohara ◽  
Cynthia Sampson ◽  
Raad H. Mohiaddin ◽  
David N. Firmin ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Aortic Coarctation ◽  
Peak Velocity ◽  
Doppler Velocity ◽  
Cine Imaging ◽  
Resonance Imaging ◽  
Velocity Mapping ◽  
Adolescents And Adults

AbstractMagnetic resonance velocity mapping of intraaortic flow was performed prospectively in adolescents and adults after coarctation repair. The aims were to assess the feasibility and clinical usefulness of the technique in this patient group, and to study flow velocity distributions in repaired regions. Twenty consecutive patients attending for follow-up after repair of aortic coarctation, aged 15–39, mean 25 years, were studied using a 0.5 tesla Picker magnetic resonance machine. Spin echo and cine imaging with phase velocity mapping, echo time 3.6 ms, were used to study anatomy and flow in the repaired region. Transcutaneous ultrasonic examination, with continuous wave Doppler velocity measurement was performed independently on the same day. Velocity maps, acquired successfully in all patients, showed asymmetry and nonhomogeneity of flow in relation to anatomical distortions of repaired regions. Magnetic resonance and Doppler measurements of peak velocity compared as follows: n=20, range 1.2–3.9 m/sec, mean 2.33 m/sec, mean of differences (Doppler-MR) 0.22 m/sec, standard deviation of differences ±0.27 m/sec. Localized velocity peaks adjacent to wall deformations were identified by magnetic resonance in five patients without significant restenosis. Magnetic resonance imaging with velocity mapping proved reliable and informative in follow-up assessment in adolescents and adults after surgical repair of aortic coarctation. There was satisfactory agreement between magnetic resonance and Doppler measurements of peak velocity. Velocity maps showed that localized velocity peaks may occur in limited parts of the stream adjacent to distorted aortic boundaries without stenosis. This could be a cause of overestimation of pressure gradients from peak velocity data, a possibility which requires further investigation.

Comparison of radio-auroral spectral characteristics at 398 MHz with incoherent scatter measurements of electric field

1980 ◽  
Vol 58 (2) ◽  
pp. 232-246 ◽  
Author(s):  
D. R. Moorcroft
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Phased Array ◽  
Spectral Characteristics ◽  
Line Of Sight ◽  
Doppler Velocity ◽  
Incoherent Scatter ◽  
Phase Velocities ◽  
Stream Drift ◽  
The Magnetic Field

Radio-auroral Doppler measurements obtained with the 398-MHz Homer phased-array radar were compared with simultaneous and coincident measurements of electron density and electric field made by the Chatanika incoherent scatter radar. The results for this post-midnight period of observation are not consistent with a direct relationship between the radio-auroral Doppler velocity and the line of sight component of the electron drift velocity, in contrast to the previous observations at VHF. Instead, the observations are consistent with the hypothesis that the echoes arise from the two-stream/drift-gradient irregularities traveling at their threshold phase velocities, close to the local acoustic velocity, Cs. Some of the Doppler velocities observed are considerably less than Cs, and may indicate propagation away from perpendicular to the magnetic field, possibly resulting from magnetic field line distortion.

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