scholarly journals Non-Maxwellian Analysis of the Transition-region Line Profiles Observed by theInterface Region Imaging Spectrograph

2017 ◽  
Vol 842 (1) ◽  
pp. 19 ◽  
Author(s):  
Jaroslav Dudík ◽  
Vanessa Polito ◽  
Elena Dzifčáková ◽  
Giulio Del Zanna ◽  
Paola Testa
Keyword(s):  
Transition Region ◽  
Line Profiles ◽  
Imaging Spectrograph ◽  
Region Line

scholarly journals Semi-empirical model atmospheres for the chromosphere of the sunspot penumbra and umbral flashes

2019 ◽  
Vol 627 ◽  
pp. A46 ◽  
Author(s):  
Souvik Bose ◽  
Vasco M. J. Henriques ◽  
Luc Rouppe van der Voort ◽  
Tiago M. D. Pereira
Keyword(s):  
Transition Region ◽  
Empirical Model ◽  
Solar Chromosphere ◽  
Line Profiles ◽  
Frequency Redistribution ◽  
Lower Transition ◽  
Semi Empirical ◽  
Complete Frequency ◽  
Imaging Spectrograph ◽  
Sunspot Penumbra

Context. The solar chromosphere and the lower transition region are believed to play a crucial role in the heating of the solar corona. Models that describe the chromosphere (and the lower transition region), accounting for its highly dynamic and structured character are, so far, found to be lacking. This is partly due to the breakdown of complete frequency redistribution (CRD) in the chromospheric layers and also because of the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all relevant heights. Aims. We aim to obtain semi-empirical model atmospheres that reproduce the features of the Mg II h&k line profiles that sample the middle chromosphere with focus on a sunspot. Methods. We used spectropolarimetric observations of the Ca II 8542 Å spectra obtained with the Swedish 1 m Solar Telescope and used NICOLE inversions to obtain semi-empirical model atmospheres for different features in and around a sunspot. These were used to synthesize Mg II h&k spectra using the RH1.5D code, which we compared with observations taken with the Interface Region Imaging Spectrograph (IRIS). Results. Comparison of the synthetic profiles with IRIS observations reveals that there are several areas, especially in the penumbra of the sunspot, where most of the observed Mg II h&k profiles are very well reproduced. In addition, we find that supersonic hot down-flows, present in our collection of models in the umbra, lead to synthetic profiles that agree well with the IRIS Mg II h&k profiles, with the exception of the line core. Conclusions. We put forward and make available four semi-empirical model atmospheres. Two for the penumbra, reflecting the range of temperatures obtained for the chromosphere, one for umbral flashes, and a model representative of the quiet surroundings of a sunspot.

scholarly journals Evaluating Possible Heating Mechanisms Using the Transition Region Line Profiles of Late‐Type Stars

1997 ◽  
Vol 478 (2) ◽  
pp. 745-765 ◽  
Author(s):  
Brian E. Wood ◽  
Jeffrey L. Linsky ◽  
Thomas R. Ayres
Keyword(s):  
Transition Region ◽  
Line Profiles ◽  
Late Type ◽  
Region Line

Effects of Ambipolar Diffusion on Prominence Thread Models

1994 ◽  
Vol 144 ◽  
pp. 315-321 ◽  
Author(s):  
M. G. Rovira ◽  
J. M. Fontenla ◽  
J.-C. Vial ◽  
P. Gouttebroze
Keyword(s):  
Energy Balance ◽  
Transition Region ◽  
Ambipolar Diffusion ◽  
Line Profiles ◽  
Balance Equations ◽  
Model Calculations ◽  
Partial Frequency ◽  
Frequency Redistribution ◽  
Partial Frequency Redistribution ◽  
Theoretical Structure

AbstractWe have improved previous model calculations of the prominence-corona transition region including the effect of the ambipolar diffusion in the statistical equilibrium and energy balance equations. We show its influence on the different parameters that characterize the resulting prominence theoretical structure. We take into account the effect of the partial frequency redistribution (PRD) in the line profiles and total intensities calculations.

scholarly journals Enhanced Turbulence and Heating Observed Preceding the Impulsive Phase in a Solar Flare

1989 ◽  
Vol 104 (2) ◽  
pp. 231-234
Author(s):  
Chung-Chieh Cheng ◽  
K.G. Widing
Keyword(s):  
Solar Flare ◽  
Transition Region ◽  
Normal Incidence ◽  
Impulsive Phase ◽  
Energetic Particles ◽  
Line Profiles ◽  
Chromospheric Evaporation

AbstractWe studied the unique EUV spectra of the 21 Jan. 1974 flare observed by the NRL Normal-Incidence Slit Spectrometer (SO 82B) onboard the Skylab. The results show that the pre-impulsive transition region plasmas exhibited enhanced turbulence and heating before the acceleration of energetic particles. The absence of blue-shifted components in the Fe XXI line profiles shows that the chromospheric evaporation is not important in this flare.

scholarly journals Reappraising Transition Region Line Widths in Light of Recent Alfvén Wave Discoveries

2008 ◽  
Vol 673 (2) ◽  
pp. L219-L223 ◽  
Author(s):  
Scott W. McIntosh ◽  
Bart De Pontieu ◽  
Theodore D. Tarbell
Keyword(s):  
Transition Region ◽  
Alfven Wave ◽  
Line Widths ◽  
Region Line

Transition region line-shifts in the rebound shock spicule model

1994 ◽  
Vol 70 (1-2) ◽  
pp. 103-106 ◽  
Author(s):  
V. H. Hansteen ◽  
�. Wikst�l
Keyword(s):  
Transition Region ◽  
Region Line

scholarly journals Evolution of supersonic downflows in a sunspot

2020 ◽  
Vol 636 ◽  
pp. A35
Author(s):  
C. J. Nelson ◽  
S. Krishna Prasad ◽  
M. Mathioudakis
Keyword(s):  
Transition Region ◽  
Spectral Resolution ◽  
Peak Velocity ◽  
Bright Region ◽  
The Core ◽  
Spatial Structuring ◽  
Spectral Profiles ◽  
Raster Scans ◽  
Imaging Spectrograph ◽  
Resolution Data

Context. Supersonic downflows have been observed in transition region spectra above numerous sunspots, however, little research has been conducted to date into how persistent these signatures are within sunspots on timescales longer than a few hours. Aims. We aim to analyse the lead sunspot of AR 12526 to infer the properties and evolution of supersonic downflows occurring within it using high-spatial and spectral resolution data. Methods. We analysed 16 large, dense raster scans sampled by the Interface Region Imaging Spectrograph. These rasters tracked the lead sunspot of AR 12526 across the solar disc at discrete times between 27 March 2016 and 2 April 2016, providing spectral profiles from the Si IV, O IV, Mg II, and C II lines. Additionally, we studied one sit-and-stare observation acquired on 1 April 2016 centred on the sunspot to analyse the evolution of supersonic downflows on shorter timescales. Results. Supersonic downflows are variable within this sunspot both in terms of spatial structuring and velocities. Thirteen of the 16 raster scans display some evidence of supersonic downflows in the Si IV 1394 Å line co-spatial to a sustained bright structure detected in the 1400 Å slit-jaw imaging channel; a peak velocity of 112 km s−1 is recorded on 29 March 2016. Evidence for supersonic downflows in the O IV 1401 Å line is found in 14 of these rasters; the spatial structuring in this line often differs from that inferred from the Si IV 1394 Å line. Only one example of a supersonic downflow is detected in the C II 1335 Å line and no downflows are found in the Mg II 2796 Å lines at these locations. In the sit-and-stare observations, no dual flow is initially detected, however, a supersonic downflow develops after approximately 60 min. This downflow accelerates from 73 km s−1 to close to 80 km s−1 in both the Si IV 1394 Å and O IV 1401 Å lines over the course of 20 min before the end of the observation. Conclusions. Supersonic downflows are found in the Si IV 1394 Å line in 13 of the 16 rasters studied in this work. The morphology of these downflows evolved over the course of both hours and days and was often different in the Si IV 1394 Å and O IV 1401 Å lines. These events were found co-spatial to a bright region in the core of the Si IV 1394 Å line, which appeared to form at the footpoints of coronal fan loops. Our results indicate that one raster is not enough to conclusively draw inferences about the properties of supersonic downflows within a sunspot during its lifetime.

scholarly journals Evolution of downflows in the transition region above a sunspot over short time-scales

2020 ◽  
Vol 640 ◽  
pp. A120
Author(s):  
C. J. Nelson ◽  
S. Krishna Prasad ◽  
M. Mathioudakis
Keyword(s):  
Transition Region ◽  
Time Scales ◽  
Spectral Lines ◽  
Formation Mechanisms ◽  
Coronal Loops ◽  
Imaging Data ◽  
Solar Dynamics Observatory ◽  
Solar Dynamics ◽  
Short Time ◽  
Imaging Spectrograph

Context. Downflows with potentially super-sonic velocities have been reported to occur in the transition region above many sunspots; however, how these signatures evolve over short time-scales in both spatial and spectral terms is still unknown and requires further research. Aims. In this article, we investigate the evolution of downflows detected within spectral lines sampling the transition region on time-scales of the order of minutes and we search for clues as to the formation mechanisms of these features in co-temporal imaging data. Methods. For the purposes of this article, we used high-resolution spectral and imaging data sampled by the Interface Region Imaging Spectrograph on the 20 and 21 May 2015 to identify and analyse downflows. Additionally, photospheric and coronal imaging data from the Hinode and Solar Dynamics Observatory satellites were studied to provide context about the wider solar atmosphere. Results. Four downflows were identified and analysed through time. The potential super-sonic components of these downflows had widths of around 2″ and were observed to evolve over time-scales of the order of minutes. The measured apparent downflow velocities were structured both in time and space, with the highest apparent velocities occurring above a bright region detected in Si IV 1400 Å images. Downflows with apparent velocities below the super-sonic threshold that was assumed here were observed to extend a few arcseconds away from the foot-points, suggesting that the potential super-sonic components are linked to larger-scale flows. The electron density and mass flux for these events were found to be within the ranges of 109.6–1010.2 cm−3 and 10−6.81–10−7.48 g cm−2 s−1, respectively. Finally, each downflow formed at the foot-point of thin “fingers”, extending out around 3–5″ in Si IV 1400 Å data with smaller widths (< 1″) than the super-sonic downflow components. Conclusions. Downflows can appear, disappear, and recur within time-scales of less than one hour in sunspots. As the potential super-sonic downflow signatures were detected at the foot-points of both extended fingers in Si IV 1400 SJI data and sub-sonic downflows in Si IV 1394 Å spectra, it is likely that these events are linked to larger-scale flows within structures such as coronal loops.

scholarly journals Measurements of Mass Flow in the Transition Region and Inner Corona

1980 ◽  
Vol 91 ◽  
pp. 375-378
Author(s):  
Gary J. Rottman
Keyword(s):  
Transition Region ◽  
Mass Flow ◽  
Spectral Resolution ◽  
Solar Disk ◽  
Velocity Fields ◽  
Emission Lines ◽  
High Spectral Resolution ◽  
Sounding Rocket ◽  
Line Profiles ◽  
Euv Emission

A recent sounding rocket experiment has provided high spectral resolution line profiles across the solar disk. The objective of this experiment is to provide information on the systematic velocity fields at the base of the corona by observing the displacement, width and shape of EUV emission lines.

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