Author name code: kuridze ADS astronomy entries on 2022-09-14 author:Kuridze, David ------------------------------------------------------------------------ Title: Dark off-limb gap: manifestation of temperature minimum and dynamic nature of the chromosphere Authors: Kuridze, D.; Heinzel, P.; Koza, J.; Oliver, R. Bibcode: 2022arXiv220814134K Altcode: We study off-limb emission of the lower solar atmosphere using high-resolution imaging spectroscopy in the H$\beta$ and Ca II 8542 Å lines obtained with the CHROMospheric Imaging Spectrometer (CHROMIS) and the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m Solar Telescope. The H$\beta$ line wing images show the dark intensity gap between the photospheric limb and chromosphere which is absent in the Ca II images. We calculate synthetic spectra of the off-limb emissions with the RH code in the one-dimension spherical geometry and find good agreement with the observations. The analysis of synthetic line profiles shows that the gap in the H$\beta$ line wing images maps the temperature minimum region between the photosphere and chromosphere due to the well known opacity and emissivity gap of Balmer lines in this layer. However, observed gap is detected farther from the line core in the outer line wing positions than in the synthetic profiles. We found that an increased microturbulence in the model chromosphere is needed to reproduce the dark gap in the outer line wing, suggesting that observed H$\beta$ gap is the manifestation of the temperature minimum and the dynamic nature of the solar chromosphere. The temperature minimum produces a small enhancement in synthetic Ca II line-wing intensities. Observed off-limb Ca II line-wing emissions show similar enhancement below temperature minimum layer near the edge of the photospheric limb. Title: The Solar Activity Monitor Network - SAMNet Authors: Erdélyi, Robertus; Korsós, Marianna B.; Huang, Xin; Yang, Yong; Pizzey, Danielle; Wrathmall, Steven A.; Hughes, Ifan G.; Dyer, Martin J.; Dhillon, Vikram S.; Belucz, Bernadett; Brajša, Roman; Chatterjee, Piyali; Cheng, Xuewu; Deng, Yuanyong; Domínguez, Santiago Vargas; Joya, Raúl; Gömöry, Peter; Gyenge, Norbert G.; Hanslmeier, Arnold; Kucera, Ales; Kuridze, David; Li, Faquan; Liu, Zhong; Xu, Long; Mathioudakis, Mihalis; Matthews, Sarah; McAteer, James R. T.; Pevtsov, Alexei A.; Pötzi, Werner; Romano, Paolo; Shen, Jinhua; Temesváry, János; Tlatov, Andrey G.; Triana, Charles; Utz, Dominik; Veronig, Astrid M.; Wang, Yuming; Yan, Yihua; Zaqarashvili, Teimuraz; Zuccarello, Francesca Bibcode: 2022JSWSC..12....2E Altcode: The Solar Activity Magnetic Monitor (SAMM) Network (SAMNet) is a future UK-led international network of ground-based solar telescope stations. SAMNet, at its full capacity, will continuously monitor the Sun's intensity, magnetic, and Doppler velocity fields at multiple heights in the solar atmosphere (from photosphere to upper chromosphere). Each SAMM sentinel will be equipped with a cluster of identical telescopes each with a different magneto-optical filter (MOFs) to take observations in K I, Na D, and Ca I spectral bands. A subset of SAMM stations will have white-light coronagraphs and emission line coronal spectropolarimeters. The objectives of SAMNet are to provide observational data for space weather research and forecast. The goal is to achieve an operationally sufficient lead time of e.g., flare warning of 2-8 h and provide many sought-after continuous synoptic maps (e.g., LoS magnetic and velocity fields, intensity) of the lower solar atmosphere with a spatial resolution limited only by seeing or diffraction limit, and with a cadence of 10 min. The individual SAMM sentinels will be connected to their master HQ hub where data received from all the slave stations will be automatically processed and flare warning issued up to 26 h in advance. Title: The Atmospheric Response to High Nonthermal Electron-beam Fluxes in Solar Flares. II. Hydrogen-broadening Predictions for Solar Flare Observations with the Daniel K. Inouye Solar Telescope Authors: Kowalski, Adam F.; Allred, Joel C.; Carlsson, Mats; Kerr, Graham S.; Tremblay, Pier-Emmanuel; Namekata, Kosuke; Kuridze, David; Uitenbroek, Han Bibcode: 2022ApJ...928..190K Altcode: 2022arXiv220113349K Redshifted components of chromospheric emission lines in the hard X-ray impulsive phase of solar flares have recently been studied through their 30 s evolution with the high resolution of the Interface Region Imaging Spectrograph. Radiative-hydrodynamic flare models show that these redshifts are generally reproduced by electron-beam-generated chromospheric condensations. The models produce large ambient electron densities, and the pressure broadening of the hydrogen Balmer series should be readily detected in observations. To accurately interpret the upcoming spectral data of flares with the DKIST, we incorporate nonideal, nonadiabatic line-broadening profiles of hydrogen into the RADYN code. These improvements allow time-dependent predictions for the extreme Balmer line wing enhancements in solar flares. We study two chromospheric condensation models, which cover a range of electron-beam fluxes (1 - 5 × 1011 erg s-1 cm-2) and ambient electron densities (1 - 60 × 1013 cm-3) in the flare chromosphere. Both models produce broadening and redshift variations within 10 s of the onset of beam heating. In the chromospheric condensations, there is enhanced spectral broadening due to large optical depths at Hα, Hβ, and Hγ, while the much lower optical depth of the Balmer series H12-H16 provides a translucent window into the smaller electron densities in the beam-heated layers below the condensation. The wavelength ranges of typical DKIST/ViSP spectra of solar flares will be sufficient to test the predictions of extreme hydrogen wing broadening and accurately constrain large densities in chromospheric condensations. Title: A Solar-cycle Study of Coronal Rotation: Large Variations, Rapid Changes, and Implications for Solar-wind Models Authors: Edwards, Liam; Kuridze, David; Williams, Thomas; Morgan, Huw Bibcode: 2022ApJ...928...42E Altcode: 2022arXiv220303447E Information on the rotation rate of the corona, and its variation over latitude and solar cycle, is valuable for making global connections between the corona and the Sun, for global estimates of reconnection rates and as a basic parameter for solar-wind modeling. Here, we use a time series of tomographical maps gained from coronagraph observations between 2007 and 2020 to directly measure the longitudinal drift of high-density streamers over time. The method reveals abrupt changes in rotation rates, revealing a complex relationship between the coronal rotation and the underlying photosphere. The majority of rates are between -1.°0 to +0.°5 day-1 relative to the standard Carrington rate of 14.°18 day-1, although rates are measured as low as -2.°2 day-1 and as high as 1.°6 day-1. Equatorial rotation rates during the 2008 solar minimum are slightly faster than the Carrington rate, with an abrupt switch to slow rotation in 2009, then a return to faster rates in 2017. Abrupt changes and large variations in rates are seen at all latitudes. Comparison with a magnetic model suggests that periods of equatorial fast rotation are associated with times when a large proportion of the magnetic footpoints of equatorial streamers are near the equator, and we interpret the abrupt changes in terms of the latitudinal distribution of the streamer photospheric footpoints. The coronal rotation rate is a key parameter for solar-wind models, and variations of up to a degree per day or more can lead to large systematic errors over forecasting periods of longer than a few days. The approach described in this paper gives corrected values that can form a part of future forecasting efforts. Title: Detecting and Characterising Small-Scale Brightenings in Solar Imaging Data Authors: Humphries, LlÅ·r. Dafydd; Morgan, Huw; Kuridze, David Bibcode: 2021SoPh..296..140H Altcode: Observations of small-scale brightenings in the low solar atmosphere can provide valuable constraints on possible heating and heat transport mechanisms. We present a method for the detection and analysis of brightenings, and demonstrate its application to time-series imagery of the Interface Region Imaging Spectrograph (IRIS) in the extreme ultraviolet (EUV). The method is based on spatio-temporal band-pass filtering, adaptive thresholding and centroid tracking, and records an event's spatial position, duration, total brightness and maximum brightness. Spatial area, brightness, and position are also recorded as functions of time throughout the event's lifetime. Detected brightenings can fragment, or merge, over time - thus the number of distinct regions constituting a brightening event is recorded over time, and the maximum number of regions recorded as Nfrag, which is a simple measure of an event's coherence or spatial complexity. A test is made on a synthetic datacube composed of a static background based on IRIS data, Poisson noise and ≈104 randomly-distributed, moving, small-scale Gaussian brightenings. Maximum brightness, total brightness, area, and duration follow power-law distributions, and the results show the range over which the method can successfully extract information. The test shows that the recorded maximum brightness of an event is a reliable measure for the brightest and most accurately detected events, with an error of 6%. Event area, duration and speed are generally underestimated by around 15% and have an uncertainty of 20-30%. The total brightness is underestimated by 30%, and has an uncertainty of 30%. Applying this detection method to real IRIS quiet-sun data spanning 19 minutes over a 54.40″×55.23″ field of view (FOV) yields 2997 detections, 1340 of these detections either remain un-fragmented or fragment to two distinct regions at least once during their lifetime (Nfrag≤2 ), equating to an event density of 3.96 ×10−4 arcsec−2 s−1. The method will be used for a future large-scale statistical analysis of several quiet-sun (QS) data sets from IRIS, other EUV imagers, and other types of data including Hα and visible photospheric imagery. Title: Temporal evolution of small-scale internetwork magnetic fields in the solar photosphere (Corrigendum) Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.; Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A. Bibcode: 2021A&A...652C...2C Altcode: No abstract at ADS Title: Flare-induced Photospheric Velocity Diagnostics Authors: Monson, Aaron J.; Mathioudakis, Mihalis; Reid, Aaron; Milligan, Ryan; Kuridze, David Bibcode: 2021ApJ...915...16M Altcode: 2021arXiv210502199M We present radiative-hydrodynamic simulations of solar flares generated by the RADYN and RH codes to study the perturbations induced in photospheric Fe I lines by electron beam heating. We investigate how variations in the beam parameters result in discernible differences in the induced photospheric velocities. Line synthesis revealed a significant chromospheric contribution to the line profiles resulting in an apparent red asymmetry by as much as 40 m s-1 close to the time of maximum beam heating, which was not reflective of the upflow velocities that arose from the radiative-hydrodynamic simulations at those times. The apparent redshift to the overall line profile was produced by significant chromospheric emission that was blueshifted by as much as 400 m s-1 and fills in the blue side of the near-stationary photospheric absorption profile. The velocity information that can be retrieved from photospheric line profiles during flares must therefore be treated with care to mitigate the effects of higher parts of the atmosphere providing an erroneous velocity signal. Title: Detecting and characterising small-scale brightenings in solar imaging data Authors: Dafydd Humphries, Llŷr; Morgan, Huw; Kuridze, David Bibcode: 2021arXiv210713635D Altcode: Observations of small-scale brightenings in the low solar atmosphere can provide valuable constraints on possible heating/heat-transport mechanisms. We present a method for the detection and analysis of brightenings and demonstrate its application to IRIS EUV time-series imagery. The method uses band-pass filtering, adaptive thresholding and centroid tracking, and records an event's position, duration, and total/maximum brightness. Area, brightness, and position are also recorded as functions of time throughout their lifetime. Detected brightenings can fragment or merge over time, thus the number of distinct regions constituting a brightening event is recorded over time and the maximum number of regions are recorded as a simple measure of an event's coherence/complexity. A test is made on a synthetic datacube composed of a static background based on IRIS data, Poisson noise and $\approx10^4$ randomly-distributed, moving, small-scale Gaussian brightenings. Maximum brightness, total brightness, area, and duration follow power-law distributions and the results show the range over which the method can extract information. The recorded maximum brightness is a reliable measure for the brightest and most accurately detected events with an error of 6%. Area, duration, and speed are generally underestimated by 15% with an uncertainty of 20-30%. Total brightness is underestimated by 30% with an uncertainty of 30%. Applying this method to real IRIS QS data spanning 19 minutes over a 54.40"$\times$55.23" FOV yields 2997 detections. 1340 of these either remain un-fragmented or fragment to two distinct regions at least once during their lifetime equating to an event density of $3.96\times10^{-4}$arcsec$^{-2}$s$^{-1}$. The method will be used for a future large-scale statistical analysis of several QS data sets from IRIS, other EUV imagers, as well as H-$\alpha$ and visible photospheric imagery. Title: Magnetic field inference in active region coronal loops using coronal rain clumps Authors: Kriginsky, M.; Oliver, R.; Antolin, P.; Kuridze, D.; Freij, N. Bibcode: 2021A&A...650A..71K Altcode: 2021arXiv210403089K
Aims: We aim to infer information about the magnetic field in the low solar corona from coronal rain clumps using high-resolution spectropolarimetric observations in the Ca II 8542 Å line obtained with the Swedish 1 m Solar Telescope.
Methods: The weak-field approximation (WFA) provides a simple tool to obtain the line-of-sight component of the magnetic field from spectropolarimetric observations. We adapted a method developed in a previous paper in order to assess the different conditions that must be satisfied in order to properly use the WFA for the data at hand. We also made use of velocity measurements in order to estimate the plane-of-the-sky magnetic field component, so that the magnetic field vector could be inferred.
Results: We have inferred the magnetic field vector from a data set totalling 100 spectral scans in the Ca II 8542 Å line, containing an off-limb view of the lower portion of catastrophically cooled coronal loops in an active region. Our results, albeit limited by the cadence and signal-to-noise ratio of the data, suggest that magnetic field strengths of hundreds of Gauss, even reaching up to 1000 G, are omnipresent at coronal heights below 9 Mm from the visible limb. Our results are also compatible with the presence of larger magnetic field values such as those reported by previous works. However, for large magnetic fields, the Doppler width from coronal rain is not that much larger than the Zeeman width, thwarting the application of the WFA. Furthermore, we have determined the temperature, T, and microturbulent velocity, ξ, of coronal rain clumps and off-limb spicules present in the same data set, and we have found that the former ones have narrower T and ξ distributions, their average temperature is similar, and coronal rain has microturbulent velocities smaller than those of spicules.

Movie associated to Fig. 1 is available at https://www.aanda.org Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST) Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST Instrument Scientists; DKIST Science Working Group; DKIST Critical Science Plan Community Bibcode: 2021SoPh..296...70R Altcode: 2020arXiv200808203R The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. Title: Temporal evolution of small-scale internetwork magnetic fields in the solar photosphere Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.; Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A. Bibcode: 2021A&A...647A.182C Altcode: 2021arXiv210200942C Context. While the longitudinal field that dominates in photospheric network regions has been studied extensively, small-scale transverse fields have recently been found to be ubiquitous in the quiet internetwork photosphere and this merits further study. Furthermore, few observations have been able to capture how this field evolves.
Aims: We aim to statistically characterize the magnetic vector in a quiet Sun internetwork region and observe the temporal evolution of specific small-scale magnetic features.
Methods: We present two high spatio-temporal resolution observations that reveal the dynamics of two disk-centre internetwork regions taken by the new GREGOR Infrared Spectrograph Integral Field Unit with the highly magnetically sensitive photospheric Fe I line pair at 15648.52 Å and 15652.87 Å. We record the full Stokes vector and apply inversions with the Stokes inversions based on response functions code to retrieve the parameters characterizing the atmosphere. We consider two inversion schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in a field free medium, and scheme 2 (S2), with two magnetic models and a fixed 30% stray light component.
Results: The magnetic properties produced from S1 inversions returned a median magnetic field strength of 200 and 240 G for the two datasets, respectively. We consider the median transverse (horizontal) component, among pixels with Stokes Q or U, and the median unsigned longitudinal (vertical) component, among pixels with Stokes V, above a noise threshold. We determined the former to be 263 G and 267 G, and the latter to be 131 G and 145 G, for the two datasets, respectively. Finally, we present three regions of interest, tracking the dynamics of small-scale magnetic features. We apply S1 and S2 inversions to specific profiles of interest and find that the latter produces better approximations when there is evidence of mixed polarities. We find patches of linear polarization with magnetic flux density of the order of 130−150 G and find that linear polarization appears preferentially at granule-intergranular lane boundaries. The weak magnetic field appears to be organized in terms of complex `loop-like' structures, with transverse fields often flanked by opposite polarity longitudinal fields. Title: Semi-empirical Models of Spicule from Inversion of Ca II 8542 Å Line Authors: Kuridze, David; Socas-Navarro, Hector; Koza, Július; Oliver, Ramon Bibcode: 2021ApJ...908..168K Altcode: 2020arXiv201203702K We study a solar spicule observed off-limb using high-resolution imaging spectroscopy in the Ca II 8542 Å line obtained with the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1 m Solar Telescope. Using a new version of the non-LTE code NICOLE specifically developed for this problem we invert the spicule single- and double-peak line profiles. This new version considers off-limb geometry and computes atomic populations by solving the 1D radiative transfer assuming a vertical stratification. The inversion proceeds by fitting the observed spectral profiles at 14 different heights with synthetic profiles computed in the model by solving the radiative transfer problem along its length. Motivated by the appearance of double-peak Ca II 8542 Å spicule profiles, which exhibit two distinct emission features well separated in wavelength, we adopt a double-component scenario. We start from the ansatz that the spicule parameters are practically constant along the spicule axis for each component, except for a density drop. Our results support this ansatz by attaining very good fits to the entire set of 14 × 4 profiles (14 heights and 4 times). We show that the double-component model with uniform temperature of 9560 K, exponential decrease of density with a height scale of 1000-2000 km, and the counter-oriented line-of-sight velocities of components reproduce the double-peak line profiles at all spicule segments well. Analyses of the numerical response function reveals the necessity of the inversions of spectra at multiple height positions to obtain height-dependent, degeneracy-free reliable models with a limited number of free parameters. Title: Mapping the Magnetic Field of Flare Coronal Loops Authors: Kuridze, David; Morgan, Huw; Oliver, Ramon; Mathioudakis, Mihalis; Koza, Julius Bibcode: 2021cosp...43E1791K Altcode: The magnetic field is key to the dynamics, evolution, and heating of the solar atmosphere, yet direct measurements are rare and highly uncertain. We report on the unique observation of flaring coronal loops at the solar limb using high-resolution imaging spectropolarimetry from the Swedish 1-m Solar Telescope. The vantage position, orientation, and nature of the chromospheric material that filled the flare loops allowed us to determine their magnetic field with unprecedented accuracy using the weak-field approximation method. Our analysis reveals coronal magnetic field strengths as high as 350 G at heights up to 25 Mm above the solar limb. These measurements are substantially higher than a number of previous estimates and may have considerable implications for our current understanding of the extended solar atmosphere. Title: An Introduction to Photospheric Flare Line Diagnostics Authors: Monson, A.; Mathioudakis, M.; Milligan, R.; Reid, A.; Kuridze, D. Bibcode: 2020AGUFMSH057..04M Altcode: In preparation for solar cycle 25, we present radiative hydrodynamic flare models from the F-CHROMA archive constructed using the RADYN and RH codes. We simulate potential observable perturbations seen in the line-of-sight velocity and heating induced in the photosphere during a flare. Many works have focused on the recreation of chromospheric spectral line profiles as the atmosphere rapidly heats and expands due to the injection of energy from magnetic reconnection. This extreme heating mechanism can permeate through the upper atmosphere and affect the lowest levels of the solar atmosphere. This results in an observable brightening and Doppler shifting of spectral lines formed in the deepest regions, though the extent of this photospheric reaction is still not fully characterised. We investigate how variations in the properties of a solar flare-accelerated electron beam result in discernible asymmetries in the flaring profiles of several deep forming Fe I spectral lines. Through analysis of the contribution functions and response functions of these lines during a flare, we have found an unprecedented level of high velocity chromospheric contribution which significantly alters the emergent profile of these lines. This comparatively weak, high velocity surplus contributing region of the chromosphere can result in false red shifts and/or significantly adds to the flaring Doppler shifted profile, resulting in a greater blue shift of the line core, which had previously been assumed as a purely photospheric velocity diagnostic. Based on this evidence, it is concluded that any future work using these photospheric lines to diagnose properties of the photosphere in a flaring atmosphere must be carefully analysed to mitigate effect of higher forming regions providing a surplus velocity signal. Title: Ubiquitous hundred-Gauss magnetic fields in solar spicules Authors: Kriginsky, M.; Oliver, R.; Freij, N.; Kuridze, D.; Asensio Ramos, A.; Antolin, P. Bibcode: 2020A&A...642A..61K Altcode: 2020arXiv200601809K
Aims: We aim to study the magnetic field in solar spicules using high-resolution spectropolarimetric observations in the Ca II 8542 Å line obtained with the Swedish 1-m Solar Telescope.
Methods: The equations that result from the application of the weak field approximation (WFA) to the radiative transfer equations were used to infer the line-of-sight (LOS) component of the magnetic field (BLOS). Two restrictive conditions were imposed on the Stokes I and V profiles at each pixel before they could be used in a Bayesian inversion to compute its BLOS.
Results: The LOS magnetic field component was inferred in six data sets totalling 448 spectral scans in the Ca II 8542 Å line and containing both active region and quiet Sun areas, with values of hundreds of Gauss being abundantly inferred. There seems to be no difference, from a statistical point of view, between the magnetic field strength of spicules in the quiet Sun or near an active region. On the other hand, the BLOS distributions present smaller values on the disc than off-limb, a fact that can be explained by the effect of superposition on the chromosphere of on-disc structures. We show that on-disc pixels in which the BLOS is determined are possibly associated with spicular structures because these pixels are co-spatial with the magnetic field concentrations at the network boundaries and the sign of their BLOS agrees with that of the underlying photosphere. We find that spicules in the vicinity of a sunspot have a magnetic field polarity (i.e. north or south) equal to that of the sunspot. This paper also contains an analysis of the effect of off-limb overlapping structures on the observed Stokes I and V parameters and the BLOS obtained from the WFA. It is found that this value is equal to or smaller than the largest LOS magnetic field components of the two structures. In addition, using random BLOS, Doppler velocities, and line intensities of these two structures leads in ≃50% of the cases to Stokes I and V parameters that are unsuitable to be used with the WFA.
Conclusions: Our results present a scarcity of LOS magnetic field components smaller than some 50 G, which must not be taken as evidence against the existence of these magnetic field strengths in spicules. This fact possibly arises as the consequence of signal superposition and noise in the data. We also suggest that the failure of previous works to infer the strong magnetic fields in spicules detected here is their coarser spatial and/or temporal resolution. Title: Multiwavelength Imaging and Spectral Analysis of Jet-like Phenomena in a Solar Active Region Using IRIS and AIA Authors: Dafydd Humphries, Llŷr; Verwichte, Erwin; Kuridze, David; Morgan, Huw Bibcode: 2020arXiv201004042D Altcode: High-resolution observations of dynamic phenomena give insight into properties and processes that govern the low solar atmosphere. We present the analysis of jet-like phenomena emanating from a penumbral foot-point in active region (AR) 12192 using imaging and spectral observations from the Interface Region Imaging Spectrograph (IRIS) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. These jets are associated with line-of-sight (LoS) Doppler speeds of $\pm$ 10-22 km s$^{-1}$ and bright fronts which seem to move across the Plane-of-Sky (PoS) at speeds of 23-130 km s$^{-1}$. Such speeds are considerably higher than the expected sound speed in the chromosphere. The jets have signatures which are visible both in the cool and hot channels of IRIS and AIA. Each jet lasts on average 15 minutes and occur 5-7 times over a period of 2 hours. Possible mechanisms to explain this phenomenon are suggested, the most likely of which involve p-mode or Alfv\' en wave shock trains impinging on the transition region (TR) and corona as a result of steepening photospheric wavefronts or gravity waves. Title: Multiwavelength Imaging and Spectral Analysis of Jet-like Phenomena in a Solar Active Region Using IRIS and AIA Authors: Humphries, Llŷr Dafydd; Verwichte, Erwin; Kuridze, David; Morgan, Huw Bibcode: 2020ApJ...898...17H Altcode: High-resolution observations of dynamic phenomena give insights into the properties and processes that govern the low solar atmosphere. We present an analysis of jet-like phenomena emanating from a penumbral footpoint in active region (AR) 12192 using imaging and spectral observations from the Interface Region Imaging Spectrograph (IRIS) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. These jets are associated with line-of-sight Doppler speeds of ±10-22 km s-1 and bright fronts that seem to move across the plane-of-sky at speeds of 23-130 km s-1. Such speeds are considerably higher than the expected sound speed in the chromosphere. The jets have signatures that are visible both in the cool and hot channels of IRIS and AIA. Each jet lasts on average 15 minutes and occurs 5-7 times over a period of 2 hr. Possible mechanisms to explain this phenomenon are suggested, the most likely of which involve p-mode or Alfvén wave shock trains impinging on the transition region and corona as a result of steepening photospheric wavefronts or gravity waves. Title: Magnetic field inference in the chromosphere and lower corona Authors: Kriginsky, M.; Oliver, R.; Freij, N.; Kuridze, D.; Asensio Ramos, A.; Antolin, P. Bibcode: 2020sea..confE.201K Altcode: The Weak Field Approximation (WFA) is used to infer the line-of-sight magnetic field of the solar chromosphere and lower corona. Using near limb spectropolarimetric observations in the Ca II 8542 Å line taken with the CRISP instrument at the Swedish 1-metre telescope in La Palma, the presence of an active region near/in the field of view allows for the presence of chromospheric spicules and coronal rain blobs to be detected. This work focuses mostly in the inference of magnetic fields of off-limb spicules, but a successful attempt to obtain Stokes V signal from the coronal rain blobs allowed for the inference of coronal magnetic fields. A careful treatment of the data pixels is undertaken in order to guarantee the correct application of the WFA, and the results show the presence of ubiquitous hundred-Gauss magnetic fields in the spicular material and in the coronal rain blobs. A Bayesian approach is used to infer the results. Title: Spectral Characteristics and Formation Height of Off-limb Flare Ribbons Authors: Kuridze, David; Mathioudakis, Mihalis; Heinzel, Petr; Koza, Július; Morgan, Huw; Oliver, Ramon; Kowalski, Adam F.; Allred, Joel C. Bibcode: 2020ApJ...896..120K Altcode: 2020arXiv200510924K Flare ribbons are bright manifestations of flare energy dissipation in the lower solar atmosphere. For the first time, we report on high-resolution imaging spectroscopy observations of flare ribbons situated off limb in the Hβ and Ca II 8542 Å lines and make a detailed comparison with radiative hydrodynamic simulations. Observations of the X8.2 class solar flare SOL 2017-09-10T16:06 UT obtained with the Swedish Solar Telescope reveal bright horizontal emission layers in Hβ line-wing images located near the footpoints of the flare loops. The apparent separation between the ribbon observed in the Hβ wing and the nominal photospheric limb is about 300-500 km. The Ca II 8542 Å line-wing images show much fainter ribbon emissions located right on the edge of the limb, without clear separation from the limb. RADYN models are used to investigate synthetic spectral line profiles for the flaring atmosphere, and good agreement is found with the observations. The simulations show that, toward the limb, where the line of sight is substantially oblique with respect to the vertical direction, the flaring atmosphere model reproduces the high contrast of the off-limb Hβ ribbons and their significant elevation above the photosphere. The ribbons in the Ca II 8542 Å line-wing images are located deeper in the lower solar atmosphere with a lower contrast. A comparison of the height deposition of electron beam energy and the intensity contribution function shows that the Hβ line-wing intensities can be a useful tracer of flare energy deposition in the lower solar atmosphere. Title: Signatures of Helium Continuum in Cool Flare Loops Observed by SDO/AIA Authors: Heinzel, Petr; Schwartz, Pavol; Lörinčík, Juraj; Koza, Július; Jejčič, Sonja; Kuridze, David Bibcode: 2020ApJ...896L..35H Altcode: 2020arXiv200600574H We present an analysis of off-limb cool flare loops observed by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) during the gradual phase of SOL2017-09-10T16:06 X8.2-class flare. In the extreme-ultraviolet (EUV) channels starting from the 335 Å one, cool loops appear as dark structures against the bright loop arcade. These dark structures were precisely coaligned (spatially and temporally) with loops observed by Swedish Solar Telescope (SST) in emission lines of hydrogen and ionized calcium. A recently published semi-empirical model of cool loops based on SST observations serves to predict the level of hydrogen and helium recombination continua. The continua were synthesized using an approximate non-LTE (I.e., departures from local thermodynamic equilibrium) approach and theoretical spectra were then transformed to AIA signals. Comparison with signals detected inside the dark loops shows that only in AIA 211 Å channel the computed level of recombination continua is consistent with observations for some models, while in all other channels that are more distant from the continua edges the synthetic continuum is far too low. In analogy with on-disk observations of flares we interpret the surplus emission as due to numerous EUV lines emitted from hot but faint loops in front of the cool ones. Finally we briefly comment on failure of the standard absorption model when used for analysis of the dark-loop brightness. Title: Spectral Diagnostics of Cool Flare Loops Observed by the SST. I. Inversion of the Ca II 8542 Å and Hβ Lines Authors: Koza, Július; Kuridze, David; Heinzel, Petr; Jejčič, Sonja; Morgan, Huw; Zapiór, Maciej Bibcode: 2019ApJ...885..154K Altcode: 2019arXiv190907356K Flare loops form an integral part of eruptive events, being detected in the range of temperatures from X-rays down to cool chromospheric-like plasmas. While hot loops are routinely observed by the Solar Dynamics Observatory’s Atmospheric Imaging Assembly, cool loops seen off-limb are rare. In this paper we employ unique observations of the SOL2017-09-10T16:06 X8.2-class flare which produced an extended arcade of loops. The Swedish 1 m Solar Telescope made a series of spectral images of the cool off-limb loops in the Ca II 8542 Å and the hydrogen Hβ lines. Our focus is on the loop apices. Non-local thermal equilibrium (non-LTE; i.e., departures from LTE) spectral inversion is achieved through the construction of extended grids of models covering a realistic range of plasma parameters. The Multilevel Accelerated Lambda Iterations code solves the non-LTE radiative-transfer problem in a 1D externally illuminated slab, approximating the studied loop segment. Inversion of the Ca II 8542 Å and Hβ lines yields two similar solutions, both indicating high electron densities around 2 × 1012 cm-3 and relatively large microturbulence around 25 km s-1. These are in reasonable agreement with other independent studies of the same or similar events. In particular, the high electron densities in the range 1012-1013 cm-3 are consistent with those derived from the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager white-light observations. The presence of such high densities in solar eruptive flares supports the loop interpretation of the optical continuum emission of stars which manifest superflares. Title: Multi-wavelength observations of the 2014 June 11 M3.9 flare: temporal and spatial characteristics Authors: Christian, Damian J.; Kuridze, David; Jess, David B.; Yousefi, Menoa; Mathioudakis, Mihalis Bibcode: 2019RAA....19..101C Altcode: 2018arXiv181107077C We present multi-wavelength observations of an M-class flare (M3.9) that occurred on 2014 June 11. Our observations were conducted with the Dunn Solar Telescope (DST), employing adaptive optics, the multi-camera system Rapid Oscillations in Solar Atmosphere (ROSA), the new Hydrogen-Alpha Rapid Dynamics camera (HARDcam) in various wavelengths, such as Ca II K, Mg I b2 (at 5172.7 Å), and Hα narrow band and G-band continuum filters. Images were re-constructed using the Kiepenheuer-Institut Speckle Interferometry Package (KISIP) code, to improve our image resolution. We observed intensity increases of ≈120%-150% in the Mg, Ca K and Hα narrow band filters during the flare. Intensity increases for the flare observed in the SDO EUV channels were several times larger, and the X-rays, as recorded by GOES, increased over a factor of 30 for the harder band. Only a modest delay was found between the onset of flare ribbons of a nearby sympathetic flare and the main flare ribbons observed in these narrow band filters. The peak flare emission occurred within a few seconds for the Ca K, Mg and Hα bands. Time-distance techniques indicate propagation velocities of ≈60 km s-1 for the main flare ribbon and as high as 300 km s-1 for smaller regions, which we attribute to filament eruptions. This result and delays and velocities observed with SDO (≈100 km s-1) for different coronal heights agree well with the simple model of energy propagation versus height, although a more detailed model for the flaring solar atmosphere is needed. Finally, we detected marginal quasi-periodic pulsations (QPPs) in the 40-60 s range for the Ca K, Mg and Hα bands, and such measurements are important for disentangling the detailed flare-physics. Title: Mapping the Magnetic Field of Flare Coronal Loops Authors: Kuridze, D.; Mathioudakis, M.; Morgan, H.; Oliver, R.; Kleint, L.; Zaqarashvili, T. V.; Reid, A.; Koza, J.; Löfdahl, M. G.; Hillberg, T.; Kukhianidze, V.; Hanslmeier, A. Bibcode: 2019ApJ...874..126K Altcode: 2019arXiv190207514K Here, we report on the unique observation of flaring coronal loops at the solar limb using high-resolution imaging spectropolarimetry from the Swedish 1 m Solar Telescope. The vantage position, orientation, and nature of the chromospheric material that filled the flare loops allowed us to determine their magnetic field with unprecedented accuracy using the weak-field approximation method. Our analysis reveals coronal magnetic field strengths as high as 350 G at heights up to 25 Mm above the solar limb. These measurements are substantially higher than a number of previous estimates and may have considerable implications for our current understanding of the extended solar atmosphere. Title: Association between Tornadoes and Instability of Hosting Prominences Authors: Mghebrishvili, Irakli; Zaqarashvili, Teimuraz; Kukhianidze, Vasil; Kuridze, David; Tsiklauri, David; Shergelashvili, Bidzina; Poedts, Stefaan Bibcode: 2018csc..confE..20M Altcode: We studied the dynamics of all prominence tornadoes detected by the Solar Dynamics Observatory/Atmospheric Imaging Assembly from 2011 January 01 to December 31. In total, 361 events were identified during the whole year, but only 166 tornadoes were traced until the end of their lifetime. Out of 166 tornadoes, 80 (48%) triggered CMEs in hosting prominences, 83 (50%) caused failed coronal mass ejections (CMEs) or strong internal motion in the prominences, and only 3 (2%) finished their lifetimes without any observed activity. Therefore, almost all prominence tornadoes lead to the destabilization of their hosting prominences and half of them trigger CMEs. Consequently, prominence tornadoes may be used as precursors for CMEs and hence for space weather predictions. Title: Association between Tornadoes and Instability of Hosting Prominences Authors: Mghebrishvili, Irakli; Zaqarashvili, Teimuraz V.; Kukhianidze, Vasil; Kuridze, David; Tsiklauri, David; Shergelashvili, Bidzina M.; Poedts, Stefaan Bibcode: 2018ApJ...861..112M Altcode: 2018arXiv180701345M We studied the dynamics of all prominence tornadoes detected by the Solar Dynamics Observatory/Atmospheric Imaging Assembly from 2011 January 01 to December 31. In total, 361 events were identified during the whole year, but only 166 tornadoes were traced until the end of their lifetime. Out of 166 tornadoes, 80 (48%) triggered CMEs in hosting prominences, 83 (50%) caused failed coronal mass ejections (CMEs) or strong internal motion in the prominences, and only 3 (2%) finished their lifetimes without any observed activity. Therefore, almost all prominence tornadoes lead to the destabilization of their hosting prominences and half of them trigger CMEs. Consequently, prominence tornadoes may be used as precursors for CMEs and hence for space weather predictions. Title: Spectropolarimetric Inversions of the Ca II 8542 Å Line in an M-class Solar Flare Authors: Kuridze, D.; Henriques, V. M. J.; Mathioudakis, M.; Rouppe van der Voort, L.; de la Cruz Rodríguez, J.; Carlsson, M. Bibcode: 2018ApJ...860...10K Altcode: 2018arXiv180500487K We study the M1.9-class solar flare SOL2015-09-27T10:40 UT using high-resolution full Stokes imaging spectropolarimetry of the Ca II 8542 Å line obtained with the CRISP imaging spectropolarimeter at the Swedish 1-m Solar Telescope. Spectropolarimetric inversions using the non-LTE code NICOLE are used to construct semiempirical models of the flaring atmosphere to investigate the structure and evolution of the flare temperature and magnetic field. A comparison of the temperature stratification in flaring and nonflaring areas reveals strong heating of the flare ribbon during the flare peak. The polarization signals of the ribbon in the chromosphere during the flare maximum become stronger when compared to its surroundings and to pre- and post-flare profiles. Furthermore, a comparison of the response functions to perturbations in the line-of-sight magnetic field and temperature in flaring and nonflaring atmospheres shows that during the flare, the Ca II 8542 Å line is more sensitive to the lower atmosphere where the magnetic field is expected to be stronger. The chromospheric magnetic field was also determined with the weak-field approximation, which led to results similar to those obtained with the NICOLE inversions. Title: Hα and Hβ emission in a C3.3 solar flare: comparison between observations and simulations Authors: Zuccarello, F.; Simoes, P. J. D. A.; Capparelli, V.; Fletcher, L.; Romano, P.; Mathioudakis, M.; Cauzzi, G.; Carlsson, M.; Kuridze, D.; Keys, P. Bibcode: 2017AGUFMSH41A2742Z Altcode: This work is based on the analysis of an extremely rare set of simultaneous observations of a C3.3 solar flare in the Hα and Hβ lines at high spatial and temporal resolution, which were acquired at the Dunn Solar Telescope. Images of the C3.3 flare (SOL2014-04-22T15:22) made at various wavelengths along the Hα line profile by the Interferometric Bidimensional Spectrometer (IBIS) and in the Hβ with the Rapid Oscillations in the Solar Atmosphere (ROSA) broadband imager are analyzed to obtain the intensity evolution. The analysis shows that Hα and Hβ intensity excesses in three identified flare footpoints are well correlated in time. In the stronger footpoints, the typical value of the the Hα/Hβ intensity ratio observed is ∼ 0.4 - 0.5, in broad agreement with values obtained from a RADYN non-LTE simulation driven by an electron beam with parameters constrained by observations. The weaker footpoint has a larger Hα/Hβ ratio, again consistent with a RADYN simulation but with a smaller energy flux. Title: Hα and Hβ Emission in a C3.3 Solar Flare: Comparison between Observations and Simulations Authors: Capparelli, Vincenzo; Zuccarello, Francesca; Romano, Paolo; Simões, Paulo J. A.; Fletcher, Lyndsay; Kuridze, David; Mathioudakis, Mihalis; Keys, Peter H.; Cauzzi, Gianna; Carlsson, Mats Bibcode: 2017ApJ...850...36C Altcode: 2017arXiv171004067C The hydrogen Balmer series is a basic radiative loss channel from the flaring solar chromosphere. We report here on the analysis of an extremely rare set of simultaneous observations of a solar flare in the {{H}}α and {{H}}β lines, at high spatial and temporal resolutions, that were acquired at the Dunn Solar Telescope. Images of the C3.3 flare (SOL2014-04-22T15:22) made at various wavelengths along the {{H}}α line profile by the Interferometric Bidimensional Spectrometer (IBIS) and in the {{H}}β with the Rapid Oscillations in the Solar Atmosphere (ROSA) broadband imager are analyzed to obtain the intensity evolution. The {{H}}α and {{H}}β intensity excesses in three identified flare footpoints are well-correlated in time. We examine the ratio of {{H}}α to {{H}}β flare excess, which was proposed by previous authors as a possible diagnostic of the level of electron-beam energy input. In the stronger footpoints, the typical value of the the {{H}}α /H β intensity ratio observed is ∼0.4-0.5, in broad agreement with values obtained from a RADYN non-LTE simulation driven by an electron beam with parameters constrained (as far as possible) by observation. The weaker footpoint has a larger {{H}}α /H β ratio, again consistent with a RADYN simulation, but with a smaller energy flux. The {{H}}α line profiles observed have a less prominent central reversal than is predicted by the RADYN results, but can be brought into agreement if the {{H}}α -emitting material has a filling factor of around 0.2-0.3. Title: Spectroscopic Inversions of the Ca II 8542 Å Line in a C-class Solar Flare Authors: Kuridze, D.; Henriques, V.; Mathioudakis, M.; Koza, J.; Zaqarashvili, T. V.; Rybák, J.; Hanslmeier, A.; Keenan, F. P. Bibcode: 2017ApJ...846....9K Altcode: 2017arXiv170800472K We study the C8.4-class solar flare SOL2016-05-14T11:34 UT using high-resolution spectral imaging in the Ca II 8542 Å line obtained with the CRISP imaging spectropolarimeter on the Swedish 1 m Solar Telescope. Spectroscopic inversions of the Ca II 8542 Å line using the non-LTE code NICOLE are used to investigate the evolution of the temperature and velocity structure in the flaring chromosphere. A comparison of the temperature stratification in flaring and non-flaring areas reveals strong footpoint heating during the flare peak in the lower atmosphere. The temperature of the flaring footpoints between {log} {τ }500 ≈ -2.5 {and} -3.5, where τ 500 is the continuum optical depth at 500 nm, is ∼ 5{--}6.5 {kK} close to the flare peak, reducing gradually to ∼ 5 {kK}. The temperature in the middle and upper chromosphere, between {log} {τ }500≈ -3.5 and -5.5, is estimated to be ∼6.5-20 kK, decreasing to preflare temperatures, ∼5-10 kK, after approximately 15 minutes. However, the temperature stratification of the non-flaring areas is unchanged. The inverted velocity fields show that the flaring chromosphere is dominated by weak downflowing condensations at the formation height of Ca II 8542 Å. Title: Observations and Simulations of the Na I D1 Line Profiles in an M-class Solar Flare Authors: Kuridze, D.; Mathioudakis, M.; Christian, D. J.; Kowalski, A. F.; Jess, D. B.; Grant, S. D. T.; Kawate, T.; Simões, P. J. A.; Allred, J. C.; Keenan, F. P. Bibcode: 2016ApJ...832..147K Altcode: 2016arXiv160908120K We study the temporal evolution of the Na I D1 line profiles in the M3.9 flare SOL2014-06-11T21:03 UT, using observations at high spectral resolution obtained with the Interferometric Bidimensional Spectrometer instrument on the Dunn Solar Telescope combined with radiative hydrodynamic simulations. Our results show a significant increase in the intensities of the line core and wings during the flare. The analysis of the line profiles from the flare ribbons reveals that the Na I D1 line has a central reversal with excess emission in the blue wing (blue asymmetry). We combine RADYN and RH simulations to synthesize Na I D1 line profiles of the flaring atmosphere and find good agreement with the observations. Heating with a beam of electrons modifies the radiation field in the flaring atmosphere and excites electrons from the ground state 3s 2S to the first excited state 3p 2P, which in turn modifies the relative population of the two states. The change in temperature and the population density of the energy states make the sodium line profile revert from absorption into emission. Furthermore, the rapid changes in temperature break the pressure balance between the different layers of the lower atmosphere, generating upflow/downflow patterns. Analysis of the simulated spectra reveals that the asymmetries of the Na I D1 flare profile are produced by the velocity gradients in the lower solar atmosphere. Title: Kelvin-Helmholtz Instability in Solar Chromospheric Jets: Theory and Observation Authors: Kuridze, D.; Zaqarashvili, T. V.; Henriques, V.; Mathioudakis, M.; Keenan, F. P.; Hanslmeier, A. Bibcode: 2016ApJ...830..133K Altcode: 2016arXiv160801497K Using data obtained by the high-resolution CRisp Imaging SpectroPolarimeter instrument on the Swedish 1 m Solar Telescope, we investigate the dynamics and stability of quiet-Sun chromospheric jets observed at the disk center. Small-scale features, such as rapid redshifted and blueshifted excursions, appearing as high-speed jets in the wings of the Hα line, are characterized by short lifetimes and rapid fading without any descending behavior. To study the theoretical aspects of their stability without considering their formation mechanism, we model chromospheric jets as twisted magnetic flux tubes moving along their axis, and use the ideal linear incompressible magnetohydrodynamic approximation to derive the governing dispersion equation. Analytical solutions of the dispersion equation indicate that this type of jet is unstable to Kelvin-Helmholtz instability (KHI), with a very short (few seconds) instability growth time at high upflow speeds. The generated vortices and unresolved turbulent flows associated with the KHI could be observed as a broadening of chromospheric spectral lines. Analysis of the Hα line profiles shows that the detected structures have enhanced line widths with respect to the background. We also investigate the stability of a larger-scale Hα jet that was ejected along the line of sight. Vortex-like features, rapidly developing around the jet’s boundary, are considered as evidence of the KHI. The analysis of the energy equation in the partially ionized plasma shows that ion-neutral collisions may lead to fast heating of the KH vortices over timescales comparable to the lifetime of chromospheric jets. Title: High-cadence observations of spicular-type events on the Sun Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.; Kuridze, D.; Henriques, V.; Woeger, F.; Ray, T. Bibcode: 2016A&A...589A...3S Altcode: 2016arXiv160108087S Context. Chromospheric observations taken at high-cadence and high-spatial resolution show a range of spicule-like features, including Type-I, Type-II (as well as rapid blue-shifted excursions (RBEs) and rapid red-shifted excursions (RREs) which are thought to be on-disk counterparts of Type-II spicules) and those which seem to appear within a few seconds, which if interpreted as flows would imply mass flow velocities in excess of 1000 km s-1.
Aims: This article seeks to quantify and study rapidly appearing spicular-type events. We also compare the multi-object multi-frame blind deconvolution (MOMFBD) and speckle reconstruction techniques to understand if these spicules are more favourably observed using a particular technique.
Methods: We use spectral imaging observations taken with the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m Solar Telescope. Data was sampled at multiple positions within the Hα line profile for both an on-disk and limb location.
Results: The data is host to numerous rapidly appearing features which are observed at different locations within the Hα line profile. The feature's durations vary between 10-20 s and lengths around 3500 km. Sometimes, a time delay in their appearance between the blue and red wings of 3-5 s is evident, whereas, sometimes they are near simultaneous. In some instances, features are observed to fade and then re-emerge at the same location several tens of seconds later.
Conclusions: We provide the first statistical analysis of these spicules and suggest that these observations can be interpreted as the line-of-sight (LOS) movement of highly dynamic spicules moving in and out of the narrow 60 mÅ transmission filter that is used to observe in different parts of the Hα line profile. The LOS velocity component of the observed fast chromospheric features, manifested as Doppler shifts, are responsible for their appearance in the red and blue wings of Hα line. Additional work involving data at other wavelengths is required to investigate the nature of their possible wave-like activity. Title: High Cadence Observations and Analysis of Spicular-type Events Using CRISP Onboard SST Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.; Kuridze, D. Bibcode: 2016ASPC..504..115S Altcode: We present spectroscopic and imaging observations of apparent ultra-fast spicule-like features observed with CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish 1-m Solar Telescope (SST). The data shows spicules with an apparent velocity above 500 km s-1, very short lifetimes of up to 20 s and length/height around 3500 km. The spicules are seen as dark absorption structures in the Hα wings ±516 mÅ, ±774 mÅ and ±1032 mÅ which suddenly appear and disappear from the FOV. These features show a time delay in their appearance in the blue and red wings by 3-5 s. We suggest that their appearance/disappearance is due to their Doppler motion in and out of the 60 mÅ filter. See Fig. 1 for the evolution of the event at two line positions. Title: Quiet-Sun Hα Transients and Corresponding Small-scale Transition Region and Coronal Heating Authors: Henriques, V. M. J.; Kuridze, D.; Mathioudakis, M.; Keenan, F. P. Bibcode: 2016ApJ...820..124H Altcode: 2016arXiv160204820H Rapid blue- and redshifted excursions (RBEs and RREs) are likely to be the on-disk counterparts of Type II spicules. Recently, heating signatures from RBEs/RREs have been detected in IRIS slit-jaw images dominated by transition region (TR) lines around network patches. Additionally, signatures of Type II spicules have been observed in Atmospheric Imaging Assembly (AIA) diagnostics. The full-disk, ever-present nature of the AIA diagnostics should provide us with sufficient statistics to directly determine how important RBEs and RREs are to the heating of the TR and corona. We find, with high statistical significance, that at least 11% of the low coronal brightenings detected in a quiet-Sun region in He II 304 Å can be attributed to either RBEs or RREs as observed in Hα, and a 6% match of Fe IX 171 Å detected events to RBEs or RREs with very similar statistics for both types of Hα features. We took a statistical approach that allows for noisy detections in the coronal channels and provides us with a lower, but statistical significant, bound. Further, we consider matches based on overlapping features in both time and space, and find strong visual indications of further correspondence between coronal events and co-evolving but non-overlapping, RBEs and RREs. Title: Hα Line Profile Asymmetries and the Chromospheric Flare Velocity Field Authors: Kuridze, D.; Mathioudakis, M.; Simões, P. J. A.; Rouppe van der Voort, L.; Carlsson, M.; Jafarzadeh, S.; Allred, J. C.; Kowalski, A. F.; Kennedy, M.; Fletcher, L.; Graham, D.; Keenan, F. P. Bibcode: 2015ApJ...813..125K Altcode: 2015arXiv151001877K The asymmetries observed in the line profiles of solar flares can provide important diagnostics of the properties and dynamics of the flaring atmosphere. In this paper the evolution of the Hα and Ca ii λ8542 lines are studied using high spatial, temporal, and spectral resolution ground-based observations of an M1.1 flare obtained with the Swedish 1 m Solar Telescope. The temporal evolution of the Hα line profiles from the flare kernel shows excess emission in the red wing (red asymmetry) before flare maximum and excess in the blue wing (blue asymmetry) after maximum. However, the Ca ii λ8542 line does not follow the same pattern, showing only a weak red asymmetry during the flare. RADYN simulations are used to synthesize spectral line profiles for the flaring atmosphere, and good agreement is found with the observations. We show that the red asymmetry observed in Hα is not necessarily associated with plasma downflows, and the blue asymmetry may not be related to plasma upflows. Indeed, we conclude that the steep velocity gradients in the flaring chromosphere modify the wavelength of the central reversal in the Hα line profile. The shift in the wavelength of maximum opacity to shorter and longer wavelengths generates the red and blue asymmetries, respectively. Title: The Dynamics of Rapid Redshifted and Blueshifted Excursions in the Solar Hα Line Authors: Kuridze, D.; Henriques, V.; Mathioudakis, M.; Erdélyi, R.; Zaqarashvili, T. V.; Shelyag, S.; Keys, P. H.; Keenan, F. P. Bibcode: 2015ApJ...802...26K Altcode: 2015arXiv150106205K We analyze high temporal and spatial resolution time-series of spectral scans of the Hα line obtained with the CRisp Imaging SpectroPolarimeter instrument mounted on the Swedish Solar Telescope. The data reveal highly dynamic, dark, short-lived structures known as Rapid Redshifted and Blueshifted Excursions (RREs, RBEs) that are on-disk absorption features observed in the red and blue wings of spectral lines formed in the chromosphere. We study the dynamics of RREs and RBEs by tracking their evolution in space and time, measuring the speed of the apparent motion, line of sight (LOS) Doppler velocity, and transverse velocity of individual structures. A statistical study of their measured properties shows that RREs and RBEs have similar occurrence rates, lifetimes, lengths, and widths. They also display non-periodic, nonlinear transverse motions perpendicular to their axes at speeds of 4-31 km s-1. Furthermore, both types of structures either appear as high speed jets and blobs that are directed outwardly from a magnetic bright point with speeds of 50-150 km s-1, or emerge within a few seconds. A study of the different velocity components suggests that the transverse motions along the LOS of the chromospheric flux tubes are responsible for the formation and appearance of these redshifted/blueshifted structures. The short lifetime and fast disappearance of the RREs/RBEs suggests that, similar to type II spicules, they are rapidly heated to transition region or even coronal temperatures. We speculate that the Kelvin-Helmholtz instability triggered by observed transverse motions of these structures may be a viable mechanism for their heating. Title: Magnetohydrodynamic oscillations in chromospheric fine structures Authors: Kuridze, David Bibcode: 2014PhDT.......537K Altcode: No abstract at ADS Title: Characteristics of Transverse Waves in Chromospheric Mottles Authors: Kuridze, D.; Verth, G.; Mathioudakis, M.; Erdélyi, R.; Jess, D. B.; Morton, R. J.; Christian, D. J.; Keenan, F. P. Bibcode: 2013ApJ...779...82K Altcode: 2013arXiv1310.3628K Using data obtained by the high temporal and spatial resolution Rapid Oscillations in the Solar Atmosphere instrument on the Dunn Solar Telescope, we investigate at an unprecedented level of detail transverse oscillations in chromospheric fine structures near the solar disk center. The oscillations are interpreted in terms of propagating and standing magnetohydrodynamic kink waves. Wave characteristics including the maximum transverse velocity amplitude and the phase speed are measured as a function of distance along the structure's length. Solar magnetoseismology is applied to these measured parameters to obtain diagnostic information on key plasma parameters (e.g., magnetic field, density, temperature, flow speed) of these localized waveguides. The magnetic field strength of the mottle along the ~2 Mm length is found to decrease by a factor of 12, while the local plasma density scale height is ~280 ± 80 km. Title: Failed filament eruption inside a coronal mass ejection in active region 11121 Authors: Kuridze, D.; Mathioudakis, M.; Kowalski, A. F.; Keys, P. H.; Jess, D. B.; Balasubramaniam, K. S.; Keenan, F. P. Bibcode: 2013A&A...552A..55K Altcode: 2013arXiv1302.5931K
Aims: We study the formation and evolution of a failed filament eruption observed in NOAA active region 11121 near the southeast limb on November 6, 2010.
Methods: We used a time series of SDO/AIA 304, 171, 131, 193, 335, and 94 Å images, SDO/HMI magnetograms, as well as ROSA and ISOON Hα images to study the erupting active region.
Results: We identify coronal loop arcades associated with a quadrupolar magnetic configuration, and show that the expansion and cancellation of the central loop arcade system over the filament is followed by the eruption of the filament. The erupting filament reveals a clear helical twist and develops the same sign of writhe in the form of inverse γ-shape.
Conclusions: The observations support the "magnetic breakout" process in which the eruption is triggered by quadrupolar reconnection in the corona. We propose that the formation mechanism of the inverse γ-shape flux rope is the magnetohydrodynamic helical kink instability. The eruption has failed because of the large-scale, closed, overlying magnetic loop arcade that encloses the active region.

Movies are available in electronic form at http://www.aanda.org Title: Observations of ubiquitous compressive waves in the Sun's chromosphere Authors: Morton, Richard J.; Verth, Gary; Jess, David B.; Kuridze, David; Ruderman, Michael S.; Mathioudakis, Mihalis; Erdélyi, Robertus Bibcode: 2012NatCo...3.1315M Altcode: 2012NatCo...3E1315M; 2013arXiv1306.4124M The details of the mechanism(s) responsible for the observed heating and dynamics of the solar atmosphere still remain a mystery. Magnetohydrodynamic waves are thought to have a vital role in this process. Although it has been shown that incompressible waves are ubiquitous in off-limb solar atmospheric observations, their energy cannot be readily dissipated. Here we provide, for the first time, on-disk observation and identification of concurrent magnetohydrodynamic wave modes, both compressible and incompressible, in the solar chromosphere. The observed ubiquity and estimated energy flux associated with the detected magnetohydrodynamic waves suggest the chromosphere is a vast reservoir of wave energy with the potential to meet chromospheric and coronal heating requirements. We are also able to propose an upper bound on the flux of the observed wave energy that is able to reach the corona based on observational constraints, which has important implications for the suggested mechanism(s) for quiescent coronal heating. Title: Transverse Oscillations in Chromospheric Mottles Authors: Kuridze, D.; Morton, R. J.; Erdélyi, R.; Dorrian, G. D.; Mathioudakis, M.; Jess, D. B.; Keenan, F. P. Bibcode: 2012ApJ...750...51K Altcode: 2012arXiv1202.5697K A number of recent investigations have revealed that transverse waves are ubiquitous in the solar chromosphere. The vast majority of these have been reported in limb spicules and active region fibrils. We investigate long-lived, quiet-Sun, on-disk features such as chromospheric mottles (jet-like features located at the boundaries of supergranular cells) and their transverse motions. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope. The data set is comprised of simultaneous imaging in the Hα core, Ca II K, and G band of an on-disk quiet-Sun region. Time-distance techniques are used to study the characteristics of the transverse oscillations. We detect over 40 transverse oscillations in both bright and dark mottles, with periods ranging from 70 to 280 s, with the most frequent occurrence at ~165 s. The velocity amplitudes and transverse displacements exhibit characteristics similar to limb spicules. Neighboring mottles oscillating in-phase are also observed. The transverse oscillations of individual mottles are interpreted in terms of magnetohydrodynamic kink waves. Their estimated periods and damping times are consistent with phase mixing and resonant mode conversion. Title: Small-scale Hα jets in the solar chromosphere Authors: Kuridze, D.; Mathioudakis, M.; Jess, D. B.; Shelyag, S.; Christian, D. J.; Keenan, F. P.; Balasubramaniam, K. S. Bibcode: 2011A&A...533A..76K Altcode: 2011arXiv1108.1043K
Aims: High temporal and spatial resolution observations from the Rapid Oscillations in the Solar Atmosphere (ROSA) multiwavelength imager on the Dunn Solar Telescope are used to study the velocities of small-scale Hα jets in an emerging solar active region.
Methods: The dataset comprises simultaneous imaging in the Hα core, Ca ii K, and G band, together with photospheric line-of-sight magnetograms. Time-distance techniques are employed to determine projected plane-of-sky velocities.
Results: The Hα images are highly dynamic in nature, with estimated jet velocities as high as 45 km s-1. These jets are one-directional, with their origin seemingly linked to underlying Ca ii K brightenings and G-band magnetic bright points.
Conclusions: It is suggested that the siphon flow model of cool coronal loops is suitable for interpreting our observations. The jets are associated with small-scale explosive events, and may provide a mass outflow from the photosphere to the corona. Title: Network Loop Oscillations with EIS/Hinode Authors: Srivastava, A. K.; Kuridze, D.; Zaqarashvili, T. V.; Dwivedi, B. N.; Rani, B. Bibcode: 2010ASSP...19..437S Altcode: 2009arXiv0903.0212S; 2010mcia.conf..437S We analyze a time sequence of He II 256.32 Å images obtained with EIS/Hinode, sampling a small magnetic loop in magnetic network. Wavelet analysis indicates 11-min periodicity close to the loop apex. We interpret this oscillation as forcing through upward leakage by the fundamental acoustic eigenmode of the underlying field-free cavity. The observed loop length corresponds to the value predicted from this mechanism. Title: Acoustic oscillations in the field-free, gravitationally stratified cavities under solar bipolar magnetic canopies Authors: Kuridze, D.; Zaqarashvili, T. V.; Shergelashvili, B. M.; Poedts, S. Bibcode: 2009A&A...505..763K Altcode: 2009arXiv0905.2302K Aims: The main goal here is to study the dynamics of the gravitationally stratified, field-free cavities in the solar atmosphere, located under small-scale, cylindrical magnetic canopies, in response to explosive events in the lower-lying regions (due to granulation, small-scale magnetic reconnection, etc.).
Methods: We derive the two-dimensional Klein-Gordon equation for isothermal density perturbations in cylindrical coordinates. The equation is first solved by a standard normal mode analysis to obtain the free oscillation spectrum of the cavity. Then, the equation is solved in the case of impulsive forcing associated to a pressure pulse specified in the lower lying regions.
Results: The normal mode analysis shows that the entire cylindrical cavity of granular dimensions tends to oscillate with frequencies of 5-8 mHz and also with the atmospheric cut-off frequency. Furthermore, the passage of a pressure pulse, excited in the convection zone, sets up a wake in the cavity oscillating with the same cut-off frequency. The wake oscillations can resonate with the free oscillation modes, which leads to an enhanced observed oscillation power.
Conclusions: The resonant oscillations of these cavities explain the observed power halos near magnetic network cores and active regions. Title: Acoustic oscillations in a field-free cavity under solar small-scale bipolar magnetic canopy Authors: Kuridze, D.; Zaqarashvili, T. V.; Shergelashvili, B. M.; Poedts, S. Bibcode: 2008AnGeo..26.2983K Altcode: 2008arXiv0801.2877K Observations show the increase of high-frequency wave power near magnetic network cores and active regions in the solar lower atmosphere. This phenomenon can be explained by the interaction of acoustic waves with a magnetic field. We consider small-scale, bipolar, magnetic field canopy structure near the network cores and active regions overlying field-free cylindrical cavities of the photosphere. Solving the plasma equations we get the analytical dispersion relation of acoustic oscillations in the field-free cavity area. We found that the m=1 mode, where m is azimuthal wave number, cannot be trapped under the canopy due to energy leakage upwards. However, higher (m≥2) harmonics can be easily trapped leading to the observed acoustic power halos under the canopy. Title: Intensity oscillations observed with Hinode near the south pole of the Sun: leakage of low frequency magneto-acoustic waves into the solar corona Authors: Srivastava, A. K.; Kuridze, D.; Zaqarashvili, T. V.; Dwivedi, B. N. Bibcode: 2008A&A...481L..95S Altcode: 2008arXiv0802.0571S Aims: We study intensity oscillations in the solar chromosphere and corona, above a quiet-Sun magnetic network.
Methods: We analyse the time series of He II 256.32 Å, Fe XI 188.23 Å and Fe XII 195.12 Å spectral lines, observed close to the south pole, by the EUV Imaging Spectrometer (EIS), onboard Hinode. We use a standard wavelet tool, to produce power spectra of intensity oscillations above the magnetic network.
Results: For all spectral lines, we detect intensity oscillations of period of approximately seven minutes; and for the He II 256.32 Å line only, we detect an intensity oscillation of period of thirteen minutes, with a probability of approximately 96-98%, which provides the most likely signature of magneto-acoustic wave propagation above the network.
Conclusions: We propose that field-free cavity areas under bipolar magnetic canopies, in the vicinity of a magnetic network, are likely to serve as resonators for the magneto-acoustic waves. The cavities with photospheric sound-speed, and granular dimensions, can produce waves with observed periods. These waves may propagate upwards in the transition region/corona and cause observed intensity oscillations. Title: Resonant energy conversion of 3-min intensity oscillations into Alfvén waves in the solar atmosphere Authors: Kuridze, D.; Zaqarashvili, T. V. Bibcode: 2008JASTP..70..351K Altcode: 2007astro.ph..3482K Nonlinear coupling between 3-min oscillations and Alfvén waves in the solar lower atmosphere is studied. Three-minute oscillations are considered as acoustic waves trapped in a chromospheric cavity and oscillating along transversally inhomogeneous vertical magnetic field. It is shown that under the action of the oscillations the temporal dynamics of Alfvén waves is governed by Mathieu equation. Consequently, the harmonics of Alfvén waves with twice period and wavelength of 3-min oscillations grow exponentially in time near the layer where the sound and Alfvén speeds equal i.e. cs[approximate]vA. Thus the 3-min oscillations are resonantly absorbed by pure Alfvén waves near this resonant layer. The resonant Alfvén waves may penetrate into the solar corona taking energy from the chromosphere. Therefore the layer cs[approximate]vA may play a role of energy channel for otherwise trapped acoustic oscillations. Title: Resonant Conversion of Standing Acoustic Oscillations Into ALFVÉN Waves in the β~1 Region of the Solar Atmosphere Authors: Kuridze, D.; Zaqarashvili, T. V.; Roberts, B. Bibcode: 2005ESASP.600E..89K Altcode: 2005dysu.confE..89K; 2005ESPM...11...89K; 2005astro.ph.10437K We show that 5-minute acoustic oscillations may resonantly convert into Alfv{é}n waves in the $\beta{\sim}1$ region of the solar atmosphere. Considering the 5-minute oscillations as pumping standing acoustic waves oscillating along unperturbed vertical magnetic field, we find on solving the ideal MHD equations that amplitudes of Alfv{é}n waves with twice the period and wavelength of acoustic waves exponentially grow in time when the sound and Alfv{é}n speeds are equal, i.e. $c_s \approx v_A$. The region of the solar atmosphere where this equality takes place we call a {\it swing layer}. The amplified Alfv{é}n waves may easily pass through the chromosphere and transition region carrying the energy of p-modes into the corona.