Observations of Extremely Strong Magnetic Fields in Active Region NOAA 12673 Using GST Magnetic Field Measurement |
|
Vasyl Yurchyshyn Submitted: 2022-04-14 08:12
We present a detailed study of very strong magnetic fields in the NOAA Active Region (AR) 12673, which was the
most flare productive AR in solar cycle 24. It produced four X-class flares including the X9.3 flare on 2017
September 6 and the X8.2 limb event on September 10. Our analysis is based on direct measurements of full
Zeeman splitting of the Fe I 1564.85 nm line using all Stokes I, Q, U, and V profiles. This approach allowed us to
obtain reliable estimates of the magnitude of magnetic fields independent of the filling factor and atmosphere
models. Thus, the strongest fields up to 5.5 kG were found in a light bridge (LB) of a spot, while in the dark umbra
magnetic fields did not exceed 4 kG. In the case of the LB, the magnitude of the magnetic field is not related to the
underlying continuum intensity, while in the case of umbral fields we observed a well-known anticorrelation between the continuum intensity and the field magnitude. In this study, the LB was cospatial with a polarity inversion line of a delta-sunspot, and we speculate that the 5.5 kG strong horizontal fields may be associated with a compact twisted flux rope at or near the photosphere. A comparison of the depth of the Zeeman π and \sigma components showed that in the LB magnetic fields are, on average, more horizontal than those in the dark umbra.
Authors: Vsevolod Lozitsky, Vasyl Yurchyshyn, Kwangsu Ahn, and Haimin Wang
Projects: BBSO/NST
|
Publication Status: Published in ApJ
Last Modified: 2022-04-15 08:28
|
 
 
|
|
Magnetic field re-configuration associated with a slow rise eruptive X1.2 flare in NOAA active region 11944 |
|
Vasyl Yurchyshyn Submitted: 2022-02-18 21:12
Using multi-wavelength observations, we analysed magnetic field variations associated with a gradual X1.2 flare that erupted on January 7, 2014 in active region (AR) NOAA 11944 located near the disk center. A fast coronal mass ejection (CME) was observed following the flare, which was noticeably deflected in the south-west direction. A chromospheric filament was observed at the eruption site prior to and after the flare. We used SDO/HMI data to perform non-linear force-free field (NLFFF) extrapolation of coronal magnetic fields above the AR and to study the evolution of AR magnetic fields prior to the eruption. The extrapolated (model) data allowed us to detect signatures of several magnetic flux ropes (MFRs) present at the eruption site several hours before the event. The eruption site was located under slanted sunspot fields with a varying decay index of 1.0-1.5. That might have caused the erupting fields to slide along this slanted magnetic boundary rather than vertically erupt, thus explaining the slow rise of the flare as well as the observed direction of the resulting CME. We employed sign-singularity tools to quantify the evolutionary changes in the model twist and observed current helicity data, and found rapid and coordinated variations of current systems in both data sets prior to the event as well as their rapid exhaustion after the event onset.
Authors: Vasyl Yurchyshyn, Xu Yang, Gelu Nita, Gregory Fleishman, Valentina Abramenko, Satoshi Inoue, Eun-Kyung Lim, Wenda Cao
Projects: None,SDO-AIA,SDO-HMI
|
Publication Status: Frontiers in Astronomy and Space Sciences, Accepted
Last Modified: 2022-02-20 00:52
|
 
 
|
|
Rapid Evolution of Type II Spicules Observed in Goode Solar Telescope On-Disk Hα Images |
|
Vasyl Yurchyshyn Submitted: 2020-02-24 09:37
We analyze ground-based chromospheric data acquired at a high temporal cadence of 2s in wings of the Hα spectral line using Goode Solar Telescope (GST) operating at the Big Bear Solar Observatory. We inspected a 30 minute long Ha-0.08nm data set to find that rapid blue-shifted Hα excursions (RBEs), which are a cool component of type II spicules, experience very rapid morphological changes on the time scales of the order of 1 second. Unlike typical reconnection jets, RBEs very frequently appear in situ without any clear evidence of Hα material being injected from below. Their evolution includes inverted "Y", "V", "N", and parallel splitting (doubling) patterns as well as sudden formation of a diffuse region followed by branching. We also find that the same feature may undergo several splitting episodes within about 1 min time interval.
Authors: V. Yurchyshyn, W. Cao, V. Abramenko, X. Yang, K.-S. Cho
Projects: BBSO/NST
|
Publication Status: ApJ Letters, accepted
Last Modified: 2020-02-24 14:13
|
 
 
|
|
Magnetic Field Dynamics and Varying Plasma Emission in Large-scale Coronal Loops |
|
Vasyl Yurchyshyn Submitted: 2019-03-28 11:53
In this study we report detailed observations of magnetic environment at four footpoints of two warm coronal loops observed on 5 May 2016 in NOAA AR 12542 (Loop I) and 17 Dec 2015 in NOAA AR 12470 (Loop II). These loops were connecting a plage region with sunspot periphery (Loop I) and a sunspot umbra (Loop II). We used Solar Dynamics Observatory (SDO) and Goode Solar Telescope (GST) data to describe the phenomenon and understand its causes. The study indicates loop brightening episodes were associated with magnetic flux emergence and cancellation processes observed in SDO's Helioseismic and Magnetic Imager (HMI) and GST's Near InfraRed Imaging Spectrapolarimeter (NIRIS) data. The observed activity was driven by magnetic reconnection between small-scale emerging dipoles and large-scale pre-existing fields, suggesting that the reconnection occurred in the lower chromosphere at the edge of an extended plage region, where the loops were rooted. We suggest that plasma, evaporated during these reconnection events, gradually filled the loops and as it cooled the visible density front propagated from one footpoint of the loop to another at a rate of 90-110 km s-1. This study also indicates that at least some of the bright loops seen in SDO Atmospheric Imaging Assembly images rooted in sunspot umbra may be heated due to magnetic activity taking place at the remote (non-sunspot) footpoint.
Authors: S. Şahin, V. Yurchyshyn , P. Kumar, A. Kilcik, K. Ahn, and X. Yang
Projects: BBSO/NST,SDO-HMI
|
Publication Status: The Astrophysical Journal, 873:75 (11pp), 2019 March 1
Last Modified: 2019-03-29 18:13
|
 
 
|
|
High Resolution Observations of a White Light Flare with NST |
|
Vasyl Yurchyshyn Submitted: 2017-03-21 19:58
Using high resolution data from the New Solar Telescope (NST) we studied fine spatial and temporal details of an M1.3 white light (WL) flare, which was one of three homologous solar flares (C6.8, M1.3, and M2.3) observed in close proximity to the west solar limb on 29 October 2014 in NOAA active region 12192. We report that the TiO WL flare consist of compact and intense cores surrounded by less intense spatial halos. The strong and compact WL cores were measured to be approx. 0.2Mm across with the area of about 1014 sq.cm. Several TiO features were not co-spatial with Hα flare ribbons and displaced toward the disk center by about 500km, which suggests that the TiO and Hα radiation probably did not originate in the same chromospheric volume. The observed TiO intensity enhancements are not normally distributed and are structured by the magnetic field of the penumbra.
Authors: Yurchyshyn, V., Kumar, P., Abramenko, V., Xu, Y., Goode, P., Cho, K.S., Lim, E.K
Projects: BBSO/NST
|
Publication Status: Published
Last Modified: 2017-03-22 05:26
|
 
 
|
|
Multiwavelength Observations of a Slow Raise, Multi-Step X1.6 Flare and the Associated Eruption |
|
Vasyl Yurchyshyn Submitted: 2015-09-21 11:30
Using multi-wavelength observations we studied a slow rise, multi-step X1.6 flare that began on November 7, 2014 as a localized eruption of core fields inside a δ-sunspot and later engulfed the entire active region. This flare event was associated with formation of two systems of post eruption arcades and several J-shaped flare ribbons showing extremely fine details, irreversible changes in the photospheric magnetic fields, and it was accompanied by a fast and wide coronal mass ejection. Data from the Solar Dynamics Observatory, IRIS spacecraft along with the ground based data from the New Solar Telescope (NST) present evidence that i) the flare and the eruption were directly triggered by a flux emergence that occurred inside a δ-sunspot at the boundary between two umbrae; ii) this event represented an example of the formation of an unstable flux rope observed only in hot AIA channels (131 and 94 Å) and LASCO C2 coronagraph images; iii) the global post eruption arcade spanned the entire AR and was due to global scale reconnection occurring at heights of about one solar radii, indicating on the global spatial and temporal scale of the eruption.
Authors: Yurchyshyn, V., Kumar, P., Cho, K.S., Lim, E.K., & Abramenko, V.
Projects: IRIS,SDO-AIA,SDO-HMI
|
Publication Status: ApJ., accepted
Last Modified: 2015-09-23 13:32
|
 
 
|
|
Dynamics of Chromospheric Upflows and Underlying Magnetic Fields |
|
Vasyl Yurchyshyn Submitted: 2013-03-22 16:08
We used Ha-0.1 nm and magnetic field (at 1.56mk) data obtained with the New Solar Telescope to study the origin of the disk counterparts to type II spicules, so-called rapid blueshifted excursions (RBEs). The high time cadence of our chromospheric (10 s) and magnetic field (45 s) data allowed us to generate x-t plots using slits parallel to the spines of the RBEs. These plots, along with potential field extrapolation, led us to suggest that the occurrence of RBEs is generally correlated with the appearance of new, mixed or unipolar fields in close proximity to network fields. RBEs show a tendency to occur at the interface between large-scale fields and small-scale dynamic magnetic loops and thus are likely to be associated with existence of a magnetic canopy. Detection of kinked and/or inverse ''Y'' shaped RBEs further confirm this conclusion.
Authors: Yurchyshyn, Vasyl; Abramenko, Valentyna; Goode, Phil
Projects: Other
|
Publication Status: 2013, ApJ, 767, 17
Last Modified: 2013-03-23 19:34
|
 
 
|
|
Chromospheric signatures of small-scale flux emergence as observed with NST and Hinode instruments |
|
Vasyl Yurchyshyn Submitted: 2010-12-10 10:19
With the ever increasing influx of high resolution images of the solar surface obtained at a multitude of wavelengths, various processes occurring at small spatial scales have become a greater focus of our attention. Complex small-scale magnetic fields have been reported that appear to have enough stored to heat the chromosphere. While significant progress has been made in understanding small-scale phenomena, many specifics remain elusive. We present here a detailed study of a single event of cancellation and associated chromospheric activity. Based on New Solar Telescope Ha data and Hinode photospheric line-of-sight magnetograms and Ca II H images we report the following. 1) Careful consideration of the magnetic environment at the cancellation site sharpened our understanding of the details of magnetic cancellation.
We argue that the apparent collision and disappearance of two opposite polarity elements may not always indicate their mutual cancellation. 2) Our analysis indicates that even very small dipoles (elements separated by about 000.5 or less) may reach the chromosphere and trigger via
non-negligible chromospheric activity. 3) Bright points seen in off-band Ha images are very well-correlated with the Ca II H bright points, which in turn are co-spatial with G-band bright points. We further speculate that, in general, Ha bright points are expected be co-spatial with
photospheric BPs, however, a direct comparison is needed to refine their relationship.
Authors: V. B. Yurchyshyn, P.R. Goode, V. I. Abramenko, J. Chae, W. Cao, A. Andic, K. Ahn
Projects: Hinode/SOT
|
Publication Status: Astrophysical Journal, Volume 722, Issue 2, pp. 1970-1976 (2010)
Last Modified: 2010-12-10 10:34
|
 
 
|
|
Orientations of LASCO Halo CMEs and Their Connection to the Flux Rope Structure of Interplanetary CMEs |
|
Vasyl Yurchyshyn Submitted: 2007-01-25 15:46
Coronal mass ejections (CMEs) observed near the Sun via LASCO coronographic imaging are the most important solar drivers of geomagnetic storms. ICMEs, their interplanetary, near-Earth counterparts, can be detected in-situ, for example, by the Wind and ACE spacecraft. An ICME usually exhibits a complex structure that very often includes a magnetic cloud (MC). They can be commonly modelled as magnetic flux ropes and there is observational evidence to expect that the orientation of a halo CME elongation corresponds to the orientation of the flux rope. In this study, we compare orientations of elongated CME halos and the corresponding MCs, measured by Wind and ACE spacecraft. We characterize the MC structures by using the Grad-Shafranov reconstruction technique and three MC fitting methods to obtain their axis directions. The CME tilt angles and MC fitted axis angles were compared without taking into account handedness of the underlying flux rope field and the polarity of its axial field. We report that for about 64% of CME-MC events, we found a good correspondence between the orientation angles implying that for the majority of interplanetary ejecta their orientations do not change significantly (less than 45 deg rotation) while travelling from the Sun to the near Earth environment.
Authors: V. Yurchyshyn, Q.Hu, R.P. Lepping, B.J. Lynch & J. Krall
Projects: SoHO-LASCO
|
Publication Status: Adv. Space Res., http://dx.doi.org/10.1016/j.asr.2007.01.059
Last Modified: 2007-02-12 10:47
|
 
 
|
|
The May 13, 2005 Eruption: Observations, Data Analysis and Interpretation |
|
Vasyl Yurchyshyn Submitted: 2006-10-04 13:11
In this study we present detailed description and analysis of the May 13, 2005 eruption, the corresponding coronal mass ejection (CME) and intense geomagnetic storm observed near the Earth on May 15, 2005. This isolated two-ribbon M8.0 flare and the very fast CME occurred in a relatively simple magnetic configuration during a quiet period of solar activity, which enabled us to reliably associate the solar surface event with its counterpart observed in the Earth magnetosphere. In our study we utilized i) various tools to analyze a multi-wavelength data set that includes ground (BBSO vector magnetograms, Hα ) and space (SOHO, TRACE, RHESSI and ACE) based data; ii) linear force free modeling to reconstruct the coronal field above the active region and iii) erupting flux rope (EFR) model to simulate a near Sun halo CME and a near Earth interplanetary CME (ICME). Our findings indicate that persisting converging and shearing motions near the main neutral line could lead to the formation of twisted core fields and eventually their eruption via reconnection. In the discussed scenario the in-situ formed erupting loop can be observed as a magnetic cloud (MC) when it reaches the Earth. The EFR model was able to produce both a model halo CME and ICME providing a good global match to the overall timing and components of the magnetic field in the observed MC. The orientation of the model ICME and the sense of the twist, inferred from the EFR model, agree well with the orientation and the magnetic helicity found in the source active region.
Authors: V. Yurchyshyn, C. Liu, V. Abramenko, J. Krall
Projects: RHESSI
|
Publication Status: Solar Physics, accepted
Last Modified: 2006-10-04 13:28
|
 
 
|
|
|
Key
|
 | Go to main E-Print page. |
 | Download Preprint. |
 | Submitters Homepage. |
 | Edit Entry. |
 | Delete abstract. |
|
|
|