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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
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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
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Dynamics in Sunspot Umbra as Seen in New Solar Telescope and Interface Region Imaging Spectrograph Data  

Vasyl Yurchyshyn   Submitted: 2014-11-05 17:13

We analyse sunspot oscillations using Interface Region Imaging Spectrograph (IRIS) slit-jaw and spectral data and narrow-band chromospheric images from the New Solar Telescope (NST) for the main sunspot in NOAA AR 11836. We report that the difference between the shock arrival times as measured the Mg II k 2796.35A and Si IV 1393.76A line formation levels changes during the observed period and peak-to-peak delays may range from 40s to zero. The intensity of chromospheric shocks also displays a long term (about 20 min) variations. NST's high spatial resolution Hα data allowed us to conclude that in this sunspot umbral flashes (UFs) appeared in the form of narrow bright lanes stretched along the light bridges and around clusters of umbral bright points. Time series also suggested that UFs preferred to appear on the sunspot-center side of light bridges, which may indicate the existence of a compact sub-photospheric driver of sunspot oscillations. The sunspot's umbra as seen in the IRIS chromospheric and transition region data appears bright above the locations of light bridges and the areas where the dark umbra is dotted with clusters of umbral dots. Co-spatial and co-temporal data from the Atmospheric Imaging Assembly on board Solar Dynamics Observatory showed that the same locations were associated with bright footpoints of coronal loops suggesting that the light bridges may play an important role in heating the coronal sunspot loops. Finally, the power spectra analysis showed that the intensity of chromospheric and transition region oscillations significantly vary across the umbra and with height, suggesting that umbral non-uniformities and the structure of sunspot magnetic fields may play a role in wave propagation and heating of umbral loops.

Authors: Vasyl Yurchyshyn, Valentyna Abramenko, Ali Kilcik
Projects: IRIS,Other

Publication Status: Accepted by ApJ
Last Modified: 2014-11-06 14:34
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High Resolution Observations of Chromospheric Jets in Sunspot Umbra  

Vasyl Yurchyshyn   Submitted: 2014-04-29 11:35

Recent observations of sunspot's umbra suggested that it may be finely structured at a sub-arcsecond scale representing a mix of hot and cool plasma elements. In this study we report the first detailed observations of the umbral spikes, which are cool jet-like structures seen in the chromosphere of an umbra. The spikes are cone-shaped features with a typical height of 0.5-1.0 Mm and a width of about 0.1 Mm. Their life time ranges from 2 to 3 min and they tend to re-appear at the same location. The spikes are not associated with photospheric umbral dots and they rather tend to occur above darkest parts of the umbra, where magnetic fields are strongest. The spikes exhibit up and down oscillatory motions and their spectral evolution suggests that they might be driven by upward propagating shocks generated by photospheric oscillations. It is worth noting that triggering of the running penumbral waves seems to occur during the interval when the spikes reach their maximum height.

Authors: Yurchyshyn, V., Abramenko, V., Kosovichev, A., and Goode, P.
Projects: Other

Publication Status: Accepted by ApJ
Last Modified: 2014-04-29 12:03
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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
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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
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RELATIONSHIP BETWEEN EARTH-DIRECTED SOLAR ERUPTIONS AND MAGNETIC CLOUDS AT 1AU: A BRIEF REVIEW  

Vasyl Yurchyshyn   Submitted: 2009-05-27 13:10

We review relationships between coronal mass ejections (CMEs), EIT post eruption arcades, and the coronal neutral line associated with global magnetic field and magnetic clouds near the Earth. Our previous findings indicate that the orientation of a halo CME elongation may correspond to the orientation of the underlying flux rope. Here we revisit these preliminary reports by comparing orientation angles of elongated LASCO CMEs, both full and partial halos, to the post eruption arcades. Based on 100 analysed events, it was found that the overwhelming majority of halo CMEs are elongated in the direction of the axial field of the post eruption arcades. Moreover, this conclusion also holds for partial halo CMEs as well as for events that originate further from the disk center. This suggests that the projection effect does not drastically change the appearance of full and partial halos and their images still bear reliable information about the underlying magnetic fields. We also compared orientations of the erupted fields near the Sun and in the interplanetary space and found that the local tilt of the coronal neutral line at 2.5 solar radii is well correlated with the magnetic cloud axis measured near the Earth. We suggest that the heliospheric magnetic fields significantly affect the propagating ejecta. Sometimes, the ejecta may even rotate so that its axis locally aligns itself with the heliospheric current sheet.

Authors: Vasyl Yurchyshyn and Durgesh Tripathi
Projects: SoHO-EIT

Publication Status: Advances in Geosciences, accepted
Last Modified: 2009-05-28 07:58
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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
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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
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STATISTICAL DISTRIBUTIONS OF SPEEDS OF CORONAL MASS EJECTIONS  

Vasyl Yurchyshyn   Submitted: 2005-04-22 19:40

We studied the distribution of plane of sky speeds determined for 4315 coronal mass ejections (CMEs) detected by Large Angle and Spectrometric Coronagraph Experiment on board Solar and Heliospheric Observatory (SOHO/LASCO). We found that the speed distributions for accelerating and decelerating events are nearly identical and to a good approximation they can be fitted with a single log-normal distribution. This finding implies that, statistically, there is no physical distinction between the accelerating and the decelerating events. The log-normal distribution of the CME speeds suggests that the same driving mechanism of a non-linear nature is acting in both slow and fast dynamical types of CMEs.

Authors: V. Yurchyshyn, S. Yashiro, V. Abramenko, H. Wang, N. Gopalswamy
Projects: None

Publication Status: 2005, Astrophys. J., 619, 599-603
Last Modified: 2005-04-22 19:40
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Structure of magnetic fields in NOAA active regions 0486 and 0501 and in the associated interplanetary ejecta  

Vasyl Yurchyshyn   Submitted: 2005-04-22 19:31

Spectacular burst of solar activity in October - November 2003, when large solar spots and intense solar flares dominated the solar surface for many consecutive days, caused intense geomagnetic storms. In this paper we analyze solar and interplanetary magnetic fields associated with the storms in October - November 2003. We used space and ground based data in order to compare the orientations of the magnetic fields on the solar surface and at 1AU as well as to estimate parameters of geomagnetic storms during this violent period of geomagnetic activity. Our study further supports earlier reports on the correlation between the CME speed and the strength of the magnetic field in an interplanetary ejecta. A good correspondence was also found between directions of the helical magnetic fields in interplanetary ejecta and in the source active regions. These findings are quite significant in terms of their potential to predict the severity of geomagnetic activity 1 - 2 days in advance, immediately after an earth-directed solar eruption.

Authors: Vasyl Yurchyshyn, Qiang Hu and Valentyna Abramenko
Projects: Soho-EIT

Publication Status: Space Weather J., accepted
Last Modified: 2005-04-22 19:31
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Magnetic Field, Hα and RHESSI Observations of the July 23, 2002 Gamma-ray Flare  

Vasyl Yurchyshyn   Submitted: 2004-01-07 13:17

In this paper we examine two aspects July 23 2002 gamma-ray flare by using multi-wavelength observations of this well-observed flare. First, the data suggests that the interaction of the erupted field with an overlaying large-scale coronal field can explain the offset between the gamma-ray and the hard X-ray sources observed in this event. Second, we pay attention to rapid and permanent changes of the photospheric magnetic field associated with the flare. MDI and BBSO magnetograms showed that the following magnetic flux had rapidly decreased by 1 imes1020Mx immediately after the flare, while the leading polarity was gradually increasing for several hours after the flare. Our study also suggests that the changes were most probably associated with the emergence of new flux and the re-orientation of the magnetic field lines. We interpret the magnetograph and spectral data for this event in terms of the tether-cutting model.

Authors: Vasyl Yurchyshyn, Haimin Wang, Valentyna Abramenko, Thomas J. Spirock and Säm Krucker
Projects: None

Publication Status: ApJ (accepted)
Last Modified: 2004-01-07 13:17
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Correlation Between Speeds of CMEs and the Intensity of Geomagnetic Storms  

Vasyl Yurchyshyn   Submitted: 2003-04-02 16:10

We studied the relationship between the projection speed of CMEs, evaluated from SOHO/LASCO images, and the hourly averaged magnitude of the B_z component of the magnetic field in an interplanetary ejecta, as measured by the ACE magnetometer in the GSM coordinate system. For CMEs, that originate at the central part of the solar disk, we found that the intensity of B_z is a function of the speed of the CME. We also present data which support earlier conclusions about the correlation of B_z and the Dst index. A possible application of the results to space weather forecasting is discussed.

Authors: Vasyl Yurchyshyn, Haimin Wang, Valentyna Abramenko
Projects: Soho-LASCO

Publication Status: Space Weather (accepted)
Last Modified: 2004-10-13 09:41
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Evidence of a Flux-Rope Model for Corona Mass Ejections Based on Observations of the Limb Prominence Eruption on 2002 January 4  

Vasyl Yurchyshyn   Submitted: 2002-10-17 13:30

We report on a prominence eruption as seen in Kanzelhöhe Solar Observatory Ha images, Solar and Heliospheric Observatory (SOHO) EUV Imaging Telescope (EIT) 195 Å images, and coronal SOHO Large Angle Spectrometric Coronograph C2 images. Our data favor the flux-rope model for coronal mass ejections (CMEs), which suggests that a flux rope is formed long before the eruption. Our conclusion is based on a three-part structure of the pre-erupted configuration of the magnetic field and on the fact that the first Ha, SOHO EIT 195 Å brightenings occurred some 15 minutes after the filament began to ascend. The data also clearly demonstrate two rarely observed components of the standard flare model: (1) magnetic loops that overlay the pre-erupted filament and (2) magnetic field lines stretched vertically by the ascending filament. These field lines are compressed horizontally and move toward each other where they reconnect to form an apparently growing post-flare loop system.

Authors: Yurchyshyn, Vasyl
Projects:

Publication Status: Published in ApJ
Last Modified: 2002-10-17 13:30
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Abstracts by Author
High Resolution Observations of a White Light Flare with NST
Multiwavelength Observations of a Slow Raise, Multi-Step X1.6 Flare and the Associated Eruption
Dynamics in Sunspot Umbra as Seen in New Solar Telescope and Interface Region Imaging Spectrograph Data
High Resolution Observations of Chromospheric Jets in Sunspot Umbra
Dynamics of Chromospheric Upflows and Underlying Magnetic Fields
Chromospheric signatures of small-scale flux emergence as observed with NST and Hinode instruments
RELATIONSHIP BETWEEN EARTH-DIRECTED SOLAR ERUPTIONS AND MAGNETIC CLOUDS AT 1AU: A BRIEF REVIEW
Orientations of LASCO Halo CMEs and Their Connection to the Flux Rope Structure of Interplanetary CMEs
The May 13, 2005 Eruption: Observations, Data Analysis and Interpretation
STATISTICAL DISTRIBUTIONS OF SPEEDS OF CORONAL MASS EJECTIONS
Structure of magnetic fields in NOAA active regions 0486 and 0501 and in the associated interplanetary ejecta
Magnetic Field, Halpha and RHESSI Observations of the July 23, 2002 Gamma-ray Flare
Correlation Between Speeds of CMEs and the Intensity of Geomagnetic Storms
Evidence of a Flux-Rope Model for Corona Mass Ejections Based on Observations of the Limb Prominence Eruption on 2002 January 4

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