MULTIWAVELENGTH OBSERVATIONS OF A SLOW-RISE, MULTISTEP X1.6 FLARE AND THE ASSOCIATED ERUPTION

Yurchyshyn, V.,Kumar, P.,Cho, K.-S.,Lim, E.-K.,Abramenko, V. I. IOP Publishing 2015 The Astrophysical journal Vol.812 No.2

<P>Using multiwavelength observations, we studied a slow-rise, multistep X1.6 flare that began on 2014 November 7 as a localized eruption of core fields inside a delta-sunspot and later engulfed the entire active region (AR). This flare event was associated with formation of two systems of post-eruption arcades (PEAs) 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 and IRIS spacecraft, along with the ground-based data from the New Solar Telescope, present evidence that (i) the flare and the eruption were directly triggered by a flux emergence that occurred inside a d-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 angstrom) and LASCO C2 coronagraph images; (iii) the global PEA spanned the entire AR and was due to global-scale reconnection occurring at heights of about one solar radius, indicating the global spatial and temporal scale of the eruption.</P>

DYNAMICS IN SUNSPOT UMBRA AS SEEN IN NEW SOLAR TELESCOPE AND INTERFACE REGION IMAGING SPECTROGRAPH DATA

Yurchyshyn, V.,Abramenko, V.,Kilcik, A. IOP Publishing 2015 The Astrophysical journal Vol.798 No.2

<P>We analyze 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 by the Mg II k 2796.35 angstrom and Si IV 1393.76 angstrom line formation levels changes during the observederiod, and peak-to-peak delays may range from 40 s to zero. The intensity of chromospheric shocks also displays long-term (about 20 min) variations. NST's high spatial resolution Ha 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. The 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 the 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.</P>

FORMATION AND ERUPTION OF A SMALL FLUX ROPE IN THE CHROMOSPHERE OBSERVED BY NST,<i>IRIS</i>, AND<i>SDO</i>

Kumar, Pankaj,Yurchyshyn, Vasyl,Wang, Haimin,Cho, Kyung-Suk IOP Publishing 2015 The Astrophysical journal Vol.809 No.1

<P>Using high-resolution images from the 1.6 m New Solar Telescope at Big Bear Solar Observatory, we report the direct evidence of chromospheric reconnection at the polarity inversion line between two small opposite polarity sunspots. Small jetlike structures (with velocities of similar to 20-55 km s(-1)) were observed at the reconnection site before the onset of the first M1.0 flare. The slow rise of untwisting jets was followed by the onset of cool plasma inflow (similar to 10 km s(-1)) at the reconnection site, causing the onset of a two-ribbon flare. The reconnection between two sheared J-shaped cool Ha loops causes the formation of a small twisted (S-shaped) flux rope in the chromosphere. In addition, Helioseismic and Magnetic Imager magnetograms show the flux cancellation (both positive and negative) during the first M1.0 flare. The emergence of negative flux and the cancellation of positive flux (with shear flows) continue until the successful eruption of the flux rope. The newly formed chromospheric flux rope becomes unstable and rises slowly with a speed of similar to 108 km s(-1) during a second C8.5 flare that occurred after similar to 3 hr of the first M1.0 flare. The flux rope was destroyed by repeated magnetic reconnection induced by its interaction with the ambient field (fan-spine topology) and looks like an untwisting surge (similar to 170 km s(-1)) in the coronal images recorded by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. These observations suggest the formation of a chromospheric flux rope (by magnetic reconnection associated with flux cancellation) during the first M1.0 flare and its subsequent eruption/disruption during the second C8.5 flare.</P>

SOLAR CYCLE 24: CURIOUS CHANGES IN THE RELATIVE NUMBERS OF SUNSPOT GROUP TYPES

Kilcik, A.,Yurchyshyn, V. B.,Ozguc, A.,Rozelot, J. P. IOP Publishing 2014 ASTROPHYSICAL JOURNAL LETTERS - Vol.794 No.1

<P>Here, we analyze different sunspot group (SG) behaviors from the points of view of both the sunspot counts (SSCs) and the number of SGs, in four categories, for the time period of 1982 January-2014 May. These categories include data from simple (A and B), medium (C), large (D, E, and F), and decaying (H) SGs. We investigate temporal variations of all data sets used in this study and find the following results. (1) There is a very significant decrease in the large groups' SSCs and the number of SGs in solar cycle 24 (cycle 24) compared to cycles 21-23. (2) There is no strong variation in the decaying groups' data sets for the entire investigated time interval. (3) Medium group data show a gradual decrease for the last three cycles. (4) A significant decrease occurred in the small groups during solar cycle 23, while no strong changes show in the current cycle (cycle 24) compared to the previous ones. We confirm that the temporal behavior of all categories is quite different from cycle to cycle and it is especially flagrant in solar cycle 24. Thus, we argue that the reduced absolute number of the large SGs is largely, if not solely, responsible for the weak cycle 24. These results might be important for long-term space weather predictions to understand the rate of formation of different groups of sunspots during a solar cycle and the possible consequences for the long-term geomagnetic activity.</P>

Active Latitude Oscillations Observed on the Sun

Kilcik, A.,Yurchyshyn, V.,Clette, F.,Ozguc, A.,Rozelot, J.-P. Springer-Verlag 2016 Solar physics Vol.291 No.4

<P>We investigate periodicities in the mean heliographic latitudes of sunspot groups, called active latitudes, for the past six complete solar cycles (1945 - 2008). For this purpose, the multitaper method and Morlet wavelet analysis were used. We found that solar rotation periodicities (26 - 38 days) are present in active latitudes of both hemispheres for all the investigated cycles (18 to 23). Both in the northern and southern hemispheres, active latitudes drifted toward the equator from the beginning to the end of each cycle and followed an oscillating path. These motions are well described by a second-order polynomial. There are no meaningful periods of between 55 and about 300 days in either hemisphere for all cycles. A periodicity of 300 to 370 days appears in both hemispheres for Cycle 23, in the northern hemisphere for Cycle 20, and in the southern hemisphere for Cycle 18.</P>

Frequently Occurring Reconnection Jets from Sunspot Light Bridges

Tian, Hui,Yurchyshyn, Vasyl,Peter, Hardi,Solanki, Sami K.,Young, Peter R.,Ni, Lei,Cao, Wenda,Ji, Kaifan,Zhu, Yingjie,Zhang, Jingwen,Samanta, Tanmoy,Song, Yongliang,He, Jiansen,Wang, Linghua,Chen, Yaji American Astronomical Society 2018 The Astrophysical journal Vol.854 No.2

Multiwavelength observations of a flux rope formation by series of magnetic reconnection in the chromosphere

Kumar, Pankaj,Yurchyshyn, Vasyl,Cho, Kyung-Suk,Wang, Haimin Springer-Verlag 2017 Astronomy and astrophysics Vol.603 No.-

Chromospheric Plasma Ejections in a Light Bridge of a Sunspot

Song, Donguk,Chae, Jongchul,Yurchyshyn, Vasyl,Lim, Eun-Kyung,Cho, Kyung-Suk,Yang, Heesu,Cho, Kyuhyoun,Kwak, Hannah American Astronomical Society 2017 The Astrophysical Journal Vol.835 No.2

<P>It is well-known that light bridges (LBs) inside a sunspot produce small-scale plasma ejections and transient brightenings in the chromosphere, but the nature and origin of such phenomena are still unclear. Utilizing the high-spatial and high-temporal resolution spectral data taken with the Fast Imaging Solar Spectrograph and the TiO 7057 angstrom broadband filter images installed at the 1.6 m New Solar Telescope of Big Bear Solar Observatory, we report arcsecond-scale chromospheric plasma ejections (1.'' 7) inside a LB. Interestingly, the ejections are found to be a manifestation of upwardly propagating shock waves as evidenced by the sawtooth patterns seen in the temporal-spectral plots of the Ca II. 8542 angstrom and Ha intensities. We also found a fine-scale photospheric pattern (1 '') diverging with a speed of about 2 km s(-1) two minutes before the plasma ejections, which seems to be a manifestation of magnetic flux emergence. As a response to the plasma ejections, the corona displayed small-scale transient brightenings. Based on our findings, we suggest that the shock waves can be excited by the local disturbance caused by magnetic reconnection between the emerging flux inside the LB and the adjacent umbral magnetic field. The disturbance generates slow-mode waves, which soon develop into shock waves, and manifest themselves as the arcsecond-scale plasma ejections. It also appears that the dissipation of mechanical energy in the shock waves can heat the local corona.</P>

Observation of a Large-scale Quasi-circular Secondary Ribbon Associated with Successive Flares and a Halo CME

Lim, Eun-Kyung,Yurchyshyn, Vasyl,Kumar, Pankaj,Cho, Kyuhyoun,Jiang, Chaowei,Kim, Sujin,Yang, Heesu,Chae, Jongchul,Cho, Kyung-Suk,Lee, Jeongwoo American Astronomical Society 2017 The Astrophysical journal Vol.850 No.2

<P>Solar flare ribbons provide an important clue to the magnetic reconnection process and associated magnetic field topology in the solar corona. We detected a large-scale secondary flare ribbon of a circular shape that developed in association with two successive M-class flares and one coronal mass ejection. The ribbon revealed interesting properties such as (1) a quasi-circular shape and enclosing the central active region (AR); (2) the size as large as 500 '' by 650 ''; (3) successive brightenings in the clockwise direction at a speed of 160 km s(-1) starting from the nearest position to the flaring sunspots; (4) radial contraction and expansion in the northern and the southern part, respectively, at speeds of <= 10 km s(-1). Using multi-wavelength data from Solar Dynamics Observatory, RHESSI, XRT, and Nobeyama, along with magnetic field extrapolations, we found that: (1) the secondary ribbon location is consistent with those of the field line footpoints of a fan-shaped magnetic structure that connects the flaring region and the ambient decaying field; (2) the second M2.6 flare occurred when the expanding coronal loops driven by the first M2.0 flare encountered the background decayed field; (3) immediately after the second flare, the secondary ribbon developed along with dimming regions. Based on our findings, we suggest that interaction between the expanding sigmoid field and the overlying fan-shaped field triggered the secondary reconnection that resulted in the field opening and formation of the quasi-circular secondary ribbon. We thus conclude that interaction between the AR and the ambient large-scale fields should be taken into account to fully understand the entire eruption process.</P>

SIMULTANEOUS OBSERVATION OF A HOT EXPLOSION BY NST AND IRIS

Kim, Yeon-Han,Yurchyshyn, Vasyl,Bong, Su-Chan,Cho, Il-Hyun,Cho, Kyung-Suk,Lee, Jaejin,Lim, Eun-Kyung,Park, Young-Deuk,Yang, Heesu,Ahn, Kwangsu,Goode, Philip R.,Jang, Bi-Ho IOP Publishing 2015 The Astrophysical journal Vol.810 No.1

<P>We present the first simultaneous observations of so-called 'hot explosions' in the cool atmosphere of the Sun made by the New Solar Telescope (NST) of Big Bear Solar Observatory and the Interface Region Imaging Spectrograph (IRIS) in space. The data were obtained during the joint IRIS-NST observations on 2014 July 30. The explosion of interest started around 19: 20 UT and lasted for about 10 minutes. Our findings are as follows: (1) the IRIS brightening was observed in three channels of slit-jaw images, which cover the temperature range from 4000 to 80,000 K; (2) during the brightening, the Si IV emission profile showed a double-peaked shape with highly blue and redshifted components (-40 and 80 km s(-1)); (3) wing brightening occurred in H alpha and Ca II 8542 angstrom bands and related surges were observed in both bands of the NST Fast Imaging Solar Spectrograph (FISS) instrument; (4) the elongated granule, seen in NST TiO data, is clear evidence of the emergence of positive flux to trigger the hot explosion; (5) the brightening in Solar Dynamics Observatory/Atmospheric Imaging Assembly 1600 angstrom images is quite consistent with the IRIS brightening. These observations suggest that our event is a hot explosion that occurred in the cool atmosphere of the Sun. In addition, our event appeared as an Ellerman bomb (EB) in the wing of H alpha, although its intensity is weak and the vertical extent of the brightening seems to be relatively high compared with the typical EBs.</P>