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Model of Local Oscillations in Sunspots  

Robert Sych   Submitted: 2015-09-24 00:25

We have analyzed the properties of oscillations in a sunspot based on SDO observations with a duration of 6 h. The 3-min oscillation spectrum has turned out to consist of dozens of spectral lines. The line widths are at the spectral resolution limit. The oscillations in a sunspot have been broken down into individual areas with a size of a few arcseconds, each having its own oscillation spectrum. These oscillation properties cannot be explained in terms of the existing models based on the assumption that the sunspot oscillates as a whole. We propose a model of local oscillations that explains the complex spectrum of the oscillations and their locality. We show that in addition to the chromospheric resonator, there exists a subphotospheric resonator for slow MHD waves. The existence of this resonance layer allows the locality of the oscillations and their complex spectrum to be explained in terms of Parker's model.

Authors: Yu. D. Zhugzhda and R.A.Sych
Projects: SDO-AIA

Publication Status: Astronomy Letters, 2014, Vol. 40, No. 9, pp. 576?593
Last Modified: 2015-09-26 14:54
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Sunspot waves and flare energy release  

Robert Sych   Submitted: 2015-09-24 00:19

We address a possibility of the flare process initiation and further maintenance of its energy release due to a transformation of sunspot longitudinal waves into transverse magnetic loop oscillations with initiation of reconnection. This leads to heating maintaining after the energy release peak and formation of a flat stage on the X-ray profile. We applied the time-distance plots and pixel wavelet filtration (PWF) methods to obtain spatio-temporal distribution of wave power variations in SDO/AIA data. To find magnetic waveguides, we used magnetic field extrapolation of SDO/HMI magnetograms. The propagation velocity of wave fronts was measured from their spatial locations at specific times. In correlation curves of the 17 GHz (NoRH) radio emission we found a monotonous energy amplification of 3-min waves in the sunspot umbra before the 2012 June 7 flare. This dynamics agrees with an increase in the wave-train length in coronal loops (SDO/AIA, 171A) reaching the maximum 30 minutes prior to the flare onset. A peculiarity of this flare time profile in soft X-rays (RHESSI, 3-25 keV) is maintaining the constant level of the flare emission for 10 minutes after the short impulse phase, which indicates at the energy release continuation. Throughout this time, we found 30-sec period transverse oscillations of the flare loop in the radio-frequency range (NoRH, 17 GHz). This periodicity is apparently related to the transformation of propagating longitudinal 3-min waves from the sunspot into the loop transverse oscillations. The magnetic field extrapolation showed the existence of the magnetic waveguide (loop) connecting the sunspot with the energy release region. A flare loop heating can be caused by the interaction (reconnections) of this transversally oscillating waveguide with the underlying twisted loops.

Authors: R. Sych, M. Karlický, A. Altyntsev, J. Dudík and L. Kashapova
Projects: SDO-AIA

Publication Status: A&A 577, A43 (2015)
Last Modified: 2015-09-26 14:57
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MHD waves in sunspots  

Robert Sych   Submitted: 2015-09-24 00:07

The review addresses the spatial frequency morphology of sources of sunspot oscillations and waves, including their localization, size, oscillation periods, height localization with the mechanism of cut-off frequency that forms the observed emission variability. Dynamic of sunspot wave processes, provides the information about the structure of wave fronts and their time variations, investigates the oscillation frequency transformation depending on the wave energy is shown. The initializing solar flares caused by trigger agents like magnetoacoustic waves, accelerated particle beams, and shocks are discussed. Special attention is paid to the relation between the flare reconnection periodic initialization and the dynamics of sunspot slow magnetoacoustic waves. A short review of theoretical models of sunspot oscillations is provided.

Authors: Robert Sych
Projects: SDO-AIA

Publication Status: Chapter in AGU Monograph (2015, in press), Review article
Last Modified: 2015-09-26 14:54
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Flare processes evolution and polarization changes of fine structures of solar radio emission in the April 11, 2013 event  

Robert Sych   Submitted: 2015-09-23 23:52

The measurement of positions and sizes of radio sources in the observations of solar radio spectral fine structures in an M6.5 flare on April 11, 2013 were observed simultaneously by several radio instruments at four different observatories: Chinese Solar Broadband Radio Spectrometers at Huairou (SBRS/Huairou), Ondřejov Radio spectrograph in the Czech Republic (ORSC/Ondřejov), Badary Broadband Microwave spectropolarimeter (BMS/Irkutsk), and spectrograph/IZMIRAN (Moscow, Troitsk). The fine structures include microwave zebra patterns (ZP) fast pulsations, and fibers. They were observed during the flare brightening located at the tops of a loop arcade as shown in images taken by the extreme ultraviolet (EUV) telescope on board NASA's satellite Solar Dynamics Observatory (SDO) images. The flare occurred at 06:58-07:26 UT in solar active region NOAA 11719 located close to the solar disk center. ZP appeared near high frequency boundaries of the pulsations, and their spectra observed in Huairou and Ondřejov agreed with each other in terms of details. At the beginning of the flare impulsive phase, a strong narrowband ZP burst occurred with a moderate left-handed circular polarization. Then a series of pulsations and ZPs were observed almost in an unpolarized emission. After 07:00 UT a ZP appeared with a moderate right-handed polarization. In the flare decay phase (at about of 07:25 UT), ZP and fiber bursts become strongly right-hand polarized. BMS/Irkutsk spectral observations indicated that the background emission showed left-handed circular polarization (similar to SBRS/Huairou spectra around 3 GHz in). However, the fine structure appeared in the right-handed polarization. The dynamics of the polarization was associated with the motion of the flare exciter, which was observed in EUV images at 171? and 131? by the SDO Atmospheric Imaging Assembly (AIA). Combining magnetograms observed by the SDO Helioseismic and magnetic Imager (HMI) with the homologous assumption of EUV flare brightenings and ZP bursts, we deduced that the observed ZPs correspond to the ordinary radio emission mode. However, future analysis needs to verify the assumption that zebra radio sources are really related to a closed magnetic loop, and are located at lower heights in the solar atmosphere than the source of pulsations.

Authors: Gennady Chernov, Robert Sych, Baolin Tan, Yihua Yan, Chengming Tan, Qijun Fu, Marian Karlický and Valery Fomichev
Projects: SDO-AIA

Publication Status: Research in Astronomy and Astrophysics, (accepted 2015), in press
Last Modified: 2015-09-26 14:58
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Frequency drifts of 3-min oscillations in microwave and EUV emission above sunspots  

Robert Sych   Submitted: 2011-11-02 19:19

We analyse 3-min oscillations of microwave and EUV emission generated at different heights of a sunspot atmosphere, studying the amplitude and frequency modulation of the oscillations, and its relationship with the variation of the spatial structure of the oscillations. High-resolution data obtained with the Nobeyama Radioheliograph, TRACE and SDO/AIA are analysed with the use of the Pixelised Wavelet Filtering and wavelet skeleton techniques. 3-min oscillations in sunspots appear in the form of repetitive trains of the duration 8-20 min (13 min in average). The typical interval between the trains is 30-50 min. The oscillation trains are transient in frequency and power. We detected a repetitive frequency drifts of 3-min oscillations during the development of individual trains. Wavelet analysis shows three types of the frequency drift: positive, negative and fluctuations without drift. The start and end of the drifts coincide with the start time and end of the train. The comparative study of 3-min oscillations in the sequences of microwave and EUV images show the appearance of new sources of the oscillations in sunspots during the development of the trains. These structures can be interpreted as waveguides that channel upward propagating waves, responsible for 3-min oscillations. A possible explanation of the observed properties is the operation of two simultaneous factors: dispersive evolution of the upwardly-propagating wave pulses and the non-uniformity of the distribution of the oscillation power over the sunspot umbra with different wave sources corresponding to different magnetic flux tubes with different physical conditions and line-of-sight angles.

Authors: R. Sych, T. V. Zaqarashvili, V. M. Nakariakov, S.A. Anfinogentov, K.Shibasaki and Y. Yan
Projects: Nobeyama Radioheliograph,SDO-AIA,TRACE

Publication Status: A&A (in press), 2011
Last Modified: 2011-11-03 15:21
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Microwave Zebra Pattern Structures in the X2.2 Solar Flare on Feb 15, 2011  

Robert Sych   Submitted: 2011-10-12 02:41

Zebra pattern structure (ZP) is the most intriguing fine structure on thedynamic spectrograph of solar microwave burst. On 15 February 2011, thereerupts an X2.2 flare event on the solar disk, it is the first X-class flaresince the solar Schwabe cycle 24. It is interesting that there are severalmicrowave ZPs observed by the Chinese Solar Broadband Radiospectrometer(SBRS/Huairou) at frequency of 6.40 ~ 7.00 GHz (ZP1), 2.60 ~ 2.75 GHz (ZP2),and the Yunnan Solar Broadband Radio Spectrometer (SBRS/Yunnan) at frequency of1.04 ~ 1.13 GHz (ZP3). The most important phenomena is the unusualhigh-frequency ZP structure (ZP1, up to 7.00 GHz) occurred in the early risingphase of the flare, and there are two ZP structure (ZP2, ZP3) with relative lowfrequencies occurred in the decay phase of the flare. By scrutinizing thecurrent prevalent theoretical models of ZP structure generations, and comparingtheir estimated magnetic field strengths in the corresponding source regions,we suggest that the double plasma resonance model should be the most possibleone for explaining the formation of microwave ZPs, which may derive themagnetic field strengths as about 230 - 345 G, 126 - 147 G, and 23 - 26 G inthe source regions of ZP1, ZP2, and ZP3, respectively.

Authors: Baolin Tan, Yihua Yan, Chengming Tan, Robert Sych, Guannan Gao
Projects: None

Publication Status: ApJ, in press, 2011
Last Modified: 2011-10-12 09:17
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Relationship between wave processes in sunspots and quasi-periodic pulsations in active region flares  

Robert Sych   Submitted: 2009-08-05 22:48

A phenomenological relationship between oscillations in a sunspot and quasi-periodic pulsations in flaring energy releases at an active region above the sunspot, is established. The analysis of the microwave emission recorded by the Nobeyama Radioheliograph at 17 GHz shows a gradual increase in the power of the 3-min oscillation train in the sunspot associated with AR 10756 before flares in this active region. The flaring light curves are found to be bursty with a period of 3 min. Our analysis of the spatial distribution of the 3-min oscillation power implies that the oscillations follow from sunspots along coronal loops towards the flaring site. It is proposed that quasi-periodic pulsations in the flaring energy releases can be triggered by 3-min slow magnetoacoustic waves leaking from sunspots.

Authors: R. Sych, V.M. Nakariakov, M. Karlický, and S. Anfinogentov
Projects: None

Publication Status: A&A (in press)
Last Modified: 2009-08-06 09:45
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Relationship between wave processes in sunspots and quasi-periodic pulsations in active region flares  

Robert Sych   Submitted: 2009-08-05 22:48

A phenomenological relationship between oscillations in a sunspot and quasi-periodic pulsations in flaring energy releases at an active region above the sunspot, is established. The analysis of the microwave emission recorded by the Nobeyama Radioheliograph at 17 GHz shows a gradual increase in the power of the 3-min oscillation train in the sunspot associated with AR 10756 before flares in this active region. The flaring light curves are found to be bursty with a period of 3 min. Our analysis of the spatial distribution of the 3-min oscillation power implies that the oscillations follow from sunspots along coronal loops towards the flaring site. It is proposed that quasi-periodic pulsations in the flaring energy releases can be triggered by 3-min slow magnetoacoustic waves leaking from sunspots.

Authors: R. Sych, V.M. Nakariakov, M. Karlický, and S. Anfinogentov
Projects:

Publication Status: Astronomy and Astrophysics, Volume 505, Issue 2, 2009, pp.791-799
Last Modified: 2009-12-09 19:10
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Abstracts by Author
Model of Local Oscillations in Sunspots
Sunspot waves and flare energy release
MHD waves in sunspots
Flare processes evolution and polarization changes of fine structures of solar radio emission in the April 11, 2013 event
Frequency drifts of 3-min oscillations in microwave and EUV emission above sunspots
Microwave Zebra Pattern Structures in the X2.2 Solar Flare on Feb 15, 2011
Relationship between wave processes in sunspots and quasi-periodic pulsations in active region flares
Relationship between wave processes in sunspots and quasi-periodic pulsations in active region flares

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