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A quantity characterizing variation of observed magnetic twist in solar active regions

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Research in Astronomy and Astrophysics 2018年第3期18卷 37-46页

作者： Yu Gao Key Laboratory of Solar Activity National Astronomical ObservatoriesChinese Academy of Sciences

An alternative parameter RJz is introduced as the ratio of one of two kinds of opposite-sign current to the total current and is used to investigate the relationship between this quantity and the hemispheric helicity sign rule（HSR） that has been established by a series of previous statistical studies. The classification of current in each hemisphere obeys the following rule： if the product of the current and the corresponding longitudinal field component contributes a consistent sign with respect to the HSR,it is called ＂HSR-compliant＂ current,otherwise it is called ＂HSR-noncompliant＂ current. Firstly,consistency between the butterfly diagram of RJz and current helicity was obtained in a statistical study.Active regions with RJzsmaller than 0.5 tend to obey the HSR whereas those with RJz greater than 0.5 tend to disobey it. The ＂HSR-compliant＂ current systems have a 60% probability of realization compared to 40% for ＂HSR-noncompliant＂ current systems. Overall,the HSR is violated for active regions in which the ＂HSR-noncompliant＂ current is greater than the ＂HSR-compliant＂ current. Secondly,the parameter RJz was subsequently used to study the evolution of current systems in the case analyses of flare-productive active regions NOAA AR 11158 and AR 11283. It is found that there is a ＂RJz-quasistationary＂ phase that is relatively flare quiescent and ＂RJz-dynamic＂ phase that is characterized by the occurrence of large flares.

关键词： sun activity - sun flares - sun magnetic fields - sun evolution - sun sunspots

flares before and after coronal mass ejections

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Research in Astronomy and Astrophysics 2018年第3期18卷 99-104页

作者： Gadikere Sheshagiriyappa Suryanarayana Indian Institute of Astrophysics Koramangala Bengaluru-560034 India

Flare characteristics such as the flare occurrence number density and the distribution of peak flux as well as duration of flares occurring on either side of a coronal mass ejection（CME） onset time are studied. While the flares are rather evenly distributed statistically on either side of the CME onset time,the flare peak flux and duration tend to decrease depending upon their occurrence either before or after the CME onset. This is consistent with the earlier findings that flares emit higher energy before a CME whereas the energy is less in flares occurring after a CME.

关键词： sun flares - sun flare durations - sun peak flux of flares - sun coronal mass ejections

Synthetic analysis of a two-ribbon microflare

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Research in Astronomy and Astrophysics 2010年第1期10卷 83-90页

作者： Cheng Fang Peng-Fei Chen Rong-Lin Jiang Yu-Hua Tang Department of Astronomy Nanjing University Nanjing 210093 China

High-resolution Stokes spectral data of Hα, Ca Ⅱ 8542A, and Fe 16302.5A lines for a two-ribbon microflare （TRMF） were simultaneously obtained by the THEMIS telescope on 2002 September 5. We derive the intensity, velocity, and longitudinal magnetic field maps. The hard X-ray emission observed by RHESSI provides evidence of nonthermal particle acceleration in the TRMF. Using Ha and Ca Ⅱ 8542A line profiles and a non-LTE calculation, we obtain semi-empirical atmospheric models for the two brightest kernels of the TRME Our result indicates that the temperature enhancement in the chromosphere is more than 2500 K. The kinetic and radiative energies at the kernels are also estimated, resulting in an estimate of the total energy of the TRMF of about 2.4×10^29 erg. Observations indicate that the TRMF results from the low coronal magnetic reconnection following the eruption of a small fila- ment. However, the local temperature ＂bump＂ in the chromosphere presents a puzzle for such a standard flare model. A possible solution to this is discussed.

关键词： sun chromosphere- sun flares - sun activity - sun magnetic fields

Magnetic interactions during sympathetic solar eruptions

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Chinese Journal of Astronomy and Astrophysics 2009年第5期9卷 603-612页

作者： Yun-Chun Jiang Yi Bi Jia-Yan Yang Rui-Sheng Zheng Jing-Xiu Wang National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

We present the first evidence for occurrences of magnetic interactions between a jet, a filament and coronal loops during a complex event, in which two flares sequentially occurred at different positions of the same active region and were closely associated with two successive coronal mass ejections （CMEs）, respectively. The coronal loops were located outside but nearby the filament channel before the flares. The jet, originating from the first flare during its rise phase, not only hit the filament body but also met one of the ends of the loops. The filament then underwent an inclined eruption followed by the second flare and met the same loop end once more. Both the jet and the filament eruption were accompanied by the development of loop disturbances and the appearances of brightenings around the meeting site. In particular, the erupting filament showed clear manifestations of interactions with the loops. After a short holdup, only its portion passed through this site, while the other portion remained at the same place. Following the filament eruption and the loop disappearance, four dimmings were formed and located near their four ends. This is a situation that we define as ＂quadrupolar dimmings.＂ It appears that the two flares consisted of a sympathetic pair physically linked by the interaction between the jet and the filament, and their sympathy indicated that of the two CMEs. Moreover, it is very likely that the two sympathetic CMEs were simultaneously associated with the disappearing loops and the quadrupole dimmings.

关键词： sun activity - sun coronal mass ejections （CMEs） - sun filaments - sun flares - sun magnetic fields - sun corona

Study of white-light flares observed by Hinode

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Chinese Journal of Astronomy and Astrophysics 2009年第2期9卷 127-132页

作者： Hai-Min Wang Space Weather Research Lab Center for Solar Terrestrial Research New Jersey Institute of Technology Newark NJ 07102 USA

White-light flares are considered to be the most energetic flaring events that are observable in the optical broad-band continuum of the solar spectrum. They have not been commonly observed. Observations of white-light flares with sub-arcsecond resolution have been very rare. The continuous high resolution observations of Hinode provide a unique opportunity to systematically study the white-light flares with a spatial resolution around 0.2 arcsec. We surveyed all the flares above GOES magnitude C5.0 since the launch of Hinode in 2006 October. 13 of these kinds of flares were covered by the Hinode G-band observations. We analyzed the peak contrasts and equivalent areas （calculated via integrated excess emission contrast） of these flares as a function of the GOES X-ray flux, and found that the cut-off visibility is likely around M1 flares under the observing limit of Hinode. Many other observational and physical factors should affect the visibility of white-light flares; as the observing conditions are improved, smaller flares are likely to have detectable white-light emissions. We are cautious that this limiting visibility is an overestimate, because G-band observations contain emissions from the upper atmosphere. Among the 13 events analyzed, only the M8.7 flare of 2007 June 4 had near-simultaneous observations in both the G-band and the blue continuum. The blue continuum had a peak contrast of 94% vs. 175% in G-band for this event. The equivalent area in the blue continuum is an order of magnitude lower than that in the G-band. Very recently, Jess et al. studied a C2.0 flare with a peak contrast of 300% in the blue continuum. Compared to the events presented in this letter, that event is probably an unusual white-light flare： a very small kernel with a large contrast that can be detected in high resolution observations.

关键词： sun activity - sun flares - sun magnetic fields

A Multi-Wavelength Study of the 3B/X1.2 Flare Observed on 2003 October 26

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Chinese Journal of Astronomy and Astrophysics 2005年第6期5卷 645-664页

作者： Hui Li Jian-Ping Li Cheng Fang Brigitte Schmieder Arkadiusz Berlicki Qiu-Sheng Du Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 Department of Astronomy Nanjing University Nanjing 210093 Observatoire de Paris Section de Meudon LESIA i~-9-2195 Meudon Principal CedexFrance Institute of Theoretical Astrophysics University of Oslo Blindern N-0315 Oslo Norway Astronomical Institute of the Wroctaw University ul.Kopernika 11 51-622 Wroctaw Poland

We report results from a multi-wavelength study of the 3B/X1.2 tworibbon disk flare （S15E44）, which was well observed by both ground-based and space-borne instruments. Two pairs of conjugate kernels - K1 and K4, and K2 and K3 - in the Ha images are identified. These kernels are linked by two different systems of EUV loops. K1 and K4 correspond to the two 17 GHz and 34 GHz microwave sources observed by the Nobeyama Radioheliograph （NoRH）, while K2 and K3 have no corresponding microwave sources. Optical spectroscopic observations suggest that all the four kernels are possible precipitating sites of non-thermal electrons. Thus the energy of electron deposited in K2 and K3 should be less than 100keV. Two-dimensional distributions of the full widths at half maximum （FWHM） of the Ha profiles and the line-of-sight （LOS） velocities derived from the Ca n 8542 A profiles indicate that the largest FWHM and LOS velocity tends to be located near the outer edges of Hα kernels, which is consistent with the scenario of current two-ribbon flare models and previous results. When non-thermal electron bombardment is present, the observed Hα and Ca II 8542 A profiles are similar to previous observational and theoretical results, while the He I 10830 A profiles are different from the theoretical ones. This puts some constraints on future theoretical calculation of the He I 10830 A line.

关键词： sun flares - sun X-rays - line profiles

Study of temporal and spectral characteristics of the X-ray emission from solar flares

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Research in Astronomy and Astrophysics 2018年第10期18卷 33-48页

作者： Veena Choithani Rajmal Jain Arun K.Awasthi Geetanjali Singh Sneha Chaudhari Som Kumar Sharma Dept.of Physics Sh.M.M.Patel Institute of Sciences&ResearchKadi Sarva VishwavidyalayaGandhinagar 382015India CAS Key Laboratory of Geospace Environment Department of Geophysics and Planetary SciencesUniversity ofScience and Technology of ChinaHefei 230026China Physical Research Laboratory NavrangpuraAhmedabad 380009India

Temporal and spectral characteristics of X-ray emission from 60 flares of intensity ≥C class observed by the Solar X-ray Spectrometer （SOXS） during 2003-2011 are presented. We analyze the X-ray emission observed in four and three energy bands by the Si and Cadmium-Zinc-Telluride （CZT） detectors, respectively. The number of peaks in the intensity profile of the flares varies between 1 and 3. We find moderate correlation （R ~=0.2） between the rise time and the peak flux of the first peak of the flare irrespective of energy band, which is indicative of its energy-independent nature. Moreover, the magnetic field complexity of the flaring region is found to be highly anti-correlated （R = 0.61） with the rise time of the flares while positively correlated （R = 0.28） with the peak flux of the flare. The time delay between the peak of the X-ray emission in a given energy band and that in 25-30keV decreases with increasing energy, suggesting conduction cooling is dominant in the lower energies. Analysis of 340 spectra from 14 flares reveals that the peak of differential emission measure （DEM） evolution is delayed by 60-360 s relative to that of the temperature, and this time delay is inversely proportional to the peak flux of the flare. We conclude that temporal and intensity characteristics of flares are dependent on energy as well as the magnetic field configuration of the active region.

关键词： sun X-rays, gamma rays - sun magnetic fields - sun flares - sun corona

Solar Impulsive Hard X-Ray Emission and Two-Stage Electron Acceleration

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Chinese Journal of Astronomy and Astrophysics 2006年第6期6卷 733-740页

作者： Tian-Xi Zhang Arjun Tan Shi Tsan Wu Physics Deparanent Alabama A ＆ M University Normal AL 35762 USA Center for Space Plasma and Aeronomic Research The University of Alabama in Huntsville AL 35899 USA

Heating and acceleration of electrons in solar impulsive hard X-ray （HXR） flares are studied according to the two-stage acceleration model developed by Zhang for solar ^3Herich events. It is shown that electrostatic H-cyclotron waves can be excited at a parallel phase velocity less than about the electron thermal velocity and thus can significantly heat the electrons （up to 40 MK） through landau resonance. The preheated electrons with velocities above a threshold are further accelerated to high energies in the flare-acceleration process. The flareproduced electron spectrum is obtained and shown to be thermal at low energies and power law at high energies. In the non-thermal energy range, the spectrum can be double power law if the spectral power index is energy dependent or related. The electron energy spectrum obtained by this study agrees quantitatively with the result derived from the Reuven Ramaty High Energy Solar Spectroscopic Imager （RHESSI） HXR observations in the flare of 2002 July 23. The total flux and energy flux of electrons accelerated in the solar flare also agree with the measurements.

关键词： acceleration of particles - instabilities - plasmas - sun flares - sun particle emission - sun X-ray

Investigation of the possible source for the solar energetic particle event on 2017 September 10

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Research in Astronomy and Astrophysics 2018年第7期18卷 1-10页

作者： Ming-Xian Zhao Gui-Ming Le Yu-Tian Chi Key Laboratory of Space Weather National Center for Space WeatherChina Meteorological AdministrationBeijing 100081China School of Computer Science Anhui University of TechnologyMa'anshan 243032China School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China

According to the solar proton data observed by Geostationary Operational Environmental Satellites （GOES）, ground-based neutron monitors on Earth and near-relativistic electron data measured by the ACE spacecraft, the onset times of protons with different energies and near-relativistic electrons have been estimated and compared with the time of solar soft and hard X-ray and radio burst data. The results show that first arriving relativistic and non-relativistic protons and electrons may have been accelerated by the concurrent flare. The results also suggest that release times of protons with different energies may be different, and the protons with lower energy may have been released earlier than those with higher energy. Some protons accelerated by concurrent flares may be further accelerated by the shock driven by the associated CME.

关键词： sun coronal mass ejections （CMEs） - sun flares - sun particle emission