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Magnetic field changes associated with three successive M-class solar flares on 2002 July 26

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Research in Astronomy and Astrophysics 2011年第6期11卷 692-700页

作者： Pu Wang Ming-De Ding hai-sheng ji hai-Min Wang epartment of Astronomy Nanjing UniversityNanjing 210093China Purple Mountain Observatory Chinese Academy of SciencesNanjing 210008China Space Weather Research Lab Center for Solar Terrestrial ResearchNew Jersey Institute of TechnologyNewarkNJ 07102US

With an extensive analysis,we study the temporal evolution of magnetic flux during three successive M-class flares in two adjacent active regions：NOAA 10039 and 10044.The primary data are full disk longitudinal magnetograms observed by SOHO/MDI.All three flares are observed to be accompanied by magnetic flux changes.The changes occurred immediately or within 1 ～ 10 minutes after the starting time of the flares,indicating that the changes are obvious consequences of the solar flares.Although changes in many points are intrinsic in magnetic flux,for some sites,it is caused by a rapid expansion motion of magnetic flux.For the second flare,the associated change is more gradual compared with the ＇step-function＇ reported in literature.Furthermore,we use the data observed by the Imaging Vector Magnetograph（IVM） at Mees Solar Observatory to check possible line profile changes during the flares.The results from the IVM data confirm the flux changes obtained from the MDI data.A series of line profiles were obtained from the IVM＇s observations and analyzed for flux change sites.We find that the fluctuations in the width,depth and central wavelength of the lines are less than 5.0 even at the flare＇s core.No line profile change is observed during or after the flare.We conclude that the magnetic field changes associated with the three solar flares are not caused by flare emission.

关键词： Sun：activity-Sun：magnetic field-Sun：flares

The impact of turbulence on electron heating and acceleration near the neutral point of externally driven reconnecting current sheets in solar flares

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Research in Astronomy and Astrophysics 2012年第12期12卷 1701-1713页

作者： Gui-Ping Wu hai-sheng ji Zong-Jun Ning Department of Physics Southeast University Nanjing 210096 China Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 China

We aim to investigate the influence of plasma instability on electron acceleration and heating near the neutral point of a turbulent reconnecting current sheet （RCS）.Through numerically solving the one dimensional relativistic Vlasov equation with typical solar coronal parameters and a realistic mass ratio in the presence of a strong inductive electric field E0,we suggest that the wave-particle scattering may produce a flat electron flux spectrum from thermal to nonthermal electrons without a sudden low-energy cutoff in the acceleration region.The ratio between electron heating and acceleration decreases with the increase of the induced electric field.It is about one for E0=1 V cm-1 and one fourth for E0=10 V cm-1.The unstable waves excited by the beam plasma instability first accelerate the electrons,then trap these electrons from further acceleration by an induced electric field through wave-particle resonant interactions.

关键词： turbulence-scattering-Sun：X-rays,gamma rays-acceleration of particles

Dependence of anomalous resistivity on bulk drift velocity of electrons in the reconnecting current sheets in solar flares

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Research in Astronomy and Astrophysics 2010年第11期10卷 1186-1194页

作者： Gui-Ping Wu Guang-Li Huang hai-sheng ji Department of Physics Southeast University Nanjing 210096 China Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 China

Anomalous resistivity is critical for triggering fast magnetic reconnection in the nearly collisionless coronal plasma. Its nonlinear dependence on bulk drift velocity is usually assumed in MHD simulations. However, the mechanism for the production of anomalous resistivity and its evolution is still an open question. We numerically solved the one dimension Vlasov equation with the typical solar coronal parameters and realistic mass ratios to infer the relationship between anomalous resistivity and bulk drift velocity of electrons in the reconnecting current sheets as well as its non- linear characteristics. Our principal findings are summarized as follows： 1） the relationship between the anomalous resistivity and bulk drift velocity of electrons relative to ions may be described as ηmax=0.03724（vd/ve）^5.702Ωm for vd/ve in the range of 1.4-2.0 and ηmax=0.8746（vd/ve）^1.284Ωm for vd/ve in the range of 2.5-4.5;2）if drift velocity is just slightly larger than the threshold of ion-acoustic instability, the anomalous resistivity due to the wave-particle interactions is enhanced by about five orders as compared with classic resistivity due to Coulomb collisions, With the increase of drift velocity from 1.4ve to 4.5Ve, the anomalous resistivity continues to increase 100 times; 3） in the rise phase of unstable waves, the anomalous resistivity has the same order as the one estimated from quasi-linear theory; after saturation of unstable waves, the anomalous resistivity decreases at least about one order as com- pared with its peak value; 4） considering that the final velocity of electrons ejected out of the reconnecting current sheet （RCS） decreases with the distance from the neutral point in the neutral plane, the anomalous resistivity decreases with the distance from the neutral point, which is favorable for the Petschek-like reconnection to take place.

关键词： instabilities -- waves -- Sun： flares -- acceleration of particles

Analysis of the coronal source of the partially limb-occulted flare on 2002 July 20

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Research in Astronomy and Astrophysics 2013年第8期13卷 961-977页

作者： jin-Hua Shen Victor Melnikov Tuan-Hui Zhou hai-sheng ji Key Laboratory for Dark Matter and Space Astronomy Purple Mountain Observatory Chinese Academy of Sciences Graduate University of Chinese Academy of Sciences Central Astronomical Observatory at Pulkovo Russian Academy of Sciences

We carry out a detailed analysis of the X3.5 solar flare that occurred on 2002 July 20, which is the strongest partially limb-occulted flare ever observed by the RHESSI satellite. The main results are：（1） during the main impulsive phase that lasts ,-10 minutes, the motion of the thermal sources follows a U-shaped trajectory. Nonthermal sources move in a similar way, but in a series of larger zigzags. We further show that the non-thermal sources are actually leading the contraction motion. （2） During the main impulsive phase, X-ray sources at different energies continuously form a loop-like configuration, with the highest energy source （up to ,- 100 keV） and the lowest energy source （down to ,- 10 keV） being located at two ends. The entire loop-like configuration moves in a U-shaped trajectory, while keeping the order of descending energy from highest to lowest during motion. Two non-thermal hard X- ray sources with different energies are spatially well separated in the distribution. The unusual complexities of the X-ray emissions in the tenuous solar corona challenge interpretations using bremsstrahlung in a simple magnetic configuration.

关键词： Sun activity - Sun X-ray - Sun flares

Recurrent coronal jets observed by SDO/AIA

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Research in Astronomy and Astrophysics 2021年第10期21卷 213-220页

作者： Yan-jie Zhang Qing-Min Zhang Jun Dai Zhe Xu hai-sheng ji Key Laboratory of Dark Matter and Space Astronomy Purple Mountain ObservatoryCASNanjing 210023China School of Astronomy and Space Science University of Science and Technology of ChinaHefei 230026China

In this paper,we carried out multiwavelength observations of three recurring jets on 2014November 7.The jets originated from the same region at the edge of AR 12205 and propagated along the same coronal loop.The eruptions were generated by magnetic reconnection,which is evidenced by continuous magnetic cancellation at the jet base.The projected initial velocity of jet2 is~402 km s^(-1).The accelerations in the ascending and descending phases of jet2 are not consistent,the former is considerably larger than the value of g_(⊙) at the solar surface,while the latter is lower than g_(⊙).There are two possible candidates of extra forces acting on jet2 during its propagation.One is the downward gas pressure from jet1when it falls back and meets with jet2.The other is the viscous drag from the surrounding plasma during the fast propagation of jet2.As a contrast,the accelerations of jet3 in the rising and falling phases are constant,implying that the propagation of jet3 is not significantly influenced by extra forces.

关键词： Sun:corona Sun:activity Sun:magnetic fields

Observation of solar coronal heating powered by magneto-acoustic oscillations in a moss region

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Research in Astronomy and Astrophysics 2021年第4期21卷 325-330页

作者： Panda Hashim Zhen-Xiang Hong hai-sheng ji jin-Hua Shen Kai-Fan ji Wen-Da Cao Graduate School of the Chinese Academy of Sciences Beijing 100871China Xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China Purple Mountain Observatory DMSA/CASNanjing 210023China CfASS China Three Gorges UniversityYichang 443002China Yunnan Astronomical Observatory Chinese Academy of SciencesKunming 830011China Big Bear Solar Observatory 40386 North Shore LaneBig Bear CityCA 922314USA

In this paper,we report the observed temporal correlation between extreme-ultraviolet(EUV)emission and magneto-acoustic oscillations in an EUV moss region,which is the footpoint region only connected by magnetic loops with million-degree plasma.The result is obtained from a detailed multiwavelength data analysis of the region with the purpose of resolving fine-scale mass and energy flows that come from the photosphere,pass through the chromosphere and finally heat the solar transition region or the corona.The data set covers three atmospheric levels on the Sun,consisting of high-resolution broad-band imaging at TiO 7057 A and the line of sight magnetograms for the photosphere,high-resolution narrowband images at helium 110830 A for the chromosphere and EUV images at 171 A for the corona.The10830 A narrow-band images and the TiO 7057 A broad-band images are from a much earlier observation on 2012 July 22 with the 1.6 meter aperture Goode Solar Telescope(GST)at Big Bear Solar Observatory(BBSO)and the EUV 171 A images and the magnetograms are from observations made by Atmospheric Imaging Assembly(AIA)or Helioseismic and Magnetic Imager(HMI)onboard the Solar Dynamics Observatory(SDO).We report the following new phenomena:(1)Repeated injections of chromospheric material appearing as 10830 A absorption are squirted out from inter-granular lanes with a period of~5 minutes.(2)EUV emissions are found to be periodically modulated with similar periods of~5 minutes.(3)Around the injection area where 10830 A absorption is enhanced,both EUV emissions and strength of the magnetic field are remarkably stronger.(4)The peaks on the time profile of the EUV emissions are found to be in sync with oscillatory peaks of the stronger magnetic field in the region.These findings may give a series of strong evidences supporting the scenario that coronal heating is powered by magneto-acoustic waves.

关键词： Sun:corona Sun:chromosphere Sun:magnetic field

Location of energy source for coronal heating on the photosphere

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Research in Astronomy and Astrophysics 2017年第3期17卷 39-48页

作者： Zhen-Xiang Hong Xu Yang Ya Wang Kai-Fan ji hai-sheng ji Wen-Da Cao University of Chinese Academy of Sciences (CAS) Beijing 100049 China Key Laboratory of DMSA Purple Mountain Observatory CAS Nanjing 210008 China Big Bear Solar Observatory NJIT 40386 North Shore Dr Big Bear City CA 92314 USA Yunnan Observatories CAS Kunming 650011 China

It is reported that ultra-fine dynamic ejections along magnetic loops of an active region origi- nate from intergranular lanes and they are associated with subsequent heating in the corona. As continu- ing work, we analyze the same set of data but focus on a quiet region and the overlying EUV/UV emis- sion as observed by the Atmospheric Imaging Assembly （AIA） on board Solar Dynamics Observatory （SDO）. We find that there appear to be dark patches scattered across the quiet region and the dark patches always stay along intergranular lanes. Over the dark patches, the average UV/EUV emission at 131, 17 1, 304 and 1600 A （middle temperature） is more intense than that of other regions and EUV brightness is negatively correlated with 10830A intensity, though, such a trend does not exist for high temperature lines at 94, 193, 211 and 335 A. For the same quiet region, where both TiO 7057 A broad band images and 10830A filtergrams are available, contours for the darkest lane areas on TiO images and clark patches on 10830A filtergrams frequently differ in space. The results suggest that the dark patches do not simply reflect the areas with the darkest lanes but are associated with a kind of enhanced absorption （EA） at 10830A,. A strict definition for EA with narrow band 10830A filtergrams is found to be difficult. In this paper, we define enhanced absorption patches （EAPs） of a quiet region as the areas where emission is less than ,-90% of the mean intensity of the region. The value is equivalent to the average intensity along thin dark loops connecting two moss regions of the active region. A more strict definition for EAPs, say 88%, gives even more intense UV/EUV emission over those in the middle temperature range. The results provide further observational evidence that energy for heating the upper solar atmosphere comes from the intergranular lane area where the magnetic field is constantly brought in by convection motion in granules.

关键词： atmosphere - Sun photosphere - Sun transition region - Sun corona

The contracting and unshearing motion of flare loops in the X 7.1 flare on 2005 January 20 during its rising phase

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Research in Astronomy and Astrophysics 2013年第5期13卷 526-536页

作者： Tuan-Hui Zhou Jun-Feng Wang Dong Li Qi-Wu Song Victor Melnikov hai-sheng ji Key Laboratory for Dark Matter and Space Science Purple Mountain Observatory Chinese Academy of Sciences Key Laboratory of Solar Activity National Astronomical Observatories Chinese Academy of Sciences Purple Mountain Observatory Chinese Academy of Sciences School of Physics Optoelectronic Engineering Nanjing University of Information Science and Technology Graduate University of Chinese Academy of Sciences

With the aim of studying the relationship between the relative motions of the loop-top （LT） source and footpoints （FPs） during the rising phase of solar flares, we give a detailed analysis of the X7.1 class flare that occurred on 2005 January 20. The flare was clearly observed by RHESSI, showing a distinct X-ray flaring loop with a bright LT source and two well-defined hard X-ray （HXR） FPs. In particular, we correct the projection effect for the positions of the FPs and magnetic polarity inversion line. We find that：（1） The LT source showed an obvious U-shaped trajectory. The source of the higher energy LT shows a faster downward/upward speed. （2） The evolution of FPs was temporally correlated with that of the LT source. The converging/separating motion of FPs corresponds to the downward/upward motion of the LT source. （3） The initial flare shear of this event is found to be nearly 50 degrees, and it has a fluctuating decrease throughout the contraction phase as well as the expansion phase. （4） Four peaks of the time profile of the unshearing rate are found to be temporally correlated with peaks in the HXR emission flux. This flare supports the overall contraction pic- ture of flares： a descending motion of the LT source, in addition to converging and unshearing motion of FPs. All results indicate that the magnetic field was very highly sheared before the onset of the flare.

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

Concerning spikes in emission and absorption in the microwave range

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Research in Astronomy and Astrophysics 2013年第1期13卷 115-128页

作者： Gennady P.Chernov Robert A.Sych Guang-Li Huang hai-sheng ji Yi-Hua Yan Cheng-Ming Tan Key Laboratory of Solar Activity National Astronomical ObservatoryChinese Academy of Sciences Pushkov Institute of Terrestrial Magnetism Ionosphere and Radio Wave PropagationRussian Academy of Sciences (IZMIRAN) Institute of Solar-Terrestrial Physics Purple Mountain Observatory Chinese Academy of Sciences

In some events, weak fast solar bursts （near the level of the quiet Sun） were observed in the background of numerous spikes in emission and absorption. In such a case, the background contains the noise signals of the receiver. In events on 2005 September 16 and 2002 April 14, the solar origin of fast bursts was confirmed by simultaneous recording of the bursts at several remote observatories. The noisy background pixels in emission and absorption can be excluded by subtracting a higher level of continuum when constructing the spectra. The wavelet spectrum, noisy pro- files in different polarization channels and a spectrum with continuum level greater than zero demonstrates the noisy character of pixels with the lowest levels of emission and absorption. Thus, in each case, in order to judge the solar origin of all spikes, it is necessary to determine the level of continuum against the background of which the solar bursts are observed. Several models of microwave spikes are discussed. The electron cyclotron maser emission mechanism runs into serious problems with the in- terpretation of microwave millisecond spikes： the main obstacles are too high values of the magnetic field strength in the source （Pe 〈 uB）. The probable mechanism is the interaction of plasma Langmuir waves with ion-sound waves （l ＋ s → t） in a source related to shock fronts in the reconnection region.

关键词： solar flare -- radio emission -- spike-bursts