Observations indicate that Ellerman bombs (EBs) and chromospheric microflares both occur in the lower solar atmosphere,and share many common features,such as temperature enhancements,accompanying jet-like mass motions,short life-time,and so on.These strongly suggest that EBs and chromospheric microflares could both probably be induced by magnetic reconnection in the lower solar atmosphere.With gravity,ionization and radiation considered,we perform two-dimensional numerical simulations of magnetic reconnection in the lower solar atmosphere.The influence of different parameters,such as intensity of the magnetic field and anomalous resistivity,on the results are investigated.Our result demonstrates that the temperature increases are mainly due to the joule dissipation caused by magnetic reconnection.The spectral profiles of EBs and chromospheric microflares are calculated with the non-LTE radiative transfer theory and compared with observations.It is found that the typical features of the two phenomena can be qualitatively reproduced.
Xiao-Yan Xu 1,2,Cheng Fang 2,Ming-De Ding 2 and Dan-Hui Gao 2 1 Purple Mountain Observatory,Chinese Academy of Science,Nanjing 210008,China 2 Department of Astronomy,Nanjing University,Nanjing 210093,China
Kinematic properties of coronal mass ejections (CMEs) suffer from projection effects,and it is expected that the real velocity should be larger and the real angular width should be smaller than the apparent values.Several attempts have been taken to correct the projection effects,which however led to an inflated average velocity probably due to the biased choice of CME events.In order to estimate the overall influence of the projection effects on the kinematic properties of the CMEs,we perform a forward modeling of real distributions of CME properties,such as the velocity,the angular width,and the latitude,by requiring their projected distributions to best match observations.Such a matching is conducted by Monte Carlo simulations.According to the derived real distributions,we found that (1) the average real velocity of all non-full-halo CMEs is about 514 km s-1,and the average real angular width is about 33°,in contrast to the corresponding apparent values of 418 km s-1 and 42.7° in observations;(2) For the CMEs with the angular width in the range of 20°-120°,the average real velocity is 510 km s-1 and the average real angular width is 43.4°,in contrast to the corresponding apparent values of 392 km s-1 and 52° in observations.
You Wu 1 and Peng-Fei Chen 1,2 1 Department of Astronomy,Nanjing University,Nanjing 210093,China 2 Key Lab of Modern Astron.and Astrophys.,Ministry of Education,Nanjing 210093,China
We report and analyze observational evidence of global kink oscillations in a solar filament as observed in Ha by instruments administered by National Solar Observatory(NSO)/Global Oscillation Network Group(GONG).An M 1.1-class flare in active region(AR) 11692 occurred on 2013 March 15 and induced a global kink mode in the filament lying towards the southwest of AR 11692.We find periods of about 61-67 minutes and damping times of 92-117 minutes at positions of three vertical slices chosen in and around the filament apex.We find that the waves are damped.From the observed period of the global kink mode and damping timescale using the theory of resonant absorption,we perform prominence seismology.We estimate a lower cut-off value for the inhomogeneity length scale to be around 0.34-0.44 times the radius of the filament cross-section.
Vaibhav PantAbhishek K SrivastavaDipankar BanerjeeMarcel GoossensPeng-Fei ChenNavin Chandra JoshiYu-Hao Zhou
Ellerman bombs(EBs) are tiny brightenings often observed near sunspots.The most impressive characteristic of EB spectra is the two emission bumps in both wings of the Hα and Ca II 8542 ?A lines. High-resolution spectral data of three small EBs were obtained on 2013 June 6 with the largest solar telescope, the 1.6 m New Solar Telescope at the Big Bear Solar Observatory. The characteristics of these EBs are analyzed. The sizes of the EBs are in the range of 0.3′′- 0.8′′ and their durations are only 3–5 min. Our semi-empirical atmospheric models indicate that the heating occurs around the temperature minimum region with a temperature increase of 2700–3000 K, which is surprisingly higher than previously thought. The radiative and kinetic energies are estimated to be as high as 5 × 1025- 3.0 × 1026 erg despite the small size of these EBs. Observations of the magnetic field show that the EBs just appeared in a parasitic region with mixed polarities and were accompanied by mass motions.Nonlinear force-free field extrapolation reveals that the three EBs are connected with a series of magnetic field lines associated with bald patches, which strongly implies that these EBs should be produced by magnetic reconnection in the solar lower atmosphere. According to the lightcurves and the estimated magnetic reconnection rate,we propose that there is a three phase process in EBs: pre-heating, flaring and cooling phases.
Zhen LiCheng FangYang GuoPeng-Fei ChenZhi XuWen-Da Cao
X-ray bright points(XBPs) are small-scale brightenings in the solar corona.Their counterparts in the lower atmosphere,however,are poorly investigated.In this paper,we study the counterparts of XBPs in the upper chromosphere where the Hα line center is formed.The XBPs were observed by the X-ray Telescope(XRT) aboard the Hinode spacecraft during the observing plan(HOP0124) in August 2009,coordinated with the Solar Magnetic Activity Research Telescope(SMART) in the Kwasan and Hida Observatory,Kyoto University.It is found that there are 77 Hα brightenings in the same field of view of XRT,and among 57 XBPs,29 have counterparts in the Hα channel.We found three types of relationship:Types a,b and c,corresponding to XBPs appearing first,Hα brightenings occurring first and no respective correspondence between them.Most of the strong XBPs belong to Type a.The Hα counterparts generally have double-kernel structures associated with magnetic bipoles and are cospatial with the footpoints of the XBP loops.The average lag time is ～3 minutes.This implies that for Type a the heating,presumably through magnetic reconnection,occurs first in the solar upper atmosphere and then goes downwards along the small-scale magnetic loops that comprise the XBPs.In this case,the thermal conduction plays a dominant role over the non-thermal heating.Only a few events belong to Type b,which could happen when magnetic reconnection occurs in the chromosphere and produces an upward jet which heats the upper atmosphere and causes the XBP.About half of the XBPs belong to Type c.Generally they have weak emission in SXR.About 62% Hα brightenings have no corresponding XBPs.Most of them are weak and have single structures.
We performed three dimensional resistive magnetohydrodynamic simulations to study the magnetic reconnection using an initially shearing magnetic field configuration(force free field with a current sheet in the middle of the computational box).It is shown that there are two types of reconnection jets:the ordinary reconnection jets and fan-shaped jets,which are formed along the guide magnetic field.The fan-shaped jets are significantly different from the ordinary reconnection jets which are ejected by magnetic tension force.There are two driving forces for accelerating the fan-shaped jets.One is the Lorentz force which initially dominates the motion of fluid elements,and then the gas pressure gradient force accelerates the fluid elements in the later stage.The dependence on magnetic reconnection angle and resistivity value has also been studied.The formation and evolution of these jets provide a new understanding of dynamic magnetohydrodynamic jets.
Owing to the largely improved facilities and working conditions,solar physics research in China has recently shown marked development.This paper reports on the recent progress of solar physics research in China's Mainland,mainly focusing on several hot issues,including instrumentations,magnetic field observations and research,solar flares,filaments and their eruptions,coronal mass ejections and related processes,as well as active regions and the corona,small-scale phenomena,solar activity and its predictions.A vision of the future is also described.
Cheng Fang 1 School of Astronomy and Space Science,Nanjing University,Nanjing 210093,China
Halo coronal mass ejections (CMEs) have been to be significantly faster than normal CMEs, which is a long-standing puzzle. In order to solve the puzzle, we first investigate the observed properties of 31 limb CMEs that clearly display loopshaped frontal loops. The observational results show a strong tendency that slower CMEs are weaker in white-light intensity. Then, we perform a Monte Carlo simulation of 20000 artificial limb CMEs that have an average velocity of ～523km s -1. The Thomson scattering of these events is calculated when they are assumed to be observed as limb and halo events, respectively. It is found that the white-light inten-sity of many slow CMEs becomes remarkably reduced when they turn from being viewed as a limb event to being viewed as a halo event. When the intensity is below the background solar wind fluctuation, it is assumed that they would be missed by coronagraphs. The average velocity of "detectable" halo CMEs is ～922km s -1, very close to the observed value. This also indicates that wider events are more likely to be recorded. The results soundly suggest that the higher average velocity of halo CMEs is due to that a majority of slow events and some of narrow fast events carrying less material are so faint that they are blended with the solar wind fluctuations, and therefore are not observed.
