Ellerman bombs(EBs) are small brightening events in the solar lower atmosphere.By their original definition,the main characteristic of EBs is the two emission bumps in both wings of chromospheric lines,such as Hα and CaII 8542 lines.Up to now,most authors have found that the temperature increase of EBs around the temperature minimum region is in the range of 600–3000 K.However,with recent IRIS observations,some authors proposed that the temperature increase of EBs could be more than 10000 K.Using non-LTE semi-empirical modeling,we investigate the line profiles,continuum emission and radiative losses for EB models with different temperature increases,and compare them with observations.Our result indicates that if the EB maximum temperature reaches more than 10000 K around the temperature minimum region,then the resulting Hα and CaII 8542 line profiles and the continuum emission would be much stronger than those of EB observations.Moreover,due to the high radiative losses,a high temperature EB would have a very short lifetime,which is not compatible with observations.Thus,our study does not support the proposal that EB temperatures are higher than 10000 K.
We attempt to propose a method for automatically detecting the solar filament chirality and barb bearing. We first introduce the concept of an unweighted undirected graph and adopt the Dijkstra shortest path algorithm to recognize the filament spine. Then, we use the polarity inversion line(PIL) shift method for measuring the polarities on both sides of the filament, and employ the connected components labeling method to identify the barbs and calculate the angle between each barb and the spine to determine the bearing of the barbs, i.e., left or right. We test the automatic detection method with Hα filtergrams from the Big Bear Solar Observatory(BBSO) Hα archive and magnetograms observed with the Helioseismic and Magnetic Imager(HMI) on board the Solar Dynamics Observatory(SDO). Four filaments are automatically detected and illustrated to show the results. The barbs in different parts of a filament may have opposite bearings. The filaments in the southern hemisphere(northern hemisphere) mainly have left-bearing(rightbearing) barbs and positive(negative) magnetic helicity, respectively. The tested results demonstrate that our method is efficient and effective in detecting the bearing of filament barbs. It is demonstrated that the conventionally believed one-to-one correspondence between filament chirality and barb bearing is not valid.The correct detection of the filament axis chirality should be done by combining both imaging morphology and magnetic field observations.
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.
Gravity is everywhere in the universe[1,2],and the same is true of the magnetic field[3-5].Similar to gravity,magnetic field also controls the dynamics of the matter in the universe,over 99.9%of which is in the plasma state.Somewhat different from gravity which becomes overwhelming in large scales,magnetic field becomes more important in smaller scales.This is probably why magnetic field has not been considered too seriously in and above the galactic scale,whereas it becomes more and more important in the stellar scale.
The standard flare model,which was proposed based on observations and magnetohydrodynamic theory,can successfully explain many observational features of solar flares.However,this model is just a framework,with many details awaiting to be filled in, including how reconnection is triggered.In this paper,we address an unanswered question:where do flare ribbons stop?With the data analysis of the 2003 May 29 flare event,we tentatively confirmed our conjecture that flare ribbons finally stop at the intersection of separatrices(or quasi-separatrix layer in a general case)with the solar surface.Once verified,such a conjecture can be used to predict the final size and even the lifetime of solar flares.
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
