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 present stereoscopic observations of six sequential eruptions of a filament in the active region NOAA 11045 on 2010 Feb 8,with the advantage of the STEREO twin viewpoints in combination with Earth's viewpoint from SOHO instruments and ground-based telescopes.The last one of the six eruptions is a coronal mass ejection,but the others are not.The flare in this successful one is more intense than in the others.Moreover,the velocity of filament material in the successful one is also the largest among them.Interestingly,all the filament velocities are found to be proportional to the power of their flares.We calculate magnetic field intensity at low altitude,the decay indexes of the external field above the filament,and the asymmetry properties of the overlying fields before and after the failed eruptions and find little difference between them,indicating the same coronal confinement exists for both the failed and successful eruptions.The results suggest that,besides the confinement of the coronal magnetic field,the energy released in the low corona should be another crucial element affecting a failed or successful filament eruption.That is,a coronal mass ejection can only be launched if the energy released exceeds some critical value,given the same initial coronal conditions.
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
We investigate the interaction between two filaments and the subsequent filament eruption event observed from different viewing angles by Hinode, the Solar and Heliospheric Observatory, and the Solar Terrestrial Relations Observatory. In the event, the two filaments rose high, interacted with each other, and finally were ejected along two different paths. We measure the bulk-flow velocity using spectroscopic data. We find significant outflows at the speed of a few hundreds of km s 1 during the filament eruption, and also some downflows at a few tens of km s 1 at the edge of the eruption region in the late stage of the eruption. The erupting material was composed of plasmas with a wide temperature range of 10 4 -10 6 K. These results shed light on the filament nature and the coronal dynamics.
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.
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.
