We present study of a typical explosive event (EE) at sub-arcsecond scale witnessed by strong non-Gaussian profiles with blue-and red-shifted emission of up to 150 km s −1 seen in the transition-region Si iv 1402.8 Å, and the chromospheric Mg ii k 2796.4 Å and C ii 1334.5 Åobserved by the Interface Region Imaging Spectrograph at unprecedented spatial and spectral resolution. For the first time a EE is found to be associated with very small-scale (∼120 km wide) plasma ejection followed by retraction in the chromosphere. These small-scale jets originate from a compact brightpoint-like structure of ∼1.5 ′′ size as seen in the IRIS 1330 Å images. SDO/AIA and SDO/HMI co-observations show that the EE lies in the footpoint of a complex loop-like brightening system. The EE is detected in the higher temperature channels of AIA 171 Å, 193 Å and 131 Å suggesting that it reaches a higher temperature of log T = 5.36 ± 0.06 (K). Brightenings observed in the AIA channels with durations 90-120 seconds are probably caused by the plasma ejections seen in the chromosphere. The wings of the C ii line behave in a similar manner as the Si iv's indicating close formation temperatures, while the Mg ii k wings show additional Doppler-shifted emission. Magnetic convergence or emergence followed by cancellation at a rate of 5 × 10 14 Mx s −1 is associated with the EE region. The combined changes of the locations and the flux of different magnetic patches suggest that magnetic reconnection must have taken place. Our results challenge several theories put forward in the past to explain non-Gaussian line profiles, i.e. EEs. Our case study on its own, however, cannot reject these theories, thus further in-depth studies on the phenomena producing EEs are required.

Between July 5th and July 7th 2004, two intriguing fast coronal mass ejection(CME)-streamer interaction events were recorded by the Large Angle and Spectrometric Coronagraph (LASCO). At the beginning of the events, the streamer was pushed aside from their equilibrium position upon the impact of the rapidly outgoing and expanding ejecta; then, the streamer structure, mainly the bright streamer belt, exhibited elegant large scale sinusoidal wavelike motions. The motions were apparently driven by the restoring magnetic forces resulting from the CME impingement, suggestive of magnetohydrodynamic kink mode propagating outwards along the plasma sheet of the streamer. The mode is supported collectively by the streamer-plasma sheet structure and is therefore named " streamer wave" in the present study. With the white light coronagraph data, we show that the streamer wave has a period of about 1 hour, a wavelength varying from 2 to 4 solar radii, an amplitude of about a few tens of solar radii, and a propagating phase speed in the range 300 to 500 km s −1 . We also find that there is a tendancy for the phase speed to decline with increasing heliocentric distance. These observations provide good examples of large scale wave phenomena carried by coronal structures, and have significance in developing seismological techniques for diagnosing plasma and magnetic parameters in the outer corona.

We identify the coronal sources of the solar winds sampled by the ACE spacecraft during [1999][2000][2001][2002][2003][2004][2005][2006][2007][2008], and examine the in situ solar wind properties as a function of wind sources. The standard two-step mapping technique is adopted to establish the photospheric footpoints of the magnetic flux tubes along which the ACE winds flow. The footpoints are then placed in the context of EIT 284Å images and photospheric magnetograms, allowing us to categorize the sources into four groups: coronal holes (CHs), active regions (ARs), the quiet Sun (QS), and "Undefined". This practice also enables us to establish the response to solar activity of the fractions occupied by each kind of solar winds, and of their speeds and O 7+ /O 6+ ratios measured in situ. We find that during the maximum phase, the majority of ACE winds originate from ARs. During the declining phase, CHs and ARs are equally important contributors to the ACE solar winds. The QS contribution increases with decreasing solar activity, and maximizes in the minimum phase when QS appear to be the primary supplier of the ACE winds. With decreasing activity, the winds from all sources tend to become cooler, as represented by the increasingly low O 7+ /O 6+ ratios. On the other hand, during each activity phase, the AR winds tend to be the slowest and associated with the highest O 7+ /O 6+ ratios, and the CH winds correspond to the other extreme, with the QS winds lying in between. Applying the same analysis method to the slow winds only, here defined as the winds with speeds lower than 500 km s −1 , we find basically the same overall behavior, as far as the contributions of individual groups of sources are concerned. This statistical study indicates that QS regions are an important source of the solar wind during the minimum phase.

We present high-resolution observations of a magnetic reconnection event in the solar atmosphere taken with the New Vacuum Solar Telescope, AIA and HMI. The reconnection event occurred between the threads of a twisted arch filament system (AFS) and coronal loops. Our observations reveal that the relaxation of the twisted AFS drives some of its threads to encounter the coronal loops, providing inflows of the reconnection. The reconnection is evidenced by flared X-shape features in the AIA images, a current-sheet-like feature apparently connecting post-reconnection loops in the Hα+1 Å images, small-scale magnetic cancellation in the HMI magnetograms and flows with speeds of 40-80 km s −1 along the coronal loops. The post-reconnection coronal loops seen in AIA 94 Å passband appear to remain bright for a relatively long time, suggesting that they have been heated and/or filled up by dense plasmas previously stored in the AFS threads. Our observations suggest that the twisted magnetic system could release its free magnetic energy into the upper solar atmosphere through reconnection processes. While the plasma pressure in the reconnecting flux tubes are significantly different, the reconfiguration of field lines could result in transferring of mass among them and induce heating therein.

Identifying the material source of coronal mass ejections (CMEs) is crucial for understanding the generation mechanisms of CMEs. The composition parameters of interplanetary coronal mass ejections (ICMEs) associated with different activities on the Sun may be diverse, as the materials come from distinct regions or are generated by different processes. We classified ICMEs into three types by associated activities on the Sun, with (T1) and without (T3) flares and hot channels, and only associated with flares (T2). The composition parameters of each type of ICMEs were analyzed. We found that all CMEs with hot channels are accompanied by flares, and strong flares are all associated with hot channels in our database. The average length of the filaments in T1 cases are much shorter than those in T3 cases. The average charge states of iron (Q Fe) and helium abundance (A He) for T3 ICMEs are less than 12% and 7%, respectively. The Q Fe and A He for T1 ICMEs present clear bimodal distributions with the minimum between two peaks at 12% and 7%, respectively. Nearly two-thirds of the hot plasma (with higher Q Fe) inside ICMEs is associated with higher A He. The Q Fe and A He are both positively correlated with the flare intensities. The A He and filament scales are not explicitly linked to each other. The statistical results demonstrate that the material contribution of the filaments to ICMEs is low and more than half of the hot materials inside ICMEs originate from the chromosphere in our database. We suggest that they are heated by the chromospheric evaporation process at the hot channel (flux rope) footpoint regions before and/or during the flaring process.