An erupting flux rope (FR) draws its overlying coronal loops upward, causing a coronal mass ejection. The legs of the overlying loops with opposite polarities are driven together. Current sheets (CSs) form, and magnetic reconnection, producing underneath flare arcades, occurs in the CSs. Employing Solar Dynamic Observatory/Atmospheric Imaging Assembly images, we study a FR eruption on 2015 April 23, and for the first time report the oscillation of CSs underneath the erupting FR. The FR is observed in all AIA extreme-ultraviolet passbands, indicating that it has both hot and warm components. Several bright CSs, connecting the erupting FR and the underneath flare arcades, are observed only in hotter AIA channels, e.g., 131 and 94 Å. Using the differential emission measure (EM) analysis, we find that both the temperature and the EM of CSs temporally increase rapidly, reach the peaks, and then decrease slowly. A significant delay between the increases of the temperature and the EM is detected. The temperature, EM, and density spatially decrease along the CSs with increasing heights. For a well-developed CS, the temperature (EM) decreases from 9.6 MK (8 × 1028 cm−5) to 6.2 MK (5 × 1027 cm−5) in 52 Mm. Along the CSs, dark supra-arcade downflows (SADs) are observed, and one of them separates a CS into two. While flowing sunward, the speeds of the SADs decrease. The CSs oscillate with a period of 11 minutes, an amplitude of 1.5 Mm, and a phase speed of 200 ± 30 km s−1. One of the oscillations lasts for more than 2 hr. These oscillations represent fast-propagating magnetoacoustic kink waves.

Aims. We report for the first time the hot and cool components of two flux ropes simultaneously observed by SDO and STEREO, and the relationship between the flux rope eruptions and the coronal mass ejection (CME). Methods. Employing SDO and STEREO A and B observations, we investigated the eruptive event of two flux ropes and their associated activities in active region (AR) 11402 on January 23, 2012. Results. In SDO/AIA 94 Å (∼6.4 MK) and 131 Å (∼10 MK) images, a twisted flux rope appeared from 00:44 UT, which was located in AR 11402. Another longer saddle-shaped flux rope, with twisted fine structures, appeared 25 min later. This was located across the two ARs 11401 and 11402. These two flux ropes initially rose rapidly, then slowly, and finally were again accelerated fast. The two flux ropes are also identified in the STEREO A and B 195 Å (∼1.4 MK), 304 Å (0.06-0.08 MK), 284 Å (∼1.8 MK), and 171 Å (∼1.0 MK) observations. We suggest that the flux ropes may have both hot and cool components. Investigating the flux rope eruptions with their associated CME, we find that the erupting flux ropes are co-spatial with the CME bright core and the expanding overlying flux loops with the CME bright front.

Context. The Sun is very quiet with less sunspots and activity since the beginning of solar cycle 24. However, the active region (AR) 11 045 emerged on February 5, 2010, is associated with 43 (8 M-and 35 C-class) flares, 53 coronal mass ejections (CMEs), 29 filament eruptions, 19 extreme ultraviolet (EUV) waves and abundant jets, indicating that this AR is the first productive one of solar cycle 24. Aims. We study the AR evolution and its associated activities, and also their relationships, to understand this productive AR. Methods. We used SOHO/MDI magnetograms to study the magnetic fields, STEREO/SECCHI images to explore the activities, and GOES measurements to investigate the soft X-ray flux of the AR. Results. During the AR evolution, six pairs of main magnetic fields emerged, and 93.1% flares and 82.75% filament eruption occurred in the emergence and stable phases of the magnetic flux. However, 43.4% CMEs occurred in the decaying phase, even though there were less flares. An example is given to show that an event is related to a flare, a filament eruption, a CME and an EUV wave from inner corona to outer corona in space, and the filament eruption and EUV wave occur near the peak time of the flare. Among the 29 filament eruptions, 79.3% are associated with CMEs, as well as 58.6%, associated with flares, and 34.5%, associated with EUV waves. During the 12-day active phase, 575 jets are detected with a daily occurrence rate of 49.3. This is the first time that so many jets have been identified in one AR, implying at least 575 lower magnetic reconnection processes during the AR evolution. We statistically studied these jets along with the AR evolution, and noticed that the jets mostly occurred surrounding the emerging flux. We also investigated the spatio-temporal relationships between the jets and the flares, and find that the jets are usually rooted around the flare cores, and the soft X-ray flux is inverse correlated with the number of the jets, especially during the beginning 9 days since the AR emergence. In comparison with AR 11045, we studied the other newly emerging AR 11045, and obtained similar results. The relationships between the jets and the flares may well represent a scenario of two-step magnetic reconnection. Using schematic diagrams, we explain the remarkable magnetic field emergence, cancelation and shear motion of AR 11045, and its associated activities.