| 其他摘要 | We use both the methods of numerical simulation and observation to explore the Associated Features of Coronal Mass Ejections. Based on the solar catastrophe model of Isenberg et al. (1993), we performed magnetohydrodynamics (MHD) numerical experiments to look into the disturbances caused by solar eruptions and the dynamic behavior of the current sheet (CS) between the coronal mass ejection (CME) and the associated solar flare. We conduct a statistical study of the kinetic features of supra-arcade downflows that are detected from multiple solar flares.In the work focusing on the disturbances, we find that, in addition to the phenomena shown by previous works, a new structure known as the plasma pile-up is also seen. As the disrupting magnetic structure moves outwards, a fast-mode shock is driven ahead of it. The fast-mode shock expands sidewards when propagating forward, and evolves to a crescent shape. Eventually the two ends of the crescent touch the bottom boundary and cause various types of disturbances behind the shock, including a shock echo. Associated is a plasma pile-up region produced by the plasma accumulation behind the echo. This is a brand new phenomenon that was not reported previously. Two features of the pile-up region draw our attention: first, its height from the bottom boundary is similar to that of some EUV waves, and second, its velocity is about 1/3 the velocity of the fast-mode shock along the low layer of the atmosphere, which is believed to be the location of the Moreton wave front. This suggests that the pile-up may be a source of the EUV waves as well. According to our numerical results, we also synthesize the “observed” SDO/AIA images in different wavebands. The results demonstrate that the characteristics of the EUV waves “observed”in different bands are indeed different, which is consistent with the true observational results regarding EUV waves in a certain sense. In addition, by comparing the simulation with the observation, the authors first proposed the method of confirming the echo, and further showed that the echo can be observed, confirming the “true wave” nature of the EUV waves. In the work of CME/flare CS, we note that, during the evolution, the disrupting magnetic configuration becomes asymmetric firstly in the buffer region at the bottom of the CME bubble. The Rayleigh-Taylor (RT) instability in the buffer region and the deflected motion of the plasma driven by the termination shock (TS) at the bottom of the CME bubble cause the buffer region to oscillate around the y-axis. The local oscillation propagates downward through the CS, prompting an overall CS oscillation. As the buffer region grows, the oscillation period becomes longer, increasing from about 30 s to about 16 min. Meanwhile, there is another separated oscillation with a period between 0.25 min to 1.5 min in the cusp region of the flare generated by velocity shearing. The tearing mode instability yields formations of plasmoids inside the CS. The motions of all the plasmoids observed in the experiment accelerate, which implies that the large scale CME/flare CS itself in the true eruptive event is filled with the diffusion region according the the standard theory of magnetic reconnection.In the work of statistical study of the kinetic features of supra-arcade downflows, we have developed a tracking algorithm to determine the speeds of supra-arcade downflows (SADs) and set up a system to automatically track the SADs and measure some interesting parameters. By conducting an analysis on six flares observed by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO), we detect more smaller and slower SADs than prior work due to the higher spatial resolution of our observational data. The inclusion of these events with smaller and slower SADs directly results in lower median velocities and widths than in prior work, but the fitted distributions and evolution of the parameters still show good consistency with prior work. The observed distributions of widths, speeds, lifetimes, and numbers of SADs in each image are consistent with log-normal distributions, indicating that there are random and unstable processes responsible for generating SADs during solar eruptions. Also, we find that the fastest SADs occur at approximately the middle of the height ranges. The number of SADs in each image versus time shows that there are “rest phases” of SADs, when few SADs are seen. These findings support the idea that SADs originate from a fluid instability. We compare our results with a numerical simulation that generates SADs using a mixture of the Rayleigh-Tayler instability (RTI) and the Richtmyer-Meshkov instability (RMI), and find that the simulation generates quantities that are consistent with our observational results. |
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