| 其他摘要 | As explosive energy release phenomena in the solar atmosphere, solar eruptions could be accompanied by the ejection of a vast amount of magnetized plasma into the interplanetary space, making our near-earth space a hazardous place. Understanding the physical origin of solar eruptions and achieving accurate predictions of their geoeffectiveness are among the most important research goals in both solar and space physics. In this thesis, taking advantage of the high-resolution and multi-wavelength data from the recent satellites and instruments，such as the Solar Dynamics Observatory(SDO)，the new vacuum solar telescope(NVST), and the Solar Terrestrial Relations Observatory(STEREO), we conduct a series of observational studies on real solar eruptions, mainly focusing on their pre-flare activities and complex dynamic phenomena. By applying the state-of-art analysis methods, i.e., magnetic field extrapolation, magnetic helicity calculation, decay index analysis, and the differential emission measure inversion，we investigate in detail the pre-eruption magnetic configuration and the triggering mechanisms of solar eruption events, and also explore the physical causes of their associated complex eruptive dynamic phenomena and behaviors. The main contents can be divided into the following three parts.1. Diagnose their pre-eruption structures and triggers from short-term precursors (1) we study the onset process of a solar eruption on 2015 February 21, focusing on its unambiguous precursor phase. With multiwavelength imaging observations from the Atmospheric Imaging Assembly (AIA), definitive tether-cutting (TC) reconnection signatures, i.e., flux convergence and cancellation, bidirectional jets, and topology change of hot loops, were clearly observed below the pre-eruption filament. As TC reconnec tion progressed between the sheared arcades that enveloped the filament, a channel-like magnetic flux rope (MFR) arose in multiwavelength AIA passbands wrapping around the main axis of the filament. With the subsequent ascent of the newborn MFR, the filament surprisingly split into three branches. After a 7 hr slow-rise phase, the high-lying branch containing the MFR abruptly accelerated causing a two-ribbon flare; while the two low-lying branches remained stable forming a partial eruption. Complemented by kinematic analysis and decay index calculation, we conclude that TC reconnection played a key role in building up the eruptive MFR and triggering its slow rise. The onset of the torus instability may have led the high-lying branch into the standard eruption scenario in the fashion of a catastrophe. (2) We study the early evolution of a hot-channel like magnetic flux rope (MFR) toward eruption in solar active region 12010. Combining with imaging observation and magnetic field extrapolation, we find that the hot channel possibly originated from a preexisting seed MFR with a hyperbolic flux tube (HFT). In the precursor phase, three-dimensional tether-cutting reconnection at the HFT is most likely resulting in the heating and buildup of the hot channel. In this process, the forming hot channel was rapidly enlarged at its spatial size and slipped its feet to two remote positions. Afterward, it instantly erupted outwards with an exponential acceleration, leaving two core dimmings near its feet. We suggest that preflare reconnection at the HFT played a crucial role in enlarging the seed MFR and facilitating the onset of its final solar eruption. Moreover, we further explain the so-called ”elongation-to-expansion” transition of two-ribbon flare based on three-dimensional eruption theory. (3) We study the triggering process of a major solar eruption within a multipolar active region 11515, which associated with a series of recurrent coronal jets and UV brightenings. We find a newly emerged filament system was moving towards the opposite-polarity feet of high-lying coronal loops, resulting in an enhanced current interface. Accordingly, recurrent magnetic reconnection took place over there, causing the formation of coronal jets and also reducing the magnetic constraint over the small filament. Afterward, the small filament gradually lost its equilibrium and further resulted in a major CME and an M5.6 flare. Via magnetic extrapolation and energy calculation, we find in the pre-flare phase of this event, there was enough free magnetic energy for major solar eruption, but it kept stable until the occurrence of recurrent jets. Moreover, a part of free energy was also recurrently released during the coronal jets. These observations provide clear evidence that pre-flare reconnection plays a key role to trigger the onset of solar eruption within a multipolar configuration. 2. Quest their structure formation and plasma supply from long-term precursors(1) We present observations of the formation process of a small-scale filament on the quiet Sun during 6 February 2016 and investigate its formation cause. We find that the dipolar twisted emerging fields within a supergranule can lead to the formation of the filament via reconnection with pre-existing fields and release of its inner magnetic twist. Consistent with the dextral chirality of the filament, magnetic helicity calculations show that an amount of negative helicity was persistently injected from the rotational positive magnetic element and accumulated during the formation of the filament. In addition, we suggest that the emergence of AFS and ensuing reconnection during the formation course of the filament may be beneficial for its final plasma accumulation. (2) With the high-resolution chromospheric observations, we study the detailed formation and destabilization of a solar mini-filament. We find that: the strong shearing flow and converging flow near the PIL play a key role in the formation of a mini-filament channel. Meanwhile, clear evidence shows that short chromospheric fibrils were keeping to reconfigure with each other and finally build up the filament channel via a cascade-like coalescence process. The off-band 𝐻𝛼 observations and reconstructed doppler proxy map show that persistent blueshift signals existed along the filament channel, implying that persistent cool plasma upflow from the chromosphere may be responsible for the filament mass supply. Besides, the activated mini-filament demonstrated several unique doppler signals, suggesting that mini-filament possessed flux-rope configuration and suffered from MHD instability before its eruption. 3. Find the physical causes of their associated complex dynamic phenomena(1) We revisit the hot channel eruption in solar active region 12010, and investigate the footpoint drift behavior of the eruptive solar magnetic flux rope(MFR). we find that MFR’s west footpoint drift was induced by a new reconnection geometry among the erupting MFR’s leg and thereby inclined arcades. As MFR’s west footpoints gradually drifted to a new position, a set of newborn atypical flare loops connected into the west core dimming, causing a rapid decrease of dimmed area inside this core dimming and also generating a secondary flare ribbon at their remote feet. This reveals that core dimmings may suffer a pronounced diminishment due to the eruptive MFR’s footpoint drift, implying that mapping the real footpoints of the erupting MFR down to the Sun’s surface is more difficult than previously thought. (2) We study two external forced magnetic reconnection events near NOAA active region 12494 for their current sheet (CS) formation. In both events, small-scale reconnection happened between mini-filaments and other preexisting magnetic fields. Initially, mini-filaments underwent obvious non-radial rotating motion due to their loss of equilibrium. With their clockwise/anti-clockwise rotation, the axial fluxes of the mini-filaments slowly came to squeeze the anti-parallel ambient fields, leading to an X-shaped structure. As the squeezing effect strengthened, CS regions gradually formed and grew in length, with a temperature of around 1.8 MK. Based on the multiwavelength imaging observations, the apparent thickness/length, temperature/emission of the CS regions, and their related plasma flows are carefully analyzed. Their reconnection rates are roughly estimated as 0.01–0.06 and 0.01–0.02. In particular, a chain of high-speed plasmoid ejections was detected along with a set of the reconnected field lines in Event1, implying the onset of tearing-mode instability inside its CS region. These observations indicate that non -radial rotating motion of filaments can serve as external flows to drive reconnection, and also provide a basic scenario of CS formation within small-scale magnetic reconnection processes. (3) With stereoscopic observations, we revisit the major solar eruption within AR 11515, and further investigate the multi-scale coupling process between a small filament eruption and a giant prominence-involved CME. We find that the erupting small filament resulted in the rapid buildup of a large-scale MFR within 20 minutes via interacting and reconnecting with background fields. During this process, the magnetic twist and cool plasma that pre-stored in the erupting small filament was observed to transform into another remote leg of the newborn MFR. Eventually, the newborn large-scale MFR soon lost its equilibrium yielding a giant CME. This research provides clear evidence that a small-scale eruption can induce a staller-sized CME by a multi-scale magnetic coupling process. |
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