| 其他摘要 | Solar filaments are fascinating and unique magnetic structures in our solarsystem. The intricate structure, dynamics and plasma parameters of filaments areclosely associated with the magnetic fields on the Sun. The filament formationinvolves the reconfiguration and then conversion of the magnetic fields on theSun to filament magnetic fields. However, how these fields are reconfigured andconverted to filament magnetic fields are not fully understood, and the detailedinformation on the magnetic structures of filaments is still unknown. The study ofthe filament formation could help not only in understanding the reconfigurationand then conversion of the magnetic fields on the Sun to filament magnetic fields,but also in understanding the supporting and the detailed magnetic structuresof filaments. In addition, as good tracers of magnetic flux ropes in the corona,the study of the filament formation could shed new light on the formation andevolution of magnetic flux ropes. In this thesis, by means of excellent observationsfrom SDO, SMART, and GONG, three filaments, which involve their completeformation process, are studied in detail. The main results are included as below:By analyzing the excellent observations derived from the SDO on 2012 August5-6, we present the first observation of the formation and eruption of a smallcircular filament driven by a rotating network magnetic field (RNF) in the quietSun. In the negative footpoint region of an inverse J-shaped dextral filament,the RNF was formed by the convergence to supergranular junctions of severalmagnetic flux patches of the same polarity, and it then rotated counterclockwise(CCW) for approximately 11 hr and showed up as a CCW rotating EUV cyclone,during which time the filament gradually evolved into a circular filamentthat surrounded the cyclone. When the calculated convergence and vortex flowsappeared around the RNF during its formation and rotation phases, the injectedmagnetic helicity calculation also showed negative helicity accumulation duringthe RNF rotation that was consistent with the dextral chirality of the filament.Finally, the RNF rotation stopped and the cyclone disappeared, and, probablydue to an emerging bipole and its forced cancellation with the RNF, the closurefilament underwent an eruption along its axis in the (clockwise) directionopposite to the rotation directions of the RNF and cyclone. These observationssuggest that the RNFs might play an important role in the formation of nearbysmall-scale circular filaments as they transport and inject magnetic energy andhelicity, and the formation of the EUV cyclones may be a further manifestationof the helicity injected into the corona by the rotation of the RNFs in thephotosphere. In addition, the new emerging bipole observed before the filamenteruption might be responsible for destabilizing the system and triggering themagnetic reconnection which proves useful for the filament eruption. From the observations of the formation of filament occurred on 2013 May29, we present rare observations that a filament is formed rapidly within 20 minutesby magnetic reconnection between two sets of dark threadlike structures.The two sets of dark threadlike structures belong to distinct flux systems withtheir adjacent ends anchored in an opposite-polarity magnetic field region, wherethe calculated photospheric velocity field showsthat converging flows dominatethere. Due to the converging flows, opposite-polarity magnetic flux convergedand then canceled, leading to the formation of extreme ultraviolet (EUV) brighteningthat spread in opposite directions along the spine of the dark threadlikestructures. Meanwhile, very weak remote brightening in the other terminalsof the dark threadlike structures, as well as EUV loops, which rooted in theopposite-polarity magnetic field region, appeared. In addition, all of the AIAFe line observations reveal that a flux rope was formed and underwent a rollingmotion during the fadeaway of the EUV brightening. Soon after, as the EUVbrightening disappeared, a filament that is very likely composed of two setsof intertwined dark threadlike structures was formed. Via differential emissionmeasure (EM) analysis, it is found that both the EM and temperature of theplasma around the flux-canceling site increased during the brightening, implyingthat there, magnetic reconnection may occur to heat the plasma. These observationsprovide evidence that the filament is formed by magnetic reconnectionassociated with flux convergence and cancellation, and the magnetic structure ofthe filament is most likely a flux rope.In addition, through detailed analysis of the growth of a filament that occurredon 2013 February 9, we present detailed observations that the growth ofthe filament caused by magnetic interaction among an active region filament,a superpenumbral filament, and a set of dark threadlike structure occurring atthe periphery of AR 11669. Multistep reconnections are identified during thewhole growing process. Magnetic flux convergence and cancellation occurring atthe positive footpoint region of the filament is the first step reconnection, whichresulted in the filament bifurcated into two sets of intertwined threads. Oneset of them anchored in situ, while the other set moved toward and interactedwith SF and part of T. This indicates the second step reconnection, which gaverise to the disappearance of SF and the formation of a long threadlike structurethat connecting the far ends of the filament and T. The long threadlike structurefurther interacted with T and then separated into two parts representing thethird step reconnection. Finally, another similar long threadlike structure, whichintertwining with the fixed filament threads, appeared. H observations showthat this twisted structure is a longer sinistral filament. Based on the observedphotospheric vector magnetograms, we performed a nonlinear force-free field extrapolationto reconstruct the magnetic fields above the photosphere and foundthat the coronal magnetic field lines associated with the filament consists of twotwisted flux ropes winding around each other. These results suggest that magneticinteractions among filaments and its adjacent superpenumbral filamentsand dark threadlike structures could lead to the growth of the filaments, and thefilament is probably supported in a flux rope. |
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