اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدPhotospheric flux cancellation and associated flux rope formation and eruption
142
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We study an evolving bipolar active region that exhibits flux cancellation at the internal polarity inversion line, the formation of a soft X-ray sigmoid along the inversion line and a coronal mass ejection. The evolution of the photospheric magnetic field is described and used to estimate how much flux is reconnected into the flux rope. About one third of the active region flux cancels at the internal polarity inversion line in the 2.5~days leading up to the eruption. In this period, the coronal structure evolves from a weakly to a highly sheared arcade and then to a sigmoid that crosses the inversion line in the inverse direction. These properties suggest that a flux rope has formed prior to the eruption. The amount of cancellation implies that up to 60% of the active region flux could be in the body of the flux rope. We point out that only part of the cancellation contributes to the flux in the rope if the arcade is only weakly sheared, as in the first part of the evolution. This reduces the estimated flux in the rope to $sim!30%$ or less of the active region flux. We suggest that the remaining discrepancy between our estimate and the limiting value of $sim!10%$ of the active region flux, obtained previously by the flux rope insertion method, results from the incomplete coherence of the flux rope, due to nonuniform cancellation along the polarity inversion line. A hot linear feature is observed in the active region which rises as part of the eruption and then likely traces out field lines close to the axis of the flux rope. The flux cancellation and changing magnetic connections at one end of this feature suggest that the flux rope reaches coherence by reconnection shortly before and early in the impulsive phase of the associated flare. The sigmoid is destroyed in the eruption but reforms within a few hours after a moderate amount of further cancellation has occurred.
قيم البحث
اقرأ أيضاً
The formation and evolution process and magnetic configuration of solar prominences remain unclear. In order to study the formation process of prominences, we examine continuous observations of a prominence in NOAA AR 10953 with the Solar Optical Tel
escope on the emph{Hinode} satellite. As reported in our previous Letter, we find a signature suggesting that a helical flux rope emerges from below the photosphere under a pre-existing prominence. Here we investigate more detailed properties and photospheric indications of the emerging helical flux rope, and discuss their relationship to the formation of the prominence. Our main conclusions are: (1) A dark region with absence of strong vertical magnetic fields broadens and then narrows in Ca textsc{ii} H-line filtergrams. This phenomenon is consistent with the emergence of the helical flux rope as photospheric counterparts. The size of the flux rope is roughly 30,000 km long and 10,000 km wide. The width is larger than that of the prominence. (2) No shear motion or converging flows are detected, but we find diverging flows such as mesogranules along the polarity inversion line. The presence of mesogranules may be related to the emergence of the helical flux rope. (3) The emerging helical flux rope reconnects with magnetic fields of the pre-existing prominence to stabilize the prominence for the next several days. We thus conjecture that prominence coronal magnetic fields emerge in the form of helical flux ropes that contribute to the formation and maintenance of the prominence.
Coronal mass ejections (CMEs) are one of the primary manifestations of solar activity and can drive severe space weather effects. Therefore, it is vital to work towards being able to predict their occurrence. However, many aspects of CME formation an
d eruption remain unclear, including whether magnetic flux ropes are present before the onset of eruption and the key mechanisms that cause CMEs to occur. In this work, the pre-eruptive coronal configuration of an active region that produced an interplanetary CME with a clear magnetic flux rope structure at 1 AU is studied. A forward-S sigmoid appears in extreme-ultraviolet (EUV) data two hours before the onset of the eruption (SOL2012-06-14), which is interpreted as a signature of a right-handed flux rope that formed prior to the eruption. Flare ribbons and EUV dimmings are used to infer the locations of the flux rope footpoints. These locations, together with observations of the global magnetic flux distribution, indicate that an interaction between newly emerged magnetic flux and pre-existing sunspot field in the days prior to the eruption may have enabled the coronal flux rope to form via tether-cutting-like reconnection. Composition analysis suggests that the flux rope had a coronal plasma composition, supporting our interpretation that the flux rope formed via magnetic reconnection in the corona. Once formed, the flux rope remained stable for 2 hours before erupting as a CME.
We investigate the formation, activation and eruption of a flux rope from the sigmoid active region NOAA 11719 by analyzing E(UV), X-ray and radio measurements. During the pre-eruption period of ~7 hours, the AIA 94 A images reveal the emergence of a
coronal sigmoid through the interaction between two J-shaped bundles of loops which proceeds with multiple episodes of coronal loop brightenings and significant variations in the magnetic flux through the photosphere. These observations imply that repetitive magnetic reconnections likely play a key role in the formation of the sigmoidal flux rope in the corona and also contribute toward sustaining the temperature of the flux rope higher than the ambient coronal structures. Notably, the formation of the sigmoid is associated with the fast morphological evolution of an S-shaped filament channel in the chromosphere. The sigmoid activates toward eruption with the ascend of a large flux rope in the corona which is preceded by the decrease of photospheric magnetic flux through the core flaring region suggesting tether-cutting reconnection as a possible triggering mechanism. The flux rope eruption results in a two-ribbon M6.5 flare with a prolonged rise phase of ~21 min. The flare exhibits significant deviation from the standard flare model in the early rise phase during which a pair of J-shaped flare ribbons form and apparently exhibit converging motions parallel to the polarity inversion line which is further confirmed by the motions of HXR footpoint sources. In the later stages, the flare follows the standard flare model and the source region undergoes a complete sigmoid-to-arcade transformation.
Flux ropes are generally believed to be core structures of solar eruptions that are significant for the space weather, but their formation mechanism remains intensely debated. We report on the formation of a tiny flux rope beneath clusters of active
region loops on 2018 August 24. Combining the high-quality multiwavelength observations from multiple instruments, we studied the event in detail in the photosphere, chromosphere, and corona. In the source region, the continual emergence of two positive polarities (P1 and P2) that appeared as two pores (A and B)is unambiguous. Interestingly, P2 and Pore B slowly approached P1 and Pore A, implying a magnetic flux convergence. During the emergence and convergence, P1 and P2 successively interacted with a minor negative polarity (N3) that emerged, which led to a continuous magnetic flux cancellation. As a result, the overlying loops became much sheared and finally evolved into a tiny twisted flux rope that was evidenced by a transient inverse S-shaped sigmoid, the twisted filament threads with blueshift and redshift signatures, and a hot channel. All the results show that the formation of the tiny flux rope in the center of the active region was closely associated with the continuous magnetic flux emergence, convergence, and cancellation in the photosphere. Hence, we suggest that the magnetic flux emergence, convergence, and cancellation are crucial for the formation of the tiny flux rope.
Zipper reconnection has been proposed as a mechanism for creating most of the twist in the flux tubes that are present prior to eruptive flares and coronal mass ejections. We have conducted a first numerical experiment on this new regime of reconnect
ion, where two initially untwisted parallel flux tubes are sheared and reconnected to form a large flux rope. We describe the properties of this experiment, including the linkage of magnetic flux between concentrated flux sources at the base of the simulation, the twist of the newly formed flux rope and the conversion of mutual magnetic helicity in the sheared pre-reconnection state into the self-helicity of the newly formed flux rope.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
