Catastrophe Of Coronal Magnetic Flux Ropes And Associated Phenomena

The solar-terrestrial system is mainly disturbed by large-scale solar eruptions,which include prominence/filament eruptions,flares and coronal mass ejections.These phe-nomena are strongly correlated with each other.In fact,they are usually considered to be different manifestations of a single coronal flux rope eruption.It is of great signif-icance in improving space weather forecast to investigate the eruptive mechanism of coronal flux ropes.In this paper,we mainly focus on the catastrophe of coronal magnetic flux rope and the associated observational phenomena.First,by numerical simulations,we in-vestigate the catastrophic behaviors of coronal magnetic flux ropes systems,including the evolutionary profiles of the system under different photospheric flux distributions,different types of catastrophes in the flux rope systems,et al.In addition,we also in-vestigate the oscillating properties of some coronal structures and the associated EUV wave,which originated from a solar eruption.1.Catastrophic behaviors of coronal magnetic flux ropesDue to the limit of current observing technologies,coronal magnetic structures can-not be directly measured.What we can observe is the photospheric magnetic conditions.In order to shed light on the flare/CME productivity of active regions,we simulate the evolutionary profile of a coronal flux rope system under different photospheric magnet-ic conditions.It is found that there is close relationship between the upward catastrophe and the photospheric flux distribution:upward catastrophe occurs only when the pho-tospheric flux is not concentrated too much toward the polarity inversion line and the source regions are not too weak,no matter whether the background field is partially open or fully closed.This implies that the openness of the background field in not the only determinant of the catastrophe:any parameter could influence the catastroph-ic behaviors of the system,provided that its different values could result in different background configurations.Moreover,the amplitude of the upward catastrophe and the released magnetic energy during it are also influenced by the photospheric magnet-ic condition:the larger the distance between the positive and the negative polarities and the stronger the source regions,the catastrophic evolution is more drastic,indicating that the flux rope system is more active.Apart from the widely analyzed upward catastrophe,we find that there also exists another catastrophe,during which the flux rope falls down to the photosphere,so that it is called downward catastrophe.Although there is no magnetic reconnection in the simulation,magnetic energy is also released by the work done by Lorentz force during the downward catastrophe.The amount of the released magnetic energy is comparable to that of a medium flare,indicating that Lorentz force plays an important role in the catastrophic evolution of the system.Furthermore,we investigate the influence of the photospheric magnetic conditions on downward catastrophes.It is also found that there is close relationship between the downward catastrophe and the photospheric magnetic conditions.Moreover,upward and downward catastrophes are always paired in differ-ent flux rope systems.2.Observational study about the solar eruptions triggered by flux-deeding proceduresBy analyzing the observations of a prominence eruption,we found that there exist flux-feeding procedures,which occurred at least 3 times within the 2-day period before the eruption.During each flux-feeding procedure,chromospheric fibrils rose upward,interacted with the target prominence,and finally merged with it.This procedure fed magnetic flux into the target prominence,which increased the slow rise speed of the prominence,finally resulting in the eruption of the prominence.By calculating the de-cay of the external magnetic field with height,we conclude that it is the flux-feeding procedures that increased the equilibrium height of the prominence,so that torus insta-bility occurred when the prominence reached the height with fast enough decay of the external magnetic field.Therefore,the flux-feeding procedure is the main trigger of this prominence eruption.By comparison with the catastrophic behaviors of coronal magnetic flux rope sys-terns obtained from numerical simulation,it is found that the eruption should correspond to a catastrophe triggered by large enough magnetic flux inside the flux rope contain-ing the prominence.The flux-feeding procedures kept feeding magnetic flux into the system,so that the magnetic flux reached the catastrophic point,which was also the marginal state of torus instability,so that the dynamic process of the catastrophe mani-fested as torus instability.3.Analysis of the wave and the oscillations resulting from solar eruptive ac-tivitiesLarge-scale solar eruptions could result in many other observational processes.Here we also study a large-scale EUV wave,which originated from a solar eruption.After the wave passage,a prominence and a bundle of coronal loops were triggered to oscillate.From the oscillating parameters of the prominence and the coronal loops,we estimate the local physical properties around the oscillating structures.Moreover,combining with the spatial properties of the relevant structures,we also roughly estimate the propagating height and the energy of the EUV wave.