Chirality And Magnetic Configurations Of Solar Filaments

Filaments are one type of significant activity in the solar atmosphere.Their erup-tions are strongly related to solar flares and coronal mass ejections,representing energy buildup and release of the magnetic field in the corona.On the other hand,their appear-ance is strongly shaped by the configuration of the supporting magnetic field.There-fore,filaments provide another window to diagnose the coronal magnetic configuration and magnetic chirality.It has been revealed that the magnetic topology in the solar atmosphere displays hemispheric preference,i.e.,negative/positive helicity in the northern/southern hemi-sphere,respectively.However,the strength of the hemispheric rule and its cyclic varia-tion are controversial.In this paper,we apply a new method based on filament drainage to 571 erupting filaments from 2010 May to 2015 December in order to determine the filament chirality and its hemispheric preference.The data cover both the rising and the beginning of the declining phase of solar cycle 24.It is found that 91.6%of our sam-ple of erupting filaments follow the hemispheric rule of helicity sign.It is found that the strength of the hemispheric preference of the quiescent filaments decreases slightly from～97%in the rising phase to～85%in the declining phase,whereas the strength of the intermediate filaments keeps a high value around 96±4%all the time.Only the active-region filaments show significant variations.Their strength of the hemispheric rule rises from～63%to～95%in the rising phase,and keeps a high value 82 ± 5%during the declining phase.Furthermore,during a half-year period around the solar maximum,their hemispheric preference totally vanishes.For the filaments that violate the hemispheric rule of helicity sign,the evolution of their magnetic fields is discussed.Besides,we also diagnose the magnetic configurations of the filaments based on our indirect method,and found that in our sample of erupting events,～89%are inverse-polarity filaments with a flux rope magnetic configuration,whereas～11%are normal-polarity filaments with a sheared arcade configuration.We also clarify two long-standing contentious issues about CMEs.First,we argue that a flux rope is not a necessary condition of a pre-eruption structure leading to a CME.Some pre-CME structures are flux ropes,and others are simply sheared arcade.As a filament rises,no matter it is supported by a flux rope or a sheared arcade,the ensuing magnetic re-connection below the core field would turn poloidal magnetic field to toroidal field,forming a new flux rope or growing a pre-existing flux rope which is later observed in CME eruptions;Second,we argue that the velocities of CMEs have nothing to do with the magnetic configurations of the accompanying filaments,they are determined by the magnetic field strength of the source region.Finally,we verify the magnetic configuration of classic barbs by comparing the longitudinal oscillation periods of the spine and barb.The results show that the spine and barb are held by magnetic dips with different curvature radii,the curvature radii of dips in the spine are larger than those in the barb terminal,and the curvature radii of the dips in the barb increase from the tip to the junction,and at the junction it becomes the same as in spine.We also find there are another type of barbs,unlike the classic one.Their endpoints do not extend downward and are not associated with parasitic polarity or minor neutral lines.They are comprised of filament threads which extend outside the spine,and their endpoints always extend upward.These barbs could be formed by the longitudinal oscillations or ordinary threads inside the filament spine.