The Observational Study Of Jets Under 3D Null Point Configuration

Magnetic reconnection is a common phenomenon that is ubiquitous in the solar atmosphere.It facilitates the release of energy stored in the magnetic field by permitting a change in the magnetic topology in an almost ideal plasma.Re-connection in three dimensions has been shown to be completely different in many fundamental respects from the classically studied process in two dimensions.The main thrust of reconnection theory at present is to understand the different ways in which it may take place in three dimensions.In the sun's atmosphere,coronal null point is common configuration,and it is often associated with the activity of solar.The jets are a common solar phenomena in the solar atmosphere,and their magnetic configuration are determined by the geometry and magnetic field of the jets,which is associated with null point reconnection.This can provide us a good experimental environment for the study of null point reconnection.The common factor in the numerous models that have been explored is the existence of a null point in the coronal magnetic field configuration that gives rise to the jet.Coronal null is a region that is susceptible to the build-up of current sheets where reconnection can occur in an explosive manner.Much of the literature on reconnection focusses on the two-dimensional problem,due to the theoretical and computational simplifications that this allows.However,it is now becoming clear that magnetic fields is rather complicated.Solar phenomena is often affected by magnetic field topology.Combined with the magnetic field topology,we can improve the understanding of the jets driving and heating mechanism.In this thesis,by means of excellent observations from SDO,GONG,and NVST,and NLFFF,three jets,which involve their complete eruption process,are studied in detail.The main results are included as below:By analyzing the excellent observations derived from the SDO on 2015 February 3,We present the detection of a small eruption and the associated quasi-circular ribbon flare during the emergence of a bipole.Under a fan dome,a sigmoid was rooted in a single magnetic bipole,which was encircled by neg-ative polarity.The nonlinear force-free field extrapolation shows the presence of twisted field lines,which can represent a sigmoid structure.The rotation of the magnetic bipole may cause the twisting of magnetic field lines.The activity of the sigmoid may be caused by collision between the positive polarity and a nearby negative polarity field region.The sigmoid displayed an ascending motion and then interacted intensively with the spine-like field.This type of null point reconnection in corona led to a violent blowout jet,and a quasi-circular flare ribbon was also produced.The magnetic emergence and rotational motion are the main contributors to the energy buildup for the flare,while the cancellation and collision might act as a trigger.By analyzing the observations obtained from the SDO and GONG on 2015 February 6,we present an observation of the interaction between a filament and coronal loops nearby the null point that produces a blowout surge.The activated filament is initially embedded below a dome of a fan spine configuration.Due to the ascending motion,the erupting filament reconnects with the outer spine-like field.We note that bidirectional flow and small bright blobs appear at the interaction region,which are direct reconnection evidence.As a result,some material of the filament blowout along the spine field line forming surge.We suggest that the successive reconnection occurring between the erupting filament and the coronal loops may lead to a strong thermal/magnetic pressure imbalance,resulting in a blowout surge.In addition,we present a study of a mini-filament erupting in association with a circular ribbon flare on 2014 March 17.The filament was initially located at the edge of sunspot,and the potential field extrapolation shows that it was embedded under a fan spine configuration.This event is different from above mentioned two events.Before the eruption,a circular flare ribbon,as a signature of reconnection at the null point,was observed around the filament at the begin of brightening of the filament.We conjecture that the null point reconnection is of the "breakout" type and facilitates the eruption of the filament by removing field lines above the filament.