Magnetic separators in three-dimensional (3D) magnetic fields are believed to be often associated with locations of magnetic reconnection. In this preliminary study, we investigate this relationship using data from a numerical resistive 3D MHD experiment of a solar flux emergence event. For the first time separators are detected in complex magnetic fields resulting from a 3D resistive MHD model of flux emergence. Two snapshots of the model, taken from different stages of its evolution, are analyzed. Numerous separators are found in both snapshots, and their properties, including their geometry, length, relationship to the magnetic null points, and integrated parallel electric field are studied. The separators reside at the junctions between the emerging flux, the overlying field, and two other flux domains that are newly formed by reconnection. The long separators, which connect clusters of nulls that lie either side of the emerging flux, pass through spatially localized regions of high parallel electric field and correspond to local maxima in integrated parallel electric field. These factors indicate that strong magnetic reconnection takes place along many of the separators, and that separators play a key role during the interaction of emerging and overlying flux.

Context. Solar coronal bright points have been studied for more than three decades, but some fundamental questions about their formation and evolution still remain unanswered. Aims. Our aim is to determine the plasma properties of a coronal bright point and compare its magnetic topology extrapolated from magnetogram data with its appearance in X-ray images.Methods. We analyse spectroscopic data obtained with EIS/Hinode, Ca ii H and G-band images from SOT/Hinode, UV images from TRACE, X-ray images from XRT/Hinode and high-resolution/high-cadence magnetogram data from MDI/SoHO. Results. The BP comprises several coronal loops as seen in the X-ray images, while the chromospheric structure consists of tens of small bright points as seen in Ca ii H. An excellent correlation exists between the Ca ii H bright points and increases in the magnetic field strength, implying that the Ca ii H passband is a good indicator for the concentration of magnetic flux. Furthermore, some of the Ca ii H bright points are the locations of the loop foot-points as determined from a comparison between the extrapolated magnetic field configuration and the X-ray images. Doppler velocities between 6 and 15 km s −1 are derived from the Fe xii and Fe xiii lines for the bright point region, while for Fe xiv and Si vii they are in the range from −15 to +15 km s −1 . The coronal electron density is 3.7 × 10 9 cm −3 . An excellent correlation is found between the positive magnetic flux and the X-ray light-curves. Conclusions. The remarkable agreement between the extrapolated magnetic field configuration and some of the loops composing the bright point as seen in the X-ray images suggests that a large fraction of the magnetic field in the bright point is close to potential. However, some loops in the X-ray images do not have a counterpart in the extrapolated magnetic field configuration implying a nonpotential component. The close correlation between the positive magnetic flux and the X-ray emission suggests that energy released by magnetic reconnection is stimulated by flux emergence or cancellation.

Aims. We present complete Hinode Solar Optical Telescope (SOT), X-Ray Telescope (XRT)and EUV Imaging Spectrometer (EIS) observations of an X-ray bright point (XBP) observed on the 10, 11 of October 2007 over its entire lifetime (∼12 h). We aim to show how the measured plasma parameters of the XBP change over time and also what kind of similarities the X-ray emission has to a potential magnetic field model. Methods. Information from all three instruments on-board Hinode was used to study its entire evolution. XRT data was used to investigate the structure of the bright point and to measure the X-ray emission. The EIS instrument was used to measure various plasma parameters over the entire lifetime of the XBP. Lastly, the SOT was used to measure the magnetic field strength and provide a basis for potential field extrapolations of the photospheric fields to be made. These were performed and then compared to the observed coronal features. Results. The XBP measured ∼15 in size and was found to be formed directly above an area of merging and cancelling magnetic flux on the photosphere. A good correlation between the rate of X-ray emission and decrease in total magnetic flux was found. The magnetic fragments of the XBP were found to vary on very short timescales (minutes), however the global quasi-bipolar structure remained throughout the lifetime of the XBP. The potential field extrapolations were a good visual fit to the observed coronal loops in most cases, meaning that the magnetic field was not too far from a potential state. Electron density measurements were obtained using a line ratio of Fe xii and the average density was found to be 4.95 × 10 9 cm −3 with the volumetric plasma filling factor calculated to have an average value of 0.04. Emission measure loci plots were then used to infer a steady temperature of log T e [K] ∼ 6.1. The calculated Fe xii Doppler shifts show velocity changes in and around the bright point of ±15 km s −1 which are observed to change on a timescale of less than 30 min.

The role of null-point reconnection in a three-dimensional numerical magnetohydrodynamic (MHD) model of solar emerging flux is investigated. The model consists of a twisted magnetic flux tube rising through a stratified convection zone and atmosphere to interact and reconnect with a horizontal overlying magnetic field in the atmosphere. Null points appear as the reconnection begins and persist throughout the rest of the emergence, where they can be found mostly in the model photosphere and transition region, forming two loose clusters on either side of the emerging flux tube. Up to 26 nulls are present at any one time, and tracking in time shows that there is a total of 305 overall, despite the initial simplicity of the magnetic field configuration. We find evidence for the reality of the nulls in terms of their methods of creation and destruction, their balance of signs, their long lifetimes, and their geometrical stability. We then show that due to the low parallel electric fields associated with the nulls, null-point reconnection is not the main type of magnetic reconnection involved in the interaction of the newly emerged flux with the overlying field. However, the large number of nulls implies that the topological structure of the magnetic field must be very complex and the importance of reconnection along separators or separatrix surfaces for flux emergence cannot be ruled out.

2005). A Topological Analysis of the Magnetic Breakout Model for an Eruptive Solar Flare.The magnetic breakout model gives an elegant explanation for the onset of an eruptive solar flare, involving magnetic reconnection at a coronal null point which leads to initially enclosed flux "breaking out" to large distances. In this paper we take a topological approach to the study of the conditions required for this breakout phenomenon to occur. The evolution of a simple delta sunspot model, up to the point of breakout, is analysed through several sequences of potential and linear force-free quasi-static equilibria. We show that any new class of field lines, such as those connecting to large distances, must be created through a global topological bifurcation, and derive rules to predict the topological reconfiguration due to various types of bifurcation.