  The knowledge of magnetic topology is the key to understand magnetic energy
release in astrophysics. Based on observed vector magnetograms, we have
determined threedimensional (3D) topology skeleton of the magnetic fields in
active region NOAA 10720. The skeleton consists of six 3D magnetic nulls and a
network of corresponding spines, fans, and null-null lines. For the first time,
we have identified a spiral magnetic null in Sun's corona. The magnetic lines
of force twisted around the spine of the null, forming a 'magnetic wreath' with
excess of free magnetic energy and resembling observed brightening structures
at extraultraviolet (EUV) wavebands. We found clear evidence of topology
eruptions which are referred to as the catastrophic changes of topology
skeleton associated with a coronal mass ejection (CME) and an explosive X-ray
flare. These results shed new lights in exploring the structural complexity and
its role in explosive magnetic activity. In solar astrophysics and space
science, the concept of flux rope has been widely used in modelling explosive
magnetic activity, although their observational identity is obscure or, at
least, lacking of necessary details. The current work suggests that the
magnetic wreath associated with the 3D spiral null is likely an important class
of the physical entity of flux ropes.
