ИСТИНА

Application of some topological concepts such as twist, writhe, linkage and helicity to astrophysical magnetic fields implies a possibility to trace magnetic field lines and magnetic flux tubes. The point is that observational basis is very limited and typically we observe only specific components of magnetic field. Extrapolation enables to reconstruct magnetic field in given 3D volume and topological structure of the field obtained contains important information about generation processes. We discuss several problems that arise on the way of practical computation of topological invariants and consider different approaches.