The dipole moment observed by the WSO during the pre-minimum years of the last 4 solar cycles are used to establish a relation with the sunspot numbers of the following maximum years. The relation is then used to calculate the dipole moment for all the past cycles.
We observed magnetoacoustic waves propagating along the magnetic field lines of a sunspot. Based on the wave periods and atmospheric characteristics, we reconstructed the magnetic field topology of the sunspot.
Numerical simulation of sunspots indicate that different subsurface structures are possible. They may be deep coherent flux tubes or twisted spaghetti or shallow structures. It may well be that all the models proposed for sunspot structures are correct for some spot somewhere.
We present potential filed and nonlinear force-free magnetic field (NLFFF) extrapolations of full-disk magnetogram observed by SDO/HMI instrument. The study shows that NLFFF model agrees significantly better with coronal magnetic loops as observed in SDO/AIA images.