Discovery of Long-Period Magnetic Field Oscillations and Motions in Isolate Sunspot

Sunspots are relatively dark regions on the solar surface where the magnetic field is strongest. This field is generated by a large-scale dynamo in the solar interior and driven upwards by plasma buoyancy until it emerges through the surface. The interaction of plasma motions and magnetic fields results in a plethora of magnetohydrodynamical processes, still poorly understood, that give rise to solar activity. Here we report on the discovery of oscillations and dynamical phenomena with characteristic periods and timescales of several hours. We analyse the temporal evolution of the inclination component of the magnetic field vector for the penumbral area of 25 isolated sunspots. The usage of data from Helioseismic and Magnetic Imager (HMI; Scherrer et al. 2012, Schou et al. 2012) on board the Solar Dynamics Observatory (SDO; Pesnell et al. 2012), allows the study of very long time-series with a good spatial and temporal resolution. We have used the wavelet technique and we have found some filamentary-shaped events with large wavelet power. Their distribution of periods is broad ranging from one hour (the lower limit for this study) up to 90 hours. An interesting property of these events is that they do not appear homogeneously all around the penumbra but they seem to concentrate at particular locations. Our data show that the motions occur predominantly in those areas of the penumbra facing the opposite magnetic polarity, either within or outside its active region. The cross-comparison of these wavelet maps with AIA data shows that the regions where these events appear are, visually, related with the coronal loops that connect the outer penumbra to one or more neighbouring opposite polarity flux patches.