OSCILLATIONS OF SUNSPOT MAGNETIC-FIELDS

We report on velocity and magnetic field oscillations observed in suns pots using the MDI instrument onboard SOHO. In addition to the well-kn own velocity oscillations, the data clearly show highly localised osci llations of the magnetogram signal in different parts of the sunspots. We show that only oscillations of the magnetic field vector can produ ce the observed magnetogram oscillations, and that the observed phase relations suggest an origin in terms of magnetoacoustic gravity waves.