Temporal fluctuations of the magnetic field in sunspots

The magnetic field strength in sunspots was derived from time series of two -dimensional spectra taken with the Gottingen 2D-spectrometer at the Vacuum Tower Telescope on Tenerife in August 1997. For the present measurements t he magnetically sensitive line Fe i 684.3 nm was selected. The main spot of the investigated sunspot group has a maximum magnetic field strength of 22 70 G. Enhanced power of the magnetic field variations was found at the boun dary between umbra and penumbra for all frequency ranges. These fluctuation s are not well correlated with those of intensity variations or line shifts . Other spatial power peaks occur in a dark patch inside the centreside pen umbra and at the centres of some accompanying small spots. Since no clear p eaks at certain frequencies are found, the variations are not harmonic osci llations. A possible relation to H alpha flares is investigated. There are several cases of published observations of magnetic field variations where flares occurred soon after the measurements, but very little before. Theref ore it is not very probable that flares act as exciters of magnetic field v ariations.