Short-period variations in the proper motions of sunspots from SOHO (MDI) observations

Short-period (1a60 min) variations in the coordinates of the centers of gravity of isolated sunspots are analyzed. The sunspot coordinated were determined using two sets of observational dataamagnetograms and intensitiesaobtained by SOHO (MDI) on December 6, 1998, from 01:00 to 21:57 UT with temporal resolution 60 s and spatial resolution 0.6a3/pixel. A slow drift in the sunspot coordinates was removed using a low-frequency filter with a 61-min integration window. The guiding errors (RMS0.014a3) were determined by analyzing correlated motions in pairs of sunspots, and were removed from the time series before determining the sunspot proper motions. Based on the calculated power spectra for the sunspot proper motions, two period intervals containing appreciable power were identified. One coincides with the well-known 5-min acoustic solar oscillations. The concentration of power in this interval is greater for the coordinate variations derived the magnetograms than those derived from the intensities; the harmonic amplitude for some peaks reaches A-30 km. The other spectral interval corresponds to periods exceeding 30 min. Overall, the rms short-period variations in the sunspot proper motions are 9.9A-2.2 and 16.7A-7.6 km (0.014a3A-0.003a3 and 0.024a3A-0.010a3) for the magnetogram and intensity data, respectively.