Sunspot transition region oscillations in NOAA 8156

Abstract

Based on observations obtained with the Solar and Heliospheric Observatory - SOHO joint observing program for velocity fields in sunspot regions, we have detected 3 min transition region umbral oscillations in NOAA 8156. Simultaneous recordings of O V $\lambda$629 and N V $\lambda$1238, $\lambda$1242 with the SUMER instrument give the spatial distribution of power in the 3 min oscillations, both in intensity and line-of-sight velocity. Comparing loci with the same phase we find that the entire umbral transition region oscillates. The observed maxima in peak line intensity are nearly in phase with the maxima in velocity directed towards the observer. We discuss the suggestion that the waves are upward propagating acoustic waves.