Oscillations in the wings of sunspot transition region lines

We explore a new approach to the investigation of optically thin emission lines by comparing the intensity variations in opposite wings of the spectral lines and apply the method to investigate the oscillations above sunspots. The observations show that it is easier to detect the 3 min oscillations above sunspots in the short wavelength ("blue") wing than in the long wavelength ("red") wing of the lines. The observed oscillations are compatible with the spectral line signatures of upwardly propagating acoustic waves.