Slow MAG waves in the sunspot umbra as observed by CDS/SoHO

We present observations, in the EUV wavelength range, of two sunspots, carried out by the Coronal Diagnostic Spectrometer (CDS) on SoHO. We examine the time series for the line intensities and relative velocities and calculate their power spectrum using wavelet transforms. We find oscillations in the chromosphere and transition region above the sunspots in the temperature range logT = 4.6 - 5.4. Most of the spectral power above the umbra are contained in the 5-7 mHz frequency range. When the CDS slit crosses the sunspot plume a clear 3 min oscillation is observed. We also present new solutions for magnetic-acoustic-gravity(or MAG) waves in the presence of radiative heat exchange based on Newton's law of cooling. The observed oscillation frequencies are compared with the computed frequencies. The observations are interpreted in terms of slow magnetoacoustic waves propagating upwards.status: publishe