ON THE NATURE OF UMBRAL OSCILLATIONS: THEORY AND OBSERVATION BY CDS/SOHO

摘要

We will present solutions for magneto-acoustic-gravity (or MAG) waves. The possible wave modes in the 3-5 min range will be discussed. We will then present observations of sunspots performed in the EUV wavelength range with 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 is contained in the 5-7 mHz frequency range. When the CDS slit crosses the sunspot plume a clear 3 min oscillation is observed. The observations are interpreted in terms of slow magnetoacoustic waves propagating upwards.