Variations of microwave emission from solar active regions

Based on observational data obtained with the RT-22 Crimean Astrophysical Observatory radio telescope at frequencies of 8.6 and 15.4 GHz, we investigate the quasi-periodic variations of microwave emission from solar active regions with periods T-p < 10 min. As follows from our wavelet analysis, the oscillations with periods of 3-5 min and 10-40 s have the largest amplitudes in the dynamic power spectra, while there are virtually no oscillations with T-p < 10 s. Our analysis shows that acoustic modes with T-p less than or similar to 1 min strongly dissipate in the lower solar corona due to thermal conduction losses. The oscillations with T-p = 10-40 s are associated with Alfven disturbances. We analyze the influence of acoustic and Alfven oscillations on the thermal mechanisms of microwave emission in terms of the homogeneous model. We discuss the probable coronal heating sources. (C) 2004 MAIK"Nauka/Interperiodica".