ARE SHORT-TIME VARIATIONS OF THE SOLAR S-COMPONENT EMISSION IDENTICALWITH MICROWAVE-BURSTS

Extended time series (time resolution about 2-3 min) of spatially reso lved observations (greater than or equal to 17 arcsec) in one dimensio n of solar S-component sources obtained at the Siberian Solar Radio Te lescope (SSRT) at 5.2 cm wavelength allow the detection of evolutional features of the growth and decay of active regions in the solar coron a. Characteristic slow flux variations with timescales of about 1-2 ho urs occurring during the decay phase of the radio emission in the low corona above plages and sunspots are compared with recently detected s tep-like flux increases on timescales of about 10-20 min followed by q uasi-constant periods appearing in the initial phase of the developmen t of active regions. Superimposed on this basic behaviour, also fluctu ations at shorter timescales (or even periodic oscillations) have been observed. As it is well known from emission-model calculations, the v ariations of the S-component radiation can be due to variations of the magnetic field and/or changes of the energy of the radiating particle s, which is basically the same emission mechanism as for microwave bur sts. Since the ''S-component'' is originally defined by its long times cale behaviour derived from whole-Sun flux density measurements, the p resently detected small-timescale features in S-component sources requ ire either a revised definition of S-component emission or must be con sidered as ''burst-like''.