COMPACT SOURCES OF SUPRATHERMAL MICROWAVE EMISSION DETECTED IN QUIESCENT ACTIVE REGIONS DURING LUNAR OCCULTATIONS

Solar quiescent active regions are known to exhibit radio emission from discrete structures. The knowledge of their dimensions and brightness temperatures is essential for understanding the physics of quiescent, confined plasma regions. Solar eclipses of 10 August, 1980 and 26 January, 1990, observed with high sensitivity and high time resolution at 22 GHz, allowed an unprecedented opportunity to identify Fresnel diffraction effects during lunar occultations of active regions. The results indicate the presence of quiescent discrete sources smaller than one arcsecond in one dimension. Assuming symmetrical sources, their brightness temperatures were larger than 2 x 10(7) K and 8 x 10(7) K, for the 1980 and 1990 observations, respectively.