Compact sources of suprathermal microwave emission detected in quiescent active regions during lunar occulatations

Abstract

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 28 January 1990, observed with high sensitivity (0.01 s.f.u.) and high time resolution (30 ms) at 22 GHz, allowed the unprecedented opportunity to identify Fresnel diffraction effects during lunar occultations of active regions. The present results indicate the presence of quiescent discrete sources smaller than one arcsecond in one dimension that can be associated to the compact sources of suprathermal microwave emission. Assuming symmetrical sources, their brightness temperatures were larger than 2x10⁷ K and 8x10⁷ K, for the 1980 and 1990 observations, respectively. From energetic point of view the results give new information about confinement of plasmas in active regions.

In memorian, 1942–1981.