Sources of the slowly-varying component of solar microwave emission and their relationship with their host active regions

Daily surveys of the solar disc made at 2.8 cm wavelength over the period 1 -13 November 1981, complemented by magnetograms and H alpha filtergrams, ar e used to examine the relationship between sources of the slowly varying co mponent of solar radio emission and properties of their host regions. Two c lasses of source are noted: diffuse and compact. Sources are designated com pact when smaller than 40''. The diffuse sources may be explained in terms of free - free thermal emission from trapped plasma in loops overlying the active region. The great majority of compact sources can be accounted for i n terms of gyroresonance from thermal electrons in the strong magnetic fiel ds overlying sunspots. A small minority are less amenable to this explanati on. They are associated with magnetic complexity and dynamism, lie close to magnetic polarity reversals, and could be non-thermal. Microwave sources a re an evolutionary feature common to all but the smallest active regions.