Very Large Array Observations of Solar Active Regions. IV. Structure and Evolution of Radio Bursts from 20 cm Loops.

The Very Large Array (VLA) has been used to study the structuree and evolution of six solar bursts near 20 cm wavelength. In most ccases the burst emission has been resolved into looplike structures with total lengths, Lapprox.3 x 10/sup 9/ cm, brightness temperatures T/sub B/approx.10/sup 7/-10/sup 8/ K, and degrees of circular polarization p/sub c/< or approx. =90%. changes in the total intensity and circular polarization of the bursts occur on time scales as short as 10 s. The individual peaks of one multiple-component burst originated in different locations within a magnetically complicated region. Preburst heating occurred minutes before the onset of the impulsive phase of one burst, and circular polarization changes occurred minutes before the onset of the impulsive phase of another burst. In one case, a loop system emerged in the vicinity of the impulsive source, and two adjacent loop systems may have emerged and triggered the burst.