Very Large Array observations of solar active regions. IV Structure and evolution of radio bursts from 20 centimeter loops
It is pointed out that centimeter wavelength (2 or 6 cm) observations with the Very Large Array (VLA) at high angular resolution and moderate time resolution have provided new insights into the physics of solar radio bursts. However, there have been comparatively few VLA observations of solar bursts at the longer 20 cm wavelength. The present investigation is concerned with a VLA analysis of six bursts from 20 cm loops. The Very Large Array was used to observe the active region AR 3804 on July 12-20, 1982 at 1380 MHz, 1540 MHz, or 1705 MHz. Attention is given to time profiles and 10 s snapshot maps which describe the evolution of the 20 cm bursts, preburst heating, and changes in magnetic structure before and during the bursts. The observations presented provide new insight into the evolution of solar microwave bursts and the physical processes which may trigger them. In one case, the intense components of multiple bursts originated in different sources, suggesting that a number of loops may have become successively activated like some complex X-ray bursts.