U-shaped type II solar radio bursts associated with the 1980 March 28 flare

Abstract

Observations of the 1980 March 28, 2B flare in optical, radio microwave and metric and X-ray wavelengths are presented. In the dynamic radio spectrum, unusual and rare U-shaped type II radio bursts associated with this flare have been observed. The normal type II bursts display negative frequency drift, due to the flare-triggered shock wave travelling outwards in the solar corona. But in this case the type II emission first showed the usual negative frequency drift, and then after reaching a plateau level, showed a positive drift, thus giving the shape of an inverted "U". The authors propose a model for this type II emission.We suggest that the shock wave generated by the flare or the flare spray propagates through sucting and repeated reflections, which takes place within a large scale coronal loop or an arcade of loops, thus resulting in reverse frequency drift in type II emission.