Expanding arch structure of a solar radio outburst

Abstract

A flare-associated complex outburst was observed on 1968, October 23–24 with the 80 MHz Culgoora radioheliograph. Two harmonic type II bursts were followed by two successive extended sources with arch structure which appeared further beyond the optical limb than the preceding sources. The second arch showed a remarkable expansion with a projected velocity of 1200 km/sec. At its maximum the arch extended to a height of 2R _⊙. The height-time plots derived from both the radioheliograph and spectrum observations suggest that two shock waves of different propagation velocities were initiated at the flash phase of the flare: the faster one was responsible for the first type II burst and the first radio-emitting arch; the slower one for the second type II burst and the second arch whose expansion advanced with the shock front.