Multi-scale temporal features of the 14 July 2000 meter- wavelength dynamic radio spectrum compared with TRACE data

Abstract

The 14 July 2000 (`Bastille Day') eruptive and geoeffective flare event was observed by the digital IZMIRAN radio spectrograph in the frequency range of 25–270 MHz. This instrument allowed the analysis of various features of the dynamic radio spectrum and their comparison with other observational data, in particular with development of a spectacular EUV post-eruption arcade recorded aboard the Transition Region and Coronal Explorer (TRACE). (1) A compressed multi-hour radio spectrum shows that the event caused a conspicuous weakening of the pre-existing noise storm. This phenomenon was perhaps caused by interaction of a large halo coronal mass ejection (CME), recorded by the the Large Angle and Spectroscopic Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO), with emitting coronal structures. (2) Several type II bands are present at the initial and maximum phases of the flare event. The frequency drifts of the clearest bands correspond to the estimated shock wave speed of 1100–2300 km s−1 that is comparable with the CME speed observed in the sky plane. (3) Significant broadband enhancements of the metric radio emission took place around of 10:24–10:27 UT coinciding with sharp development of the EUV arcade in the northeast direction. It appears to correspond to the intensification of the electron acceleration in a process of post-eruption loop formation. (4) The high-resolution radio spectrum revealed a superposition of numerous type III-like bursts and/or pulsations with a time scale ranging from a few seconds to several tens of seconds. These features can be attributed particularly to successive formation of new loops of the arcade and corresponding temporal fragmentation of the electron acceleration in the course of the post-eruption reconnection. In summary, the analysis demonstrates the correspondence between the multi-scale temporal features of the metric radio emission and such phenomena as the CME and post-eruption EUV arcade. Some spectra, images, and movies illustrating the event are presented also on the accompanying CD-ROM.