Radio bursts with rapid frequency variations - Lace bursts

The Ondrejov radiospectrograph operating in the 0.8-2.0 GHz frequency range recorded in recent years (1998-2000), three (August 10, 1998; August 17, 1 999; June 27, 2000) unique bursts with rapid frequency variations (lace bur sts) lasting for several minutes. On August 17, 1999, the same burst was re corded simultaneously by the Brazilian Solar Spectroscope in the 1.0-2.5 GH z frequency range. The frequency variations of these bursts in four time in tervals were analyzed by the Fourier method and power-law spectra with powe r-law indices close to -2 were found. The Fourier spectra show the presence of frequency variations in the 0.01-3.0 Hz interval which indicate fast ch anges of plasma parameters in the radio source. Due to the similarities in the line features of these bursts with zebra pattern lines, a model similar to that of the zebra pattern was suggested. The model radio spectra, compu ted using this model with a turbulent state of the solar are atmosphere, ar e similar to those observed by the radiospectrographs.