Decimetric dot-like structures

Abstract

Various types of fine structures have been observed by the Brazilian Solar Spectroscope (BSS) in the frequency range of (1000 – 2000) MHz, since its regular operation from 1998. Here, we report for the first time statistical analysis of the 165 isolated dot-like emissions and their chains observed, from September 1999 to September 2000, in the decimetric band. Dots are observed in groups spread over the frequency - time plane. Rarely their chains are observed. Chains of dots cover the frequency range of ∼ 150 MHz and hardly cover the entire frequency range of observations. Isolated dot-like emission has been observed to the limit of the BSS resolutions (3 MHz, 50 ms). In 50 % of the cases the observed instantaneous bandwidth and flux values are 5 MHz and ∼ 20 sfu, respectively. Also, in 90 % of the cases total duration is of about 50 ms, equal to the limit of BSS time resolution. The groups of the dots have been found to be associated with the rising part of the impulsive flares and a radio-continuum. A model of dot-like emissions based on the anisotropic beam instability is suggested.