Solar S-Bursts at Decameter Wavelengths

Abstract

The properties of solar S-bursts observed within 10 to 30 MHz at the UTR-2 radio telescope in 2001 – 2002 are studied. Three storms of these bursts occurred on May 23 – 26, 2001, July 13 – 16 and July 27 – 30, 2002 were chosen for a detailed analysis. More than 800 S-bursts were recorded during the days of these storms. All bursts were always observed against the background of other solar radio activity such as Type III and IIIb bursts, Type III-like bursts, drift pairs and spikes. S-bursts storms occurred in the days when the related active region was located near the central meridian. The durations of S-bursts were constant during one storm and equal to about 0.3 s for the 2001 storm and 0.4 to 0.6 s for the 2002 storms. It was found that the instantaneous frequency width of S-bursts increased with frequency sensibly linearly. The frequency drift rate of S-bursts changes with frequency according to the McConnell’s dependence derived for higher frequencies. We propose the model of S-bursts based on assumption that they are generated due to the confluence of Langmuir waves with fast magnetosonic waves whose phase and group velocities are equal.