Properties of Powerful Solar Type III Bursts at Decameter Wavelengths

Abstract

The properties of powerful (larger than 10^-19W/(m²⋅Hz)) Type III bursts observed in July-August 2002 using the UTR-2 radio telescope at frequencies 10 ÷30 MHz are analyzed. The majority of these bursts were found to be observed on the days when an active region was located near the central meridian or at 40°÷60° eastwards or westwards from it. All these bursts drift from high frequencies to low ones, their frequency drift rates being within 1÷2.5 MHz/s in most cases. The frequency drift rate increases linearly with frequency for all days of observations. Duration of powerful Type III bursts varies within 6÷12 s with smaller values at high frequencies. Instantaneous frequency widths of these bursts do not depend on the day of observations and show a linear growth with frequency. The results of these observations are discussed in the frame of the plasma model for the Type III bursts generation.