Solar S-bursts observed by the radio telescope UTR-2 in the period 2001 -2002 are studied. The bursts chosen for a detailed analysis occurred in the periods 23 -26 May 2001, 13 -16 and 27 -39 July 2002 during three solar radio storms. More than 800 S-bursts were registered in these days. Properties of S-bursts are studied in the frequency band 10 -30 MHz. All bursts were always observed against a background of other solar radio activity such as type III and IIIb bursts, type III-like bursts, drift pairs and spikes. Moreover, Sbursts were observed during days when the active region was situated near the central meridian. Characteristic durations of S-bursts were about 0.35 and 0.4 -0.6 s for the May and July storms, respectively. For the first time, we found that the instantaneous frequency width of S-bursts increased with frequency linearly. The dependence of drift rates on frequency followed the McConnell dependence derived for higher frequencies. We propose a model of S-bursts based on the assumption that these bursts are generated due to the confluence of Langmuir waves with fast magnetosonic waves, whose phase and group velocities are equal.

The properties of powerful (flux > 10 −19 W m −2 Hz −1 ) type III bursts observed in July -August 2002 by the radio telescope UTR-2 at frequencies 10 -30 MHz are analyzed. Most bursts have been registered when the active regions associated to these bursts were located near the central meridian or at 40°-60°to the East or West from it. All powerful type III bursts drift from high to low frequencies with frequency drift rates 1 -2.5 MHz s −1 . It is important to emphasize that according to our observations the drift rate is linearly increasing with frequency. The duration of the bursts changes mainly from 6 s at frequency 30 MHz up to 12 s at 10 MHz. The instantaneous frequency bandwidth does not depend on the day of observations, i.e. on the disk location of the source active region, and is increasing with frequency.The results of observational properties are discussed in the frame of the standard plasma model of type III bursts radio emission.

The results of the first observations of Type IV bursts at frequencies 10-30 MHz are presented. These observations were carried out at radio telescopes UTR-2 (Kharkov, Ukraine) and URAN-2 (Poltava, Ukraine) during the period

The results of observations of solar decametric drift pair bursts are presented. These observations were carried out during a Type III burst storm on July 11-21, 2002, with the decameter radio telescope UTR-2, equipped with new back-end facilities. High time and frequency resolution of the back-end allowed us to obtain new information about the structure and properties of these bursts. The statistical analysis of more than 700 bursts observed on 13-15 July was performed separately for "forward" and "reverse" drift pair bursts. Such an extensive amount of these kind of bursts has never been processed before. It should be pointed out that "forward" and "reverse" drift pair bursts have a set of similar parameters, such as time delay between the burst elements, duration of an element, and instant bandwidth of an element. Nevertheless some of their parameters are different. So, the absolute average value of frequency drift rate for "forward" bursts is 0.8 MHz s −1 , while for "reverse" ones it is 2 MHz s −1 . The obtained functional dependencies "drift rate vs. frequency" and "flux density vs. frequency" were found to be different from the current knowledge. We also report about the observation of unusual variants of drift pairs, in particular, of "hook" bursts and bursts with fine time and frequency structure. A possible mechanism of drift pairs generation is proposed, according to which this emission may originate from the interaction of Langmuir waves with the magnetosonic waves having equal phase and group velocities.

A decameter solar radio storm of type IIIb and III bursts has been analysed, using single frequency records at frequencies 12.5 and 25.0 MHz.Several kinds of burst associations are classified. As a result it is shown that in double oblique burst-traces of type IIIb +III on the frequency-time plane the type III burst is shifted by an octave above the type IIIb burst at any moment of the IIIb +III pair's lifetime. In particular, the harmonic structure of the spectrum is peculiar to the event of type IIIb +III in the initial and the final stages. This property of the pair is clear if the type IIIb and III radiations occur at the fundamental coronal plasma frequency and its harmonic respectively. On the other hand, if it is assumed that a type IIIb burst is the precursor of a type III one, there is no reason why the two bursts should be harmonically related.

We report the first observations of Type III-like bursts at frequencies 10 -30 MHz. More than 1000 such bursts during 2002 -2004 have been analyzed. The frequency drift of these bursts is several times that of decameter Type III bursts. A typical duration of the Type III-like bursts is 1 -2 s. These bursts are mainly observed when the source active region is located within a few days from the central meridian. The drift rate of the Type IIIlike bursts can take a large value by considering the velocity of Type III electrons and the group velocity of generated electromagnetic waves.

The UTR-2 antenna has been used to measure angular sizes of sources of narrow-band short-lived solar stria-bursts at frequencies 24-26 MHz. The majority of these sources have apparent diameters between 20 and 40'. According to this parameter they do not differ noticeably from that of type III bursts at the same frequency. The short duration of the stria-bursts prevents explanation of the large diameter by scattering in the solar corona.

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