Fig. 1. Type IIIb burst (11:20:10) against Type III bursts dynamical spectrum;

1. Type IIIb bursts infrequency band 18-30 MHzV.N. Melnik (1), H.O. Rucker(2), A. A. Konovalenko(1), N.V. Shevchuk (1),E.P. Abranin (1), V. V. Dorovskyy (1), A. Lecacheux (3) (1) Institute of Radio Astronomy, Ukrainian Academy of Sciences, Kharkov, Ukraine; (2) Space Research Institute, Austrian Academy of Sciences, Graz, Austria; (3) Departement de Radioastronomie, Observatoire de Paris, Paris, France. b) a) • Fig. 1. Type IIIb burst (11:20:10) against Type III bursts • dynamical spectrum; • frequency profile of stria at 11:20:10; • time profile of stria at 22.8 MHz. c)

2. Main properties of the decameter Type IIIb radio bursts. b) a) Fig. 2.The distribution of striae on their duration for IIIb burst observed on 15.07.02(a)); on their frequency width for all analyzed bursts (b)). a) b) Fig. 3.Dependences of average striae parameters from position of active region on the solar disk: a) duration; b) frequency width.

3. a) b) c) d) • Fig. 4.Dependences of average Type IIIb bursts parameters from the position of an active region on the solar disk: • number of striae; • number of striae for 1 MHz; • flux; • frequency drift rate of Type IIIb burst.

4. Conclusions Our analysis shows that decameter Type IIIb bursts usually formed by more than 30 striae. The average value of durations is about 1,2s and the average frequency bandwidth is about 50 kHz at frequencies from 18 MHz to 30 MHz. The frequency drift rate of Type IIIb bursts is about 3 MHz/s. The important obtained result is the dependence of bursts parameters from active region longitude that indicates the importance of propagation effects. At the same time the bandwidth is defined, on our opinion, by average parameters of coronal plasma (density, magnetic field, temperature) only. We couldn’t find any characteristic dependence between radio emission fluxes and observation frequencies. Nevertheless radio fluxes have maximum values at the frequencies 21 - 22 MHz.