PARAMETERS OF THE DYNAMIC SPECTRA OF TYPE IIID SOLAR DECAMETER RADIO FLARES WITH ECHO COMPONENTS

New observations of a two-week, radio noise storm of type IIId decamet er flares on the UTR-2 antenna at Khar'kov in July 1992 show that the shape and certain parameters of the flares depend significantly on the longitude of the studied region in the solar corona. During several d ays in the middle of the storm, the dynamical spectra of the flares ha d a clearly-visible echo component. In amplitude channels at several f requencies from 30 to 7 MHz, the radio storm was not usually observed below 25 MHz. On July 6, however, when the echo delay reached its maxi mum value (approximate to 7 s), emission was detected at all working f requencies greater than or equal to 14.7 MHz. The rates of the frequen cy drift indicate that complex ''central'' flares do not differ on ave rage from ordinary (''limb'') type IIId flares and from other type III emission generated at the second harmonic. The frequency dependence o f the delay of the echo flares reveals a modest decrease with decreasi ng frequency, instead of the expected monotonic growth, The ratio of t he amplitude maxima of the two-peaked intensity time profile and the i ntermediate minimum level of this profile changed significantly with f requency, The temporal splitting and longitude evolution of type IIId radio flares can be qualitatively explained in the framework of a simp le coronal model with a source at the second harmonic of the local pla sma frequency, which can be observed directly and after reflection. Th is model must be updated, taking account of these new experimental dat a.