DELAY BETWEEN THE CIRCULARLY-POLARIZED COMPONENTS IN FINE-STRUCTURES DURING SOLAR-TYPE-IV EVENTS

We analyzed intermediately polarized (20-80%) fine structures (pulsati ons, sudden reductions, fiber bursts and zebras) that were recorded in type IV events. The mean polarization degree was practically the same for all the fine structures recorded in an interval lasting a few min utes and it was similar to the polarization of the continuum. A detail ed analysis during the evolution of single structures reveals changes in polarization (in particular an 'undulation' at Bur density minima) even stronger than 20%. They were caused by a delay, up to 0.1 s, betw een the two circularly polarized components. The weaker polarimetric c omponent was delayed in 2 sets and the stronger one in 1 set. In the e vent of April 24, 1985 different types of fine structures were sporadi cally detected in more than one hour long time interval. Short delays of the stronger or of the weaker component were sometimes observed. Th e events characterized by fine structures are generally totally polari zed in the ordinary mode. We assume that this holds also for the pheno mena studied here. The observed intermediate polarization therefore re quires a depolarization due to propagation effects. We discuss the mod e coupling and the reflection of the original radio signal that could also generate the delay of the weaker and the stronger component respe ctively. The possibility of polarization variation due to the change o f the angle between the direction of the propagation and the magnetic field in a quasi-transversal region and in a low intensity magnetic fi eld in a current sheet is also given.