KILOMETER-WAVE RADIO OBSERVATIONS OF SOLAR-TYPE-III BURSTS BY ULYSSESCOMPARED WITH DECAMETER-WAVE OBSERVATIONS FROM THE EARTH

Observations of solar type III bursts, made at kilometric frequencies by the radio receiver of the Ulysses Unified Radio and Plasma Wave (UR AP) investigation, are compared with simultaneous observations, made a t decametric frequencies at the Nancay Radio Astronomy Station of the Paris-Meudon Observatory, during the period following the spacecraft e ncounter with Jupiter until the south solar polar pass. Of the events suitable for study, 57 can be identified in both frequency bands havin g delay times consistent with prediction based upon geometry and upon the frequency drift between the lowest frequency observed on the groun d (25 MHz) and the highest frequency observed by URAP (940 kHz). The g ood agreement between calculated and measured delay times suggests tha t the large delay anomalies, reported by Steinberg et al. (1984) somet imes to be in excess of 8 minutes in duration, may be confined to freq uencies below the 500 kHz limit studied by these authors and not detec table at 940 kHz with the time resolution of the URAP receiver obtaine d in this study. There are cases when bursts recorded at Ulysses are n ot seen at Nancay. This may just be due to the source at 25 MHz being beyond the solar limb and so obscured from the Earth. There are other cases, however, when bursts recorded at the Earth are not seen at Ulys ses. Such cases do not appear to be correlated with either the Earth-S un-Ulysses (ESU) angle or with the heliographic latitude of the spacec raft. As the source region at 940 kHz is large and at a considerable d istance from the Sun, some part of it will usually be visible from the spacecraft no matter what the relative positions of the Sun, the sour ce and Ulysses may be; this suggests either that there may sometimes b e a low frequency cutoff, inherent to the burst itself somewhere betwe en 940 kHz and 25 MHz, or else that the emission has somehow been occu lted. Representative examples are presented and discussed.