TYPE-III RADIO-BURSTS OBSERVED BY ULYSSES POLE TO POLE, AND SIMULTANEOUSLY BY WIND

We consider 555 type III bursts observed by Ulysses and/or Wind while Ulysses traversed a large range of longitude and latitude. We find: 1) The percentage of bursts seen by both spacecraft was 59.5%. It was hi gher, about 80%, when Ulysses was to the south and east of the Sun as seen from Wind. It decreased to about 50% when Ulysses was near the ec liptic behind the Sun, and it remained near 50% as Ulysses moved to th e north and west. 2) The distribution of low frequency cutoffs f(lo) o f type III radiation is very similar for bursts seen by Ulysses and th ose seen by Wind, whereas the distribution of the in-situ plasma frequ ency f(p) at the two spacecraft is very different. Many bursts descend to close to f(p) similar to 30 kHz at Wind but few descend to the low er f(p) similar to 10 kHz at Ulysses We confirm earlier findings that f(lo) is rarely lower than about 20 kHz. 3) Statistically, the low fre quency limit depends strongly on the burst intensity, being about four times lower for strong bursts than for weak bursts. We consider three hypotheses for the close relation between intensity and f(lo): proxim ity of the burst source to one spacecraft or the other, directivity an d propagation effects, and density and speed of the fast electron stre am. We conclude that, while the first two may be important for some bu rsts, for many others the character of the electron stream is the domi nant factor in establishing both the burst intensity and the lowest fr equency attained.