THE RELATIONSHIP BETWEEN INTERPLANETARY DISCONTINUITIES AND ALFVEN WAVES - ULYSSES OBSERVATIONS

The rate of occurrence of interplanetary discontinuities (ROID) is exa mined using Ulysses magnetic field and plasma data from 1 to 5 AU radi al distance from the Sun and at high heliographic latitudes. We find t wo regions where the ROID is high: in stream-stream interaction region s and in Alfven wave trains. This latter feature is particularly obvio us at high latitudes when Ulysses enters a high speed stream associate d with a polar coronal hole. These streams are characterized by the pr esence of continuous, large-amplitude (DELTAB/\B\ approximately 1-2) A lfven waves and an extraordinarily high ROID value (approximately 150 discontinuities/day). In a number of intervals examined, it is found t hat (rotational) discontinuities are an integral part of the Alfven wa ves. The nonlinear Alfven waves are spherically polarized, i.e., the t ip of the perturbation vector resides on the surface of a sphere (a co nsequence of constant \B\). The slowly rotating part of the waves rota tes approximately 270-degrees in phase. There is a slight arc in the B 1-B2 hodogram, suggesting an almost linear polarization. The phase rot ation associated with the discontinuity is approximately 90-degrees, l ies in the same plane as the slowly rotating part of the Alfven wave, and therefore completes the 360-degrees phase rotation. The best descr iption of the overall Alfven wave plus discontinuity is a spherical, a rc-polarized, phase-steepened wave.