THE RELATIONSHIP BETWEEN INTERPLANETARY DISCONTINUITIES AND ALFVEN WAVES - ULYSSES OBSERVATIONS

The rate of occurrence of interplanetary discontinuities (ROID) is examined using Ulysses magnetic field and plasma data from 1 to 5 AU radial distance from the Sun and at high heliographic latitudes. We find two regions where the ROID is high: in stream-stream interaction regions and in Alfven wave trains. This latter feature is particularly obvious at high latitudes when Ulysses enters a high speed stream associated with a polar coronal hole. These streams are characterized by the presence of continuous, large-amplitude (DELTAB/\B\ approximately 1-2) Alfven waves and an extraordinarily high ROID value (approximately 150 discontinuities/day). In a number of intervals examined, it is found that (rotational) discontinuities are an integral part of the Alfven waves. The nonlinear Alfven waves are spherically polarized, i.e., the tip of the perturbation vector resides on the surface of a sphere (a consequence of constant \B\). The slowly rotating part of the waves rotates approximately 270-degrees in phase. There is a slight arc in the B1-B2 hodogram, suggesting an almost linear polarization. The phase rotation associated with the discontinuity is approximately 90-degrees, lies in the same plane as the slowly rotating part of the Alfven wave, and therefore completes the 360-degrees phase rotation. The best description of the overall Alfven wave plus discontinuity is a spherical, arc-polarized, phase-steepened wave.