PROPERTIES OF ARC-POLARIZED ALFVEN WAVES IN THE ECLIPTIC-PLANE - ULYSSES OBSERVATIONS

Ulysses observations of the interplanetary magnetic field reveal well- ordered rotations on the timescale of several hours. These have been p reviously identified as ''arc-polarized'' Alfven waves. Rotational dis continuities (RDs) are often an integral part of the wave. This study focuses on a statistical description of these rotations (ARCs) in the ecliptic plane. It is found that (1) most ARCs are limited to 180 degr ees or less in rotation; (2) these ARCs account for between 5 and 10% of the total data set; (3) there appears to be no preferred helicity; (4) the minimum-variance direction typically makes a large oblique ang le with the average magnetic field (< B >), while the intermediate-var iance direction is loosely aligned with < B >; (5) most of the events display a small but significant nonzero magnetic field component in th e direction of minimum variance; (6) the cross helicity of the ARCs te nds to be higher than during non-ARC intervals; (7) there are 2.4 time s more discontinuities during ARC intervals than during non-ARC interv als; (8) essentially all ARCs are propagating outward in the rest fram e of the solar wind plasma; and (9) there is no simple relationship be tween the rate of occurrence of the ARCs and heliocentric distance. Co mparing these results with the predicted signatures of a number of mod els, it is found that arc-polarized Alfven waves with embedded RDs pro pagating along the minimum-variance direction best fit the majority of events.