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 previously identified as ''arc-polarized'' Alfven waves. Rotational discontinuities (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 degrees 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 angle with the average magnetic field (< B >), while the intermediate-variance direction is loosely aligned with < B >; (5) most of the events display a small but significant nonzero magnetic field component in the direction of minimum variance; (6) the cross helicity of the ARCs tends to be higher than during non-ARC intervals; (7) there are 2.4 times more discontinuities during ARC intervals than during non-ARC intervals; (8) essentially all ARCs are propagating outward in the rest frame of the solar wind plasma; and (9) there is no simple relationship between the rate of occurrence of the ARCs and heliocentric distance. Comparing these results with the predicted signatures of a number of models, it is found that arc-polarized Alfven waves with embedded RDs propagating along the minimum-variance direction best fit the majority of events.