Properties of arc‐polarized Alfvén 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” Alfvén 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° 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 Alfvén waves with embedded RDs propagating along the minimum‐variance direction best fit the majority of events.